A potent, ATP-competitive inhibitor of mTOR kinase (both mTORC1 and mTORC2) with an IC50 of 0.8 nM. AZD8055 displays excellent selectivity (~ 1,000-fold) against all class I PI3K isoforms and other members of the PI3K-like kinase family. In addition, it shows no significant activity against a panel of 260 kinases at concentrations up to 10 µM. AZD8055 inhibits the phosphorylation of mTORC1 substrates p70S6K and 4E-BP1 as well as phosphorylation of the mTORC2 substrate AKT and downstream proteins.