Comparative studies of radiotracer citrates in oncological models--2. 153Sm-citrate and 67Ga-citrate

153Sm-citrate solutions were prepared from enriched 152Sm2O3 which had been irradiated at 10(12)n cm-2 s-1 in the University of Alberta Slowpoke reactor. 153Sm was rapidly bound (93% in 2 h) by Melanoma 2AB cells in tissue culture upon incubation in the presence of 153Sm-citrate (1.9 nmol 10(6) cells). In vitro ultracentrifugation studies of 153Sm-citrate solutions showed that colloid formation under incubation conditions could have been responsible in part for the uptake by cultured cells. Low uptakes (less than 1% in 2h) of 67Ga-citrate were seen under similar conditions. 153Sm-citrate injected into BDF1 mice (Lewis lung carcinoma) and Copenhagen x Fisher rats (Dunning R3327-H prostatic tumors) was concentrated mainly in the liver, with some tumor and bone uptake. The percent of injected dose per organ for 153Sm and 67Ga in the murine and rat models respectively, 24 h after i.v. dosing, was 17.2 +/- 4.7 and 2.0 +/- 0.6 (tumor), 63.9 +/- 7.9 and 14.4 +/- 1.4 (liver) and 0.6 +/- 0.1 and 1.3 +/- 0.1 (blood); % injected dose g-1 femur was 6.2 +/- 2.7 and 12.9 +/- 2.7, respectively. Scintigrams of rats showed qualitative biodistributions similar to the quantitative mouse data obtained by dissection studies. The high hepatic uptake detracted from the otherwise superior tumor localization of 153Sm-citrate when compared to 67Ga-citrate in these models. The murine Lewis lung tumor index (% injected dose g-1 tumor x tumor: blood) was 303.6 for 153Sm-citrate and 48.9 for 67Ga-citrate, 24 h after injection.