Topotecan modulation of HIF1α in ovarian cancer cell lines blocks VEGF expression in a topoisomerase I-dependent manner Free

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Topotecan targets topoisomerase I (Topo I) and is used to treat ovarian cancer. While topotecan has been reported to inhibit hypoxia inducible factor 1α (HIF1α) mRNA translation in a Topo I dependent manner, leading to decreased HIF1α protein and depression of vascular endothelial growth factor (VEGF) levels in some tissue types, this has not been studied in ovarian cancer. These effects could augment therapy with antiangiogenesis agents such as bevacizumab, which is active in ovarian cancer. We therefore set out to determine whether topotecan could downregulate HIF1α and VEGF protein levels in ovarian cancer cell lines. Resveratrol, a stilbene in red wine also suppresses HIF1α accumulation, and its effects were examined in combination with topotecan. Three ovarian cell lines were studied: CAOV3, CAOV4, and TOV112D. Cell line dose response to topotecan was determined using the XTT assay. Topoisomerase I and HIF1α protein levels were determined by Western Blots or immunohistochemistry. Cells were exposed to low oxygen conditions (0.5% O2) or varying concentrations of cobalt chloride (CoCl2) to mimic tumor hypoxia and stabilize HIF1α protein. Topotecan showed a range of activity against the cell lines studied; the CAOV3 line was most sensitive (IC50 = 0.02 nM), while CAOV4 cells were the most resistant (IC50 = 394.5 nM). Topotecan-mediated inhibition of ovarian cancer cell line growth was dependent on Topo I expression levels (r= 0.99, p<0.001). Hypoxia and CoCl2 treatment of all lines resulted in comparable levels of HIF1α stabilization and upregulation of VEGF levels. Topotecan blockade of both HIF1α and VEGF accumulation after hypoxia or CoCl2 varied for the cell lines and was directly related to their IC50 and Topo I expression levels. Resveratrol had little direct effect on cell line proliferation over the dose range studied, but effectively blocked HIF1α accumulation in all lines, and produced an additive effect in combination with topotecan. Topotecan inhibition of ovarian cancer cell line proliferation, and HIF1α and VEGF accumulation after hypoxia or CoCl2 was dependent on Topo I levels. Downregulation of HIF1α and VEGF after topotecan treatment may be of clinical benefit when used in combination with antiangiogenesis agents that target the VEGF pathway. Determination of Topo I levels in clinical specimens may provide a predictive test to select patients for this treatment approach.