Synergistic Combination Therapy with ONC201 or ONC206, and Enzalutamide or Darolutamide in Preclinical Studies of Castration-Resistant Prostate Cancer

Androgen receptor (AR) signaling is a target in prostate cancer therapy and can be treated with non-steroidal anti-androgens (NSAA) including enzalutamide, and apalutamide for patients with advanced disease. Metastatic castration-resistant prostate cancer (mCPRC) develop resistance becomes refractory to therapy limiting patient overall survival. 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 imipridone that activates the integrated stress response (ISR), upregulates TNF-related apoptosis-inducing ligand (TRAIL) and has activity against CRPC alone or in combination with enzalutamide in preclinical models. We hypothesized that combination of imipridones with androgen receptor signaling blockers such as darolutamide may synergize in anti-tumor efficacy against mCRPC cells. mCRPC cell lines 22RV1, LNCaP, DU145 and PC3 were treated with imipridones ONC201, ONC206, apalutamide, darolutamide, or enzalutamide as single agents or in combinations. Combinations of ONC201 or ONC206 and androgen receptor signaling blockers 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 ONC206 in combination with enzalutamide or darolutamide for treatment of castrate resistant advanced or metastatic prostate cancer.