(from Abstract): A wide variety of drugs which are currently used in clinical practice possess chemical structures similar to small peptides. Examples of these peptidomimetic drugs include several antibacterial, antiviral, antihypertensive, and antineoplastic agents. The efficiency with which these drugs are absorbed in the gastrointestinal tract after oral administration is an important determinant of their bioavailability. Once they enter the circulation, their half-life in the system becomes an important parameter in their therapeutic efficacy. The kidneys play a crucial role in determining the half-life of these drugs in the circulation. The peptide-like structures make these drugs potential substrates for peptide transporters which are primarily expressed in the intestinal and renal tubular absorptive cells. It is most likely that the peptide transporters are involved in the absorption of the peptidomimetic drugs in the intestine and also in the reabsorption of these drugs in the kidney. The overall objectives of the current project are to investigate the interaction of several therapeutic classes of peptidomimetic drugs with the peptide transporters in the intestine and kidney and thereby to understand the role of these transporters in determining the bioavailability and therapeutic efficacy of these drugs. Recent molecular cloning studies have shown that the intestinal and renal peptide transporters are structurally and functionally different. The intestinal peptide transporter, PEPT1, is of the low-affinity/high-capacity type whereas the primary transporter in the kidney, PEPT2, is of the high- affinity/low-capacity type. However, in both cases the transport process is H+-dependent and rheogenic. The proposed studies will investigate the interaction of peptidomimetic drugs with PEPT1 and PEPT2 using cultured cell lines of intestinal and renal origin which differentially express PEPT1 and PEPT2. Parallel studies will also be conducted using cloned human PEPT1 and PEPT2 by functionally expressing the transporters in HeLa cells and in Xenopus laevis oocytes. The activity of the transporters will be monitored in HeLa cells by measuring the transport of radiolabeled substrates. The interaction of various peptidomimetic drugs with the transporters will be assessed by analyzing the influence of these drugs on the transport of radiolabeled substrates. In Xenopus oocytes, the activity of the transporters will be determined by measuring membrane currents associated with the transport of unlabeled peptidomimetic drugs. There are marked differences between PEPT1 and PEPT2 in the recognition of peptidomimetic drugs as substrates. The proposed studies will identify the structural domains in PEPT1 and PEPT2 which are responsible for differential recognition. These studies will be carried out by comparing the substrate recognition patterns of the wild-type PEPT1 and PEPT2 with those of several chimeric transporters consisting of specific regions of PEPT1 and PEPT2. When successfully completed, the project will generate important information on the interaction of peptidomimetic drugs with human intestinal and kidney peptide transporters that can be directly applied to improve the delivery and therapeutic efficacy of the peptidomimetic drugs in humans.
