Fig. 4. In vivo evaluation of [²²³Ra][Ra(macropa)]. (a) [²²³Ra]RaCl₂ and (b) [²²³Ra][Ra(macropa)] radioactive organ distribution (% injected activity normalized to weight; % IA per g) was assessed utilizing healthy, skeletally mature mice sacrificed at 15 min and 24 h p.i. Differences in splenic, renal, and bone uptake were observed between the two groups. (c) Mice administered [²²³Ra][Ra(macropa)] exhibited 10 to 25-fold lower osseous uptake than that of free ²²³Ra at 15 min and 24 h p.i. (**p = 0.0096; ****p < 0.0001).