Session: 604. Molecular Pharmacology and Drug Resistance: Myeloid Neoplasms: Poster II
Hematology Disease Topics & Pathways:
Research, MDS, Acute Myeloid Malignancies, AML, Translational Research, Chronic Myeloid Malignancies, Diseases, Myeloid Malignancies
To seek molecular basis of EZH2 inhibitor-mediated apoptosis induction, we performed CUT&Tag sequence for H3K27me3 using vehicle or valemetostat-treated cells. Strikingly, promoter region of GADD45γ was the most robustly and significantly decreased annotated peak locus of H3K27me3 in valemetostat-treated OCI-AML20. H3K27me3 peak in GADD45γ locus was also significantly decreased in valemetostat-treated YCU-AML1 but not in FKH-1 and Kasumi-3. As expected, valemetostat treatment induced increased expression of GADD45γ in OCI-AML20. Moreover, transcriptomic analysis also demonstrated GADD45γ as the most robustly upregulated gene in valemetostat-treated YCU-AML1 compared to vehicle-treated cells. GADD45γ is known to be an upstream regulator of stress-activated protein kinases such as p38 and JNK in which signaling pathways activation induce apoptosis upon various cellular stresses. GADD45γ promoter region possessed putative EVI1 binding site predicted by rVista2.0 software, indicating that EVI1 may directly bind and recruit PRC2 complex to GADD45γ locus. We further confirmed phosphorylation of Thr180/Tyr182 (T180/Y182) residues of p38α in valemetostat-treated YCU-AML1 and OCI-AML20 but not in SKM-1 and Kasumi-3. p38 is known to phosphorylate Ser33 (S33) and Ser46 residues of TP53, leading to apoptosis in lung cancer cells (Yogosawa et al. Cancer Sci. 2018). In line with this finding, valemetostat treatment induced phosphorylation of Ser33 residue of TP53 in YCU-AML1 and OCI-AML20. Phosphorylations of p38α (T180/Y182) and TP53 (S33) were also noted in tazemetostat-treated YCU-AML1 and OCI-AML20, suggesting that EZH2 inhibition directly activates GADD45γ-p38α-TP53 axis leading to apoptosis preferentially in MDS/AML cells with inv(3)/t(3;3) and -7. As a proof of concept, p38MAPK inhibitor SB203580 restored valemetostat-induced colony growth inhibition as well as apoptosis induction in YCU-AML1 and OCI-AML20.
Importantly, valemetostat treatment significantly reduced leukemic burden and improved overall survival in xenotransplant mouse model of YCU-AML1. Moreover, primary MDS/AML patient bone marrow (BM) sample harboring inv(3) and -7 exhibited preferential sensitivity to valemetostat compared to BM samples derived from healthy control or MDS/AML patients with or without -7 in vitro.
Taken together, our study unraveled PRC2-mediated inactivation of GADD45γ-p38α-TP53 axis as a molecular basis for evasion of apoptosis in MDS/AML with inv(3)/t(3;3) and -7, which can be preferentially abrogated by EZH2 inhibition leading to efficient induction of apoptosis in this high-risk MDS/AML.
Disclosures: Kunimoto: Daiichi Sankyo: Research Funding. Honma: Daiichi Sankyo Co., Ltd.: Current Employment. Tsutsumi: Daiichi Sankyo Inc.: Current Employment. Doki: Janssen Pharmaceutical K.K.: Honoraria; Novartis Pharma K.K.: Honoraria. Cai: Imago Biosciences: Consultancy, Current equity holder in private company. Levine: Zentalis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Mission Bio: Membership on an entity's Board of Directors or advisory committees; Ajax: Membership on an entity's Board of Directors or advisory committees, Research Funding; Auron: Membership on an entity's Board of Directors or advisory committees; Prelude: Membership on an entity's Board of Directors or advisory committees; C4 Therapeutics: Membership on an entity's Board of Directors or advisory committees; Isoplexis: Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy; Qiagen: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy; AstraZeneca: Consultancy, Honoraria; Novartis: Consultancy; Roche: Honoraria; Lilly: Honoraria; Amgen: Honoraria. Nakajima: Novartis: Speakers Bureau; Takeda: Research Funding; Eisai: Research Funding; Astellas: Research Funding; Pfizer: Research Funding; Daiichi Sankyo: Research Funding, Speakers Bureau.
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