Increased glucocorticoid receptor (GR) expression and activity following androgen blockade can contribute to castration-resistant prostate cancer (CRPC) progression. Therefore, we hypothesized that GR antagonism will have therapeutic benefit in CRPC. However, the FDA-approved nonselective, steroidal GR antagonist, mifepristone, lacks GR specificity, reducing its therapeutic potential. Here we report that two novel non-steroidal and highly selective GR modulators (SGRMs), CORT118335 and CORT108297, have the ability to block GR activity in prostate cancer (PC) and slow CRPC progression. In contrast to mifepristone, these novel SGRMs did not affect AR signaling, but potently inhibited GR transcriptional activity. Importantly, SGRMs decreased GR-mediated tumor cell viability following AR blockade. In vivo, SGRMs significantly inhibited CRPC progression in high GR-expressing, but not in low GR-expressing xenograft models. Transcriptome analysis following AR blockade and GR activation revealed that these SGRMs block GR-mediated proliferative gene expression pathways. Furthermore, GR-regulated proliferation-associated genes AKAP12, FKBP5, SGK1, CEBPD, and ZBTB16 are inhibited by CORT108297 treatment in vivo. Together, these data suggest that GR-selective non-steroidal SGRMs potently inhibit GR activity and PC growth despite AR pathway inhibition demonstrating the therapeutic potential of SGRMs in GR-expressing CRPC.
- Received December 29, 2016.
- Revision received April 7, 2017.
- Accepted April 14, 2017.
- Copyright ©2017, American Association for Cancer Research.