a) Project Summary Our studies have shown that the nuclear export inhibitors selinexor and eltanexor are highly active against AML cells and leukemia initiating cells (LICs) in patient-derived xenograft (PDX) models of human AML, with minimal toxicity to normal hematopoietic and progenitor cells (HSPCs) (Leukemia, 2013 and Leukemia, 2015). Thus, selinexor or eltanexor treament provides a therapeutic window for elimination of relapse-driving LICs while sparing normal cells. Our published earlier studies show that the BCL2 protein prevents XPO1 inhibitor mediated cell death, which suggests that selinexor or eltanexor will be highly synergistic and produce greater AML cell death if given in combination with a BCL2 inhibitor. Combinations of the BCL2 inhibitor venetoclax plus the methylation inhibitor decitabine (dacogen) have been shown to induce remission in AML (DiNardo CD et al. Blood 2019). Both venetoclax and selinexor or eltanxor are active against LICs as well as fast-proliferating bulk AML cells in patient-derived xenograft (PDX) models suggesting the hypothesis that selinexor or eltanexor together with venetoclax, and the decitabine equivalent ASTX727 will exhibit synergy in killing the LIC that sustain the AML cells in patients. Based on this hypothesis, we will perform preclinical studies to test the activity of selinexor or eltanexor in combination with venetoclax and dacogen against bulk AML cells and LICs in AML PDX models with NPM1 mutations. In Aim 1 we will determine the maximum tolerated dose of selinexor or eltanexor in combination with venetoclax and ASTX727 in NSG mice. In Aim2 we will compare the activity of venetoclax plus ASTX727 with the activity of all three drugs together to assess the added benefit of selinexor or eltanexor in killing AML LIC and determine disease-free survival. In Aim 3 we will assess the mechanism of drug interactions by measuring apoptosis by TUNEL assay on LICs and performing BH3 profiling of patient AML cells prior to therapy. It is becoming very clear that achieving complete cure for AML will require combination of multiple non-cross-resistant therapeutics. Thus, our goal for the UM1 award is to perform the preclinical studies to test the activity of selinexor, eltanexor, venetoclax and decitabine against AML cells and LICs to promote the prompt advancement of this multi-drug therapy into the clinic.