Phase I/II Study of MAK683 in Patients with Advanced Malignancies, Including Diffuse Large B-Cell Lymphoma

Abstract Introduction: Polycomb repressive complex 2 (PRC2) regulates transcription via trimethylation of histone H3 at lysine 27 (H3K27me3). Enhancer of zeste homolog 2 (EZH2) in conjunction with embryonic ectoderm development (EED) is a catalytic subunit of PRC2 and functions as a histone methyltransferase for H3K27. H3K27me3 appears to be a unifying component in many malignancies, inducing transcriptional repression. EED is a core component of PRC2 that modifies the epigenetic status of target genes, including cell cycle control genes. Dysregulation of this pathway leads to tumorigenesis in several diseases. MAK683 is a specific oral inhibitor that impairs EED binding to H3K27me3. This is a Phase I/II study of MAK683 in adult patients with advanced malignancies for whom no effective standard treatment is available. Here, we present data from a subset of patients with diffuse large B-cell lymphoma (DLBCL). Methods: Patients with DLBCL received escalating doses of MAK683 in fasted conditions. Patients were administered MAK683 10, 20, 40, 80, 120, 240, 300, 500, and 800 mg once daily (QD) or 60, 80, 120, 150, and 300 mg twice daily (BID) orally in 28-day cycles until unacceptable or dose-limiting toxicities (DLTs) had developed, disease progression, or death. The primary objective was to characterize safety and tolerability and determine the maximum tolerated dose and/or recommended Phase II dose (RP2D). Results: As of March 5, 2021, 31 patients with an Eastern Cooperative Oncology Group Performance Status of 0-2 were treated. Median age was 70 years (range: 33-84) and patients were heavily pre-treated, with a median of 4 (range: 1-16) prior lines of therapy. Overall, 30 patients (97%) discontinued treatment due to progressive disease (26 patients, 84%), adverse events (3 patients, 10%), and physician's decision (1 patient, 3%). In total, 21 (68%) patients experienced ≥1 treatment-related adverse event (TRAE) of any grade, and the most common (≥20%) TRAEs were thrombocytopenia (29%) and anemia (23%). Grade 3/4 TRAEs were reported in 14 (45%) patients, with ≥15% of patients reporting thrombocytopenia (19%), neutropenia, and decreased neutrophil count (16% each). DLTs were reported in 7 patients, all of which were hematological and therefore may be related to the underlying disease in this subset of patients. Patients in both the QD dosing group (120 mg, 240 mg, and 800 mg; n=1 each) and BID dosing group (60 mg, n=1; 80 mg, n=2; 150 mg, n=1) reported DLTs. There were no treatment-related deaths in this study. Overall response rate was 16% (95% CI: 5─34) and the disease control rate was 29% (95% CI: 14─48). Two patients (6%) achieved a complete response (CR) and 3 patients (10%) achieved a partial response. Four patients (13%) reported stable disease. Pharmacokinetic data showed rapid absorption of MAK683 across all dosing regimens tested and drug exposure increased with dose. Conclusions: MAK683 was generally well tolerated and there were preliminary signs of activity in patients with treatment-resistant DLBCL. The use of MAK683 as a novel strategy for the inhibition of EED may have potential in relapsed/refractory DLBCL. Disclosures Ribrag: PharmaMar: Honoraria, Membership on an entity's Board of Directors or advisory committees; Servier: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; Astex Pharmaceuticals: Research Funding; Roche: Membership on an entity's Board of Directors or advisory committees; MSD Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Epizyme: Honoraria, Research Funding; Argen-X: Research Funding; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Nanostring: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Infinity Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; GSK: Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees. Michot: GSK: Honoraria; MSD: Consultancy, Honoraria; Celgene: Honoraria; Innate Pharma: Research Funding; Incyte: Research Funding; H3 biomedecine: Research Funding; GSK: Consultancy, Honoraria, Research Funding; Genentech: Research Funding; Gamamabs: Research Funding; Forma: Research Funding; Exelixis: Research Funding; Eos: Research Funding; Eisai: Research Funding; Debiopharm: Research Funding; Daiichi Sankyo,: Research Funding; Clovis: Research Funding; Chugai: Research Funding; Boeringer Ingelheim: Research Funding; Celgene: Research Funding; Blueprint: Research Funding; Beigene: Research Funding; Bayer: Research Funding; Argen-x: Research Funding; Amgen: Research Funding; Agios: Research Funding; Aduro: Research Funding; Abbvie: Research Funding; ASTEX: Research Funding, Speakers Bureau; Astra Zeneca: Honoraria, Research Funding; Roche: Honoraria; Bristol Myers Squibb: Consultancy, Honoraria, Research Funding. Igleias: Merck Serono, MSD, BMS, Lilly, Roche, Bayer, Sanofi: Consultancy. Tan: Novartis, Bayer, Boehringer Ingelheim, MSD, Astra Zeneca, Eli-Lilly, Loxo: Consultancy; Astra Zeneca, Pfizer, Novartis: Research Funding; Merck, Pfizer, Novartis, Takeda, Bayer, Boehringer Ingelheim, Roche: Honoraria. Ma: Novartis, Merck, Y-Biologies, Taiho, Daiichi: Honoraria, Speakers Bureau; Novartis, Inglheim: Research Funding. Wainberg: Plexxikon, BMS, EMD Serono: Research Funding; Roche, Novartis, BMS, Merck, Pfizer, Lilly, Bayer, Astra Zeneca, Daiichi, Astellas, Amgen: Consultancy. Fan: Novartis Institutes for Biomedical Research: Current Employment. Suenaga: Novartis Pharma K.K.: Current Employment. Cheng: Novartis: Current Employment. Lai: Novartis: Current equity holder in publicly-traded company; Novartis Institutes for Biomedical Research: Current Employment. Yokota: AstraZeneca, Chugai Pharma, MSD, Syneos Health, Lilly, Incyte, Novartis, GlaxoSmithKline, Ascent: Research Funding; Abbott Japan, Ono Pharmaceutical, Chugai Pharma, Bristol-Myers Squibb, Merck Biopharma, MSD, Rakuten Medical, Eisai: Honoraria; Merck Biopharma, MSD, Rakuten Medical: Membership on an entity's Board of Directors or advisory committees.