Resistance mechanisms of prostate cancer to anti-androgen treatment include the emergence of different androgen receptor (AR) mutations. Here we report that darolutamide, a novel investigational AR antagonist, exhibits in vitro antagonism for several AR mutants identified in the clinic. In vivo studies additionally show that darolutamide has a superior activity to enzalutamide in the KuCaP-1 prostate cancer model, which harbors the AR W742C mutation.

Methods: AR mutants leading to therapy resistance were tested in PC-3 cells transiently transfected with an androgen-controlled reporter and stimulated with 0.1 nM R1881. In vivo efficacy studies were performed on SCID CB17 male mice inoculated subcutaneously with KuCaP-1 tumor fragments. Oral treatment started on day 35 post tumor inoculation at a mean tumor size of about 150 mm3. Mouse body weight and tumors were measured at least twice weekly. The study was stopped on day 68 post tumor implantation, and efficacy evaluated by calculating the % ΔT/ΔC. Efficacy was declared according to NCI criteria with ΔT/ΔC ≤ 42%. For gene expression analysis, RNA was extracted from 20 mg of tumor.

Results: Several clinically relevant AR mutants including W742C, W742L, H875Y, F877L, T878A, F877L/T878A, T878G and M896V were tested. Enzalutamide and apalutamide had IC50 values approximately 200 nM and higher for the W742C and W742L mutants, and showed agonistic activity for the F877L and F877L/T878A mutants. For darolutamide the IC50 values were below 200 nM, except for the T878A and F877L/T878A mutants where the value was 1-1.5 µM, and no agonistic activity was observed. As the activity of darolutamide for the W742C mutant was about threefold better than that of enzalutamide in vitro, we performed in vivo studies with the KuCaP-1 xenograft model which harbors this mutation to further confirm these results. At day 68 post tumor implantation, the ΔT/ΔC values for enzalutamide were 70% and 99% for the 30 and 100 mg/kg daily treatments, respectively. The situation was different for darolutamide where a marked reduction of tumor growth was observed when mice were given oral doses of 40 or 100 mg/kg twice-daily. At day 68, the ΔT/ΔC was 45% for the 40 mg/kg twice-daily doses and 26% for the 100 mg/kg twice-daily doses. The treatments were well tolerated, with only limited body weight loss. Expression of androgen target genes was determined at the end of the study and a strong reduction was observed in the 100 mg/kg daily enzalutamide group. In conclusion, darolutamide showed in vitro antagonism for several AR mutants identified in the clinic. For the W742C mutation, a threefold better activity was measured compared to enzalutamide. This also translated in vivo where a strong efficacy was observed in the KuCaP-1 xenograft for darolutamide, but not for enzalutamide.

Citation Format: Bernard Haendler, Tatsuo Sugawara, Simon J. Baumgart, Pascale Lejeune. Darolutamide demonstrates greater in vivo activity than enzalutamide in prostate cancer model with therapy-resistant androgen receptor mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1795.