Shr3680, A Novel Antiandrogen, For The Treatment Of Metastatic Castration-Resistant Prostate Cancer (Mcrpc): A Phase I/Ii Study

90 Background: SHR3680 is a novel and pure androgen-receptor (AR) antagonist that shows a potent antitumor activity against CRPC but with much less brain distribution than enzalutamide in preclinical study. In this first-in-human phase 1/2 study, the safety and efficacy of SHR3680 were assessed in patients with mCRPC. Methods: This phase 1/2 study was conducted in 11 hospitals in China. Patients with progressive mCRPC that was not previously treated with novel AR-targeted agents were eligible for this study. In the phase 1 part, patients received oral SHR3680 at a starting daily dose of 40 mg, which was subsequently escalated to 80 mg, 160 mg, 240 mg, 360 mg, and 480 mg. In phase 2, patients were randomized to receive one of three daily doses of SHR3680 (80 mg, 160 mg, and 240 mg). The primary endpoint in phase 1 was safety and tolerability, and in phase 2 was the proportion of patients with a PSA response (≥50% decrease of PSA level at week 12). Results: From Apr 2016 to Sep 2018, a total of 197 patients (median age 67 years, range 45−80; visceral metastases in 29 patients; previous chemotherapy history in 80 patients) were enrolled (phase 1, n = 18; phase 2, n = 179). No dose-limiting toxicities were reported and the maximum tolerated dose was not reached. Most adverse events were grade 1/2 (87.3%). The most common adverse events were anemia (22.8%), back pain (16.2%), and proteinuria (13.2%). The antitumor activity was observed at all doses, including PSA response in 134 (68.7%) of 195 evaluable patients, stabilized bone disease in 169 (86.7%) of 195 patients at week 12, and responses in soft tissue lesions in 22 (36.7%) of 60 patients. No obvious dose-related activity benefits were found. As of Sep 26, 2019, the median time to PSA progression was 36 weeks (95% CI 24−47), while that to radiological progression was 73 weeks (95% CI 49−96). As expected, patients without previous chemotherapy showed relatively longer time to PSA and radiological progression than those with previous chemotherapy. Conclusions: SHR3680 is safe and well tolerated, and exhibits high efficacy in mCRPC patients. Clinical trial information: NCT02691975.