Background: Smooth muscle proliferation and extracellular matrix formation in the subintimal region of blood vessels that have been subjected to intimal injury are responsible for restenosis following balloon angioplasty of the coronary arteries and for accelerated atherosclerosis in a variety of other pathophysiological states. The immediate early-response gene c-myc is overexpressed in proliferating vascular smooth muscle cells in vitro, and c-myc antisense oligomers have been shown to reduce c-myc expression and to inhibit proliferation of vascular smooth muscle cells in culture. Mithramycin is a commercially available G-C-specific DNA binding drug that selectively inhibits transcription of genes, such as c-myc, that have G-C-rich promoter sequences. This study tested the hypothesis that mithramycin inhibits transcription of the c-myc proto-oncogene and prevents myointimal proliferation after balloon injury of the rat carotid artery in vivo.
Methods and results: Ten-week-old male Sprague-Dawley rats received mithramycin (150 micrograms/kg IP) or distilled H2O 1 hour before and 1 hour after balloon injury of the right common carotid artery. After 2 weeks, the rats were killed by overdose of pentobarbital, and the injured right and uninjured control left arteries were pressure-fixed and subjected to morphological analysis for evaluation of the degree of myointimal thickening. Separate groups of rats were killed at 2 and 6 hours after vascular injury, and total RNA from injured and control vessels of mithramycin- and vehicle-treated rats was subjected to Northern analysis for assessment of steady-state c-myc mRNA levels. The areas of neointima and the ratios of neointimal to medial area were significantly less in mithramycin-treated than in control rats (0.6 +/- 0.1 versus 1.2 +/- 0.1 mm2, P < .01 and 95 +/- 16% versus 190 +/- 14%, P < .01). Lumen size was significantly greater in mithramycin-treated than in control rats (1.5 +/- 0.1 versus 0.8 +/- 0.1 mm2, P < .01). Steady-state c-myc mRNA levels were increased 10-fold and 2-fold (compared with undamaged carotid arteries) at 2 and 6 hours after balloon injury, respectively; mithramycin treatment reduced c-myc mRNA levels at 2 and 6 hours by 66% and 53%, respectively.
Conclusions: These results support the hypothesis that systemic administration of mithramycin immediately (1 hour before and after intervention effectively inhibits transcription of the c-myc proto-oncogene and prevents myointimal proliferation after balloon injury of the rat carotid artery in vivo. Because mithramycin has been shown to be well tolerated by humans and to effectively inhibit transcription of c-myc in proliferating human cells, this agent may be useful in the prevention of coronary restenosis.