Heptadentate chelates for 89 Zr-radiolabelling of monoclonal antibodies.

Herein, we report the synthesis of three new bifunctional heptadentate metal ion binding chelates derived from desferrioxamine B (DFO) linked to a tripeptide unit that comprises of a glutamic acid and two glycine residues. The three DFO derivatives were also functionalised with a photoactivatable aryl azide unit for light-triggered labelling of proteins. The chelates were obtained in 3 synthetic steps in good overall yields by using solid phase peptide synthesis (SPPS). Density Functional Theory (DFT) calculations were used to estimate thermodynamic formation constants (log  β ) of the corresponding Zr 4+ complexes. Quantitative zirconium-89 radiolabelling (>95%) was obtained in <5 min at room temperature, and the stability of the radioconjugates toward different competitors (human serum, EDTA and Fe 3+ ) was assessed in vitro . One-pot 89 Zr-photoradiosynthesis produced [ 89 Zr]Zr-2-onartuzumab directly from the formulated, clinical-grade sample MetMAb™, without pre-purifying the monoclonal antibody (mAb) component, with an isolated decay-corrected radiochemical yield of 36.4 ± 2.4%. PET imaging and biodistribution studies were performed in female athymic nude mice bearing subcutaneous xenografts derived from the MKN-45 human gastric cancer cell line to assess the pharmacokinetic profile and tumour binding of [ 89 Zr]Zr-2-onartuzumab. Specific tumour uptake of [ 89 Zr]Zr-2-onartuzumab was confirmed by using competitive inhibition (blocking) studies and bone uptake was significantly reduced compared to the parent DFO analogue.