PDGF-RECEPTOR PROTEIN-TYROSINE KINASE-ACTIVITY IN CAROTID-ARTERY IS ENHANCED BY INJURY AND INHIBITED INVIVO BY TYRPHOSTIN RG 13291

Tyrphostins (TKI) are synthetic low molecular weight compounds which inhibit in vitro platelet-derived growth factor (PDGF) mitogenesis by blocking PDGF receptor protein tyrosine kinase activity (PDGF R-PTK). To determine whether TKIs act by this mechanism in vivo, a rat model of vascular injury was used. Rat carotid arteries were injured by implantation of a tygon cuff machined so that 1 mm of each end touched the artery. PDGF R-PTK was measured ex vivo by incubation of the excised denuded artery with porcine PDGF followed by homogenization and Western blotting with antiphosphotyrosine/antiPDGF-R antisera. In arteries from control rats, PDGF produced a maximal 2-fold increase in R-PTK at 120 ng/ml. In cuffed arteries, PDGF stimulated R-PTK in a dose-related manner after one day of injury; R-PTK remained elevated for 4-5 days post injury (6-fold increase in R-PTK activity at 180 ng/ml). A similar response to PDGF was also evident in contralateral uncuffed arteries. Intraperitoneal injection (+ 2 h) of TKI RG 13291 inhibited PDGF R-PTK of cuffed artery with an IC50 value of approximately 2 mg/kg and of the uncuffed artery with IC50 value of approximately 30 mg/kg. It is concluded that TKIs are potential in vivo inhibitors of injury-induced PDGF R-PTK activity and may be useful as inhibitors of PDGF-dependent effects such as proliferation.