Targeting mitochondrial calcium to eradicate leukemia-initiating cells

SUMMARY The goal of this project is to develop strategies for the eradication of leukemia-initiating cells (LICs) in AML patients who have received initial therapy with venetoclax and azacitidine (ven/aza). As demonstrated previously, almost all AML patients treated with ven/aza will eventually relapse. Thus, providing improved

therapeutic regimens is an urgent unmet need. Our previous studies have demonstrated that more than one subtype of LIC can exist simultaneously in the same patient. Importantly, different LIC subtypes can demonstrate highly variable responses to therapy, including resistance to ven/aza. Thus, LIC heterogeneity may be a

prevalent feature of AML biology, and as such poses a significant challenge in designing optimal therapies that effectively eradicate them. Consequently, a major goal of this project is to characterize and target ven/aza resistant LICs. Our preliminary data indicate that reliance on uptake of calcium into mitochondria is a distinct

feature and vulnerability of ven/aza resistant AML cells. Thus, we have investigated the role of the calcium uniporter, MCU, as a potential therapeutic target. Our findings show that both genetic and pharmacological inhibition of MCU is highly cytotoxic to ven/aza resistant LICs. Importantly, normal hematopoietic stem/progenitor

cells do not share this extensive reliance upon MCU for mitochondrial metabolism and survival. Thus, this axis appears to represent a unique feature of ven/aza-resistant LIC and in turn, an attractive opportunity for therapeutic intervention. To translate this strategy to clinical practice, we have leveraged a recent finding that

shows the well characterized chemotherapy agent, mitoxantrone (mitox), is a strong inhibitor of MCU. Intriguingly, we demonstrate that mitox is effective in suppressing mitochondrial calcium uptake and downstream metabolism at doses 10-100 fold lower than used for conventional chemotherapy purposes. Indeed, at doses

as low as 10nM, we observe potent eradication of ven/aza resistant LICs, with no evidence of DNA damage, and no discernable effect on the growth of normal hematopoietic stem/progenitor cells. Based on these findings, our goals are to: 1) perform preclinical modeling studies as a prelude to clinical investigation and to better understand

the mitox mechanism of action, 2) conduct a clinical trial using lower-dose mitox in combination with ven/aza as a strategy to target drug-resistant LICs and thereby increase remission duration, and 3) to perform a detailed in vivo analysis of LIC subtypes in patients undergoing ven/aza/mitox therapy to better define the role of

mitochondrial calcium uptake and any other molecular events that contribute to therapy resistance in the heterogenous LIC compartment. Taken together, the proposed studies will provide a comprehensive evaluation of mitox as a clinical strategy to augment ven/aza therapy and will determine the prevalence and role of calcium

uptake in the biology of drug resistant LICs.