Abstract 4821: A targeted differentiation therapy for the treatment of acute myeloid leukemia

Objectives: Acute myeloid leukemia (AML) is a heterogeneous disease with diverse genetic abnormalities present in all ages, but mainly prevalent in an elderly population with an average age of above 60 years. The treatment of elderly AML remains a formidable challenge as the long-term outcomes of elderly AML patients have not improved in the last three decades, with ≤5% overall survival recorded at 5 years, calling for novel treatment options. Epigenetic therapy has a significant impact on the management of hematologic malignancies. Recent findings show that using very low dosages of decitabine depletes DNA methyl transferase 1 (DNMT1) without cytotoxicity. Decitabine-mediated epigenetic therapy does not induce FLT3 (fms-like tyrosine kinase 3) ligand, which hinders the effectiveness of FLT3 inhibitors. The inhibition of FLT3 and DNMT1 is associated with terminal myeloid differentiation of AML cells. Therefore, combining the inhibitors of FLT3 and DNMT1 may be an effective therapeutic approach for the treatment of poor-risk AML. Ponatinib is a third-generation receptor tyrosine kinase inhibitor. Various in vitro and in vivo preclinical studies demonstrated antileukemic activities of ponatinib against AML cells bearing FLT3-ITD mutations. Methods: Apoptosis and CD11b were measured by flow cytometry. FLT3 signaling and DNMT1 levels were analyzed by immunoblotting. Results: FLT3-ITD expressing AML cell lines MV4-11, MOLM-13, and MOLM-14 were used in the study. Co-treatment with decitabine (10-100 nM) and ponatinib (2 nM) in AML cells induced apoptosis in association with PARP cleavage. Increased levels of pro-apoptotic protein BAD and decreased levels of anti-apoptotic protein MCL1 were observed in these treated cells. The combination of decitabine and ponatinib also showed similar effects in primary AML cells expressing FLT3-ITD. The Western blot analysis demonstrated that treatment of decitabine decreased levels of DNMT1 and ponatinib inhibited FLT3 signaling and activation of downstream effectors STAT5, AKT, and ERK1/2 with induction of PU.1 a key regulator of myeloid differentiation. Co-treatment with ponatinib and decitabine using low concentrations in MV4-11 and MOLM14 cells induced myeloid differentiation. The percentage of differentiated cells was measured by increased surface expression of CD11b analyzed by flow cytometry and granulocytic/monocytic morphology examined by Wright-Giemsa staining. Conclusions: Mechanistically, the hypomethylating agent initiates the differentiation process and FLT3 inhibition augments differentiation leading to apoptosis of AML cells. Altogether, these preclinical findings of downregulation of DNMT1 and induction of PU.1 are a novel differentiation approach to induce apoptosis in AML cells and warrant future therapeutic potential for the treatment of AML patients expressing FLT3 mutations. Citation Format: Sudhakiranmayi Kuravi, Myles Taylor, Tara L. Lin, Jensen Roy, Joseph McGuirk, Ramesh Balusu. A targeted differentiation therapy for the treatment of acute myeloid leukemia [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 4821.