c-MET Receptor–Targeted Fluorescence on the Road to Image-Guided Surgery in Penile Squamous Cell Carcinoma Patients

Abstract

In penile squamous cell carcinoma (pSCC), primary surgery aims to obtain oncologically safe margins while minimizing mutilation. Surgical guidance provided by receptor-specific tracers could potentially improve margin detection and reduce unnecessary excision of healthy tissue.Here, we present the first results of a prospective feasibility study for real-time intraoperative visualization of pSCC using a fluorescent mesenchymal-epithelial transition factor (c-MET) receptor targeting tracer (EMI-137). MethodsEMI-137 tracer performance was initially assessed ex vivo (N=10) via incubation of freshly excised pSCC in a solution containing EMI-137 (500 nM). The in vivo potential of c-MET targeting and intraoperative tumour visualization was assessed after intravenous administration of EMI-137 in five pSCC patients scheduled for surgical resection using a Cyanine-5 (Cy5) fluorescence camera.Fluorescence imaging results were related to standard pathological tumour evaluation and c-MET immunohistochemistry. Three of the five in vivo patients also underwent a sentinel node resection after local administration of the hybrid tracer indocyanine green (ICG)-99m Tcnanocolloid, which could be imaged using a near-infrared fluorescence camera. ResultsNo tracer-related adverse events were encountered. Both ex vivo and in vivo, EMI-137 enabled c-MET based tumour visualization in all patients. Histopathological analyses showed that all pSCC's expressed c-MET, with expression levels of ≥70% in 14/15 patients. Moreover, the highest c-MET 4 4 expression levels were seen on the outside rim of the tumours, and a visual correlation was found between c-MET expression and fluorescence signal intensity. No complications were encountered when combining primary tumour targeting with lymphatic mapping. As such, simultaneous use of Cy5 and ICG in the same patient proved to be feasible. ConclusionFluorescence imaging of c-MET receptor-expressing pSCC tumours after intravenous injection of EMI-137 was shown to be feasible and can be combined with fluorescence-based lymphatic mapping. This combination is unique and paves the way towards further development of this surgical guidance approach.

Translation of c-Met Targeted Image-Guided Surgery Solutions in Oral Cavity Cancer—Initial Proof of Concept Data

“…While for tissue incubation the maximum depth of tracer penetration is not yet well understood, there are studies that show that at least several cell layers (up to 300 µm) can be effectively stained and evaluated [ 28 , 29 ]. And while physics will dictate the superficial nature of fluorescence imaging, in vivo use of EMI-137 suggest that the issues behind tracer penetration in tissue are overcome when applying EMI-137 (or any other fluorescent tracer) in humans [ 8 , 9 , 25 ]. More specifically, in penile cancer patients, the presence of fluorescence was not limited to the rim of the tumor but could be detected throughout the tumor (tumor infiltration depth up to 24 mm [ 8 ]).…”

“…And while physics will dictate the superficial nature of fluorescence imaging, in vivo use of EMI-137 suggest that the issues behind tracer penetration in tissue are overcome when applying EMI-137 (or any other fluorescent tracer) in humans [ 8 , 9 , 25 ]. More specifically, in penile cancer patients, the presence of fluorescence was not limited to the rim of the tumor but could be detected throughout the tumor (tumor infiltration depth up to 24 mm [ 8 ]). This utility of EMI-137 is strengthened by other critical findings.…”

“…The holy grail in image-guided surgery, however, is direct identification of the primary tumor (margins) and/or (macro)metastases. This is based on the assumption that, through the direct illumination of tumor cells, image guidance supports intraoperative tumor delineation [ 8 ] and could aid in the resection of lesions that could not be identified otherwise [ 9 ].…”

“…Expansion of the arsenal of tracers seems to be limited by a translational gap between preclinical work in artificial tumor models and in vivo implementation in clinical trials. We, and others, have argued that receptor-targeting tracers can be evaluated using an ex vivo topical application setting first, using fresh surgical samples [ 8 , 15 ]. Such evaluations help circumvent the notoriously poor correlation between mRNA and protein expression and cytoplasmic target presence using immunohistochemistry (IHC; [ 16 , 17 , 18 ]).…”

“…EMI-137 is a c-Met targeting fluorescent tracer that, following extensive tracer optimization and preclinical evaluations, has been translated to the clinic and comes with thoroughly documented pharmacokinetics [ 9 ]. This tracer also previously demonstrated its ability to apply c-Met targeted resection of colorectal polyps, Barret’s neoplasia and penile cancer, based on far-red related fluorescence after intravenous administration [ 8 , 9 , 25 ].…”