The indazole derivative YD-3 inhibits thrombin-induced vascular smooth muscle cell proliferation and attenuates intimal thickening after balloon injury.

Proliferation of vascular smooth muscle cells (VSMCs) is postulated to be one of the key events in the pathogenesis of atherosclerosis and restenosis. We investigated whether YD-3, a lowmolecular weight, non-peptide compound, could modulate proliferation of VSMCs in vitro and restenosis after balloon angioplasty in vivo. We examined the effect of YD-3 on thrombininduced VSMC proliferation by [(3)H]thymidine incorporation assay. The data demonstrated that YD-3 inhibited VSMC proliferation in a concentration-dependent manner. To define the mechanisms of YD-3 action, we found that YD-3 showed a profound inhibition on thrombin-induced Ras and ERK1/2 activities by using Western blotting analysis. Furthermore, oral administration of YD-3 exhibited a marked reduction in neointimal thickness using the carotid injury model in rats. Using immunochemical detection, our experiments also revealed that YD-3 significantly suppressed expression of the PAR-1 receptor, and markedly inhibited PAR-1-activating peptide (SFLLRN)-induced VSMC proliferation in a concentration-dependent manner. These results suggest that YD-3 inhibits thrombin-induced VSMC growth via the Ras- and ERK1/2-mediated signaling pathway. Moreover, YD-3 also shows a developmental potential in the treatment of atherosclerosis and restenosis after vascular injury.