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

PEPT1是一种识别多种物质的多肽转运体，因此我们的研究将该转运体应用于药物传递系统的构建。我们的策略是，当我们将药物附着到由底物识别不严格的转运体运输的底物上时，这种药物可能很快就会被吸收。作为模型细胞，我们选择了表达PEPT1的Caco-2细胞作为唯一的多肽转运体，并选择了荧光染料(荧光素异氰酸酯和香豆素-3-羧酸)和二肽(Val-Lys和Lys-Sar)作为药物和底物的组合模型，这些药物的初始摄取速度与药物的浓度成正比。由于PEPT1输运的驱动力是质子动力，加入解偶联剂后，CCCP会减弱或减弱PEPT1的输运。事实上，对Lys-Sar的摄取完全减弱。与我们的预期相反，模型药物(带有荧光探针的多肽)的摄取率明显增加。这些事实表明，外排转运体可能表达细胞并排出这些荧光药物。当加入被认为是运输的物质时，荧光药物的摄取显著增加。抗癌药物是通过这种外排转运体排出的，因此这一事实表明，这些荧光药物的存在抑制了抗癌药物的外流，从而增加了抗癌药物的利用率。此外，我们可以估计决定PEPT1底物识别的因素，尽管本研究合成的荧光化合物没有被转运到细胞内。

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.