Browsing by Author "Guilloteau, D"

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    Decreased vesicular acetylcholine transporter and α4β2 nicotinic receptor density in the rat brain following 192 IgG-saporin immunolesioning
    (Elsevier, 2007-03-26) Quinlivan, M; Chalon, S; Vergote, J; Henderson, J; Katsifis, A; Kassiou, M; Guilloteau, D
    Degeneration of cholinergic neurons is a well known characteristic of Alzheimer's disease (AD). Two radioligands were studied in a rat model of cholinergic degeneration to evaluate their potential efficacy for molecular imaging of AD. Following specific cholinergic-cell immunolesioning with 192 IgG-saporin (SAP), ex vivo autoradiography was performed with 123IBVM, a radioligand which targets the vesicular acetylcholine transporter (VAChT). Following the decay of 123I, the same animals had in vitro autoradiography performed with 125I-A-85380, a marker for nicotinic acetylcholine receptors (nAChRs). As expected significant, widespread decreases in 123IBVM uptake were observed in SAP treated animals. Moderate but significant reductions in 125I-A-85380 binding in the hippocampus (Hip) and cerebellum (Cbm) were also observed following SAP immunolesioning. The results with 123IBVM confirm and extend previous work investigating the uptake of radioiodinated IBVM in this animal model. The results with 125I-A-85380 are unique and are in contrast with work performed in this animal model with other nAChR radioligands, indicating the favourable properties of this radioligand for molecular imaging. © 2006 Elsevier Ireland Ltd.
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    Detection and quantification of remote microglial activation in rodent models of focal ischaemia using the TSPO radioligand CLINDE.
    (Springer, 2010-12-01) Arlicot, N; Petit, E; Katsifis, A; Toutain, J; Divoux, D; Bodard, S; Roussel, S; Guilloteau, D; Bernaudin, M; Chalon, S
    Purpose: Neuroinflammation is involved in stroke pathophysiology and might be imaged using radioligands targeting the 18 kDa translocator protein (TSPO). Methods: We studied microglial reaction in brain areas remote from the primary lesion site in two rodent models of focal cerebral ischaemia (permanent or transient) using [125I]-CLINDE, a promising TSPO single photon emission computed tomography radioligand. Results: In a mouse model of permanent middle cerebral artery occlusion (MCAO), ex vivo autoradiographic studies demonstrated, besides in the ischaemic territory, accumulation of [125I]-CLINDE in the ipsilateral thalamus with a binding that progressed up to 3 weeks after MCAO. [125I]- CLINDE binding markedly decreased in animals preinjected with either unlabelled CLINDE or PK11195, while no change was observed with flumazenil pre-treatment, demonstrating TSPO specificity. In rats subjected to transient MCAO, [125I]-CLINDE binding in the ipsilateral thalamus and substantia nigra pars reticulata (SNr) was significantly higher than that in contralateral tissue. Moreover, [125I]-CLINDE binding in the thalamus and SNr was quantitatively correlated to the ischaemic volume assessed by MRI in the cortex and striatum, respectively. Conclusion: Clinical consequences of secondary neuronal degeneration in stroke might be better treated thanks to the discrimination of neuronal processes using in vivo molecular imaging and potent TSPO radioligands like CLINDE to guide therapeutic interventions. © 2010, Springer.
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    Development of PET and SPECT radiopharmaceuticals to study multi-drug resistance (MDR)
    (Australian Nuclear Science and Technology Organisation, 2002-04-29) Katsifis, A; Guilloteau, D; Dikic, B; Garrigos, M; Emond, P; Greguric, I; Knott, RB; Marvel, S; Mattner, F
    Cellular resistance or Multidrug Resistance (MDR) to cytotoxic agents is the major cause of treatment failure in many human cancers. P-glycoprotein (Pgp), a Mr 17,0000 transmembrane protein and Multi Resistance Protein (MRP) are two proteins that are over expressed and confer resistance to a large number of chemotherapeutic agents by enhancing their extracellular transport. P-glycoprotein is expressed at a relative high level in treated and untreated human malignant tumours, including renal, colonic, adrenal, hepatocellular carcinoma and a considerable percentage of breast carcinomas. 99mTc-Sestamibi, a lipophilic cationic complex is a transport substrate for Pgp. In clinical studies of human neoplasms it was found that tumour uptake and clearance of this tracer correlate with Pgp expression and may be used for the phenotypic assessment of MDR. However, new tracers with better substrate specificity for Pgp and other drug transporters would greatly assist in optimising chemotherapeutic treatment and improving patient management by predicting tumour response to therapy and to assist in the development of antagonists, which may reverse or halt MDR. The aim of this project is therefore to develop PET and SPECT radiopharmaceuticals with improved affinity and selectivity for Pgp and MRP for the clinical evaluation of MDR in cancer patients. To optimise cellular transport characteristics, a number of chemical families that have been found to be substrates of Pgp and other drug efflux pumps, will be investigated. In the first instance, a series of drugs based on the flavonol natural product, Quercetin will be developed, screened for MDR and radiolabelled with PET and SPECT isotopes. Quercetin and related flavonol derivatives have been selected for this project because of their moderate to good affinity for Pgp. With the assistance of molecular modeling and in vitro studies, structural modification will be undertaken to improve the specificity and affinity for PgP. This generic structure also offers the flexibility to prepare a wide range of molecules that are readily suitable for halogenation with either Iodine-123 or F-18 for radiopharmaceutical development. Finally these phenolic type of molecules based on Quercetin are relatively less toxic than equivalent drugs. In this proposal an extensive research program is required to develop specific drugs for the different efflux pumps present in the body, which represent multi drug resistance. A successful outcome is critically dependent on the initial synthesis of a large number of compounds for screening. The combined effort of the three institutions will boost resources significantly to a critical level required to competitively produce successful outcomes in the project. Optimisation studies on derivatives of these flavonols will be made in parallel with the assistance of in vitro studies by measuring the binding of compounds to the ATP sites of Pgp. An extensive in vitro screening program has been established in Paris, prior to radiolabelling and in vivo evaluation. Structural optimisation and attachment of radionuclides to promising molecular targets will be explored using molecular modelling. Initially computational chemistry using Sybyl will be undertaken to develop a pharmacophore and to assist with the incorporation of the radionuclide in the appropriate position. In vivo evaluation will be undertaken in specific animal models both at the University of Tours in France as well as at the Sydney Cancer Centre in Australia. PET functional imaging studies may be undertaken on successful candidates at the SHFJ in Orsay, France whilst SPECT imaging will be undertaken in both Tours and in Sydney. In addition to intellectual property and potential commercial product(s), specific PET or SPECT radiopharmaceuticals can provide valuable information on the assessment of MDR in cancer patients through functional, non-invasive, imaging and therefore make significant contributions to the understanding of MDR. Scientific and clinical researchers from both countries identified the use of PET and SPECT functional imaging of MDR as a priority area of research. Finally the clear benefits to cancer patients include choice of treatment, with minimisation of ineffective drug treatments at an earlier stage, hence reduced drug side effects and discomfort to patients and improvements in their quality of life. There are also reduced health costs by avoiding expensive and ineffective drug treatments,
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    Evaluation of CLINDE as potent translocator protein (18 kDa) SPECT radiotracer reflecting the degree of neuroinflammation in a rat model of microglial activation
    (Springer Nature, 2008-06-07) Arlicot, N; Katsifis, A; Garreau, L; Mattner, F; Vergote, J; Duval, S; Bodard, S; Guilloteau, D; Chalon, S
    The translocator protein (TSPO; 18 kDa), the new name of the peripheral-type benzodiazepine receptor, is localised in mitochondria of glial cells and expressed in very low concentrations in normal brain. Their expression rises after microglial activation following brain injury. Accordingly, TSPO are potential targets to evaluate neuroinflammatory changes in a variety of CNS disorders. To date, only a few effective tools are available to explore TSPO by SPECT. We characterised here 6-chloro-2-(4'iodophenyl)-3-(N,N-diethyl) -imidazo[1,2-a]pyridine-3-acetamide or CLINDE in a rat model with different stages of excitotoxic lesion. Excitotoxicity was induced in male Wistar rats by unilateral intrastriatal injection of different amounts of quinolinic acid (75, 150 or 300 nmol). Six days later, two groups of rats (n = 5-6/group) were i.v. injected with [125I]-CLINDE (0.4 MBq); one group being pre-injected with PK11195 (5 mg/kg). Brains were removed 30 min after tracer injection and the radioactivity of cerebral areas measured. Complementary ex vivo autoradiography, in vitro autoradiography ([3H]-PK11195) and immunohistochemical studies (OX-42) were performed on brain sections. In the control group, [125I]-CLINDE binding was significantly higher (p < 0.001) in lesioned than that in intact side. This binding disappeared in rats pre-treated with PK11195 (p<0.001), showing specific binding of CLINDE to TSPO. Ex vivo and in vitro autoradiographic studies and immunohistochemistry were consistent with this, revealing a spatial correspondence between radioactivity signal and activated microglia. Regression analysis yielded a positive relation between the ligand binding and the degree of neuroinflammation. These results demonstrate that CLINDE is suitable for TSPO in vivo SPECT imaging to explore their involvement in neurodegenerative disorders associated with microglial activation. © 2008 Springer International Publishing