Significant Antitumor Effect from Bone-seeking, -Particle-emitting 223Ra Demonstrated in an Experimental Skeletal Metastases Model1

The therapeutic efficacy of the -particle-emitting radionuclide 223Ra (t1/2 11.4 days) in the treatment against experimental skeletal metasta-ses in rats was addressed. Biodistribution studies, involving measurement of 223Ra in bone marrow samples, were performed in rats after i.v. injection. To study the therapeutic effect of 223Ra, an experimental skel-etal metastases model in nude rats was used. Animals that had received 106 MT-1 human breast cancer cells were treated with 223Ra doses in the range of 6–30 kBq after 7 days. The biodistribution experiment demon-strated that 223Ra was selectively concentrated in bone as compared with soft tissues. The femur content of 223Ra was 800 56 % of injected dose per gram tissue times gram body weight (b.w.; mean SD) 1 day after the injection and 413 23 % of injected dose per gram tissue times gram b.w. at 14 days. The femur:kidney ratio increased from (5.9 2.0)102 at 1 day to (7.2 3.0)102 at 14 days, whereas the femur:liver ratio increased fro