A synthetic inhibitor of factor Xa, DX-9065a, reduces proliferation of vascular smooth muscle cells in vivo in rats

The effect of factor Xa inactivation on the proliferation of vascular smoot h muscle cells in vivo was investigated in an experimental restenosis model in rats by using the direct factor Xa inhibitor DX-9065a. In the left comm on carotid artery, an injury of the vascular endothelium was produced by fo ur external vessel clamps for 60 minutes. After 14 days, H-3-labeled methyl thymidine and 5-bromo-2'-deoxyuridine, respectively, were injected intrape ritoneally. After 24 hours, both the left (damaged) and right (nondamaged) carotid arteries were removed, and the incorporation of H-3-methyl thymidin e/mu g protein was determined. For morphological analysis, the cells were l abeled with hematoxylin as well as 5-bromo-2'-deoxyuridine. Stained vascula r smooth muscle cell nuclei were counted, and the proliferation index (perc entage of 5-bromo-2'-deoxyuridine-positive nuclei to total nuclei stained w ith hematoxylin) was determined. An external damage of the carotid artery i nduced proliferation of vascular smooth muscle cells and formation of a neo intima within 2 weeks after vessel injury. As compared with control animals , single subcutaneous injection of DX-9065a (2.5, 5, and 10 mg/kg) given 30 minutes before vessel injury significantly reduced the incorporation of H- 3-methyl thymidine/mu g protein and the total cell number, as well as the p roliferation index. The antiproliferative action of DX-9065a was not dose d ependent in the range from 2.5 to 10 mg/kg s.c. A combination of bolus inje ction (5 mg/kg s.c.) with continuous administration (5 mg/kg/d s.c. for 7 a nd 14 days, respectively) did not increase the antiproliferative effect of DX-9065a. The results indicate a role of factor Xa in the complex pathogene sis of restenosis and the usefulness of a highly effective and selective in hibitor of factor Xa to inhibit. proliferative processes. (C) 2000 Elsevier Science Ltd. All rights reserved.