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 cycline-dependent kinase inhibitors?

The bis-indole indirubin is an active ingredient of Danggui Longhui Wan, a traditional Chinese medicine recipe used in the treatment of chronic diseas es such as leukemias. The antitumoral properties of indirubin appear to cor relate with their antimitotic effects. Indirubins were recently described a s potent (IC50: 50-100 nm) inhibitors of cyclin-dependent kinases (CDKs), W e report here that indirubins are also powerful inhibitors (IC50: 5-50 nM) of an evolutionarily related kinase, glycogen synthase kinase-3 beta (GSK-3 beta), Testing of a series of indoles and bis-indoles against GSK-3 beta, CDK1/cyclin B, and CDK5/p25 shows that only indirubins inhibit these kinase s, The structure-activity relationship study also suggests that indirubins bind to GSK-3 beta 's ATP binding pocket in a way similar to their binding to CDKs, the details of which were recently revealed by crystallographic an alysis. GSK-3 beta, along with CDK5, is responsible for most of the abnorma l hyperphosphorylation of the microtubule-binding protein tau observed in A lzheimer's disease. Indirubin-3'-monoxime inhibits tau phosphorylation in v itro and in vivo at Alzheimer's disease-specific sites. Indirubins may thus have important implications in the study and treatment of neurodegenerativ e disorders. Indirubin-3'-monoxime also inhibits the in vivo phosphorylatio n of DARPP-32 by CDK5 on Thr-75, thereby mimicking one of the effects of do pamine in the striatum, Finally, we show that many, but not all, reported C DK inhibitors are powerful inhibitors of GSK-3 beta, To which extent these GSK-3 beta effects of: CDK inhibitors actually contribute to their antimito tic and antitumoral properties remains to be determined. Indirubins constit ute the first family of low nanomolar inhibitors of GSK-3 beta to be descri bed.