The increased potential for growth of vascular smooth muscle cells (VSMCs) is a key abnormality in the development of atherosclerosis and postangioplasty restenosis. Platelet-derived growth factor (PDGF)-BB is a potent mitogen for VSMCs that plays an important role in the intimal accumulation of VSMCs. This study examined the effect of JM91, a newly synthesized indoledione derivative, on the proliferation of PDGF-BB-stimulated rat aortic VSMCs. The antiproliferative effect of JM91 on rat aortic VSMCs was examined by cell counting and [(3)H]thymidine incorporation assay. The pre-incubation of JM91 (0.5-3.0 microM) significantly inhibited the proliferation and DNA synthesis of 25 ng/mL PDGF-BB-stimulated rat aortic VSMCs in a concentration-dependent manner. JM91 inhibited the PDGF-BB-stimulated phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and Akt kinase, while had no effect on PLCgamma1 and PDGF-Rbeta activation. In addition, treatment with JM91 (0.5-3.0 microM) induced cell-cycle arrest in the G(1) phase, which was associated with the down-regulation of cyclins and CDKs. These findings suggest that the inhibitory effects of JM91 against proliferation, DNA synthesis and cell cycle progression of PDGF-BB-stimulated rat aortic VSMCs are mediated by the suppression of the ERK1/2 and PI3K/Akt signaling pathways. Furthermore, JM91 may be a potential antiproliferative agent for the treatment of atherosclerosis and angioplasty restenosis.