Rapamycin in cardiovascular medicine

The cellular action of rapamycin (sirolimus), a natural fermentation product produced by Streptomyces hygroscopicus, is mediated by binding to the FK506 binding protein. By inhibiting a kinase known as the target of rapamycin, it restricts the proliferation of smooth-muscle cells by blocking cell-cycle progression at the G1/S transition. The finding that rapamycin possesses both antiproliferative and antimigratory activity suggests that it could contribute to the control of arterial renarrowing after percutaneous intervention and control the vascular manifestations of chronic rejection in transplanted hearts. The first clinical trials of implantation of rapamycin-coated stents in obstructive coronary artery lesions have been reported and, in selected patient groups, it appears that the restenosis process has been abolished. Studies are underway to establish the benefits of rapamycin-coated stents in day-to-day interventional practice, including small vessels, long lesions and patients with multivessel disease. With the addition of novel antiplatelet agents and delivery systems, it is possible that the two major limitations of percutaneous coronary intervention - restenosis and stent thrombosis - will be overcome. Cardiac graft loss due to intimal hyperplasia and accelerated atherosclerosis remains the major limitation to long-term survival following cardiac transplantation. Animal studies of rapamycin have suggested that this process can be reduced or abolished. Human studies of the efficacy of rapamycin in preventing both acute rejection and allograft arterial disease are in progress. Concerns regarding toxicity, carcinogenicity, delayed healing and endothelialization remain. As with any new agent or technology, we must remain vigilant to late adverse side-effects.