Interaction of Cladribine and Fludarabine with Genetic Variants in the Concentrative Nu- Cleoside

INTERACTION OF CLADRIBINE AND FLUDARABINE WITH GENETIC VARIANTS IN THE CONCENTRATIVE NUCLEOSIDE TRANSPORTER, CNT3. I. Badagnani, PharmD, and K. M. Giacomini, PhD, Department of Biopharmaceutical Sciences, University of California, San Francisco, CA. The concentrative nucleoside transporter, CNT3 (SLC28A3), mediates the intracellular uptake of the anti-cancer nucleoside analogs, cladribine and fludarabine. Wide variation in intracellular levels of these analogs has been described. To test the hypothesis that coding variants in CNT3 may contribute to this phenotype, we identified and functionally tested missense variants of CNT3. Ten missense variants were found in a collection of 256 ethnically diverse DNA samples; three of these had total allele frequencies 1%. The activity of the missense variants was determined by isotopic uptake of model nucleosides in X. laevis oocytes expressing the CNT3 variants. The rare variant, CNT3-G R, showed an 85% and 83% reduction in the transport of inosine and thymidine, respectively. All other variants had similar activity as the reference. There was no difference in the interaction kinetics of the three common variants with adenosine when compared to reference (Km 69 11, 91 24, 78 9, 94 3 M for CNT3, CNT3-S N, -Y C and -I V, respectively). These studies indicate that common missense variants of CNT3 have similar activities as the reference and suggest that they do not contribute to variation in intracellular levels of nucleosides and nucleoside analogs. Studies are underway to assess the interaction kinetics of nucleoside analogs with the common CNT3 variants and to test whether variation in CNT3 expression contributes to variation in intracellular levels of nucleoside analogs.