Clinical evaluation of [^99mTc]Tc-PSMA-P1: a promising SPECT radiotracer for prostate cancer imaging

This study aimed to design and synthesize a prostate-specific membrane antigen inhibitor (PSMA-P1) and to formulate a freeze-dried kit for radiolabeling with Technetium-99m (^99mTc) to improve prostate cancer detection. A molecular docking study was carried out to calculate affinity parameters against four targeted protein structures (PDB IDs: 2ZCH, 2XW1, 2OOT, and 2XV7) to provide a comprehensive understanding of ligand-receptor interactions, along with structural features of synthesized PSMA to explain their QSAR. PSMA-P1 was efficiently synthesized using solid-phase peptide synthesis (SPPS), which served as the basis for its chemical synthesis. The freeze-dried kit of PSMA-P1 was formulated for the easy preparation of [^99mTc]Tc-PSMA-P1 with high radiochemical purity (≥99%). [^99mTc]Tc-PSMA-P1 showed strong binding affinity (K _i = 69.14 μM) with PDB ID: 2OOT. The [^99mTc]Tc-PSMA-P1 demonstrated high stability (≥95% up to 4 h) in vitro in serum, hydrophilicity (log D _7.4 = -2.55 ± 0.130), and strong PSMA binding affinity (K _d = 16.14 ± 1.452 nM). The accumulation of [^99mTc]Tc-PSMA-P1 (1.68 ± 0.16% ID g^-1) was prominently observed at 4 h post-injection in the 22Rv1 tumor model. The co-injection of 2-PMPA significantly inhibited the uptake of [^99mTc]Tc-PSMA-P1 to PSMA-expressing tumors and tissues, indicating that PSMA selectively mediates these uptakes. The SPECT/CT results are consistent with the in vivo biodistribution. The first single-patient study further revealed that [^99mTc]Tc-PSMA-P1 is an efficient imaging agent for PSMA-expressing tumors. This will be a promising candidate for prostate cancer.