B53: A HER2 selective theranostic agent for surgical resection guidance and photodynamic therapy.
1Department for Tissue & Energy, University College London, London, UK,2Upper Gastrointestinal Service, University College Hospital, London, UK,3Department of Chemistry, University College London, London, UK,4Antikor BioPharma, Stevenage Bioscience Catalyst, London, UK,5Department of Chemistry, Imperial College London, London, UK
In many cancers early intervention involves surgical resection of small localised tumour masses, inadequate resection leads to recurrence whereas overzealous treatment can lead to organ damage. The use of an imaging agent to help identify tumour margin alongside post resection treatment of the tumour bed and surrounding area to kill any remaining cancer cells would be a useful tool to help improve tumour resection outcome. This work describes production of a HER2 targeting antibody Fab fragment that could be used for real time near-infrared fluorescent imaging, i.e during endoscopic diagnosis for oesophageal adenocarcinoma, the attached photodynamic therapy drug could then be instantaneously activated via laser to treat any outlying regions of interest, infiltrated lymph nodes, or the tumour bed area. The theranostic agent was prepared by functional disulfide re-bridging of the single accessible disulfide in the Fab fragment of trastuzumab, via an alkyne bearing next generation maleimide, followed by the site-specific click reaction of a near-infrared imaging agent. Further reaction with a pre-activated form of the chlorin e6 photosensitiser resulted in amide bond formation of numerous photosensitiser molecules to the exposed nucleophilic amine of lysine residues. Specific binding of the theranostic agent was seen in vitro with a HER2 positive cell line and cell near-infrared fluorescence was observed with flow cytometry. The specific photo-activity of the conjugates when exposed laser light was also seen on HER2 positive vs HER2 negative cell lines in vitro and the theranostic showed significantly improved light dependant cytotoxicity and specificity compared to equivalent unconjugated drug. This theranostic agent shows potential for application to endoscopic resection of early HER2 positive oesophageal adenocarcinoma.