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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 99mTc-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 [99mTc(CO)3]+ core (L8-10), traditional NxSy-based chelating agents with varying charge and polarity for the 99mTc-oxo core (L11-18), and a 99mTc-organohydrazine-labeled radioligand (L19). 99mTc(I)-Tricarbonyl-labeled [99mTc]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 99mTc-labeled radiopharmaceuticals targeting PSMA.

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