CHIR-99021 （CT99021） HCl is a glycogen synthase kinase 3β （GSK3β） inhibitor that has antiproliferative activity in vitro and in vivo. [1] CHIR-99021 inhibits GSK-3 with IC50 at 7 nM. In a series of carcinoma cell lines, the IC50 of CHIR99021 for proliferation is about 10μM. [1] CHIR-99201 does not exhibit cross-reactivity against cyclin-dependent kinases （CDKs） with 350-fold selectivity toward GSK-3β compared to CDKs . [1]