/sup 99m/Tc-labeled nucleotides as tumor-seeking radiodiagnostic agents

Several lines of human tumor cells in monolayer and soft agar cultures allow permeation of low levels of adenine nucleotides through their plasma membranes, while, in general, untransformed cells do not incorporate adenine nucleotides into their cellular pools without prior degradation of the nucleotides to adenosine. This study determined the uptake of /sup 99m/Tc-radiolabeled chelated forms of adenine nucleotides, /sup 99m/Tc-Ap4A (diadenosine 5',5''',P1,P4-tetraphosphate) and /sup 99m/Tc-ATP chelates as radiodiagnostic agents suitable for the in vivo detection of tumors by radionuclide imaging. Biodistribution studies revealed that Ap4A accumulated preferentially in RT-24 tumors implanted in rats and that V2 carcinoma implanted in rabbits could be readily visualized by in vivo imaging. The biodistribution at various time points showed increased tumor-to-muscle ratios after /sup 99m/Tc-Ap4A or /sup 99m/Tc-ATP injections when compared with a nonspecific marker of the extracellular fluid space, /sup 99m/Tc-labeled diethylenetriaminepentaacetic acid and with an agent known to localize in some tumors, 67Ga-labeled citrate. Studies of ectoenzymatic activities of virus-transformed animal cells and their untransformed counterparts in monolayer cultures showed marked decreases in the ectoenzymatic activities that degrade Ap4A in the transformed cells. Incorporation of en bloc [3H, 32P]Ap4A into cellular acid-soluble nucleotide pools of certain transformed cells was observed. Normal untransformed cells incorporated the radioactive label only by prior degradation to [3H]adenosine and 32P/sub i/. 19 references, 2 figures, 3 tables