In vitro evaluation of nucleoside transport inhibition in vivo

A method is described which permits rapid evaluation of the effects of nucleoside transport inhibitors on [3H]thymidine uptake into mouse whole blood cells. The uptake is measured after 15-20 sec by withdrawing 100 microliters of blood from the orbital sinus into microcapillary pipets that have been prelabeled with [3H]thymidine. Blood cells are rapidly separated from plasma by centrifugation through a layer of dibutyl phthalate using an Eppendorf microcentrifuge. The acid-soluble radio-activity associated with the cell pellet is then determined. Treatment of mice with the nucleoside transport inhibitors dipyridamole or p-nitrobenzylthioinosine 5'-monophosphate reduces uptake of the radioisotope into the cells. The assay allows for estimation of the dose- and time-effect relationships for inhibition of nucleoside transport by these agents. Advantages of the method are its simplicity, its speed, and the fact that the biological sample and drug are not diluted before measurement of the drug effect.