Inhibition of neuronal apoptosis by the cyclin-dependent kinase inhibitor GW8510: Identification of 3′ substituted indolones as a scaffold for the development of neuroprotective drugs

Increasing evidence suggests that neuronal apoptosis is triggered by the inappropriate activation of cyclin-dependent kinases leading to an abortive re-entry of neurons into the cell cycle. Pharmacological inhibitors of cell-cycle progression may therefore have value in the treatment of neurodegenerative diseases in humans. GW8510 is a 3′ substituted indolone that was developed recently as an inhibitor of cyclin-dependent kinase 2 (CDK2). We found that GW8510 inhibits the death of cerebellar granule neurons caused by switching them from high potassium (HK) medium to low potassium (LK) medium. Although GW8510 inhibits CDK2 and other CDKs when tested in in vitro biochemical assays, when used on cultured neurons it only inhibits CDK5, a cytoplasmic CDK that is not associated with cell-cycle progression. Treatment of cultured HEK293T cells with GW8510 does not inhibit cell-cycle progression, consistent with its inability to inhibit mitotic CDKs in intact cells. Neuroprotection by GW8510 is independent of Akt and MEK-ERK signaling. Furthermore, GW8510 does not block the LK-induced activation of Gsk3β and, while inhibiting c-jun phosphorylation, does not inhibit the increase in c-jun expression observed in apoptotic neurons. We also examined the effectiveness of other 3′ substituted indolone compounds to protect against neuronal apoptosis. We found that like GW8510, the VEGF Receptor 2 Kinase Inhibitors [3-(1H-pyrrol-2- ylmethylene)-1,3-dihydroindol-2-one], {(Z)-3-[2,4-Dimethyl-3-(ethoxycarbonyl) pyrrol-5-yl)methylidenyl]indol-2-one} and [(Z)-5-Bromo-3-(4,5,6,6-tetrahydro-1H- indol-2-ylmethylene)-1,3-dihydroindol-2-one], the Src family kinase inhibitor SU6656 and a commercially available inactive structural analog of an RNA-dependent protein kinase inhibitor 5-Chloro-3-(3,5-dichloro-4- hydroxybenzylidene)-1,3-dihydro-indol-2-one, are all neuroprotective when tested on LK-treated neurons. Along with our recent identification of the c-Raf inhibitor GW5074 (also a 3′ substituted indolone) as a neuroprotective compound, ourfindings identify the 3′ substituted indolone as a core structure for the designing of neuroprotective drugs that may be used to treat neurodegenerative diseases in humans.