RPS6KB1 and breast carcinoma: We previously demonstrated that the bi-steric mTORC1 inhibitor RMC-4627 potently inhibits phosphorylation of the mTORC1 substrates 4E-BP1 and S6K at concentrations that do not suppress phosphorylation of the mTORC2 substrate AKT S473, exhibiting 13- to 18-fold selectivity for mTORC1 in breast cancer cell lines in vitro (19).