Treatment-induced hypoxia attenuates Enzalutamide response and promotes resistance in pre-clinical models of prostate cancer

Background: Inhibition of androgen signalling remains the therapeutic mainstay in castrate-resistant prostate cancer. Retention of active AR signalling or acquisition of splice variants have been reported as mechanisms of resistance to the anti-androgen Enzalutamide. Other non-AR dependent mechanisms of resistance have also emerged including acquisition of a hypoxic microenvironment. We propose treatment-induced hypoxia and the induction of angiogenesis may define a novel mechanism of relapse to Enzalutamide. Methods: Preclinical experiments were conducted in LNCaP tumors and established human prostate cancer cell lines. Tumour growth, intra-tumoral hypoxia and blood vessel density were measured in vivo. AR expression, activation and target gene expression were measured in vitro. Effects of Enzalutamide on hypoxia-driven, disease-progressing pathways and genes of interest and the role of these genes in resistance to Enzalutamide was investigated. Results: Enzalutamide promoted persistent hypoxia in LNCaP tumours in vivo, followed by increased blood vessel density and restoration of oxygen tension (>14 days). In vitro, hypoxia increased AR expression and transcriptional activity in LNCaP cells and sustained but did not further potentiate high basal AR and ARv7 activity in 22Rv1 cells. Enzalutamide failed to attenuate the concurrent hypoxia-induced HIF-1 and NF-κB signalling, resulting in up-regulation of disease-progressing genes and pathways. Administration of neutralizing antibodies to two hypoxia-regulated genes, IL-8 and VEGF prolonged Enzalutamide-mediated LNCaP tumour growth control over 28 days in vivo (p < 0.001) and re-sensitised enzalutamide-resistant LNCaP cells in vitro. Conclusions: Enzalutamide-induced hypoxia upregulates the expression of VEGF and IL-8, whose multi-model signalling effects contribute to microenvironment-promoted resistance in prostate tumours.