Anticancer Effect of Osmanthus Heterophilus Leaf Extract Through Inhibition of mTOR Phosphorylation And Upregulation of Cytokeratin 18 in Head and Neck Squamous Cell Carcinoma

Background: Head and neck squamous cell carcinoma (HNSCC) generally begins in the squamous cells of the head and neck mucosal surfaces, and are the sixth most common cancers worldwide. The leaf extract of Osmanthus heterophyllus contains lignans and secoiridoids, which have various biological activities including anticancer activity. This study aimed to investigate the potential anticancer effects of O. heterophyllus leaf extract on HNSCC FaDu cells and its underlying mechanism. Methods: The extract of O. heterophyllus leaves was obtained using a Dionex™ ASETM 350 Accelerated Solvent Extractor. After treating FaDu cells with the extract for 24 h, cell viability was evaluated using an MTT assay, and apoptosis-related proteins, mammalian target of rapamycin (mTOR) phosphorylation, and cytokeratin (CK) 18 expression were detected by western blotting. Cells were stained with an Annexin-V/PI double-staining assay using an Arthur image-based cytometric assay. Results: O. heterophyllus ethanol extract (OHEE) significantly reduced FaDu cell viability, increased cleaved caspase 3 and PARP, and also increased Annexin-V/PI double-stained cells. The expression of CK18 by OHEE increased while that of phospho-mTOR decreased, and the expression of CK18 decreased when mTOR phosphorylation was restored by glucose. Conclusions: OHEE induces apoptosis in HNSCC FaDu cells, which is associated with the regulation of mTOR and CK18.