HIF Inactivation of p53 in Ovarian Cancer Can Be Reversed by Topotecan, Restoring Cisplatin and Paclitaxel Sensitivity

Ovarian cancer growth under hypoxic conditions results in hypoxia-inducible factor-1 alpha (HIF1 alpha) stabilization. HIF1 alpha is an adverse prognostic factor that may contribute to worse outcomes via its capacity to bind to p53, potentially blocking p53-mediated apoptosis. We determined whether HIF1 alpha-p53 binding occurred in hypoxic ovarian cancer cell lines, and if this blocked p53 transcriptional activity. Topotecan (TPT), used in the treatment of ovarian cancer, inhibits HIF1 alpha translation via a topoisomerase-1 (TOPO1)-dependent mechanism. We examined if TPT knockdown of HIF1 alpha restored p53 transcriptional function. TPT effects on HIF1 alpha and p53-related transcriptional targets were assessed by PCR. Associations between TPT effects and TOPO1 expression levels were examined by Western blots and knockdown by siRNA. RNA-binding protein immunoprecipitation was used to assess if TOPO1 was resident on HIF1 alpha mRNA. We determined if sublethal doses of TPT, used to knockdown HIF1 alpha, reversed hypoxia-related cisplatin and paclitaxel resistance (XTT assay). Flow cytometry was used to assess HIF1 alpha-mediated upregulation of ABCB1 and ABCB5 efflux pump expression. We found that HIF1 alpha binding to, and inhibition of, p53 transcriptional activity in hypoxic ovarian cancer cells was associated with drug resistance. TPT-mediated downregulation of HIF1 alpha in hypoxic cells required TOPO1 resident on HIF1 alpha mRNA, restored p53 transcriptional activity, downregulated ABCB1/ABCB5 cell surface expression, and reversed hypoxia-related cisplatin and paclitaxel resistance.