HIF1A signaling selectively supports proliferation of breast cancer in the brain [F1 vs parental]

Blood-borne metastasis to the brain is a major complication of breast cancer, but cellular pathways that enable cancer cells to selectively grow in the brain microenvironment are poorly understood. We find that cultured circulating tumor cells (CTCs), derived from blood samples of women with advanced breast cancer and directly inoculated into the mouse frontal lobe, exhibit striking differences in proliferative potential in the brain. Derivative cell lines generated by serial intracranial injections acquire selectively increased proliferative competency in the brain, with reduced orthotopic tumor growth. Increased Hypoxia Inducible Factor 1A (HIF1A)-associated signaling correlates with enhanced proliferation in the brain, and shRNA-mediated suppression of HIF1A or drug inhibition of HIF-associated glycolytic pathways selectively impairs brain tumor growth while minimally impacting mammary tumor growth. In clinical specimens, brain metastases have elevated HIF1A protein expression, compared with matched primary breast tumors, and, in patients with brain metastases, hypoxic signaling in CTCs predicts decreased overall survival. The selective activation of hypoxic signaling by metastatic cancers in the brain may be an opportunity for therapeutic intervention. We injected cells from CTC-derived cell lines (i.e., parental cell lines) from two patients into mice intracranially. We harvested the resulting tumors and sorted for GFP expression to remove mouse cells. We expanded the sorted cells in vitro under anchorage-independent conditions for less than four weeks. We then performed RNA-seq on the resulting F1 cell lines.