Synthesis and evaluation of novel bifunctional chelating agents based on 1,4,7,10-Tetraazacyclododecane-N,N′,N″,N‴-Tetraacetic acid for radiolabeling proteins

Detailed synthesis of the bifunctional chelating agents 2-methyl-6-(p-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7, 10-tetraacetic acid (1B4M-DOTA) and 2-(p-isothiocyanatobenzyl)-5, 6-cyclohexano-1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetate (CHX-DOTA) are reported. These chelating agents were compared to 2-(p-isothiocyanatobenzyl)-1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid (C-DOTA) and 1, 4, 7, 10-Tetraaza-N-(1-carboxy-3-(4- nitrophenyl)propyl)-N′, N″, N‴-tris(acetic acid) cyclododecane (PA-DOTA) as their ¹⁷⁷Lu radiolabeled conjugates with Herceptin™. In vitro stability of the immunoconjugates radiolabeled with ¹⁷⁷Lu was assessed by serum stability studies. The in vivo stability of the radiolabeled immunoconjugates and their targeting characteristics were determined by biodistribution studies in LS-174T xenograft tumor-bearing mice. Relative radiolabeling rates and efficiencies were determined for all four immunoconjugates. Insertion of the 1B4M moiety into the DOTA backbone increases radiometal chelation rate and provides complex stability comparable to C-DOTA and PA-DOTA while the CHX-DOTA appears to not form as stable a ¹⁷⁷Lu complex while exhibiting a substantial increase in formation rate. The 1B4M-DOTA may have potential for radioimmunotherapy applications. Published by Elsevier Inc. All rights reserved.