A bioorthogonal ⁶⁸Ga-labelling strategy for rapid in vivo imaging

Abstract

Herein, we describe a fast and robust method for achieving (68)Ga-labelling of the EGFR-selective monoclonal antibody (mAb) Cetuximab using the bioorthogonal Inverse-electron-Demand Diels-Alder (IeDDA) reaction. The in vivo imaging of EGFR is demonstrated, as well as the translation of the method within a two-step pretargeting strategy.

In vivo imaging with antibodies and engineered fragments

“…Evans et al extended the concept by demonstrating pretargeted click labeling of cetuximab- trans -cyclooctene followed by 68 Ga-DOTA-tetrazine administration. Pretargeting for 23 hours increased the tumor:liver ratio to 2.64, compared with a ratio of < 0.5 for free 68 Ga-DOTA-tetrazine or 3 hour pretargeting (Evans et al, 2014). …”

Emerging formats for next-generation antibody drug conjugates

“…This is a fertile area as azides are absent in biology and are completely inert in vivo but have unique reactivity with alkynes. Such bioorthogonal chemistry is already being used to produce homogeneous ADCs with a variety of payloads and more elaborate bio-orthogonal reactions such as the inverse-electron demand Diels-Alder (IeDDA) between a tetrazine and a strained alkene have already been reported to label antibodies [117].…”

Radiopharmaceuticals as probes to characterize tumour tissue

“…Regarding radiolabelled cetuximab, the advantage of using a directly radiolabelled clinically available IgG (reduced regulatory burden) should be balanced against the slow pharmacokinetics of 89 Zr-cetuximab. As recently demonstrated, new methods for pretargeting involving a bioorthogonal inverse electron-demand Diels-Alder reaction may allow the use of an appropriately radiolabelled tetrazine in conjunction with the IgG, following clearance from the circulation, to improve contrast and reduce dose to subjects [100]. Recently possibilities for detecting activating mutations of EGFR have also been outlined [101][102][103].…”