Image-Guided Surgery using Invisible Near-Infrared Fluorescent Light: "Clinical introduction of a novel, optimized fluorescent contrast agent"

Despite many improvements in pre- and postoperative imaging modalities (e.g. CT, MRI, PET, SPECT), during oncologic surgeries, the surgeon mainly has to rely on visual inspection and palpation to determine what structures should be resected (tumors, lymph nodes) and what structures should be spared (e.g. nerves, bile ducts, ureters). Near infrared (NIR) fluorescence imaging is a novel imaging modality that can provide the surgeon with real-time image-guidance during surgery for the complete and safe resection of tumor tissue. Moreover, this technology can be used for the real-time identification of sentinel lymph nodes in several types of cancer patients. This will tailor surgical treatment and has the potential to improve survival and quality of life of cancer patients. For this purpose, our collaborating group headed by prof. John Frangioni (Harvard Medical School, Boston, USA) has developed NIR fluorescence imaging systems, termed FLARE and Mini-FLARE that have been designed specifically for (oncologic) surgery (1;2). Besides imaging systems, exogenous contrast agents in the form of NIR fluorophores are necessary to visualize specific structures (3). A NIR contrast agent contains a chemical called a fluorophore, which absorbs light at a specific wavelength and emits light with a slightly higher wavelength. Targeted imaging can be obtained by conjugating the fluorophore to a ligand specific to the cells of interest, for example tumour cells. Visualisation is based on the signal of the NIR contrast agent in the region of interest versus the background signal. Currently, only indocyanine green (ICG) is approved for clinical use by the FDA and EMA. Although ICG is a non-specific contrast agent that does not directly target tumor cells or other structures, it has allowed the execution of the first clinical pilot trials using intraoperative NIR fluorescence imaging. The AGIKO-candidate has been involved in several studies in which the Mini-FLARE camera system was used to perform sentinel lymph node (SLN) mapping using ICG in breast cancer, colorectal cancer, vulvar cancer, cervical cancer, bladder cancer, cutaneous melanoma and head-and-neck cancer in over 200 patients (figure 1). Although ICG has allowed NIR fluorescence guided surgery to be introduced into clinical trials, it is not an optimal fluorophore: it has relatively low fluorescence brightness (quantum yield) and due to its small size, it can flow through to higher tier nodes when used in sentinel lymph node mapping. Importantly, as ICG does not contain any carboxylic acid groups, it is not conjugatable to targeting agents. Using ICG, the AGIKO-candidate has gained extensive experience in NIR fluorescence imaging, which provides a basis for the current project. Prof. Frangioni has developed a novel zwitterionic NIR fluorophore called ZW800-1, which is optimized for in vivo imaging (4), and will be translated to the clinic within this project by the AGIKO-candidate and the research group. Major benefits of this molecule could be derived from conjugating it covalently to other molecules, such as antibodies, peptides or other specific ligands. As ZW800-1 has a single carboxylic acid, it is easily conjugatable to various ligands through the commonly used NHS-ester coupling reactions. The main aim of the AGIKO-candidate is to improve NIR fluorescence image-guided surgery by translating optimized tracers, based on ZW800-1, to the clinic: 1) Tumor imaging: By conjugating ZW800-1 to tumor-specific ligands, it will be possible to demarcate tumors from their surrounding tissue. In this project, the already clinically available tumor-specific small peptide cRGD will be used for this purpose. 2) Sentinel lymph node mapping: In previous studies, we have shown that by conjugation of macromolecules to NIR fluorescent dyes, the properties as a lymphatic tracer improve greatly (5;6). The AGIKO-candidate will develop and use an optimized lymphatic tracer, by conjugating ZW800-1 to clinically available polyethylene glycol (PEG), thereby increasing the hydrodynamic diameter and improving retention in the sentinel lymph node. 3) Imaging of the ureter: As ZW800-1 (not conjugated) is renally cleared, it will be used for intraoperative imaging of ureters by injection of unbound ZW800-1 intravenously.