The Role of HIF-1a and TGF-8 Signaling in Breast Cancer Bone Metastasis

Seventy percent of patients with advanced breast cancer develop bone metastases, which cause severe pain, hypercalcemia, pathologic fracture, nerve compression syndromes, and paralysis. Bone is a site of hypoxia and high concentrations of active transforming growth factor (TGF)-. Skeletal metastases involve interactions between tumor and bone cells driven by locally secreted proteins, many of which are increased by hypoxia and TGF-. We asked whether these two factors promote bone metastases independently or synergistically. Of sixteen prometastatic candidates, only VEGF and CXCR4 mRNA expression and promoter activity were additively increased by TGF- and hypoxia. We tested interaction of hypoxia inducible factor (HIF)-1 and TGF- pathways by HIF-1 knockdown and TGF- blockade with a dominant-negative type II receptor. Inhibition of either pathway in tumor cells decreased osteolytic lesion area and improved survival in a mouse model of bone metastases, with no additive effect when inhibiting both pathways. In contrast, combined inhibition of these pathways in both tumor and host cells using small molecule inhibitors, 2-methoxyestradiol to inhibit HIF signaling and SD-208 to inhibit TGF- signaling, reduced tumor burden more than either alone. The results suggest that hypoxia and TGF- independently drive tumor responses in bone metastases, but that combined systemic targeting of HIF-1 and TGF- may provide additive benefit for the treatment of bone metastases and improve patient survival. DEDICATION ii This thesis is dedicated to my husband Ryan, my parents Charles and Carol, and my sister Megan for their support and encouragement in this and all that I endeavor.

Note: Abstract extracted from PDF text