Platelet-derived growth factor receptor tyrosine kinase inhibitor AG1295 attenuates rat hepatic stellate cell growth

Enhanced activity of receptor tyrosine kinases such as the platelet-derived growth factor-receptor beta (PDGF-R beta) has been implicated as a contrib uting factor in the development of hepatic fibrosis. In this study we have used tyrosine kinase inhibitors of the tyrphostin class (AG1295) to specifi cally block autophosphorylation of PDGF-R beta and proliferation of rat hep atic stellate cells. We also examined the effect of AG1295 on the PDGF-BB-i nduced activation of the 44 kd and 42 kd mitogen-activated protein (MAP) ki nase isoforms (p44(mapk)/p42(mapk)). Rat hepatic stellate cells were treate d with AG1295 (10 mu mol/L) for 24 hours and stimulated with PDGF-BB for 5 minutes. AG1295 specifically inhibited autophosphorylation of PDGF-R beta a nd caused a 20% decrease in PDGF-BB-stimulated bromodeoxyuridine incorporat ion by rat hepatic stellate cells. Treatment of rat hepatic stellate cells with AG1295 resulted in an inhibition of the PDGF-BB-induced activation of MAP kinase isoforms, Quantification of the immunoprecipitated tyrosine-phos phorylated phosphatidylinositol 3-kinase, phospholipase C-gamma, and p21(ra s) guanosine triphosphatase-activating protein by Western blotting revealed that AG1295 treatment effectively inhibits tyrosine phosphorylation of the se kinases in hepatic stellate cells. Our findings demonstrate that AG1295 is a selective inhibitor of the tyrosine phosphorylation of PDGF-R beta and its downstream signaling pathway, and this compound could offer a strategy for the treatment of fibrotic liver diseases.