Corynoxeine is able to inhibit the PDGF-BB-stimulated proliferation of VSMCs through downregulation of PDGF-BB-induced ERK1/2 activation. Pre-incubation of VSMCs with Corynoxeine significantly inhibits PDGF-BB-induced extracellular signal-regulated kinase 1/2 (ERK1/2) activation, whereas Corynoxeine has no effects on mitogen-activated protein kinase (MAPK/ERK)-activating kinase 1 and 2 (MEK1/2), Akt, or phospholipase C (PLC) γ 1 activation or on PDGF receptor beta (PDGF-Rβ) phosphorylation. Corynoxeine inhibits PDGF-BB-induced ERK1/2 activation, in the same concentration range that inhibits VSMC proliferation and DNA synthesis. Corynoxeine inhibits VSMC numbers in response to PDGF-BB with 50% inhibitory concentrations (IC ₅₀ ) of 13.7 μM. Corynoxeine inhibits DNA synthesis in response to PDGF-BB (24 h) with IC ₅₀ of 9.2 μM. Pre-treatment of VSMCs with Corynoxeine (5-50 μM) for 24 h results in significant decreases in cell number without any cytotoxicity; the inhibition percentages are 25.0±12.5, 63.0±27.5 and 88.0±12.5% at 5, 20 and 50 μM, respectively. Corynoxeine also significantly inhibits the 50 ng/mL PDGF-BB-induced DNA synthesis of VSMCs in a concentration-dependent manner without any cytotoxicity; the inhibitions are 32.8±11.0, 51.8±8.0 and 76.9±7.4% at concentrations of 5, 20 and 50 μM, respectively.