EIF4EBP1 and cancer: R5 significantly inhibits the phosphorylation of mTORC1 substrates S6K1 and 4E-BP1 with an IC50 of 10 nM for T389p-S6K1, resulting in cancer cytotoxicity, and it inhibits the proliferation of HeLa cells with a IC50 of 3.5 nM.