Identification of two novel inhibitors of mTOR signaling pathway based on high content screening

Abstract

Mammalian target of rapamycin (mTOR) signaling pathway plays a critical role in regulating cell growth, proliferation and survival. Dysregulation of mTOR signaling pathway is closely involved in cancer development and chemotherapy resistance. Inhibitors of mTOR signaling pathway have been demonstrated to be attractive therapeutics for cancer therapy. In the present study, we aim to discover novel mTOR signaling pathway inhibitors from a natural compound library. Inhibitors of mTOR signaling pathway were discovered via high content screen assay based on the subcellular localization of eukaryotic initiation factor 4E (eIF4E) in mouse embryonic fibroblast cells. Candidate compounds were further assessed in cancer cells. Phosphorylation levels of mTOR complexes downstream targets were analyzed using Western blot. Cell cytotoxicity and apoptosis were evaluated using MTS assay and flow cytometry, respectively. Two compounds, 1,4-O-diferuloylsecoisolariciresinol (IM-1) and Pierreione B (IM-2), were identified which induced significant nuclear translocation of eIF4E in a panel of cancer cells. Both of the compounds decreased the phosphorylation levels of p70 ribosomal protein S6 kinase (S6K) and eIF4E binding protein 1 (4E-BP1), resulting in cancer cell cytotoxicity and apoptosis. Via high content screen assay, two novel inhibitors of mTOR signaling, IM-1 and IM-2, were identified with strong anticancer activity. IM-1 and IM-2 could be potential candidates for anticancer therapeutics by targeting mTOR signaling pathway and as such warrants further exploration.