2-Methoxyestradiol (2ME2) is a naturally occurring derivative of estradiol currently in Phase l/ll clinical trials as an inhibitor of tumor angiogenesis. We have recently reported that 2ME2 potently inhibits the protein levels and transcriptional activity of the pro-angiogenic and pro-survival transcription factor HIF-1 alpha. Moreover, we showed that HIF-1 alpha inhibition occurs downstream of disruption of the microtubule cytoskeleton by 2ME2. These data provide the first mechanistic link between targeting of the microtubule cytoskeleton and inhibition of tumor angiogenesis. However, the cellular signals that lead from microtubule disruption to HIF-1 alpha inhibition remain unknown. With this proposal, we seek to build upon our previous work in order to investigate in detail the molecular mechanism(s) that lead from microtubule disruption to inhibition of tumor angiogenesis and survival. Our hypothesis is that 2ME2 has a bivalent effect on the chemomechanics of microtubule-dependent HIF-1 alpha activation. By disrupting cellular microtubules, 2ME2 inhibits HIF-1 alpha nuclear translocation and HIF-1 alpha translation, thus, resulting in inhibition of HIF-1 alpha activity. To elucidate the mechanism by which microtubule disruption regulates HIF-1 alpha activity we plan to: I) Elucidate the mechanism by which 2ME2 inhibits HIF-1 nuclear translocation, II) Define the mechanism by which 2ME2 inhibits HIF-1 alpha translation and III) Investigate whether abrogation of microtubule-dependent regulation of HIF-1 alpha in VHL-mutant renal cell carcinomas (RCCs), results in 2ME2 resistance. We will also expand these observations to additional classes of microtubule-targeting drugs, such as the taxanes, the epothilones and the vinca alkaloids. With this proposal we are seeking to build on our previous work and advance our understanding of the basic mechanisms governing the microtubule-dependent regulation of the HIF pathway, as well as their impact on tumor survival and chemosensitivity.
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