Signaling pathways in medullary thyroid carcinoma: therapeutic implications

Antineoplastic Activity of an Old Natural Antidiabetic Biguanoid on the Human Thyroid Carcinoma Cell Line

BACKGROUND

In the last decades, metformin (Met), an herbal anti-diabetic medicine, has been proposed as an anti-cancer agent.

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.

Altered Epigenetic Mechanisms in Thyroid Cancer Subtypes

Thyroid carcinoma (TC) is the most frequent malignant neoplasm of the endocrine system. Molecular methods for diagnosis of invasive thyroid disease can be effectively adopted. Epigenetic factors play an important role in the diversity patterns of gene expression and the phenotypic and biological characteristics of TC subtypes. We aimed to review epigenetic changes in the main subtypes of TC, along with a presentation of the methods that have examined these changes, and active clinical trials for the treatment of advanced TCs targeting epigenetic changes. A literature analysis was performed in MEDLINE using PubMed, Elsevier, and Google Scholar for studies published up to 2016, using the keywords: "Epigenetic alterations" OR "Epigenetic changes", "thyroid cancers", "papillary thyroid cancer", "medullary thyroid cancer", "follicular thyroid cancer", and "anaplastic thyroid cancer", which resulted in 310 articles in English. All related abstracts were reviewed and studies were included that were published in English, had available full text, and determined the details of the methods and materials associated with the epigenetic patterns of TC and its subtypes (100 articles). Analysis of epigenetic alterations in TC subtypes helps to identify pathogenesis and can play an important role in the classification and diagnosis of tumors. Epigenetic mechanisms, especially aberrant methylation of DNA and microRNAs (miRs), are likely to play an important role in thyroid tumorigenesis. Further studies are required to elucidate the role of histone modification mechanisms in TC development.

Effects of metformin on the PI3K/AKT/FOXO1 pathway in anaplastic thyroid Cancer cell lines

Background

The PI3K/AKT/FOXO signaling pathway plays an important role in the survival, proliferation and apoptosis of tumor cells. The aim of the present study was to explore whether metformin could affect insulin-promoting cell growth by regulation of this pathway.

Material and methods

Anaplastic thyroid cancer cells were treated with 0–60 mM metformin for 24, 48 and 72 h. Cell viability, morphology, apoptosis and migration were investigated by MTT assay, microscopy observation, AnexinV-PI and the wound healing assay, respectively. Expression levels of PI3K, AKT and FOXO1 were detected by RT-qPCR, and proteins phosphorylated levels were determined by ELISA.

Results

Metformin decreased cell viability and migration in a significant time-and dose-dependent manner, and induced apoptosis and morphological changes in the cells. RT-qPCR results showed that expression levels of PI3K, AKT and FOXO1 was inhibited by metformin (P < 0.05). However, there was no significant change in the expression level of AKT following metformin treatment for C643 cell line (P > 0.05). ELISA results showed that metformin treatment had no significant effects on the phosphorylated levels of PI3K, AKT and FOXO1 (P > 0.05).

Conclusuion

The downregulation of FOXO1 was intensified by metformin, but no increase in cell viability was observed following FOXO1 downregulation by metformin. However, the exact molecular mechanism of metformin on inhibition of the PI3K/AKT pathway and subsequent decrease in cell viability remains unclear and further studies are required for its clarification.

Electronic supplementary material

The online version of this article (10.1007/s40199-018-0208-2) contains supplementary material, which is available to authorized users.