Inhibition of the human P2X7 receptor by a novel protein tyrosine kinase antagonist

A panel of 18 protein tyrosine kinase antagonists were tested for their inhibitory effect on human P2X7 receptor-mediated 86Rb+ (K+) efflux. The most potent compound (compound P), a phthalazinamine derivative and an inhibitor of vascular endothelial growth factor receptor kinase, blocked ATP-induced 86Rb+-efflux in human B-lymphocytes and erythrocytes by 76% and 66%, respectively. This inhibition was dose-dependent in both cell types with an IC50 of ∼5 μM. Kinetic analysis showed compound P was a non-competitive inhibitor of P2X7. This compound also inhibited ATP-induced ethidium+ influx into B-lymphocytes and P2X7-transfected-HEK-293 cells, as well as ATP-induced 86Rb+-efflux from canine erythrocytes. Externally, but not internally, applied compound P impaired ATP-induced inward currents in P2X7-transfected-HEK-293 cells. This study demonstrates that a novel protein tyrosine kinase antagonist directly impairs native and recombinant human P2X7 receptors. The data suggests that antagonists which target ATP-binding sites of kinases may potentially block the P2X7 receptor.