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

We report the characterization and evaluation of a novel Zr-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 -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-huA33) with equivalent antigen binding affinity to its parent immunoglobulin but attenuated affinity for the FcγRI receptor. This construct was subsequently radiolabeled with [Zr]Zr to create a radioimmunoconjugate - [Zr]Zr-DFO-huA33 - in high yield and specific activity that exhibited excellent behavior in two murine models of human colorectal carcinoma.