Targeting Hypoxia-Inducible Factor to Reverse Drug Resistance in Cancer

HIF-1 alpha is an adverse prognostic factor that has been shown to contribute to hypoxia-induced treatment resistance in many cancer types. Topotecan [TPT], which is used to treat platinum-resistant ovarian cancer, downregulates HIF-1 alpha even with metronomic doses. We first evaluated topotecan eliciting its inhibitory effect on HIF-1 alpha protein stabilization with pharmacologic doses. Furthermore, we also evaluated markers downstream of HIF involved in angiogenesis, VEGF, and markers associated with drug resistance, ABCB1 and ABCB5. We demonstrated down-modulation of hypoxia-induced VEGF protein upregulation with TPT treatment. We also demonstrated down-modulation of HIF-mediated ABCB1 and ABCB5 protein expression.;We evaluated the mechanism by which TPT inhibits HIF-1 alpha protein accumulation. We found that topotecan mediates inhibition of HIF-1 alpha protein stabilization in a Topoisomerase I (Topo I) dependent manner. Using RNA-protein immunoprecipitation studies, we found that Topo I binds to HIF-1 alpha mRNA directly, suggesting that to be TPT's target for inhibiting HIF-1 alpha protein translation.;The crosstalk between HIF-1 alpha and p53 in hypoxia has not extensively been evaluated. Both HIF and p53 play critical roles in promoting signaling pathways that are crucial to tumor progression, since at least 50% of solid tumors contain p53 mutations resulting in altered function of p53 transcriptional activity. We further evaluated topotecan's role in modulating HIF and p53 interactions, and whether TPT-mediated blockade of HIF-1 alpha accumulation would increase p53 function and promote chemosensitivity. We found direct p53: HIF binding in both ovarian and melanoma cells. Simultaneously, increased p53 expression levels after TPT in conjunction with enhanced p53 downstream transcriptional activity was also seen and confirmed to be a p53-specific modulation with the use p53 siRNA studies with a wt-p53 cell line (OVCA429). We evaluated TPT's role in reversing chemosensitivity. We demonstrated that topotecan-mediated down-regulation of HIF-1 alpha caused reversal of hypoxia-related chemoresistance to both cisplatin and paclitaxel, which was also shown with HIF knockdown studies. TPT may be a clinically useful agent for inhibiting HIF function and chemosensitization when used in combination therapy.;Resveratrol, a polyphenol compound, has also shown to elicit anti-angiogenic effects. We showed that resveratrol combined with topotecan elicited a synergistic effect in both melanoma cell lines A375, YUZAZ6, M14 and primary melanoma tumors MELV2. This interaction warrants further evaluation in vivo.