Assay for inhibitors of equilibrative or concentrative nucleoside transporters

A method for identifying an agent as an inhibitor of an equilibrative nucleoside transporter (ENT) comprising

• contacting a recombinant yeast, in the presence of a cytotoxic nucleoside and in a yeast culture medium with the agent for a first time period under conditions permitting yeast growth,
• wherein the cytotoxic nucleoside is present in the yeast growth medium at a level which has been predetermined to be a minimum concentration of cytotoxic nucleoside that causes complete killing of the recombinant yeast,
• and wherein the recombinant yeast comprises a deletion of a yeast de novo purine biosynthetic pathway gene in a genome thereof and expresses a heterologous equilibrative nucleoside transporter (ENT), wherein the gene is a fuil gene or Saccharomyces cerevisiae ADE4;
• ADE5;
• ADE7;
• ADE8;
• ADE6;
• ADE1;
• ADE2;
• ADE13;
• ADE16;
• ADE17;
• or ADE12 gene:
• quantifying the growth of the recombinant yeast in the presence of the agent;
• comparing the growth of the recombinant yeast in the presence of the agent to the growth of the recombinant yeast for a second predetermined time period in the absence of the agent;
• and
• identifying the agent as an inhibitor or not of the ENT,
• wherein an increased growth in the presence of the agent as compared to in the absence of the agent indicates that the agent is an inhibitor of the ENT, and wherein no growth in the presence of the agent as compared to in the absence of the agent indicates that the agent is not an inhibitor of the ENT.