Detection of Sessile Serrated Adenomas in the Proximal Colon Using Wide-Field Fluorescence Endoscopy

Abstract

Background & Aims Many cancers in the proximal colon develop via from sessile serrated adenomas (SSAs), which have flat, subtle features that are difficult to detect with conventional white-light colonoscopy. Many SSA cells have the V600E mutation in BRAF. We investigated whether this feature could be used with imaging methods to detect SSAs in patients. Methods We used phage display to identify a peptide that binds specifically to SSAs, using subtractive hybridization with HT29 colorectal cancer cells containing the V600E mutation in BRAF and Hs738.St/Int cells as a control. Binding of fluorescently labeled peptide to colorectal cancer cells was evaluated with confocal fluorescence microscopy. Rats received intra-colonic 0.0086 mg/kg, 0.026 mg/kg, or 0.86 mg/kg peptide or vehicle and morbidity, mortality, and injury were monitored twice daily to assess toxicity. In the clinical safety study, fluorescently labeled peptide was topically administered, using a spray catheter, to the proximal colon of 25 subjects undergoing routine outpatient colonoscopies (3 subjects were given 2.25 µmol/L and 22 patients were given 76.4 µmol/L). We performed blood cell count, chemistry, liver function, and urine analyses approximately 24 hrs after peptide administration. In the clinical imaging study, 38 subjects undergoing routine outpatient colonoscopies, at high risk for colorectal cancer, or with a suspected unresected proximal colonic polyp, were first evaluated by white-light endoscopy, to identify suspicious regions. The fluorescently labeled peptide (76.4 µmol/L) was administered topically to proximal colon, unbound peptide was washed away, and white-light, reflectance, and fluorescence videos were recorded digitally. Fluorescence intensities of SSAs were compared with those of normal colonic mucosa. Endoscopists resected identified lesions, which were analyzed histologically by gastrointestinal pathologists (reference standard). We also analyzed the ability of the peptide to identify SSAs vs adenomas, hyperplastic polyps, and normal colonic mucosa in specimens obtained from the tissue bank at the University of Michigan. Results We identified the peptide sequence KCCFPAQ, and measured an apparent dissociation constant of kd = 72 nM and an apparent association time constant of k = 0.174 min−1 (5.76 min). During fluorescence imaging of patients during endoscopy, regions of SSA had 2.43-fold higher mean fluorescence intensity than that for normal colonic mucosa. Fluorescence labeling distinguished SSAs from normal colonic mucosa with 89% sensitivity and 92% specificity. The peptide had no observed toxic effects in animals or patients. In the analysis of ex vivo specimens, peptide bound to SSAs had significantly higher mean fluorescence intensity than to hyperplastic polyps. Conclusions We have identified a fluorescently labeled peptide that has no observed toxic effects in animals or humans and can be used for wide-field imaging of lesions in the proximal colon. It distinguishes SSAs from normal colonic mucosa with 89%...

Molecular imaging within the lower gastrointestinal tract: From feasibility to future

“…In this report, the authors were able to show that SSAs had >2 higher fluorescence intensity during fluorescence colonoscopy compared to normal colonic mucosa and that molecular imaging with topically applied KCCFPAQ distinguished SSAs from normal colonic mucosa with high sensitivity and specificity (Fig. ) . Hence, this targeted imaging approach might be used to facilitate early detection of premalignant serrated lesions during routine colonoscopies.…”

“…Hence, SSAs represent lesions that can be challenging to detect and means to improve and facilitate SSA detection are certainly needed. In a recent study, Joshi and co‐workers identified the peptide KCCFPAQ which exhibited specific binding to SSA . In this report, the authors were able to show that SSAs had >2 higher fluorescence intensity during fluorescence colonoscopy compared to normal colonic mucosa and that molecular imaging with topically applied KCCFPAQ distinguished SSAs from normal colonic mucosa with high sensitivity and specificity (Fig.…”

“…(F) Corresponding histology of the SSA. Reproduced from Joshi et al ., with permission from Elsevier.…”

“…2). 38 Hence, this targeted imaging approach might be used to facilitate early detection of premalignant serrated lesions during routine colonoscopies. Importantly, in none of the above-discussed studies toxic side effects associated with topical or systemic peptide administration were observed.…”

The Serrated Polyp Pathway: Is It Time to Alter Surveillance Guidelines?

“…Histopathological investigations of microsatellite instable, proximal, and interval CRCs may help identify the features of high-risk premalignant lesions and have important implications for screening, surveillance, and treatment. Also, the development of technologies that improve detection and/or resection of SPs would be welcome tools to prevent CRC arising from serrated precursors, and there are some compelling recent reports along these lines [73]. …”