Electrogenic uptake of nucleosides and nucleoside‐derived drugs by the human nucleoside transporter 1 (hCNT1) expressed in Xenopus laevis oocytes

Abstract

The concentrative pyrimidine-preferring nucleoside transporter 1 (hCNT1), cloned from human fetal liver, was expressed in Xenopus laevis oocytes. Using the two-electrode voltage-clamp technique, it is shown that translocation of nucleosides by this transporter generates sodium inward currents. Membrane hyperpolarization (from 3 350 to 3 3150 mV) did not affect the K 0X5 for uridine, although it increased the transport current approximately 3-fold. Gemcitabine (a pyrimidine nucleoside-derived drug) but not fludarabine (a purine nucleosidederived drug) induced currents in oocytes expressing the hCNT1 transporter. The K 0X5 value for gemcitabine at 3 350 mV membrane potential was lower than that for natural substrates, although this drug induced a lower current than uridine and cytidine, thus suggesting that the affinity binding of the drug transporter is high but that translocation occurs more slowly. The analysis of the currents generated by the hCNT1-mediated transport of nucleoside-derived drugs used in anticancer and antiviral therapies will be useful in the characterization of the pharmacological profile of this family of drug transporters and will allow rapid screening for uptake of newly developed nucleoside-derived drugs. ß

Nucleoside transporters in chronic lymphocytic leukaemia

“…The latter show significantly lower affinities for substrates than CNTs and may be reversible depending on how the substrate concentration gradients change across the plasma membrane. Substrate selectivity and their pharmacological profiles, [35][36][37][40][41][42][43] still incomplete, are summarized in Table 2.…”

“…A similar specificity profile seems to apply to cladribine. 41,46,47 Which nucleoside transporters do CLL cells express?…”

“…This is relevant because this transporter is responsible for the high-affinity uptake of various fluoropyrimidines, including the capecitabine intermediate 5 0 -deoxy-5-fluorouridine (5-DFUR), a direct precursor of the anticancer drug 5-fluorouracil (5-FU). 41,43 Leukaemia cell lines such as NB4, Raji and BLS1 also show a Na-dependent, guanosine preferring, nucleoside transport activity that appears to be highly sensitive to inhibition by the analogue NBTI, 47,56,57 a unique property among putative CNT transporters. Nevertheless, no cDNA related to this transport activity has been isolated so far and there is no evidence that additional SLC28 members remain to be discovered.…”

Polymorphisms in ABCG2, ABCC3 and CNT1 genes and their possible impact on chemotherapy outcome of lung cancer patients

“…The distribution of the genotypes of the SNPs analyzed is given in Table III (28), paclitaxel (2), tomudex (2), ifosamid (44), cyclophosphamide (1), doxorubincine (27), topotecan (5) as well as undisclosed drugs (7), that were given as part of a clinical trial. previously published for Caucasians by other groups.…”

“…25 Gemcitabine, which is frequently used in the treatment of NSCLC, is also a substrate of CNT1. 26,27 In some gynaecological tumors, the expression of CNT1 was found to be reduced, and this reduction of CNT1 protein was correlated with poor prognosis. 28 The SNP G565A results in reduced affinity for gemcitabine.…”