67Ga-Citrate and 1251-lododeoxyuridine as Markers for In Vivo Evaluation of

uridine (125IUDR) and gallium-67 (67Ga).citrate before transplantation into new, nonradioactive hosts. The fate of the labeled cells and their progeny was monitored at daily intervals by measuring the retention of radioactive iodine (1251) and 67Ga in live mice in a well-type crystal scintillation counter. The excretion of 1251 from the test animals was taken as an index of tumor cell death in vivo and the anatomic distribution of 1251UDR was linked to the organ distribution of the labeled cells. While 1251 from dying cells was rapidly excreted from the test animals, large fractions of the 67Ga activity released by cell death and a slight leakage of 67Ga out of living cells were reutilized in various tissues of the hosts. Attempts to accelerate 67Ga clearance from animals by administration of stable gallium or scandium were only marginally successful. Consequently, the rate of 67Ga excretion from tumor-bearing mice did not constitute a measure of the rate of tumor cell death in vivo, and the organ distribution of 67Ga activity did not provide an accurate index of tumor cell metastasis. The shortcomings of 67Ga, although not precluding its use as a medical tumor-scanning agent, suggest that 67Ga is a poor tracer for quantitating the precise magnitude of neoplastic involvement and metastatic spread.-J Natl Cancer Inst 50: 1039-1045,1973. CARRIER-FREE gallium-67 (67Ga) concentrates in a variety of human and animal tumors (1-4)