Influence of different 99mTc cores on the physicochemical and biodistribution behaviours of 99mTc-labelled complexes of pamidronate dithiocarbamate

This study sought to evaluate the impact of (TcO)-Tc-99m and (99m) N cores on the physicochemical and biodistribution properties of Tc-99m-labelled complexes of pamidronate dithiocarbamate. We successfully converted the commercially available pamidronate to pamidronate dithiocarbamate (PAMDTC) and its Tc-99m-labelled complexes were prepared with high radiochemical yield (97.95 +/- 0.59% and 97.66 +/- 1.53% for (TcN)-Tc-99m-PAMDTC and (TcO)-Tc-99m-PAMDTC, respectively). Both complexes were stable in vitro. The partition coefficient results showed that both of them were hydrophilic and (TcN)-Tc-99m-PAMDTC exhibited more hydrophilic than (TcO)-Tc-99m-PAMDTC. The binding rate of (TcN)-Tc-99m-PAMDTC to human serum albumin was lower than that of (TcO)-Tc-99m-PAMDTC. (TcN)-Tc-99m-PAMDTC performed better affinity to hydroxyapatite than (TcO)-Tc-99m-PAMDTC. From the biodistribution study results, (TcN)-Tc-99m-PAMDTC showed higher bone uptake and ratios of bone/blood and bone/muscle at 4 h post-injection. Further, single photon emission computed tomography (SPECT) imaging study of (TcN)-Tc-99m-PAMDTC showed that there was a clear accumulation in bone, suggesting it would be a potential novel bone imaging agent. It was concluded that different Tc-99m cores had an important impact on the physicochemical and biological properties of Tc-99m-labelled complexes of pamidronate dithiocarbamate.