AT-7519 diHCl is a novel and potent multi-CDK (cyclin-dependent kinase) inhibitor for Cdk1/cyclin B, Cdk2/Cyclin A, Cdk3/Cyclin E, Cdk4/Cyclin D1, Cdk5/p35, and Cdk6/Cyclin D3 with IC50s of 210, 47, 100, 13, 170, and<10 nM for CDK1, CDK2, CDK4 to CDK6, and CDK9, respectively. AT7519 is an ATP competitive Cdk inhibitor but is inactive against all non-Cdk kinases with the exception of GSK3β. AT7519 shows potent antiproliferative activity in a variety of human tumor cell lines such as SW620. AT7519 induces activation of GSK-3β by down-regulating GSK-3β phosphorylation, which also contributes to AT7519 induced apoptosis independent of the inhibition of transcription.