PT  - JOURNAL ARTICLE
AU  - Jing Zhang
AU  - Kyla M. Smith
AU  - Tracey Tackaberry
AU  - Frank Visser
AU  - Morris J. Robins
AU  - Lars P. C. Nielsen
AU  - Ireneusz Nowak
AU  - Edward Karpinski
AU  - Stephen A. Baldwin
AU  - James D. Young
AU  - Carol E. Cass
TI  - Uridine Binding and Transportability Determinants of Human Concentrative Nucleoside Transporters
AID  - 10.1124/mol.105.012187
DP  - 2005 Sep 01
TA  - Molecular Pharmacology
PG  - 830--839
VI  - 68
IP  - 3
4099  - http://molpharm.aspetjournals.org/content/68/3/830.short
4100  - http://molpharm.aspetjournals.org/content/68/3/830.full
SO  - Mol Pharmacol2005 Sep 01; 68
AB  - Human concentrative nucleoside transporters 1, 2, and 3 (hCNT1, hCNT2, and hCNT3) exhibit different functional characteristics, and a better understanding of their permeant selectivities is critical for development of nucleoside analog drugs with optimal pharmacokinetic properties. In this study, the sensitivity of a high-throughput yeast expression system used previously for hCNT1 and hCNT3 was improved and used to characterize determinants for interaction of uridine (Urd) with hCNT2. The observed changes of binding energy between hCNT2 and different Urd analogs suggested that it interacts with C(3′)-OH, C(5′)-OH, and N(3)-H of Urd. The C(2′) and C(5) regions of Urd played minor but significant roles for Urd-hCNT2 binding, possibly through Van der Waals interactions. Because the yeast assay only provided information about potential transportability, the permeant selectivities of recombinant hCNT1, hCNT2, and hCNT3 produced in Xenopus laevis oocytes were investigated using a two-electrode voltage clamp assay. hCNT1-mediated transport was sensitive to modifications of the N(3), C(3′), and C(5′) positions of Urd. hCNT2 showed some tolerance for transporting Urd analogs with C(2′) or C(5) modifications, little tolerance for N(3) modifications, and no tolerance for any modifications at C(3′) or C(5′) of Urd. Although hCNT3 was sensitive to C(3′) modifications, it transported a broad range of variously substituted Urd analogs. The transportability profiles identified in this study, which reflected the binding profiles well, should prove useful in the development of anticancer and antiviral therapies with nucleoside drugs that are permeants of members of the hCNT protein family.