CHO/hPEPT1 cells overexpressing the human peptide transporter (hPEPT1) as an alternative in vitro model for peptidomimetic drugs

The present study characterized Chinese hamster ovary cells overexpressing a human intestinal peptide transporter, CHO/hPEPT1 cells, as an in vitro mo del for peptidomimetic drugs. The kinetic parameters of Gly-Sar uptake were determined in three different cell culture systems such as untransfected C HO cells (CHO-K1), transfected CHO cells (CHO/hPEPT1) and Caco-2 cells. V-m ax in CHO/hPEPT1 cells was approximately 3-fold higher than those in Caco-2 cells and CHO-K1 cells, while K-m values were similar in all cases. The up take of beta-lactam antibiotics in CHO/hPEPT1 cells was three to twelve fol d higher than that in CHO-Kf cells, indicating that CHO/hPEPT1 cells signif icantly enhanced the peptide transport activity. However, amino acid drugs also exhibited high cellular uptake in both CHO-K1 and CHO/hPEPT1 cells due to the high background level of amino acid transporters. Thus, cellular up take study in CHO/hPEPT1 cells is not sensitive enough to distinguish the p eptidyl drugs from amino acid drugs. The potential of CHO/hPEPT1 cells as a n in vitro model for peptidomimetic drugs was also examined through the inh ibition study on Gly-Sar uptake. Peptidomimetic drugs such as beta-lactam a ntibiotics and enalapril significantly inhibited Gly-Sar uptake whereas the nonpeptidyl compounds, L-dopa and alpha-methyldopa, did not compete with G ly-Sar for cellular uptake within the therapeutic concentrations. In conclu sion, the present study demonstrates the further characterization of CHO/hP EPT1 cells as an uptake model as well as inhibition study and suggests thei r utility as an alternative in vitro model for drug candidates targeting th e hPEPT1 transporter.