Abstract LB426: Targeting Oncogenic FLT3-ITD by USP10 Inhibitors for the Treatment of FLT3-ITD AML

Acute myeloid leukemia (AML) is an aggressive hematologic disease with a dismal prognosis. Each year in the US, there are approximately 20,000 new cases of AML and about 11,000 deaths. For adults, the 5-year overall survival rate is only 31.9%. One-third of AML patients harbor activating mutations in FMS-like tyrosine kinase 3 (FLT3) gene resulting in constitutive activation of downstream survival pathways. The most common FLT3 mutation is internal tandem duplication (FLT3-ITD), which occurs in approximately 25% of all AML patients. FLT3-ITD AML patients have reduced survival rates and an increased risk of relapse compared to AML patients with wild-type FLT3. Gilteritinib was recently approved for relapsed/refractory (R/R) FLT3-mutated AML patients. Although gilteritinib significantly improves clinical outcome for R/R FLT3-mutated AML patients, the 1-year survival rate is merely 37.1%, highlighting the need for new strategies for treating R/R FLT3-ITD positive AML. One common mechanism of resistance to FLT3 inhibition is inherent or acquired FLT3 mutations. To circumvent this, an alternative approach is to induce degradation of FLT3-ITD oncoprotein. Recently, the ubiquitin-specific peptidase 10 (USP10) was identified as a deubiquitinase (DUB) that stabilizes the FLT3-ITD oncoprotein, while sparing wild-type FLT3. The USP10 inhibitor Wu-5 downregulates FLT3-ITD and has antileukemic activity. Additionally, the USP7 inhibitor P22077 has demonstrated antileukemic activity and also targets USP10 in AML cells. While these covalent USP10 inhibitors are promising, they lack specificity for USP10 and/or potency. Therefore, there is an unmet need to develop potent USP10-selective inhibitors. We found that AML cells with acquired resistance to AraC (a main drug used for the treatment of AML) expressed high levels of FLT3-ITD and USP10 proteins, suggesting that degrading FLT3-ITD will show antileukemic activity against R/R AML cells. We used structure-activity relationship (SAR) and computational studies to develop non-covalent USP10 inhibitors. Our initial in vitro screening identified two compounds with antileukemic activity against FLT3-ITD AML cells with acquired resistance to AraC. Focusing on one of these novel USP10 inhibitors, GL-320, we show that it has significantly greater in vitro potency against AML cells than the reported USP10 inhibitors P-22077 and Wu-5. Cellular thermal shift assays show that GL-320 binds to USP10. Furthermore, GL-320 induces apoptosis in FLT3-ITD AML cells through inhibition of USP10 and subsequent downregulation of FLT3-ITD and PARP1 independent of caspase activation, and pharmacological inhibition of these two proteins induced apoptosis in a cooperative manner. Our results demonstrate that GL-320 is a non-covalent USP10 inhibitor that shows potent in vitro antileukemic activity against FLT3-ITD AML. Amirreza Samarbakhsh, Jianlei Zhao, Sadaf Dorandish, Jenna Thibodeau, Elyas Khan, Q. Ping Dou, Lisa Polin, Juiwanna Kushner, Jeffrey W. Taub, Yubin Ge, Navnath S. Gavande. Targeting oncogenic FLT3-ITD by USP10 inhibitors for the treatment of FLT3-ITD AML [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB426.