An enzyme-mediated methodology for the site-specific radiolabeling of antibodies based on catalyst-free click chemistry

Objectives To develop an enzyme- and click chemistry-mediated methodology for the site-specific radiolabeling of antibodies on the heavy chain glycans. Such constructs would suffer neither from the reduced immunoreactivity nor the somewhat inadequate chemical definition due to superfluous binding in the antigen-binding site that often occurs with traditional amino acid residue reaction based binding.

Methods The methodology consists of four steps: (1) removal of sugars on the heavy chain region to expose terminal N-acetylglucosamine residues; (2) incorporation of an azide-modified N-acetylgalactosamine sugar into the antibody glycans; (3) click conjugation of a desferrioxamine-modified dibenzocyclooctyne to the azido-labeled sugar; and (4) radiolabeling with 89Zr.

Results The site-specifically labeled radioimmunoconjguates displayed high immunoreactivity in vitro (>95%) in addition to high specific tumor uptake (67.5 ± 5.0 %ID/g) and tumor-to-background contrast in athymic nude mice bearing PSMA-expressing subcutaneous LNCaP xenografts.

Conclusions Ultimately, this strategy could play a critical role in the development of novel well-defined and highly immunoreactive radioimmunoconjugates for both the laboratory and clinic.

Research Support This work received financial support from the NIH (1F32CA1440138-01, BMZ) and the DOE (DE-SC0002184, JSL). Services provided by the MSKCC Small-Animal Imaging Core Facility were supported in part by NIH grants R24-CA83084 and P30-CA08748.