Abstract 4439: BR101801 triggers anti-tumor immunity and enhances efficacy of immune checkpoint antibodies in syngeneic model
Authors: Wang Seungho , Son Mi kwon , Lee Bo Ram , Jeon Byeongwook , Kim Soo Jung , Yang Eunhui , Park Min , Lee Joo Han , Myung Jayhyuk 
Published: September 2020

Introduction: BR101801 received U.S. FDA approval of Phase Ia/Ib clinical trial as an anti-cancer drug candidate. PI3K γ / δ and DNA-PK inhibitory potency of BR101801 exerts anti-cancer efficacy as a target anticancer agent in hematologic malignancies. Recent studies have reported anti-cancer immunity by use of PI3K-δ inhibitor (Idelalisib), PI3K-γ inhibitor (IPI-549) and DNA-PK inhibitor (NU7441). Considering triple inhibitory activity of the BR101801. First, we investigated the anti-cancer efficacy of monotherapy by BR101801 in syngeneic model. Second, synergistic efficacy was confirmed through the combination of BR101801 with anti-PD1 or anti-PDL1, which are known as anti-tumor immunotherapeutics. Finally, immune cell response by BR101801 in human PBMC was tested. Overall, This study aims to demonstrate efficacy of the BR101801 as a potent immunocancer drug.

Methods: The enzymatic potency of the PI3K isotype and DNA-PK was analyzed by Eurofin. Proliferation of 4T1(breast cancer) and CT26(colon cancer) cells following a 4 h treatment with the indicated BR101801, WST-8 staining after 72 h culture. Mice bearing syngeneic 4T1 or CT-26 cell lines were treated with vehicle, BR101801, anti-PD1, anti-PD1 + BR101801, anti-PDL1, anti-PDL1 + BR101801. Tumor volumes were measured by caliper. Tregs and CD8+ T cells were quantified by flow cytometry from mice bearing spleen. In addition, CD3 + cells were isolated from human PBMCs and stimulated with CD3/CD28 and analyzed for immunofluorescence by FACS for expression of PD-1, TIM3, LAG3 and TIGIT in Tregs and CD8.

Results: In vitro selectivity and target potency of BR101801 on different PI3K subtypes including DNA-PK were studied in cell-free system. The biochemical IC50 values of BR101801 for PI3K-α, -β, -γ, -δ and DNA-PK were 106 nM, 171 nM, 15 nM, 2 nM and 6 nM. 50% growth inhibition in 4T1 and CT26 cell lines was measured above 10 uM. BR101801 showed tumor inhibitor efficacy in 4T1 and CT26 syngeneic models. In 4T1 or CT-26 bearing mouse spleens, Tregs decreased and CD8 + T cells increased. Strong anti-tumor efficacy was observed with about 70% reduction in tumor growth when using BR101801 with anti-PD1 or anti-PDL1 in 4T1 and CT26 syngeneic models. Finally, Tregs decreased and anticancer effects were increased by decreasing the expression of PD1, LAG3, TIM3 and TIGIT of CD8+ T cells.

Conclusions: The immunosuppressive effect of BR101801 changing the tumor microenvironment was verified without cancer cells. It is demonstrated that anticancer immunity by decreasing Tregs and increasing CD8. Anti-tumor immunity was enhanced by decreasing the expression of PD1, TIM3, LAG3 and TIGIT in CD8 + cells. In this study, In addition to monotherapy of BR101801, It's synergistic effects with PD-1 or PDL1 have been proposed. This data supports the evidence that it is applicable not only to blood cancer but also to various cancer patients.

Citation Format: Seungho Wang, Mi kwon Son, Bo Ram Lee, Byeongwook Jeon, Soo Jung Kim, Eunhui Yang, Min Park, Joo Han Lee, Jayhyuk Myung. BR101801 triggers anti-tumor immunity and enhances efficacy of immune checkpoint antibodies in syngeneic model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4439.