Background: In the last decades, metformin (Met), an herbal anti-diabetic medicine, has been proposed as an
Objective: Thyroid cancers are the most common malignancy of the endocrine system. Therefore, the current study was
performed to assess the effects of Met on cell proliferation and activation of the Phosphoinositide 3-Kinase (PI3K)/Protein
kinase B (AKT)/Forkhead Box O1 (FOXO1) signaling pathway in the Medullary Thyroid Carcinoma (MTC) cells. The
effects of Met on the expression of REarranged during Transfection (RET) proto-oncogene were also investigated.
Methods: MTC cell line (TT) was treated with 0, 2.5, 5, 10, 20, 30, 40, 50, and 60 mM concentrations of Met for 24, 48, and
72h. The viability and apoptosis of the treated cells were measured by the 3-(4,5-Dimethylthiazol-2-yl)-2,5-
diphenyltetrazolium bromide (MTT) and Annexin V- Propidium Iodide (PI) assays. The expression level of PI3K, AKT,
FOXO1, and RET genes was investigated by quantitative Real-Time Polymerase Chain Reaction (qRT-PCR), and
phosphorylation of their proteins was determined by the Enzyme-Linked Immunosorbent Assay (ELISA).
Results: Results showed that Met significantly decreased the viability of the MTC cells. Met also reduced the expression
level of PI3K, AKT, and FOXO1 genes (P<0.05), whereas it elevated the expression level of RET proto-oncogene (P<0.05).
Conclusion: It seems that the Met has cytostatic effect on the TT cells. Our results showed that anti-tumoral effects of Met
may be cell type-specific, and according to the induction of RET (as a proto-oncogene) and inhibition of FOXO1 (as a tumor
suppressor gene), Met could not be an appropriate agent in treatment of MTC. The antineoplastic activity of Met has been
confirmed against several malignancies in "in vitro" and "in vivo" studies. However, its molecular mechanisms in the
treatment of different carcinomas particularly in thyroid cancers are not clearly understood and more studies are required to
confirm its exact effect on the MTC.