Rapamycin analogs for stent-based local drug delivery. Everolimus- and tacrolimus-eluting stents

The inhibitory action of the sirolimus-like agent everolimus on smooth muscle cell proliferation, evidenced in animal models, has triggered the interest in everolimus as stent coating for local inhibition of in-stent restenosis. For preclinical and clinical evaluation of safety and efficacy of an everolimus-eluting stent design, a new stent has recently been introduced by Biosensors International Inc, covered by a resorbable "composite" coating, that contains the immunosuppressive drug within a polyhydroxyacid biodegradable polymer matrix with roughly equal resorption rates. FUTURE I, the feasibility trial of this new stent concept, revealed a 30-day MACE (major adverse cardiac events) rate of 0% as well as a restenosis rate of 0% at 6-month follow-up in a total of 32 patients included. The more sensitive QCA (quantitative computerized analysis) and IVUS (intravascular ultrasound) parameters showed an 88% reduction of in-stent late loss and an 87% reduction of the neointimal volume. Adding a second feasibility trial including diabetics, the multicenter trial FUTURE II confirmed the initial beneficial findings of FUTURE I in a total of 64 patients in a 1 : 2 randomization to a bare metal control stent. Based on these results, the FUTURE program has now been expanded by Guidant with two large-scale multicenter studies, FUTURE III and IV, which evaluate this stent design in a larger patient population. Furthermore, FUTURE IV is addressed to demonstrate the non-inferiority of this stent concept in a head-to-head comparison to an approved drug-eluting stent (DES) concept. In contrast to everolimus, tacrolimus is a well-known potent antiproliferative agent, already used in various therapeutic areas. Preclinical studies on tacrolimus-eluting stents for treatment of native coronary artery lesions demonstrated safety and efficacy of this stent concept with significant reduction of neointimal proliferation within the implanted study stents. However, the clinical trial program of the first tacrolimus-eluting stent system in the treatment of native coronary lesions (PRESENT I, II) and saphenous vein graft lesions (EVIDENT) failed to prove the clinical benefit of the stent systems tested and demonstrated the impact of specific stent designs, especially the drug carrier characteristics, on the patient outcome. The progressive PRESET study, evaluating a directly coated tacrolimus-eluting stent, will provide important insights, that will clarify the potential of tacrolimus for prevention of neointimal proliferation in clinical practice without being affected by any additional artificial surface compounds.