Indirubin-5-sulfonate is a cyclin-dependent kinase (CDK) inhibitor, with IC50 values of 55 nM, 35 nM, 150 nM, 300 nM and 65 nM for CDK1/cyclin B, CDK2/cyclin A, CDK2/cyclin E, CDK4/cyclin D1, and CDK5/p35, respectively[1]. Indirubin-5-sulfonate also shows inhibitory activity against GSK-3β[2]. Cdk1/cyclin B|55 nM (IC50)|cdk2/cyclin A|35 nM (IC50)|CDK2/cyclinE|150 nM (IC50)|Cdk4/cyclin D1|300 nM (IC50)|CDK5/p35|65 nM (IC50)|GSK-3β
[1]. Hoessel R, et al. Indirubin, the active constituent of a Chinese antileukaemia medicine, inhibits cyclin-dependent kinases. Nat Cell Biol. 1999 May;1(1):60-7. [2]. Leclerc S, et al. Indirubins inhibit glycogen synthase kinase-3 beta and CDK5/p25, two protein kinases involved in abnormal tau phosphorylation in Alzheimer's disease. A property common to most cyclin-dependent kinase inhibitors• J Biol Chem. 2001 Jan 5;276(1):251-60.