Effect of Chelators on the Pharmacokinetics of 99mTc-Labeled Imaging Agents for the Prostate-Specific Membrane Antigen (PSMA)

Technetium-99m, the most commonly used radionuclide in nuclear medicine, can be attached to biologically important molecules through a variety of chelating agents, the choice of which depends upon the imaging application. The prostate-specific membrane antigen (PSMA) is increasingly recognized as an important target for imaging and therapy of prostate cancer (PCa). Three different Tc-99m-labeling methods were employed to investigate the effect of the chelator on the biodistribution and PCa tumor uptake profiles of 12 new urea-based PSMA-targeted radiotracers. This series includes hydrophilic ligands for radiolabeling with the [Tc-99m(CO)(3)](+) core (L8-L10), traditional NxSy-based chelating agents with varying charge and polarity for the Tc-99m-oxo core (L11-L18), and a Tc-99m-organohydrazine-labeled radioligand (L19). Tc-99m(I)-Tricarbonyl-labeled [Tc-99m]L8 produced the highest PSMA+ PC3 PIP to PSMA- PC3 flu tumor ratios and demonstrated the lowest retention in normal tissues including kidney after 2 h. These results suggest that choice of chelator is an important pharmacokinetic consideration in the development of Tc-99m-labeled radiopharmaceuticals targeting PSMA.