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

Purpose: Recurrent small-cell lung cancer (SCLC) has few effective treatments. The EZH2-SLFN11 pathway is a driver of acquired chemoresistance that may be targeted.

Patients And Methods: 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, tolerability, and a recommended phase II dose (RP2D). The phase II primary objective was overall response rate (ORR), with secondary objectives of determining duration of response (DoR), progression-free survival (PFS), and overall survival (OS). Correlative analyses included immunohistochemistry of pretreatment and on-treatment tumor biopsies and pharmacokinetics analysis.

Results: Twenty-two patients were enrolled (phase I, n = 12; phase II, n = 10); one withdrew consent prior to treatment. Three dose-limiting toxicities (DLT) in dose-escalation resulted in valemetostat 100 mg orally daily selected as RP2D. Among 21 evaluable patients, the most frequent (≥20%) treatment-related adverse events were diarrhea, fatigue, nausea, and rash; three patients discontinued treatment for toxicity. Three of the first 10 patients in phase II experienced DLTs triggering a stopping rule. The ORR was 4/19 or 21% [95% confidence interval (CI), 6%-46%]. The median DoR, PFS, and OS were 4.6 months, 2.2 months (95% CI, 1.3-7.6 months), and 6.6 months (95% CI, 4.3 to not reached), respectively. SLFN11/EZH2 expression and SCLC subtyping markers did not correlate with response, but MHC-I expression did increase with treatment. Two responders demonstrated subtype switching on treatment.

Conclusions: Combination valemetostat and irinotecan was not tolerated but demonstrated efficacy in recurrent SCLC. Valemetostat, combined with agents without overlapping toxicity, warrants further investigation in SCLC.