A SELECTIVE AND COVALENT INHIBITOR OF ITK BLOCKS TCR SIGNALING, INHIBITS PROLIFERATION OF HUMAN SÉZARY CELLS IN VITRO, AND INDUCES TUMOR REGRESSION IN DOGS WITH T‐CELL LYMPHOMA (2019)

Introduction: ITK is a tyrosine kinase involved in T-cell receptor (TCR) signaling and differentiation of naïve T cells. ITK is closely related to RLK, a kinase of redundant function that is expressed in cytotoxic T cells and Th1 but not Th2 cells. Studies in knockout mice indicate that selective inhibition of ITK will inhibit Th2 differentiation and allow normal T cell immunity. ITK is widely expressed in T cell malignancies and signaling is associated with poor survival in peripheral T cell lymphoma (PTCL). Copy number gain of the ITK gene is often seen in PTCL and ITK is frequently overexpressed in cutaneous T-cell lymphoma (CTCL). Therefore, selective inhibition of ITK may be a new treatment strategy. Here we describe CPI-818, a compound designed to bind covalently and selectively to the CYS-442 residue of ITK. Methods: Human PBMC, T cell lines and Sézary cells were stimulated in vitro with anti CD3/CD28 with or without CPI-818. TCR signaling and proliferation were evaluated by flow cytometry and western blots. Mice were treated with CPI-818 and effects on immune cell subsets, humoral and cellular immune response were evaluated. Th skewing in mice was determined using an ovalbumin vaccine adoptive transfer model. Companion dogs with TCL were treated with CPI-818 at 20mg P.O. BID and evaluated for safety and tumor response. Results: CPI-818 inhibits kinase activity with IC50 values of 2.3nM, 430nM and 850nM for ITK, RLK and BTK, respectively. In a wider survey of 468 human kinases, CPI-818 (1μM) was highly selective for ITK. CPI-818 inhibited anti-CD3/28 induced phosphorylation of ERK and PLCγ1 in PBMC and inhibited IL-2 secretion in stimulated Jurkat T cells (75 nM). in vitro proliferation of human Sézary cells was inhibited with 200nM of CPI-818, a concentration that did not affect the proliferation of autologous normal T cells. Anti CD3/28-induced Th2 cytokine production in Sézary cells was also inhibited by CPI-818. in vivo studies showed no changes in blood counts or T, B, NK cell subsets in lymphoid organs of mice given CPI-818 for 28 days. Neither primary nor secondary antibody responses nor CD4 T cell responses to KLH antigen were inhibited. Spleen cells from treated mice demonstrated an increase in the ratio of IFNγ/IL-4 cells indicative of Th1 skewing. Three dogs with T-cell lymphoma; 1 PTCL and 2 CTCL were treated with CPI-818 for 2-20 weeks. Treatment was well tolerated with no dose limiting toxicities and no changes in lymphocyte counts. One complete (CTCL, 5 months duration) and two partial responses were observed. Conclusions: CPI-818 blocks TCR signaling and T cell activation and also affects T cell differentiation with a biasing to Th1 cells. There are preferential anti-proliferative effects in Sézary cells compared to autologous normal T cells. The demonstration of safety and clinical activity in dogs with T-cell lymphoma support recently initiated clinical trials in patients with TCL. Keywords: T-cell lymphoma (TCL); T-cell receptor (TCR). Disclosures: Buggy, J: Employment Leadership Position: Corvus Pharmaceuticals; Stock Ownership: Corvus Pharmaceuticals. Ng, P: Employment Leadership Position: Corvus Pharmaceuticals; Stock Ownership: Corvus Pharmaceuticals. Janc, J: Employment Leadership Position: Corvus Pharmaceuticals; Stock Ownership: Corvus Pharmaceuticals. Hotson, A: Employment Leadership Position: Corvus Pharmaceuticals; Stock Ownership: Corvus Pharmaceuticals. Hill, C: Employment Leadership Position: Corvus Pharmaceuticals; Stock Ownership: Corvus Pharmaceuticals. Thamm, D: Consultant Advisory Role: Corvus Pharmaceuticals. Kim, Y: Consultant Advisory Role: Corvus Pharmaceuticals. Khodadoust, M: Consultant Advisory Role: Corvus Pharmaceuticals. Mobasher, M: Employment Leadership Position: Corvus Pharmaceuticals; Stock Ownership: Corvus Pharmaceuticals. Miller, R: Employment Leadership Position: Corvus Pharmaceuticals; Stock Ownership: Corvus Pharmaceuticals.