Quantitative analysis of peripheral benzodiazepine receptor in the human brain using PET with (11)C-AC-5216

Peripheral benzodiazepine receptor (PBR) is upregulated in activated glial cells and is therefore a useful biomarker for inflammation in the brain and neurodegenerative disorders. We developed a new PET radioligand, (11)C-AC-N-benzyl-N-ethyl-2-(7-methyl-8-oxo-2-pheyl-7,8-dihydro-9H-purin-9-yl)acetamide ((11)C-AC-5216), that allows the imaging and quantification of PBRs in monkey and mouse brains. The aim of this study was to evaluate a quantification method of (11)C-AC-5216 binding in the human brain.

A 90-min dynamic PET scan was obtained for each of 12 healthy men after an intravenous injection of (11)C-AC-5216. Regions of interest were drawn on several brain regions. Binding potential, compared with nondisplaceable uptake (BP(ND)), was calculated by a nonlinear least-squares fitting (NLS) method with the 2-tissue-compartment model, and total volume of distribution (V(T)) was estimated by NLS and graphical analysis methods.

BP(ND) was highest in the thalamus (4.6 +/- 1.0) and lowest in the striatum (3.5 +/- 0.7). V(T) obtained by NLS or graphical analysis showed regional distribution similar to BP(ND). However, there was no correlation between BP(ND) and V(T) because of the interindividual variation of K(1)/k(2). BP(ND) obtained with data from a scan time of 60 min was in good agreement with that from a scan time of 90 min (r = 0.87).

Regional distribution of (11)C-AC-5216 was in good agreement with previous PET studies of PBRs in the human brain. BP(ND) is more appropriate for estimating (11)C-AC-5216 binding than is V(T) because of the interindividual variation of K(1)/k(2). (11)C-AC-5216 is a promising PET ligand for quantifying PBR in the human brain.