Preclinical Evaluation of T-Cell Prolymphocytic Leukemia Demonstrates Heterogeneous BCL2-Family Dependency That May be Effectively Targeted with Small Molecule Inhibitors

• Published in: Blood Vol. 142; no. Supplement 1; p. 4192
• Main Authors: Pawar, Vishakha Anand, Aradhya, Akanksha, Galvan, Daniel, Borthakur, Gautam, Iyer, Swami P., Kirschbaum, Mark, Blake, David, Kadia, Tapan M., Sampath, Deepa, Vega, Francisco
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 02.11.2023
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2023-178256

T-cell prolymphocytic leukemia (T-PLL) is a rare, aggressive, mature T-cell leukemia with very few treatment options and adverse prognosis. There are currently no approved therapies for patients with relapsed T-PLL, where the median OS is less than 6 months. There are limited reports suggesting clinical activity of the BCL2 inhibitor venetoclax in patients with T-PLL. We aimed to characterize the dependencies of T-PLL on members of the BCL2-family of antiapoptotic proteins using BH3 profiling, a functional assay to assess the propensity of a cell to undergo apoptosis (priming) and the relative dependence of a cell on different antiapoptotic proteins. We then sought to experimentally exploit these dependencies with targeted therapies alone, and in combination, designed to inhibit the antiapoptotic proteins towards a therapeutic goal. Cell lines of mature T cell lymphomas/leukemias (TCL/L) including SUPT11 (T-cell leukemia with rearranged TCL1) (n=10) and bone marrow and peripheral blood samples from untreated patients with T-PLL (n=7) were analyzed by BH3 profiling. We also used a relapsed/refractory T-PLL patient sample that were able to engraft and expand in a PDX model. Finally, scRNA/ATAC seq has also been performed in a set of naïve-treated T-PLL patients. In contrast to TCL/L that demonstrated heterogeneity on BCL2 family member dependency, T-PLL samples were primed and consistently exhibited dependency on BCL2/BCL-xL and MCL1. Integration of scRNA/ATAC seq confirmed high expression of BCL2 and MCL1 in T-PLL cells from four patients supporting the premise that BCL2 and MCL1 could potentially be targeted for therapeutic benefit. Therefore, SUPT11 cells (used as a model of T-PLL) were exposed to venetoclax (25 and 50nM; BCL-2inh), fadraciclib (25 and 50nM; CDK2/9inh - indirect inhibitor of MCL-1 as it decreases mRNAs with high decay rates including MCL1 and MYC) or a combination of venetoclax and fadraciclib. We demonstrate that exposure to fadraciclib caused a rapid decline in the levels of phosphorylation on Serine 2 of RNA polymerase II C-terminal domain, as well as decline in the levels of MCL1 within 4 hours and completely depleted these proteins by 8-12 h of exposure. We also show that there was a synergistic increase both in mitochondrial dysfunction as measured by cytochrome C release by 18h and in cell death in cells exposed to the combination at 24h. These results suggest that combining venetoclax and fadraciclib might represent a potential therapeutic approach for T-PLL. In conclusion, preclinical evaluation of a T-PLL cell line and primary patient samples demonstrate BCL2-family dependency that can be effectively targeted with small molecule inhibitors of BCL2 and CDK2/9. In vivo studies in PDX models of T-PLL are underway to form the basis for clinical trials to study these combinations. Borthakur:Pacylex, Novartis, Cytomx, Bio Ascend:: Membership on an entity's Board of Directors or advisory committees; Astex Pharmaceuticals, Ryvu, PTC Therapeutics: Research Funding; Catamaran Bio, Abbvie, PPD Development, Protagonist Therapeutics, Janssen: Consultancy. Iyer:Yingli: Consultancy, Research Funding; CRISPR: Consultancy, Research Funding; Innate: Research Funding; Acrotech: Consultancy, Research Funding; Legend: Research Funding; Astra Zeneca: Research Funding; Ono: Research Funding; Pfizer: Research Funding; Salarius: Consultancy; Drenbio: Research Funding; Merck: Research Funding; American Society of Transplant and Cellular Therapy: Speakers Bureau; CuraBio: Speakers Bureau; American Society of Hematology: Speakers Bureau; Seagen: Consultancy, Research Funding. Kirschbaum:Cyclacel: Current Employment. Blake:Cyclacel Limited: Current Employment; Cyclacel Pharmaceuticals: Divested equity in a private or publicly-traded company in the past 24 months. Kadia:Biologix, Cure, Hikma Pharmaceuticals: Speakers Bureau; Celgene: Research Funding; Cellenkos Inc.: Research Funding; Hikma Pharmaceuticals: Speakers Bureau; AbbVie, Amgen, Inc, Ascentage Pharma Group, Astellas Pharma Global Development, Astex, AstraZeneca, BMS, Celgene, Cellenkos Inc, Cyclacel, Delta-Fly Pharma, Inc, Genentech, Inc., Genfleet, Glycomimetics, Iterion, Janssen Research and Development: Research Funding; Astellas Pharma Global Development: Research Funding; Cure: Speakers Bureau; Regeneron Pharmaceuticals: Research Funding; Novartis: Consultancy; Glycomimetics: Research Funding; Pfizer: Consultancy, Research Funding; Pulmotect, Inc.: Consultancy, Research Funding; Amgen, Inc.: Research Funding; AstraZeneca: Research Funding; Iterion: Research Funding; Genentech: Consultancy, Research Funding; GenFleet Therapeutics: Research Funding; Janssen Research and Development: Research Funding; Liberum: Consultancy; Sanofi-Aventis: Consultancy; SELLAS Life Sciences Group: Research Funding; Genzyme: Honoraria; Ascentage Pharma Group: Research Funding; Jazz Pharmaceuticals, Pfizer, Pulmotect, Inc, Regeneron Pharmaceuticals, SELLAS Life Sciences Group: Research Funding; Cyclacel: Research Funding; Delta-Fly Pharma, Inc.: Research Funding; Daiichi Sankyo, Genentech, Inc., Genzyme, Jazz Pharmaceuticals, Liberum, Novartis, Pfizer, PinotBio, Inc, Pulmotect, Inc, Sanofi-Aventis, Servier: Consultancy; Agios: Consultancy; Servier: Consultancy; Pinotb-Bio: Consultancy; BMS: Consultancy, Research Funding; Astex: Honoraria. Vega:Allogene: Research Funding; Geron: Research Funding.