A Randomised, Multi-centre Phase II Trial of Weekly Paclitaxel and Vistusertib in Platinum-Resistant Ovarian High-Grade Serous Carcinoma: OCTOPUS Arm 1

BackgroundPreclinical studies support targeting PI3K/AKT/mTOR signalling in platinum-resistant ovarian cancer (PROC). A phase I study of the dual mTORC1/mTORC2 inhibitor vistusertib with weekly paclitaxel (wP) showed activity. We report the results of Arm 1 of OCTOPUS, the first randomised trial of weekly paclitaxel and dual mTORC1/2 inhibition in ovarian cancer. MethodsPatients with platinum-resistant or refractory high grade serous carcinoma were randomised (1:1) to wP (80mg/m2 D1,8,15 of 28 day cycle) plus oral vistusertib (50mg BD) or placebo (P). The primary endpoint was progression-free survival (PFS). Secondary endpoints included response rate (RR) and overall survival (OS). Results140 patients (median age 63, range: 36-86; 18% platinum-refractory; 54% [≥]3 prior therapies) were randomised. There was no difference in PFS (median 4.5 vs 4.1m (HR 0.84; 80% CI (0.67, 1.07); 1-sided p=0.18), OS (median 9.7 vs 11.1m (HR 1.21; 80% CI (0.91, 1.60); 1-sided p=0.80) or RR (odds ratio 0.86; 80% CI (0.55, 1.36); 1-sided p=0.66). Grade 3/4 adverse events were 41.2% (wP+V) vs 36.7% (wP+P). Low tumour PTEN expression was associated with longer PFS in the wP+V arm (9.4 vs 4.1m p=0.003) but not in the wP arm (4.8 vs 4.2m p=0.60). Tumour genome-wide copy number (CN) analysis suggested that high CN signature 4 was associated with worse outcome in the wP+P arm (2.3 vs 4.6m p=0.018) but not the wP+V arm (5.4 vs 3.3m). ConclusionsVistusertib did not improve clinical activity of wP in PROC. However, low tumour cell PTEN expression may be a predictive biomarker for vistusertib activity. Translational RelevancePreclinical studies suggest that activation of the PI3K/AKT/mTOR signalling pathway contributes to platinum-resistance in ovarian high grade serous carcinoma (HGSC). Based on activity in a phase I study, we evaluated the clinical efficacy of the dual mTORC1/mTORC2 inhibitor vistusertib in combination with weekly paclitaxel in the OCTOPUS study - a multi-centre, randomised, placebo-controlled, phase II trial in platinum-resistant ovarian (HGSC). In the first randomised trial of weekly paclitaxel and dual mTORC1/2 inhibition in ovarian cancer, vistusertib did not improve clinical activity of weekly paclitaxel. However, translational analyses indicated that low tumour cell PTEN expression may be a predictive biomarker for vistusertib activity. We also showed genome-wide copy number (CN) analysis, in particular high exposure to CN signature 4, may also allow identification of patients with greater chance of benefit from dual mTORC inhibition. Potential predictive biomarkers identified in our study should be evaluated in ongoing/future studies.