99mTc-Labelled Low Molecular Weight Inhibitors of Prostate-Specific Membrane Antigen

High morbidity and mortality rates of prostate cancer (PCa) determine the requirement of looking for new methods of its early diagnosis. Methods of nuclear medicine have a special place in addressing this problem as they allow functional, metabolic and other processes imaging in body, which occur during the cancer development. This approach supposes the use of radiopharmaceuticals (RP), which are capable of selective binding to a specific biological target, for example, prostate-specific membrane antigen (PSMA), which is known to be overexpressed in PCa. Current development of new radiotracers for PCa imaging is focused on low molecular weight PSMA inhibitors due to their high specific binding to PSMA and rapid urinary excretion. Technetium-99m remains the appropriate radionuclide for diagnostic studies due to its optimal nuclear properties, ease of production and versatile coordination chemistry. Therefore, single-photon emission computed tomography (SPECT) imaging with 99mTc-PSMA radioligands can be a cost effective alternative to PET with 68Ga- or 18F-labeled RP. The aim of this review is to summarize and analyze currently available data on 99mTc-labeled low molecular weight PSMA inhibitors for metastatic PCa imaging.