EIF4EBP1 and head and neck squamous cell carcinoma: User Metformin activates AMPK and inhibits mTOR by targeting complex I in HNSCC cells, inhibits mitochondrial complex I activity in HNSCC cells and causes the association of dephosphorylated 4E-BP1 with eIF4E and the disruption of the association between eIF4E and eIF4G