Abstract
This study evaluated the use of molecular imaging of fluorescent glucose analog 2-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose (2-NBDG) as a discriminatory marker for intraoperative tumor border identification in a murine glioma model.
2-NBDG was assessed in GL261 and U251 orthotopic tumor-bearing mice. Intraoperative fluorescence of topical and intravenous 2-NBDG in normal and tumor regions was assessed with an operating microscope, handheld confocal laser scanning endomicroscope (CLE), and benchtop confocal laser scanning microscope (LSM). Additionally, 2-NBDG fluorescence in tumors was compared with 5-aminolevulinic acid-induced protoporphyrin IX fluorescence.
Intravenously administered 2-NBDG was detectable in brain tumor and absent in contralateral normal brain parenchyma on wide-field operating microscope imaging. Intraoperative and benchtop CLE showed preferential 2-NBDG accumulation in the cytoplasm of glioma cells (mean [SD] tumor-to-background ratio of 2.76 [0.43]). Topically administered 2-NBDG did not create sufficient tumor-background contrast for wide-field operating microscope imaging or under benchtop LSM (mean [SD] tumor-to-background ratio 1.42 [0.72]). However, topical 2-NBDG did create sufficient contrast to evaluate cellular tissue architecture and differentiate tumor cells from normal brain parenchyma. Protoporphyrin IX imaging resulted in a more specific delineation of gross tumor margins than intravenous or topical 2-NBDG and a significantly higher tumor-to-normal-brain fluorescence intensity ratio.
After intravenous administration, 2-NBDG selectively accumulated in the experimental brain tumors and provided bright contrast under wide-field fluorescence imaging with a clinical-grade operating microscope. Topical 2-NBDG was able to create a sufficient contrast to differentiate tumor from normal brain cells on the basis of visualization of cellular architecture with CLE. 5-Aminolevulinic acid demonstrated superior specificity in outlining tumor margins and significantly higher tumor background contrast. Given the nontoxicity of 2-NBDG, its use as a topical molecular marker for noninvasive in vivo intraoperative microscopy is encouraging and warrants further clinical evaluation.