Influence of pretreatment with 3-amino-1-hydroxypropylidene-1,1-bisphosphonate (APB) on organ uptake of 211At and 125I-labeled amidobisphosphonates in mice

To minimize nontarget organ uptake in animals receiving radiolabeled amidobisphosphonates, the influence of pretreatment with cold 3-amino-1-hydroxypropylidene-1,1-bisphosphonate (APB, pamidronate) was studied. Three groups of animals were given pure 3-[125I]iodobenzamide-N-3-hydroxypropylidene-3,3-bisphosphonate (IBPB) and 3-[211At]astatobenzamide-N-3-hydroxypropylidene-3,3-bisphosphonate (ABPB) (control); co-injection of APB and IBPB/ABPB; and 1 h preinjection of APB followed by IBPB/ABPB, respectively. A significant reduction of uptake in normal tissue was observed, whereas the bone uptake remained constant at 35-50%ID/g tissue. This study suggests that co- or preinjection of pamidronate may reduce the normal organ radiation doses when using these radiohalogenated bisphosphonates for endoradiotherapeutic procedures.