Drug Delivery System Utilizing Transporters That Recognize Substrates of Relatively Large Molecular Sizes

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PEPT1 is a peptide-transporter that recognizes a wide variety of substances, then our investigation focused this transporter for construction of drug delivery system. Our strategy is that when we attach a drug to a substrate that is transported by a transporter whose substrate recognition is not strict, this drug may be taken up fast. As a model cell, we chosen Caco-2 cell that expresses PEPT1 as an only peptide transporter, and as a model combination of drugs and substrates, we chosen fluorescent dyes (fluorescein isocyanate and coumarin-3-carboxylic acid) and dipeptides (Val-Lys and Lys-Sar).Initial uptake rates of these 'drugs' were proportional to the concentrations of the drug. Since the drivingforce of the transport by PEPT1 is a proton-motive-force, addition of an uncoupler, CCCP should decrease or diminish the transport. In fact, the uptake of Lys-Sar was diminished completely. The uptake rate of model drugs (the peptides with fluorescent probes), on the contrary to our expectation, increased appreciably. These facts imply that an efflux transporter may express the cell and extrude these fluorescent drugs. When substances that are considered to be transported were added, the uptake of the fluorescent drugs increased markedly. Anti-cancer drugs are expelled by this efflux transporters, hence this fact suggests that the presence of these fluorescent drugs suppress the efflux of anti-cancer drugs, which increases the availability of anticancer drugs.In addition, we can estimate the factors that determine the substrate recognition of PEPTl, although fluorescent compounds synthesized in this study are not transported into cells.