Fluorescence-guided Tumor Visualization Using the Tumor Paint BLZ-100

Abstract

Objective: Intraoperatively delineating between normal tissue and tumorous tissue in real time ensures near-complete tumor resection. Recently, this has been shown by using targeted fluorescent agents that bind to tumor cells, conjugated to a fluorophore that can be detected with fluorescence imaging methods. One promising tumor ligand for in vivo fluorescence imaging is chlorotoxin (CTX), which has been conjugated to indocyanine green (ICG), and named BLZ-100. In conjunction with BLZ-100, we are nearing completion of developing and optimizing an imaging system (SIRIS) for in-vivo imaging of BLZ-100 for use in surgical resections of gliomas. Methods: BLZ-100 concentrations were prepared in a 5% intralipid solution. The concentrations tested ranged from 1 µMolar to 100 picoMolar. Serial dilutions of ICG were prepared in aqueous concentrations ranging from 3.23 mM to 66.1 pM. The tray was imaged using the commercial Zeiss Pentero surgical microscope and SIRIS. Finally, BLZ-100 was injected in animals implanted with intracranial human glioblastoma cells 48 hours prior to euthanasia. Fluorescence imaging was performed by SIRIS, a camera system developed that simultaneously acquires both white light and NIR images, while combining these images via super-imposition on a high-definition (HD) video monitor. Results: The NIR imaging system developed (SIRIS) is capable of visualizing concentrations of ICG down to 1 nM and BLZ-100 to well below 1 nM (extinction at 100 pM). Glioma and medulloblastoma implanted in mouse brains demonstrated that BLZ-100 has a high affinity for both tumor types compared to normal brain where there is no measurable fluorescence. Conclusions: We have developed a camera system for NIR detection of fluorescence tumor ligands, and demonstrated the utility of this camera for detecting BLZ-100 both in vivo and in vitro. The system is designed to permit simultaneous tumor resection and NIR visualization, and has been developed as an ergonomic and surgeon-friendly device.