Amino Acid Ester Prodrugs of the Anticancer Agent Gemcitabine:  Synthesis, Bioconversion, Metabolic Bioevasion, and hPEPT1-Mediated Transport

Abstract

Gemcitabine, a clinically effective nucleoside anticancer agent, is a polar drug with low membrane permeability and is administered intravenously. Further, extensive degradation of gemcitabine by cytidine deaminase to an inactive metabolite in the liver affects its activity adversely. Thus, strategies that provide both enhanced transport and high metabolic bioevasion would potentially lead to oral alternatives that may be clinically useful. The objective of this study was to evaluate whether amino acid ester prodrugs of gemcitabine would (a) facilitate transport across intestinal membranes or across cells that express hPEPT1 and (b) provide resistance to deamination by cytidine deaminase. 3'-Monoester, 5'-monoester, and 3',5'-diester prodrugs of gemcitabine utilizing aliphatic (L-valine, D-valine, and L-isoleucine) and aromatic (L-phenylalanine and D-phenylalanine) amino acids as promoieties were synthesized and evaluated for their affinity and direct hPEPT1-mediated transport in HeLa/hPEPT1 cells. All prodrugs exhibited enhanced affinity (IC(50): 0.14-0.16 mM) for the transporter. However, only the 5'-L-valyl and 5'-L-isoleucyl monoester prodrugs exhibited (a) increased uptake (11.25- and 5.64-fold, respectively) in HeLa/hPEPT1 cells compared to HeLa cells and (b) chemical stability in buffers, that were comparable to valacyclovir, a commercially marketed oral amino acid ester prodrug. The widely disparate enzymatic bioconversion profiles of the 5'-L-valyl and 5'-L-isoleucyl prodrugs in Caco-2 cell homogenates along with their significant resistance to deamination by cytidine deaminase suggest that the disposition of gemcitabine following oral administration would be controlled by the rate of bioconversion following transport across the intestinal epithelial membrane. The combined results also suggest that it may be possible to modulate these characteristics by the choice of the amino acid promoiety.

Preparation of albumin nanospheres loaded with gemcitabine and their cytotoxicity against BXPC-3 cells in vitro

“…An important feature of the method in this study was that the molecular structure of GEM remained unchanged, as compared with other GEM-loaded particledelivery systems, in which the particles were prepared with GEM precursors, derivatives, or other modified structures [36][37][38][39] . Although such changes might improve GEM loading or stability, and might even maintain the drug's cytotoxicity, these modified products introduced new chemical compounds, and their pharmacodynamics, pharmacokinetics, safety, and clinical effects must be re-evaluated.…”

Enhanced cellular uptake of Ara-C via a peptidomimetic prodrug, L-valyl-ara-C in Caco-2 cells

“…The L-valyl ester prodrugs, valaciclovir and valganciclovir, increase the bioavailability of their parent drugs 3-to 5-fold and 10-fold, respectively, via the peptide transportermediated transport pathway (Weller et al 1993;Jung & Dorr 1999). Recently, Song et al (2005) have reported that amino acid ester prodrugs of the anti-cancer agent gemcitabine could effectively enhance the transport of gemcitabine via the peptide transporter. Furthermore, it has been reported that targeted delivery of drugs to cancer cells would be possible if the peptide transporters exhibit differential expression in cancer cells compared with normal healthy cells.…”

Discovery of novel antitumor nitric oxide-donating β -elemene hybrids through inhibiting the PI3K/Akt pathway

“…Considering that the poor oral bioavailability of β-elemene is one of the main factors that lead to its moderate antitumor activity, some amino acids were introduced into the linker to improve the druggability of β-elemene [23][24][25][26] and further investigated for the structure-activity relationships. As a result, compounds 14 and 18a-f were synthesized and evaluated for their antiproliferative activities against SGC-7901, HeLa and U87 cells.…”