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).
Authors: Tie Zhou, Dingwei Ye, Zhongquan Sun, Qinggui Meng, Dalin He, Guowei Shi, Jie Jin, Weibing Sun, Lijun Chen, Ben Liu, Jingen Wang, Jiwen Cheng, Zhiquan Hu, Yong Yang, Xishuang Song, Yinhuai Wang, Cheng Fu, Qiaoxia Zhou, Youzhi Tong, Ying-Hao Sun
Journal: Journal of Clinical Oncology (2021)

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.