Description_x000D_ Biochem/physiol Actions_x000D_ A-770041 is an orally available (rat F = 34.1%; 10 mg/kg p.o.), ATP-competitive, potent and selctive Lck inhibtor (IC50 = 147 nM/Lck, 1.18 μM/Lyn, 1.22 μM/Hck, 9.05 μM/Src, 14.1 μM/Fgr, 44.1 μM/Fyn; >25 μM/IKK1, IKK2, IRAK4, p38, JAK3, ZAP70, ITK, PKC, MK2, PKA, TYK2, COT,Syk; >50 μM/Tie-2 & Kdr; 1 mM ATP). A-770041 inhibits CD3 mAb-induced IL-2 production in human whole blood in vitro (IC 50 = 80 nM) and in mice in vivo (IC50 = 78 nM plasma conc.), and significantly lengthens graft survival time in a rat heterotopic heart transplant model (2.5 & 5 mg/kg bid p.o.).