UNIVERSITY OF CALGARY Effect of the human serum albumin concentration on the metabolism of cisplatin in vitro by Thomas Terry Morris A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE DEPARTMENT OF CHEMISTRY CALGARY, ALBERTA APRIL, 2014 © Thomas Terry Morris 2014 Abstract Size-exclusion chromatography (SEC) coupled to an inductively coupled plasma atomic emission spectrometer (ICP-AES) was employed to study the effect of the human serum albumin (HSA) concentration on the metabolism of cisplatin (CP) in human blood plasma in vitro. Plasma from 14 healthy adults and 11 pediatric cancer patients was spiked with CP and the Pt distribution was determined at the 5 min and 2 hr time point. The results revealed that as the HSA concentration decreased, the percent of Pt-bound to HSA decreased; whereas the percent of Pt-hydrolysis products increased, while other Pt-species were largely unaffected. These changes were corroborated by fortifying the cancer patient plasma with HSA to healthy concentrations followed by the addition of CP. In summary, these findings imply that the infusion of cancer patients with HSA to healthy plasma levels may decrease the fraction of free hydrolysis products, which may alleviate the severe toxic side effects of CP. ii Acknowledgements I would like to express my sincere gratitude to my supervisor Dr. Jürgen Gailer for giving me the opportunity to work on these fascinating projects. His perpetual enthusiasm, encouragement, and guidance have inspired me to broaden my knowledge and strengthen my analytical skills. I owe my deepest gratitude to Dr. Aru Narendran for his assistance and advice, as well as for his help with the recruitment of cancer patients. I would also like to thank Karen Mazil for her constant assistance with the ethics submission for this project, as well as with the recruitment of the cancer patients. I wish to express my warm and sincere thanks to Prof. Kevin Thurbide for being in my supervisory committee and for all of the analytical knowledge he passed on. I am very grateful to Dr. Roland Roesler for serving on my supervisory committee. It is a pleasure for me to thank Dr. Ann-Lise Norman for accepting to be the internal examiner, and to Dr. Thomas Baumgartner for being the neutral chair on my defense committee. I am grateful to Mandy Chan at the Canadian Sport Centre, University of Calgary for being so helpful in drawing blood from my volunteers for research. I would like to thank all of the volunteers for being so generous to donate blood for my research. Many thanks go to the Department of Chemistry administrative staff, especially to Bonnie King and Janice Crawford for being so kind in clarifying all my questions. Alberta Innovates Health Solution is greatly acknowledged for their financial support for my project, as well as the University of Calgary for their financial support during my degree period. It was a great pleasure to work with the past and current members of the Gailer group. I would like to thank Melani and Elham for all of their help, advice, and support they provided iii during my degree. I greatly appreciated having them both around, and could not imagine better group members to share this experience with. Finally, I would like to convey my deepest gratitude to my parents and sister for their love and support throughout my life, without whom I would not be where I am today. This dissertation would not have been possible without all of you. iv Dedication To my loving parents and sister… v Table of Contents Abstract ............................................................................................................................... ii Acknowledgements ............................................................................................................ iii Dedication ............................................................................................................................v Table of Contents ............................................................................................................... vi List of Tables ................................................................................................................... viii List of Figures and Illustrations ...........................................................................................x List of Symbols, Abbreviations and Nomenclature ......................................................... xiii CHAPTER 1 INTRODUCTION .........................................................................................1 1.1 Cancer as a public health problem .............................................................................1 1.2 Cancer treatment methods .........................................................................................2 1.1.1 Radiation therapy...............................................................................................2 1.1.2 Chemotherapy....................................................................................................2 1.3 Cisplatin (CP) ............................................................................................................3 1.3.1 Discovery ...........................................................................................................3 1.3.2 Mechanism of action .........................................................................................5 1.3.3 Limitations of cisplatin in the treatment of cancer patients ..............................8 1.3.3.1 Adverse toxic side effects ........................................................................8 1.3.3.2 Ameliorating agents that modulate the metabolism of cisplatin..............9 1.3.3.3 Resistance ..............................................................................................10 1.3.4 Strategies to optimize selective toxicity ..........................................................12 1.4 Interactions between metal based drugs and blood constituents .............................14 1.4.1 Human serum albumin (HSA) .........................................................................15 1.4.2 Transferrin (Tf) ................................................................................................18 1.4.3 α2-macroglobulin ............................................................................................18 1.4.4 Hemoglobin (Hb).............................................................................................18 1.5 Influence of plasma protein concentrations on the metabolism/toxicity of medicinal drugs .......................................................................................................................19 1.6 Determination of metalloproteins in plasma by SEC-ICP-AES ..............................21 1.6.1 Analytical complexity of plasma .....................................................................21 1.6.2 SEC-ICP-AES .................................................................................................21 1.7 Research objectives..................................................................................................23 CHAPTER 2 EXPERIMENTAL.......................................................................................26 2.1 Chemicals and solutions ..........................................................................................26 2.2 SEC-ICP-AES system..............................................................................................26 2.3 Blood collection and plasma analysis by Calgary Laboratory Services (Project 1) 27 2.4 Analysis of CP spiked human plasma......................................................................30 2.4.1 Analysis of plasma from healthy adults ..........................................................30 2.4.2 Analysis of plasma from pediatric cancer patients ..........................................32 2.5 Plasma protein binding of potentially novel anticancer compounds (Project 2) .....33 CHAPTER 3 EFFECT OF THE PLASMA HUMAN SERUM ALBUMIN CONCENTRATION ON THE METABOLISM OF CISPLATIN IN VITRO........35 vi 3.1 Overview ..................................................................................................................35 3.2 Metabolism of CP in plasma of healthy controls .....................................................35 3.2.1 Quality control of analytical results ................................................................35 3.2.2 Cu-specific chromatograms .............................................................................36 3.2.3 Fe and Zn-specific chromatograms .................................................................38 3.2.4 Pt-specific chromatograms ..............................................................................39 3.3 Metabolism of CP in plasma of pediatric cancer patients .......................................44 3.3.1 Quality control of analytical results ................................................................45 3.3.2 Cu-specific chromatograms .............................................................................46 3.3.3 Fe and Zn-specific chromatograms .................................................................46 3.3.4 Pt-specific chromatograms ..............................................................................47 3.4 Comparison of plasma from healthy adults with pediatric cancer plasma ..............49 3.5 Comparison of pediatric cancer patient plasma with HSA fortified plasma ...........51 CHAPTER 4 PLASMA PROTEIN BINDING OF POTENTIALLY NOVEL METALBASED ANTICANCER COMPOUNDS.................................................................56 4.1 Investigation of 56MESS and 56MESSCu ..............................................................56 4.2 Investigation of DiPy and SOOS .............................................................................59 CHAPTER 5 CONCLUSIONS .........................................................................................61 5.1 Effect of the plasma HSA concentration on the metabolism of CP in vitro ............61 5.2 Plasma protein binding of potentially novel metal-based anticancer compounds ...63 CHAPTER 6 FUTURE WORK ........................................................................................64 CHAPTER 7 REFERENCES ............................................................................................66 APPENDIX A ....................................................................................................................78 APPENDIX B ....................................................................................................................79 APPENDIX C ....................................................................................................................83 APPENDIX D ....................................................................................................................87 APPENDIX E ....................................................................................................................90 APPENDIX F.....................................................................................................................91 APPENDIX G ....................................................................................................................94 APPENDIX H ....................................................................................................................96 APPENDIX I .....................................................................................................................98 vii List of Tables Table 1.1: Toxic side effects exerted by CP and carboplatin [74, 75]. ........................................... 9 Table 1.2: Variations of CP binding to HSA following the use of different incubation conditions and analysis techniques. ...................................................................................... 17 Table 2.1: Reference values for investigated blood plasma parameters provided by CLS [35]. .. 29 Table 3.1: Plasma concentrations of chosen constituents from healthy controls. For comparison, the reference range pertaining to healthy adults is depicted at the bottom. Italicized values are outside of the reference range. ............................................................. 36 Table 3.2: Areas of all Pt peaks expressed as % values of total Pt obtained after SEC-ICPAES analysis of human plasma spiked with CP after incubation at 37°C. * Corresponds to the average of two determinations. ................................................................................... 42 Table 3.3: A more detailed analysis of the Pt peak areas and retention times observed at the 2 hr time point expressed as % values of total Pt obtained after SEC-ICP-AES analysis of human plasma spiked with CP. * Corresponds to one analysis. **Corresponds to the average of two analyses. The average difference between the analyses for PP-3 was 0.7% PP = Protein bound Pt-species, HP = Pt-containing hydrolysis product. .................... 43 Table 3.4: Concentration of HSA, Tf, creatinine, and B.U.N. in blood plasma of pediatric cancer patients compared to healthy levels. The ranges pertaining to healthy children are depicted at the bottom of the table. ....................................................................................... 45 Table 3.5: Peak areas of all Pt peaks expressed as % values of total Pt obtained after SECICP-AES analysis of human plasma spiked with CP after incubation at 37°C. ................... 47 Table 3.6: Peak areas of all Pt peaks expressed as % of total Pt obtained after SEC-ICP-AES analysis of human plasma spiked with CP after incubation at 37°C for 2 hr. PP = Protein bound Pt-species, PH = Pt-containing hydrolysis product.................................................... 49 Table 3.7: Peak areas of all Pt peaks expressed as % of total Pt obtained after SEC-ICP-AES analysis of plasma from healthy adults (Avg. 42 g HSA/L) and pediatric cancer patients (Avg. 26 g HSA/L) spiked with CP after incubation at 37°C for 2 hr. PP = Protein bound Pt-species, HP = Pt-containing hydrolysis product, H = Healthy adults, C = Pediatric cancer patients........................................................................................................ 50 Table 3.8: Peak areas of all Pt peaks expressed as % of total Pt obtained after SEC-ICP-AES analysis of plasma from pediatric cancer patients (Avg. 26 g HSA/L) and the HSA fortified plasma spiked with CP after incubation at 37°C for 2 hr. PP = Protein bound Pt-species, HP = Pt-containing hydrolysis product, H = Healthy adults, C = Pediatric cancer patients. ...................................................................................................................... 52 viii Table 3.9: Peak areas of all Pt peaks expressed as % of total Pt obtained after SEC-ICP-AES analysis of plasma from C-11 after being spiked with CP and varying amounts of HSA. PP = Protein bound Pt-species, HP = Pt-containing hydrolysis product. ............................. 54 Table 3.10: Peak areas of all Pt peaks expressed as % of total Pt obtained after SEC-ICPAES analysis of plasma from C-02 after being spiked with CP and varying amounts of HSA. PP = Protein bound Pt-species, HP = Pt-containing hydrolysis product. ................... 54 Table 3.11: Linear regression analysis showing the increase of Pt-bound HSA per gram of HSA added to plasma. ........................................................................................................... 55 ix List of Figures and Illustrations Figure 1.1: Methyl-bis(beta-chloroethyl)amine hydrochloride – one of the mustard gases used to treat lymphsarcoma [20]. In the form of its hydrochloride salt, it can be readily dissolved in saline for intravenous administration [18]. ......................................................... 3 Figure 1.2: Structure of Pt-based anti-cancer drugs that are (A) in worldwide clinical use [34] and (B) approved for use in Asia. ........................................................................................... 4 Figure 1.3: Schematic illustration of the hydrolysis of CP in aqueous solution [41, 44]. .............. 5 Figure 1.4: Schematic depiction of the intracellular fate of CP in mammalian cells. Abbreviations: MRP2 – multidrug resistance-associated protein 2, Ctr1 – copper transport protein 1, OCT2 – organic cation transport protein 2. GSH-Pt complex obtained in cell-free systems as well as extracted from L1210 murine leukemia cells, as determined by mass spectroscopic analysis [43]. ................................................................... 6 Figure 1.5: Different types of DNA-CP adducts. Y=H2O/OH, Cl, or protein [34]. Republished with permission from Elsevier. .......................................................................... 7 Figure 1.6: Ameliorating agents co-administered with CP used to reduce nephrotoxicity. ........... 9 Figure 1.7: Schematic representation of the main biochemical mechanisms that are involved in the development of resistance of a tumor cell to CP treatment. ....................................... 10 Figure 1.8: Schematic of tumor targeting by nanohybrids via the EPR effect [119]. Reproduced with permission from Elsevier. ......................................................................... 14 Figure 1.9: Conceptual depiction of the biochemistry of CP after it is introduced into the mammalian bloodstream. Abbreviations: BP – binding protein, Ctr1 – copper transport protein, OCT2 – organic cation transport protein 2 [128]. ................................................... 15 Figure 1.10: Medicinal drugs used for the treatment of anxiety. .................................................. 20 Figure 1.11: Novel potential anticancer compounds for plasma protein binding investigation. (A) 56MESS, (B) 56MESSCu, (C) [u[2-[2-(2-mercapto-ethoxy)-ethoxy]ethanethiol]]bis(2,2':6',2''-terpyridine)platinum(II) [{Pt(terpy)} 2(SOOS)], which will be referred to as SOOS, and (D) [u-4,4′-dipyridine bis(2,2':6',2''-terpyridine)platinum(II)] [{Pt(terpy)}2(DiPy)], which will be referred to as DiPy. ..................................................... 25 Figure 2.1: C and Fe specific chromatograms obtained for plasma from healthy adults after the addition of CP after 5 min (H-02 no peak splitting, H-16 HSA & Tf peak splitting)..... 31 Figure 3.1: SEC-ICP-AES derived C-specific chromatograms obtained for the analysis of 14 plasma samples from healthy controls spiked with CP (0.04 mg/mL). The mixtures were incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS x buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 193.091 nm (C). (A) No splitting of peaks corresponding to HSA, (B) peak splitting of HSA peak. The retention times of the molecular weight markers are depicted on top. ... 37 Figure 3.2: SEC-ICP-AES derived Cu-specific chromatograms for the analysis of 14 plasma samples from healthy controls spiked with CP (0.04 mg/mL). The mixtures were incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 324.754 nm (Cu). The retention times of the molecular markers are depicted on top. The most intense ceruloplasmin peak was observed after the ICP torch was exchanged and shifted. ............................................................................................................................ 38 Figure 3.3: Representative SEC-ICP-AES derived Cu-specific chromatograms for the analysis of H-12-2 spiked with CP (0.04 mg/mL). The mixture was incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 324.754 nm (Cu). The retention times of the molecular markers are depicted on top. ...................................... 39 Figure 3.4: Representative Pt-specific chromatograms obtained for the analysis of H-17-1 spiked with CP (0.04 mg/mL). The mixture was incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 214.423 nm (Pt). Peaks 1-3: protein bound Pt-species, peaks 4-5: Pt-containing hydrolysis products, peak 6: CP. The retention times of the molecular weight markers are depicted on top. ................................. 41 Figure 3.5: HSA concentrations plotted against their corresponding Pt peak areas of Pt-bound HSA expressed as a percentage. ........................................................................................... 44 Figure 3.6: Representative SEC-ICP-AES derived Cu-specific chromatograms for the analysis of 11 cancer patients spiked with CP (0.04 mg/mL). The mixture was incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 324.754 nm (Cu). The retention times of the molecular weight markers are depicted on top. .......... 46 Figure 3.7: Representative Pt-specific chromatograms obtained for the analysis of C-11 spiked with CP (0.04 mg/mL). The mixture was incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 214.423 nm (Pt). The retention times of the molecular weight markers are depicted on top. .......................................................... 48 Figure 3.8: Proposed model to link the observed in vitro observed results with (A) high HSA concentrations in healthy controls and the (B) lower concentrations of HSA in pediatric xi cancer patients with the increase in severe toxic side effects. The font size corresponds to the relative concentration of metabolites or plasma proteins in plasma. .......................... 51 Figure 3.9: HSA concentrations of pediatric cancer patients as well as their plasma fortified with HSA (36 g HSA/L and 42 g HSA/L) plotted against their corresponding Pt peak areas of Pt-bound HSA expressed as a %. ............................................................................ 53 Figure 4.1: Representative C, Fe, and Pt-specific chromatograms obtained for the analysis of rabbit plasma spiked with 56MESS (100 µmol/L). The mixture was incubated at 37 °C and samples were analyzed after 5 min and 1 hr . Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. The retention times of the molecular markers are depicted on top. ...................................................................... 57 Figure 4.2: Representative C, Fe, and Cu-specific chromatograms obtained for the analysis of rabbit plasma spiked with 56MESSCu (100 µmol/L). The mixture was incubated at 37 °C and samples were analyzed after 5 min and 1 hr . Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. The retention times of the molecular markers are depicted on top. ...................................................................... 58 Figure 4.3: Representative C, Fe, and Pt-specific chromatograms obtained for the analysis of rabbit plasma spiked with DiPy (100 µmol/L). The mixture was incubated at 37 °C and samples were analyzed after 5 min and 1 hr . Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. The retention times of the molecular markers are depicted on top. ................................................................................ 59 Figure 4.4: Representative C, Fe, and Pt-specific chromatograms obtained for the analysis of rabbit plasma spiked with SOOS. The mixture was incubated at 37 °C and samples were analyzed after 4 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. The retention times of the molecular markers are depicted on top. ..................................................................................................................... 60 xii List of Symbols, Abbreviations and Nomenclature Symbol A AES ATP7A/ATP7B B.U.N. BP CE CLS CNS CP CTR1 CuZnSOD EPR G GFR GSH GSTπ Hb HP HPLC HSA ICP MRP MS NAC NER OCT PBS PP SEC STS Tf Definition Adenine Atomic emission spectroscopy Copper transporting ATPase 1&2 Blood urea nitrogen Binding protein Capillary electrophoresis Calgary Laboratory Services Central nervous system Cisplatin Copper transport protein Copper-zinc superoxide dismutase Enhanced permeability and retention effect Guanine Glomular filtration rate Glutathione Glutathione-S-transferase-π Hemoglobin Hydrolysis Products High performance liquid chromatography Human serum albumin Inductively coupled plasma Multidrug resistance protein Mass spectrometry N-acetyl cysteine Nucleotide excision repair Organic cation transport protein Phosphate buffered saline Plasma protein Size exclusion chromatography Sodium thiosulfate Transferrin xiii CHAPTER 1 INTRODUCTION 1.1 Cancer as a public health problem All mammalian organisms are made up of ~200 cell types [1], all of which grow and divide in a controlled way to replenish those that have become non-viable. Aged or damaged cells are removed from the organism by a process known as apoptosis, and are replaced with new cells. When the genetic material of a cell is damaged by mutations of the DNA, it can adversely affect cell growth and division, and result in their uncontrolled proliferation. The plethora of diseases in which abnormal cells divide without control is referred to as cancer [2], with more than 75,000 people expected to die from the disease each year in Canada alone [3]. This corresponds to cancer being the primary cause of all deaths in Canada (~30%) [4], and approximately half of all men and one third of women will develop cancer in their lifetime [5]. Currently there are ~100 different types of cancer, typically named for the organ or cell type in which the disease started (e.g., leukemia, lymphoma, and head and neck cancers) [2]. The most frequent types of cancers are lung, colorectal, breast, pancreas and prostate cancer, with lung cancer alone expected to cause 20,100 deaths/year in Canada [3]. Among males, the three most prevalent cancers are prostate (43%), colorectal (9%), and melanoma of the skin (7%), whereas the most common ones among females are breast (41%), uterus (8%), and colorectal cancer (8%) [5]. Cancer cells can spread from their point of origin to other parts of the body via the bloodstream and lymph system by a process referred to as metastasis. Metastasis is the last stage of cancer, and is the hardest to treat since every cancer cell must be eradicated from the body to achieve remission, making it extremely difficult to accomplish. 1 In terms of cancer treatments, only a few methods are available, including surgery, radiation therapy, and chemotherapy, but promising new approaches such as immunotherapy and stem cell therapy are also currently being explored. 1.2 Cancer treatment methods 1.1.1 Radiation therapy Radiation therapy employs the utilization of X-rays to kill cancer cells. The generated free oxygen radicals will damage vital biochemical molecules, such as DNA, and eventually kill the irradiated cell. While radiation therapy can eradicate cancer, it may sometimes just slow its growth [6]. However, better results are being achieved through advances in radiation equipment [7], and optimizing the radiation schedule [8]. Although radiation therapy has curative or palliative potential in roughly half of all incident solid tumors [9], its side effects, such as mucosal and skin damage, can be quite severe [10]. In addition, fundamental activities of daily life, such as speech, breathing, eating, and drinking may also be negatively affected [11, 12]. 1.1.2 Chemotherapy The term “chemotherapy” was coined in the early 1900’s by German chemist Paul Ehrlich who began to develop drugs to treat bacterial diseases and defined it as the use of chemicals to treat illnesses [13]. At the time, he referred to these chemicals as ‘magic bullets’, which were intended to bind to receptors on the surface of disease causing bacteria and kill the latter, therefore achieving selective toxicity. The development of chemotherapy for the treatment of cancer began in the mid 1940’s [14] and involved observations made during World War I and II. People who had died because of exposure to mustard gases displayed atrophy of their bone 2 marrow and their lymph nodes, but not of other cell types [15, 16]. These findings suggested that mustard gas (Figure 1.1) appeared to selectively affect only certain populations of cells [17, 18], and led to the testing of mustard gases in animal tumors (e.g. lymphosarcoma in mice) [17-20]. These promising results led to its testing in a human patient, which resulted in a significant regression of the tumor mass over two weeks [21]. These strongly encouraging findings resulted in the discovery of other families of antitumor drugs, such as anticancer antibiotics (e.g. bleomycin), antimitotics, and cisplatin in 1969 [14]. Currently, there are over 100 drugs that are being used for cancer chemotherapy [6], and each of these is typically used in combination with other drugs/therapies to shrink tumors before and/or after surgery or radiation therapy. Figure 1.1: Methyl-bis(beta-chloroethyl)amine hydrochloride – one of the mustard gases used to treat lymphsarcoma [20]. In the form of its hydrochloride salt, it can be readily dissolved in saline for intravenous administration [18]. 1.3 Cisplatin (CP) 1.3.1 Discovery The serendipitous discovery of the antineoplastic (inhibiting or preventing the proliferation of malignant cells) activity of this metal-based drug emerged from a seemingly unrelated experiment on the effects of an electric field on the cell division of Escherichia coli [22-24]. Using Pt electrodes in a buffer solution, researchers observed that the bacteria extruded 3 long filaments, and stopped replicating. More detailed analysis revealed that the cell division cycle was inhibited by Pt-amine complexes that had formed near the surface of Pt electrodes, and eventually resulted in the development of CP (Figure 1.2) as an anticancer drug [22]. After its approval for clinical use by the Food and Drug Administration in 1978, the intravenous administration with CP was discovered to be particularly useful for the treatment of testicular and ovarian cancers, due to their inherent sensitivity to CP treatment [25-27]. The overall cure rate exceeds 90% for testicular cancer, and is nearly 100% if this type of cancer is detected early [28]. Treatment with CP is also a more common treatment option against other types of solid tumors including head/neck, lung, cervical, bladder, and breast cancer [29-32]. Today, Pt-based anti-cancer therapeutics are among the most frequently used chemotherapeutic agents employed to treat cancer patients worldwide (Figure 1.2), with CP still holding the status of being one of the world’s best-selling anti-cancer drugs [33]. Figure 1.2: Structure of Pt-based anti-cancer drugs that are (A) in worldwide clinical use [34] and (B) approved for use in Asia. 4 1.3.2 Mechanism of action Ever since the discovery of the anticancer activity of CP, major efforts have been devoted to elucidate the biochemical mechanisms of its antitumor activity in order to possibly design novel Pt based drugs with superior pharmacological profiles. Once intravenously administered, the comparatively high chloride blood plasma concentration of ~105 mM [35] greatly diminishes the hydrolysis of CP. Its translocation from the bloodstream into cells is driven by passive diffusion, and/or active transport mediated by copper transport protein 1 (CTR1) or organic cation transporters (OCT) [36-38]. The comparatively low intracellular [Cl-] of ~4-20 mM [39, 40] allows CP to undergo hydrolysis reactions to form a variety of positively charged hydrolysis products (Figure 1.3) [41]. It is the latter that are capable of reacting with numerous intracellular biomolecules, such as the tri-peptide, glutathione (GSH) (Figure 1.4) [42, 43], as well as reacting mono and bi-functionally with the negatively charged DNA (Figure 1.4 & 1.5) [34]. Figure 1.3: Schematic illustration of the hydrolysis of CP in aqueous solution [41, 44]. 5 Figure 1.4: Schematic depiction of the intracellular fate of CP in mammalian cells. Abbreviations: MRP2 – multidrug resistance-associated protein 2, Ctr1 – copper transport protein 1, OCT2 – organic cation transport protein 2. GSH-Pt complex obtained in cell-free systems as well as extracted from L1210 murine leukemia cells, as determined by mass spectroscopic analysis [43]. 6 Figure 1.5: Different types of DNA-CP adducts. Y=H2O/OH, Cl, or protein [34]. Reproduced from Pizarro, A.M.. Unusual DNA binding modes for metal anticancer complexes.Biochemie; 91(10): 1198-1211. Copyright © 2009. Published by Elsevier Masson SAS. All rights reserved. The antitumor activity of CP is believed to be due to its capability to form bi-functional DNA cross-links. The N7 atom of guanine - the preferred target due to it having the highest electron density of all four nucleobases [45] - and adenine located in the major groove of the double helix are the most accessible and reactive nucleophilic sites for the coordination of Pt to DNA [46]. The predominant adducts that are formed between CP hydrolysis products and DNA are the intrastrand crosslinks 1,2-d(GG) (65%), 1,2-d(AG) (25%), and 1,3-d(GG) (5-10%), as well as a small percentage of interstrand crosslinks and mono-functional adducts (Figure 1.5) [47-55]. Although it has not been definitively proven, it is generally believed that the 1,27 intrastrand DNA adduct, which bends the double helix towards the major groove is responsible for apoptosis of the cell. This premise is based on the discovery of a group of chromosomal proteins that are involved in the regulation of DNA-dependent processes, such as transcription, replication, recombination and DNA repair [56]. These proteins specifically recognize this type of Pt-DNA adduct and inhibit the repair of 1,2-intrastrand crosslinks that were formed by CP [57]. Further support in favour of this hypothesis came from the finding that nucleotide excision repair, an important DNA repair system, repairs 1,3-intrastrand adducts with higher efficiency than the 1,2-instrastrand adducts [58]. However, it is generally thought that the kink in the overall DNA structure forces the individual strands to remain together when replication requires that they must be unravelled. Since cellular processes like transcription and replication are adversely affected, the result is cellular death by apoptosis or necrosis [59] [60]. Transplatin has substantially lower cytotoxicity than CP [61, 62]. Since both isomers bind to DNA almost exclusively by coordination to the N7 nitrogen atom of purine bases (higher affinity for guanine over adenine) [63, 64], the lack of cytotoxicity of transplatin must be related to the different type of DNA adducts that are formed by this isomer. This may be attributed to transplatin lacking the ability to form 1,2-intrastrand crosslinks with DNA due to steric constraints, which are the most abundant adducts formed by CP [65]. Indeed, transplatin mainly forms 1,3-intrastrand and interstrand cross-links [66]. 1.3.3 Limitations of cisplatin in the treatment of cancer patients 1.3.3.1 Adverse toxic side effects The intravenous administration of patients with CP is associated with severe, doselimiting toxic side effects, including nephrotoxicity and ototoxicity (Table 1.1) [67]. Because of 8 this, research efforts are aimed at synthesizing advanced / 3rd generation metal complexes for chemotherapy which exert a higher selective toxicity, and should therefore diminish the severe toxic side effects [34]. However, of the ~3000 tested newly synthesized Pt compounds [68], only a fraction (about 30) have entered clinical trials, and merely three Pt drugs have been approved worldwide (Figure 1.2A) [69, 70], with nedaplatin, lobaplatin, and heptaplatin being approved in China, South Korea, and Japan (Figure 1.2B) [70-73]. Table 1.1: Toxic side effects exerted by CP and carboplatin [74, 75]. Cisplatin Carboplatin Nephrotoxicity Myelosuppression Peripheral Neuropathy (50%) Peripheral Neuropathy (4-6%) Ototoxicity (31%) Ototoxicity (1.1%) Gastrointestinal Toxicity 1.3.3.2 Ameliorating agents that modulate the metabolism of cisplatin The toxic side effects of CP, however, have also been ameliorated in model organisms by the co-administration with sodium thiosulfate (STS) [42], N-acetylcysteine (NAC) (Figure 1.6) [76, 77], and D-methionine [78]. When STS is incubated in plasma with CP, a biologically inactive Pt-STS complex is formed which provides a feasible bio-molecular mechanism by which the toxic side effects of CP could be reduced by this ameliorating agent in vivo [79]. Figure 1.6: Ameliorating agents co-administered with CP used to reduce nephrotoxicity. 9 1.3.3.3 Resistance Although CP is widely used to treat cancer patients, its efficacy is limited to certain types of cancers, and the development of resistance during the treatment is a frequently encountered problem [34]. This phenomenon is generally considered to be multifactorial, and may be attributed to: (i) reduced drug accumulation & enhanced cell efflux, (ii) intracellular inactivation by thiol containing species (e.g. glutathione), and (iii) increased repair of Pt-DNA adducts (Figure 1.7) [46]. These resistance mechanisms have been demonstrated to be cell line-dependent so that a particular tumor may exhibit one, two, or even all of these resistance mechanisms [80, 81]. Figure 1.7: Schematic representation of the main biochemical mechanisms that are involved in the development of resistance of a tumor cell to CP treatment. 10 Reduced drug accumulation of CP has been observed in a variety of CP-resistant cell lines, and is the principal mechanism of resistance [82]. Previous studies have shown that Ctr1, a copper transport protein, is regulated by extracellular Cu+ concentration; high extracellular Cu+ triggers internalization and degradation of Ctr1 [83, 84]. Since Ctr1 is involved in CP uptake, the internalization of Ctr1 has been reproduced in human ovarian cancer cells with CP within minutes [85, 86], and has also been shown to occur in yeast cells [36]. Enhanced cell efflux of Pt species by molecular pumps in response to CP treatment has been demonstrated in several studies, and revealed the multidrug resistance protein (MRP) family to play a major role. This family of proteins is composed of at least seven members (MRP1-7), all of which are ATP-dependent transmembrane proteins [87]. Several of these MRPs are associated with the cellular efflux of a variety of drugs [88]. However, only MRP1 and MRP2 appear to be of significance in some CP-resistant tumor models [89]. MRP2 seems to have a more significant effect on the efflux of Pt species, since it is associated with an increased expression in CP resistant cells [90-92]. In the past few years, an additional family of protein efflux pumps has been linked to CP resistance. ATP7A and ATP7B are two copper-transporting proteins which have been shown to be overexpressed in CP resistant tumor cells [93, 94]. It is thought that these two copper transporting proteins initiate the efflux of CP and/or its hydrolysis products from the Golgi apparatus directly for elimination from the cell [82] [95]. This reduces the amount of CP interacting with DNA, in turn reducing its cytotoxicity. With regard to the cytosolic fate of CP, aquation reactions inside the cell lead to the formation of hydrolysis products which can interact with other nucleophilic components inside the cell, such as GSH. These side reactions inactivate CP, and reduce the availability of the drug to form the intended DNA adducts. Additionally, several clinical studies have demonstrated a 11 correlation between increased GSH synthesis and CP resistance [96, 97]. Although the reaction between GSH and CP’s hydrolysis products can occur spontaneously in the cytosol (Figure 1.4), it can also be catalyzed by the enzyme GSH-S-transferase-π (GSTπ), which may be up-regulated in CP resistant cells [98]. An involvement of this enzyme in CP resistance is further supported by studies documenting less favorable responses to treatment with CP for cases with elevated expressions of GSTπ, such as a high GSTπ expression found in 87.5% of patients without clinical response to chemotherapy [99]. This effect results in shorter overall survival times and progression-free time with respect to patients with lower levels of GSTπ [100-103]. Increased repair of Pt DNA adducts is another important mechanism of resistance, having already been demonstrated in several murine and human tumor cell lines [82]. Excision of the Pt DNA adducts is associated with the nucleotide excision repair (NER) pathway, a complex process involving ~17 different proteins [104-106]. Cells deficient in NER show extreme sensitivity to Pt damage [107]. Likewise, increased expression of the ERCC1 gene, an essential gene in the NER pathway, directly correlates with increased resistance to Pt therapy in ovarian cancer, gastric cancer, colorectal cancer, and lung cancer [107]. 1.3.4 Strategies to optimize selective toxicity Since CP is associated with severe toxic side effects, alternative approaches are continuously being developed to diminish the side effects in patients. These include, but are not limited to: 1. The tethering of cell-targeting moieties to CP allows for an increase in cellular targeting, while also reducing toxic side effects. One such molecule is folic acid. Folate receptors are overexpressed in cancer cells, allowing for the selective uptake of folic acid [108, 12 109]. In ovarian, uterus, brain, kidney, head and neck, mesothelium, and endometrium tumors, the receptors are overexpressed by up to two orders of magnitude [110-114]. The receptors on tumor cells are expressed on the cells that are in contact with circulating blood [115]. 2. Use of liposomes to exploit the enhanced permeability and retention (EPR) effect: The EPR effect describes how certain sizes of molecules tend to accumulate in cancerous tissue much more than they do in normal tissues due to the gaps (200 to 2000 nm) in the endothelial tumor tissue (Figure 1.8) [116-118]. By exploiting the differences between normal and cancerous tissues, it allows for improved targeting and delivery of anticancer drugs to improve efficacy and potentially reduce toxic side-effects. This effect is evident in a large number of tumor types, and is used as a strategy for the creation of novel cancer-specific drugs that are comprised of but not limited to micelles (1:10 CP to lipid ratio) and nanocapsules (10:1 CP to lipid ratio) [118-120]. The nanoscale size of these carriers is important, since it prevents them from entering normal tissues or removal by renal clearance. As a result, these drugs have greater exposure to the tumor sites compared to the low molecular weight drugs, which can be rapidly cleared from circulation [120]. One of the most promising and highly developed drug carriers currently used are liposomes (phospholipid bilayer vesicles) [121]. Liposomal delivery can improve the amount of drug available to the tumor cell by increasing the vascular permeability and therefore the influx and retention of the drug [122]. Liposomes have many advantages such as biocompatibility, versatility (allowing the existence of biologically active drugs either within the hydrophobic phospholipid bilayers or within the hydrophilic aqueous cavity), and the potential to shield drugs from inactivation before 13 delivery to the target site (such as plasma proteins deactivating CP) [122]. The physicochemical properties of the liposome can be varied by manipulation of size, charge and surface properties during formulation [123]. A liposomal formulation of doxorubicin, an anticancer drug, is already in use in the clinic [124]. Figure 1.8: Schematic of tumor targeting by nanohybrids via the EPR effect [118]. Reproduced from Prakash, S. Polymeric nanohybrids and functionalized carbon nanotubes as drug delivery carriers for cancer chemotherapy. Adv. Drug. Deliv. Rev; 63(14-15): 1340-1351. Copyright © 2011. Published by Elsevier Masson SAS. All rights reserved. 1.4 Interactions between metal based drugs and blood constituents Since CP is intravenously administered to patients, its interaction with all blood constituents must be considered. CP is known to be absorbed by erythrocytes, where it fragments hemoglobin (Hb) [125], and its hydrolysis products interact with plasma proteins [46]. In fact, the half-life of CP in blood plasma after the treatment of adults is approximately five months, but several factors can affect this (e.g. age, glomular filtration rate) [126]. The interactions of CP 14 hydrolysis products with plasma proteins play a key role not only in the context of its therapeutic effects, but also in mediating its toxic side effects [67]. It is currently unclear how many plasma proteins are involved (Figure 1.9) and whether the associated interactions are reversible or irreversible. Figure 1.9: Conceptual depiction of the biochemistry of CP after it is introduced into the mammalian bloodstream. Abbreviations: BP – binding protein, Ctr1 – copper transport protein, OCT2 – organic cation transport protein 2 [127]. 1.4.1 Human serum albumin (HSA) In humans, HSA (66.3 kDa) is the most abundant protein in blood plasma [40-45 g/L (0.6 mM)] [45, 128]. One of its main functions is the transport of fatty acids, bilirubin, essential metal ions, steroid hormones, vitamins, and pharmaceuticals, including metallodrugs, to organs [129-131]. HSA also performs a variety of other physiologically important functions, such as 15 controlling osmotic blood pressure [129, 132, 133]. In vitro studies have shown that 3 hr after CP was added to human plasma, ~50% of the Pt was bound to HSA [127], mainly via Cys-34 and Met-298 [67, 134]. A pharmacologically relevant dose of CP was added to bovine plasma and incubated at 37°C for 45.5 hr and after 48 hr of dialysis there was only an approximate loss of 1% of Pt that was once bound to BSA [135]. These results suggest that the binding of CPhydrolysis products to HSA is predominantly irreversible. Controversy surrounds the role that HSA-bound Pt plays in the context of exerting its desired antitumor activity of CP as well as its unintended toxic side effects. CP derived Pt-species that were bound to HSA have been demonstrated to be therapeutically inactive in a human ovarian cancer cell line [136]. In addition, various studies with human cell lines, including the human epidermoid carcinoma A431 cell line, have shown cytotoxic effects only at comparatively high concentrations of a largely uncharacterized synthetic HSA-CP adduct [IC50 (72 hr) of 85 µM vs 0.61 µM of free CP] [137, 138]. In contrast, a study involving animals implanted with tumors has shown HSA-bound Pt to have equivalent activity compared to free CP at equal dosages [139]. Related to this, hypoalbuminemic patients responded poorly to CP treatment [140-142], and HSA-CP complexes exerted cytotoxicity to cancer cells [139, 143]. In support of these findings, infusion of a preformed HSA-CP complex significantly increased patient survival times compared to untreated patients (median survival time of 109 days compared to 56 days) [139, 143] and revealed an even higher Pt tumor concentrations after the administration of a synthetic HSA-CP adduct to cancer patients compared to free CP at the same dosage [143]. Thus, the antitumor activity of intravenous administration of CP appears to be determined in vivo by both free CP as well as HSA-CP adducts that are formed in the bloodstream. 16 With regard to the toxic side effects of CP hydrolysis products bound to HSA, there is a similar ambiguity. Compared to conventional CP therapy, for example, the administration of HSA-CP complexes to patients has resulted in fewer toxic side effects, such as nephrotoxicity and ototoxicity at the same dose [143-145], while increasing the tumor Pt concentrations [143]. The parameters which govern the HSA-CP adduct formation in vitro are not fully understood either. It can be influenced by the molar ratio between the drug and the protein, initial concentration of the protein, incubation time, and pH of the solution (Table 1.2). For example, HSA was shown to bind as much as 20 mol of CP after 14 days of incubation at 37°C when a 60fold drug excess over the protein was used [146]. These studies, however, only examined the binding capacity in vitro, and not the cytotoxicity of the formed complex. Thus, it is unclear if different Pt-bound HSA complexes exert different antitumor activities, especially in vivo. Table 1.2: Variations of CP binding to HSA following the use of different incubation conditions and analysis techniques. Method Drug Concentration (M) 5 x 10-5 to 6 x 10-4 Protein Incubation Concentration Conditions (M) 1 x 10-5 pH 7.4, 100 mM Gel-filtration[146] NaCl, 37°C, 48photometry 144 hr -3 -5 8 x 10 pH 7.4, 37°C, 48 Gel filtration- 1.6 x 10 hr ICP-AES[147] -5 -5 [148] 5 x 10 to 1 x 5 x 10 pH 7.4, 100 mM CE-ICP-MS 10-3 NaCl, 37°C, 48 hr -5 -5 [149] 1 x 10 to 1 x 5 x 10 pH 7.4, 100 mM CE 10-3 NaCl, 37°C, 48 hr 17 Drug Molecules / Protein 3.5-20.0 5.1 0.7-10.2 6.3 1.4.2 Transferrin (Tf) Tf (79 kDa [150]) is found in human blood plasma at a concentration of ~2.5 g /L (35 µM) [151] and serves as a Fe3+ transporter, for which it has two binding sites. CP derived hydrolysis products are capable of binding to Tf, competing directly with Fe3+ at Thr-457, located in the C-lobe of Tf [152, 153]. Additionally, CP-derived hydrolysis products will bind to O donors (Tyr136, Tyr317) and S donors (Met256, His273, His578) on the surface of both apoand holo-Tf, [150]. CP derived hydrolysis products bound to holo-Tf do not interfere with the recognition of this protein by the Tf receptor, and can therefore enter the cell at a similar rate as holo-Tf [150]. However, the conjugation of CP derived hydrolysis products to holo-Tf greatly reduced the amount of platinated DNA adducts compared to free CP in the human breast cancer cell line MCF-7, as CP was unable to be released from the protein intracellularly, thus leading to reduced cytotoxicity compared to CP [150]. 1.4.3 α2-macroglobulin α2-macroglobulin (820 kDa, 2.5-4 g/L ) [154] has also been shown to play a role in the pharmacokinetics of CP [155]. For example, 0.14 µM α2-macroglobulin once incubated with 1.7 mM CP for 4 hr, 95% of the CP-derived Pt was bound to the protein [155]. There are a limited number of studies that have been performed to investigate the interaction of CP with this protein in detail. 1.4.4 Hemoglobin (Hb) Hb (65 kDa, 120-170 g/L) [156], the Fe containing protein which is responsible for the transportation of O2 by its heme group, can also form adducts with CP derived hydrolysis 18 products [125]. After the incubation of Hb (typically 2 mM in red blood cells [157]) in whole blood from healthy human volunteers with CP at a clinically relevant concentration (0.05 µM) and a higher concentration (10 µM) for 24 hr, the heme group was cleaved from the protein, leaving only CP-Hb complexes and no free drug [125, 158, 159]. 1.5 Influence of plasma protein concentrations on the metabolism/toxicity of medicinal drugs Plasma protein concentrations can greatly influence the distribution, the metabolism, and the excretion of medicinal drugs, leading to variances in their pharmacokinetics which may directly affect the toxic side effects [160]. An example that illustrates how HSA may potentially play a role in mediating toxic side effects of medicinal drugs was uncovered for methadone, a drug which is used to relieve pain [160]. Using human plasma in vitro, the % binding of methadone was investigated as a function of various HSA plasma concentrations (between 4 g HSA/L – 50 g HSA/L). The study revealed that increasing HSA concentrations in plasma increased the percent of methadone bound (~8% at 4 g HSA/L and ~44% at 50 g HSA/L), while only changing the drug concentration and leaving the HSA constant had little effect on the % of methadone that was bound to HSA. Another study investigated the effect of varying the HSA concentration on the pharmacokinetics of chlordiazepoxide and diazepam (used to treat anxiety) and their undesired effects (CNS depression) in vivo (Figure 1.10) [161]. Of 1037 patients receiving diazepam, 9.3% of patients with hypoalbuminemia (less than 30 g HSA/L) had CNS depression, while this was only seen in 2.9% of patients with normal serum HSA levels (≥ 40 g HSA/L). Similar trends were observed with chloriazepoxide. These results clearly demonstrate that the plasma 19 concentration of HSA can directly affect the pharmacokinetics and the toxicity of the drug in vivo. Since HSA represents 50% of the total protein content in human blood plasma (healthy adults) [162] and it has been demonstrated to interact with CP-derived hydrolysis products, its plasma concentration will significantly affect the pharmacokinetics of CP. Figure 1.10: Medicinal drugs used for the treatment of anxiety. Since cancer patients have much lower blood plasma concentration of HSA due to impaired renal and/or liver function and a general lack of appetite [163], it is important to understand the interaction between pharmacological relevant doses of CP and varying HSA plasma concentrations as this could pave the way to improve treatment methods to reduce the toxic side effects. 20 1.6 Determination of metalloproteins in plasma by SEC-ICP-AES 1.6.1 Analytical complexity of plasma From an analytical point of view, the separation of plasma proteins represents a herculean task since plasma contains between 3700-10000 proteins [164-166]. In addition, the concentrations of individual plasma proteins can vary up to 10 orders of magnitude [167]. A variety of instrumental analytical techniques have therefore been developed to address the complexity that is associated with the analysis of plasma. Conceptually, one can either attempt to analyze the entire plasma proteome (2D gel electrophoresis) [165], or one can simplify the problem by analyzing an inherently less complex subproteome. The mammalian plasma metalloproteome represents such a subproteome [168, 169]. The most abundant 22 proteins represent 99% of the total protein content of plasma [170], and since ~half of these contain metal cofactors, the analysis of metalloproteins greatly simplifies the analysis as well as provides valuable information. The most frequently used instrumental approaches for the analysis of plasma for the contained metalloproteins are hyphenated techniques, which are based on a separation method and a high sensitivity method for metal detection and quantification [171]. One such technique is size-exclusion chromatography (SEC) coupled on-line to an inductively coupled plasma atomic-emission spectrometer (ICP-AES), which was developed by Shawn Manley et al. [172]. 1.6.2 SEC-ICP-AES SEC-ICP-AES is a comparatively inexpensive [compared to SEC-ICP mass spectrometry (MS)], multi-element detection approach that one can employ to determine the plasma distribution of metals from metalloproteins, such as Fe, Cu, and Zn in less than 25 min. The use 21 of phosphate buffered saline (PBS) as the mobile phase allows one to maintain conditions as close as possible to physiological as the mobile phase buffer can adversely affect the stability of metal-protein bonds during analysis. This can result in a re-distribution of zinc among various plasma proteins during analysis [173]. With this in mind, two main applications of this approach can be envisioned. The first application is the use of this hyphenated technique as a diagnostic tool to test for human disease by detecting increased or decreased concentrations of plasma metalloproteins [174]. Since the analysis only takes 25 min, changes in the concentrations of the target metalloproteins can be monitored, while information on other metalloproteins can be simultaneously obtained. Since CP rapidly hydrolyses in plasma and interacts with proteins such as HSA, the distribution of Pt among plasma proteins can be examined in 40 min intervals. The second application involves probing the bio-inorganic chemistry of environmentally abundant toxic metals (e.g. Cd) [174] with various blood constituents in the mammalian bloodstream to better understand their toxicity. Recently, our research group investigated the plasma protein binding of arsenobetaine in human and rabbit plasma [175]. Through the use of this technique, it was revealed that arsenobetaine does not bind to plasma proteins > 300 Da over a 6 hr period. Hence, this study provided direct experimental evidence that metallodrug-plasma protein interactions which are amendable with this technique can explain the rapid clearance of arsenobutaine in urine. Subsequently, this technique was applied to study the comparative hydrolysis and plasma protein binding of CP and carboplatin in human plasma [127] using this technique. Most recently, this methodology was applied to gain insight into the molecular basis of how the “ameliorating agents” of STS, NAC, and D-methionine in human plasma in vitro. 22 SEC-ICP-MS is a related methodology that can be employed to investigate the aforementioned. Due to the much lower detection limits of ICP-MS (0.01-0.1 ppt for Pt) compared to ICP-AES (20 ppb for Pt) [176], it offers some advantages. However, its incompatibility to accept PBS buffer due to its high salt content is a major disadvantage that would render this technique incapable of mimicking physiological conditions. Therefore, SECICP-AES was the method of choice for the study of the metabolism of CP in human plasma in vitro. 1.7 Research objectives The interactions of CP with plasma proteins have in general only been investigated under non-physiological conditions (with regard to the mobile phase) with ICP-MS [60, 177-179]. This thesis marks the first time that the effect of the HSA concentration on the metabolism of CP in vitro has been investigated under physiological conditions. Effect of the plasma HSA concentration on the metabolism of CP in vitro (Chapter 3): Since HSA plays a key role in the pharmacokinetics of any medicinal drug, as well as CP [67], varying blood plasma concentrations of this protein may greatly affect the metabolism and therefore the distribution of Pt to potential target organs. Therefore, the plasma HSA concentration may play a more important role in mediating the toxic side effects on healthy cells as well as their effect on cancer cells. The objective of this project was to systematically evaluate the effect of varying HSA plasma concentrations on the metabolism of CP. A pharmacologically relevant dose of CP was added to blood plasma of twenty healthy adults (33 – 50 g HSA/L) and eleven cancer patients (8 – 34 g HSA/L) and the Pt distribution of the obtained mixture was 23 determined after 5 min and 2 hr. In addition, HSA was directly added to the plasma of cancer patients to be able to investigate the effect of increasing HSA concentration on the metabolism of CP. Plasma protein binding of potentially novel metal-based anticancer compounds (Chapter 4): In collaboration with Dr. Janice Aldrich-Wright (University of Western Sydney), four potential novel anticancer compounds (Figure 1.11), including 56MESS and 56MESSCu, were examined with regard to their binding to plasma proteins using rabbit plasma. [(5,6-dimethyl1,10-phenanthroline)(1S-2S-diaminocyclohexane)platinum(II)]2+, also referred to as 56MESS (Figure 1.11), has been demonstrated to exhibit a significantly lower LC 50 than CP in L1210 cells (mouse lymphocytic leukemia cell line), while also displaying activity in CP resistant cell lines [180]. The structurally related compound 56MESSCu in which the Pt atom is replaced by Cu has also been demonstrated to exert anticancer activity in L1210 cells (LC50 0.42 µM) [181]. Pharmacologically relevant concentrations of each compound were added to rabbit plasma, and the latter was analyzed by SEC-ICP-AES over a 2 hr period to examine their comparative hydrolysis and plasma protein binding. 24 Figure 1.11: Novel potential anticancer compounds for plasma protein binding investigation. (A) 56MESS, (B) 56MESSCu, (C) [u[2-[2-(2-mercapto-ethoxy)-ethoxy]ethanethiol]]bis(2,2':6',2''-terpyridine)platinum(II) [{Pt(terpy)}2(SOOS)], which will be referred to as SOOS, and (D) [u-4,4′-dipyridine bis(2,2':6',2''-terpyridine)platinum(II)] [{Pt(terpy)}2(DiPy)], which will be referred to as DiPy. 25 CHAPTER 2 EXPERIMENTAL 2.1 Chemicals and solutions Blue dextran (M.W. 2 000 000 g/mol) and phosphate buffered saline tablets (PBS, 0.01 M phosphate, 0.0027 M KCl, 0.137 M NaCl) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Cisplatin (1 mg cis-Pt(NH3)2Cl2/mL; this solution also contained 1 mg mannitol and 9 mg NaCl / mL; sterile) was obtained from Hospira (Montreal, QC, Canada) and carboplatin (10 mg cis-Pt(NH3)2C4H6(COO)2/mL) from Mayne Pharma (Montreal, QC, Canada). HSA (12.5 g in 50 mL of buffered diluent, stabilized with 0.02 M sodium caprylate and 0.02 M sodium acetyltryptophanate) was obtained from CSL Behring AG (Bern, Switzerland). PBS buffer (10 mM phosphate, 2.7 mM KCl, 137 mM NaCl, pH 7.4) was prepared by dissolving PBS tablets in the appropriate volume of water (followed by pH adjustment with dilute HCl) and filtration through 0.45 µm Nylon filter membranes (Mandel Scientific Company Inc., Guelph, ON, Canada) before use. A mixture of protein standards for SEC column calibration was obtained from Bio-Rad Laboratories (Hercules, CA, USA) and contained thyroglobulin (670 kDa), ɣglobulin (158 kDa), ovalbumin (44 kDa), myoglobin (17 kDa), and vitamin B12 (1.35 kDa). All solutions were prepared with water from a Simplicity water purification system (Millipore, Billerica, MA, USA). The novel anticancer compounds were obtained from Dr. Janice AldrichWright from the University of Western Sydney, Australia. 2.2 SEC-ICP-AES system The SEC-ICP-AES system was comprised of a Smartline 1000 HPLC pump (Knauer, Berlin, Germany) and a Rheodyne 9010 PEEK injection valve (Rheodyne, Rhonert Park, CA, USA) which was equipped with a PEEK injection loop (0.5 mL). A pre-packed SuperdexTM 200 26 10/300 GL TricornTM high performance size-exclusion chromatography column (30 x 1.0 cm I.D., 13 µm particle size, separates globular proteins between ~600 and ~10 kDa; GE Healthcare, Piscataway, NJ, USA) was used for the separation of plasma proteins using PBS-buffer as the mobile phase at a flow rate of 1.0 mL/min (column temperature 22°C) [174]. Simultaneous multielement-specific detection of C (193.091 nm), S (180.731 nm), P (213.618 nm), Cu (324.754 nm), Fe (259.940 nm), Zn (213.856 nm) and Pt (214.423 nm) was achieved with a Prodigy, high-dispersion, radial-view ICP-AES (Teledyne Leeman Labs, Hudson, NH, USA) at an Ar gas-flow rate of 19 L/min, an RF power of 1.3 kW, and a nebulizer gas pressure of 35 psi. A 6.0 min delay was implemented between injection and data acquisition based on the void volume (440 s/ 7.33 mL) that was determined by the injection of blue dextran and C-specific detection. The SEC column was calibrated using a mixture of protein standards and the retention time obtained for each protein standard is indicated on top of each chromatogram along with the corresponding molecular weight. The data acquisition windows were 1500 s for plasma spiked with cisplatin and 1140 s for carboplatin. The obtained raw data were imported into SigmaPlot 12 software and smoothed using the bisquare algorithm. Baseline correction and integration of peak areas were performed with OriginPro 9.1. 2.3 Blood collection and plasma analysis by Calgary Laboratory Services (Project 1) The collection of blood from humans was approved by the Calgary Conjoint Health Research Ethics Board (Ethics I.D. E-25315, see Appendix A). Twenty healthy adults (12 males and 8 females) were recruited for analysis (Adult consent form, see Appendix B). Since it is logistically and ethically difficult to collect blood from healthy children (age 2-18) which would have been our first choice for a control group, blood plasma from healthy adults was used as a 27 control group instead. Approximately 12 mL of blood was collected by a certified nurse from the Department of Kinesiology at the University of Calgary. However, some adults were not able to donate the full 12 mL for various reasons. After centrifugation at 1000 g (4°C) for 10 min, the supernatant plasma was removed using a micropipette and pooled. 1.6 mL aliquots of this homogenous plasma stock were transferred to cyrovials and stored in liquid nitrogen. This size of aliquot was used to allow for 2 sample injections per vial (800 µL per injection to allow for rinsing of the 500 µL sample loop). In order to ensure that the total time from blood collection to sample storage was less than an hr; samples were collected on four different days to allow for an adequate amount of time to centrifuge the blood and aliquot the plasma. Eleven pediatric cancer patients were also recruited to the study (Parental consent form, see Appendix C & Assent form, see Appendix D). Only 11 cancer patients could be recruited from the Alberta Children’s Hospital over an 8 month period due to time constraints and based on various inclusion and exclusion criteria (see Appendix E). A one-time donation of ~12 mL of blood was taken and deposited into two 6 mL heparinized trace metal testing blood collection tubes (Greiner-Bio-One VacuetteTM, NC, USA). Even though 12 mL of blood does not produce enough plasma to do triplicate studies, taking a low amount was necessary, since the amount of blood that can be collected from a child is dependent on their body weight. The blood was then centrifuged to produce plasma, which was then aliquoted into cryovials and kept frozen until analysis. Blood plasma was analyzed by Calgary Laboratory Services (CLS) using the following techniques (Services Agreement for CLS - Appendix F): 28 Albumin: Determined by using a colorimetric assay. Knowing the HSA concentration is essential for determining a relationship between HSA concentrations and the Pt distribution. Transferrin: Determined by using an immunoturbidimetric assay. Tf plays an important role in the pharmacokinetics of CP [182]. Creatinine: Determined by using a colorimetric assay. This parameter was analyzed because it is an important indicator of renal health. Blood Urea Nitrogen (B.U.N.): Determined by using a kinetic UV assay. Its levels are related to the hydration status, as well as renal health of plasma. Any data obtained from a control blood sample with abnormal levels of these compounds (except albumin) was excluded from analysis (Table 2.1). Table 2.1: Reference values for investigated blood plasma parameters provided by CLS [35]. Compound Healthy Gender/Age Reference Range Albumin 33-48 g/L Males & Females > 1 year old Transferrin 2.00-3.60 g/L Males & Females all ages Creatinine 50-120 µmol/L Males > 15 years old 35-100 µmol/L Females > 15 years old 3.0-7.5 mmol/L Males 15-54 years old 2.0-7.0 mmol/L Females 15-54 years old B.U.N. One way to assess a patient’s nutritional status is through the measurement of the HSA [183], as well as the Tf concentration in plasma [184, 185]. The plasma HSA concentration is a proxy for the rate of protein synthesis and thus overall health [163]. Depending on the stage of 29 the cancer, patients will generally have lower levels of HSA, and in the later stages of cancer, malnutrition and inflammation can reduce the synthesis of albumin in the liver [186] due to the increased production of cytokines (small proteins involved in cell signaling), as part of the inflammatory response to the tumor [186-188]. Therefore, the plasma albumin levels won’t drop in early stages of cancer, but as the disease progresses, the levels will drop significantly [186, 189]. In addition, a study which investigated the effect of HSA levels in 180 breast cancer patients found that normal levels of HSA (> 35 g HSA/L) reduced the risk of death by 72%, and that low levels of HSA adversely affected survival by a statistically significant level for all stages of the disease [190]. The hydration state can also obscure the effects of a patient’s nutritional status [191]. B.U.N. levels increase with dehydration (reabsorption), and levels can also build up if kidney function is impaired. Creatinine is another reliable indicator of kidney function, as poor clearance will cause a build-up. Typically the B.U.N. to creatinine weight ratio provides more precise information about dehydration. Ratios greater than 20:1 of B.U.N. to creatinine suggest dehydration. Since one of CP’s toxic side effects is renal damage, chemotherapy as a treatment option is limited if creatinine levels are high. However, a decreased dietary intake, as well as decreasing muscle mass, will reduce levels of creatinine. 2.4 Analysis of CP spiked human plasma 2.4.1 Analysis of plasma from healthy adults Plasma (1.6 mL) was thawed at room temperature for 45 min and incubated in closed cryovials at 37°C while gently shaken (125 rpm) for 30 min before CP (67 µL, 0.04 mg/mL) was added. The obtained mixture was incubated at 37°C for 5 min and then 0.5 mL were withdrawn for analysis by SEC-ICP-AES. Another aliquot was analyzed 2 hr after CP had been added to 30 plasma. All experiments were carried out in duplicate since the amount of plasma that could be obtained was limited. With this setup, the 5 min time point served as a control since almost all of the CP existed as the free drug, whereas the 2 hr time point reflected the metabolism of CP in plasma. If less than 1.6 mL of plasma was available, only the 2 hr time point was analyzed. The C, Cu, Fe, and Zn specific chromatograms were simultaneously obtained. C-specific chromatograms which displayed peak splitting (800-1200 s range) were not included in data analysis (Figure 2.1). The abrupt loss of the ICP-AES plasma during analysis and software crashes also meant no results were obtained for some analyses. Thus, 5 controls were not used in the discussion. 100 40000 PBS-H-02 5 min Carbon PBS-H-02 5 min Iron 80 Transferrin HSA Fe Intensity (CPS) C Intensity (CPS) 30000 20000 10000 60 40 20 Ferritin V0 V0 0 0 40000 100 PBS-H-16 5 min Carbon PBS-H-16 2 5 min Iron HSA Transferrin 80 Fe Intensity (CPS) C Intensity (CPS) 30000 20000 10000 60 40 Ferritin 20 V0 V0 0 0 400 600 800 1000 1200 1400 1600 1800 2000 400 600 800 1000 1200 1400 1600 1800 2000 Retention Time (s) Retention Time (s) Figure 2.1: C and Fe specific chromatograms obtained for plasma from healthy adults after the addition of CP after 5 min (H-02 no peak splitting, H-16 HSA & Tf peak splitting). 31 2.4.2 Analysis of plasma from pediatric cancer patients Plasma (1.6 mL) was thawed at room temperature for 45 min, incubated at 37°C for 30 min, and analyzed 5 min and 2 hr after CP addition. In contrast to the control plasma analyses, different amounts of highly pure HSA were added to establish the effect that an increased HSA concentration has on the metabolism of CP in each investigated plasma sample. The addition of HSA was thought to increase the percentage of protein bound Pt-species, due to an increase in the Pt-HSA peak. This would enable us to compare these results to those from the control samples, as well as potentially see the expected stepwise change in the distribution of Pt. Vial 1: 67 µL of CP stock solution was added to plasma (final concentration of 0.04 mg/mL). Vial 2: HSA was added to plasma to increase the final HSA concentration to 36 g HSA/L; then 67 µL of CP stock solution was added (final concentration of 0.04 mg/mL). Vial 3: HSA was added to plasma to increase the final HSA concentration to 42 g HSA/L; then 67 µL of CP stock solution was added (final concentration of 0.04 mg/mL). In cases that HSA was added to plasma, the CP addition had to be slightly adjusted so the dosage would remain the same. Since the amount of plasma in the vials from the cancer patients varied, the volumes of CP and HSA stock solutions added to the plasma needed to be adjusted. Thus, these two formulas with the CP volume as well as the HSA stock solution volume to be added were used to calculate the precise amounts needed to acquire proper dosages: 1. (67 µL CP) / (1667 µL total solution) = (Volume of CP added) / (Volume of plasma + Volume of CP added + Volume of HSA added) 32 2. (Volume of plasma x [HSA] in plasma) + (250 g HSA/L x Volume of HSA stock solution added) = (Volume of plasma + Volume of CP added + Volume of HSA added) x Desired [HSA] When a limited amount of blood plasma was obtained, only the 2 hr time point with a 36 g/L concentration of HSA was determined. Compared to the other time points with the addition of no HSA and 42 g HSA/L, the 36 g HSA/L time point is in the middle, and thus the least amount of information would be obtained from this experiment in particular. Therefore, if there was a low amount of blood plasma from the patient, this experiment was excluded. The obtained mixtures were incubated at 37°C for 5 min and then 0.5 mL were immediately injected onto the SEC-ICP-AES system. Another injection was performed 2 hr after the addition of CP/HSA. A solution containing carboplatin in PBS buffer at equal Pt concentrations compared to the CP spiked plasma was injected at the beginning and end of each day to assess the integrity of the SEC column and to calculate the % recovery of Pt from plasma spiked with CP. A % recovery of 97 ± 14 was calculated. Due to time constraints and eligibility criteria (see Appendix E), only 11 cancer patients could be recruited from the Alberta Children’s Hospital over an 8 month period. Different SEC columns were used for the healthy adults and cancer patients due to the development of a gap in the SEC column for the healthy adults. 2.5 Plasma protein binding of potentially novel anticancer compounds (Project 2) After thawing rabbit plasma for 45 min at room temperature, it was spiked with 10-50 µL (concentration dependent) of a solution containing the dissolved compound in PBS buffer to achieve a final concentration of 100 µmol/L, which is similar to concentrations previously investigated with the A549 cell line (human lung carcinoma) (150-750 µmol/L) [192].The pH 33 was adjusted to ~7.40 using dilute HCl or NaOH. Three replicates were performed with each compound, with injection times of 5 min and 1 hr after the compound was added to plasma. During this time, the plasma was kept in an incubator at 37°C. The SEC column was calibrated using a mixture of protein standards and the retention time obtained for each protein standard is indicated at the top of each chromatogram along with the corresponding molecular weight. The same parameters were used for the SEC-ICP-AES system as described in section 2.2 for project 1. 34 CHAPTER 3 EFFECT OF THE PLASMA HUMAN SERUM ALBUMIN CONCENTRATION ON THE METABOLISM OF CISPLATIN IN VITRO 3.1 Overview The goal of this project was to investigate the metabolism of CP in plasma in vitro in 20 healthy adult volunteers and compare them to that in 11 cancer patients. The results of these studies were intended to provide insight into the development of treatment protocols which may possibly reduce the toxic side effects of CP in cancer patients. 3.2 Metabolism of CP in plasma of healthy controls Blood was collected from 20 adults and assigned ID #s (privacy protection). Plasma was analyzed for creatinine, B.U.N., Tf, and HSA (Table 3.1). Almost all concentrations were within the reference range for healthy adults. Because the creatinine and B.U.N plasma concentrations of H-09 were outside the reference range, the result of its analysis was excluded from the discussion. Since the plasma of the ICP extinguished during the analyses of CP-spiked plasma for the 2 hr time points of samples H-01, H-03, and H-10, no results could be obtained. 3.2.1 Quality control of analytical results Based on the relative C-peak intensities of all 4 detected peaks in plasma (Figure 3.1A) compared to previous studies [174], exclusion criteria to reject results from the discussion were defined. Since the most intense C-peak corresponds to HSA, the overall shape of this peak was used as a proxy to guage the quality of the chromatographic separation for all investigated plasma samples. If peak splitting was observed, the obtained results were excluded from the discussion. This occured with sample H-18 (Figure 3.1B) and H-20. Therefore, only 14 of the 35 collected blood plasma samples provided results that were used for comparison with the results from the plasma from the pediatric cancer patients. Table 3.1: Plasma concentrations of chosen constituents from healthy controls. For comparison, the reference range pertaining to healthy adults is depicted at the bottom. Italicized values are outside of the reference range. ID # Gender H-01 Male H-02 H-03 H-04 H-05 H-06 H-07 H-08 H-09 H-10 H-11 H-12 H-13 H-14 H-15 H-16 H-17 H-18 H-19 H-20 Male Female Male Female Male Male Female Female Male Female Female Male Male Female Male Male Female Male Male Reference range HSA (g/L) 43 Tf (g/L) 3.15 Creatinine (µmol/L) 83 B.U.N. (mmol/L) 5.0 B.U.N. : Creatinine 14.9 43 44 46 35 40 41 40 33 45 44 44 41 50 39 43 40 38 44 38 33-48 2.61 2.74 3.10 3.39 2.81 3.04 2.69 3.30 2.72 2.64 2.99 2.48 2.60 3.25 2.70 2.96 3.56 2.67 2.52 2.003.60 111 67 95 61 72 81 75 31 72 74 81 78 95 78 68 73 65 99 88 50-120 (Males) 35-100 (Females) 4.1 3.3 3.9 4.6 4.2 5.4 3.0 1.9 5.8 3.9 4.2 3.8 5.6 4.6 6.6 5.1 3.6 7.5 5.1 3.0-7.5 (Males) 2.0-7.0 (Females) 9.1 12.2 10.2 18.7 14.4 16. 9.9 15.2 19.9 13.1 12.8 12.1 14.6 14.6 24.0 17.3 13.7 18.8 14.4 > 20 = Dehydratio n 3.2.2 Cu-specific chromatograms When fresh rabbit plasma was analyzed previously, 5 Cu-containing entities, namely coagulation factor V, transcuprein, ceruloplasmin, albumin bound Cu, and small molecular 36 670 kDa 158 kDa 44 kDa 17 kDa 670 kDa 1.35 kDa 158 kDa 44 kDa 17 kDa 1.35 kDa 40000 C Intensity (CPS) A n=14 5 min HSA B H-18-1-5min HSA 30000 20000 V0 V0 10000 0 400 600 800 1000 1200 1400 400 Retention Time (s) 600 800 1000 1200 1400 Retention Time (s) Figure 3.1: SEC-ICP-AES derived C-specific chromatograms obtained for the analysis of 14 plasma samples from healthy controls spiked with CP (0.04 mg/mL). The mixtures were incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 193.091 nm (C). (A) No splitting of peaks corresponding to HSA, (B) peak splitting of HSA peak. The retention times of the molecular weight markers are depicted on top. weight Cu were detected [174]. Some of these Cu-moieties (coagulation factor V and transcuprein), however, could not be detected at the 1 hr time point due to the instability of the involved Cu-protein bonds at room temperature [174]. Since in the present study the control plasma samples were kept stored frozen until analysis, we did not expect to detect 5 Cu peaks. Since in ceruloplasmin, all 6 Cu atoms are firmly protein bound [193], this plasma metalloprotein served as an internal standard, and produced a distinct Cu signal for all 14 plasma samples from healthy adults at both time points. All retention times of the Cu peaks corresponding to this metalloprotein were highly reproducible which indicates that data acquisition was carried out diligently for all samples (Figure 3.2). The reproducibility is further 37 illustrated by plotting the results that were obtained for the analysis of an individual plasma sample after incubation for 5 min and 2 hr (Figure 3.3). Based on these results, it can be inferred that all simultaneously obtained Pt-specific chromatograms are reliable. 670 kDa 44 kDa 17 kDa 158 kDa 670 kDa 1.35 kDa 1200 Ce ruloplas m in 5 min n=14 44 kDa 17 kDa 158 kDa 1.35 kDa Ce ruloplas m in 2 hr n=14 Cu Intensity (CPS) 1000 800 600 400 Album in bound Cu Album in bound Cu 200 V0 Sm all m ole cular w e ight Cu V0 Sm all m ole cular w e ight Cu 0 400 600 800 1000 1200 1400 400 Retention Time (s) 600 800 1000 1200 1400 Retention Time (s) Figure 3.2: SEC-ICP-AES derived Cu-specific chromatograms for the analysis of 14 plasma samples from healthy controls spiked with CP (0.04 mg/mL). The mixtures were incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 324.754 nm (Cu). The retention times of the molecular markers are depicted on top. The most intense ceruloplasmin peak was observed after the ICP torch was exchanged and shifted. 3.2.3 Fe and Zn-specific chromatograms Since the Fe and Zn specific chromatograms that were obtained after the addition of CP to plasma were very similar between the 5 min and the 2 hr time point, they are presented in Appendix G & H. 38 670 kDa 158 kDa 44 kDa 17 kDa 1.35 kDa 800 Ceruloplasmin H-12-2 5 min 2 hr Cu Intensity (CPS) 600 400 Albumin bound Cu 200 V0 Small molecular weight Cu 0 400 600 800 1000 1200 1400 Retention Time (s) Figure 3.3: Representative SEC-ICP-AES derived Cu-specific chromatograms for the analysis of H-12-2 spiked with CP (0.04 mg/mL). The mixture was incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 324.754 nm (Cu). The retention times of the molecular markers are depicted on top. 3.2.4 Pt-specific chromatograms In principle, three separate events occur after CP is injected into the bloodstream; (a) hydrolysis, (b) the binding of CP hydrolysis products to plasma proteins, and (c) the uptake of CP and/or its hydrolysis products (free or protein bound) into cells [127]. The hydrolysis of CP results in the formation of the aqua adducts [PtClOH2(NH3)2]+ and [Pt(OH2)2(NH3)2]2+ [75], as well as other Pt-containing compounds, such as dimer and trimer complexes [194-196]. These hydrolysis products can then bind to plasma proteins, including HSA. Thus, the analysis of blood plasma by SEC-ICP-AES allows one to probe the metabolism of CP by determining the size 39 distribution of Pt species at a given time point. The Pt distribution (protein bound Pt, Pthydrolysis products, and free drug) that was obtained at the 5 min and the 2 hr time point (Figure 3.4) for all 14 plasma samples from healthy controls are summarized in Table 3.2, and will be discussed first. A more detailed view of all detected Pt peaks at the 2 hr time point is displayed in Table 3.3 and will be discussed thereafter. No protein bound Pt was detected 5 min after the addition of a pharmacologically relevant dose of CP, 2.4 ± 0.3% of CP eluted in the form of hydrolysis products, and 97.6% remained as the free drug. These findings are in contrast to a previous study which reported that 5 min after spiking human plasma with CP [127], 6.5% of Pt eluted as Pt-bound proteins, 4.6 ± 0.4% as Pt-hydrolysis products, and 89 ± 0.6% as CP for males (n = 3). Similar results were reported for females (n = 3). In the present study and at the 2 hr time point, 53.0 ± 2.8% of the Pt was protein bound, while 15.9 ± 1.7% of CP eluted as hydrolysis products, and 31.1 ± 1.7% as the free drug. Previous studies which determined the Pt distribution after the addition of the same dose of CP to human plasma at the 3 hr time point were in general agreement with the results obtained in the present study. For example, the relative peak intensities of all protein bound Pt peaks and that of the 2 hydrolysis products are very similar to results that were previously obtained at the 3 hr time point. [127]. A closer look at the obtained Pt-specific chromatograms in the context of the size calibration markers revealed that the retention times of the first 3 Pt peaks corresponded to protein bound Pt-species, followed by 2 Pt peaks corresponding to hydrolysis products which eluted near the inclusion volume. The last Pt peak eluted past the inclusion volume, and corresponded to the parent drug. The first protein bound Pt peak (PP-1) co-eluted with Zn (data not shown). This Zn peak likely corresponds to α2-macroglobulin, which is a Zn metalloprotein 40 that is known to interact with CP hydrolysis products [155]. Thus, PP-1 was assigned to a Pt-α2macroglobulin complex. 670 k Da 158 k Da 44 k Da 17 k Da 1.35 k Da H-17-1 5 min 80 CP 60 40 Pt Intensity (CPS) 20 Pt-containing hydrolysis products 0 40 H-17-1 2 hr CP 6 30 Protein bound Pt-species 20 3 2 10 V0 1 Pt-containing hydrolysis products 5 4 0 400 600 800 1000 1200 1400 1600 1800 2000 Retention Time (s) Figure 3.4: Representative Pt-specific chromatograms obtained for the analysis of H-17-1 spiked with CP (0.04 mg/mL). The mixture was incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 214.423 nm (Pt). Peaks 1-3: protein bound Pt-species, peaks 4-5: Pt-containing hydrolysis products, peak 6: CP. The retention times of the molecular weight markers are depicted on top. 41 Table 3.2: Areas of all Pt peaks expressed as % values of total Pt obtained after SEC-ICP-AES analysis of human plasma spiked with CP after incubation at 37°C. * Corresponds to the average of two determinations. ID # HSA (g/L) H-02 H-04 H-05 H-06 H-07 H-08 H-11 H-12 H-13 H-14 H-15 H-16 H-17 H-19 Avg ± STD 43 46 35 40 41 40 44 44 41 50 39 43 40 44 42 ± 4 5 min Protein Bound Pt 0 0 0* 0* 0* 0* 0 0* 0* 0* 0* N/A 0 0 0±0 PtHydrolysis Products 2.8 2.4 2.6* 2.1* 2.7* 2.0* 2.3 2.5* 2.5* 2.4* 2.4* N/A 1.9 2.6 2.4 ± 0.3 Free Drug 97.2 97.6 97.4* 97.9* 97.3* 98.0* 97.7 97.5* 97.5* 97.6* 97.6* N/A 98.1 97.4 97.6 ± 0.3 2 hr Protein Bound Pt 53.7 53.5 49.1* 55.3* 52.2 55.0* 53.5 52.3* 47.6* 49.4 53.1 54.7 53.7* 58.7 53.0 ± 2.8 PtHydrolysis Products 17.1 16.2 17.9* 15.5* 17.1 14.6* 15.6 16.1* 16.9* 18.2 15.2 15.8 14.9* 11.4 15.9 ± 1.7 Free Drug 29.2 30.3 33.0* 29.3* 30.6 30.5* 30.9 31.6* 35.5* 32.4 31.7 29.5 31.3* 29.9 31.1 ± 1.7 Since PP-3 co-eluted with HSA (this has also been previously observed) [127], it was assigned to a Pt-HSA complex [67]. Due to the fact that CP derived hydrolysis products are known to bind to Tf (see section 1.4.2) and Tf has a molecular mass of 79 kDa [150] which is close to that of HSA (66.3 kDa), the inherently limited resolution offered by the employed SEC column is incapable of delineating whether the Pt peak corresponds to Pt-Tf or Pt-HSA. However, the major contribution of this Pt peak is attributed to Pt-HSA due to the higher affinity of CP hydrolysis products for HSA over Tf [60], as well as the > 10 fold higher molar concentration of HSA in plasma compared to Tf (Table 2.1). PP-2 was assigned to Pt-HSA multimer complexes because a previous study has demonstrated that the incubation of CP with 42 Table 3.3: A more detailed analysis of the Pt peak areas and retention times observed at the 2 hr time point expressed as % values of total Pt obtained after SEC-ICP-AES analysis of human plasma spiked with CP. * Corresponds to one analysis. **Corresponds to the average of two analyses. The average difference between the analyses for PP-3 was 0.7% PP = Protein bound Pt-species, HP = Pt-containing hydrolysis product. ID # PP-1 (tr=527 ± 9s) PP-2 (tr=751 ± 8s) H-02* H-04* H-05** H-06** H-07* H-08** H-11* H-12** H-13** H-14* H-15* H-16* H-17** H-19* Avg ± STD 8.1 7.7 6.8 12.2 9.2 8.7 8.3 7.3 9.3 6.7 8.5 9.1 6.9 7.9 8.3 ± 1.4 13.5 11.7 11.2 12.6 13.1 14.8 11.9 12.5 9.7 11.6 12.6 12.4 13.3 13.2 12.4 ± 1.2 PP-3 HSA (tr=890 ± 7s) 32.1 34.2 31.1 30.5 29.9 31.5 33.2 32.5 28.6 31.0 32.0 33.1 33.6 37.6 32.2 ± 2.2 HP-1 (tr=1273 ± 20s) HP-2 (tr=1388 ± 10s) CP (tr=1830 ± 12s) 3.7 3.8 4.0 2.7 4.3 2.9 3.3 2.9 2.5 3.0 1.6 3.1 2.6 1.3 3.0 ± 0.8 13.3 12.5 13.9 12.8 12.8 11.7 12.3 13.1 14.4 15.2 13.6 12.7 12.3 10.0 12.9 ± 1.2 29.2 30.3 33.0 29.3 30.6 30.5 30.9 31.6 35.5 32.4 31.7 29.5 31.3 29.9 31.1 ± 1.7 HSA results in their formation [67]. Pt-peaks 4 & 5 likely correspond to Pt-containing hydrolysis products (HP-1 and HP-2) because they eluted near the inclusion volume. HP-2, being the more abundant species, was tentatively identified in a previous study as [PtClOH2(NH3)2]+ [127], since the formation of the first hydrolysis product of CP involves the substitution of one chlorine atom of CP by a H2O molecule (Figure 1.3). Any attempts to characterize this metabolite by ESI-MS and APCI-MS in this previous study were unsuccessful, possibly due to low concentrations of the Pt species as well as the high salt content in the collected fraction [127]. HP-2 was also the only Pt peak other than free CP to be present at the 5 min time point (Figure 3.4). Based on the 43 smaller intensity of HP-1, the latter likely represents [Pt(OH2)2(NH3)2]+. The last Pt peak that was detected eluted past the inclusion volume and was previously assigned to the parent drug CP. This unusually long retention time is attributed to an unknown interaction between CP and the stationary phase, and has also been observed on closely related stationary phases, such as Superdex 75 [197]. In the context of relating the plasma [HSA] to the metabolism of CP (% Pt-bound HSA) in all investigated plasma samples (n=14), no correlation was observed at the 2 hr time point (Figure 3.5). 40 % Pt-bound HSA 38 36 R2 = 0.08 34 32 30 28 34 36 38 40 42 44 46 48 50 52 HSA (g/L) Figure 3.5: HSA concentrations plotted against their corresponding Pt peak areas of Pt-bound HSA expressed as a percentage. 3.3 Metabolism of CP in plasma of pediatric cancer patients Blood was collected from 11 pediatric cancer patients and assigned I.D. #s (privacy protection). All plasma samples were analyzed for creatinine, B.U.N., Tf, and HSA (Table 3.4). 44 Table 3.4: Concentration of HSA, Tf, creatinine, and B.U.N. in blood plasma of pediatric cancer patients compared to healthy levels. The ranges pertaining to healthy children are depicted at the bottom of the table. ID # C-01 C-02 C-03 C-04 C-05 C-06 C-07 C-08 C-09 C-10 C-11 Reference range Reference range Reference range Reference range Gender / Age Male / 13 Male / 3 Male / 15 Female / 15 Male / 14 Female / 12 Female / 14 Female / 16 Female / 14 Male / 18 Female / 3 M/F 0-5 HSA (g/L) 28 34 30 21 26 28 30 28 28 29 8 33-48 M/F 6-12 33-48 M/F 13-14 33-48 M 15-18 F 15-18 33-48 Tf (g/L) 1.48 2.19 1.70 0.93 1.23 1.97 1.73 0.81 N/A 2.05 0.26 2.003.60 2.003.60 2.003.60 2.003.60 Creatinine (µmol/L) 24 23 63 30 44 28 37 44 34 65 18 20-60 B.U.N. (mmol/L) 2.4 1.7 5.7 2.3 1.9 3.9 5.6 1.0 4.5 5.7 8.8 2.0-7.0 30-70 2.0-7.0 40-85 2.0-7.0 50-120 35-100 3.0-7.5 2.0-7.0 B.U.N. : Creatinine 24.8 18.3 22.4 19.0 10.7 34.5 37.5 5.6 32.8 21.7 121.1 > 20 = Dehydration > 20 = Dehydration > 20 = Dehydration > 20 = Dehydration The concentrations for the measured plasma constituents were all below the reference range or on a lower tier. These findings are in accord with earlier studies showing patients with lung cancer becoming malnourished in part because of a lack of appetite [198]. 3.3.1 Quality control of analytical results The same exclusion criteria that were previously defined were applied to the results obtained for plasma from pediatric cancer patients spiked with CP (see Appendix I). No results obtained for the analysis of plasma were excluded from the discussion. 45 3.3.2 Cu-specific chromatograms The retention times of ceruloplasmin were highly reproducible for all 11 cancer patient plasma samples at both time points (Figure 3.6). Therefore, based on these results, all simultaneously obtained Pt-specific chromatograms must be reliable. 670 k Da 5 min n = 11 Ceruloplasmin 158 k Da 44 k Da 17 k Da 1.35 k Da 670 k Da 158 k Da 44 k Da 17 k Da 1.35 k Da 1000 Ceruloplasmin 2 hr n = 10 Cu Intensity (CPS) 800 600 400 V0 V0 200 0 400 600 800 1000 1200 1400 400 Retention Time (s) 600 800 1000 1200 1400 Retention Time (s) Figure 3.6: Representative SEC-ICP-AES derived Cu-specific chromatograms for the analysis of 11 cancer patients spiked with CP (0.04 mg/mL). The mixture was incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 324.754 nm (Cu). The retention times of the molecular weight markers are depicted on top. 3.3.3 Fe and Zn-specific chromatograms Since the Fe and Zn specific chromatograms that were obtained after the addition of CP to plasma were very similar between the 5 min and the 2 hr time point, they are presented in Appendix G & H. These data were accumulated since they can be simultaneously obtained and 46 because these results may help to explain some of the results obtained from the Ptchromatograms. 3.3.4 Pt-specific chromatograms The Pt distribution in plasma that was determined for all 11 cancer plasma samples at the 5 min and the 2 hr time points are summarized in Table 3.5 and will be discussed first. A sample Pt-chromatogram is shown in Figure 3.7 for C-11. A more detailed view of all detected Pt peaks at the 2 hr time point is displayed in Table 3.6. Table 3.5: Peak areas of all Pt peaks expressed as % values of total Pt obtained after SEC-ICPAES analysis of human plasma spiked with CP after incubation at 37°C. HSA (g/L) ID # C-01 C-02 C-03 C-04 C-05 C-06 C-07 C-08 C-09 C-10 C-11 Avg ± STD 28 34 30 21 26 28 30 28 28 29 8 26 ± 7 5 min Protein Bound Pt 0 0 0 0 0 0 0 0 0 0 0 0±0 PtHydrolysis Products 1.8 2.4 3.0 2.6 2.0 1.7 2.5 2.2 2.7 2.9 2.5 2.4 ± 0.4 Free Drug 98.2 97.6 97.0 97.4 98.0 98.3 97.5 97.8 97.3 97.1 97.5 97.6 ± 0.4 2 hr Protein Bound Pt N/A 39.5 44.0 40.3 55.3 56.8 47.4 39.5 35.4 49.2 25.1 43.2 ± 9.5 PtHydrolysis Products N/A 23.1 19.2 24.1 14.1 14.1 19.2 19.4 26.9 19.2 32.6 21.2 ± 5.7 Free Drug N/A 37.4 36.8 35.6 30.6 29.1 33.3 41.1 37.8 31.6 42.3 35.6 ± 4.4 5 min after the addition of CP, no protein bound Pt was detected, 2.4 ± 0.4% eluted in the form of hydrolysis products, and 97.6% remained as the free drug. At the 2 hr time point, 43.2 ± 47 670 k Da 158 k Da 44 k Da 17 k Da1.35 k Da 160 5 min CP 140 120 100 80 60 Pt Intensity (CPS) 40 Pt-containing hydrolysis products 20 0 80 2 hr CP 60 Pt-containing hydrolysis products 40 Protein bound Pt-species 20 V0 0 400 600 800 1000 1200 1400 1600 1800 2000 Retention Time (s) Figure 3.7: Representative Pt-specific chromatograms obtained for the analysis of C-11 spiked with CP (0.04 mg/mL). The mixture was incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 214.423 nm (Pt). The retention times of the molecular weight markers are depicted on top. 48 9.5% of the Pt was protein bound, with the majority bound to HSA (22.3 ± 5.7%), while 21.2 ± 5.7% eluted as hydrolysis products, and 35.6 ± 4.4% as the free drug. Table 3.6: Peak areas of all Pt peaks expressed as % of total Pt obtained after SEC-ICP-AES analysis of human plasma spiked with CP after incubation at 37°C for 2 hr. PP = Protein bound Pt-species, PH = Pt-containing hydrolysis product. ID # C-01 C-02 C-03 C-04 C-05 C-06 C-07 C-08 C-09 C-10 C-11 Avg ± STD PP-1 (tr= 510 ± 9s) N/A 6.4 10.1 9.7 7.2 13.0 11.2 8.4 11.7 13.6 10.8 10.2 ± 2.4 PP-2 (tr= 724 ± 8s) N/A 8.9 9.8 8.8 21.3 15.5 11.2 7.9 7.0 11.6 5.5 10.8 ± 4.6 PP-3 HSA (tr= 868 ± 12s) N/A 24.2 24.1 21.8 26.8 28.3 25.0 23.2 16.6 24.0 8.9 22.3 ± 5.7 PH-1 (tr= 1259 ± 15s) N/A 4.7 3.3 5.6 2.3 2.4 3.8 3.1 6.3 3.1 7.2 4.2 ± 1.7 PH-2 (tr= 1377 ± 8s) N/A 18.4 15.9 18.5 11.8 11.7 15.4 16.3 20.6 16.1 25.4 17.0 ± 4.1 CP (tr= 1820 ± 8s) N/A 37.4 36.8 35.6 30.6 29.1 33.3 41.1 37.8 31.6 42.3 35.6 ± 4.4 3.4 Comparison of plasma from healthy adults with pediatric cancer plasma The comparison of the Pt results for healthy adults (n=14) with pediatric cancer patients (n=11) is depicted in Table 3.7. The results that were obtained for the 5 min time point are virtually identical between the healthy adults and the pediatric cancer patients. In order to discuss the differences at the 2 hr time point, it is most instructive to put it in a biochemical context. Therefore, the results pertaining to CP will be discussed first, and then the hydrolysis products, and lastly the protein bound Pt. In addition, it will be attempted to rationalize the obtained results based on the molar ratio between CP and HSA, which had a range of 0.177-0.252 for the healthy adults and 0.260-1.105 for the pediatric cancer patients. 49 Table 3.7: Peak areas of all Pt peaks expressed as % of total Pt obtained after SEC-ICP-AES analysis of plasma from healthy adults (Avg. 42 g HSA/L) and pediatric cancer patients (Avg. 26 g HSA/L) spiked with CP after incubation at 37°C for 2 hr. PP = Protein bound Pt-species, HP = Pt-containing hydrolysis product, H = Healthy adults, C = Pediatric cancer patients. Time PP-1 PP-2 HP-1 0±0 PP-3 Total (HSA) PP 0±0 0±0 H - 5 min n =13 C - 5 min n = 11 H – 2 hr n =14 C – 2 hr n = 10 0±0 0±0 0±0 0±0 0±0 0±0 8.3 ± 1.4 10.2 ± 2.4 12.4 ± 1.2 10.8 ± 4.6 32.2 ± 2.2 22.3 ± 5.7 53.0 ± 2.8 43.2 ± 9.5 3.0 ± 0.8 4.2 ± 1.7 0±0 HP-2 Total HP 2.4 ± 2.4 ± 0.3 0.3 2.4 ± 2.4 ± 0.4 0.4 12.9 ± 15.9 ± 1.2 1.7 17.0 ± 21.2 ± 4.1 5.7 CP 97.6 ± 0.3 97.6 ± 0.5 31.1 ± 1.7 35.6 ± 4.4 Overall, on average, 4.5% more of the parent CP as well as 5.3% more of the total HP were present in the pediatric cancer patients compared to the healthy adults. Related to this, the total protein bound Pt was 9.8% less in the pediatric cancer patients compared to the healthy adults. In order to rationalize these findings, and taking into account the differences in molar ratio between CP and HSA, it appears that a high molar ratio is associated with elevated concentrations of hydrolysis products and a concomitant decrease in plasma protein bound Pt. With regard to the individual hydrolysis products, the difference in HP-1 and HP-2 was 1.2% and 4.1% higher in the pediatric cancer patients compared to the healthy adults. This corresponds to a 32% increase in the total HP Pt area, and implies that the number of occupied binding sites for HP is much lower in plasma compared to the maximum number of binding sites deducted from experiments conducted with pure HSA and CP (~20 molecules of CP / HSA, Table 1.2). With regard to protein bound Pt, the percentage of Pt bound to PP-1 was 1.9% higher in the pediatric cancer patients, which is in contrast to the lower total protein bound Pt in this group. This observation can be rationalized by the apparently increased concentration of α250 macroglobulin in the plasma from pediatric cancer patients compared to that in healthy controls (see Appendix H). Based on the assumption that PP-2 and PP-3 both contain HSA bound Pt, it is unsurprising that both Pt peak areas were lower in the pediatric cancer patients (1.6% and 9.9%) compared to the healthy adults. In general, these results can be rationalized by a model outlined in Figure 3.8. Figure 3.8: Proposed model to link the observed in vitro results with (A) high HSA concentration (bold font) in healthy controls and (B) lower concentrations of HSA in pediatric cancer patients (normal font) with the increase in severe toxic side effects. 3.5 Comparison of pediatric cancer patient plasma with HSA fortified plasma In order to corroborate the differences that were observed between the metabolism of CP in healthy adults and pediatric cancer patients, the HSA concentration of plasma from individual pediatric cancer patients (26 ± 7 g HSA /L HSA) was fortified with highly pure HSA to achieve final plasma concentrations of 36 g HSA /L and 42 g HSA /L. At the 5 min time point, the Pt distribution was largely independent of the HSA concentration in plasma. In order to discuss the differences between the plasma from pediatric cancer patients and their HSA fortified plasma at the 2 hr time point in a biochemical context, we will discuss the results pertaining to CP first, 51 then the HP, and lastly the protein bound Pt. It will be attempted to rationalize the obtained results based on the molar ratio between CP and HSA, which had a range of 0.260-1.105 for the unfortified pediatric cancer patient plasma, 0.246 for 36 g HSA /L, and 0.210 for 42 g HSA/L. The Pt eluting as CP appeared to be independent of the HSA concentration in plasma (Table 3.8). However, the Pt area corresponding to the total HP gradually decreased by 5.6% upon fortification to 36 g HSA/L, and decreased by another 2.7% with 42 g HSA/L. In fact, the Pt area corresponding to total HP in the HSA fortified plasma from pediatric cancer patients (42 g HSA/L) at the 2 hr time point was 12.9%, which was reasonably close to the value obtained for the healthy adults (42 ± 4 g HSA/L) of 15.9%. Related to this, the total protein bound Pt increased by 5.3% and another 4.1% with HSA plasma concentrations of 36 g HSA/L and 42 g HSA/L, respectively. These results can be accounted for by the differences in the molar ratio between CP and HSA, and the associated increased protein binding of the hydrolysis products. Table 3.8: Peak areas of all Pt peaks expressed as % of total Pt obtained after SEC-ICP-AES analysis of plasma from pediatric cancer patients (Avg. 26 g HSA/L) and the HSA fortified plasma spiked with CP after incubation at 37°C for 2 hr. PP = Protein bound Pt-species, HP = Ptcontaining hydrolysis product, H = Healthy adults, C = Pediatric cancer patients. Time / [HSA] PP-1 PP-2 Total PP 0±0 HP-1 0±0 PP-3 (HSA) 0±0 C - 5 min (Avg 26 g HSA/L) n =11 C - 5 min (36 g HSA/L) n = 3 C – 5 min (42 g HSA/L) n=9 C – 2 hr (Avg 26 g HSA/L) n =10 C – 2 hr (36 g HSA/L) n = 10 C – 2 hr (42 g HSA/L) n = 10 0±0 0±0 0±0 0±0 0±0 0±0 0±0 0±0 0±0 0±0 0±0 10.2 ± 10.8 ± 22.3 2.4 4.6 5.7 9.9 ± 9.1 ± 29.6 3.0 3.3 2.5 10.4 ± 9.5 ± 32.8 2.6 2.8 1.6 0±0 HP-2 Total HP 2.4 ± 2.4 ± 0.4 0.4 2.3 ± 2.3 ± 0.4 0.4 2.1 ± 2.1 ± 0.4 0.4 CP 97.6 ± 0.4 97.7 ± 0.4 98.0 ± 0.4 ± 43.2 ± 4.2 ± 17.0 ± 21.2 ± 35.6 ± 9.5 1.7 4.1 5.7 4.4 ± 48.5 ± 2.4 ± 13.2 ± 15.6 ± 35.9 ± 5.7 0.9 2.3 3.0 4.1 ± 52.6 ± 1.8 ± 11.1 ± 12.9 ± 34.5 ± 4.3 0.6 2.1 2.5 3.0 52 With regard to the individual hydrolysis products, the Pt peak areas corresponding to HP1 and HP-2 gradually decreased by 2.4% and 5.9% at 42 g HSA/L respectively. These findings further imply that the introduction of additional HSA binding sites for the HP in pediatric cancer patient plasma may be used to decrease the fraction of free hydrolysis products in plasma. With regard to protein bound Pt, the percentage of Pt bound to PP-1 was essentially unaffected by the HSA concentration, which may be attributed to the constant α2-macroglobulin concentration in the corresponding HSA spiked plasma samples. The amount of Pt that eluted as PP-2 first decreased by 1.7% upon addition of HSA to 36 g HSA/L and remained essentially unchanged upon further addition of HSA to 42 g HSA/L. This general trend is significantly different from PP-3, which gradually increased by 10.5% over the same HSA range. In the context of relating the [HSA] in plasma to results obtained for the metabolism of CP over a 2 hr period, the concentration of HSA in the plasma from pediatric cancer patients was correlated to the % Pt-bound HSA (Figure 3.9) with an R2 value of 0.79. 40 R2 = 0.79 35 % Pt-bound HSA 30 25 20 15 10 5 10 20 30 40 HSA (g/L) Figure 3.9: HSA concentrations of pediatric cancer patients as well as their plasma fortified with HSA (36 g HSA/L and 42 g HSA/L) plotted against their corresponding Pt peak areas of Ptbound HSA expressed as a %. 53 Despite the comparatively high standard deviations for the various Pt-bound protein species (Table 3.8), the percent variation of PP-1 and PP-2 was low for individual patients. To illustrate this, Table 3.9 and Table 3.10 provide all data that were obtained for patients C-11 (lowest HSA concentration – 8 g HSA/L) and C-02 (randomly chosen). For example, at the 2 hr time point for C-11, PP-1 corresponded to 11.3 ± 1.2% of total Pt, and 6.4 ± 0.1% for C-02, which is much lower than the standard deviation obtained for all samples (e.g., PP-1 is 3.0% at 36 g HSA/L). This trend was also evident with PP-2, as well as free CP. Table 3.9: Peak areas of all Pt peaks expressed as % of total Pt obtained after SEC-ICP-AES analysis of plasma from C-11 after being spiked with CP and varying amounts of HSA. PP = Protein bound Pt-species, HP = Pt-containing hydrolysis product. Time / [HSA] PP-1 PP-2 Total PP 0 HP1 0 HP2 2.5 Total HP 2.5 CP 0 PP-3 HSA 0 5 min – No additional HSA (8 g HSA/L) 5 min – 42 g HSA/L 2 hr – No additional HSA (8 g HSA/L) 2 hr – 36 g HSA/L 2 hr – 42 g HSA/L 0 0 10.8 0 5.5 0 8.9 0 25.1 0 7.2 2.1 25.4 2.1 32.6 97.9 42.3 10.5 12.6 5.5 5.8 29.7 31.1 45.7 49.5 2.6 1.8 11.4 9.3 14.0 11.1 40.3 39.4 97.5 Table 3.10: Peak areas of all Pt peaks expressed as % of total Pt obtained after SEC-ICP-AES analysis of plasma from C-02 after being spiked with CP and varying amounts of HSA. PP = Protein bound Pt-species, HP = Pt-containing hydrolysis product. Time / [HSA] PP-1 PP-2 Total PP 0 HP1 0 HP2 2.4 Total HP 2.4 CP 0 PP-3 HSA 0 5 min – No additional HSA (34 g HSA/L) 5 min – 42 g HSA/L 2 hr – No additional HSA (34 g HSA/L) 2 hr – 36 g HSA/L 2 hr – 42 g HSA/L 0 0 6.4 0 8.9 0 24.2 0 39.5 0 4.7 2.7 18.4 2.7 23.1 97.3 37.4 6.2 6.4 7.6 7.9 27.6 30.6 41.4 45.0 3.6 2.5 17.2 15.6 20.8 18.0 37.7 37.0 54 97.6 Linear regression analysis (g HSA/L versus % Pt-bound HSA) was performed on all 11 pediatric cancer patients except for C-01 and C-03 because either insufficient amounts of plasma were obtained or the plasma extinguished during analysis. The data are shown in Table 3.11. C05, C-06, and C-09 exhibited much different results. The underlying differences pertaining to these particular samples are currently unknown. Table 3.11: Linear regression analysis showing the increase of Pt-bound HSA per gram of HSA added to plasma. Sample C-02 C-04 C-05 C-06 C-07 C-08 C-09 C-10 C-11 Average ± Std. Dev. % Increase of Pt-bound HSA / g of HSA added 0.73 0.69 0.37 0.27 0.59 0.62 1.30 0.72 0.68 0.68 ± 0.29 55 CHAPTER 4 PLASMA PROTEIN BINDING OF POTENTIALLY NOVEL METALBASED ANTICANCER COMPOUNDS In order to potentially replace some of the established Pt-based anticancer drugs with ones that exhibit less toxic side effects and are as effective, potential drug candidates must fulfill desirable physical chemical properties. Among some of these, such as water solubility, an ideal drug should rather selectively target cancer cells and be up-taken by them, while exerting less severe toxic side effects than CP for example. Since virtually all anticancer drugs are intravenously administered, the interaction of potential anticancer drug candidates with plasma proteins is another extremely important criterion which determines a drug’s efficacy and safety [45, 199]. We obtained metal-based compounds which exhibited high cytotoxicity (low IC50 values) from a collaborator and employed SEC-ICP-AES to conduct preliminary experiments to assess the interaction of these Pt and Cu-based drugs with rabbit plasma in vitro, over a 1 hr period. 4.1 Investigation of 56MESS and 56MESSCu The C, Fe, and Pt-specific chromatograms that were obtained at the 5min and the 1 hr time point for 56MESS revealed a single Pt peak which eluted past the inclusion volume (Figure 4.1). This behavior indicates that this Pt compound – which displayed a 10 times lower IC50 than CP - either did not form adducts with plasma proteins within 1 hr or that the compound was rapidly converted into a Pt species that did not interact with plasma proteins. This behavior is in stark contrast to CP, which undergoes partial hydrolysis and plasma protein binding over the same time period [79]. Given that 56MESS has been demonstrated to be able to intercalate into the DNA in L1210 murine leukemia cells [181], our results indicate that in these cell culture 56 experiments, the transport of this compound across the cell membrane must involve a mechanism that does not require plasma protein binding. Considering the hydrophobicity of the phenanthroline-moiety of 56MESS, it is possible that its cell uptake involves passive diffusion (Figure 1.11A). Interestingly, 56MESS has already been investigated in vivo and displayed no antitumoral activity in BD-IX rats whatsoever [200]. These findings may be rationalized in terms of the unselective uptake of 56MESS into all cells, therefore not exhibiting the desired selective toxicity. 158 kDa 44 kDa 17 kDa 1.35 kDa 50 Carbon Platinum Iron Transferrin 40 30 56MESS 15000 20 Ferritin Vo 0 0 30000 C Intensity (CPS) 0 50 Carbon Platinum Iron Albumin 40 150 Transferrin 30 56MESS 15000 20 Ferritin Vo 100 50 10 5000 0 0 400 200 1 hr 20000 10000 50 10 5000 25000 100 Fe Intensity (CPS) 10000 Pt Intensity (CPS) 150 20000 Pt Intensity (CPS) C Intensity (CPS) 25000 200 5 min Albumin Fe Intensity (CPS) 670 kDa 30000 600 800 1000 1200 1400 1600 0 1800 Retention Times (s) Figure 4.1: Representative C, Fe, and Pt-specific chromatograms obtained for the analysis of rabbit plasma spiked with 56MESS (100 µmol/L). The mixture was incubated at 37 °C and samples were analyzed after 5 min and 1 hr . Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. The retention times of the molecular markers are depicted on top. 57 In contrast, the results that were obtained for the closely related 56MESSCu indicated a completely different solution chemistry than 56MESS at both time points (Figure 4.2). Compared to the control plasma (data not shown), the most intense Cu peak in the 56MESSCu spiked rabbit plasma corresponded to a Cu-entity (either 56MESSCu or a Cu containing degradation product bound thereof) to a plasma protein with a molecular weight of > 44kDa. Since this molecular weight corresponds to the elution of Tf and HSA, 56MESSCu and/or its Cu containing degradation product rapidly hydrolyzes in plasma and the generated Cu moieties then bind/coordinate to highly abundant plasma proteins. The strikingly different behavior of 56MESSCu compared to 56MESS is noteworthy and can be rationalized by the known lability of Cu-NH2 bonds in the former compared to the analogous Pt bonds in the latter. 670 kDa 158 kDa 44 kDa 17 kDa 1.35 kDa 30000 1600 200 1200 150 C Intensity (CPS) 20000 15000 800 10000 400 Vo 100 50 Fe Intensity (CPS) Carbon Copper Iron 25000 Cu Intensity (CPS) 5 min 5000 0 30000 0 0 1600 200 1200 150 15000 800 10000 5000 400 Vo 0 0 400 600 800 1000 1200 1400 1600 100 50 Fe Intensity (CPS) C Intensity (CPS) 20000 Cu Intensity (CPS) 1 hr Carbon Copper Iron 25000 0 1800 Retention Times (s) Figure 4.2: Representative C, Fe, and Cu-specific chromatograms obtained for the analysis of rabbit plasma spiked with 56MESSCu (100 µmol/L). The mixture was incubated at 37 °C and samples were analyzed after 5 min and 1 hr . Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. The retention times of the molecular markers are depicted on top. 58 4.2 Investigation of DiPy and SOOS The C, Fe, and Pt-specific chromatograms that were obtained at the 5 min and the 1 hr time point for DiPy revealed a single Pt peak (Fig 4.3), the retention time of which indicated that this Pt compound, unlike 56MESS, rapidly forms adducts with plasma proteins (within 5 min). Given that DiPy and/or its hydrolysis products appear to form adducts with HSA and/or Tf (coelution with Fe), our results suggest that it may possibly enter cells via the Tf-mediated uptake pathway. 158 kDa 44 kDa 17 kDa 1.35 kDa 5 min Carbon Platinum Iron 200 40 150 20000 30 15000 20 10000 Vo 100 50 Fe Intensity (CPS) C Intensity (CPS) 25000 50 Pt Intensity (CPS) 670 kDa 30000 10 5000 0 0 0 50 200 30000 1 hr Carbon Platinum Iron 40 30 15000 20 10000 Vo 50 10 5000 0 0 400 100 Fe Intensity (CPS) 150 20000 Pt Intensity (CPS) C Intensity (CPS) 25000 600 800 1000 1200 1400 1600 0 1800 Retention Times (s) Figure 4.3: Representative C, Fe, and Pt-specific chromatograms obtained for the analysis of rabbit plasma spiked with DiPy (100 µmol/L). The mixture was incubated at 37 °C and samples were analyzed after 5 min and 1 hr . Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. The retention times of the molecular markers are depicted on top. 59 Unlike the other three compounds, SOOS displayed poor solubility in aqueous buffers. Although it appeared that the compound had not dissolved, the solution was still mixed with the rabbit plasma, and then injected onto the SEC column. After injection, the backpressure of the column significantly increased due to a precipitate forming on the column, and the ICP plasma extinguished. The 1 hr time point was missed while trying to stabilize the ICP plasma. After 4 hr, another injection was performed and results were obtained (Figure 4.4). Since precipitate was forming on the column, further injections with SOOS were not performed. Given that SOOS and/or its hydrolysis products appear to form adducts with HSA and/or Tf (co-elution with Fe), our results suggest that it may possibly enter cells via the Tf-mediated uptake pathway. SOOS 670 kDa 158 kDa 44 kDa 17 kDa 1.35 kDa 35000 30 180 4 hr 30000 Carbon Platinum Iron 20000 15 15000 10 10000 5 120 100 80 60 Fe Intensity (CPS) 140 20 Pt Intensity (CPS) 25000 C Intensity (CPS) 160 25 40 5000 20 0 0 0 -5 400 600 800 1000 1200 1400 1600 1800 Retention Times (s) Figure 4.4: Representative C, Fe, and Pt-specific chromatograms obtained for the analysis of rabbit plasma spiked with SOOS. The mixture was incubated at 37 °C and samples were analyzed after 4 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. The retention times of the molecular markers are depicted on top. 60 CHAPTER 5 CONCLUSIONS 5.1 Effect of the plasma HSA concentration on the metabolism of CP in vitro The analysis of CP spiked blood plasma from 14 healthy adults (control, 42 ± 4 g HSA/L) and 11 pediatric cancer patients (26 ± 7 g HSA/L) at the 5 min and 2 hr time point revealed differences in the Pt distribution and therefore the metabolism of CP. Since HSA is known to play a key role in the metabolism of CP in plasma, the observed differences were rationalized in terms of the different HSA concentrations between healthy adults and pediatric cancer patients. In general and at the 2 hr time point, a decrease in the HSA concentration in plasma resulted in less Pt being present in form of Pt-protein adducts (including HSA). Concomitantly, an increased percentage of total Pt was present in form of free hydrolysis products. To corroborate these results, HSA was added to plasma from individual cancer patients to achieve final concentrations of 36 and 42 g HSA/L, and the metabolism of CP was determined as outlined above. Overall, the metabolism of CP in the HSA fortified plasma was rather similar to that of plasma in healthy adults. These experiments conclusively demonstrate that HSA plays an important role in the metabolism of CP in human plasma in vitro. More importantly, our in vitro results indicate that the concentration of biologically highly reactive free CP hydrolysis products in human plasma may be decreased by the administration of HSA to pediatric cancer patients. Since it is presently unknown which Pt species are predominantly responsible for exerting its toxic side effects in patients and given that circumstantial evidence suggests that Pt-HAS adducts are associated with less toxic side effects than CP [143], our in vitro experiments suggest that these CP derived hydrolysis products may play a more critical role than is currently acknowledged. Furthermore, our results represent an important first step towards optimizing the 61 treatment protocol of cancer patients that are administered with CP to mitigate the severe toxic side effects. 62 5.2 Plasma protein binding of potentially novel metal-based anticancer compounds Since virtually all anticancer drugs are intravenously administered, the interaction of potential anticancer drugs with plasma proteins represents one important criterion (in addition to IC50, Kd, etc.) which determines the drug’s efficacy and its toxic side effects. In order to assess the comparative biochemical transformations of 4 metallo-compounds (Pt-containing compounds: 56MESS, DiPy, and SOOS, and a Cu-containing compound: 56MESSCu) in plasma, we added pharmacologically relevant doses of each of these metallo-compounds to rabbit plasma, and analyzed it by SEC-ICP-AES after 5 min and 1 hr. 56MESS, or a Pt containing degradation product thereof, did not form adducts with plasma proteins within 1 hr, suggesting that the transport of this anticancer active metallo-compound across the cell membrane may be driven by its hydrophobicity and does not involve plasma proteins. Interestingly, the exchange of the Pt metal center in this compound for Cu (56MESSCu) produced drastically different results in the sense that this metal based compound or a Cu containing hydrolysis product thereof bound to HSA and/or Tf. This result can be rationalized in terms of the known lability of Cu-NH2 bonds compared to the analogous Pt bonds which are more stable. The interaction of 56MESSCu with plasma proteins and its established cytotoxicity suggest that this metal based drug may enter cells via the Tf-mediated uptake pathway. The addition of DiPy (5 min and 1 hr) and SOOS (4 hr) produced results that were very similar to those of 56MESSCu. 63 CHAPTER 6 FUTURE WORK SEC-ICP-AES represents a unique tool to probe the metabolism of metal-based drugs in plasma in vitro and also potentially in vivo. In particular, one can simultaneously observe the metabolism of the metal-based drug of choice, as well as potential perturbations caused by the drug at the Cu, Fe, and Zn metalloprotein level which can possibly be linked to side effects. One important next step would be to probe the interaction of CP with varying levels of HSA in vivo in animal studies and/or patients. This would allow one to determine how quickly all Pt metabolites disappear from the blood plasma. If this information were combined with the potential different distributions of Pt in the organs of the animal, it could potentially provide insight into the toxic side effects that are caused by CP. Thus, it may support the development of new treatment protocols for optimizing the treatment of cancer patients with CP to mitigate the toxic side effects. Another potential application would be to establish the molecular basis by which ameliorating agents (e.g. STS, NAC, and D-methionine) mitigate some of the toxic side effects of CP in vivo. To that end, previous studies have shown that STS will greatly reduce the amount of CP based Pt-bound proteins as well as Pt-hydrolysis products by producing a Pt-STS complex which is likely to play a role in the mitigation of these toxic side effects. 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Invest New Drugs, 2011. 29(6): p. 1164-1176. 77 APPENDIX A Ethics form removed for online submission 78 APPENDIX B 79 80 81 82 APPENDIX C 83 84 85 86 APPENDIX D 87 88 89 APPENDIX E 90 APPENDIX F 91 Signature sheet removed for online submission 92 93 APPENDIX G 670 kDa 158 kDa 44 kDa 17 kDa 670 kDa 1.35 kDa 100 5 min n=14 Trans fe rrin 158 kDa 44 kDa 17 kDa 1.35 kDa 2 hr n=14 Trans fe rrin Fe Intensity (CPS) 80 60 40 Fe rritin Fe rritin 20 V0 V0 0 400 600 800 1000 1200 1400 400 600 800 1000 1200 1400 Retention Time (s) Retention Time (s) SEC-ICP-AES derived Fe-specific chromatograms for the analysis of 14 plasma samples from healthy controls spiked with CP (0.04 mg/mL). The mixtures were incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 259.940 nm (Fe). The retention times of the molecular markers are depicted on top of the figure. 94 670 k Da 5 min n = 11 Transferrin 300 Fe Intensity (CPS) 670 k Da 158 k Da 44 k Da 17 k Da 1.35 k Da 350 158 k Da 44 k Da 17 k Da 1.35 k Da 2 hr n = 10 Transferrin 250 200 Ferritin 150 Ferritin 100 V0 V0 50 0 400 600 800 1000 1200 1400 400 Retention Time (s) 600 800 1000 1200 1400 Retention Time (s) SEC-ICP-AES derived Fe-specific chromatograms for the analysis of 11 pediatric cancer patients spiked with CP (0.04 mg/mL). The mixtures were incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 259.940 nm (Fe). The retention times of the molecular markers are depicted on top of the figure. 95 APPENDIX H 670 kDa 44 kDa 17 kDa 158 kDa 670 kDa 1.35 kDa 60 1.35 kDa 2 hr n=14 5 min n=14 Album in 50 Zn Intensity (CPS) 44 kDa 17 kDa 158 kDa Album in 40 2-m acroglobulin 2-m acroglobulin Extrace llular CuZnSOD 30 Extrace llular CuZnSOD 20 V0 V0 10 0 400 600 800 1000 1200 1400 400 Retention Time (s) 600 800 1000 1200 1400 Retention Time (s) SEC-ICP-AES derived Zn-specific chromatograms for the analysis of 14 plasma samples from healthy controls spiked with CP (0.04 mg/mL). The mixtures were incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 213.856 nm (Zn). The retention times of the molecular markers are depicted on top of the figure. 96 670 k Da Zn Intensity (CPS) 50 670 k Da 158 k Da 44 k Da 17 k Da 1.35 k Da 60 2-m acroglobulin 5 min n = 11 Album in 158 k Da 44 k Da 17 k Da 1.35 k Da 2 hr n = 10 Album in 2-m acroglobulin 40 30 20 Extrace llular CuZnSOD Extrace llular CuZnSOD V0 V0 10 0 400 600 800 1000 1200 1400 400 Retention Time (s) 600 800 1000 1200 1400 Retention Time (s) SEC-ICP-AES derived Zn-specific chromatograms for the analysis of 11 plasma samples from pediatric cancer patients spiked with CP (0.04 mg/mL). The mixtures were incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 213.856 nm (Zn). The retention times of the molecular markers are depicted on top of the figure. . 97 APPENDIX I 670 kDa 158 kDa 44 kDa 17 kDa 1.35 kDa 50000 n = 11 HSA C Intensity (CPS) 40000 30000 20000 10000 V0 0 400 600 800 1000 1200 1400 Retention Time (s) SEC-ICP-AES derived C-specific chromatograms for the analysis of 11 plasma samples from pediatric cancer patients spiked with CP (0.04 mg/mL). The mixtures were incubated at 37 °C and analyzed after 5 min and 2 hr. Stationary phase: Superdex 200 10/300 GL column (30x1.0 cm i.d., 13 µm particle size) at 22°C. Mobile phase: PBS buffer (pH 7.4). Flow rate: 1.0 mL/min. Injection volume: 500 µL. Detector: ICP-AES at 193.091 nm (C). The retention times of the molecular markers are depicted on top of the figure. 98