Background:
Fluorescence-guided cancer surgery is an evolving field. Indocyanine green (ICG) is limited by its lack of specificity, so there is a need for tumour-targeting fluorescent probes. A novel class of fluorescent probe known as Activity-based probes (ABP) targets the protease ‘cathepsin’, which is expressed by cancer cells to promote tumour progression. ABPs maximise target signal by reducing background fluorescence using a process known as quenching. We evaluated the fluorescent activity of ABPs using pre-clinical models of Oesophagogastric (OG) cancer.
Methods:
We assessed ABP activity in OG cancer cell lines and patient biopsies using in-gel fluorescence, Western blot and qPCR. Cell line xenografts were established in immunocompromised (NSG) mice using subcutaneous and orthotopic models. Tumour-bearing mice were injected with ABP and imaged at specific timepoints using the IVIS® spectrum imager.
Results:
ABP fluorescence appeared to increase in OG cancer and metastatic cell lines. OG cancer biopsies from 50 patients exhibited significantly higher fluorescence than normal oesophageal and gastric biopsies (p <0.05). In NSG mice, optimal ABP dose and imaging time-points were determined to be 4mg/ml and 48hr post injection. Fluorescence in orthotopic tumours was 4-7 fold higher than normal tissue and visualised in liver and peritoneal metastasis.
Conclusion:
Our pre-clinical results showed tumour-targeting fluorescent probe such as ABP can help to delineate OG cancer from normal tissue. Hence, we plan to conduct a clinical trial to assess ABP potential to assist surgeons to reduce positive tumour margin rates and to identify nodal metastasis.