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In Vivo Imaging of Translocator Protein Expression in Gliomas by Positron Emission Tomography (PET). In: Abstracts from the 2012 BNOS Meeting.
Su ZJ, Gerhard A, Hinz R, Roncaroli F, Coope DJ, Thompson G, Karabatsou K, Sofat A, Leggate J, du Plessis D, Turkheimer FE, Jackson A, Brodbelt A, Jenkinson MD, Das K, Crooks D, Herholz K.
Neuro-Oncology. 2012;14 (suppl 2):ii8
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Abstract
INTRODUCTION: The translocator protein (TSPO) is a 18 kDa mitochondrial molecule associated with neuroinflammation and over-expressed in several brain diseases. 11C-(R)PK11195 is a specific ligand of TSPO for PET studies. We investigated the in vivo TSPO expression in high- and low-grade gliomas using 11C-(R)PK11195 PET, and applied it in guiding tumour biopsies. METHOD: 24 patients underwent volumetric MRI and dynamic 11C-(R)PK11195 PET scans. Reference tissue input function was obtained from the grey matter of cerebellum to determine the 11C-(R)PK11195 uptake in the tumours and the mirrored regions of interest (ROIs) in the contralateral hemispheres. Co-registered MR/PET images were used to guide tumour biopsies prior to surgical debulking, with high and/or low 11C-(R)PK11195 uptake foci defined as biopsy targets. Biopsy specimens were assessed for TSPO expression by immunohistochemical staining. RESULTS: In low-grade gliomas (14 cases), 11C-(R)PK11195 uptake within the tumours was lower than the contralateral ROIs (p = 0.001); sporadic high uptake foci were found in 8 tumours. In high-grade gliomas, 7 out of the 10 tumours showed higher uptake than the contralateral ROIs (p = 0.016), 4 of which displayed intensive 11C-(R)PK11195 signal despite only minor contrast enhancement on the MRI. There was low 11C-(R)PK11195 uptake and no contrast enhancement in 3 anaplastic asctrocytomas. Immunostains on tissue sections confirmed variable TSPO expression in neoplastic cells and activated microglia/macrophages. CONCLUSION: TSPO expression is decreased in low-grade gliomas and increased in most high-grade gliomas. TSPO expression within gliomas is inhomogeneous as detected by 11C-(R)PK11195 PET and confirmed by immunohistochemistry.