Valemetostat for Relapsed or Refractory B-Cell Lymphomas: Primary Results from a Phase 1 Trial

Introduction: B-cell non-Hodgkin lymphomas (B-NHLs), including diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL), are among the most common NHLs. Enhancer of zeste homolog (EZH)2 and EZH1 are methyltransferases that catalyze the trimethylation of histone H3 at lysine 27 (H3K27me3); this repressive transcriptional mark is broadly associated with gene silencing. EZH2 is involved in mediating B-cell development.

Valemetostat tosylate (valemetostat) is a novel, potent, and selective dual inhibitor of EZH2 and EZH1. The clinical activity of valemetostat in patients (pts) with relapsed or refractory (R/R) NHL was investigated in the phase 1 DS3201-A-J101 (“J101”; NCT02732275) trial. Interim data were reported previously. Here we report primary clinical outcomes for the subgroup of pts in J101 with R/R B-NHLs, including DLBCL and FL.

Methods: This phase 1, open-label, multicenter study was conducted in Japan and the United States (US). Eligible pts were aged ≥ 18 years (y; US) or ≥ 20 y (Japan), had confirmed B-NHL or T-cell NHL (T-NHL), and were relapsed from, refractory to, or ineligible for standard therapies. The trial included a dose-escalation portion (Japan only) followed by a dose-expansion phase (Japan & US). Pts with a histological diagnosis of B-NHL were enrolled in the dose-escalation phase and received valemetostat once daily at doses of 150-300 mg/day (d) in continuous 28-d treatment (Tx) cycles.

Preliminary efficacy assessment included objective response rate (ORR), complete response (CR) rate, and duration of response (DOR). DOR was estimated for responding pts using Kaplan-Meier methods. Due to the small number of pts with B-NHL, safety was assessed among all enrolled pts, including those with T-NHL in the dose-escalation and dose-expansion cohorts.

Results: At the primary trial cutoff (Dec 31, 2022), 19 pts with R/R B-NHLs were registered and had received ≥ 1 dose of study drug, including 7 with DLBCL, 7 with FL, 3 with indolent B-NHL, and 2 with other B-NHLs. Median age was 66 (range 44-88) y. Most (79%) pts had an Eastern Cooperative Oncology Group performance status score of 0. Median number of prior therapies was 2.0 (range 0-6); no pt in this cohort had received prior hematopoietic cell transplantation.

Overall, 90 pts with R/R NHLs were enrolled. All pts experienced at least 1 treatment-emergent adverse event (TEAE), including 78 (87%) who had treatment-related TEAEs. The most common TEAEs (any grade) were decreased platelet count (64%), dysgeusia (50%), anemia (43%), decreased neutrophil count (34%), and alopecia (33%). The most common grade ≥ 3 TEAEs were cytopenias, including decreased neutrophil count (24%), platelet count (24%), and lymphocyte count (19%). TEAEs required Tx interruption for 42 (47%) pts, dose reduction for 9 (10%) pts, and Tx discontinuation for 7 (8%) pts.

The overall response rate in pts with R/R B-NHL was 47% (9/19; 95% confidence interval [CI], 24.4-71.1). Clinical responses were seen in 3/7 pts with DLBCL and 4/7 pts with FL; 1 pt in each of these groups achieved CR ( Table). Of 19 pts, 9 (47%) achieved reductions of ≥ 50% from baseline in the sum of target lesion areas during valemetostat Tx ( Figure). A gain-of-function EZH2 mutation was identified in 1 pt with FL, and this pt achieved a partial response. Median time to response overall was 3.7 (range 1.9-10.1) months (mo) and estimated median DOR for the 9 responding pts was 18.4 mo (95% CI, 5.3 mo to not reached). Among all pts who received valemetostat 200 mg/d with pharmacokinetic (PK) data available (n = 74), mean [standard deviation; SD] maximum plasma concentration (C _max) on cycle 1 day 1 was 2140 [1620] ng/mL, with a median time to C _max (T _max) of 3.9 (range 0.2-27.8) h and a mean [SD] AUC _tau of 17,500 [21,400] ng × h/mL.

Conclusions: Valemetostat demonstrated encouraging clinical activity in pts with R/R B-NHLs. The safety profile of valemetostat was acceptable; cytopenias were common but manageable and did not require Tx discontinuation between 150-300 mg/d. Clinical responses were durable, with a median DOR of > 1.5 y. Results for pts in this trial with R/R T-NHLs are presented in another abstract (Jacobsen et al.) at this congress. Ongoing trials of valemetostat in pts with R/R B-NHLs include a phase 2 monotherapy trial in France and Belgium (NCT04842877) and a phase 1/2 trial of valemetostat plus rituximab and lenalidomide (R ²) in the US (NCT05683171).