NBMPR( NBTI) is a nucleoside analog that competitively inhibits the equilibrative nucleoside transporter 1 (Kd = 0.1-1.0 nM, IC50s = 4.6 and 3.6 nM in rat and human, respectively).NBMPR is routinely used at concentrations of 0.10 μM and 0.10 mM to specifically inhibit transport of nucleosides mediated by equilibrative nucleoside transporters 1 (ENT1) and 2 (ENT2), respectively. NBMPR at a concentration of 0.10 mM abolishes ABCG2 activity.