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Telomere maintenance is essential to preserve genomic stability and involves telomere-specific proteins, DNA replication and repair proteins. Lamins are key components of the nuclear envelope and play numerous roles, including maintenance of the nuclear integrity, regulation of transcription, and DNA replication. Elevated levels of lamin B1, one of the major lamins, have been observed in some human pathologies and several cancers. Yet, the effect of lamin B1 dysregulation on telomere maintenance remains unknown. Here, we unveil that lamin B1 overexpression drives telomere instability through the disruption of the shelterin complex. Indeed, lamin B1 dysregulation leads to an increase in telomere dysfunction-induced foci, telomeric fusions and telomere losses in human cells. Telomere aberrations were preceded by mislocalizations of TRF2 and its binding partner RAP1. Interestingly, we identified new interactions between lamin B1 and these shelterin proteins, which are strongly enhanced at the nuclear periphery upon lamin B1 overexpression. Importantly, chromosomal fusions induced by lamin B1 in excess were rescued by TRF2 overexpression. These data indicated that lamin B1 overexpression triggers telomere instability through a mislocalization of TRF2. Altogether our results point to lamin B1 as a new interacting partner of TRF2, that is involved in telomere stability., (© The Author(s) 2021. Published by Oxford University Press on behalf of Nucleic Acids Research.)

Double-strand breaks (DSBs) are harmful lesions and a major cause of genome instability. Studies have suggested a link between the nuclear envelope and the DNA damage response. Here, we show that lamin B1, a major component of the nuclear envelope, interacts directly with 53BP1 protein, which plays a pivotal role in the DSB repair. This interaction is dissociated after DNA damage. Lamin B1 overexpression impedes 53BP1 recruitment to DNA damage sites and leads to a persistence of DNA damage, a defect in nonhomologous end joining and an increased sensitivity to DSBs. The identification of interactions domains between lamin B1 and 53BP1 allows us to demonstrate that the defect of 53BP1 recruitment and the DSB persistence upon lamin B1 overexpression are due to sequestration of 53BP1 by lamin B1. This study highlights lamin B1 as a factor controlling the recruitment of 53BP1 to DNA damage sites upon injury., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

The accumulation of senescent cells accompanies organismal aging. Senescent cells produce an inflammatory microenvironment that is conducive to the development of many age-related diseases. Here we describe the different situations leading to cellular senescence and show that these situations are frequently associated with DNA damage. We also discuss the intimate link between cell aging and perturbations in the nuclear envelope, namely in nuclear lamins, as seen in progeroid syndromes. Finally, we present evidence that these alterations are associated with DNA repair defects, the persistence of DNA damage, and an inflammatory phenotype., (© 2020 médecine/sciences – Inserm.)

The tumor microenvironment is highly heterogeneous. For gliomas, the tumor-associated inflammatory response is pivotal to support growth and invasion. Factors of glioma growth, inflammation, and invasion, such as the translocator protein (TSPO) and matrix metalloproteinases (MMP), may serve as specific imaging biomarkers of the glioma microenvironment. In this study, noninvasive imaging by PET with [ 18 F]DPA-714 (TSPO) and [ 18 F]BR-351 (MMP) was used for the assessment of localization and quantification of the expression of TSPO and MMP. Imaging was performed in addition to established clinical imaging biomarker of active tumor volume ([ 18 F]FET) in conjunction with MRI. We hypothesized that each imaging biomarker revealed distinct areas of the heterogeneous glioma tissue in a mouse model of human glioma. Tracers were found to be increased 1.4- to 1.7-fold, with [ 18 F]FET showing the biggest volume as depicted by a thresholding-based, volumes of interest analysis. Tumor areas, which could not be detected by a single tracer and/or MRI parameter alone, were measured. Specific compartments of [ 18 F]DPA-714 (14%) and [ 18 F]BR-351 (11%) volumes along the tumor rim could be identified. [ 18 F]DPA-714 (TSPO) and [ 18 F]BR-351 (MMP) matched with histology. Glioma-associated microglia/macrophages (GAM) were identified as TSPO and MMP sources. Multitracer and multimodal molecular imaging approaches may allow us to gain important insights into glioma-associated inflammation (GAM, MMP). Moreover, this noninvasive technique enables characterization of the glioma microenvironment with respect to the disease-driving cellular compartments at the various disease stages. Cancer Res; 77(8); 1831-41. ©2017 AACR ., (©2017 American Association for Cancer Research.)

Introduction: A growing area of research suggests that neuroimmunity may impact the pharmacology of opioids. Microglia is a key component of the brain immunity. Preclinical and clinical studies have demonstrated that microglial modulators may improve morphine-induced analgesia and prevent the development of tolerance and dependence. Positron emission tomography (PET) using translocator protein 18kDa (TSPO) radioligand is a clinically validated strategy for the non-invasive detection of microglial activation. We hypothesized that TSPO PET imaging may be used to study the neuroimmune component of opioid tolerance and withdrawal., Methods: Healthy rats (n=6 in each group) received either saline or escalating doses of morphine (10-40mg/kg) on five days to achieve tolerance and a withdrawal syndrome after morphine discontinuation. MicroPET imaging with [ 18 F]DPA-714 was performed 60h after morphine withdrawal. Kinetic modeling was performed to estimate [ 18 F]DPA-714 volume of distribution (V T ) in several brain regions using dynamic PET images and corresponding metabolite-corrected input functions. Immunohistochemistry (IHC) experiments on striatal brain slices were performed to assess the expression of glial markers (Iba1, GFAP and CD68) during 14days after morphine discontinuation., Results: The baseline binding of [ 18 F]DPA-714 to the brain (V T =0.086±0.009mLcm -3 ) was not increased by morphine exposure and withdrawal (V T =0.079±0.010mLcm -3 ) indicating the absence of TSPO overexpression, even at the regional level. Accordingly, expression of glial markers did not increase after morphine discontinuation., Conclusions: Morphine tolerance and withdrawal did not detectably activate microglia and had no impact on [ 18 F]DPA-714 brain kinetics in vivo., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

Key Points: Vascular brain lesions and atherosclerosis are two similar conditions that are characterized by increased inflammation and oxidative stress. Non-invasive imaging in a murine model of atherosclerosis showed vascular brain damage and peripheral inflammation. In this study, exercise training reduced magnetic resonance imaging-detected abnormalities, insulin resistance and markers of oxidative stress and inflammation in old ApoE -/- mice. Our results demonstrate the protective effect of exercise on neurovascular damage in the ageing brain of ApoE -/- mice., Abstract: Vascular brain lesions, present in advanced atherosclerosis, share pathological hallmarks with peripheral vascular lesions, such as increased inflammation and oxidative stress. Physical activity reduces these peripheral risk factors, but its cerebrovascular effect is less documented, especially by non-invasive imaging. Through a combination of in vivo and post-mortem techniques, we aimed to characterize vascular brain damage in old ApoE -/- mice fed a high-cholesterol (HC) diet with dietary controlled intake. We then sought to determine the beneficial effects of exercise training on oxidative stress and inflammation in the brain as a treatment option in an ageing atherosclerosis mouse model. Using in vivo magnetic resonance imaging (MRI) and biological markers of oxidative stress and inflammation, we evaluated the occurrence of vascular abnormalities in the brain of HC-diet fed ApoE -/- mice >70 weeks old, its association with local and systemic oxidative stress and inflammation, and whether both can be modulated by exercise. Exercise training significantly reduced both MRI-detected abnormalities (present in 71% of untrained vs. 14% of trained mice) and oxidative stress (lipid peroxidation, 9.1 ± 1.4 vs. 5.2 ± 0.9 μmol mg -1 ; P < 0.01) and inflammation (interleukin-1β, 226.8 ± 27.1 vs. 182.5 ± 21.5 pg mg -1 ; P < 0.05) in the brain, and the mortality rate. Exercise also decreased peripheral insulin resistance, oxidative stress and inflammation, but significant associations were seen only within brain markers. Highly localized vascular brain damage is a frequent finding in this ageing atherosclerosis model, and exercise is able to reduce this outcome and improve lifespan. In vivo MRI evaluated both the neurovascular damage and the protective effect of exercise., (© 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society.)

Characterizing tumor heterogeneity using texture indices derived from PET images has shown promise in predicting treatment response and patient survival in some types of cancer. Yet, the relationship between PET-derived texture indices, precise tracer distribution, and biologic heterogeneity needs to be clarified. We investigated this relationship using PET images, autoradiographic images, and histologic images., Methods: Three mice bearing orthotopically implanted mammary tumors derived from transgenic MMTV-PyMT mice were scanned with 18 F-FDG PET/CT. The tumors were then sliced, and the slices were imaged with autoradiography and stained with hematoxylin and eosin. Six texture indices derived from the PET images, autoradiographic images, and histologic images were compared for their ability to capture heterogeneity on different scales., Results: The PET-derived indices correlated significantly with the autoradiography-derived ones (R = 0.57-0.85), but the values differed in magnitude. The histology-derived indices correlated poorly with the autoradiography- and PET-derived ones (R = 0.06-0.54). All indices were slightly to moderately influenced by the difference in voxel size and spatial resolution in the autoradiographic images. The autoradiography-derived indices differed significantly (P < 0.05) between regions with a high density of cells and regions with a low density and between regions with different spatial arrangements of cells., Conclusion: Heterogeneity derived in vivo from PET images accurately reflects the heterogeneity of tracer uptake derived ex vivo from autoradiographic images. Various tumor-cell densities and spatial cell distributions seen on histologic images can be distinguished using texture indices derived from autoradiographic images despite the difference in voxel size and spatial resolution. Yet, tumor texture derived from PET images only coarsely reflects the spatial distribution and density of tumor cells., (© 2016 by the Society of Nuclear Medicine and Molecular Imaging, Inc.)

Aim: Advanced atherosclerosis increases inflammation and stroke risk in the cerebral vasculature. Exercise is known to improve cardio-metabolic profiles when associated with a caloric restriction, but it remains debated whether it is still beneficial without the dietary control. The aim of this study was to determine both the peripheral and central effects of exercise training combined with a cholesterol-rich diet given ad libitum in old ApoE -/- mice. Methods : Forty-five-weeks old obese ApoE -/- mice fed with a high cholesterol diet ad libitum were divided into Exercise-trained (EX; running wheel free access) and Sedentary (SED) groups. Insulin tolerance and brain imaging were performed before and after the twelve-weeks training. Tissue insulin resistance, oxidative stress, and inflammation markers in plasma, aorta, and brain were then assessed. Results : In EX ApoE -/- mice, no beneficial effect of exercise was observed on weight, abdominal fat, metabolic parameters, oxidative stress, or inflammation compared to SED. Despite the regular exercise training in ApoE -/- EX mice (mean of 12.5 km/week during 12 weeks), brain inflammation imaging score was significantly associated with increased blood brain barrier (BBB) leakage evaluated by imaging follow-up ( r 2 = 0.87; p = 0.049) with a faster evolution compared to SED ApoE -/- mice. Conclusion : We conclude that in a context of high cardio-metabolic risk, exercise does not provide any protective effect in old ApoE -/- animals under high cholesterol diet given ad libitum . Peripheral (insulin sensitivity and oxidative/inflammatory status) but also central features (BBB preservation and protection against inflammation) did not show any benefits of exercise. Indeed, there was a fast induction of irreversible brain damage that was more pronounced in exercise-trained ApoE -/- mice.

Purpose: Transgenic mice expressing the polyoma middle T oncoprotein (PyMT) in the mammary epithelium were explored by multimodal imaging to monitor longitudinally spontaneous tumor growth and response to chemotherapy., Procedures: Positron emission tomography (PET) with 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) and 3'-deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT), single photon emission tomography (SPECT) with [(99m)Tc]TcO4 ([(99m)Tc]TEC), X-ray computed tomography, and fluorescent confocal endomicroscopy (FCE) images were acquired during tumor progression in female PyMT mice. Imaging with [(18)F]FDG and [(99m)Tc]TEC was also performed in untreated, doxorubicin-treated, and docetaxel-treated PyMT mice. Total tumor volumes were quantified. Tumors were collected and macroscopic and histological examinations were performed., Results: All PyMT mice developed multifocal tumors of the mammary epithelium that became palpable at 8 weeks of age (W8). Computed tomography (CT) detected tumors at W14, while a clear tumoral uptake of [(99m)Tc]TEC and [(18)F]FDG was present as early as W6 and W8, respectively. No contrast between mammary tumors and surrounding tissue was observed at any stage with [(18)F]FLT. FCE detected an angiogenic switch at W10. Lung metastases were not clearly evidenced by imaging. Doxorubicin and docetaxel treatments delayed tumor growth, as shown by [(18)F]FDG and [(99m)Tc]TEC, but tumor growth resumed upon treatment discontinuation. Tumor growth fitted an exponential model with time constant rates of 0.315, 0.145, and 0.212 week(-1) in untreated, doxorubicin, and docetaxel groups, respectively., Conclusions: Molecular imaging of mammary tumors in PyMT is precocious, precise, and predictive. [(18)F]FDG-PET and [(99m)Tc]TEC SPECT monitor tumor response to chemotherapy.

Fluorescence imaging techniques could be used in different ways to study the interaction of aptamers with biological systems from cell culture to animal models. Here, we present the methods developed in our laboratory for fluorescently labeled aptamers, study their internalization inside living cells using time-lapse microscopy, and monitor their biodistribution in mice bearing subcutaneous xenograft tumors using planar fluorescence imaging and fluorescence diffuse optical tomography (fDOT).

Background: Clinical studies implying the sunitinib multi-kinase inhibitor have led to disappointing results for breast cancer care but mostly focused on HER2-negative subtypes. Preclinical researches involving this drug mostly concern Triple Negative Breast Cancer (TNBC) murine models. Here, we explored the therapeutic efficacy of sunitinib on a PyMT-derived transplanted model classified as luminal B (HER2-positive) and monitored the response to treatment using both in vivo and ex vivo approaches., Methods: Tumour-induced animals were treated for 9 (n = 7) or 14 (n = 8) days with sunitinib at 40 mg/kg or with vehicle only. Response to therapy was assessed in vivo by monitoring glucose tumour metabolism and hypoxia using 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) and [(18)F]fluoromisonidazole ([(18)F]FMISO) Positron Emission Tomography (PET). After primary tumour excision, ex vivo digital microscopy was performed on treated and control samples to estimate vascular density (CD31), apoptosis (Tunel), proliferation (Ki-67), Tumour-Associated Macrophage (TAM) infiltration (F4/80), metabolism (GLUT1) and cellular response to hypoxia (HIF1 alpha). The drug impact on the metastasis rate was evaluated by monitoring the PyMT gene expression in the lungs of the treated and control groups., Results: Concomitant with sunitinib-induced tumour size regression, [(18)F]FDG PET imaging showed a stable glycolysis-related metabolism inside tumours undergoing treatment compared to an increased metabolism in untreated tumours, resulting at treatment end in 1.5 less [(18)F]FDG uptake in treated (n = 4) vs control (n = 3) tumours (p < 0.05). With this small sample, [(18)F]FMISO PET showed a non-significant decrease of hypoxia in treated vs control tumours. The drug triggered a 4.9 fold vascular volume regression (p < 0.05), as well as a 17.7 fold induction of tumour cell apoptosis (p < 0.001). The hypoxia induced factor 1 alpha (HIF1 alpha) expression was twice lower in the treated group than in the control group (p < 0.05). Moreover, the occurrence of lung metastases was not reduced by the drug., Conclusions: [(18)F]FDG and [(18)F]FMISO PET were relevant approaches to study the response to sunitinib in this luminal B (HER2-positive) model. The sunitinib-induced vascular network shrinkage did not significantly increase tumour hypoxia, suggesting that tumour regression was mainly due to the pro-apoptotic properties of the drug. Sunitinib did not inhibit the metastatic process in this PyMT transplanted model.

Purpose: The purpose of the study was to validate [18F]DPA-714, a translocator protein (TSPO) 18 kDa radioligand, as a probe to non-invasively quantify the inflammatory state in inflammatory bowel disease (IBD) animal models., Procedures: Quantitative positron emission tomography (PET) imaging of intestinal inflammation was conducted with 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) a glucose metabolism surrogate marker and [18F]DPA-714 a ligand of the 18 kDa TSPO, on two IBD models. The first model was induced using dextran sodium sulfate (DSS), creating global inflammation in the colon. The second model was induced by rectally administering trinitrobenzenesulfonic acid (TNBS), creating local and acute inflammation., Results: The level of inflammation was analyzed using PET imaging on days 7 and 8. The analysis obtained with [18F]DPA-714, yielded a significant difference between the DSS treated (0.50 ± 0.17%ID/cc) and non-treated rats (0.35 ± 0.15%ID/cc). [18F]FDG on the other hand did not yield a significant difference. We did observe a mean glucose consumption in the colon increase from 0.40 ± 0.11 %ID/cc to 0.54 ± 0.17 %ID/cc. In the TNBS model, the uptake level of [18 F]DPA-714 increased significantly from 0.46 ± 0.23%ID/cc for the non-treated group, to 1.30 ± 0.62%ID/cc for those treated. PET signal was correlated with increased TSPO expression at cellular level., Conclusions: Results indicate that [18F]DPA-714 is suitable for studying inflammation in IBD models. [18F]DPA-714 could be a good molecular probe to non-invasively evaluate the level and localization of inflammation. Moreover, in vivo imaging using this TSPO ligand is potentially a powerful tool to stage and certainly to follow the evolution and therapeutic efficiency at molecular level within this disease family.

Background: Cell-SELEX is now widely used for the selection of aptamers against cell surface biomarkers. However, despite negative selection steps using mock cells, this method sometimes results in aptamers against undesirable targets that are expressed both on mock and targeted cells. Studying these junk aptamers might be useful for further applications than those originally envisaged., Methodology/principal Findings: Cell-SELEX was performed to identify aptamers against CHO-K1 cells expressing human Endothelin type B receptor (ETBR). CHO-K1 cells were used for negative selection of aptamers. Several aptamers were identified but no one could discriminate between both cell lines. We decided to study one of these aptamers, named ACE4, and we identified that it binds to the Annexin A2, a protein overexpressed in many cancers. Radioactive binding assays and flow cytometry demonstrated that the aptamer was able to bind several cancer cell lines from different origins, particularly the MCF-7 cells. Fluorescence microscopy revealed it could be completely internalized in cells in 2 hours. Finally, the tumor targeting of the aptamer was evaluated in vivo in nude mice xenograft with MCF-7 cells using fluorescence diffuse optical tomography (fDOT) imaging. Three hours after intravenous injection, the aptamer demonstrated a significantly higher uptake in the tumor compared to a scramble sequence., Conclusions/significance: Although aptamers could be selected during cell-SELEX against other targets than those initially intended, they represent a potential source of ligands for basic research, diagnoses and therapy. Here, studying such aptamers, we identify one with high affinity for Annexin A2 that could be a promising tool for biomedical application.

Unlabelled: On the one hand, the translocator protein (TSPO) radioligand N,N-diethyl-2-(2-(4-(2-(18)F-fluoroethoxy)phenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl)acetamide ((18)F-DPA-714) has been suggested to serve as an alternative radiotracer to image human glioma, and on the other hand the alkylphosphocholine erufosine (ErPC3) has been reported to induce apoptosis in otherwise highly apoptosis-resistant glioma cell lines. The induction of apoptosis by ErPC3 requires TSPO, a mitochondrial membrane protein highly expressed in malignant gliomas. In this preclinical study, we monitored the effect of ErPC3 treatment in vivo using (18)F-DPA-714 PET., Methods: In vitro studies investigated the antitumor effect of ErPC3 in 9L rat gliosarcoma cells. In vivo, glioma-bearing rats were imaged with (18)F-DPA-714 for the time of treatment., Results: A significant decrease in 9L cell proliferation and viability and a significant increase in apoptosis and caspase-3 activation were demonstrated on ErPC3 treatment in cell culture. In the rat model, ErPC3 administration resulted in significant changes in (18)F-DPA-714 tumor uptake over the course of the treatment. Immunohistochemistry revealed reduced tumor volume and increased cell death in ErPC3-treated animals accompanied by infiltration of the tumor core by CD11b-positive microglia/macrophages and glial fibrillary acidic protein-positive astrocytes., Conclusion: Our findings demonstrate a potent antitumor effect of ErPC3 in vitro, in vivo, and ex vivo. PET imaging of TSPO expression using (18)F-DPA-714 allows effective monitoring and quantification of disease progression and response to ErPC3 therapy in intracranial 9L gliomas.

Purpose: Given the progress of fluorescence diffuse optical tomography (fDOT) technology, here, we study the additional benefits provided by multimodal PET/fDOT imaging by comparing the biodistribution of 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) in tumors with three fluorescent probes: a glucose analog, a protease activatable optical probe, and a ligand of αvβ3 integrin., Procedures: Sequential fDOT/PET/computed tomography (CT) imaging of mice was performed with a custom multimodal mouse support that allows the subject to be transferred between the fDOT and the PET/CT scanners. Experiments were performed in xenografted tumor models derived from the human breast cancer line MDA-MB 231 and compared to ex vivo analysis., Results: The three-dimensional signals showed that the fluorescent glucose analog is not colocalized with [(18)F]FDG, raising questions about its use as a surrogate probe of the PET tracer. Fusion of [(18)F]FDG with the other fluorescent probes showed evidence of high variability both for the protease activity and the αvβ3 integrin expression during tumor growth., Conclusion: The added value of hybrid PET/fDOT over the two modalities was demonstrated for cross-validation of probes and for better characterization of tumor models.

Polydiacetylene (PDA) micelles coated with either carboxylate-, ammonium-, or methoxy-polyethyleneglycol (PEG) chains were assembled and loaded with a fluorescent dye (DiO). Their interaction with MCF-7 human breast tumor cells was investigated by epi-fluorescence microscopy and fluorescence-activated cell sorting (FACS) to determine their internalization pathway and intracellular fate. It was found that the ionic character of the micelles influenced their internalization kinetics through a caveolae-mediated pathway and that all micelle types behaved somewhat similarly inside cells.

Blood flow interruption in a cerebral artery causes brain ischemia and induces dramatic changes of perfusion and metabolism in the corresponding territory. We performed in parallel positron emission tomography (PET) with [(15)O]H(2)O, single photon emission computed tomography (SPECT) with [(99m)Tc]hexamethylpropylene-amino-oxime ([(99m)Tc]HMPAO) and ultrasonic ultrafast shear wave imaging (SWI) during, immediately after, and 1, 2, 4, and 7 days after middle cerebral artery occlusion (MCAO) in rats. Positron emission tomography and SPECT showed initial hypoperfusion followed by recovery at immediate reperfusion, hypoperfusion at day 1, and hyperperfusion at days 4 to 7. Hyperperfusion interested the whole brain, including nonischemic areas. Immunohistochemical analysis indicated active angiogenesis at days 2 to 7, strongly suggestive that hyperperfusion was supported by an increase in microvessel density in both brain hemispheres after ischemia. The SWI detected elastic changes of cerebral tissue in the ischemic area as early as day 1 after MCAO appearing as a softening of cerebral tissue whose local internal elasticity decreased continuously from day 1 to 7. Taken together, these results suggest that hyperperfusion after cerebral ischemia is due to formation of neovessels, and indicate that brain softening is an early and continuous process. The SWI is a promising novel imaging method for monitoring the evolution of cerebral ischemia over time in animals.

Purpose: In recent years there has been an increase in the development of radioligands targeting the 18-kDa translocator protein (TSPO). TSPO expression is well documented in activated microglia and serves as a biomarker for imaging neuroinflammation. In addition, TSPO has also been reported to be overexpressed in a number of cancer cell lines and human tumours including glioma. Here we investigated the use of [(18)F]DPA-714, a new TSPO positron emission tomography (PET) radioligand to image glioma in vivo., Methods: We studied the uptake of [(18)F]DPA-714 in three different rat strains implanted with 9L rat glioma cells: Fischer (F), Wistar (W) and Sprague Dawley (SD) rats. Dynamic [(18)F]DPA-714 PET imaging, kinetic modelling of PET data and in vivo displacement studies using unlabelled DPA-714 and PK11195 were performed. Validation of TSPO expression in 9L glioma cell lines and intracranial 9L gliomas were investigated using Western blotting and immunohistochemistry of brain tissue sections., Results: All rats showed significant [(18)F]DPA-714 PET accumulation at the site of 9L tumour implantation compared to the contralateral brain hemisphere with a difference in uptake among the three strains (F > W > SD). The radiotracer showed high specificity for TSPO as demonstrated by the significant reduction of [(18)F]DPA-714 binding in the tumour after administration of unlabelled DPA-714 or PK11195. TSPO expression was confirmed by Western blotting in 9L cells in vitro and by immunohistochemistry ex vivo., Conclusion: The TSPO radioligand [(18)F]DPA-714 can be used for PET imaging of intracranial 9L glioma in different rat strains. This preclinical study demonstrates the feasibility of employing [(18)F]DPA-714 as an alternative radiotracer to image human glioma.

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS. Activated microglia/macrophages play a key role in the immunopathogenesis of MS and its corresponding animal models, experimental autoimmune encephalomyelitis (EAE). Microglia activation begins at early stages of the disease and is associated with elevated expression of the 18 kDa mitochondrial translocator protein (TSPO). Thus, positron emission tomography (PET) imaging of microglial activation using TSPO-specific radioligands could be valuable for monitoring disease-associated neuroinflammatory processes. EAE was induced in rats using a fragment of myelin basic protein, yielding acute clinical disease that reflects extensive spinal cord inflammation. Enhanced TSPO expression in spinal cords of EAE rats versus those of controls was confirmed by Western blot and immunohistochemistry. Biodistribution studies in control and EAE rats were performed using the TSPO radioligand [¹⁸F]DPA-714 [N,N-diethyl-2-(2-(4-(2-fluoroethoxy)phenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl)acetamide]. At 1 h after injection, almost fivefold higher levels of [¹⁸F]DPA-714 were measured in spinal cords of EAE rats versus controls. The specific binding of [¹⁸F]DPA-714 to TSPO in spinal cords was confirmed in competition studies, using unlabeled (R,S)-PK11195 [(R,S)-N-methyl-N-(1-methylpropyl)-1-(2-chlorophenyl)isoquinoline-3-carboxamide)] or DPA-714 in excess. MicroPET studies affirm that this differential radioactivity uptake in spinal cords of EAE versus control rats could be detected and quantified. Using [¹⁸F]DPA-714, neuroinflammation in spinal cords of EAE-induced rats could be visualized by PET, offering a sensitive technique for monitoring neuroinflammatory lesions in the CNS and particularly in the spinal cord. In addition to current MRI protocols, this approach could provide molecular images of neuroinflammation for detection, monitoring, and research in MS.

Purpose: The key role of neuroinflammation in acute and chronic neurological disorders has stimulated the search for specific radiotracers targeting the peripheral benzodiazepine receptor (PBR)/18 kDa translocator protein (TSPO), a hallmark of neuroinflammation. Here we evaluate the new radiotracer for positron emission tomography (PET) [(18)F]PBR111 in a rodent model of acute inflammation and compare it with [(11)C]CLINME, an (11)C-labelled tracer of the same chemical family, and with the isoquinolinic carboxamide [(11)C]PK11195., Methods: We studied radiometabolites by HPLC, in vitro binding by autoradiography and in vivo brain kinetics as well as in vivo specificity of binding using PET imaging., Results: We show that this radiotracer has a high in vitro specificity for PBR/TSPO versus central benzodiazepine receptors, as reflected by the drastic reduction of its binding to target tissue by addition of PK11195 or PBR111, while addition of flumazenil does not affect binding. Only intact [(18)F]PBR111 is detected in brain up to 60 min after i.v. injection, and PET imaging shows an increased uptake in the lesion as compared to the contralateral side as early as 6 min after injection. Administration of an excess of PK11195 and PBR111, 20 min after [(18)F]PBR111 administration, induces a rapid and complete displacement of [(18)F]PBR111 binding from the lesion. Modelling of the PET data using the simplified reference tissue model showed increased binding potential (BP) in comparison to [(11)C]PK11195., Conclusion: [(18)F]PBR111 is a metabolically stable tracer with a high specific in vitro and in vivo binding to TSPO. In addition, considering the longer half-life of (18)F over (11)C, these results support [(18)F]PBR111 as a promising PET tracer of the PBR/TSPO for neuroinflammation imaging.

Focal cerebral ischemia leads to an inflammatory reaction involving an overexpression of the peripheral benzodiazepine receptor (PBR)/18-kDa translocator protein (TSPO) in the cerebral monocytic lineage (microglia and monocyte) and in astrocytes. Imaging of PBR/TSPO by positron emission tomography (PET) using radiolabeled ligands can document inflammatory processes induced by cerebral ischemia. We performed in vivo PET imaging with [(18)F]DPA-714 to determine the time course of PBR/TSPO expression over several days after induction of cerebral ischemia in rats. In vivo PET imaging showed significant increase in DPA (N,N-diethyl-2-(2-(4-(2-fluoroethoxy)phenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl)acetamide) uptake on the injured side compared with that in the contralateral area on days 7, 11, 15, and 21 after ischemia; the maximal binding value was reached 11 days after ischemia. In vitro autoradiography confirmed these in vivo results. In vivo and in vitro [(18)F]DPA-714 binding was displaced from the lesion by PK11195 and DPA-714. Immunohistochemistry showed increased PBR/TSPO expression, peaking at day 11 in cells expressing microglia/macrophage antigens in the ischemic area. At later times, a centripetal migration of astrocytes toward the lesion was observed, promoting the formation of an astrocytic scar. These results show that [(18)F]DPA-714 provides accurate quantitative information of the time course of PBR/TSPO expression in experimental stroke.

Purpose: 6-[(18)F]Fluoro-3,4-dihydroxy-L-phenylalanine (6-[(18)F]F-L-DOPA) is increasingly used for PET imaging of neuroendocrine tumours. In this study, we investigated the use of 6-[(18)F]F-L-DOPA to detect and to monitor the progression of medullary thyroid carcinoma (MTC) in a genetically engineered mouse model of multiple endocrine neoplasia type 2A (MEN2A)., Methods: Dynamic [(18)F]FDG and 6-[(18)F]F-L-DOPA small animal PET scans were acquired during 60 or 90 min in 8- to 20-month-old MEN2A transgenic mice. The kinetics of 6-[(18)F]F-L-DOPA, standardized uptake values (SUV) at 60 min and tumour volumes were recorded. The detection of MTCs using PET was confirmed by autopsy and histological analysis., Results: 6-[(18)F]F-L-DOPA performs better than [(18)F]FDG for MTC detection in this transgenic mouse model. Uptake kinetics of 6-[(18)F]F-L-DOPA in MTCs are very different between mice but, in all cases, high contrast could be observed. Furthermore, 6-[(18)F]F-L-DOPA can detect tumours with sizes (1.8 mm(3)) that are near the resolution limit of PET, whereas they were undetectable by autopsy at the macroscopic level., Conclusion: 6-[(18)F]F-L-DOPA PET imaging can monitor the progression of MTCs in a genetically engineered mouse model.

Delivery of drugs to the appropriate target cells would improve efficacy and reduce potential side effects. The nontoxic B-subunit of the intestinal pathogen-produced Shiga toxin (STxB) binds specifically to the glycosphingolipid Gb3, overexpressed in membranes of certain tumor cells, and enters these cells through the retrograde pathway. Therefore, STxB binding to Gb3 receptors may be useful for cell-specific vectorization or imaging purposes. Here we labeled STxB with a fluorophore to evaluate its potential as an in vivo cell-specific targeting reagent in two different models of human colorectal carcinoma. Fluorescent STxB was administered systemically to xenografted nude mice, and its biodistribution was studied by optical imaging. The use of fluorescent STxB allowed the combination of the macroscopic observations with analyses at the cellular level using confocal microscopy. After administration, the fluorescent STxB was slowly eliminated by renal excretion. However, it accumulated in the tumor area. Furthermore, STxB was demonstrated to enter the Gb3-expressing tumoral cells, as well as the epithelial cells of the neovascularization and the monocytes and macrophages surrounding the xenografts.

We have designed new nanoprobes applicable for both positron emission tomography (PET) and optical fluorescence in vivo imaging. Fluorine-18, which is commonly used for clinical imaging, has been coupled to phospholipid quantum dot (QD) micelles. This probe was injected in mice and we demonstrated that its dynamic quantitative whole body biodistribution and pharmacokinetics could be monitored using PET as well as the kinetics of their cellular uptake using in vivo fibered confocal fluorescence imaging. Phospholipid micelle encapsulation of QDs provides a highly versatile surface chemistry to conjugate multiple chemicals and biomolecules with controlled QD:molecule valency. Here, we show that, in contrast with several previous studies using other QD polymer coatings, these phospholipid QD micelles exhibit long circulation half-time in the bloodstream (on the order of 2 h) and slow uptake by reticulo-endothelial system.