Linker Manipulation with Beta3-Amino Acids Potentiates the Efficacy and Safety of PSMA Radiopharmaceuticals.

[177Lu]Lu-PSMA-617 has achieved remarkable efficacy in the targeted radionuclide therapy (TRT) of metastatic castration-resistant prostate cancer (mCRPC), yet challenges like salivary gland and renal toxicity remain. Linker manipulation is a well-established strategy to enhance the efficacy and safety of prostate-specific membrane antigen (PSMA)-targeting radioligands. Notably, beta (β)-amino acid moieties could improve in vivo pharmacological and pharmacokinetic profiles through modulating conformation, dynamics, and proteolytic susceptibility. Nevertheless, limited exploration of such moieties in PSMA-targeting radioligands has been reported. Therefore, this study first developed a series of novel PSMA-targeting radioligands through linker manipulation with beta3 (β3)-amino acids, aiming to potentiate the efficacy and safety. Preclinical evaluations showed that [68Ga]Ga-PSMA-HK4 outperformed [68Ga]Ga-PSMA-617 in tumor uptake, likely attributable to its optimized hydrophilicity and conformational flexibility. In a first-in-human trial involving 15 patients, [68Ga]Ga-PSMA-HK4 demonstrated reduced salivary gland uptake (reductions of 35.8% and 48.1%) compared to [18F]PSMA-1007. It also exhibited superior diagnostic accuracy for equivocal lesions. Notably, the tumor uptake of [68Ga]Ga-PSMA-HK4 in patients is overall higher than that of [68Ga]Ga-PSMA-617. These findings underscore β3-amino acid linker manipulation with β3-amino acids as an effective strategy to enhance the performance of PSMA-targeting radiopharmaceuticals, paving a new avenue for developing next-generation agents and improving the precision of PSMA-targeting TRT.