The influence of substituents in 99mTc-benzylidenediphosphonate complexes on their organ distribution in rats

The biodistribution of a series of new 99mTc-benzylidenediphosphonate complexes (99mTc-BDP) in rats was found to vary considerably with substituents in the alpha (X) and para (R) position of the BDP ligands. From the in vivo behaviour of the 99mTc-BDP complexes the following conclusions could be drawn: 1. the blood clearance was accelerated by X = NH2; 2. the kidney uptake was decreased by X = OH; 3. the bone uptake was enhanced by X = OH and R = OH; and 4. R = Cl retarded the blood clearance, increased the kidney and lowered the bone uptake. A subcutaneously transplantable osteosarcoma was tested with 99mTc-BDP complexes as a bone lesion model. Although rapidly growing the osteosarcoma accumulated less activity than the femur diaphysis. The small amount of binding sites in the tumor tissue for osteotropic radiopharmaceuticals was attributed to the formation of necroses.