Abstract 7185: Optimization of an epigenetic based combination platform for patients with peripheral t cell lymphoma

Abstract Introduction: Our previous work demonstrated that combinations of HDAC and DNMT3 inhibitors were synergistic in preclinical models of T-cell lymphoma, and produced compelling activity in patients with relapsed or refractory disease. This combination was identified based on high-throughput chemical screening seeking to identify synthetically lethal combinations in a disease directed fashion. Here, we present a similar approach to rationally identify a third drug to complement the epigenetic-based combinations established to date. Results: First, we optimized the schedule of an HDACi [romidepsin, (Romi)] and a DNMT3i [5-azacytidine, (Aza)] across T-cell lymphoma lines. Results revealed that simultaneous exposure to Aza+Romi exhibited superior synergistic cytotoxicity compared to all other schedules tested in vitro. Using this schedule, we screened a library of drugs for synergy with the cornerstone combination of Aza + Romi. These drugs included agents targeting HMTs, KDMs, SWI/SNF, BET, CDK9, JAK, PI3K, Bcl-2, Bcl-xL, and Mcl-1. The combination drug screen was performed in three representative PTCL lines [H9 (CTCL), SMZ1 (PTCL-NOS), and FEPD (ALCL-ALKNEG)] using cell proliferation assay. The synergy between drugs was determined based on excess over Bliss (EOB) scores established using the Bliss model of independence (EOB ≥10, synergy; EOB ≥0-10, additive). The results revealed potent synergy between Aza+Romi and drugs targeting HMTs [PRMT5i (mean EOB, 18.5), EZH1/2i (mean EOB, 9.0)], SWI/SNF [SMARCA2-SMARCA4-PBRM1-degrader (mean EOB, 15.1)] and kinases [JAK1i (mean EOB, 17.6), PI3Ki (mean EOB, 15.5)]. In further characterization of schedule dependent activity, we noted that preexposure to PRMT5i, EZH1/2i, SWI/SNFi, or JAK1i followed by Aza+Romi treatment produced superior synergy in PTCL cells in vitro. The flow cytometric analysis revealed that these combinations induced apoptotic cell death in PTCL cell lines in vitro and these drug combinations, except Aza+Romi with SWI/SNFi and PI3Ki, exhibited a broad therapeutic window inducing preferential cell killing in the PTCL lines (cleaved PARP, 66-80%) compared to healthy PBMCs (cleaved PARP, 27-36%). Ongoing studies will decipher mechanisms of action using RNA-Seq and explore the ideal combinations in in vivo model of PTCL. Summary: The development of combination therapy for PTCL patients has been largely predicated on random ad hoc combinations. We describe herein a rational approach to the optimization of a new backbone for the disease. Simultaneous exposure of Aza and Romi coupled to a preexposure to drugs targeting PTMT5, EZH1/2, and JAK1 inhibitors produced potent synergy with a broad therapeutic window. We believe our ongoing investigation on these combinations will soon lead to the development of a new, chemotherapy free combination tailored to treat PTCL. Citation Format: Kallesh D. Jayappa, Andrea Joyner, Archana Thakur, Owen A. O’Connor. Optimization of an epigenetic based combination platform for patients with peripheral t cell lymphoma [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 7185.