Synthesis and evaluation of ⁶⁸GaGa-/¹⁷⁷LuLu-PSMA-SCN as a novel prostate-specific membrane antigen-targeting agent for theranostics

Metastatic castration-resistant prostate cancer (mCRPC) is an advanced stage of prostate cancer. It is resistant to first-line prostate cancer treatments and poses a significant threat to men's health. The prostate-specific membrane antigen (PSMA)-targeting radiopharmaceutical ¹⁷⁷LuLu-PSMA-617 has been approved by the FDA in 2022 to treat PSMA-positive patients with mCRPC, demonstrating significant clinical benefits on patients. In this work, we introduced a chelator, p-SCN-Bn-DOTA, instead of DOTA for radiolabeling and constructed the radioligand, PSMA-SCN, and systematically evaluated its diagnostic and therapeutic performance in prostate cancer. Both molecular docking and cellular competitive inhibition assays indicated that the introduction of p-SCN-Bn-DOTA enhanced the binding affinity of PSMA-SCN for the target protein PSMA compared to PSMA-617. For diagnosis, ⁶⁸GaGa-PSMA-SCN was used to evaluate the tumor imaging capability and in vivo metabolic profiling by microPET/CT. Quantitative analysis of microPET images shows higher tumor uptake of ⁶⁸GaGa-PSMA-SCN (46.27 ± 0.45) and (31.15 ± 0.21)%ID·g^-1 than that of ⁶⁸GaGa-PSMA-617 (16.8 ± 0.98) and (13.38 ± 1.44)%ID·g^-1 in LNCaP and RM-1 (PSMA⁺) tumor-bearing mouse models, respectively. ⁶⁸GaGa-PSMA-SCN also has faster clearance rates in non-targeted organs. The possible reason is that the introduction of p-SCN-Bn-DOTA improves the affinity of PSMA-SCN to the targeting protein and has no significant effect on pharmacokinetic metabolism. For therapeutics, ¹⁷⁷LuLu-PSMA-SCN was used in the treatment of tumor-bearing mice to assess its inhibitory effect on tumor growth, and the results demonstrated a favorable safety profile. These results confirm that PSMA-SCN has significant advantages in the theranostics of prostate cancer in comparison with PSMA-617. In conclusion, both theoretical analysis and biological evaluation of the PSMA-targeting molecule PSMA-SCN confirm its potential value for the diagnosis and treatment of prostate cancer. All experimental procedures involving animals were conducted in strict accordance with the ethical guidelines of the Institute of Materia Medica, Chinese Academy of Medical Sciences (ethics approval No. 00002217).