In vitro metabolism and transport of the new dipeptidyl peptidase 4 inhibitors, KR66222 and KR66223

1. We investigated the in vitro metabolism and transport of KR66222 and KR66223, new inhibitors of dipeptidyl peptidase (DPP) 4, using human liver microsomes (HLMs) and a Caco-2 cell monolayer. 2. Human liver microsomal incubation of KR66222 in the presence of the NADPH-generating system resulted in the formation of two metabolites, identified as S-oxidation (KR68334) and hydrolysis (KR66223) products using liquid chromatography/tandem mass spectrometry. The formation of KR66223 via an esterase and the formation of KR68334 via CYP3A5 and CYP3A4 seem to be major factors in the in vitro metabolism of KR66222 using HLMs. Additionally, KR66222 had a significantly greater basal to apical transport rate (2.5-fold) than apical to basal transport in the Caco-2 cell monolayer, suggesting the involvement of an efflux transport system. Further studies using inhibitors of efflux transporters and P-glycoprotein (P-gp) overexpressed cells revealed that P-gp was involved in the basal to apical transport of KR66222. These findings suggest that KR66222 undergoes a significant first pass effect, which may serve to decrease the bioavailability of KR66222. 3. The active metabolite, KR66223, was stable for 1 h at 37 degrees C in pooled HLMs (98.9 +/- 2.6% of control) and did not undergo P-gp-mediated efflux in Caco-2 cells. Apparent permeability of KR66223 (4.96 x 10(-6) cm/s) was comparable to that of KR66222 (4.08 x 10(-6) cm/s). 4. In conclusion, considering pharmacokinetic variability and the intestinal first-pass effect caused by the involvement of CYP3A and P-gp, KR66223 seems to have better in vitro metabolism and permeability characteristics than KR66222.