A novel molecular agent for glioma angiogenesis imaging.

Abstract

Gliomas are rich in blood vessels and are the most primary and malignant type of brain tumor affecting the central nervous system. A few fluorine-18 (F)-labeled imaging agents can be used for imaging of tumor angiogenesis. In the current study, F-labeled recombinant human endostatin (rh-endostatin) was developed and evaluated as a probe for PET imaging of tumor angiogenesis. F-fluorobenzoyl-endostatin (F-FB-endostatin) was synthesized from radiolabeling of rh-endostatin with N-succinimidyl-4-F-fluorobenzoate produced by a facile module-assisted radiosynthesis procedure. Blocking studies were used to measure the relative affinities of F-FB-endostatin to human glioblastoma U87MG cells in tumor tissues rich with vessels. In addition, biodistribution, metabolic stability, and small-animal PET imaging studies were carried out with F-FB-endostatin using Institute of Cancer Research and U87MG tumor-bearing mice. Noninvasive small-animal PET imaging indicated that F-FB-endostatin showed rapid and good tumor uptake. The probe was rapidly cleared from the blood and most organs, resulting in excellent tumor-to-normal tissue contrasts. Tumor uptake and rapid clearance were further confirmed with biodistribution studies. Metabolite assays showed that the probe was highly stable, making it suitable for in-vivo applications. F-FB-endostatin shows promising in-vivo properties. Therefore, the promising properties of F-FB-endostatin indicate that this probe can be a powerful tool to evaluate the antiangiogenic therapy for gliomas and thus warrants further investigation as a novel PET probe for imaging of tumor angiogenesis.