Differential Regulation of T Cells By PI3K Delta Inhibitors in a CLL Murine Model

Abstract

In the microenvironment of chronic lymphocytic leukemia (CLL), T cells are typically dysfunctional. Idelalisib, a PI3Kδ inhibitor, is approved for R/R CLL but trials in treatment-naïve patients were discontinued due to immune-mediated severe adverse events (SAE). Duvelisib is a PI3Kγ/δ inhibitor also in clinical development with a similarly high incidence of immune-mediated SAEs. By contrast, umbralisib (TGR-1202) is a next-generation PI3Kδ inhibitor associated with lower rates of SAEs in clinical trials, even with long-term followup, which has also demonstrated activity against CK1e. Previously, we demonstrated in normal human T cells that ex vivo treatment with umbralisib relatively preserved Treg number (CD4+ CD25hi CD127lo FoxP3+) and function (Treg co-culture supression assay) compared to treatment with idelalisib or duvelisib. FoxP3 mRNA levels and IL-10 secretion from T cells also remained closer to normal after umbralisib treatment compared to idelalisib or duvelisib.The purpose of the current study was to compare the effects of umbralisib, duvelisib, and idelalisib on T cells in a CLL mouse model and analyze immune-mediated adverse events following oral administration. We hypothesized that umbralisib may preserve the number and function of the regulatory T cell (Treg) population, translating to decreased immune-mediated side effects after treatment. Leukemic euTCL1 splenocytes were adoptively transferred into wildtype mice to induce CLL disease and treated via oral administration with vehicle, umbralisib, idelalisib or duvelisib. Tcon:Treg and Teff:Treg ratios in periphery and spleen measured by flow cytometry were found to be spared in the umbralisib-treated group and decreased on duvelisib and idealisib groups. Expression of functional Treg markers TGFB-1, CD39, CD103, PD-1 and CTLA-4 was also spared in the umbralisib group but affected in the other two. To assess immune-mediated toxicity, GI tract and liver tissues were collected and H&E stained. Pathology analysis was performed and immune-mediated toxicity was scored according to the following parameters: inflammatory cell infiltrate, kuppfer cell hyperplasia, microvesicular steatosis, cell degeneration (liver) and denuded mucosa, chronic inflammation, acute inflammation (GI tract). Overall toxicity grade was significantly lower in umbralisib-treated group compared to duvelisib-treated group in both liver (p=0.0009) and GI tract (p=0.0025). Toxicity grade in these tissues negatively correlated with total Treg count in spleen (R-squared~0.7). Immunohistochemistry staining of FoxP3+ Tregs in liver and GI tract was concordant with the assessment of Treg count in spleen by flow cytometry, as the number of FoxP3+ cells was closer to normal in umbralisib-treated mice compared to duvelisib-treated mice. Next, we investigated whether co-inhibition of CK1e by umbralisib may be involved in the differential regulation of T cells. Combination of a selective CK1e inhibitor, SR-4471, with duvelisib, prevented the reduction of total Treg number and functional markers in ex vivo culture of murine euTCL1 T cells, mimicking the effect of umbralisib. We have found that canonical Wnt signaling is inhibited dose-dependantly in euTCL1 T cells treated with umbralisib, demonstrated by lower levels of B-catenin and downstream TCF-1/7. These data determine Tregs to be a major player involved in immune-mediated toxicity characteristic of the PI3K inhibitor class of drugs. Umbralisib may differentially regulate CLL T cells through complimentary inhibition of both PI3Kδ and CK1e, potentially preserving Treg number and function to provide protection from immune-mediated SAEs. DisclosuresMiskin:TG Therapeutics, Inc.: Employment, Equity Ownership. Maryanski:TG Therapeutics, Inc.: Employment, Equity Ownership. Pinilla-Ibarz:ARIAD: Consultancy, Honoraria; BMS: Honoraria, Speakers Bureau; Pfizer: Honoraria, Speakers Bureau.