TY - JOUR T1 - A-770041, a Novel and Selective Small-Molecule Inhibitor of Lck, Prevents Heart Allograft Rejection JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 36 LP - 41 DO - 10.1124/jpet.105.089169 VL - 315 IS - 1 AU - Robert F. Stachlewitz AU - Michelle A. Hart AU - Brian Bettencourt AU - Tegest Kebede AU - Annette Schwartz AU - Sheldon E. Ratnofsky AU - David J. Calderwood AU - Wendy O. Waegell AU - Gavin C. Hirst Y1 - 2005/10/01 UR - http://jpet.aspetjournals.org/content/315/1/36.abstract N2 - Lck, one of eight members of the Src family of tyrosine kinases, is activated after T cell stimulation and is required for T-cell proliferation and interleukin (IL)-2 production. Inhibition of Lck has been a target to prevent lymphocyte activation and acute rejection. Here, we report the pharmacologic characterization of 1-methyl-1H-indole-2-carboxylic acid (4-{1-[4-(4-acetyl-piperazin-l-yl)-cyclohexyl]-4-amino-1H-pyrazolo[3,4-d]pyrimidin-3-yl}-2-methoxy-phenyl)-amide (A-770041), an orally bioavailable pyrazolo[3,4-d]pyrimidine with increased selectivity for Lck compared with previously reported compounds. A-770041 is a 147 nM inhibitor of Lck (1 mM ATP) and is 300-fold selective against Fyn, the other Src family kinase involved in T-cell signaling. Concanavalin A-stimulated IL-2 production in whole blood is inhibited by A-770041 with an EC50 of approximately 80 nM. A-770041 is orally bioavailable (F = 34.1 ± 7.2% at 10 mg/kg) and has a t1/2 of 4.1 ± 0.1 h. Concanavalin A-induced IL-2 production in vivo is inhibited by oral administration of A-770041 (in vivo EC50 = 78 ± 28 nM). Doses of A-770041 at or above 10 mg/kg/day prevent rejection of hearts transplanted heterotopically in rats from Brown Norway donors to Lewis recipients across a major histocompatibility barrier for least 65 days. Grafts from animals treated with 20 mg/kg/day A-770041 or 10 mg/day Cyclosporin A had minimal microvascular changes or multifocal mononuclear infiltrates. However, mineralization in myocytes from the grafts from A-770041-treated animals was less than animals treated with Cyclosporin A. Lck inhibition is an attractive target to prevent acute rejection. The American Society for Pharmacology and Experimental Therapeutics ER -