PROJECT SUMMARY The objective of this study is to define the molecular mechanisms that control survival of malignant stem cells in acute myeloid leukemia (AML). Acute myeloid leukemia (AML) is a hematologic malignancy characterized by poorly differentiated hematopoietic stem cells (25). Traditionally, outcomes have been poor with a 30% response rate to standard of care in patients 65 years and older (25,26). A large cause of resistance and relapse to therapy is the persistence of leukemia stem cells (LSCs) (27-30). LSCs are a population of self-renewing cells that are able to initiate and maintain disease in immune-compromised animals (27). Traditional chemotherapy agents do not efficiently eradicate LSCs, and development of more effective therapies is a significant unmet need (27-30). Previous work from the Jordan lab has shown that LSCs have a unique dependence on oxidative phosphorylation (OXPHOS) for energy production (1-3,24). Further, BCL2 has a non-canonical role in regulating LSC metabolism as inhibition of BCL2 led to decreased OXPHOS and subsequent cell death in primary human LSCs (1-3,24). Analysis of samples from AML patients treated with the BCL2 inhibitor drug venetoclax revealed direct targeting of LSCs, which correlated with a 70% response rate (3). Thus, the underlying premise of the current proposal is that BCL2-mediated control of OXPHOS represents a key vulnerability that can be exploited to selectively target LSCs. Further, determining how OXPHOS is inhibited through BCL2 has implications for improving therapeutic strategies for AML patients. This proposal aims to elucidate the mechanistic link between BCL2 and LSC OXPHOS. In several model systems, BCL2 has been shown to have a non-canonical function in influencing calcium uptake and release at the ER and mitochondria through direct interactions with membrane bound calcium channels (7). Intracellular calcium homeostasis is crucial for cell survival, signaling and metabolism. In particular, the three rate limiting enzymes of the TCA cycle, pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase and isocitrate dehydrogenase are calcium dependent reactions (7). Therefore, BCL2 mediated calcium movement between the ER and mitochondria could be a mechanistic link between BCL2 and OXPHOS activity. BCL2 modulates the activity of calcium channels at the ER and mitochondria differently, based on the cell type being studied (7). Therefore, my proposal is focused on determining how BCL2 modulates OXPHOS activity by regulating calcium channel biology in leukemia stem cells. My hypothesis is that BCL2 mediated calcium localization is a critical regulator of OXPHOS activity in leukemia stem cells. This proposal will determine whether 1) BCL2 mediates calcium channel biology in LSCs 2) calcium channel biology modulates LSC metabolism/function and 3) regulation of calcium localization is the mechanism of action of BCL2 inhibition in LSCs.