Evaluation of a Thiodipeptide, l-Phenylalanyl-Ψ[CS-N]-l-alanine, as a Novel Probe for Peptide Transporter 1

Possible utility of peptide-transporter-targeting [19F]dipeptides for visualization of the biodistribution of cancers by nuclear magnetic resonance imaging

Stable-isotope-labeled probes suitable for magnetic resonance imaging (MRI) would have various potential medical applications, such as tumor imaging. Here, with the aim of developing MRI probes targeting peptide transporters, we synthesized a series of [¹⁹F]dipeptides by introducing one or two fluorine atoms or a trifluoromethyl group into the benzene ring of l-phenylalanyl-ψ[CS-N]-l-alanine (Phe-ψ-Ala), which is resistant to cleavage by peptidases. The mono- and difluoro dipeptides were efficiently transported by PEPT1 and PEPT2. Moreover, (3,5)-difluoro Phe-ψ-Ala was metabolically stable in human hepatocyte culture, and had a low distribution volume in mice. An acute toxicity study in mice revealed no apparent effect on body weight or behavior. The biodistribution and biodynamics of this compound could be clearly visualized by ¹⁹F-MRI in vivo, although specific signal enhancement was observed only in the bladder, but not in the tumor of tumor-xenografted mice. Although there was no specific signal enhancement of the tested compound at the tumor, the present study provides some challenging points regarding ¹⁹F-MRI probes for future investigation.

Stereoselective synthesis of Gly-Gly-type (E)-methylalkene and (Z)-chloroalkene dipeptide isosteres and their application to 14-mer RGG peptidomimetics

An efficient synthesis of Gly-Gly-type (E)-methylalkene and (Z)-chloroalkene dipeptide isosteres is realized by organocuprate-mediated single electron transfer reduction.

Possible interaction of quinolone antibiotics with peptide transporter 1 in oral absorption of peptide-mimetic drugs

The study investigated whether quinolone antibiotics inhibit the PEPT1-mediated uptake of its substrates. Among the quinolones examined, lomefloxacin, moxifloxacin (MFLX) and purlifloxacin significantly inhibited the uptake of PEPT1 substrate phenylalanine-Ψ(CN-S)-alanine (Phe-Ψ-Ala) in HeLa/PEPT1 cells to 31.6 ± 1.3%, 27.6 ± 2.9%, 36.8 ± 2.2% and 32.6 ± 1.4%, respectively. Further examination showed that MFLX was an uncompetitive inhibitor, with an IC50 value of 4.29 ± 1.29 mm. In addition, MFLX significantly decreased the cephalexin and valacyclovir uptake in HeLa/PEPT1 cells. In an in vivo study in rats, the maximum plasma concentration (C(max)) of orally administered Phe-Ψ-Ala was significantly decreased in the presence of MFLX (171 ± 1 ng/ml) compared with that in its absence (244 ± 9 ng/ml). The area under the concentration-time curve (AUC) of orally administered Phe-Ψ-Ala in the presence of MFLX (338 ± 50 ng/ml · h) tended to decrease compared with that in its absence (399 ± 75 ng/ml · h). The oral bioavailability of Phe-Ψ-Ala in the presence and absence of MFLX was 41.7 ± 6.2% and 49.2 ± 9.2%, respectively. The results indicate that administration of quinolone antibiotics concomitantly with PEPT1 substrate drugs may potentially result in drug-drug interaction.