1 In the present study we examined the effects of PCA-4230, A novel antithrombotic agent, on the growth of cultured A10 vascular smooth muscle cells (rat aorta). 2 The action of PCA-4230 on cell proliferation and on serum-induced DNA synthesis was determined by measuring the cell number and the incorporation of the thymidine analogue 5-bromo-2'-deoxyuridine (BrdU), respectively. 3 PCA-4230 reversibly inhibited vascular smooth muscle cell proliferation. The increase in cell number was significantly reduced in the presence of 1 and 50 mu M PCA-4230. 4 DNA synthesis was concentration-dependently inhibited by PCA-4230 (0.5 to 50 mu M) in A10 cells that were synchronized by 48 h serum starvation and then re-stimulated by serum repletion, with an IC50 value of 13 mu M. However, serum-induced DNA synthesis in bovine aortic endothelial cells was not significantly affected by PCA-4230. In addition, PCA-4230 (50 mu M) caused a significant drop in PDGF-BB-mediated BrdU incorporation in A10 cells. 5 The effect of PCA-4230 on serum-induced DNA synthesis was compared to that elicited by nifedipine, another dihydropyridine-class inhibitor of vascular smooth muscle proliferation. PCA-4230 (10 mu M) elicited a degree of inhibition similar to that of nifedipine at equimolar concentration. 6 To define the nature of the cell proliferation inhibition, an evaluation of cell cycle progression was undertaken. Flow cytometry studies of DNA content in synchronized cells revealed a block of the serum-inducible cell cycle progression. This inhibitory effect was markedly reduced when PCA-4230 was added 2 h after serum repletion. 6 Accordingly, PCA-4230 (50 mu M) caused a 95 and 90% decrease in the elevation of c-fos and c-jun proto-oncogenes expression as evaluated by Northern blot analysis of mRNA induced early after serum addition. 7 The present results indicate that PCA-4230 inhibits vascular smooth muscle cell proliferation, in culture, by altering the cell cycle progression. Flow cytometric studies of DNA content and the down regulation of c-fos and c-jun proto-oncogenes, suggest that the drug is acting at the early G(0)/G(1) transition phase. PCA-4230 may hold promising potential for the prevention of structural abnormalities of blood vessels associated with atherosclerosis and vascular diseases.
