PSMA inhibitors(Alpha-9 Theranostics)

CTT1403 (¹⁷⁷Lu-CTT2001), an irreversible phosphoramidate PSMA inhibitor developed by Cancer Targeted Technology, was initially synthesized using a two-step radiolabeling method and has previously been evaluated in first-in-human studies. This two-step approach protected the phosphoramidate pharmacophore-containing a temperature- and pH-labile PN bond-from the harsh conditions required for lutetium-177 (¹⁷⁷Lu) chelation. Although the final chemical structure of CTT1403 is identical regardless of the radiolabeling route, it was not clear that CTT2001 could tolerate one-step labeling conditions while preserving PSMA-binding integrity. Therefore, the aim of the study was to develop, optimize, and automate a one-step radiolabeling method for CTT1403 and to confirm that the resulting product is biologically equivalent and exhibits comparable in vitro and in vivo behavior to CTT1403 produced by the original two-step process.

CTT2001 was synthesized and radiolabeled with ¹⁷⁷Lu using an optimized one-step procedure that was subsequently automated on a Trasis AllinOne synthesizer. Radiochemical purity, stability, cellular uptake/internalization, and biodistribution in PC3-PIP tumor-bearing mice were evaluated.

CTT1403 synthesized via the one-step method demonstrated cellular uptake and internalization in PC3-PIP cells, as well as in vivo biodistribution in PC3-PIP tumor-bearing mice, that were comparable to those of the two-step-labeled product. The one-step procedure was successfully automated on the Trasis All-in-One synthesizer, producing CTT1403 with a radiochemical yield of 86.5 ± 4.27% (n = 3), a molar activity of 30.3 ± 1.11 MBq/nmol, and a radiochemical purity of 97.6 ± 0.80% (n = 3) in a total synthesis time of 38 min. The final product remained stable for at least 24 h at -4 °C and -20 °C.

The one-step radiolabeling method yields CTT1403 that is biologically equivalent to the two-step product and can be reliably produced using fully automated synthesis. This streamlined, efficient, and reproducible approach supports routine clinical manufacturing of CTT1403.