Targeted delivery to PEPT1-overexpressing cells: Acidic, basic, and secondary floxuridine amino acid ester prodrugs

Abstract

Floxuridine is a clinically proven anticancer agent in the treatment of metastatic colon carcinomas and hepatic metastases. However, prodrug strategies may be necessary to improve its physiochemical properties and selectivity and to reduce undesirable toxicity effects. Previous studies with amino acid ester prodrugs of nucleoside drugs targeted to the PEPT1 transporter coupled with recent findings of the functional expression of the PEPT1 oligopeptide transporter in pancreatic adenocarcinoma cell lines suggest the potential of PEPT1 as therapeutic targets for cancer treatment. In this report, we show the feasibility of achieving enhanced transport and selective antiproliferative action of amino acid ester prodrugs of floxuridine in cell systems overexpressing PEPT1. All prodrugs exhibited affinity for PEPT1 (IC 50 , 1.1 -2.3 mmol/L). However, only the prolyl and lysyl prodrugs exhibited enhanced uptake (2-to 8-fold) with HeLa/PEPT1 cells compared with HeLa cells, suggesting that the aspartyl prodrugs are PEPT1 inhibitors. The selective growth inhibition of Madine-Darby canine kidney (MDCK)/PEPT1 cells over MDCK cells by the prodrugs was consistent with the extent of their PEPT1-mediated transport. All ester prodrugs hydrolyzed to floxuridine fastest in Caco-2 cell and MDCK homogenates and slower in human plasma and were most chemically stable in pH 6.0 buffer. Prolyl and lysyl prodrugs were relatively less stable compared with aspartyl prodrugs in buffers and in cell homogenates. The results suggest that optimal design for targeted delivery would be possible by combining both stability and transport characteristics afforded by the promoiety. [Mol Cancer Ther 2005;4(4):659 -67]

A new target ligand Ser–Glu for PEPT1-overexpressing cancer imaging

“…In the previous study, PEPT1 was used to target and inhibit cancer. 23,24 Recently, a dipeptide Ser-Glu was identified to have high affinity and specificity with PEPT1. Further, Ser-Glu with a smaller molecular size may result in little characteristic alteration of NPs after conjugation.…”

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

“…Reaction of 10a with Boc-L-Asp in the presence of DCC and DMAP using dry DMF as the solvent generated intermediate 12 [23], followed by esterification with 5b to give intermediate 13, which was deprotected using trifluoroacetic acid (TFA) to provide compound 14. Similarly, condensation of 10a and varying Bocamino acids in dichloromethane produced intermediates 15a-f, followed by N-Boc deprotection to give intermediates 16a-f.…”

“…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.…”

“…The reaction mixture was added 8 mL H2O and extracted with ethyl acetate (15 mL× 3). The combined organic extracts were washed with water (10 mL × 2), dried over anhydrous Na2SO4 and concentrated to give the crude intermediate 12 in 62% yield without further purification [23].…”

Prodrug Applications for Targeted Cancer Therapy

“…In the case of conjugates, the active drug moiety is colored in red. a Examples of prodrugs that are substrates for endogenous proteases (① prostate-specific antigen, PSA) (8), membrane transporters (② PEPT1 oligopeptide transporter in pancreatic carcinomas) (14), or intracellular reductases (③ DT-diaphorase and ④ NADPH:cytochrome P450 reductase). b Prodrugs requiring exogenously administered enzymes or energy for activation.…”