Inhibition of Vascular Smooth Muscle Cell Proliferation and Neointimal Formation in Injured Arteries by a Novel, Oral Mitogen-Activated Protein Kinase/Extracellular Signal–Regulated Kinase Inhibitor

Abstract

Background— Mitogen-activated protein kinases (MAPKs) are rapidly induced after arterial injury in different animal models. However, their precise role in vascular smooth muscle cell (VSMC) proliferation and neointimal formation in vivo remains to be determined. Methods and Results— We investigated the properties of a novel, selective inhibitor of the upstream kinase, MAPK/extracellular signal–regulated kinase, that is orally active (PD0185625). In vitro, PD0185625 was shown to abrogate p44/p42 MAPK activation in VSMCs after serum stimulation. This was associated with a dose-dependent inhibition of VSMC proliferation. In vivo, PD0185625 was administered orally to rats (200 mg · kg⁻¹ · d⁻¹) beginning 2 days before balloon injury of the left carotid artery and for 2 weeks thereafter. Treatment with PD0185625 led to nearly complete inhibition of p44/p42 MAPK activation after balloon injury. This resulted in a significant decrease in VSMC proliferation (BrdU incorporation) at day 7 after injury. Moreover, neointimal formation was significantly reduced in PD0185625-treated animals at 14 and 28 days after arterial injury. We found that PD0185625 did not increase the rate of apoptotic cell death but prevented cell cycle progression and induced a G1 block. Conclusions— PD0185625 reduced neointimal formation after arterial injury. The mechanism involved inhibition of VSMC proliferation via a G1 block of the cell cycle. Orally active selective MAPK inhibitors could represent a novel therapeutic approach for vascular diseases.