Sirolimus:A naturally occurringsubstancediscoveredina soil sample from Easter Island.Sirolimuswas initially thought to hold promise as anantifungal抗生素but this idea was dropped when sirolimus was unexpectedly found to haveimmunosuppressiveactivity. The USFood and Drug Administrationin 1999 approved the use of sirolimus as animmunosuppressantagent. But earlier in the nineties, evidence had been uncovered that sirolimus was also a potent inhibitor of the growth ofsmooth musclecells inbloodvessels. The idea was then "hatched" that sirolimus might be used to inhibit therestenosis(reclosure) ofcoronary arteries. (Today, after aballoon angioplastyhas been done to open a clogged coronaryartery, a meshtubecalled a stent is often inserted to keep the artery open. However, restenosis occurs in up to a third of cases when smoothmusclecells migrate from thevesselwall into the stent. The muscle cells proliferate there and narrow the interior diameter of the stent.) To prevent restenosis, stents coated, or "medicated", with sirolimus came into use. The sirolimus is eluted continuously from the stent and deters or slows restenosis.
