Indirubin (Couroupitine B) is a potent inhibitor of cyclin-dependent kinases and GSK-3β, with IC50 values of approximately 5 µM and 0.6 µM, respectively.

GSK-3β:0.6 μM, Cyclin-dependent kinase:5 μM

Indirubin is the active ingredient of Danggui Longhui Wan, a mixture of plants that is used in traditional Chinese medicine to treat chronic diseases. Indirubin inhibits CDKs activity with IC50 of 2.2 - 10 μM resulting in cell cycle arrest in the G2/M phase. [1] Indirubin also inhibits GSK-3β with an IC50 of 0.6 μM, attenuating CDK5- and GSK-3β-mediated tau phosphorylation, a process over-active in Alzheimer disease states. [2] It also suppresses tumor necrosis factor (TNF)-induced NF-κB activation in a dose- and time-dependent manner. Indirubin also suppresses the NF-κB activation induced by various inflammatory agents and carcinogens. Indirubin blocks the phosphorylation and degradation of IκBα through the inhibition of activation of IκBα kinase and phosphorylation and nuclear translocation of p65. [3]