Rapamycin (Sirolimus; AY 22989) is a potent and specific mTOR inhibitor with an IC50 of 0.1 nM in HEK293 cells. Rapamycin binds to FKBP12 and specifically acts as an allosteric inhibitor of mTORC1. Rapamycin is an autophagy activator, an immunosuppressant.