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Background: Isocitrate dehydrogenase 1 mutations (IDH1m) occur in 7-14% of AML patients (pts) and approximately 3-4% of MDS pts. Olutasidenib is a highly potent, selective small molecule inhibitor of IDH1m with the therapeutic potential to restore normal cellular differentiation. Azacitidine (AZA) has shown synergistic effects with IDHm inhibitors on releasing differentiation block in IDHm leukemia models in vitro. Methods: The Phase 1 study (NCT02719574) assessed the safety, PK/PD, and clinical activity of olutasidenib in patients with IDH1m AML or MDS. Eligibility criteria included: IDH1m AML or MDS [relapsed/refractory (R/R) or treatment naïve (TN) pts not eligible for or refusing standard therapy], adequate liver and renal function. There were no restrictions for concomitant non-anticancer medications. IDH1m variant allele frequency (VAF) and co-mutations were measured at baseline and during treatment. Available safety data are presented for all pts (AML/MDS); efficacy data are presented for AML pts only. Results: As of April 12, 2019, 32 pts had been treated with single agent (SA) olutasidenib and 46 pts with olutasidenib in combination (COMBO) with AZA; median time on treatment was 4.2 mo for SA (range: <1-32) and 4.6 mo for COMBO (<1-18). The median age was 72 yrs (35-87) for SA pts and 67 yrs (31-88) for COMBO pts. SA-treated pts included 26 with AML (22 R/R; 4 TN); COMBO treated pts included 39 with AML (26 R/R; 13 TN). For AML pts, the median number of prior regimens was 2 (0-9) for SA pts and 3 (0-6) for COMBO pts. A limited dose escalation was performed exploring 150 mg QD (SA or COMBO) and 300 mg administered QD (SA) or divided BID (SA or COMBO). No DLTs were observed; dose escalation was completed based on normalization of plasma 2-HG levels observed across all treatment groups. 150 mg BID was selected for expansion and as the recommended Phase 2 dose (RP2D) for both SA and COMBO. Sixty-two pts (29 SA; 33 COMBO) discontinued treatment, most commonly due to progressive disease (n=18 [11 SA; 7 COMBO]), HSCT (n=14 [4 SA; 10 COMBO]), death (n=9 [5 SA; 4 COMBO]), or other reasons (n=6 [3 SA; 3 COMBO], including lack of response [n=4], transition to hospice, and alternative therapy [n=1 each]). SA- or COMBO-treated pts had similar Gr 3/4 AEs, regardless of causality, occurring in >10% of pts, including thrombocytopenia (28% vs 33%), febrile neutropenia (22% vs 28%), anemia (22% vs 20%), pneumonia (16% vs 11%), and leukocytosis (13% vs 15%); COMBO-treated pts had more Gr 3/4 neutropenia (6% vs 28%), fatigue (6% vs 15%), and nausea (0% vs 9%). No QTcF prolongation was reported in SA while 3 (7%) pts treated with COMBO reported prolonged QTcF (1 Gr 3). Ten (13%) pts had differentiation syndrome (4 SA; 6 COMBO), which resolved with temporary interruption of olutasidenib and treatment with dexamethasone, hydroxyurea, and/or supportive care. None led to treatment discontinuation. Nineteen (24%) pts died on treatment or within 28 days of the last dose, no deaths were considered treatment-related. For AML pts, clinical responses occurred in 39% SA and 54% COMBO (CR 15% and 23%, respectively; Table 1). CRs were durable (up to >27 mo); disease control (SD >13 mo) was observed in pts without an IWG-defined response. Of the 59 AML pts (23 SA; 36 COMBO) who were transfusion-dependent at baseline, 26 (11 [48%] SA; 15 [42%] COMBO) and 21 (9 [39%] SA; 12 [33%] COMBO) became transfusion-independent (seen in all response categories) during 28 and 56 days on treatment, respectively. For R/R AML pts, median survival was 8.7 mo for SA and 12.1 mo for COMBO; for TN AML pts, median survival was 8.8 mo for SA (n=4) and not reached for COMBO. For R/R and TN AML patients with available pre- and on-treatment samples, IDH1m clearance or significant reduction (VAF <1%) was observed in 10/25 pts (40%) achieving an objective response and in 3/6 pts (50%) with stable disease. Mutation and 2-HG analyses suggest that pts who progressed on olutasidenib had a non-IDH1m-driven mechanism; updated analyses will be presented. Conclusions: SA and COMBO olutasidenib has shown favorable safety and clinical activity in IDH1m R/R AML with a SA ORR of 41% (95% CI: 21, 64) and a COMBO ORR of 46% (27, 67), and durable disease control. Olutasidenib induces deep responses with IDH1 mutation clearance in a subset of treated pts. Phase 2 investigations of SA and COMBO olutasidenib at the RP2D are ongoing in multiple IDH1m AML populations. Additional combinations are also being explored. Disclosures Watts: Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Takeda: Research Funding. Baer:Forma: Research Funding; Kite: Research Funding; Astellas: Research Funding; Incyte: Research Funding; Takeda: Research Funding; Abbvie: Research Funding; Al Therapeutics: Research Funding. Yang:Agios: Consultancy; AstraZeneca: Research Funding. Prebet:pfizer: Honoraria; novartis: Honoraria; pfizer: Honoraria; Boehringer Ingelheim: Research Funding; novartis: Honoraria. Lee:Helsinn: Consultancy; Jazz Pharmaceuticals, Inc: Consultancy; Roche Molecular Systems: Consultancy; AstraZeneca Pharmaceuticals: Consultancy; Karyopharm Therapeutics: Consultancy; Ai Therapeutics: Research Funding. Schiller:Biomed Valley Discoveries: Research Funding; Bristol Myer Squibb: Research Funding; Astellas: Research Funding; Agios: Research Funding, Speakers Bureau; Celgene: Research Funding, Speakers Bureau; Constellation Pharmaceutical: Research Funding; Daiichi Sankyo: Research Funding; Eli Lilly and Company: Research Funding; FujiFilm: Research Funding; Genzyme: Research Funding; Gilead: Research Funding; Incyte: Research Funding; J&J: Research Funding; Jazz Pharmaceuticals: Honoraria, Research Funding; Karyopharm: Research Funding; Novartis: Research Funding; Onconova: Research Funding; Pfizer Pharmaceuticals: Equity Ownership, Research Funding; Sangamo Therapeutics: Research Funding; Amgen: Other, Research Funding. Dinner:Agios: Consultancy; Pfizer: Consultancy; AstraZeneca: Consultancy. Pigneux:Roche: Honoraria; F. Hoffmann-La Roche Ltd: Honoraria; Pfizer: Honoraria; Abbvie: Honoraria; Jazz: Honoraria; Amgen: Honoraria; Daichi: Honoraria; Astellas: Honoraria; Novartis: Honoraria. Montesinos:Abbvie: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Research support, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Research support, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Karyopharm: Membership on an entity's Board of Directors or advisory committees, Other: Research support; Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau; Teva: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau. Wang:Stemline: Other: Advisory role, Speakers Bureau; Daiichi: Other: Advisory role; Amgen: Other: Advisory role; Abbvie: Other: Advisory role; Kite: Other: Advisory role; Jazz: Other: Advisory role; Astellas: Other: Advisory role, Speakers Bureau; celyad: Other: Advisory role; Pfizer: Other: Advisory role, Speakers Bureau; Agios: Other: Advisory role. Seiter:Novartis, Incyte, Celgene, Astellas, Sanofi: Speakers Bureau; Novartis, Astellas,: Consultancy; Novartis, Forma, Sun Pharma, Celgene, Jazz, Roche: Research Funding. Wei:Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Macrogenics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Genentech: Honoraria, Membership on an entity's Board of Directors or advisory committees; Servier: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astra Zeneca: Honoraria, Research Funding; Janssen: Honoraria; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties: AHW is a former employee of the Walter and Eliza Hall Institute and receives a fraction of its royalty stream related to venetoclax, Research Funding, Speakers Bureau; Astellas: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. De Botton:Agios: Consultancy, Research Funding; Celgene: Consultancy, Speakers Bureau; Pierre Fabre: Consultancy; Servier: Consultancy; Pfizer: Consultancy; Novartis: Consultancy; Janssen: Consultancy; FORMA: Consultancy, Research Funding; Syros: Consultancy; Bayer: Consultancy; Abbvie: Consultancy; Daiichi: Consultancy; Astellas: Consultancy. Jonas:AbbVie, Accelerated Medical Diagnostics, AROG, Celgene, Daiichi Sankyo, Esanex, Forma, Genentech/Roche, GlycoMimetics, Incyte, LP Therapeutics, Pharmacyclics: Research Funding; AbbVie, Amgen, GlycoMimetics: Other: Travel expenses; AbbVie, Amgen, Celgene, GlycoMimetics, Jazz, Pharmacyclics, Tolero: Consultancy, Membership on an entity's Board of Directors or advisory committees. Ferrell:Astex Pharmaceuticals: Research Funding; Incyte: Research Funding; Agios: Consultancy; Forma Therapeutics: Research Funding. Dao:Incyte Corporation: Membership on an entity's Board of Directors or advisory committees, Research Funding. Kelly:FORMA Therapeutics: Employment. Sweeney:FORMA Therapeutics: Employment. Forsyth:FORMA Therapeutics: Employment. Guichard:FORMA Therapeutics: Employment. Brevard:FORMA Therapeutics: Employment. Henrick:FORMA Therapeutics: Employment. Mohamed:FORMA Therapeutics: Employment. Cortes:Pfizer: Consultancy, Honoraria, Research Funding; Immunogen: Consultancy, Honoraria, Research Funding; Merus: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Research Funding; Daiichi Sankyo: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Astellas Pharma: Consultancy, Honoraria, Research Funding; BiolineRx: Consultancy; Forma Therapeutics: Consultancy, Honoraria, Research Funding; Biopath Holdings: Consultancy, Honoraria; Jazz Pharmaceuticals: Consultancy, Research Funding; Sun Pharma: Research Funding.

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