title: Role of human nucleoside transporters in the uptake and cytotoxicity of azacitidine and decitabine.
abstract: The nucleoside analogs 5-azacytidine (azacitidine) and 5-aza-2'-deoxycytidine (decitabine) are active against acute myeloid leukemia and myelodysplastic syndromes. Cellular transport across membranes is crucial for uptake of these highly polar hydrophilic molecules. We assessed the ability of azacitidine, decitabine, and, for comparison, gemcitabine, to interact with human nucleoside transporters (hNTs) in Saccharomyces cerevisiae cells (hENT1/2, hCNT1/2/3) or Xenopus laevis oocytes (hENT3/4). All three drugs inhibited hCNT1/3 potently (K (i) values, 3-26 μM), hENT1/2 and hCNT2 weakly (K (i) values, 0.5-3.1 mM), and hENT3/4 poorly if at all. Rates of transport of [(3)H]gemcitabine, [(14)C]azacitidine, and [(3)H]decitabine observed in Xenopus oocytes expressing individual recombinant hNTs differed substantially. Cytotoxicity of azacitidine and decitabine was assessed in hNT-expressing or hNT-deficient cultured human cell lines in the absence or presence of transport inhibitors where available. The rank order of cytotoxic sensitivities (IC (50) values, μM) conferred by hNTs were hCNT1 (0.1) > hENT1 (0.3) ≫ hCNT2 (8.3), hENT2 (9.0) for azacitidine and hENT1 (0.3) > hCNT1 (0.8) ⋙ hENT2, hCNT2 (>100) for decitabine. Protection against cytotoxicity was observed for both drugs in the presence of inhibitors of nucleoside transport, thus suggesting the importance of hNTs in manifestation of toxicity. In summary, all seven hNTs transported azacitidine, with hCNT3 showing the highest rates, whereas hENT1 and hENT2 showed modest transport and hCNT1 and hCNT3 poor transport of decitabine. Our results show for the first time that azacitidine and decitabine exhibit different human nucleoside transportability profiles and their cytotoxicities are dependent on the presence of hNTs, which could serve as potential biomarkers of clinical response.
authors.affiliation: Department of Oncology, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Vijaya L
authors.initials: VL
authors.lastname: Damaraju
authors.forename: Delores
authors.initials: D
authors.lastname: Mowles
authors.forename: Sylvia
authors.initials: S
authors.lastname: Yao
authors.forename: Amy
authors.initials: A
authors.lastname: Ng
authors.forename: James D
authors.initials: JD
authors.lastname: Young
authors.forename: Carol E
authors.initials: CE
authors.lastname: Cass
authors.forename: Zeen
authors.initials: Z
authors.lastname: Tong
mesh_terms: D000818:Animals; D001374:Azacitidine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000493:pharmacokinetics* / Q000633:toxicity*; D002250:Carbon Radioisotopes / Q000378:metabolism; D000077209:Decitabine; D003841:Deoxycytidine / Q000031:analogs & derivatives / Q000378:metabolism; D033721:Equilibrative Nucleoside Transporter 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D014316:Tritium / Q000378:metabolism; D014981:Xenopus; D000093542:Gemcitabine
chemical_list: D002250:Carbon Radioisotopes; D033721:Equilibrative Nucleoside Transporter 1; D026901:Membrane Transport Proteins; C438649:SLC29A1 protein, human; C065171:cif nucleoside transporter; D003841:Deoxycytidine; D014316:Tritium; D000077209:Decitabine; D001374:Azacitidine; D000093542:Gemcitabine