Novel Small-Molecule Inhibitors of Protein Kinase C Epsilon Reduce Ethanol Consumption in Mice

BACKGROUND: Despite the high cost and widespread prevalence of alcohol use disorders, treatment options are limited, underscoring the need for new, effective medications. Previous results using protein kinase C epsilon (PKC epsilon) knockout mice, RNA interference against PKC epsilon, and peptide inhibitors of PKC epsilon predict that small-molecule inhibitors of PKCe should reduce alcohol consumption in humans. METHODS: We designed a new class of PKC epsilon inhibitors based on the Rho-associated protein kinase (ROCK) inhibitor Y-27632. In vitro kinase and binding assays were used to identify the most potent compounds. Their effects on ethanol-stimulated synaptic transmission; ethanol, sucrose, and quinine consumption; ethanol-induced loss of righting; and ethanol clearance were studied in mice. RESULTS: We identified two compounds that inhibited PKCe with Ki <20 nM, showed selectivity for PKC epsilon over other kinases, crossed the blood-brain barrier, achieved effective concentrations in mouse brain, prevented ethanol-stimulated gamma-aminobutyric acid release in the central amygdala, and reduced ethanol consumption when administered intraperitoneally at 40 mg/kg in wild-type but not in Prkce(-/-) mice. One compound also reduced sucrose and saccharin consumption, while the other was selective for ethanol. Both transiently impaired locomotion through an off-target effect that did not interfere with their ability to reduce ethanol intake. One compound prolonged recovery from ethanol-induced loss of righting but this was also due to an off-target effect since it was present in Prkce(-/-) mice. Neither altered ethanol clearance. CONCLUSIONS: These results identify lead compounds for development of PKCe inhibitors that reduce alcohol consumption.