Abstract 1813: Selective ITK blockade induces antitumor responses and enhances efficacy to immune checkpoint inhibitors in preclinical models
Authors: Hsu Lih-Yun , Pawar Rahul D. , Li Dan , Ghosh Poorva , Nguyen Kevin , Williams Carlene , Song Yuqin , Ding Ning , Verner Erik , Miller Richard A. 
Published: April 2023

Interleukin 2 inducible T cell kinase (ITK) plays a role in both T cell receptor (TCR) signaling and T helper cell differentiation. ITK-/- mice exhibit defects in Th2 differentiation while retaining the ability to differentiate into Th1 cells that secrete IFNγ. We generated CPI-818, a covalent inhibitor of ITK (KD 2.5nM) with &gt; 100 fold selectivity over resting lymphocyte kinase (RLK) and other TEC family kinases. This drug is now being evaluated as a single agent in an ongoing Phase 1 clinical trial in refractory T cell lymphoma where objective tumor responses have been observed. In the studies reported here, we have investigated the immunomodulatory effects of specific ITK blockade of human T cells with CPI-818 in vitro and in vivo in murine tumor models.

Analysis of the cytokine profiles in human CD4 T cells differentiated under non-polarizing, Th1 or Th2 polarizing conditions showed that CPI-818 inhibited generation of Th2-associated cytokines whereas, production of Th1 cytokines such as IFNγ were largely unaffected. Suppression of IL-2-mediated proliferative response occurred only at high concentrations of CPI-818 (&gt;1uM). The effect of CPI-818 on anti-tumor immunity was evaluated in both murine syngeneic CT26 colon cancer and EL4 T cell lymphoma models. In vivo treatment of animals with established tumors showed single-agent anti-tumor activity in both models. Combining CPI-818 with suboptimal doses of anti-PD1 and anti-CTLA4 synergistically inhibited the growth of established CT26 tumors, leading to complete tumor elimination in 100% treated animals. Furthermore, triple combination therapy elicited durable anti-tumor immune memory after animals were rechallenged with a new engraftment of CT26 cells. Enhancement of anti-tumor activity required CD8+ T cells as in vivo antibody-mediated depletion of CD8, but not CD4, abolished the efficacy of CPI-818 monotherapy. Consistent with that, we found increased tumor-infiltrating CD8+ T cells and increased ratio of CD8: Treg in the responding tumors of CPI-818 treated animals. Levels of several exhaustion makers were down-regulated by treatment with CPI-818, suggesting that inhibition of ITK by CPI-818 produces favorable changes in the tumor microenvironment. Our findings provide insights into the effects of selective ITK blockade on tumor immunity and its potential role in immunotherapy.

Citation Format: Lih-Yun Hsu, Rahul D. Pawar, Dan Li, Poorva Ghosh, Kevin Nguyen, Carlene Williams, Yuqin Song, Ning Ding, Erik Verner, Richard A. Miller. Selective ITK blockade induces antitumor responses and enhances efficacy to immune checkpoint inhibitors in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1813.