A dual inhibitor of platelet-derived growth factor beta-receptor and Src kinase activity potently interferes with mitogenic and mitogenic responses to PDGF in vascular smooth muscle cells - A novel candidate for prevention of vascular remodeling

PP1 has previously been described as an inhibitor of the Si-c-family kinase s p56(Lck) and FynT We have therefore decided to use PPI to determine the f unctional role of Src in platelet-derived growth factor (PDGF)-induced prol iferation and migration of human coronary artery smooth muscle cells (HCASM Cs). A synthetic protocol for PP1/AGL1872 has been developed, and the inhib itory activity of PP1/AGL1872 against Src was examined. PP1/AGL1872 potentl y inhibited recombinant p60(c-src) in vitro and Src-dependent tyrosine phos phorylation in p60(c-srcF572)-transformed NIH3T3 cells. PP1/AGL1872 also po tently inhibited PDGF-stimulated migration of HCASMCs, as determined in the modified Boyden chamber, as well as PDGF-stimulated proliferation of HCASM Cs. Surprisingly, in addition to inhibition of Src kinase, PP1/AGL1872 was found: to inhibit PDGF receptor kinase in cell-free assays and in various t ypes of intact cells, including HCASMCs PP1/AGL1872 did not inhibit phospho rylation:pf the vascular endothelial growth factor receptor KDR (VEGF recep tor-2 kinase-insert domain containing receptor) in cell-free assays as well as in intact human coronary artery endothelial cells. in line with the ins ensitivity of KDR PP1/AGL1872 had only a weak effect on vascular endothelia l growth factor-stimulated migration of human: coronary artery endothelial cells. On treatment of cells expressing different receptor tyrosine kinases , the activities of the epidermal growth factor receptor, fibroblast growth factor receptor-1, and insulin-like growth factor-1 receptor were resistan t to PP1/AGL1872, whereas PDGF alpha-receptor was susceptible, albeit to a lesser extent than PDGF beta-receptor. These-data suggest that the previous ly described tyrosine kinase inhibitor PP1/AGL1872 is not selective for the Src family of tyrosine kinases. It is also a potent inhibitor of the PDGF beta-receptor kinase but is not a ubiquitous tyrosine kinase inhibitor: PP1 /AGL1872 inhibits migration and proliferation of HCASMCs probably by interf erence with 2 distinct tyrosine phosphorylation events, creating a novel an d potent inhibitory principle with possible relevance for the treatment of pathological HCASMC activity, such as vascular remodeling and restenosis.