Monoclonal antibodies (mAbs), immunoglobulin fragments, and other proteins are important scaffolds in the development of radiopharmaceuticals for diagnostic immuno-positron emission tomography (immuno-PET) and targeted radioimmunotherapy (RIT). Conventional methods for radiolabelling proteins with metal ions such as 68Ga, 64Cu, 89Zr, and 90Y require multi-step procedures involving pre-purification, functionalisation with a chelate, and subsequent radiolabelling. Standard coupling chemistries are time-consuming, difficult to automate, and involve synthesis, isolation, and storage of an intermediate, new molecular entity (the conjugated mAb) whose biochemical properties can differ from those of the parent protein. To circumvent these issues, we developed a photoradiochemical approach that uses fast, chemoselective, light-induced protein modification under mild conditions with novel metal-ion-binding chelates derivatised with aryl azide (ArN3) groups. Experiments show that one-pot photochemical conjugation and radiolabelling of formulated mAbs can be achieved in <20 min.

A method for the simultaneous (one-step) photochemical conjugation and 89 Zr-radiolabeling of antibodies is introduced. A photoactivatable chelate based on the functionalization of desferrioxamine B with an arylazide moiety (DFO-ArN 3 , [1]) was synthesized. The radiolabeled complex, 89 Zr-1 + , was produced and characterized. Density functional theory calculations were used to investigate the mechanism of arylazide photoactivation. 89 Zr-radiolabeling experiments were also used to determine the efficiency of photochemical conjugation. A standard two-step approach gave a measured conjugation efficiency of 3.5% G 0.4%. In contrast, the one-step process gave a higher photoradiolabeling efficiency of $76%. Stability measurements, cellular saturation binding assays, positron emission tomographic imaging, and biodistribution studies in mice bearing SK-OV-3 tumors confirmed the biochemical viability and tumor specificity of photoradiolabeled [ 89 Zr]ZrDFO-azepin-trastuzumab. Experimental data support the conclusion that the combination of photochemistry and radiochemistry is a viable strategy for producing radiolabeled proteins for imaging and therapy.

New photoactivatable ligands have been developed that facilitate one-pot photoradiochemical labelling of proteins with different radioactive metal ions.

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