PT-88 is a highly selective inhibitor of mTOR (Mammalian target of rapamycin) ( IC 50 =1.2 nM). PT-88 inhibits both mTORC1 and mTORC2 complexes, both of which are active forms of mTOR protein kinases and are closely associated with cell growth, proliferation, and survival. PT-88 can be used to study the role of mTOR in tumorigenesis and development, especially in the treatment of breast cancer.