Human equilibrative nucleoside transporter-1 (hENT1) is required for the transcriptomic response of the nucleoside-derived drug 5′-DFUR in breast cancer MCF7 cells

Nucleoside analogues are broadly used in cancer treatment. Although nucleoside metabolism is a necessary step in the development of their cytotoxicity, mediated transport across the plasma membrane might be needed for nucleoside-derived drugs to exert their pharmacological action. In this study, we have addressed the question of whether particular plasma membrane transporters contribute to the transcriptomic response associated with nucleoside-derived drug therapy. Firstly, we have characterized the nucleoside transporters responsible for 5′-DFUR uptake into the breast cancer cell line MCF7. 5′-DFUR is the immediate precursor of 5-FU and a metabolite of the orally administered pro-drug capecitabine, currently used in the treatment of breast cancer and other solid tumors. Although 5′-DFUR is a substrate for both plasma membrane equilibrative nucleoside carriers, hENT1 shows higher affinity for this molecule than hENT2. Inhibition of hENT1 function partially protected MCF7 cells from 5′-DFUR-induced cytotoxicity. Secondly, we have used a pharmacogenomic approach to determine how inhibition of hENT1 function contributes to the transcriptomic response associated to 5′-DFUR treatment. Under hENT1 inhibition most of the transcriptional targets of 5′-DFUR action, which were genes associated with apoptosis and cell cycle progression were blocked. This study demonstrates that although 5′-DFUR is substrate for both equilibrative nucleoside carriers, hENT1 function is essential for the full transcriptional response to 5′-DFUR treatment.