Abstract 1824: EZH2 inhibition induces blast differentiation in acute myeloid leukemia

Abstract

Enhancer of zeste homolog 2 (EZH2) is a part of the polycomb repressive complex and catalyzes the trimethylation of lysine 27 on histone H3 (H3K27me3). EZH2 inhibition has a complex role in the pathogenesis of acute myeloid leukemia (AML), in that it has been shown to be either a tumor suppressor or an oncogene depending on the stage of AML development and the genes that EZH2 is regulating during each stage. Unlike follicular and diffuse large B-cell lymphoma where EZH2 mutations result in gain of function, EZH2 mutations are typically loss of function in myeloid diseases. However, we hypothesized that in AML patients without EZH2 mutations, loss of EZH2 function may produce a phenotype that would allow for therapeutic targeting without influencing normal hematopoiesis. We used EPZ011989 (EPZ), an EZH2 inhibitor tool compound, to inhibit H3K27me3 in our studies. We started by treating the MOLM-13 AML cell line with EPZ and confirmed a decrease in H3K27me3. This reduction in H3K27me3 resulted in a slight decrease in metabolic activity via MTS assays as well as decreased colony formation in methocult. These studies were followed up with EPZ inhibition in primary AML samples in vitro. We found that EZH2 inhibition resulted in decreased self-renewal of primary AML samples but not of CD34+ bone marrow cells from normal donors. Furthermore, we found that after 7-day treatment with EPZ, primary AML samples undergo moderate differentiation as suggested by an increase in CD11b surface expression via flow cytometry. These results are further supported by the morphological changes seen after 14-days of EPZ treatment in vitro. Based on these results, we hypothesize that EZH2 inhibition in primary AML samples promotes the differentiation of AML blasts. Furthermore, our preliminary data suggests that daily treatment with 150 mg/kg of EPZ results in a survival advantage and reduced disease burden in the MOLM-13-luciferase murine xenograft model. Despite loss of function EZH2 mutations portending poor outcomes in myeloid malignancies, we demonstrate that pharmacologic EZH2 inhibition reduces AML blast stemness and promotes differentiation into mature myeloid cells. In contrast, no change in normal CD34+ stem cells occurs with EZH2 inhibition, offering the opportunity to selectively target myeloid leukemia. Citation Format: Sydney Fobare, Ola A. Elgamal, Emily H. Stahl, Abeera Mehmood, Jean Truxall, Mariah L. Johnson, Amina Abdul-Aziz, John C. Byrd, Erin Hertlein. EZH2 inhibition induces blast differentiation in acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1824.