ADENOVIRUS-MEDIATED TRANSFER OF THE HERPES-SIMPLEX VIRUS THYMIDINE KINASE GENE INHIBITS VASCULAR SMOOTH-MUSCLE CELL-PROLIFERATION AND NEOINTIMA FORMATION FOLLOWING BALLOON ANGIOPLASTY OF THE RAT CAROTID-ARTERY

Background: Vascular smooth muscle cell (VSMC) proliferation following arterial injury plays a critical role in a variety of vascular prolif erative disorders, including atherosclerosis and restenosis after ball oon angioplasty. in this study, we tested the hypothesis that localize d arterial infection at the time of balloon angioplasty with an adenov irus (ADV-tk) encoding the herpes simplex virus thymidine kinase gene (HSV-tk), followed by systemic ganciclovir administration, can inhibit VSMC proliferation and neointima formation in a well-characterized mo del of arterial injury and restenosis. Materials and Methods: The left carotid arteries of 31 male Sprague-Dawley rats were subjected to bal loon angioplasty and immediately infected with 2 X 10(9) pfu of either ADV-tk or a control adenovirus that does not encode a recombinant pro tein (ADV-Delta E1). Twenty-four hours after injury, animals from each experimental group were randomized to receive a course of systemic ga nciclovir (ADV-tk/+GC, ADV-Delta E1/+GC) or saline (ADV-tk/-GC, ADV-De lta E1/-GC). VSMC DNA synthesis was measured by 5'-bromodeoxyuridine ( BrdU) incorporation 2-4 days after balloon injury. The extent of reste nosis, expressed as the neointima to media (I/M) area ratio was determ ined by digital planimetry 20 days after balloon injury in each of the four treatment groups. Immunohistochemistry using a mAb to von Willeb rand factor (VWF) was used to determine the effects of ADV-tk infectio n and ganciclovir treatment on re-endothelialization of the carotid ar teries 20 days following balloon angioplasty. Results: Forty-one perce nt of the medial VSMCs in the ADV-tk/-GC arteries were labeled with Br dU 4 days after balloon injury. Ln contrast, ADV-tk infected animals t hat were treated with systemic ganciclovir (ADV-tk/+GC) displayed a 40 % reduction in BrdU-staining medial VSMCs (p < 0.03). I/M area ratios of the three control groups were 1.17 +/- 0.18 (ADV-tk/-GC, n = 5), 1. 15 +/- 0.10 (ADV-Delta E1/+GC, n = 6), and 0.91 +/- 0.08 (ADV-Delta E1 /-GC, n = 6). These differences were not statistically significant (p > 0.05). In contrast, the ADV-tk/+GC animals (n = 6) displayed an I/M area ratio of 0.49 +/- 0.13 which was significantly lower than that se en in each of the three control groups (p < 0.02). None of the treated animals showed evidence of significant organ toxicity at autopsy. A r egenerated endothelium was observed in the ADV-tk/+GC animals 20 days after balloon injury. Conclusions: Localized arterial infection with A DV-tk at the time of balloon angioplasty followed by systemic ganciclo vir therapy reduces VSMC proliferation and neointimal expansion in the rat carotid artery injury model. Moreover, combined treatment with AD V-tk and systemic ganciclovir does not result in systemic toxicity and appears to selectively eliminate proliferating VSMCs, while preservin g the capacity of the injured arterial segments to re-endothelialize w ithin 3 weeks of injury. Taken together, these results support the fea sibility of using this gene therapy approach for the treatment of huma n vascular proliferative disorders.