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Figure S4 from Concurrent Inhibition of Pim and FLT3 Kinases Enhances Apoptosis of FLT3-ITD Acute Myeloid Leukemia Cells through Increased Mcl-1 Proteasomal Degradation

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posted on 2023-03-31, 19:29 authored by Shivani Kapoor, Karthika Natarajan, Patrick R. Baldwin, Kshama A. Doshi, Rena G. Lapidus, Trevor J. Mathias, Mario Scarpa, Rossana Trotta, Eduardo Davila, Manfred Kraus, Dennis Huszar, Adriana E. Tron, Danilo Perrotti, Maria R. Baer

Combined AZD1208 and quizartinib treatment does not abrogate growth of KG-1a cells, expressing FLT3-WT, in a xenograft model.

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Leukemia and Lymphoma Society

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ARTICLE ABSTRACT

Purpose: fms-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) is present in 30% of acute myeloid leukemia (AML), and these patients have short disease-free survival. FLT3 inhibitors have limited and transient clinical activity, and concurrent treatment with inhibitors of parallel or downstream signaling may improve responses. The oncogenic serine/threonine kinase Pim-1 is upregulated downstream of FLT3-ITD and also promotes its signaling in a positive feedback loop, suggesting benefit of combined Pim and FLT3 inhibition.Experimental Design: Combinations of clinically active Pim and FLT3 inhibitors were studied in vitro and in vivo.Results: Concurrent treatment with the pan-Pim inhibitor AZD1208 and FLT3 inhibitors at clinically applicable concentrations abrogated in vitro growth of FLT3-ITD, but not wild-type FLT3 (FLT3-WT), cell lines. AZD1208 cotreatment increased FLT3 inhibitor–induced apoptosis of FLT3-ITD, but not FLT3-WT, cells measured by sub-G1 fraction, annexin V labeling, mitochondrial membrane potential, and PARP and caspase-3 cleavage. Concurrent treatment with AZD1208 and the FLT3 inhibitor quizartinib decreased growth of MV4-11 cells, with FLT3-ITD, in mouse xenografts, and prolonged survival, enhanced apoptosis of FLT3-ITD primary AML blasts, but not FLT3-WT blasts or remission marrow cells, and decreased FLT3-ITD AML blast colony formation. Mechanistically, AZD1208 and quizartinib cotreatment decreased expression of the antiapoptotic protein Mcl-1. Decrease in Mcl-1 protein expression was abrogated by treatment with the proteasome inhibitor MG132, and was preceded by downregulation of the Mcl-1 deubiquitinase USP9X, a novel mechanism of Mcl-1 regulation in AML.Conclusions: The data support clinical testing of Pim and FLT3 inhibitor combination therapy for FLT3-ITD AML. Clin Cancer Res; 24(1); 234–47. ©2017 AACR.