Drug-induced perturbations in the in vivo distribution of oncological radiotracers--II. 5-[125I]iodo-2'-deoxyuridine influenced by nitrobenzylthioinosine-5'-phosphate (NBMPR-P) and acyclothymidine (ACT).
Nitrobenzylthioinosine (NBMPR), a potent inhibitor of facilitated nucleoside transport in vitro and in vivo, and acyclothymidine (ACT), a potent inhibitor of pyrimidine nucleoside phosphorylase in vitro, have been used in an attempt to modulate the biodistribution of 125I-labelled iododeoxyuridine ([125I]IUdR). ACT or NBMPR-P (a water-soluble prodrug of NBMPR) were injected into BDF1 mice bearing implanted Lewis lung tumors, according to protocols which would provide high and low plasma levels of the inhibitor. Compared with controls, both inhibitors induced transient, marginal increases in hepatic, renal and blood levels of [125I]IUdR, and decreased levels in tumors at short time intervals after injection. It is concluded that there is a mild tumor-sparing effect when either NBMPR or ACT are administered together with single i.v. diagnostic doses of [125I]IUdR.