Abstract 6248: Inhibiting β-catenin in AML by targeting DDX5

Despite the use of high-dose chemotherapy and HSCT, less than 70% of adult AML patients enter complete remission and most patients relapse in less than two years. These poor outcomes have motivated intensive searches for effective and safe targeted agents. Asp-Glu-Ala-Asp (DEAD)-box protein DDX5 was found to be highly expressed in several solid cancers. DDX5, especially its phosphorylated form at Y593, has been reported to promote β-catenin cytoplasm-to-nucleus shuttling and subsequently facilitate the transcriptional activities of the β-catenin/T-cell factor (TCF) complex leading to enhanced expression of genes that are critical for growth, including MYC and CCND1. Knockdown of DDX5 has also been reported to reduce the growth of AML cells, indicating that DDX5 is a potential therapeutic target in AML. However, it remains unknown whether the growth dependence of AML on DDX5 is mainly mediated by β-catenin signaling. Importantly, drugs that selectively target DDX5 have not been tested in AML. In this study, we first analyzed the TCGA AML dataset and found that DDX5 gene is significantly overexpressed in the AML cohort compared to normal bone marrow samples. High DDX5 expression is associated with worse overall survival in AML patients. Moreover, DDX5 correlates with CTNNB1 which encodes β-catenin, at transcript levels. We further found that DDX5 is constitutively phosphorylated at Y593 and predominantly present in the nucleus of 10 AML cell lines tested. These results indicate the clinical relevance of DDX5 whose functional impact may link to β-catenin signaling in AML. We then determined the therapeutic efficacy of targeting DDX5 in human AML using RX-5902, a quinoxalinyl-piperazine compound. RX-5902 was previously shown to interfere with the interaction between phosphorylated DDX5 and β-catenin, inhibiting β-catenin signaling in some solid tumors. We found that RX-5902 attenuated phosphorylation of DDX5 at Y593, led to accumulation of β-catenin in the cytoplasm and consequently downregulated c-MYC in human AML cells within 24 hours. Treatment with RX-5902 dramatically increased cellular ROS level, induced cleaved-caspase3 mediated apoptosis and eventually inhibited cell growth of most human AML cell lines and primary AML cells in culture. These results mirrored what we observed following DDX5 depletion by shRNAs in AML cell lines. Also, dosing of RX-5902 in vivo significantly suppressed the growth of AML xenotransplants in immunocompromised mice and prolonged survival. Finally, we performed dynamic BH3 profiling and showed that RX-5902 increased apoptotic priming and BCL-2 dependence in AML cells. Therefore, we reasoned that simultaneous targeting DDX5 and BCL-2 may improve the therapeutic efficacy in AML. Indeed, concurrent treatment using RX-5902 and Venetoclax, a BCL-2 inhibitor, synergistically induced apoptosis in AML cells. Collectively, therapeutic targeting of DDX5 may be a novel and effective approach in AML and warrants further study. Citation Format: WEI NI, Swati Garg, Fen Zhu, Ellen L. Weisberg, Basudev Chowdhury, Martin Sattler, Amulya Jakkani, Suiyang Liu, Dana M. Sanchez, Lizi Wu, Richard M. Stone, Matthew S. Davids, James D. Griffin. Inhibiting β-catenin in AML by targeting DDX5 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6248.