Establishment of a dipeptidyl peptidases (DPP) 8/9 expressing cell model for evaluating the selectivity of DPP4...

Dipeptidyl peptidases (DPPs) 8 and 9 are homologous, cytoplasmic postproline-cutting enzymes, which have similar enzymatic activity and preferred substrates as DPP4. DPP4 is a well-known target for treating diabetes mellitus. With the increased concern of non-selectivity and toxicities caused by DPP4 inhibitors, it is essential to establish new ex vivo system to investigate DPP4 inhibitors' effect on DPP8 and DPP9.

Here we reported a newly established cell model system by cloning and transfecting human DPP8/9 genes into HEK 293 cells. We then used this model to evaluate the clinically applied DPP4 inhibitors' effect on DPP8/9, by direct enzymatic activity assay. Given the difference of cellular locations between DPP4 and DPP8/9, we also evaluated the influence of these drugs on intracellular DPP8/9 activity and cell viability by extracellular treatment with different inhibitors.

Direct enzymatic activity assay revealed significant and concentration-dependent inhibition effect of vildagliptin, saxagliptin on DPP8/9. Extracellular incubation of DPP8/9 over expressed cells with sitagliptin, vildagliptin, saxagliptin, alogliptin and linagliptin, showed only mild inhibition on DPP8/9. Moreover, all of these drugs showed no significant influence on cell viability.

Our results demonstrated that the DPP8/9 over-expressing cell model system is a very useful and promising system for investigating the selectivity and associated toxicity of DPP4 inhibitors on DPP8/9.