A phase II, multicenter, randomized, open-label study to evaluate the safety and tolerability of proxalutamide (GT0918) in subjects with metastatic castrate-resistant prostate cancer (mCRPC).

Abstract

108 Background: GT0918 is a 2nd generation of AR antagonist and capability to down-regulate AR level. This study is an open-label, randomized, multicenter, Ph II study to evaluate the safety and efficacy in patients with mCRPC, and to determine the optimal dose for Ph III study. Methods: Patients with historically confirmed mCRPC who progressed after/intolerant to/reluctant to receive Docetaxel and previously treated with abiraterone or enzalutamide were excluded. All the patients received up to 6 cycles or, unacceptable toxicity, or loss of clinical benefit as recommended by PCWG3. Primary endpoint was prostate-specific antigen (PSA) reduction from baseline. Secondary endpoints included time to PSA progression (TTPP), objective response rate (ORR), progression free survival (PFS), disease control rate (DCR) and safety profiles. Results: As of June 30, 2019, 108 treated with GT0918 at three dose levels: 100 mg (n =37), 200 mg (n = 35) and 300 mg (n = 36), the median age of patients was 70.0 years (range 63-77), 88% of patients had stage IV disease at the initial diagnosis and 69.4% had Gleason score ≥ 8. The median duration of disease was 2.88 years. All received prior endocrine therapy, 35.2% received prior chemotherapy, 29.6% received Docetaxel. The median PSA at baseline was 35.285ng/ml, PSA response rate (≥50 % reduction from baseline) was 41.9%. The median time to PSA progression was not reached. There was no significant difference among three arms. Of 19 evaluable patients with target lesions at baseline, the ORR was 15.8% (all were PR) assessed by IRC with RECIST v 1.1, with 20.0% (1/5), 22.2% (2/9), 0 (0/5) at 100, 200, 300 dose level, respectively. The DCR assessed by IRC was 78.9% (CR 0+PR15.8%+SD 63.2%). Of 26 evaluable patients with target lesions at baseline, the ORR was 19.2% assessed by investigators (CR 3.8%+PR 15.4%), with 11.1% (1/9), 20.0% (2/10), 28.6% (2/7) at 100, 200, 300 dose level, respectively. Overall, AEs were experienced by most of patients (94.4 %, n=102). AEs leading to drug interruption were reported in 13 patients (12.0%), 9 (8.3%)of them were suspected to be drug related. AEs leading to discontinuation were reported in 6 patients (5.6%), 3(2.8%) were possibly related to GT0918. 14 patients (13.0%) experienced Grade 3 and 4 AEs. 17 patients (15.7%)experienced SAE, 5(4.6%) of them were suspected to be related to study drug. Most of AEs were mild or moderate. The common suspected AE (≥10%) were asthenia (17.6%, n=19), anemia (14.8%, n=16), AST increased (14.8%, n=16), ALT increased (13.0%, n=14), decreased appetite (13.0%, N=14), white blood cell count decreased (12.0%, n=13), proteinuria (12.0%, n=13). Conclusions: GT0918 showed a manageable safety profile. This study provided preliminary anti-tumor activity in patients with mCRPC. 200mg/day is recommended dose for Ph III trial. Clinical trial information: CTR20170177.