INTRODUCTION: TGR-1202 is a novel, next-generation PI3Kδ inhibitor presenting significant structural and pharmacological differences from prior small-molecule PI3Kδ inhibitors. TGR-1202 has high clinical efficacy in treatment of B cell malignancies with a substantially differentiated adverse event profile compared to previous PI3Kδ inhibitors, specifically concerning hepatotoxicity or colitis which have been minimal or non-existent. It has been postulated that these effects may be due to T cell immune-mediated mechanisms. We hypothesized that TGR-1202 preserves the function of the regulatory T cell (Treg) population, translating to decreased immune-mediated side effects after treatment. Here, we aimed to compare effects of clinically available PI3Kδ inhibitors on T cells with an emphasis on Tregs.

METHODS: We compared activity of idelalisib, duvelisib, and TGR-1202 as single agents in vitro in isolated human T cells. Viability, apoptosis, and proliferation were determined using CellTiter Blue®, annexin V/PI and CFSE staining. CBA and qRT PCR were used to measure cytokines and transcription factors. Flow cytometry was used to detect subset ratios and surface marker expression.

RESULTS: First, we observed comparable dose-dependent increases in cytotoxicity beginning at 25uM following treatment of isolated T cell populations with idelalisib, duvelisib, or TGR-1202. At this dose, apoptosis was induced between 48 and 72h. Second, all inhibitors reduced cytokine production in CD3+ T cells upon stimulation. Particularly, IFN-γ, IL-10 and IL-17a reduction was less pronounced after TGR-1202 treatment, indicating relative conservation of T cell response. All inhibitors lowered mRNA expression of T-bet (Th1), GATA-3 (Th2) and FoxP3 (Treg), however FoxP3 levels were consistently higher in TGR-1202 treated T cells. Third, we detected normal CD4:CD8 ratio and unaffected proliferative capacity of CD4+ and CD8+ subsets after drug treatment. Finally, all inhibitors decreased total percent of Tregs following stimulation (CD4+ CD25HI FoxP3+) accompanied by decreased expression of co-inhibitory molecules CTLA-4 and PD-1 on the Tregs. Interestingly, TGR-1202 significantly preserved the percent of Tregs closer to normal as well as surface expression of CTLA-4 and PD-1 on Tregs, indicating greater retention of immune checkpoint blockade and suppressive phenotype.

CONCLUSIONS: We report herein that TGR-1202 affects human T cells differently than idelalisib and duvelisib. TGR-1202 sustains IL-10 production, FoxP3 mRNA expression, and maintains Treg percentage and expression of immune checkpoint molecules, suggesting relative preservation of numbers and function of Tregs. Data presented begin to provide novel insight into immune mediated cellular mechanisms responsible for lack of side effects in clinical trials of TGR-1202. In vivo models to further characterize effects on the T cell compartment are ongoing.

Citation Format: Kamira K. Maharaj, John Powers, Renee Fonseca, Hari Miskin, Dave Maryanski, Eva Sahakian, Javier Pinilla-Ibarz. Differential regulation of human T-cells by TGR-1202, a novel PI3Kδ inhibitor. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 545.