Site-selective radiolabeling using mushroom tyrosinase and the strain-promoted oxidation-controlled 1,2-quinone...

We report the in vitro characterization and in vivo evaluation of a novel ⁸⁹Zr-labeled radioimmunoconjugate synthesized using a site-selective bioconjugation strategy based on the oxidation of tyrosinase residues exposed by the deglycosylation of the IgG and the subsequent strain-promoted oxidation-controlled 1,2-quinone cycloaddition between these amino acids and trans-cyclooctene-bearing cargoes. More specifically, we site-selectively modified a variant of the A33 antigen-targeting antibody huA33 with the chelator desferrioxamine (DFO), thereby producing an immunoconjugate (DFO-^SPOCQhuA33) with equivalent antigen binding affinity to its parent immunoglobulin but attenuated affinity for the FcγRI receptor. This construct was subsequently radiolabeled with [⁸⁹Zr]Zr⁴⁺ to create a radioimmunoconjugate - [⁸⁹Zr]Zr-DFO-^SPOCQhuA33 - in high yield and specific activity that exhibited excellent in vivo behavior in two murine models of human colorectal carcinoma.