Indirubin-3’-oxime is a potent inhibitor of glycogen synthase kinase 3β (GSK3β; IC50 = 22 nM). As GSK3β phosphorylates tau protein, indirubin-3’-oxime prevents tau phosphorylation both in vitro and in vivo at Alzheimer’s disease-relevant sites. It also inhibits cyclin-dependent kinases (CDKs) at higher concentrations, including Cdk1/cyclin B (IC50 = 180 nM), Cdk2/cyclin A (IC50 ~500 nM), Cdk2/cyclin E (IC50 = 250nM), Cdk4/cyclin D1 (IC50 = 3.3 μM) and Cdk5/p35 (IC50 = 100 nM). Indirubin-3’-oxime reversibly inhibits the proliferation of many cells types, arresting cycling in the G2/M phase.
