Site-specific conjugation of a radioiodinated phenethylamine derivative to a monoclonal antibody results in increased radioactivity localization in tumor

Abstract

The preparation of a novel radioiodination reagent, the (aminooxy)acetyl derivative of (p-[125]-iodophenyl)ethylamine, is described. Conventional radioiodination of proteins involves the formation of iodotyrosine residues, but for in vivo applications such as thyroid or stomach immunoscintigraphy, the susceptibility of these residues to tissue dehalogenases constitutes a serious disadvantage. Using our new compound, which has a particularly nonreactive aromatic ring, we confirm and extend studies published by other workers indicating the much greater in vivo stability of iodophenyl compounds compared to the more conventional iodophenolic ones. In addition, the aminooxy group of our reagent gives a stable and specific linkage to aldehyde groups formed by periodate oxidation on the sugar moiety of antibody molecules. In vitro, favorable binding activity and high stability was obtained with a (([125I]iodoaryl)amino)oxy labeled monoclonal antibody directed against carcinoembryonic antigen. In vivo, using paired labeling experiments in nude mice bearing colon carcinoma xenografts, the (([125I]iodoaryl)amino)oxy-MAb (MAb = monoclonal antibody) was compared with the same MAb 131I-labeled by conventional chloramine-T method. Tumor 125I concentration of (arylamino)oxy MAb (measured as percent injected dose per gram) was significantly higher as compared to values obtained with a conventionally labeled 131I antibody. Additionally, thyroid uptake, an indicator of iodine release from the antibody, was up to 25 times lower after injection of 125I-MAb obtained by the new method as compared to the conventionally iodinated 131I-MAb.

Noninternalizing Monoclonal Antibodies Are Suitable Candidates for 125I Radioimmunotherapy of Small-Volume Peritoneal Carcinomatosis

“…Methodologies aimed at producing residualizing peptides, which can be conjugated to mAbs before the iodination process, have been developed. In this case, catabolism produces iodinated residual peptides that are trapped within the lysosomes to increase tumor retention time (38)(39)(40)(41). However, with residualizing peptides tumor irradiation could be increased by a factor of 3-4, whereas in our study a 7.4-fold increase (i.e., from 15.1 to 111.6 Gy) was observed with noninternalizing mAbs in comparison to internalizing mAbs.…”

Site-Specifically Labeled Immunoconjugates for Molecular Imaging—Part 1: Cysteine Residues and Glycans

“…2o–p ) [ 88 ]. Kurth and colleagues applied this strategy to the development of a radioimmunotherapeutic agent, using an aminooxy-bearing, I-125-labeled iodophenyl construct and the mAb 35, which targets the Gold 3 epitope of the carcinoembryonic antigen [ 89 ]. The site-specifically labeled I-125 mAb 35 radioimmunoconjugates were synthesized in high specific activity and immunoreactivity and were shown to be highly stable.…”

Synthesis of Novel 1,4,7,10‐Tetraazacyclodecane‐1,4,7,10‐Tetraacetic Acid (DOTA) Derivatives for Chemoselective Attachment to Unprotected Polyfunctionalized Compounds

“…The oxime ligation denotes the highly selective reaction between an aminooxy component and aldehydes or methyl ketones [22] under formation of an oxime bond, which is known to be stable both in vitro and in vivo. [23] The reaction was shown to tolerate every free amino acid side chain except an N-terminal cysteine and found widespread use, for example, in the synthesis of template-assembled synthetic proteins, [24,25] radioactive labeled peptide conjugates, [23,26] cyclic peptides [27] and protein analogues. [28,29] The Cu I -catalyzed azide-alkyne cycloaddition is a catalyzed variant of the chemoselective Huisgen 1,3-dipolar cycloaddition [30][31][32][33] of an azide and an alkyne for the formation of a triazole which has found application in various developments in medicinal chemistry.…”