Targeting the Unfolded Protein Response in Leukemia Biology and Chemotherapy Resistance

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Project Summary/Abstract Acute myeloid leukemia (AML) is an aggressive blood cancer that encompasses a variety of genetically distinct sub-types. AML patients overall, display one of the lowest overall 5-year survival rates (<25%) of all cancer diagnoses and currently ranks as the deadliest form of leukemia. These unsatisfactory outcomes are largely the result of the ineffectiveness and toxicities of existing chemotherapies and highlight the urgent need for more-effective therapies that either replace or improve the effectiveness these chemotherapies. The development of more-effective therapies begins by identifying the molecular mechanisms that underpin AML pathogenesis and chemotherapy ineffectiveness. We recently discovered that the two transcription factors (TFs) TFs, ATF4 and XBP1s, which are components of the signal transduction network, the unfolded protein response (UPR), are key mediators of AML cell survival and disease progression. Specifically, we have found that inhibition of ATF4 or XBP1s antagonizes AML cell survival and disease progression in multiple in vitro and in vivo models of AML. We also found that small-molecule inhibitors of PERK and IRE1, which are upstream activators of ATF4 and XBP1s, respectively, antagonizes AML cell survival and enhances the effectiveness of first-line chemotherapies. The collective goals of this proposal aim to address two key unanswered questions: 1. What are the downstream transcriptional targets of ATF4 and XBP1s that support AML biology and 2. What are the molecular nodes of the UPR that can be targeted with chemical strategies? With respect to the first question, we have identified two candidates, DDIT4 and SREBF1, which are known regulators of autophagy and cholesterol biology, respectively. We will use a combination of established genetically engineered mouse models of AML and patient-derived AML samples to assess the functional roles of DDIT4 and SREBF1 in AML as well as their relationship to the UPR. Additionally, we will assess the contribution of DDIT4 and SREBF1 – as well as the downstream-regulated processes contribute to the pro-leukemia functions of ATF4 and XBP1s. Second, we will assess therapeutic strategies for targeting the UPR, autophagy and cholesterol biology either alone or simultaneously in experimental models of AML. The results of these studies will provide new insight on the molecular mechanisms that support the pathogenesis and chemotherapy responses of AML and establish a platform for developing novel therapeutic strategies. Moreover, components of the UPR support the pathophysiology of many other tumor settings and thus results from our proposed studies will likely have implications for other forms of human cancers.