title: Prodrugs of purine and pyrimidine analogues for the intestinal di/tri-peptide transporter PepT1: affinity for hPepT1 in Caco-2 cells, drug release in aqueous media and in vitro metabolism.
abstract: A general drug delivery approach for increasing oral bioavailability of purine and pyrimidine analogues such as acyclovir may be to link these compounds reversibly to stabilized dipeptide pro-moieties with affinity for the human intestinal di/tri-peptide transporter, hPepT1. In the present study, novel L-Glu-Sar and D-Glu-Ala ester prodrugs of acyclovir and 1-(2-hydroxyethyl)-linked thymine were synthesized and their affinities for hPepT1 in Caco-2 cells were determined. Furthermore, the degradation of the prodrugs was investigated in various aqueous and biological media and compared to the corresponding hydrolysis of the prodrug valaciclovir. Affinity studies showed that the L-Glu-Sar prodrugs had high affinity for hPepT1 (K(i) approximately 0.2-0.3 mM), whereas the D-Glu-Ala prodrugs had poor affinity (K(i) approximately 50 mM). The pH-rate profiles of the prodrugs D-Glu[1-(2-hydroxyethyl)thymine]-Ala and L-Glu[acyclovir]-Sar showed specific base catalyzed degradation at pH above 4.5 and 5.5, respectively. This implicates that the degradation rates at pH approximately 7.4 (t(1/2) approximately 3.5 and 5.5 h) are approximately 25 times faster than at upper small intestinal pH approximately 6.0. In 10% porcine intestinal homogenate and 80% human plasma the half-lives of the L-Glu-Sar prodrugs were approximately between 45 and 90 min indicating a limited enzyme catalyzed degradation. In contrast, valaciclovir underwent extensive enzyme catalyzed hydrolysis in 10% porcine intestinal homogenate (t(1/2) approximately 1 min). In conclusion, L-Glu-Sar may potentially function as pro-moiety for purine and pyrimidine analogues, where release of parent compound primarily is controlled by a specific base catalyzed hydrolysis. Acyclovir is quantitatively released at the relevant pH 7.4, whereas the 1-(2-hydroxyethyl)-linked thymine is released instead of the parent compound thymine.
authors.affiliation: Department of Pharmaceutics, The Royal Danish School of Pharmacy, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
authors.forename: Anne Engelbrecht
authors.initials: AE
authors.lastname: Thomsen
authors.forename: Gerda Marie
authors.initials: GM
authors.lastname: Friedrichsen
authors.forename: Arne Hagsten
authors.initials: AH
authors.lastname: Sørensen
authors.forename: Rikke
authors.initials: R
authors.lastname: Andersen
authors.forename: Carsten Uhd
authors.initials: CU
authors.lastname: Nielsen
authors.forename: Birger
authors.initials: B
authors.lastname: Brodin
authors.forename: Mikael
authors.initials: M
authors.lastname: Begtrup
authors.forename: Sven
authors.initials: S
authors.lastname: Frokjaer
authors.forename: Bente
authors.initials: B
authors.lastname: Steffansen
mesh_terms: D018938:Caco-2 Cells / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D006801:Humans; D000074011:Peptide Transporter 1; D011355:Prodrugs / Q000737:chemistry / Q000378:metabolism*; D011687:Purines / Q000737:chemistry / Q000378:metabolism*; D011743:Pyrimidines / Q000737:chemistry / Q000378:metabolism*; D012996:Solutions / Q000378:metabolism; D027981:Symporters
chemical_list: D002352:Carrier Proteins; D000074011:Peptide Transporter 1; D011355:Prodrugs; D011687:Purines; D011743:Pyrimidines; C082186:SLC15A1 protein, human; D012996:Solutions; D027981:Symporters