Characterisation of Ki11502 as a potent inhibitor of PDGF β receptor-mediated proteoglycan synthesis in vascular smooth muscle cells

Platelet-derived growth factor (PDGF) receptor signalling is implicated in cardiovascular diseases such as atherosclerosis and restenosis. PDGF expression levels are elevated in atherosclerotic lesions and play a key role in migration and proliferation of vascular smooth muscle cells in the neointima. PDGF stimulates glycosaminoglycan elongation on vascular proteoglycans biglycan and decorin, a process implicated in the aetiology of atherosclerosis. We investigated the ability of the specific kinase inhibitor Ki11502 to inhibit PDGF β receptor phosphorylation and proteoglycan synthesis in human vascular smooth muscle cells. Ki11502 inhibited PDGF-mediated tyrosine phosphorylation of the PDGF β receptor autophosphorylation site and at least six other receptor-associated proteins. Ki11502 also caused a concentration-dependent inhibition of PDGF-stimulated [3H]-thymidine incorporation. Total proteoglycan synthesis was assessed as incorporation of [35S]-sulfate. PDGF-induced a two-fold increase in [35S]-sulfate incorporation into proteoglycans secreted over 24 h and was inhibited in a concentration-dependent manner by Ki11502. PDGF treatment resulted in a statistically significant (P < 0.01) increase in total proteoglycan core protein secretion. Treatment of cells with Ki11502 (300 nM) had no effect on basal core protein secretion and completely abolished the PDGF-stimulated component. Analysis of isolated cleaved glycosaminoglycan chains by size-exclusion chromatography demonstrated that PDGF stimulated the synthesis and secretion of proteoglycans with elongated glycosaminoglycan chains and this effect was inhibited by Ki11502. Inhibition was also seen in the length of xyloside-glycosaminoglycan chains. The results demonstrate that Ki11502 is a potent and selective inhibitor of PDGF β receptor phosphorylation, proliferation and proteoglycan synthesis in human vascular smooth muscle cells.