Glioma Imaging and Novel Agents

Glioma is one of the most frequently observed and aggressive brain tumors. Glioma forms 50-60% of brain tumors including astrocytoma, oligodendroglioma, and glioblastoma. Although the integrity of the blood-brain barrier (BBB) is destroyed somehow in glioblastoma (high-grade glioma) patients, similar to many central nervous system diseases, the main anatomical obstacle remains BBB in effective diagnosis, imaging, and therapy.

The survival rate of glioblastoma patients is very low. Early and accurate diagnosis of glioma is essential for therapy chance. When compared with other techniques, noninvasive medical imaging methods provide high specificity and sensitivity. Although MRI is one of the most commonly used modalities in glioma diagnosis and imaging, it possesses limited differentiation in tumor recurrence and pseudoprogression after radiotherapy and combined chemotherapy. Improved MRI techniques can exhibit higher potential in evaluating the pathological features and grading of gliomas before treatment. As a novel method, molecular imaging techniques such as PET/CT can detect genetic mechanisms and related molecular and metabolic differentiation for accurate diagnosis of diseases.

18F-FDG, one of the most commonly used PET radiopharmaceuticals, is highly accumulated in the cerebral cortex. Therefore, 18F-FDG is a non-specific agent in glioma diagnosis and imaging. Non-specific radiopharmaceuticals are not sufficient depending on low sensitivity and specificity in early diagnosis and imaging of proliferation index of tumor cells, the place of hypoxic focuses, tumor load, differentiation of tumor/necrosis, and tumor/inflammation and therapy monitoring of glioma. Therefore, target-specific radiocontrast/contrast agents have been searched for accurate diagnosis, imaging, and therapy monitoring of glioma. Specific PET agents provide differentiation of tumor, necrosis, or inflammation. More specific glioma imaging agents including novel specific Gd or SPIO comprising MRI contrast agents, amino acid tracers like 18F-FET, and peptide tracers like αvβ3 integrin specific 68Ga- RGD and radiolabeled, targeted drug delivery systems have been searched for accurate and early diagnosis of all stages of glioma.

Keywords: Blood-brain barrier, Diagnosis, Enhanced-permeability and retention effect, Glioma, Glioma targeting, Imaging, Multifunctional drug delivery systems, Nanocarriers, Radiopharmaceuticals, Specific probes, Theranostics for glioma.