Dual Targeting of the Androgen Receptor and Hypoxia-Inducible Factor 1a Pathways Synergistically Inhibits Castration-Resistant Prostate Cancer Cells

Enzalutamide is a potent second-generation androgen receptor (AR) antagonist with activity in metastatic castrate-resistant prostate cancer (CRPC). Although enzalutamide is initially effective, disease progression inevitably ensues with the emergence of resistance. Intratumoral hypoxia is also associated with CRPC progression and treatment resistance. Given that both AR and hypoxia inducible factor-1 a (HIF-1a) are key regulators of these processes, dual targeting of both signaling axes represents an attractive therapeutic approach. Crosstalk of the AR and HIF-1a signaling pathways were examined in prostate cancer cell lines (LNCaP, 22Rv1) with assays measuring the effect of androgen and hypoxia onAR-dependent and hypoxia-inducible gene transcription, protein expression, cell proliferation, and apoptosis. HIF-1a inhibition was achieved by siRNA silencing HIF-1a or via chetomin, a disruptor of HIF-1a-p300 interactions. In prostate cancer cells, the gene expression of AR targets (KLK3, FKBP5, TMPRSS2) was repressed by HIFsignaling; conversely, specific HIF-1a target expression was induced by dihydrotestosterone-mediated AR signaling. Treatment of CRPC cells with enzalutamide or HIF-1a inhibition attenuated AR-regulated and HIF-1a–mediated gene transcription. The combination of enzalutamide and HIF-1a inhibition was more effective than either treatment alone. Similarly, the combination also reduced vascular endothelial growth factor protein levels. HIF-1a siRNA synergistically enhanced the inhibitory effect of enzalutamide on cell growth in LNCaP and enzalutamide-resistant 22Rv1 cells via increased enzalutamide-induced apoptosis. In conclusion, the combination of enzalutamide with HIF-1a inhibition resulted in synergistic inhibition of AR-dependent and genespecific HIF-dependent expression and prostate cancer cell growth.