Abstract 1387: Superoxide induces phosphorylation-mediated Mcl-1 stability to promote vresistance in hematologic malignancies

Abstract Acquired resistance to Bcl-2 inhibitor, venetoclax, poses a therapeutic challenge in the management of chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML). Venetoclax-resistant cells exhibit increased accumulation of Mcl-1, thereby switching dependence from Bcl-2 to Mcl-1. However, the mechanism behind increased Mcl-1 accumulation upon the acquisition of venetoclax resistance remains elusive. Given that a change in cellular redox state affects cell survival and drug sensitivity, we sought to investigate the interplay between cellular redox state and Mcl-1 accumulation in venetoclax-resistant cells. Our findings reveal that increased Mcl-1 levels in venetoclax-resistant hematologic malignant cells is associated with increased mitochondrial oxygen consumption and intracellular superoxide (O2 .-) levels. Corroborating the link between cellular redox state and Mcl-1 accumulation, increased O2 .- levels in venetoclax sensitive cells was accompanied by enhanced threonine-163 phosphorylation of Mcl-1 (T163pMcl-1), thereby reducing Mcl-1 ubiquitination and degradation. Furthermore, O2 .--induced T163pMcl-1 is mediated by AKT, as evidenced by increased serine-473 phosphorylation. Notably, reducing O2 .- levels or inhibiting AKT decreases T163pMcl-1 and Mcl-1 levels, heightens mitochondrial apoptotic-priming, and restores sensitivity to venetoclax-induced apoptosis. Collectively, our findings unravel redox-dependent mechanism of Mcl-1 stability and accumulation upon the acquisition of venetoclax resistance, which could have implications for the design of novel therapeutic strategy targeting cellular pro-oxidant state or AKT in various venetoclax-resistant hematologic malignancies. Citation Format: Stephen J. Chong, Jolin X. Lai, Kartini Iskandar, Chuqi Wang, Yuhan Wang, Romaine Guieze, Deepika Raman, Rachel H. Lim, Catherine J. Wu, Wee Choo Chng, Alice M. Cheung, Charles T. Chuah, Matthew S. Davids, Shazib Pervaiz. Superoxide induces phosphorylation-mediated Mcl-1 stability to promote vresistance in hematologic malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1387.