Unique compound with anti-allergic action: inhibition of kinase activity of Lyn by KIRA6

Goshi Matsushima¹Yuri Matsui¹Hanano Okamoto¹Nagisa Umeda¹Mai Kakimoto¹Megumi Mino¹Tadashi Nakagawa²Kaori Ishii³Yoshimi Matsuo³Daiki Matsubara³Akio Tanaka³Michiko Yoshii¹Mitsuhiro Goda¹Yuhki Yanase^1*Toru Hosoi^2*Koichiro Ozawa^1,4

• ¹Department of Pharmacotherapy, Graduate School of Biomedical and Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, Japan
• ²Department of Clinical Pharmacology, Faculty of Pharmaceutical Sciences, Sanyo-Onoda City University, 1-1-1 Daigaku-dori, Sanyo Onoda City, Yamaguchi, Japan
• ³Department of Dermatology, Graduate School of Biomedical and Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, Japan
• ⁴Faculty of Pharmacy, Yasuda Women's University, 6-13-1 Yasuhigashi, Asakita-ku, Hiroshima, Japan

Mast cells and basophils play important roles in allergic disorders associated with specific antigens and IgE. Crosslinking of high-affinity IgE receptor (FcεRI) by specific antigens activates several tyrosine kinases, such as Lyn and spleen-associated tyrosine kinase (Syk), resulting in the release of calcium ions (Ca 2+ ) from the endoplasmic reticulum (ER) into the cytoplasm. As Ca 2+ release from ER is essential for the release of pro-inflammatory mediators, ER stress-related molecules, inositolrequiring enzyme 1α (IRE1α), may play roles in mast cell and basophil activation. However, the associations between ER stress-related molecules and mast cell and basophil activation remain unclear.In this study, we aimed to investigate the roles of ER stress-related molecules in mast cell and basophil activation. Activation of the IRE1α-spliced form of X-box-binding protein 1 (sXBP1) axis, an ER stress-related pathway, was observed during the antigen-induced activation of mast cells. Moreover, IRE1α inhibitor, KIRA6, suppressed antigen-induced release of pro-inflammatory mediators from RBL-2H3 cells, BMMCs, human basophils, and human mast cells with low doses (< 1 μM). However, to our surprise, IRE1α knockout did not inhibit antigen-induced release of pro-inflammatory mediators.Instead, KIRA6 blocked the antigen-induced activation of Syk by inhibiting kinase activity of Lyn.Additionally, KIRA6 exerted anti-allergic effects in vivo. Overall, our findings suggest that KIRA6 prevents allergic reactions by inhibiting kinase activity of Lyn via an IRE1α-independent pathway.