Rapamycin is a drug of interest because researchers know that the TOR gene (which stands for Target of Rapamycin, so you can probably guess the order of discovery) is involved the big tangled mess of biochemistry relating to the calorie restriction response. Less food while maintaining adequate nutrition modulates the functions of metabolism in ways that lead to longer lives and slower aging. Unless you've spent the past few years living in a basket, you'll know that this is of considerable interest to the gerontological and pharmaceutical research communities, and many efforts are underway to develop means of achieving or bettering this biochemical response without modifying diet.
Personally, I think this is all a sideshow of limited benefit in comparison to research that aims to repair and reverse the damage of aging rather than merely slowing it a little. But the sideshow has the main stage and the attention of the tent for now. Sideshow or not, it will produce a vast amount of new information on the way in which our biochemistry works - so it isn't a waste, it's just not very efficient if the end goal is for humans to live much longer in good health than they presently do.
But back to rapamycin. The news for today is that researchers ran lifespan studies on mice where rapamycin was administered comparatively late in life, yet still produced noteworthy gains in overall life expectancy. Via the Nature article:
Problems formulating the feed meant that the teams couldn't start the treatment until the mice were rather older than they had planned - 20 months of age, or the equivalent of about 60 years in human terms.
As it happened, this delay was a fortuitous accident. Compared with the non-drug-taking group, the lifespans of the mice given rapamycin increased by up to 14%, even though they were middle-aged when treatment began. Their life expectancy at 20 months shot up by 28% for the males and 38% for the females.
This is actually good enough to be worth running in the Rejuvenation Prize component of the MPrize for longevity science - it's about the same as the record for late onset calorie restriction started at that age. It has to be said that I'm surprised to see a presently available drug capture a similar level of additional longevity given the past few years of less stellar results from sirtuin-manipulating drugs.
Those of a more scientific mindset should take a look at the original paper. I'm wondering whether the diet of these mice was controlled for calorie restriction, so as to eliminate the old, old issue of drugs that make your mice eat less and thereby extend their lives that way. Given the researchers listed, I'd assume that care was taken here, but it's always worth checking.
Harrison, D., Strong, R., Sharp, Z., Nelson, J., Astle, C., Flurkey, K., Nadon, N., Wilkinson, J., Frenkel, K., Carter, C., Pahor, M., Javors, M., Fernandez, E., & Miller, R. (2009). Rapamycin fed late in life extends lifespan in genetically heterogeneous mice Nature DOI: 10.1038/nature08221