MTOR and neoplasm: The biguanides metformin and phenformin inhibit mitochondrial electron transport chain complex I. Inhibition of mTORC1 restored autophagy in cells treated with these drugs, helping cancer cells bypass the blockage of phosphorylation of the E1 subunit α of PDH and making it a potential therapeutic target in tumor cells that are resistant to mTOR-mediated therapies.460