Abstract 5654: Degradation of Bcl-xL by DT2216 is lethal to T-cell acute lymphoblastic leukemia

Abstract Cancer is a multistep process where genomic and epigenomic alterations results in abnormal cellular proliferation and dissemination. This unregulated cellular proliferation can be interrupted through intervention therapy. One such strategy utilizes proteolysis targeting chimeras (PROTACs). PROTACs are heterobifunctional small molecular structures consisting of a ligand that binds to a target protein, and upon binding can recruit an E3 ligase which ubiquitinates the target protein, and eventually directs ubiquitinated protein for proteasomal degradation. This has been exploited as a revolutionary therapeutic strategy to degrade oncogenic and/or anti-apoptotic protein(s) that are overly expressed and offer a growth advantage in actively growing tumors. The accumulation of anti-apoptotic proteins creates resistance within the tumor against cancer treatments and preventative strategies in the clinical setting. In the present study, we used DT2216, a PROTAC that targets and promotes degradation of the anti-apoptotic protein Bcl-xL via the VHL (E3 ligase) pathway in T-cell acute lymphoblastic leukemia cells (T-ALL). Unlike other preclinical studies, like ABT263, DT2216 does not cause thrombocytopenia because VHL is poorly expressed in platelets. In our preclinical study, we treated thirteen human T-ALL cells with varying concentrations of DT2216 (0-1 µM) for 24 h and analyzed Bcl-xL expression by western blot analysis. Our data suggests that DT2216 results in the robust degradation of Bcl-xL in a dose-dependent manner at a minimal dose of 10 nM in eight of the cell lines studied (ALL-SIL, P12-Ichikawa, Jurkat, SUP-T1, HBP-ALL, HSB-2, PEER, and DND-41). Bcl-xL degradation triggers apoptosis, which was evident through the presence of cleaved products for Caspase-3 and PARP-1. We examined the expression of other anti-apoptotic proteins, Bcl-2 and Mcl-1 in response to DT2216 and neither protein was changed, which highlights DT2216’s specificity. We further evaluated the effect of DT2216 on the survival of T-ALL cells. Our data suggests that the IC50 for all the T-ALL cell lines ranges from 2-100 nM, with the exception of SUP-T1, which exhibited an IC50 above 1 µM. Our data suggests that DT2216 could serve as a viable, safe, and potent alternative or addition to traditional clinical treatments of T-ALL. Citation Format: Arunima S. Jaiswal, Elizabeth Williamson, Robert A. Hromas, Daohong Zhou. Degradation of Bcl-xL by DT2216 is lethal to T-cell acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5654.