Synergistic combination therapy with ONC201 or ONC206, Enzalutamide and Darolutamide in preclinical studies of castration-resistant prostate cancer

Androgen receptor (AR) signaling plays a primary role in prostate cancer progression. Non-steroidal anti- androgens (NSAA) including enzalutamide, and apalutamide have been used to treat patients with advanced disease. However, patients with metastatic castration-resistant prostate cancer (mCPRC) develop resistance, resulting in limited overall survival benefit. Darolutamide is a novel next-generation androgen receptor- signaling inhibitor that is FDA approved for non-metastatic castration resistant prostate cancer (nmCRPC). Imipridone ONC201/TIC10 is first-in-class small molecule that activates the integrated stress response (ISR) and upregulates TNF-related apoptosis-inducing ligand (TRAIL). Our study investigates ISR and AR signaling in anti-tumor efficacy with ONC201 and enzalutamide or darolutamide against mCRPC cells. mCRPC cell lines 22RV1, LNCaP, DU145 and PC3 were treated with ONC201, darolutamide, and enzalutamide as single agents or in combinations. Combinations of ONC201 and darolutamide or enzalutamide demonstrated synergistic effects in mCRPC cells. Combinations of ONC201 and darolutamide or enzalutamide reduced PSA levels in LNCaP cells and induced of ATF4 in both LNCaP and 22RV1 cell lines. Darolutamide synergized with ONC201 regardless of AR status or castration sensitivity in vitro. Flow cytometric analysis showed increased intra-tumoral NK cells in mice treated with ONC201 and combination of ONC201 and darolutamide. Trends of increased TRAIL activation within NK cells were also observed in treatment groups. ONC201 and darolutamide demonstrated anti-tumor effects in vivo in the 22RV1 CRPC model. Our results prompt further translational and clinical studies with imipridones ONC201 or ONC201 in combination with enzalutamide or darolutamide for treatment of castrate resistant advanced or metastatic prostate cancer.