Abstract 1313: CPI-818: A selective inhibitor of interleukin-2-inducible T-cell kinase (ITK) that inhibits T-cell receptor signaling, promotes Th1 skewing, and achieves objective tumor responses when administered to dogs with T cell lymphomas

Abstract

Background: ITK is a non-receptor tyrosine kinase that modifies T cell receptor (TCR) signaling. Mice deficient in ITK, but not resting lymphocyte kinase (RLK), exhibit defects in Th2 differentiation while retaining the ability to differentiate into Th1 cells and secrete IFNγ. Combined disruption of ITK and RLK in mice leads to more severe T cell functional defects compared to disrupting ITK alone, and paradoxically allows for normal Th2 responses. Thus, selective pharmacologic inhibition of ITK versus RLK is necessary to inhibit Th2 responses without affecting Th1-dependent immunity. ITK is widely expressed in T cell malignancies, and activation of ITK upregulates GATA-3, a transcription factor that drives Th2 differentiation and is associated with poor survival. Here we report the discovery and characterization of CPI-818, an irreversible inhibitor of ITK. CPI-818 is highly selective for ITK over RLK allowing for an assessment of pure ITK inhibition on normal and malignant T cells. Results: CPI-818 irreversibly inhibited ITK (IC502.3 nM) with >100-fold selectivity over RLK (430 nM) and BTK (850 nM). The mechanism of ITK inhibition involves covalent binding to CYS-442 confirmed by mass spectrometry. Irreversible inhibition of ITK in vitroand in vivowas demonstrated using an active site competitive probe. CPI-818 inhibited anti-CD3/28 induced phosphorylation of ERK (T202/Y204) and PLCγ (Y783) in PMBCs, and inhibited IL2 secretion in Jurkat T cells (IC5075 nM). CPI-818 demonstrated dose dependently inhibition of TCR-induced proliferation of malignant T cells from Sezary Syndrome patients. In mice orally treatedwith CPI-818 an increase in the ratio of IFNγ/IL-4 (p Citation Format: James W. Janc, Craig M. Hill, Patrick P. Ng, Andrew N. Hoston, Antonett Madriaga, Trang P. Dao-Pick, Kitman S. Yeung, Ryan Hudson, Anne-Marie Beausoleil, Erin Bradley, Erik Verner, Douglas H. Thamm, Richard A. Miller, Joseph J. Buggy. CPI-818: A selective inhibitor of interleukin-2-inducible T-cell kinase (ITK) that inhibits T-cell receptor signaling, promotes Th1 skewing, and achieves objective tumor responses when administered to dogs with T cell lymphomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1313.