Gmp-Compliant Fully Automated Radiosynthesis Of [F-18]Feppa For Pet/Mri Imaging Of Regional Brain Tspo Expression

Background Expression of translocator protein (TSPO) on the outer mitochondrial membrane of activated microglia is strongly associated with neuroinflammation. The second-generation PET ligand [F-18]FEPPA specifically binds TSPO to enable in vivo visualization and quantification of neuroinflammation. We optimized a fully automated radiosynthesis method and evaluated the utility of [F-18]FEPPA, the second-generation PET ligand specifically binds TSPO, in a mouse model of systemic LPS challenge to detect TSPO-associated signals of central and peripheral inflammation. In vivo dynamic PET/MR imaging was performed in LPS-induced and control mice after [F-18]FEPPA administration. The relationship between the [F-18]FEPPA signal and the dose of LPS was assessed. The cytokine levels (i.e., TNF-alpha, Il-1 beta, Il-6) in LPS-induced mice were measured by RT-PCR. Standard uptake value (SUV), total volume of distribution (VT) and area under the curve (AUC) were determined based on the metabolite-uncorrected plasma input function. Western blotting and immunostaining were used to measure TSPO expression in the brain. Results The fully automated [F-18]FEPPA radiosynthesis produced an uncorrected radiochemical yield of 30 +/- 2% within 80 min, with a radiochemical purity greater than 99% and specific activity of 148.9-216.8 GBq/mu mol. Significant differences were observed in the brain after [F-18]FEPPA administration: SUV, VT and AUC were 1.61 +/- 0.1, 1.25 +/- 0.12 and 1.58 +/- 0.09-fold higher in LPS-injected mice than controls. TNF-alpha, Il-1 beta and Il-6 mRNA levels were also elevated in the brains of LPS-injected mice. Western blotting revealed TSPO (p < 0.05) and Iba-1 (p < 0.01) were upregulated in the brain after LPS administration. In LPS-injected mice, TSPO immunoactivity colocalized with Iba-1 in the cerebrum and TSPO was significantly overexpressed in the hippocampus and cerebellum. The peripheral organs (heart, lung) of LPS-injected mice had higher [F-18]FEPPA signal-to-noise ratios than control mice. Conclusions Based on the current data on ligand specificity and selectivity in central tissues using 7 T PET/MR imaging, we demonstrate that [F-18]FEPPA accumulations significant increased in the specific brain regions of systemic LPS-induced neuroinflammation (5 mg/kg). Future investigations are needed to determine the sensitivity of [F-18]FEPPA as a biomarker of neuroinflammation as well as the correlation between the PET signal intensity and the expression levels of TSPO.