title: Interaction of fused-pyrimidine nucleoside analogs with human concentrative nucleoside transporters: High-affinity inhibitors of human concentrative nucleoside transporter 1.
abstract: Human concentrative nucleoside transporters (hCNTs) mediate electrogenic secondary active transport of physiological nucleosides and nucleoside drugs into cells. Six fused-pyrimidine ribonucleosides and one 2'-deoxynucleoside were assessed for their abilities to inhibit [(3)H]uridine transport in the yeast Saccharomyces cerevisiae producing recombinant hCNT1, hCNT2 or hCNT3. Six of the analogs inhibited hCNT1 with K(i) values<1μM whereas only two analogs inhibited hCNT3 with K(i) values<1μM and none inhibited hCNT2. To assess if the inhibitory analogs were also permeants, currents evoked were measured in oocytes of Xenopus laevis producing recombinant hCNT1, hCNT2 or hCNT3. Significant inward currents, indicating permeant activity, were generated with (i) three of the analogs in hCNT1-producing oocytes, (ii) none of the analogs in hCNT2-producing oocytes and (iii) all of the analogs in hCNT3-producing oocytes. Four were not, or were only very weakly, transported by hCNT1. The thienopyrimidine 2'-deoxynucleoside (dMeThPmR, 3) and ribonucleoside (MeThPmR, 4) were the most active inhibitors of uridine transport in hCNT1-producing oocytes and were an order of magnitude more effective than adenosine, a known low-capacity transport inhibitor of hCNT1. Neither was toxic to cultured human leukemic CEM cells, and both protected CEM cell lines with hCNT1 but not with hENT1 against gemcitabine cytotoxicity. In summary, dMeThPmR (3) and MeThPmR (4) were potent inhibitors of hCNT1 with negligible transportability and little apparent cytotoxicity, suggesting that pending further evaluation for toxicity against normal cells, they may have utility in protecting normal hCNT1-producing tissues from toxicities resulting from anti-cancer nucleoside drugs that enter via hCNT1.
authors.affiliation: Department of Oncology, University of Alberta, Edmonton, Alberta, Canada T6G1Z2.
authors.forename: Vijaya L
authors.initials: VL
authors.lastname: Damaraju
authors.forename: Kyla M
authors.initials: KM
authors.lastname: Smith
authors.forename: Delores
authors.initials: D
authors.lastname: Mowles
authors.forename: Ireneusz
authors.initials: I
authors.lastname: Nowak
authors.forename: Edward
authors.initials: E
authors.lastname: Karpinski
authors.forename: James D
authors.initials: JD
authors.lastname: Young
authors.forename: Morris J
authors.initials: MJ
authors.lastname: Robins
authors.forename: Carol E
authors.initials: CE
authors.lastname: Cass
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000009:adverse effects; D001692:Biological Transport / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D019610:Cytoprotection / Q000187:drug effects*; D003841:Deoxycytidine / Q000031:analogs & derivatives / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007938:Leukemia / Q000188:drug therapy; D026901:Membrane Transport Proteins / Q000378:metabolism*; D015394:Molecular Structure; D009865:Oocytes; D011741:Pyrimidine Nucleosides / Q000737:chemistry / Q000494:pharmacology*; D012441:Saccharomyces cerevisiae; D014982:Xenopus laevis; D000093542:Gemcitabine
chemical_list: D000970:Antineoplastic Agents; D026901:Membrane Transport Proteins; D011741:Pyrimidine Nucleosides; C065171:cif nucleoside transporter; D003841:Deoxycytidine; D000093542:Gemcitabine