[Active drug delivery by heterologous expression of membrane transporters]

The oligopeptide transporter PEPT1 is predominantly expressed in the brush-border membranes of small intestinal epithelial cells, where it plays pivotal roles in the efficient absorption of di-/tripeptides. PEPT1 has enormous potential as an oral drug delivery target, because it also mediates the intestinal absorption of peptide-mimetic and nonpeptide substrates. We demonstrated that the peptide derivation of amino acid-related drugs is applicable to improve their intestinal absorption. We have found that oligopeptide transport activity is also expressed in cancer cell lines. The tissue distribution of bestatin was significantly increased in solid tumors that overexpress PEPT1 in nude mice. Orally administered bestatin strongly suppressed tumor growth. These results provided the first demonstration of the tumor-selective delivery of a drug by specific transport activity. The absolute degree of PEPT1 mRNA expression in the small intestine was determined using real-time PCR in rats. Starvation of the animals increased the mRNA expression level profoundly in the upper small intestine. The longitudinal expression pattern was well correlated with the intestinal transport of cefadroxil in rats. We constructed a recombinant adenovirus vector encoding PEPT1 cDNA. Heterologous expression of PEPT1 in the liver was successfully achieved by simple intvavenous. Administration of the vector, resulting in increased liver distribution of [3H] carnosine. In situ perfusion of the brain with the vector doubled the brain distribution of cefadroxil. Heterologous expression of the drug transporter in vivo could be a useful approach for drug delivery.