Functional characterization of the ivosidenib (AG-120) and azacitidine combination in a mutant IDH1 AML cell model

Approximately 6-10% of patients with acute myeloid leukemia (AML) have a mutation in the metabolic enzyme isocitrate dehydrogenase 1 (IDH1), which leads to production of the oncometabolite 2-hydroxyglutarate (2-HG). Accumulation of 2-HG inhibits α-ketoglutarate-dependent enzymes, resulting in epigenetic dysregulation and a block in cell differentiation, promoting AML. Ivosidenib (IVO; AG-120) is a targeted inhibitor of the mutant IDH1 (mIDH1) enzyme in development for the treatment of AML with an IDH1 mutation. Clinical responses to IVO have been observed in mIDH1 AML, with differentiation of myeloblasts seen in responders indicative of the mechanism of action. Azacitidine (AZA) is a hypomethylating agent that has shown clinical activity in AML. We hypothesized that the combination of IVO + AZA would have a synergistic effect on the release of differentiation block in mIDH1 cells. In an in vitro erythropoetin differentiation assay, human TF-1 erythroleukemia cells expressing the IDH1-R132H mutation (TF1-IDH1R132H) were treated with vehicle, IVO alone (0.2 or 1 µM), AZA alone (0.1, 0.3, or 1 µM), or IVO + AZA concurrently. Assessments were hemoglobinization (red color change), expression of CD235a (erythroid differentiation marker) by flow cytometry, and Kruppel-like factor 1 (KLF1) and hemoglobin gene A/B (HBG) RNA levels by qRT-PCR. Apoptosis was assessed using IncuCyte ZOOM real-time imaging. AZA alone had little or no effect on hemoglobinization, but IVO alone showed dose-dependent increases in hemoglobinization. Concurrent IVO + AZA treatment had a greater effect on hemoglobinization than IVO alone. Increases in CD235a expression were seen with IVO and AZA as single agents, and expression was further increased with the combination of IVO + AZA (at AZA doses ≥0.3 µM). Expression of HBG and KLF1 RNA was not increased by single agent AZA, but was increased by single agent IVO. Concurrent IVO + AZA treatment resulted in potentiation of HBG expression (46-fold increase with IVO [0.2 µM] + AZA [1.0 µM] combination versus 25-fold and 1-fold increases for IVO [0.2 µM] and AZA [1.0 µM] alone, respectively); potentiation of KLF1 expression was less marked. IVO alone had no effect on induction of apoptosis, AZA increased apoptosis versus control, and concurrent treatment with IVO (0.1 and 0.3 µM) + AZA (1 µM) showed greater induction of apoptosis than AZA alone, suggesting potentiation. We have demonstrated that combining IVO + AZA in the TF1-IDH1R132H AML cell line enhanced cell differentiation, as measured by increases in hemoglobinization and expression of differentiation markers, and potentiated cell death, compared with either agent alone. Further exploration of the AZA + IVO combination in AML is ongoing in two clinical trials (NCT03173248 and NCT02677922). Citation Format: Katharine Yen, Vivek S. Chopra, Erica Tobin, Brian Avanzino, Konstantinos Mavrommatis, Jorge DiMartino, Kyle J. MacBeth. Functional characterization of the ivosidenib (AG-120) and azacitidine combination in a mutant IDH1 AML cell model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4956.