UNIVERSITY OF CALGARY Model of Osteolytic Breast Cancer Metastasis”

UNIVERSITY OF CALGARY
“Targeting the PI3K and Ras Signal Transduction Pathways in a Murine
Model of Osteolytic Breast Cancer Metastasis”
by
Nicholas Adam Joseph Bosma
A THESIS
SUBMITTED TO THE FACULTY OF GRADUATE STUDIES
IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE
DEGREE OF MASTER OF SCIENCE
DEPARTMENT OF BIOCHEMISTRY AND MOLECULAR BIOLOGY
CALGARY, ALBERTA
JANUARY 2013
© Nicholas Bosma 2013

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Abstract
Bone metastasis frequently occurs in patients with advanced breast cancer, and leads to
widespread bone destruction. Aberrant activation of the PI3K and Ras-MAPK pathways
are consistently observed in high-grade metastatic breast cancers, making these pathways
attractive targets for therapeutic intervention. Complex signal crosstalk between these
pathways is implicated in cancer cell perpetuation; therefore, dual inhibition should
theoretically provide maximal targeting. The PI3K and MEK inhibitors, PX866 and
AZD6244 were employed to investigate the therapeutic potential in an in vivo model of
MDA-MB-231-EGFP/Luc2 human breast cancer osteolytic metastases. PI3K inhibition
did not directly affect bone-colonized cancer cells, however, it demonstrated an
attenuation of bone loss, whereas MEK inhibition resulted in a significant reduction of
both tumor growth and osteolysis. Simultaneous inhibition of PI3K and MEK resulted in
a reduction of tumor growth, but paradoxically exhibited an exacerbation of bone
damage. These findings suggest that MEK inhibition alone may be a valuable additional
treatment for breast cancer osteolytic metastasis.

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Preface
It is apparent that cancer cells have developed sophisticated mechanisms to sustain
proliferative expansion and survival, even in the face of toxic stimuli. Therefore,
strategies that target the aberrant molecular machinery of cancer cells will be essential for
future therapeutics. Signal crosstalk in aberrantly activated signal transduction pathways
is a prime example of this. Furthermore, in order to investigate the therapeutic potential
of certain agents relevant to human malignancies, the specific micro-environment of the
primary or metastatic niche also needs to be taken into consideration. Therefore, this
study employed small-molecule inhibitors to target potential signal pathway crosstalk in
an in vivo model that recapitulates many of the processes in osteolytic breast cancer
metastasis. Systematic investigation into molecular mechanisms that govern cancer cell
fate, and the development of more accurate in vivo models will be essential for the
progression of effective treatment modalities.

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Acknowledgements
This thesis would not have been possible without the guidance and support of several
individuals who have contributed in one form or another. First and foremost, I would like
to thank my supervisor Dr. Frank Jirik. His vast repository of knowledge and endless
assistance and direction was a prominent reason for my success.
I would also like to acknowledge all of my lab members, as they all contributed to this
work in one way or another. Everyone’s contribution was invaluable.
Dr. Helen Buie helped with much of the microCT work, and was an extreme asset to the
completion and success of this work.
I would also like to acknowledge Leona Barclay’s vast contribution in the sectioning and
staining of the majority of histology slides.
My committee members, Dr. Shirin Bonni and Dr. Steven Boyd also provided a
tremendous amount of influence and supportive guidance through the learning process of
this research.
Lastly, I would like to acknowledge the tremendous influence my family and friends
provided throughout. They all taught me to strive for nothing but perfection. I would
especially like to thank my parents and Laura Evans for their indispensable support that
motivated my passionate ambition for success.

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Dedication
I would like to dedicate the work of this thesis to the memory of my grandmother
and grandfather, who passed away from breast cancer and pancreatic cancer, respectively.
Having experienced the detrimental power that cancer delivers has been a profound
influence in my desire to uncover effective strategies for therapeutic opportunities.
They will be forever missed, but never forgotten.