Indirubin-5-sulfonic acid sodium salt is a cyclin-dependent kinase (CDK) inhibitor, in particular CDK1/cyclin B (IC50 = 55 nM), CDK2/cyclin A (IC50 = 35 nM), CDK2/cyclin E (IC50 = 150 nM), CDK4/cyclin D1(IC50 = 300 nM), and CDK5/p35 (IC50 = 65 nM), with additional inhibitory activity against GSK-3β.
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