Abstract CT007: Phase 2-3 trial of pegargiminase plus chemotherapy versus placebo plus chemotherapy in patients with non-epithelioid pleural mesothelioma

Abstract Background: Arginine deprivation with ADI-PEG20 (pegargiminase) alone or combined with chemotherapy displayed antitumor activity in early phase clinical trials of argininosuccinate synthase 1 (ASS1)-deficient cancers, including pleural mesothelioma (PM). The non-epithelioid subtype of mesothelioma is particularly aggressive and arginine-auxotrophic due to frequent ASS1 loss. ATOMIC-meso is a pivotal phase 2-3 trial comparing standard of care (SOC) chemotherapy plus pegargiminase or placebo for patients (pts) with non-epithelioid PM. Methods: In this double-blind, placebo-controlled, phase 2-3 trial, we randomly assigned ECOG PS 0-1 pts with chemonaïve non-epithelioid PM in an intention-to-treat 1:1 ratio to receive q3 week SOC chemotherapy with pemetrexed (500mg/m2 i.v.) and cisplatin (75mg/m2 i.v.) with q1 week pegargiminase (36 mg/m2 i.m.) or placebo i.m. up to 6 cycles. Carboplatin (AUC5) was permitted in the phase 3 portion instead of cisplatin. Maintenance therapy with pegargiminase or placebo was continued until progression, toxicity or 24 months. The primary end point was median OS (mOS) and secondary end points included median PFS (mPFS), safety, pharmacodynamics and immunogenicity. ORR was assessed by blinded independent central review (BICR) for the phase 2 portion only using modified RECIST or RECIST v1.1. Results: 249 pts with non-epithelioid PM (median age 71, range 28-86; male 82.7%; 48.2% biphasic and 51.8% sarcomatoid) from 5 countries were randomized between Aug 2017 and Aug 2021: 125 pts were assigned to the pegargiminase-chemotherapy group and 124 pts to the placebo-chemotherapy group. The experimental arm showed a superior mOS respect to SOC: 9.3 months (95% confidence interval [CI], 7.9-11.8) vs. 7.7 months (95% CI, 6.1-9.5) (hazard ratio [HR], 0.71; 95% CI, 0.55-0.93; p=0.023). Also, the mPFS was higher in the experimental vs. control arm: 6.2 months (95% CI, 5.8-7.4) vs. 5.6 months (95% CI, 4.14-5.91) ([HR], 0.65; 95% CI, 0.46-0.90; p=0.019). The ORR by BICR was 13.8% in the pegargiminase-chemotherapy group vs. 13.5% in the placebo-chemotherapy group (p=0.95) with more stable disease in the former (71.3% vs. 62.9%). Plasma arginine declined with a reciprocal increase in citrulline. Anti-ADI-PEG20 antibodies were detected in 97.4% of patients by week 25 on pegargiminase. Grade ≥ 3 treatment-related adverse events to pegargiminase occurred in 28.8% and to placebo in 16.9%; grade ≥ 3 drug hypersensitivity and skin reactions occurred in 3.2% and 1.6% in the experimental arm, respectively, and none on placebo. Post-study drug treatment was comparable in both arms (45.6% post-pegargiminase vs. 46.8% post-placebo). Conclusions: In this first randomized trial of an arginine-depleting chemotherapy in cancer, the pegargiminase-pemetrexed-platinum triplet prolonged survival and had a favorable safety profile in pts with non-epithelioid PM (ClinicalTrials.gov Identifier NCT02709512) Citation Format: Peter W. Szlosarek, Ben Creelan, Thomas Sarkodie, Luke Nolan, Paul Taylor, Olga Olevsky, Federica Grosso, Diego Cortinovis, Meenali Chitnis, Amy Roy, David Gilligan, Hedy Kindler, Dionysis Papadatos-Pastos, Giovanni L. Ceresoli, Aaron Mansfield, Anne Tsao, Ken O’Byrne, Anna K. Nowak, Jeremy Steele, Michael Sheaff, Amanda Johnston, John Bomalaski, Marjorie Zauderer, Dean A. Fennell. Phase 2-3 trial of pegargiminase plus chemotherapy versus placebo plus chemotherapy in patients with non-epithelioid pleural mesothelioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT007.