Abstract 2661: Novel pharmacological approaches of inhibiting the PI3K/AKT/mTOR signaling pathway in T-cell lymphoma (TCL)
Authors: Hartman Gabrielle , Mavis Cory , Gu Juan J. , White Amber , Mandeville Taylor , Torka Pallawi , Ghione Paola , Hernandez-Ilizaliturri Francisco J. 
Published: June 2022

Introduction: T-cell lymphoma (TCL) accounts for 15% of all non-Hodgkin’s lymphoma cases with most patients developing relapsed/refractory (R/R) disease. The management of R/R TCL is challenging and responses to second and beyond-line therapy are generally poor. Pre-clinical and clinical studies have identified the relevance of PI3K/AKT/mTOR signaling pathway in TCL biology. The combination of PI3K inhibitor (PI3Ki) Duvelisib and the HDACi Romidepsin improved the overall response rate (ORR) of R/R TCL to 50-55% in a phase I/II study (Horwitz et. al. ASH 2018, Lugano 2021). Evaluation of PI3Ki and HDACi combinations in TCL pre-clinical models is needed to guide the design of future clinical trials.

Methods: A panel of TCL cells lines were chosen representing T-cell acute lymphoblastic leukemia, T-lymphoblastic lymphoma, cutaneous T-cell lymphoma. A panel of PI3Ki (Omipalisib, Umbralisib and Duvelisib) and HDACi (Entinostat and Romidepsin) were selected to determine which combination would be most synergistic. Entinostat, an oral HDACi, was chosen for its remarkable preclinical and clinical activity in other lymphoma subtypes. Umbralisib is a new PI3Kδ inhibitor which was recently approved for treatment of follicular lymphoma and marginal zone lymphoma. Cells were exposed to Omipalisib (3.125-100nM), Umbralisib (1-320uM), or Duvelisib (1-100uM) alone or in combination with Entinostat (0.08-10uM) or Romidepsin (0.25-6) for 24, 48 and 72 hrs. Cell viability was measured using the CellTiter-Glo viability assay. Half-maximal inhibitory concentration (IC50) at 72hrs was determined for each drug and coefficient of synergy was calculated using Calcusyn Software. Changes in cellular metabolism and cell cycle distribution after exposure to PI3Ki were determined using DiOC6 staining and Propidium Iodide staining respectively. Epigenetic changes following exposure to Entinostat or Romidepsin were investigated for possible mechanisms.

Results: In vitro exposure of TCL cell lines to PI3Ki or HDACi resulted in dose-dependent cell death. The IC50 at 72 hrs was 30-500nM for Omipalisib, 9-35uM for Umbralisib, 1-35uM for Duvelisib, 0.2-2uM for Entinostat and for 1-4nM Romidepsin. All HDACi and Pi3Ki combinations demonstrated additive and/or synergistic activity. Duvelisib combined with Entinostat or Romidepsin exhibited the most synergy. Methylation profiling demonstrated genomic wide hypomethylation, specifically DNMT3A, in Romidepsin treated samples compared to Entinostat.

Conclusions: PI3Ki and HDACi combinations show significant synergy in TCL preclinical models. DNMT3A hypomethylation following Romidepsin exposure is being explored as the basis of PI3Ki and HDACi synergy. If confirmed in clinical trials, these results may refine the tolerability of the regimen for patients treated with this very promising PI3Ki/HDACi combination.

Citation Format: Gabrielle Hartman, Cory Mavis, Juan J. Gu, Amber White, Taylor Mandeville, Pallawi Torka, Paola Ghione, Francisco J. Hernandez-Ilizaliturri. Novel pharmacological approaches of inhibiting the PI3K/AKT/mTOR signaling pathway in T-cell lymphoma (TCL) [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 2661.