Determination of IDH1 Mutational Burden and Clearance Via Next Generation Sequencing in Patients with IDH1 Mutation Positive Hematologic Malignancies Receiving AG 120, a First in Class Inhibitor of Mutant IDH1

Recurrent somatic mutations in the metabolic enzymes isocitrate dehydrogenase 1 and 2 (IDH1/2) confer gain of function activity in cancer cells, resulting in accumulation of the oncometabolite, D 2 hydroxyglutarate (2 HG) High levels of 2 HG result in epigenetic changes and impaired cellular differentiation. IDH mutations have been identified in multiple solid tumors and hematologic malignancies. Approximately 6 10% and 9 13% of adults with acute myeloid leukemia (AML) carry mutations in IDH1 (mIDH1) or IDH2 (mIDH2) respectively. AG 120 is a first in class, oral, potent, reversible, selective inhibitor of the IDH1 mutant enzyme under evaluation in multiple ongoing single agent and combination clinical trials [NCT02074839, NCT02073994, NCT02632708, NCT02677922] This is the first report of IDH1 mutation clearance assessed by variant allele frequency (VAF) analysis using next generation sequencing (NGS) in patients treated on the dose escalation portion of the first in human phase 1 study [NCT02074839]  Patients with advanced mIDH1 positive hematologic malignancies received AG 120 as a single agent orally once daily (QD) or twice daily (BID) continuously in 28 day cycles. Primary objectives were determination of safety, maximum tolerated dose (MTD) and selection of a dose schedule for expansion cohorts and future studies. Secondary objectives included clinical activity assessed by investigators using modified 2003 International Working Group Criteria in AML. Determination of mIDH1 VAF was performed using the FoundationOne(r) Heme test on mononuclear cells from the bone marrow or peripheral blood at screening and subsequent time points on study. This NGS assay reports IDH1 mutations for samples with VAF =1% with median coverage 500X. Patients with IDH1 mutational clearance (IDH1 MC) were defined as having mIDH1 at baseline and at least one on study sample with no reported mIDH1.  Seventy eight patients were treated in the dose escalation portion, which is now closed to enrollment. As of the data cut off of May 12, 2016, the median duration on treatment was 3.2 months and 9 (11.5% patients remain on treatment, with an additional 8 (10.3% patients transitioned to stem cell transplant. Doses ranged from 300 1200 mg QD with 1 cohort at 100 mg BID. Though the MTD was not reached, the recommended phase 2 dose was determined to be 500 mg QD. The majority of adverse events (AEs) were grade 1 and 2, the most common =30% being diarrhea, fatigue, and nausea; the most common grade =3 AEs =15% were febrile neutropenia, anemia, leukocytosis and pneumonia. The most common serious AEs were febrile neutropenia (16.7% and pneumonia (12.8% The overall response rate (ORR) was 38.5% (n=30) with 17.9% (n=14) achieving a complete remission (CR) Longitudinal mIDH1 VAF data were available for 51 patients; of these, 22% (n=11) achieved a CR. IDH1 MC was observed in 27.3% (3/11) patients who achieved CR  In contrast, only 1/40 patients who did not achieve CR experienced IDH1 MC. This occurred in a patient with an initially low mIDH1 VAF who had clinical progression despite IDH1 MC  In all 3 patients with CR who achieved IDH1 MC, an initial increase in mIDH1 VAF, or early peak, was observed prior to IDH1 MC, suggesting that early clonal expansion might have occurred as part of the mechanism of action of AG 120.  This is the first demonstration that treatment with single agent AG 120 can result in mIDH1 clearance as determined by NGS. Further analysis of the mutational profiles is planned. AG 120, a potent, selective, oral inhibitor of mIDH1 continues to demonstrate a well tolerated safety profile in patients with advanced hematologic malignancies, and induced objective single agent durable responses. The data continue to support the efficacy and safety of single agent AG 120 and provide evidence that the underlying biology of the disease is altered by treatment.  advisory board, Research Funding; Novartis: Other: advisory board,  Research Funding; Agios: Other: advisory board,  Consultancy; Agios: Consultancy,  Consultancy, Honoraria, Membership on an entity9s Board of Directors or advisory committees; : advisory board; Novartis: Other: advisory board.  Advisory Board participation; Agios Pharmaceuticals: Other: Advisory Board participation; Seattle Genetics: Consultancy, Other: Advisory Board participation,  Advisory Board participation;  Consultancy, Syros: Honoraria; BMS: Honoraria; Janssen Pharmaceuticals: Honoraria; Novartis: Honoraria.  Research Funding; Pharmacyclics LLC,  Research Funding; Gilead Sciences: Research Funding; ARIAD: Research Funding; RainTree Oncology Services: Equity Ownership.