A potent, specific, orally active inhibitor of JAK3 with IC50 of 1 nM in cell-free assays; displays 20- to 100-fold less potency for JAK2 and JAK1 (IC50=20 nM and 112 nM, respectively), and shows no potent activity against 30 other kinases at >3 uM (CaMK1, ROCK2, Lck, MST2, etc.); effectively inhibits a murine mixed lymphocyte reaction (MLR) with IC50 of 91 nM, significantly prolonges survival in a murine model of heart transplantation and in cynomolgus monkeys receiving kidney transplants.
