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[1]. Rapamycin is an autophagy activator, an immunosuppressant[2].