385. TRANSLATING MOLECULAR-TARGETING FLUORESCENT PROBES IN OESOPHAGEAL CANCER PRE-CLINICAL MODELS

Background Intra-operative molecular imaging (IMI) is an emerging field that utilises tumour-targeting fluorescent probes to improve oncological outcomes. A novel class of probe known as quenched activity-based probes (qABP), developed to measure enzyme activity in-vitro, has been repurposed to target tumour-expressed proteases known as cathepsins. Unlike other tumour-targeting probes, fluorescence is inhibited up until the qABP covalently bonds to cathepsins, releasing an inhibitory quencher which results in fluorescence. This may improve the contrast between normal tissue and tumour. Our laboratory group sought to obtain pre-clinical evidence to eventually translate qABP’s into the operating room for oesophageal, junctional and gastric cancer. Methods Cathepsin activity was screened in cell lines from the normal oesophagus, Barrett’s metaplasia, oesophageal adenocarcinoma (OAC), squamous cell carcinoma (SCC) and gastric adenocarcinoma (GAC) with two qABP’s known as BMV109 and VGT309. We additionally screened patient biopsies from oesophageal, junctional and gastric cancers. Cell line and tissue samples were analysed using in-gel fluorescence (Amersham Typhoon®) and Western blot. In-vivo, cell line xenografts were established in NSG mice using subcutaneous and orthotopic models. Tumour-bearing mice were then injected with VGT-309 and then imaged at specific timepoints using the IVIS® spectrum imager. Results Cathepsin activity was found in all oesophago-gastric cell lines and selectivity proven with a cathepsin inhibitor. Matched biopsies were collected from patients prior before and after neoadjuvant chemo-radiotherapy. Baseline tumour biopsies exhibited significantly higher cathepsin activity than normal biopsies, with these differences preserved in biopsies collected after chemo-radiotherapy (p <0.001). In-vivo, OAC and GAC xenografts were identified in NSG mice as early as 12 hours post injection of VGT-309, exhibiting a 2.5-fold increase in fluorescence compared to normal background stomach. Bio-distribution analysis demonstrated that VGT-309 accumulated in liver and kidney, but less so in the murine oesophagus and stomach. Conclusion Translating qABP’s into the operating room has the potential to detect early cancers in Barrett’s metaplasia, reduce positive margin rates and identify lymph node metastasis. Our research group continues to investigate qABP’s, including determining their sensitivity to detect lymph node metastasis with the aim of translating this technology into a phase 1 clinical trial.