Uptake of Tc-99m monophosphate complexes in bone and myocardial necrosis in animals

Bidentate monophosphates--phosphonoacetate (PAA), 2-phosphonoproprionate (PPA), 2-methyl-2-phosphonoproprionate (MPPA), and carbamyl phosphate (CAP)--which are pyrophosphate analogs, were successfully labeled with Sn(II)-reduced [99mTc] pertechnetate in high yield (greater than 95%). Biodistribution studies show that these Tc-99m-labeled monophosphates do localize in bone. At 2 hr after injection, Tc-99m CAP has average femur uptakes of 1.9% in rats and 2.9% in rabbits, which correspond to calculated total-bone uptakes of 38% and 58%, respectively. These are comparable with the femur uptakes for Tc-99m methylene diphosphonate (MDP), which are 1.8% in rats and 2.7% in rabbits. However, the blood clearance rate for Tc-99m CAP was slower than that observed for Tc-99m MDP making the former less desirable for use as a bone-scanning agent. The femur uptakes for Tc99m PAA are 0.9% in rats and 1.2% in rabbits, corresponding to 18% and 24% in total bone, respectively. The PAA derivatives PPA and MPPA have much lower bone uptake. Technetium-99m CAP also concentrates in necrotic myocardium in rats, in amounts comparable to Tc-99m pyrophosphate.