Preclinical evaluation and automated synthesis of [⁸⁹Zr]ZrDFOSquaramide-girentuximab for diagnostic imaging of carbonic anhydrase IX positive tumours

Background: Carbonic Anhydrase IX (CAIX) is a zinc metalloenzyme that is over-expressed in many cancers making it a valid target for targeted diagnostic imaging with Positron Emission Tomography (PET). The monoclonal antibody girentuximab binds to CAIX and when radiolabelled with positron-emitting zirconium-89 can be used for diagnostic PET imaging of CAIX positive tumours.

Results: Reaction of desferrioxamine squaramide ethyl ester with girentuximab allowed isolation of a conjugate with desferrioxamine squaramide (DFOSq) covalently attached to girentuximab through stable vinylogous amide linkages to give DFOSq-girentuximab. This conjugate was radiolabelled with zirconium-89 to give [⁸⁹Zr]ZrDFOSq-girentuximab and the tumour uptake of the tracer was evaluated in CAIX positive HT29 tumour-bearing mice. Analysis of the PET images and biodistribution studies showed that the tracer displays high tumour uptake. An automated process for production of [⁸⁹Zr]ZrDFOSq-girentuximab was developed, using [⁸⁹Zr]ZrCl₄ as a starting material that was also synthesized in an automated process. This automated process allows isolation of [⁸⁹Zr]ZrDFOSq-girentuximab in radiochemical yields of 80-90% and in > 95% radiochemical purity.

Conclusions: [⁸⁹Zr]ZrDFOSq-girentuximab has high uptake in CAIX positive tumours. An automated procedure for the synthesis of [⁸⁹Zr]ZrDFOSq-girentuximab using [⁸⁹Zr]ZrCl₄ as a starting material has been developed. This automated process could be readily adapted to other antibodies.