Evaluation and an Exploratory Human Study of 99mTc-Labeled PSMA-Targeting Agents with Reduced Renal Uptake via Proline Incorporation

Excessive renal uptake of prostate-specific membrane antigen (PSMA)-targeted radiopharmaceuticals remains a major challenge in prostate cancer (PCa) detection and therapy. We developed 99mTc-labeled PSMA radioligands incorporating d- or l-proline as a conformationally constrained linker combined with optimized co-ligands to reduce kidney accumulation. The resulting hydrophilic complexes achieved high radiochemical yields and strong in vitro stability. The optimal radiotracer, [99mTc]Tc-L-M1, exhibited high LNCaP (PSMA++) cell affinity (Kd = 19.09 nM) and the lowest kidney uptake (6.50 ± 0.32% ID/g, Kunming mice, 2 h p.i.). It accumulated effectively in both LNCaP (PSMA++) and 22Rv1 (PSMA+) tumors with excellent target-to-nontarget ratios and strong PSMA specificity. SPECT/CT imaging confirmed low renal accumulation, consistent with biodistribution data. Preliminary clinical trials demonstrated clear delineation of small PCa lesions, highlighting [99mTc]Tc-L-M1 as a promising PSMA-specific radiotracer with reduced kidney uptake for clinical application.