Preparation, in vitro evaluation, and biodistribution study of a novel PSMA-targeted radioligand

PSMA-617, the benchmark PSMA ligand widely used in targeted radionuclide therapy for prostate cancer (PCa), is limited by dose-dependent toxicity to key organs including the kidneys and salivary glands. In this study, a series of novel linker-modified compounds (P-1 to P-6) was rationally designed and synthesized to improve the therapeutic window. Using PSMA-617 as a positive control, systematic in vitro evaluations were performed for P-1 to P-6. All compounds exhibited strong hydrophilicity, good cellular internalization rates and plasma stability (half-life >48 h), but differed in enzyme inhibitory activity and cell-binding affinity. Compound P-6 exhibited in vitro activity comparable to that of PSMA-617, with a higher internalization (7.04% vs 5.17%) in LNCaP C42B cells, and therefore was selected for in vivo validation. In LNCaP PSMA-positive tumor-bearing mice, tumor uptake of ¹⁷⁷Lu-P-6 was significantly higher than that of ¹⁷⁷Lu-PSMA-617 at both 24 h post-injection (p.i.) (31.36 ± 7.42 vs 24.20 ± 3.20% ID/g) and 72 h p.i. (23.05 ± 5.15 vs 13.66 ± 4.50% ID/g). At 4 h p.i., renal exposure of ¹⁷⁷Lu-P-6 was markedly lower than that of ¹⁷⁷Lu-PSMA-617 (4.66% ID/g vs 6.90% ID/g). The tumor-to-kidney (T/K) ratios of ¹⁷⁷Lu-P-6 at 4 h p.i. and 72 h p.i. were significantly higher than those of PSMA-617 (10.80 vs 8.10 and 51.29 vs 47.18, respectively). Moreover, accumulation in salivary glands and blood was lower for ¹⁷⁷Lu-P-6. In conclusion, through linker optimization, ¹⁷⁷Lu-P-6 achieves dual advantages of higher tumor retention and lower renal exposure while maintaining PSMA potency, demonstrating clear clinical translation potential.