MECHANISTIC AND TRANSLATIONAL STUDIES OF THE HYPOXIA RESPONSE IN CANCER

University Of Arizona, Tucson AZ

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Abstract

Solid tumors exist in an extremely hostile environment for cell growth. As even the smallest tumors grow they rapidly outstrip new blood vessel formation leading to poor perfusion and hypoxia. Cancer cells adapt by changes in key cell survival signaling pathways leading to an increased glycolytic metabolism, resistance to apoptosis, and the production of factors that increase angiogenesis. Cancer cells frequently also develop constitutive upregulation of the genes regulating the hypoxia response leading to rapidly growing tumors with a poor patient prognosis. These changes also make tumors resistant to radiation and chemotherapy, and are a major reason for the failure of cancer therapy. The hypothesis upon which our studies are based is that the signaling pathways that regulate the growing tumor's response to hypoxia provide novel targets for the development of agents to selectively treat solid tumors. The pathways we will study are the phosphoinositide-3-kinase cell survival signaling pathway,the thioredoxin-1 redox signaling stress pathway and the hypoxia mediated increase in redox sensitive transcription factors. The most studied hypoxia induced transcription factor is the hypoxia inducible factor-1 (HIF-1), a heterodimer of a hypoxia inducible subunit and HIF-1(3. We have developed a novel inhibitor of HIF-1a, PX-478, which shows remarkable single agent antitumor activity in animaj studies and synergy with radiation We will conduct a Phase I trial of PX-478 together with radiation in patients with metastatic cancer to the bone employing molecular imaging and other molecular markers to assess drug effect and early patient response. We have also developed a novel inhibitor of Ptdlns-3-K, PX-866, that also inhibits HIF-1 a and the hypoxia response and will conduct a second clinical trail in later years of the grant. While HIF-1 is an important mediator of the hypoxic response, it is not the only transcription factor involved. We have used transcription factor profiling to identify two other transcription factors, Sp1 and Nrf2, that play an independent role in the hypoxia response and will study their mechanisms of action. The objective of our work is to understand the mechanisms of hypoxia induced gene expression that will allow the development of strategies and new drugs for treating cancer.