CHIR99021 is an aminopyrimidine derivative that is an extremely potent glycogen synthase kinase (GSK) 3 inhibitor, inhibiting both GSK3β (IC50 = 6.7 nM) and GSK3α (IC50 = 10 nM)
GSK3 is a serine/threonine kinase that is a key inhibitor of the WNT pathway; therefore CHIR99021 functions as a WNT activator
It shows little activity against a large panel of kinases including CDK2 and other serine/threonine kinases such as MAPK and PKB
