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.

Zhong Y, et al. Targeting interleukin-2-inducible T-cell kinase (ITK) and resting lymphocyte kinase (RLK) using a novel covalent inhibitor PRN694. J Biol Chem. 2015 Mar 6;290(10):5960-78.