A phase I/II study of valemetostat (DS-3201b), an EZH1/2 inhibitor, in combination with irinotecan in patients with recurrent small cell lung cancer.

Abstract

Recurrent small cell lung cancer (SCLC) has few effective treatments. The EZH2-SLFN11 pathway is a driver of acquired chemoresistance that may be targeted. This phase I/II trial investigated valemetostat, an EZH1/2 inhibitor, with fixed-dose irinotecan in patients with recurrent SCLC. Phase I primary objectives were to assess safety and a recommended phase II dose (RP2D). The phase II primary objective was to determine overall response rate (ORR), with secondary objectives of duration of response (DoR), progression-free survival (PFS) and overall survival (OS). Immunohistochemistry of pre- and on-treatment tumor biopsies and pharmacokinetics analysis were performed. Twenty-two patients enrolled (phase I, n=12; phase II n=10); one withdrew consent prior to treatment. Three dose-limiting toxicities (DLTs) in dose-escalation resulted in valemetostat 100 mg orally daily selected as RP2D. Among 21 toxicity-evaluable patients, the most frequent (≥20%) treatment-related adverse events were diarrhea, fatigue, nausea, and rash; 3 patients discontinued treatment for toxicity. In phase II, 3/10 patients experienced DLTs triggering a stopping rule. The ORR was 4/19 (21%, 95% CI 6 to 46%). The median DoR, PFS and OS were 4.6 mo, 2.2 mo (95% CI 1.3 to 7.6 mo) and 6.6 mo (95% CI 4.3 to not reached). SLFN11, EZH2 and SCLC subtyping markers did not correlate with response. MHC-I protein expression increased in 4/4 patients with paired biopsies, including 3/3 responders; two responders demonstrated subtype switching on treatment. Valemetostat and irinotecan was not tolerated but demonstrated efficacy in recurrent SCLC. Valemetostat may warrant further investigation in SCLC.