Abstract
Second-generation translocator protein (TSPO) radioligands were developed to circumvent the technical short comings of 11C-PK11195, the first TSPO targeting tracer. However, in early clinical positron emission tomography (PET) studies they displayed greater inter- and intra-subject variability than was expected given the promising characteristics they showed in preclinical and in vitro studies. A great deal of this variability, although not all, can be explained by the rs6971 polymorphism in the gene encoding TSPO. This polymorphism causes a single amino acid substitution in the TSPO which, for all second-generation tracers tested in man hitherto, reduces binding affinity in mutants relative to wild type. This has obvious implications for interpretation of data, because inter-subject comparisons in PET studies are predicated on the assumption that binding affinity is consistent across all subjects. In this paper, we discuss the implications of the rs6971 polymorphism on study design, analysis and interpretation of data for clinical PET studies using second-generation TSPO radioligands.
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References
Hinz R, Boellaard R (2015) Challenges of quantification of TSPO in the human brain. Clin Transl Imaging. doi:10.1007/s40336-015-0138-7
Imaizumi M, Briard E, Zoghbi SS, Gourley JP, Hong J, Fujimura Y et al (2008) Brain and whole-body imaging in nonhuman primates of [11C] PBR28, a promising PET radioligand for peripheral benzodiazepine receptors. Neuroimage 39(3):1289–1298
Chauveau F, Boutin H, Van CN, Dolle F, Tavitian B (2008) Nuclear imaging of neuroinflammation: a comprehensive review of [11C] PK11195 challengers. Eur J Nucl Med Mol Imagin 35(12):2304–2319
Brown AK, Fujita M, Fujimura Y, Liow JS, Stabin M, Ryu YH et al (2007) Radiation dosimetry and biodistribution in monkey and man of 11C-PBR28: a PET radioligand to image inflammation. J Nucl Med 48(12):2072–2079
Fujita M, Imaizumi M, Zoghbi SS, Fujimura Y, Farris AG, Suhara T et al (2008) Kinetic analysis in healthy humans of a novel positron emission tomography radioligand to image the peripheral benzodiazepine receptor, a potential biomarker for inflammation. Neuroimage 40(1):43–52
Ikoma Y, Yasuno F, Ito H, Suhara T, Ota M, Toyama H et al (2007) Quantitative analysis for estimating binding potential of the peripheral benzodiazepine receptor with [(11)C] DAA1106. J Cereb Blood Flow Metab 27(1):173–184
Fujimura Y, Zoghbi SS, Simeon FG, Taku A, Pike VW, Innis RB et al (2009) Quantification of translocator protein (18 kDa) in the human brain with PET and a novel radioligand, (18)F-PBR06. J Nucl Med 50(7):1047–1053
Owen DR, Howell OW, Tang SP, Wells LA, Bennacef I, Bergstrom M et al (2010) Two binding sites for [3H] PBR28 in human brain: implications for TSPO PET imaging of neuroinflammation. J Cereb Blood Flow Metab 30(9):1608–1618
Guo Q, Owen DR, Rabiner EA, Turkheimer FE, Gunn RN (2012) Identifying improved TSPO PET imaging probes through biomathematics: the impact of multiple TSPO binding sites in vivo. NeuroImage 60(2):902–910
Owen DR, Gunn RN, Rabiner EA, Bennacef I, Fujita M, Kreisl WC et al (2011) Mixed-affinity binding in humans with 18-kDa translocator protein ligands. J Nucl Med 52(1):24–32
Owen DR, Lewis AJ, Reynolds R, Rupprecht R, Eser D, Wilkins MR et al (2011) Variation in binding affinity of the novel anxiolytic XBD173 for the 18 kDa translocator protein in human brain. Synapse (NY) 65(3):257–259
Guo Q, Colasanti A, Owen DR, Onega M, Kamalakaran A, Bennacef I et al (2013) Quantification of the specific translocator protein signal of 18F-PBR111 in healthy humans: a genetic polymorphism effect on in vivo binding. J Nucl Med 54(11):1915–1923
Mizrahi R, Rusjan PM, Kennedy J, Pollock B, Mulsant B, Suridjan I et al (2012) Translocator protein (18 kDa) polymorphism (rs6971) explains in vivo brain binding affinity of the PET radioligand [(18)F]-FEPPA. J Cereb Blood Flow Metab 32(6):968–972
Lavisse S, Garcia-Lorenzo D, Peyronneau MA, Bodini B, Thiriez C, Kuhnast B et al (2015) Optimized quantification of translocator protein radioligand 18F-DPA-714 uptake in the brain of genotyped healthy volunteers. J Nucl Med 56(7):1048–1054
Yoder KK, Nho K, Risacher SL, Kim S, Shen L, Saykin AJ (2013) Influence of TSPO genotype on 11C-PBR28 standardized uptake values. J Nucl Med 54:1320–1322
Kreisl WC, Jenko KJ, Hines CS, Lyoo CH, Corona W, Morse CL et al (2013) A genetic polymorphism for translocator protein 18 kDa affects both in vitro and in vivo radioligand binding in human brain to this putative biomarker of neuroinflammation. J Cereb Blood Flow Metab 33(1):53–58
Kobayashi M, Jenko K, Zoghbi S, Lohith T, Rallis-Frutos D, Page E, Ikawa M, Pike V, Innis R, Fujita M (2015) Blockade of translocator protein (TSPO) to measure specific binding of 11C-(R)-PK 11195 in human brain. J Nucl Med 56:467
Owen DR, Guo Q, Kalk NJ, Colasanti A, Kalogiannopoulou D, Dimber R et al (2014) Determination of [(11)C] PBR28 binding potential in vivo: a first human TSPO blocking study. J Cereb Blood flow Metab 34(6):989–994
Jucaite A, Cselenyi Z, Arvidsson A, Ahlberg G, Julin P, Varnas K et al (2012) Kinetic analysis and test-retest variability of the radioligand [11C] (R)-PK11195 binding to TSPO in the human brain—a PET study in control subjects. EJNMMI Res 2:15
Park E, Gallezot JD, Delgadillo A, Liu S, Planeta B, Lin SF et al (2015) (11)C-PBR28 imaging in multiple sclerosis patients and healthy controls: test-retest reproducibility and focal visualization of active white matter areas. Eur J Nucl Med Mol Imagin 42(7):1081–1092
Salinas CA, Searle GE, Gunn RN (2015) The simplified reference tissue model: model assumption violations and their impact on binding potential. J Cereb Blood Flow Metab 35(2):304–311
Canat X, Carayon P, Bouaboula M, Cahard D, Shire D, Roque C et al (1993) Distribution profile and properties of peripheral-type benzodiazepine receptors on human hemopoietic cells. Life Sci 52(1):107–118
Rizzo G, Veronese M, Tonietto M, Zanotti-Fregonara P, Turkheimer FE, Bertoldo A (2014) Kinetic modeling without accounting for the vascular component impairs the quantification of [(11)C] PBR28 brain PET data. J Cereb Blood Flow Metab 34(6):1060–1069
Fan Z, Harold D, Pasqualetti G, Williams J, Brooks DJ, Edison P (2015) Can studies of neuroinflammation in a TSPO genetic subgroup (HAB or MAB) be applied to the entire AD cohort? J Nucl Med 56(5):707–713
Lyoo CH, Ikawa M, Liow JS, Zoghbi SS, Morse CL, Pike VW et al (2015) Cerebellum can serve as a pseudo-reference region in Alzheimer disease to detect neuroinflammation measured with PET radioligand binding to translocator protein. J Nucl Med 56(5):701–706
Hannestad J, Gallezot JD, Schafbauer T, Lim K, Kloczynski T, Morris ED et al (2012) Endotoxin-induced systemic inflammation activates microglia: [11C] PBR28 positron emission tomography in nonhuman primates. NeuroImage 63(1):232–239
Yoder KK, Territo PR, Hutchins GD, Hannestad J, Morris ED, Gallezot JD et al (2015) Comparison of standardized uptake values with volume of distribution for quantitation of [(11)C] PBR28 brain uptake. Nucl Med Biol 42(3):305–308
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This review was not funded. This is a review paper, and as such no experiments were performed, and hence no animals or humans were involved and no approval was required.
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D. R. Owen declares that he has no conflict of interest. Q. Guo declares that she has no conflict of interest. E. A. Rabiner declares that he has no conflict of interest. R. N. Gunn declares that he has no conflict of interest.
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Owen, D.R., Guo, Q., Rabiner, E.A. et al. The impact of the rs6971 polymorphism in TSPO for quantification and study design. Clin Transl Imaging 3, 417–422 (2015). https://doi.org/10.1007/s40336-015-0141-z
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DOI: https://doi.org/10.1007/s40336-015-0141-z