The molecular target of rapamycin (mTOR) is central to a complex intracellular 
signaling pathway and is involved in diverse processes including cell growth and 
proliferation, angiogenesis, autophagy, and metabolism. Although sirolimus 
(rapamycin), the oldest inhibitor of mTOR, was discovered more than 30 years 
ago, renewed interest in this pathway is evident by the numerous rapalogs 
recently developed. These newer agents borrow from the structure of sirolimus 
and, although there are some pharmacokinetic differences, they appear to differ 
little in terms of pharmacodynamic effects and overall tolerability. Given the 
multitude of potential applications for this class of agents and the decrease in 
cost that can be expected upon the expiration of sirolimus patents, renewed 
focus on this agent is warranted.