Ipatasertib plus abiraterone and prednisolone in metastatic castration-resistant prostate cancer (IPATential150): a multicentre, randomised, double-blind, phase 3 trial

Background: The PI3K/AKT and androgen-receptor pathways are dysregulated in metastatic castration-resistant prostate cancers (mCRPCs); tumours with functional PTEN-loss status have hyperactivated AKT signalling. Dual pathway inhibition with AKT inhibitor ipatasertib plus abiraterone might have greater benefit than abiraterone alone. We aimed to compare ipatasertib plus abiraterone with placebo plus abiraterone in patients with previously untreated mCRPC with or without tumour PTEN loss.

Methods: We did a randomised, double-blind, phase 3 trial at 200 sites across 26 countries or regions. Patients aged 18 years or older with previously untreated asymptomatic or mildly symptomatic mCRPC who had progressive disease and Eastern Collaborative Oncology Group performance status of 0 or 1 were randomly assigned (1:1; permuted block method) to receive ipatasertib (400 mg once daily orally) plus abiraterone (1000 mg once daily orally) and prednisolone (5 mg twice a day orally) or placebo plus abiraterone and prednisolone (with the same dosing schedule). Patients received study treatment until disease progression, intolerable toxicity, withdrawal from the study, or study completion. Stratification factors were previous taxane-based therapy for hormone-sensitive prostate cancer, type of progression, presence of visceral metastasis, and tumour PTEN-loss status by immunohistochemistry. Patients, investigators, and the study sponsor were masked to the treatment allocation. The coprimary endpoints were investigator-assessed radiographical progression-free survival in the PTEN-loss-by-immunohistochemistry population and in the intention-to-treat population. This study is ongoing and is registered with ClinicalTrials.gov, NCT03072238.

Findings: Between June 30, 2017, and Jan 17, 2019, 1611 patients were screened for eligibility and 1101 (68%) were enrolled; 554 (50%) were assigned to the placebo-abiraterone group and 547 (50%) to the ipatasertib-abiraterone group. At data cutoff (March 16, 2020), median follow-up duration was 19 months (range 0-33). In the 521 (47%) patients who had tumours with PTEN loss by immunohistochemistry (261 in the placebo-abiraterone group and 260 in the ipatasertib-abiraterone group), median radiographical progression-free survival was 16·5 months (95% CI 13·9-17·0) in the placebo-abiraterone group and 18·5 months (16·3-22·1) in the ipatasertib-abiraterone group (hazard ratio [HR] 0·77 [95% CI 0·61-0·98]; p=0·034; significant at α=0·04). In the intention-to-treat population, median progression-free survival was 16·6 months (95% CI 15·6-19·1) in the placebo-abiraterone group and 19·2 months (16·5-22·3) in the ipatasertib-abiraterone group (HR 0·84 [95% CI 0·71-0·99]; p=0·043; not significant at α=0·01). Grade 3 or higher adverse events occurred in 213 (39%) of 546 patients in the placebo-abiraterone group and in 386 (70%) of 551 patients in the ipatasertib-abiraterone group; adverse events leading to discontinuation of placebo or ipatasertib occurred in 28 (5%) in the placebo-abiraterone group and 116 (21%) in the ipatasertib-abiraterone group. Deaths due to adverse events deemed related to treatment occurred in two patients (<1%; acute myocardial infarction [n=1] and lower respiratory tract infection [n=1]) in the placebo-abiraterone group and in two patients (<1%; hyperglycaemia [n=1] and chemical pneumonitis [n=1]) in the ipastasertb-abiraterone group.

Interpretation: Ipatasertib plus abiraterone significantly improved radiographical progression-free survival compared with placebo plus abiraterone among patients with mCRPC with PTEN-loss tumours, but there was no significant difference between the groups in the intention-to-treat population. Adverse events were consistent with the known safety profiles of each agent. These data suggest that combined AKT and androgen-receptor signalling pathway inhibition with ipatasertib and abiraterone is a potential treatment for men with PTEN-loss mCRPC, a population with a poor prognosis.

Funding: F Hoffmann-La Roche and Genentech.