Interleukin-2-inducible T-cell kinase (ITK) and resting lymphocyte kinase (RLK or TXK) are essential mediators of intracellular signaling in both normal and neoplastic T-cells and natural killer (NK) cells. Thus, ITK and RLK inhibitors have therapeutic potential in a number of human autoimmune, inflammatory, and malignant diseases. In this study, Yiming Zhong, et al described an ITK/RLK inhibitor PRN694. Especially, PRN694 exhibits extended target residence time on ITK and RLK and is highly selective for a subset of the TEC kinase family. PRN694 covalently binds to cysteine residues 442 of ITK and 350 of RLK and blocks kinase activity.
PRN694 prevents T-cell receptor- and Fc receptor-induced cellular and molecular activation. Besides, PRN694 inhibits T-cell receptor-induced T-cell proliferation, and blocks proinflammatory cytokine release as well as activation of Th17 cells. Finally, in vivo experiments demonstrate the pharmacokinetics and pharmacodynamics of PRN694 and show that it attenuates a delayed type hypersensitivity (DTH) reaction in a well established murine model system. PRN694 blocks cellular and molecular activation of T-lymphocytes and the Jurkat T-ALL cell line. Particularly, PRN694 blocks Fc receptor-induced cellular and molecular activation in primary natural killer (NK) cells. Moreover, PRN694 inhibits T-cell Receptor (TCR)-induced primary T-cell proliferation and pro-inflammatory cytokine production without direct cytotoxicity. PRN694 attenuates TCR-induced signaling in primary human T-prolymphocytic leukemia (T-PLL). In particular, PRN694 forms an irreversible covalent bond with C442 in ITK or C350 in RLK. PRN694 selectively inhibits ITK and RLK in T cells.
All in all, PRN694 is a highly selective and potent covalent inhibitor of ITK and RLK, and its extended target residence time enables durable attenuation of effector cells in vitro and in vivo.