The dipeptidyl peptidase-IV inhibitor gemigliptin alone or in combination with NVP-AUY922 has a cytotoxic activity in thyroid carcinoma cells

Abstract

The effect of the dipeptidyl peptidase-IV inhibitor gemigliptin alone or in combination with the heat shock protein 90 inhibitor NVP-AUY922 (AUY922) on survival of thyroid carcinoma cells was elucidated. The SW1736 and TPC-1 human thyroid carcinoma cells were used. Cell viability, the percentage of viable cells, cytotoxic activity, the percentage of apoptotic cells, and mitochondrial membrane potential were measured. To evaluate the combined effect of gemigliptin with AUY922, the interactions were estimated by calculating combination index. Gemigliptin led to cell death in conjunction with overexpression of the phosphorylated protein levels of Akt, extracellular signal–regulated kinase 1/2, and adenosine monophosphate–activated protein kinase. In gemigliptin-treated cells, wortmannin augmented cell death, whereas AZD6244 and compound C did not affect cell survival. Wortmannin decreased phosphorylated adenosine monophosphate–activated protein kinase protein levels, and AZD6244 increased phosphorylated Akt protein levels. Meanwhile, cotreatment of both gemigliptin and AUY922, compared with treatment of AUY922 alone, potentiated cell death. All the combination index values were lower than 1.0, suggesting synergistic cytotoxicity of gemigliptin with AUY922. In treatment of both gemigliptin and AUY922, compared with AUY922 alone, the protein levels of total and phosphorylated Akt, phosphorylated extracellular signal–regulated kinase 1/2, and phosphorylated adenosine monophosphate–activated protein kinase increased without alteration in those of total extracellular signal–regulated kinase 1/2 and total adenosine monophosphate–activated protein kinase. The percentage of apoptotic cells increased. The protein levels of Bax and cleaved poly (ADP-ribose) polymerase increased, whereas Bcl2 protein levels were unchanged, resulting in increment of Bax/Bcl2 ratio. Transfection of Bax small interfering RNA did not cause any variation in cell viability, the percentage of viable cells and cytotoxic activity. Our results demonstrate that gemigliptin exerts a cytotoxic activity with concomitant alterations in expression of Akt, extracellular signal–regulated kinase 1/2, and adenosine monophosphate–activated protein kinase in thyroid carcinoma cells. Furthermore, gemigliptin synergizes with AUY922 in induction of cytotoxicity via regulation of Akt, extracellular signal–regulated kinase 1/2, and adenosine monophosphate–activated protein kinase as well as involvement of Bcl2 family proteins in thyroid carcinoma cells.