Abstract
Purposes Chlorotoxin can specifically bind to matrix metalloproteinase 2 (MMP-2), which are overexpressed in the glioma. In this work, radiosynthesis of [18F]-fluoropropionyl-chlorotoxin ([18F]-FP-chlorotoxin) as a novel PET tracer was investigated, and biodistribution in vivo and PET imaging were performed in the C6 glioma model. Procedures [18F]-FP-chlorotoxin was prepared from the reaction of chlorotoxin with [18F]-NFB (4-nitrophenyl 2-[18F]-fluoropropionate), which was synthesized from multistep reactions. Biodistribution was determined in 20 normal Kunming mice. Small-animal PET imaging with [18F]-FP-chlorotoxin was performed on the same rats bearing orthotopic C6 glioma at different time points (60 min, 90 min, and 120 min) after injection and compared with 2-deoxy-2-[18F] fluoro-D-glucose ([18F]-FDG). Results [18F]-FP-Chlorotoxin was successfully synthesized in the radiochemical yield of 41% and the radiochemical purity of more than 98%. Among all the organs, the brain had the lowest and stable uptake of [18F]-FP-chlorotoxin, while the kidney showed the highest uptake. Compared with [18F]-FDG, a low uptake of [18F]-FP-chlorotoxin was detected in normal brain parenchyma and a high accumulation of [18F]-FP-chlorotoxin was found in the gliomas tissue. The glioma to normal brain uptake ratio of [18F]-FP-chlorotoxin was higher than that of [18F]-FDG. Furthermore, the uptake of [18F]-FP-chlorotoxin at 90 min after injection was better than that at 60 min after injection. Conclusions Compared with [18F]-FDG, [18F]-FP-chlorotoxin has a low and stable uptake in normal brain parenchyma. [18F]-FP-Chlorotoxin seems to be a potential PET tracer with a good performance in diagnosis of the glioma.
Highlights
Amongst primary brain tumors, gliomas can be considered as the most lethal malignant tumors [1, 2]
Radiosynthesis Results. e radiosynthesis scheme of [18F]-FP-chlorotoxin is shown in Figure 1. e automatic synthesis of [18F]-NFP was completed in 80 min with an overall radiochemical yield of 23 ± 5% (n 5) with decay correction
The manual synthesis of [18F]FP-chlorotoxin was completed in 20 min with an overall radiochemical yield of 41% (n 5) with decay correction
Summary
Gliomas can be considered as the most lethal malignant tumors [1, 2]. It is possible to roughly visualize the glioma with current imaging techniques, preoperative imaging does not always clearly define the tumor parenchyma and the edge of the tumor invasion. Positron emission tomography (PET) provides additional insights beyond magnetic resonance imaging (MRI) into the biology of gliomas. Amino acid tracers have been used predominantly for glioma imaging and exhibit lower uptake in normal brain tissue, which. Among all types of amino acid tracers, S-[11C]methyl-L-methionine ([11C]-MET) and [18F]-FET PET are preferred for clinical use [5, 8, 9]. [11C]-MET is not the ideal tumor tracer, since inflammatory processes are known to show increased [11C]-MET uptake [5]. Unspecific [18F]-FET uptake has been observed in nonspecific brain lesions [10, 11], and a lack of [18F]-FET uptake does not exclude a glioma, as approximately onethird of WHO grade II gliomas and most dysembryoplastic neuroepithelial tumors are [18F]-FET negative [12]
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