Hypoxia induced paclitaxel resistance in human ovarian cancers via hypoxia-inducible factor 1α

Purpose Chemoresistance severely restricts the anti-cancer medicines from effectively treating human ovarian cancer, which has been shown to develop and survive in the specific hypoxic environments. To understand the relationship between hypoxia and chemoresistance, we investigated the potential role of hypoxia in the pathophysiology of chemoresistance, especially focusing on hypoxia-inducible factor 1α (HIF-1α). Methods The A2780 ovarian cancer cells are cultured in gradient hypoxic conditions (5% O₂, 3% O₂, and 1% O₂), the sensitivity of the cells to paclitaxel and the cell inhibitory rate were determined by MTT assay. The expression and the transcriptional activity of HIF-1α were examined by western blot, Immunocytochemical staining, reverse transcription-polymerase chain reaction (RT-PCR), and the dual luciferase reporter system, respectively. The cell cycle distribution was analyzed by flow cytometry. In addition, we silence HIF-1α expression by performing RNA interference. Results MTT assay demonstrates that hypoxic challenge substantially reduces the susceptibility of cells to paclitaxel at all the tested concentrations. Coincident with this is the activation of HIF-1α in nuclear, which displays the increased transcriptional activity and high protein expression. Hypoxic manipulation (5% O₂, ~1% O₂) significantly increased the cell population at G0/G1. Interestingly, knockdown of endogenous HIF-1α significantly alleviates the chemoresistance and promotes G1/S transition with the increased sensitivity of A2780 cells to paclitaxel under each hypoxic condition. Conclusions It suggests that HIF-1α, stimulated by hypoxia, exerts a pivotal role in chemoresistance by G0/G1 arrest. Eliminating hypoxic conditions or silencing HIF-1α by siRNA might provide a potent tool to enhance paclitaxel effectiveness in treatment of human ovarian cancer.