Enhanced Cancer Cell Growth Inhibition by Dipeptide Prodrugs of Floxuridine: Increased Transporter Affinity and Metabolic Stability

Abstract

Dipeptide monoester prodrugs of floxuridine were synthesized, and their chemical stability in buffers, resistance to glycosidic bond metabolism, affinity for PEPT1, enzymatic activation and permeability in cancer cells were determined and compared to those of mono amino acid monoester floxuridine prodrugs. Prodrugs containing glycyl moieties were the least stable in pH 7.4 buffer (t1/2 < 100 min). The activation of all floxuridine prodrugs was 2- to 30-fold faster in cell homogenates than their hydrolysis in buffer, suggesting enzymatic action. The enzymatic activation of dipeptide monoester prodrugs containing aromatic promoieties in cell homogenates was 5- to 20-fold slower than that of other dipeptide and most mono amino acid monoester prodrugs (t1/2 ∼ 40 to 100 min). All prodrugs exhibited enhanced resistance to glycosidic bond metabolism by thymidine phosphorylase compared to parent floxuridine. In general, the 5′-O-dipeptide monoester floxuridine prodrugs exhibited higher affinity for PEPT1 than the corresponding 5′-O-mono amino acid ester prodrugs. The permeability of dipeptide monoester prodrugs across Caco-2 and Capan-2 monolayers was 2- to 4-fold higher than the corresponding mono amino acid ester prodrug. Cell proliferation assays in AsPC-1 and Capan-2 pancreatic ductal cell lines indicated that the dipeptide monoester prodrugs were equally as potent as mono amino acid prodrugs. The transport and enzymatic profiles of 5′-l-phenylalanyl-l-tyrosyl-floxuridine, 5′-l-phenylalanyl-l-glycyl-floxuridine, and 5′-l-isoleucyl-l-glycyl-floxuridine suggest their potential for increased oral uptake, delayed enzymatic bioconversion and enhanced resistance to metabolism to 5-fluorouracil, as well as enhanced uptake and cytotoxic activity in cancer cells, attributes that would facilitate prolonged systemic circulation for enhanced therapeutic action.

Upregulation of Peptide Transporters PEPT1 and PEPT2 by Janus Kinase JAK2

“…Peptide transporters are further important carriers involved in drug transport, such as beta-lactam antibiotics, angiotensin-converting enzyme inhibitors, antiviral drugs and anti-cancer agents [26,44,47,49,50,51]. JAK2 sensitive nutrient and drug uptake by peptide transporters may be relevant for the growth, survival and drug sensitivity of tumor cells [25,31,52,53]. Peptide transporters have thus been considered as potential targets for tumor therapy [54].…”

Hijacking Solute Carriers for Proton-Coupled Drug Transport

“…In mice, oral bestatin accumulates in xenografts of PepT1-transfected HeLa cells and inhibits the growth of these tumors (74). Pro-drugs of floxuridine and cytarabine may also be transported by PepT1 (97,117) (FIGURE 1A).…”

Impact of Peptide Transporter 1 on the Intestinal Absorption and Pharmacokinetics of Valacyclovir after Oral Dose Escalation in Wild-Type and PepT1 Knockout Mice

“…The pharmacological relevance of PepT1 lies mainly in its ability to transport a wide spectrum of drugs from some important therapeutic classes (Brandsch et al, 2008;Rubio-Aliaga and Daniel, 2008;Tsume et al, 2008). For example, many b-lactam antibiotics (e.g., oral cephalosporin and penicillin drugs) and some angiotensin-converting enzyme inhibitors (e.g., captopril and enalapril) are known substrates of PepT1.…”