The Effect of Anti-Diabetic Drugs on the Metabolism of Papillary Thyroid Cancer

Abstract

Background: Thyroid cancer (TC) is the most prevalent endocrine cancer and the 9th most prevalent cancer worldwide. The incidence rates have been increasing in the last decades, which has been attributed not only to overdiagnosis, but also to changes in environmental exposures and the concomitant increase in metabolic diseases, namely diabetes mellitus. The most common TC subtype, papillary thyroid cancer, responsible for 80-90% of new cases, presents an excellent prognosis in most cases. Nonetheless, 5-10% of patients develop aggressive metastatic disease, requiring further investigation on the molecular mechanisms involved. The underlying molecular pathology of PTC involves the dysfunction of signalling pathways, such as MAPK and PI3K/AKT/mTOR, related to cellular energy metabolism. Since these pathways are involved in metabolic disorders such as diabetes mellitus, this evidence paved the way for the study of anti-diabetic drugs, such as metformin, a mitochondrial complex I inhibitor, and canagliflozin, a sodium-glucose co-transporter 2 (SGLT2) inhibitor, as potential therapeutics for TC. Methods: The effect of anti-diabetic drugs metformin and canagliflozin on PTC cell lines was evaluated through transmission electronic microscopy (TEM) to assess changes in cell morphology, particularly mitochondrial changes. Glycolysis stress test was conducted to determine the ability of both drugs to induce metabolic shifts in the cells. Additionally, GLUT1, GLUT3, GLUT4, SGLT2, MCT1 and MCT4 protein expression was observed through immunofluorescence and quantified through western blot assay. Moreover, a proteomic analysis of the BCPAP, TPC-1 and Nthy Ori 3-1 cell lines was conducted. Results: TEM results show a significant canagliflozin-induced increase in mitochondrial total area in Nthy Ori 3-1 cell line, while metformin induced a significant increase in the number of lipid droplets in the TPC-1 cell line. Glycolysis stress test demonstrated the ability of canagliflozin to significantly empty the glycolytic reserve of BCPAP cells, whilst metformin induced significant decreases in the glycolytic reserve as a percentage in the BCPAP and Nthy Ori 3-1 cell lines. Glycolysis during drug response was also significantly lower after metformin treatment in both tumour cell lines. All transporters and co-transporters in study were observed through immunofluorescence. However, GLUT4 and SGLT2 were not observed through western blot analysis. Relatively to Nthy Ori 3-1 expression levels, BCPAP shows lower expression levels of GLUT1, GLUT3, MCT1 and MCT4, while TPC-1 only shows lower expression levels of the monocarboxylate family proteins. Proteomics analysis successfully identified differently expressed proteins and enriched Gene Ontology and Reactome pathways between the three cell lines and between both cancer cell lines versus the Nthy Ori 3-1 cell line. Conclusions: Both metformin and canagliflozin induced a metabolic shift in favour of glycolysis in papillary thyroid cancer cell lines. The results of this study indicate a potential role of anti-diabetic drugs as co-adjuvant therapy for papillary thyroid cancer.