Aberrant tumor metabolism to enable glucocorticoid receptor takeover in enzalutamide-resistant prostate cancer.

Abstract

157 Background: Prostate cancer is driven by androgen stimulation of the androgen receptor (AR). The next-generation AR antagonist, enzalutamide, prolongs progression-free and overall survival, but resistance and lethal disease eventually prevail. Emerging data suggest that the glucocorticoid receptor (GR) is upregulated in this context, stimulating expression of approximately 50% of genes normally stimulated by AR, thereby permitting continued growth despite AR blockade. However, countering this mechanism by administration of GR antagonists is problematic because GR is essential for life. Methods: We assessed the effects of enzalutamide on metabolism of cortisol to cortisone in the LAPC4 and VCaP models of prostate cancer using [3H]-cortisol and high performance liquid chromatography. Expression of 11β-hydroxysteroid dehydrogenase-2, encoding the enzyme 11βHSD2, which converts cortisol to cortisone, was assessed by immunoblot, in models of prostate cancer, tissues from patients treated with enzalutamide and prostate tissues treated exogenously with enzalutamide. The effect of shRNA knockdown of the AMFR ubiquitin E3-ligase on 11βHSD2 protein expression and enzyme activity was assessed. Finally, the potential therapeutic effects of 11βHSD2 re-expression on enzalutamide resistance was assessed in xenograft models. Results: Enzalutamide impedes inactivation of cortisol to cortisone, thereby sustaining tumor cortisol concentrations, permitting GR stimulation and enzalutamide resistance. Impeded cortisol inactivation by enzalutamide occurs by way of 11β-HSD2 expression loss in models of prostate cancer, prostate tissues from enzalutamide-treated patients and fresh prostatic tissues treated exogenously with enzalutamide. AMFR mediates loss of 11β-HSD2, which otherwise inactivates cortisol. Remarkably, reinstatement of 11β-HSD2 expression, or AMFR loss, reverses enzalutamide resistance in mouse xenograft tumors. Conclusions: Together, these findings reveal a surprising metabolic mechanism of enzalutamide resistance that may be targeted with a strategy that circumvents a requirement for systemic GR ablation.