ABSTRACT
Purpose
To evaluate the utility of new Translocator protein 18 kDa (TSPO)-targeted fluorescent probes for in vivo molecular imaging of activated microglia.
Methods
Compounds 2–4 were synthesized; their stability and affinity for TSPO were determined. Compounds 2–4 were incubated both with Ra2 cells in the presence of LPS, a potent activator of microglia, and with tissue sections of normal and chemically injured brains. Compounds 2–4 were injected into carotid artery or directly in striatum of mice. Cells and tissue sections from these in vitro and in vivo studies were observed by fluorescence microscopy after histochemical treatments.
Results
Compounds 2–4 are stable in both buffer and physiological medium and showed high affinity for TSPO and were found to stain live Ra2 microglial cells effectively. Double staining with Mito Tracker Red suggested that binding sites of compounds 2 and 3 may exist on mitochondria. In vivo studies showed that compounds 2–4 may penetrate in part into brain; moreover, cells in mouse striatum were stained with compounds 2–4 and microglial marker CD11b.
Conclusion
Compounds 2–4 can fluorescently label activated microglia in vitro and in vivo.
Similar content being viewed by others
Abbreviations
- FITC:
-
fluorescein isothiocyanate isomer 1
- LPS:
-
lipopolysaccharide
- PBR:
-
peripheral benzodiazepine receptor
- PET:
-
positron emission tomography
- RBITC:
-
rhodamine B isothiocyanate
- TSPO:
-
translocator protein 18 kDa
REFERENCES
Venneti S, Lopresti BJ, Wiley CA. The peripheral benzodiazepine receptor (Translocator protein 18 kDa) in microglia: From pathology to imaging. Progr Neurobiol. 2006;80:308–22.
Cagnin A, Brooks DJ, Kennedy AM, Gunn RN, Myers R, Turkheimer FE. In-vivo measurement of activated microglia in dementia. Lancet. 2001;358:461–7.
Papadopoulos V, Baraldi M, Guilarte TR, Knudsen TB, Lacapere JJ, Lindemann P, et al. Translocator protein (18 kDa): new nomenclature for the peripheral-type benzodiazepine receptor based on its structure and molecular function. Trends Pharmacol Sci. 2006;27:402–9.
Cicchetti F, Brownell AL, Williams K, Chen YI, Livni E, Isacson O. Neuroinflammation of the nigrostriatal pathway during progressive 6-OHDA dopamine degeneration in rats monitored by immunohistochemistry and PET imaging. Eur J Nerurosci. 2002;15:991–8.
Schweitzer PJ, Fallon BA, Mann JJ, Kumar JS. PET tracers for the peripheral benzodiazepine receptor and uses thereof. Drug Discov Today. 2010;15:933–42.
Papadopoulos V, Lecanu L, Brown RC, Han Z, Yao Z-X. Peripheral-type benzodiazepine receptor in neurosteroid biosynthesis, neuropathology and neurological disorders. Neuroscience. 2006;138:749–56.
Costantini P, Jacotot E, Decaudin D, Kroemer G. Mitochondrion as a novel target of anticancer chemotherapy. J Natl Canc Inst. 2000;92:1042–53.
Banati RB. Visualizing microglial activation in vivo. Glia. 2002;40:206–17.
Doorduin J, de Vries EFK, Dierckx RA, Klein HC. PET imaging of the peripheral benzodiazepine receptor: monitoring disease progression and therapy response in neurodegenerative disorders. Curr Pharmaceut Des. 2008;14:3297–315.
Romeo E, Auta J, Kozikowski AP, Ma A, Papadopoulos V, Puia G, et al. 2-Aryl-3-indoleacetamides (FGIN-1): a new class of potent and specific ligands for the mitochondrial DBI receptor. J Pharmacol Exp Ther. 1992;262:971–8.
Le Fur G, Terrier ML, Vaucher N, Imbault F, Flamier A, Uzan A, et al. Peripheral benzodiazepine binding sites: effect of PK11195, 1-(2-chlorophenyl)-n-(1-methylpropyl)-3-isoquinolinecarboxamide I. In vitro studies. Life Sci. 1983;32:1839–47.
Marangos PL, Pate J, Boulenger JP, Clark-Rosenberg R. Characterization of peripheral-type benzodiazepine binding sites in brain using [3H]Ro 5–4864. Mol Pharmacol. 1982;22:26–32.
Chauveau F, Boutin H, Van Camp N, Dollé F, Tavitian B. Nuclear imaging of neuroinflammation: a comprehensive review of [11C]PK11195 challengers. Eur J Nucl Med Mol Imag. 2008;35:2304–19.
Boutin H, Chauveau F, Thominiaux C, Kuhnast B, Grégoire MC, Jan S, et al. In vivo imaging of brain lesions with [(11)C]CLINME, a new PET radioligand of peripheral benzodiazepine receptors. Glia. 2007;55:1459–68.
Trapani G, Franco M, Latrofa A, Ricciardi L, Carotti A, Serra M, et al. Novel 2-phenylimidazo[1,2-a]pyridine derivatives as potent and selective ligands for peripheral benzodiazepine receptors. synthesis, binding affinity, and in vivo studies. J Med Chem. 1999;42:3934–41.
Trapani G, Laquintana V, Denora N, Trapani A, Lopedota A, Latrofa A, et al. Structure-activity relationships and effects on neuroactive steroids in a series of 2-phenylimidazo-[1,2-a]pyridineacetamide peripheral benzodiazepine receptors ligands. J Med Chem. 2005;48:292–305.
Sekimata K, Hatano K, Ogawa M, Abe J, Magata Y, Biggio G, et al. Radiosynthesis and in vivo evaluation of N-[11C]methylated imidazopyridineacetamides as PET tracers for peripheral benzodiazepine receptors. Nucl Med Biol. 2008;35:327–34.
Denora N, Laquintana V, Pisu MG, Dore R, Murru L, Latrofa A, et al. 2-Phenyl-imidazo[1,2-a]pyridine compounds containing hydrophilic groups as potent and selective ligands for peripheral benzodiazepine receptors: synthesis, binding affinity and electrophysiological studies. J Med Chem. 2008;51:6876–88.
Kozikowski AP, Kotoula M, Ma D, Boujrad N, Tuckmantel W, Papadopoulos V. Synthesis and biology of a 7-nitro-2,1,3-benzoxadiazol-4-yl derivative of 2-phenylindole-3-acetamide: a fluorescent probe for the peripheral-type benzodiazepine receptor. J Med Chem. 1997;40:2435–9.
Manning HC, Goebel T, Thompson RC, Price RR, Lee H, Bornhop DJ. Targeted molecular imaging agents for cellular-scale bimodal imaging. Bioconjugate Chem. 2004;15:1488–95.
Manning HC, Smith SM, Sexton M, Haviland S, Bai M, Cederquist K, et al. A peripheral benzodiazepine receptor targeted agent for in vitro imaging and screening. Bioconjugate Chem. 2006;17:735–40.
Bai M, Rone MB, Papadopoulos V, Bornhop DJ. A novel functional translocator protein ligand for cancer imaging. Bioconjugate Chem. 2007;18:2018–23.
Chen Y, Zheng X, Dobhal MP, Gryshuk A, Morgan J, Dougherty TJ, et al. Methyl pyrophorbide-R analogues: potential fluorescent probes for the peripheral-type benzodiazepine receptor. Effect of central metal in photosensitizing efficacy. J Med Chem. 2005;48:3692–5.
Taliani S, Da Pozzo E, Bellandi M, Bendinelli S, Pugliesi I, Simorini F, et al. Novel irreversible fluorescent probes targeting the 18 kDa translocator protein: synthesis and biological characterization. J Med Chem. 2010;53(10):4085–1093.
Samuelson LE, Dukes MJ, Hunt CR, Casey JD, Bornhop DJ. TSPO targeted dendrimer imaging agent: synthesis, characterization and cellular internalization. Bioconjugate Chem. 2009;20(11):2082–9.
Laquintana V, Denora N, Lopedota A, Suzuki H, Sawada M, Serra M, et al. N-Benzyl-2-(6,8-dichloro-2-(4-chlorophenyl)imidazo[1,2-a]pyridin-3-yl)-N-(6- (7-nitrobenzo[c][1,2,5]oxadiazol-4-ylamino)hexyl)acetamide as a new fluorescent probe for peripheral benzodiazepine receptor and microglial cell visualization. Bioconjugate Chem. 2007;18:1397–407.
Clark DE. Rapid calculation of polar molecular surface area and its application to the prediction of transport phenomena. 2. Prediction of blood-brain barrier penetration. J Pharm Sci. 1999;88:815–21.
Ertl P, Rohde B, Selzer P. Fast calculation of molecular polar surface area as a sum of fragment-based contributions and its application to the prediction of drug transport properties. J Med Chem. 2000;43:3714–7.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Denora, N., Laquintana, V., Trapani, A. et al. New Fluorescent Probes Targeting the Mitochondrial-Located Translocator Protein 18 kDa (TSPO) as Activated Microglia Imaging Agents. Pharm Res 28, 2820–2832 (2011). https://doi.org/10.1007/s11095-011-0552-0
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11095-011-0552-0