Synthesis And Evaluation Of Tc-99m-Tricabonyl Labeled Isonitrile Conjugates For Prostate-Specific Membrane Antigen (Psma) Image

Prostate-specific membrane antigen (PSMA) is a biomarker expressed on the surface of prostate cancer (PCa). In an effort to improve the detection and treatment of PCa, small urea-based PSMA inhibitors have been studied extensively. In the present study, we aimed to develop Tc-99m-tricabonyl labeled urea-based PSMA conjugates containing isonitrile (CN-R)-coordinating ligands ([Tc-99m]Tc-15 and [Tc-99m]Tc-16). Both the PSMA conjugates were obtained at high radiochemical efficiency (>= 98.5%). High in vitro binding affinity was observed for [Tc-99m]Tc-15 and [Tc-99m]Tc-16 (K-d = 5.5 and 0.2 nM, respectively) in PSMA-expressing 22Rv1 cells. Tumor xenografts were conducted using 22Rv1 cells and rapid accumulation of [Tc-99m]Tc-16 (1.87 +/- 0.11% ID/g) was observed at 1 h post-injection, which subsequently increased to (2.83 +/- 0.26% ID/g) at 4 h post-injection. However, [Tc-99m]Tc-15 showed moderate tumor uptake (1.48 +/- 0.18% ID/g), which decreased at 4 h post-injection (0.81 +/- 0.09% ID/g). [Tc-99m]Tc-16 was excreted from non-targeted tissues with high tumor-to-blood (17:1) and tumor-to-muscle ratio (41:1) at 4 h post-injection at approximately 4 times higher levels than [Tc-99m]Tc-15. Uptakes of [Tc-99m]Tc-15 and [Tc-99m]Tc-16 to PSMA-expressing tumor and tissues were significantly blocked by co-injection of 2-(Phosphonomethyl)-pentandioic acid (2-PMPA), suggesting that their uptakes are mediated by PSMA specifically. Whole-body single photon emission computed tomography imaging of [Tc-99m]Tc-16 verified the ex vivo biodistribution results and demonstrated clear visualization of tumors and tissues expressing PSMA compared to [Tc-99m]Tc-15. In conclusion, using [Tc-99m]Tc-16 rather than [Tc-99m]Tc-15 may be the preferable because of its relatively high tumor uptake and retention.