Pembrolizumab with platinum-based chemotherapy with or without epacadostat as first-line treatment for metastatic non-small cell lung cancer: a randomized, partially double-blind, placebo-controlled phase II study.

Background: The combination of the checkpoint inhibitor (CPI) pembrolizumab and platinum-based chemotherapy is effective frontline therapy for advanced non-small cell lung cancer (NSCLC) lacking targetable mutations. Indoleamine 2,3- dioxygenase 1 (IDO1), an enzyme involved in kynurenine production, inhibits immune responses. Inhibition of IDO1 may restore antitumor immunity and augment CPI activity. This trial evaluated addition of epacadostat, a potent and highly selective IDO1 inhibitor, to pembrolizumab and chemotherapy for metastatic NSCLC.

Methods: ECHO-306/KEYNOTE-715 was a partial double-blind, randomized phase II study of adults with treatment-naïve stage IV NSCLC not indicated for EGFR-, ALK-, or ROS1-directed therapy. Patients were randomized to one of three treatment arms: epacadostat-pembrolizumab-chemotherapy (E + P + C; blinded), epacadostat-pembrolizumab (E + P; open-label) or placebo-pembrolizumab-chemotherapy (PBO + P + C; blinded). Stratification was by PD-L1 tumor proportion score (< 50% vs. ≥ 50%) and tumor histology (non-squamous vs. squamous). A protocol amendment closed enrollment in the open-label E + P group, excluding it from efficacy analyses. Intravenous pembrolizumab (200 mg) was administered every 21 days and epacadostat 100 mg or matching placebo (oral) twice daily (BID) for ≤ 35 3-week cycles. The primary objective was objective response rate (ORR) for E + P + C vs. PBO + P + C.

Results: 178 patients were randomized to E + P + C (n = 91) or PBO + P + C (n = 87); 55 were enrolled in the E + P group. The E + P + C group had a lower confirmed ORR (26.4%; 95% CI 17.7-36.7) than the PBO + P + C group (44.8%; 95% CI 34.1-55.9), with a difference of - 18.5% (95% CI - 32.0 - (- 4.3); one-sided P = 0.9948). The E + P + C group had a numerically higher percentage of confirmed responders with extended response ≥ 6 months (29.2% vs. 15.4%). Circulating kynurenine levels at C1D1 were similar to those at C2D1 in all treatment groups and were not reduced to normal levels with epacadostat 100 mg BID plus P + C. The safety profile of E + P + C was consistent with that for PBO + P + C.

Conclusions: Addition of epacadostat 100 mg BID to pembrolizumab and platinum-based chemotherapy was generally well tolerated but did not improve ORR in patients with treatment-naïve metastatic NSCLC. Evaluating epacadostat doses that normalize circulating kynurenine in combination with CPIs may help determine the clinical potential of this combination.

Trial Registration: NCT03322566. Registered October 26, 2017.