PROJECT SUMMARY/ABSTRACT Acute myeloid leukemia (AML) is a lethal blood cancer characterized by a clonal expansion of precursor blood- forming cells. Intensive chemotherapy has been the mainstay of AML therapy for decades. Unfortunately, not all patients are fit enough to receive it and mortality due to relapse despite intensive treatment is common. Recently, the FDA approved a lower intensity regimen combining a hypomethylating agent, such as azacitidine (aza), with the BCL2 inhibitor venetoclax (ven), based on phase 3 randomized data showing an overall survival benefit and high response rates across AML prognostic subtypes. The success of aza/ven highlights the apoptotic pathway as an exciting therapeutic target. Venetoclax induces apoptosis by antagonizing the anti-apoptotic function of BCL2, one of many mitochondrial BH3-domain proteins that regulate the threshold at which an AML blast dies. This apoptotic threshold, or priming, in viable leukemic blasts can be measured via a functional cell death assay, called BH3 profiling. I have recently demonstrated that the cell of origin of leukemic transformation influences apoptotic priming and resultant therapeutic sensitivity via alterations in p53 activity. I am interested in understanding how AML cell state, whether established by AML genotype or apoptotic priming, can influence drug sensitivity and clinical outcomes in the context of attenuated p53 function. I hypothesize that BH3 profiling of AML patient samples can serve as a biomarker to predict treatment response to aza/ven. I also hypothesize that complex cytogenetic changes – ensuing from mutant TP53-induced genomic instability – promote AML progression and therapeutic resistance to aza/ven independent of mutant TP53. I believe that this work will address important biological questions with therapeutic implications: 1. Can BH3 profiling assays predict treatment response to aza/ven in xenograft mouse models? 2. Which transcriptional and epigenetic pathways are engaged in AML cells with low apoptotic priming and blunted responsiveness to aza/ven? 3. Is complex karyotype AML in the setting of TP53 loss of function a bystander phenomenon, or does it enhance leukemogenicity and/or resistance to therapies such as aza/ven and chemotherapy? Dr. Sheng Cai, an Assistant Attending at MSKCC, will conduct this study as part of his career development plan, dedicating 85% of his time to research. Dr. Cai is mentored by Dr. Ross Levine, a world expert in hematologic malignancies. He is also advised by Drs. Anthony Letai (who developed the BH3 profiling assay), Scott Lowe, Michael Kharas, Richard Koche, and Andriy Derkach. Dr. Cai's training will include gaining knowledge in biomarker validation and expertise in bioinformatics and genetic mouse models, with the long term goal of developing a research program as an independent investigator in hematologic malignancies developing functionalized biomarker assays for precision oncology.