We started the development and evaluation of biodegradable near-infrared fluorescent silica nanoparticles, also known as Theraprobes, that have the potential to improve adenoma detection during fluorescence-assisted white-light colonoscopic surveillance. He recently demonstrated that 100-nm fluorescent silica nanoparticles (FSN700s and FSN800s) that embed a near-infrared fluorescent (NIRF) dye (λex: 680; λem: >700 nm and λex: ~785; λem: >800 nm, respectively) enable endoscopic detection of premalignant lesions in transgenic animal models of colorectal carcinogenesis following intravenous administration. These studies were performed in genetically engineered rodent and human-scale, porcine models of GI carcinogenesis - the Apcmin/+ mouse, ApcPirc/+ rat, and APC1311/+ pig. The rodent models have been criticized for not (or rarely) progressing to invasive carcinoma, which is as yet an open question for the porcine models. However, in all species, the lesions develop via the Vogelstein-sequence, and, as such, the Apc-driven carcinogenesis animal models are particularly useful for our purpose of evaluating endoscopic detection of dysplastic lesions using FSNs. In fact, we demonstrated that after intravenous administration the FSNs enable detection of colorectal adenomas as small as 0.5 mm2 throughout the intestinal tract of ApcMin/+ mice and in the larger ApcPirc/+ rat and APC1311/+ porcine model. A positive predictive value (PPV) of 78% was determined. However, this number is likely higher for FSN-guided endoscopy. Unlike (epi)fluorescence wide-field NIRF imaging, which was used here to establish the PPV, where the tissue is illuminated at a 90° angle, fluorescence endoscopic imaging is performed along the luminal surface at a 145°–180° angle. In this way, only superficial mucosal lesions will be detected and not Peyer’s patches, which are located in the deeper submucosal tissue layer. Widespread improvement in the endoscopic recognition of colorectal adenomas will have important implications for the surveillance and management of incipient colorectal cancers and cancer prevention. Our proposed use of intravenous FSNs as positive contrast agents for endoscopic detection of (pre)malignant lesions of the GI tract is fully compatible with current clinical practice and instrumentation. For instance, an intravenous bolus injection can be administered during the obligate blood draw procedure prior to endoscopic surveillance. Furthermore, since the FSNs are fully biodegradable, they can be used routinely in high-risk patients. Moreover, the FSN700 provided high tumour-to-background ratios indicating that the FSN700s selectively accumulate in tumours versus normal adjacent tissues. The TBR produced by FSN-augmented, fluorescence-assisted endoscopy enables a binary (“yes or no”) read-out to reduce interoperator variability, improve (pre)malignant lesion detection and diagnostic accuracy, and enable targeted sampling and resection of visualized lesions to allow a shift in practice away from the random biopsy technique, where less than 0.1% of the mucosal surface area is blindly sampled, and away from aggressive intervention (e.g. colectomy) for the management of dysplasia in high-risk patients. Dr Harmsen further demonstrated that the FSN700s and FSN800s were well tolerated and do not induce any noticeable toxicity as evidenced by lack of histopathological features in major organs following long-term exposure. Lastly, he showed the FSNs were biodegradable (t1/2 ~3 wks) and fully cleared 4 months after intravenous administration (dose 30 pmol/kg). Due to these favourable pharmacokinetic properties, he envisioned a viable path towards clinical translation of FSNs for early (endoscopic) cancer detection. Further, he proposed to incorporate photodynamic therapeutic functionality into the silica nanoparticle matrix as well as to enable image-guided photodynamic therapy (PDT) as a first-line therapy or after tumour resection to reduce recurrence risk.
