Dipeptide Derivatives of AZT: Synthesis, Chemical Stability, Activation in Human Plasma, hPEPT1 Affinity, and Antiviral Activity

Abstract

5′‐O‐Dipeptide ester prodrugs of antiviral zidovudine (AZT) were designed to target the human intestinal oligopeptide transporter, hPEPT1, and were evaluated for their stability at pH 7.4 in buffer and in human plasma, affinity toward hPEPT1, cytotoxicity, and antiretroviral activity. The dipeptide esters of AZT undergo cyclization in buffer at pH 7.4 to release the parent drug at a rate that depends on the size of the side chains of the peptide carrier; the prodrug is considerably more stable if bulky β‐branched amino acids such as Ile and Val are present, particularly as C‐terminal residues. Incubation in human plasma showed that most of the dipeptide esters of AZT release the parent drug through two aminopeptidase‐mediated pathways: 1) stepwise cleavage of each of the amino acids and 2) direct cleavage of the dipeptide–drug ester bond. However, the plasma hydrolysis of Gly‐Gly‐AZT and Phe‐Gly‐AZT showed only direct cleavage of the dipeptide–drug ester bond. Substrate half‐lives in plasma were again remarkably high when hydrophobic β‐branched amino acids (Val, Ile) were present. The esters were also good substrates for the intestinal oligopeptide transporter hPEPT1 in vitro, with Val‐Gly‐AZT and Val‐Ala‐AZT presenting the highest affinity toward the transporter (IC50: 0.20 and 0.15 mM, respectively). The AZT dipeptide esters were assayed against the IIIB and ROD strains of HIV, and their cytotoxicity was evaluated in MT‐4 cells. The selectivity index of the prodrugs was two‐ to threefold higher than that of AZT for all compounds analyzed. These results point to the potential of dipeptide‐based carriers for the development of effective antiviral drug‐delivery systems. Val‐Ala‐AZT appears to combine chemical stability with good affinity for the hPEPT1 transporter and an improved cytotoxicity/antiretroviral index relative to AZT.

Peptidomimetic and Organometallic Derivatives of Primaquine Active against Leishmania infantum

“…It is possible that this particular feature favors uptake by L. infantum parasites, mediated by specific amino acid permeases or transmembrane peptide transporters (28) parallel to, e.g., the Arg-specific transporter previously reported for L. donovani (9). Curiously, enhanced activity and uptake when ␤-ramified amino acids were present were previously described by us, though with other compounds and pathogens (30,31). Although the most active compounds had high lipophilicity, we found no direct correlation between this parameter and antiparasitic activity (Table 1).…”

Transcorneal Permeation of l- and d-Aspartate Ester Prodrugs of Acyclovir: Delineation of Passive Diffusion Versus Transporter Involvement

“…These transporters may be targeted, through rational prodrug design, to enhance permeability of the parent molecules(18-22). Although hydrophilic compounds are ideal for prodrug derivatization, this approach has been demonstrated to be useful for lipophilic compounds also(23). Amino acid and peptide transporters are considered to be the most favorable for drug targeting, as these transporters accept a wide range of substrates and can tolerate significant structural modification to their substrates(24).…”

Anti-tumoral activity of imidazoquines, a new class of antimalarials derived from primaquine

“…2 26 ) have not. Apparently, specific amino acid or oligopeptide transporters like hPept1 27,28 do not have a role here, or else better results would expected for 3a, 6, and 7 on Caco-2 cells, given their high expression of such transporters and their consequent use in intestinal absorption studies of compounds bearing oligopeptide moieties. 27,28 At this preliminary stage, we can say that results are promising concerning compounds' specific anti-proliferative action against the MCF-7 cell line model of breast cancer.…”

“…Apparently, specific amino acid or oligopeptide transporters like hPept1 27,28 do not have a role here, or else better results would expected for 3a, 6, and 7 on Caco-2 cells, given their high expression of such transporters and their consequent use in intestinal absorption studies of compounds bearing oligopeptide moieties. 27,28 At this preliminary stage, we can say that results are promising concerning compounds' specific anti-proliferative action against the MCF-7 cell line model of breast cancer. Though primaquine (1) and its N-alanylprolyl derivative (7) were better than imidazoquine 3a against MCF-7 cells, the latter has the advantage of being both resistant against proteases (that promptly degrade the peptide moiety of 7) and oxidative deamination (the main metabolic process behind premature deactivation and low oral bioavailability of primaquine).…”