PHOSPHOROTHIOATE OLIGODEOXYRIBONUCLEOTIDES ANTISENSE TO PAI-1 MESSENGER-RNA INCREASE FIBRINOLYSIS AND MODIFY EXPERIMENTAL THROMBOSIS IN RATS

The effect of systemic inhibition of PAI-1 expression in rats by PS-16 R, a phosphorothioate analogue of hexadecadeoxyribonucleotide compleme ntary to a signal peptide coding sequence of rat PAI-1 mRNA, on PAI-1 activity in blood plasma and thrombus formation was studied in rat mod els for experimental thrombosis. In previous in vitro studies, oligonu cleotides of PS-16R family have been shown to inhibit efficiently PAI- 1 synthesis in endothelial cells by antisense mechanism. When PS-16R w as administered intravenously as a single bolus injection (1 to 5 mg p er rat), it produced a significant reduction in PAI-1 activity of bloo d plasma. This effect was both time-and concentration-dependent. Under the same conditions, three groups of rats were treated with control o ligodeoxynucleotides such as PS-16R with double mismatches, with scram bled sequence; and an oligodeoxynucleotide with sense sequence (comple mentary to PS-16R), respectively. Based on these preliminary experimen ts, a low dose of 1.5 mg per rat was selected to produce approximately 20-30% reduction of PAI-1 activity in blood plasma and the effect of such a decrease in PAI-1 expression was tested on thrombus formation i n two rat models for experimentally induced thrombosis. Such a limited decrease in PAI-1 activity produced a significant antithrombotic effe ct in the arterial thrombosis model. There was a profound delay in the occlusion time in rats treated with PS-16R when compared to control a nimals (80 +/- 3 and 55 +/- 3 h, respectively), although blood plasma activity of PAI-1 in the same groups of rats differed only by 20%. The re was also a tendency to reduce both an incidence of venous thrombosi s (58.33 and 68.11%, respectively) and thrombus weight (2.1 +/- 0.4 an d 2.9 +/- 0.9 mg, respectively) in the animals treated with PS-16R. Ho wever, this effect was not significant. Thus, low dose of PS-16R throu gh inhibition of PAI-1 synthesis in targeted cells in rats reduced PAI -1 activity in blood plasma and protected against arterial thrombus fo rmation in the rat.