RT Journal Article SR Electronic T1 A Comparison of the Transportability, and Its Role in Cytotoxicity, of Clofarabine, Cladribine, and Fludarabine by Recombinant Human Nucleoside Transporters Produced in Three Model Expression Systems JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 346 OP 353 DO 10.1124/mol.105.015768 VO 69 IS 1 A1 Karen M. King A1 Vijaya L. Damaraju A1 Mark F. Vickers A1 Sylvia Y. Yao A1 Thach Lang A1 Tracey E. Tackaberry A1 Delores A. Mowles A1 Amy M. L. Ng A1 James D. Young A1 Carol E. Cass YR 2006 UL http://molpharm.aspetjournals.org/content/69/1/346.abstract AB 2-Chloro-9-(2′-deoxy-2′-fluoro-β-d-arabinofuranosyl)adenine (Cl-F-ara-A, clofarabine), a purine nucleoside analog with structural similarity to 2-chloro-2′-deoxyadenosine (Cl-dAdo, cladribine) and 9-β-d-arabinofuranosyl-2-fluoroadenine (F-ara-A, fludarabine), has activity in adult and pediatric leukemias. Mediated transport of the purine nucleoside analogs is believed to occur through the action of two structurally unrelated protein families, the equilibrative nucleoside transporters (ENTs) and the concentrative nucleoside transporters (CNTs). The current work assessed the transportability of Cl-F-ara-A, Cl-dAdo, and F-ara-A in cultured human leukemic CEM cells that were either nucleoside transport-defective or possessed individual human nucleoside transporter types and in Xenopus laevis oocytes and Saccharomyces cerevisiae yeast that produced individual recombinant human nucleoside transporter types. Cells producing hENT1 or hCNT3 exhibited the highest uptake of Cl-F-ara-A, whereas nucleoside transport-deficient cells and cells producing hCNT1 lacked uptake altogether. When Cl-F-ara-A transport rates by hENT1 were compared with those of Cl-dAdo and F-ara-A, Cl-dAdo had the highest efficiency of transport, although Cl-F-ara-A showed the greatest accumulation during 5-min exposures. In cytotoxicity studies with the CEM lines, Cl-F-ara-A was more cytotoxic to cells producing hENT1 than to the nucleoside transport-deficient cells. The efficiency of Cl-F-ara-A transport by oocytes with recombinant transporters was hCNT3 > hENT2 > hENT1 > hCNT2; no transport was observed with hCNT1. Affinity studies with recombinant transporters produced in yeast showed that hENT1, hENT2, and hCNT3 all had higher affinities for Cl-F-ara-A than for either Cl-dAdo or F-ara-A. These results suggest that the nature and activity of the plasma membrane proteins capable of inward transport of nucleosides are important determinants of Cl-F-ara-A activity in human cells.