Abstract LB354: Pharmacologic TSC2 inhibition sensitizes acute myeloid leukemia to proteasome inhibition via mTORC1 mediated mitochondrial catastrophe

Abstract Introduction: mTORC1 activity is widely regarded as oncogenic; however, under therapeutic stress, suppression of mTORC1 can promote adaptive survival programs and contribute to drug resistance. Despite extensive efforts to inhibit mTORC1, pharmacologic strategies to transiently activate this pathway remain unexplored. Physiologic activation of mTORC1 occurs through inhibition of the tuberous sclerosis complex (TSC), suggesting TSC2 as a druggable node to therapeutically rewire stress responses in cancer. Moreover, p53-mutant acute myeloid leukemia (AML) represents a high-risk disease state characterized by profound resistance to cytotoxic therapy. Methods: Through structure-guided in silico screening and medicinal chemistry optimization, we developed AcTor, a first-in-class small-molecule inhibitor of TSC2. Based on the established vulnerability of TSC2-deficient cells to proteasome inhibition, we evaluated AcTor in combination with the proteasome inhibitor ixazomib (IXZ) in AML cell lines, patient-derived samples, and xenograft models. Results: AcTor markedly potentiated IXZ-induced cytotoxicity across genetically diverse AML models. The combination triggered rapid apoptosis driven by mitochondrial dysfunction, characterized by loss of mitochondrial integrity and bioenergetic failure. Transcriptomic profiling revealed induction of a p53-associated stress response in p53-deficient AML cells treated with AcTor/IXZ, indicating activation of non-canonical p53 pathway outputs independent of p53 genotype. In vivo, brief exposure to AcTor combined with IXZ significantly suppressed leukemic burden in patient-derived AML xenografts, irrespective of p53 status. This response was associated with efficient elimination of circulating blasts and leukemic stem cells. Notably, sensitivity to the combination was preserved in relapsed disease models. Conclusions: These findings identify TSC2 inhibition as a previously unrecognized therapeutic strategy to activate mTORC1 in a controlled, context-dependent manner. While AcTor lacks antileukemic activity as a single agent, its combination with proteasome inhibition converts mTORC1 signaling from a survival pathway into a driver of mitochondrial catastrophe. This mechanistically defined vulnerability enables durable targeting of aggressive and treatment-refractory AML and provides a strong rationale for translational development of mTORC1-activating combination therapies. Citation Format: Shakti Pattanayak, Boaz Tirosh, Omid Hajihassani, Jordan M. Winter, Kelsey H Fisher-Wellman, Leif A Eriksson. Pharmacologic TSC2 inhibition sensitizes acute myeloid leukemia to proteasome inhibition via mTORC1 mediated mitochondrial catastrophe [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(8_Suppl):Abstract nr LB354.