cancers Review CD26/DPP-4: Type 2 Diabetes Drug Target with Potential Influence on Cancer Biology Emi Kawakita 1 , Daisuke Koya 2,3 and Keizo Kanasaki 1,3,* 1 Internal Medicine 1, Shimane University Faculty of Medicine, 89-1 Enya-cho, Izumo 693-8501, Japan;
[email protected] 2 Department of Diabetology & Endocrinology, Kanazawa Medical University, Uchinada 920-0293, Japan;
[email protected] 3 Division of Anticipatory Molecular Food Science and Technology, Medical Research Institute, Kanazawa Medical University, Uchinada 920-0293, Japan * Correspondence:
[email protected]; Tel.: +81-853-20-2183 Simple Summary: Dipeptidyl peptidase (DPP)-4 inhibitor is widely used for type 2 diabetes. Al- though DPP-4/CD26 has been recognized as both a suppressor and inducer in tumor biology due to its various functions, how DPP-4 inhibitor affects cancer progression in diabetic patients is still unknown. The aim of this review is to summarize one unfavorable aspect of DPP-4 inhibitor in cancer-bearing diabetic patients. Abstract: DPP-4/CD26, a membrane-bound glycoprotein, is ubiquitously expressed and has diverse biological functions. Because of its enzymatic action, such as the degradation of incretin hormones, DPP-4/CD26 is recognized as the significant therapeutic target for type 2 diabetes (T2DM); DPP- 4 inhibitors have been used as an anti-diabetic agent for a decade. The safety profile of DPP-4 inhibitors for a cardiovascular event in T2DM patients has been widely analyzed; however, a clear association between DPP-4 inhibitors and tumor biology is not yet established. Previous preclinical Citation: Kawakita, E.; Koya, D.; Kanasaki, K.