Author Correction: Selective, high-contrast detection of syngeneic glioblastoma in vivo.

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Selective, high-contrast detection of syngeneic glioblastoma in vivo.

Glioblastoma is a highly malignant, largely therapy-resistant brain tumour. Deep infiltration of brain tissue by neoplastic cells represents the key problem of diffuse glioma. Much current research focuses on the molecular makeup of the visible tumour mass rather than the cellular interactions in the surrounding brain tissue infiltrated by the invasive glioma cells that cause the tumour's ultimately lethal outcome. Diagnostic neuroimaging that enables the direct in vivo observation of the tumour infiltration zone and the local host tissue responses at a preclinical stage are important for the development of more effective glioma treatments. Here, we report an animal model that allows high-contrast imaging of wild-type glioma cells by positron emission tomography (PET) using [18 F]PBR111, a selective radioligand for the mitochondrial 18 kDa Translocator Protein (TSPO), in the Tspo-/- mouse strain (C57BL/6-Tspotm1GuMu(GuwiyangWurra)). The high selectivity of [18 F]PBR111 for the TSPO combined with the exclusive expression of TSPO in glioma cells infiltrating into null-background host tissue free of any TSPO expression, makes it possible, for the first time, to unequivocally and with uniquely high biological contrast identify peri-tumoral glioma cell invasion at preclinical stages in vivo. Comparison of the in vivo imaging signal from wild-type glioma cells in a null background with the signal in a wild-type host tissue, where the tumour induces the expected TSPO expression in the host's glial cells, illustrates the substantial extent of the peritumoral host response to the growing tumour. The syngeneic tumour (TSPO+/+) in null background (TSPO-/-) model is thus well suited to study the interaction of the tumour front with the peri-tumoral tissue, and the experimental evaluation of new therapeutic approaches targeting the invasive behaviour of glioblastoma.

Translocator protein localises to CD11b+ macrophages in atherosclerosis.

BACKGROUND AND AIMS: Atherosclerosis is characterized by lipid deposition, monocyte infiltration and foam cell formation in the artery wall. Translocator protein (TSPO) is abundantly expressed in lipid rich tissues. Recently, TSPO has been identified as a potential diagnostic tool in cardiovascular disease. The purpose of this study was to determine if the TSPO ligand, 18F-PBR111, can identify early atherosclerotic lesions and if TSPO expression can be used to identify distinct macrophage populations during lesion progression. METHODS: ApoE-/- mice were maintained on a high-fat diet for 3 or 12 weeks. C57BL/6J mice maintained on chow diet served as controls. Mice were administered 18F-PBR111 intravenously and PET/CT imaged. After euthanasia, aortas were isolated, fixed and optically cleared. Cleared aortas were immunostained with DAPI, and fluorescently labelled with antibodies to TSPO, the tissue resident macrophage marker F4/80 and the monocyte-derived macrophage marker CD11b. TSPO expression and the macrophage markers were visualised in fatty streaks and established plaques by light sheet microscopy. RESULTS: While tissue resident F4/80 + macrophages were evident in the arteries of animals without atherosclerosis, no CD11b + macrophages were observed in these animals. In contrast, established plaques had high CD11b and low F4/80 expression. A ∼3-fold increase in the uptake of 18F-PBR111 was observed in the aortas of atherosclerotic mice relative to controls. CONCLUSIONS: Imaging of TSPO expression is a new approach for studying atherosclerotic lesion progression and inflammatory cell infiltration. The TSPO ligand, 18F-PBR111, is a potential clinical diagnostic tool for the detection and quantification of atherosclerotic lesion progression in humans.

In vivo [64Cu]CuCl2 PET imaging reveals activity of Dextran-Catechin on tumor copper homeostasis.

Given the strong clinical evidence that copper levels are significantly elevated in a wide spectrum of tumors, copper homeostasis is considered as an emerging target for anticancer drug design. Monitoring copper levels in vivo is therefore of paramount importance when assessing the efficacy of copper-targeting drugs. Herein, we investigated the activity of the copper-targeting compound Dextran-Catechin by developing a [64Cu]CuCl2 PET imaging protocol to monitor its effect on copper homeostasis in tumors. Methods: Protein expression of copper transporter 1 (CTR1) in tissue microarrays representing 90 neuroblastoma patient tumors was assessed by immunohistochemistry. Western blotting analysis was used to study the effect of Dextran-Catechin on the expression of CTR1 in neuroblastoma cell lines and in tumors. A preclinical human neuroblastoma xenograft model was used to study anticancer activity of Dextran-Catechin in vivo and its effect on tumor copper homeostasis. PET imaging with [64Cu]CuCl2 was performed in such preclinical neuroblastoma model to monitor alteration of copper levels in tumors during treatment. Results: CTR1 protein was found to be highly expressed in patient neuroblastoma tumors by immunohistochemistry. Treatment of neuroblastoma cell lines with Dextran-Catechin resulted in decreased levels of glutathione and in downregulation of CTR1 expression, which caused a significant decrease of intracellular copper. No changes in CTR1 expression was observed in normal human astrocytes after Dextran-Catechin treatment. In vivo studies and PET imaging analysis using the neuroblastoma preclinical model revealed elevated [64Cu]CuCl2 retention in the tumor mass. Following treatment with Dextran-Catechin, there was a significant reduction in radioactive uptake, as well as reduced tumor growth. Ex vivo analysis of tumors collected from Dextran-Catechin treated mice confirmed the reduced levels of CTR1. Interestingly, copper levels in blood were not affected by treatment, demonstrating potential tumor specificity of Dextran-Catechin activity. Conclusion: Dextran-Catechin mediates its activity by lowering CTR1 and intracellular copper levels in tumors. This finding further reveals a potential therapeutic strategy for targeting copper-dependent cancers and presents a novel PET imaging method to assess patient response to copper-targeting anticancer treatments.

Positron emission tomography and functional characterization of a complete PBR/TSPO knockout.

The evolutionarily conserved peripheral benzodiazepine receptor (PBR), or 18-kDa translocator protein (TSPO), is thought to be essential for cholesterol transport and steroidogenesis, and thus life. TSPO has been proposed as a biomarker of neuroinflammation and a new drug target in neurological diseases ranging from Alzheimer's disease to anxiety. Here we show that global C57BL/6-Tspo(tm1GuWu(GuwiyangWurra))-knockout mice are viable with normal growth, lifespan, cholesterol transport, blood pregnenolone concentration, protoporphyrin IX metabolism, fertility and behaviour. However, while the activation of microglia after neuronal injury appears to be unimpaired, microglia from (GuwiyangWurra)TSPO knockouts produce significantly less ATP, suggesting reduced metabolic activity. Using the isoquinoline PK11195, the ligand originally used for the pharmacological and structural characterization of the PBR/TSPO, and the imidazopyridines CLINDE and PBR111, we demonstrate the utility of (GuwiyangWurra)TSPO knockouts to provide robust data on drug specificity and selectivity, both in vitro and in vivo, as well as the mechanism of action of putative TSPO-targeting drugs.

Effect of pioglitazone on L-NAME induced hypertension in diabetic rats.

The present study investigates the effect of pioglitazone treatment on blood pressure, vascular reactivity and antioxidant enzymes in L-NAME induced hypertension in normal and STZ-diabetic rats. Diabetes was induced in male Sprague Dawley rats (200+/-15 g) by single intravenous injection of 55 mg/kg of streptozotocin (STZ). Rats were randomized into diabetic and nondiabetic groups, Nomega-nitro-L-arginine-methyl ester (L-NAME, 50 mg/kg) was administered in drinking water for 4 weeks. They were treated with pioglitazone (10 mg/kg/day, p.o.) for 4 weeks and following protocol was carried out. Blood pressure, blood glucose levels and body weight were measured. Thoracic aorta was isolated and dose response curve of phenylephrine (PE) with intact and denuded endothelium was recorded. Dose response curve of acetylcholine (Ach) and sodium nitroprusside (SNP) was recorded in precontracted rings. Lipid peroxidation, superoxide dismutase, catalase, and reduced glutathione were estimated in liver, kidney, and aorta. Pioglitazone produced no significant effect on blood glucose levels, body weight and blood pressure of L-NAME administered nondiabetic and diabetic rats. Pioglitazone treatment had no significant effect on PE induced contraction and Ach induced relaxation in L-NAME diabetic and nondiabetic rats. SNP completely relaxed aortic rings of all the groups. Higher oxidative stress in case of diabetic rats was significantly (p<0.05) reduced by pioglitazone treatment. Although pioglitazone reduced oxidative stress in diabetic rats, there was no significant effect on blood pressure as there was complete absence of nitric oxide due to administration of L-NAME. Hence from the present study it can be concluded that reduction in blood pressure in case of STZ-diabetic rats is nitric oxide mediated.