GSK2646264 (Compound 44) is a potent and selective spleen tyrosine kinase (SYK) inhibitor with a pIC 50 of 7.1. GSK2646264 also inhibits other kinases with pIC 50 values of 5.4, 5.4, 5.3, 5, 4.5, In Vitro GSK2646264 (0.01-10 μM; 1 h) significantly inhibits anti‐IgE (but not C5a)‐induced histamine release from skin mast cells in a concentration‐dependent manner. The IC 50 is 0.7 μM and the IC 90 is 6.8 μM. GSK2646264 cream (0.5, 1, and 3% [wt/wt]; 1 cm 2 ; 4 and 24 h) inhibits anti‐IgE‐induced histamine release from mast cells in ex vivo human skin. MCE has not independently confirmed the accuracy of these methods. They are for reference only. Form:Solid IC50& Target:SYK 7.1 (pIC 50 ) LCK 5.4 (pIC 50 ) LRRK2 5.4 (pIC 50 ) GSK3β 5.3 (pIC 50 ) JAK2 5 (pIC 50 ) VEGFR2 4.5 (pIC 50 ) Aurora B