Synergistic Anti-leukemic Activity And Underlying Molecular Mechanism Of MRX-2843 Combined With Venetoclax In FLT3-mutated Acute Myeloid Leukemia

Acute myeloid leukemia（AML）is a highly heterogeneous disease caused by the malignant proliferation of myeloid hematopoietic cells.About one-third of AML patients harbor FMS-like tyrosine kinase 3（FLT3）mutations,of which 25% are FLT3-internal tandem duplications（FLT3-ITD）and 5%～10% are point mutations in the FLT3-tyrosine kinase domain（FLT3-TKD）.These mutations result in constitutive activation of FLT3 without binding to its ligand,promoting cell proliferation and survival.Generally,AML patients with FLT3-ITD mutation have high recurrence probability,low survival rate,and poor prognosis post treatment.At present,the U.S.Food and Drug Administration（FDA）has approved two FLT3 inhibitors,Midostaurin and Gilteritinib,for the treatment of patients with FLT3-mutated AML,but there is still much room for improvement in their efficacy.MRX-2843 is a novel FLT3 inhibitor with antileukemic activity against FLT3-mutated AML both in vitro and in vivo.The Bcl-2 selective inhibitor Venetoclax（VEN）was approved by the US FDA in 2018 in combination with low-dose cytarabine,azacitidine,or decitabine for the treatment of AML,but the efficacy of these combination therapies is also limited.Previous studies from our laboratory and other groups have demonstrated that Mcl-1 is a key factor in VEN resistance in AML cells;both Midostaurin and Gilteritinib can synergistically enhance the antileukemic activity of VEN via downregulation of Mcl-1.In this Master’s dissertation,we demonstrate that MRX-2843 alone and in combination with VEN can downregulate the transcription and protein levels of Mcl-1.Further,combination of the two agents results in synergistic induction of apoptosis.Compared with MRX-2843 and VEN alone,the combination of the two drugs shows significantly stronger ability to inhibit colony formation of leukemic progenitor cells.However,the combination of MRX-2843 and VEN has no effect on normal hematopoietic cells from healthy donors,suggesting that the combination is leukemia-selective.c-Myc has critical regulatory effects on cell survival and proliferation of AML cells.We demonstrate that besides Mcl-1,MRX-2843 downregulates c-Myc by inhibiting the JAK2/STAT5 signaling pathway to enhance the antileukemic activity of VEN against FLT3-mutated AML.Finally,we demonstrate that MRX-2843 and VEN also synergize in inducting apoptosis in chemoresistant AML cells.The results of this dissertation study form a solid theoretical and experimental basis for the clinical evaluation of the combination of MRX-2843 and VEN.