For PET imaging of 18-kDa translocator protein (TSPO), a biomarker of neuroinflammation, most second-generation radioligands are sensitive to the single nucleotide polymorphism rs6971; however, this is probably not the case for the prototypical agent 11C-PK11195 (11C-labeled N-butan-2-yl-1-(2-chlorophenyl)-N-methylisoquinoline-3-carboxamide), which has a relatively lower signal-to-noise ratio. We recently found that 11C-ER176 (11C-(R)-N-sec-butyl-4-(2-chlorophenyl)-N-methylquinazoline-2-carboxamide), a new analog of 11C-(R)-PK11195, showed little sensitivity to rs6971 when tested in vitro and had high specific binding in monkey brain. This study sought, first, to determine whether the sensitivity of 11C-ER176 in humans is similar to the low sensitivity measured in vitro and, second, to measure the nondisplaceable binding potential (BPND, or the ratio of specific-to-nondisplaceable uptake) of 11C-ER176 in human brain. METHODS: Nine healthy volunteers-3 high-affinity binders (HABs), 3 mixed-affinity binders (MABs), and 3 low-affinity binders (LABs)-were studied with whole-body 11C-ER176 PET imaging. SUVs from 60 to 120 min after injection derived from each organ were compared between genotypes. Eight separate healthy volunteers-3 HABs, 3 MABs, and 2 LABs-underwent brain PET imaging. The 3 HABs underwent a repeated brain scan after TSPO blockade with XBD173 (N-benzyl-N-ethyl-2-(7-methyl-8-oxo-2-phenylpurin-9-yl)acetamide) to determine nondisplaceable distribution volume (VND) via Lassen occupancy plotting and thereby estimate BPND in brain. RESULTS: Regional SUV averaged from 60 to 120 min after injection in brain and peripheral organs with high TSPO densities such as lung and spleen were greater in HABs than in LABs. On the basis of VND determined via the occupancy plot, the whole-brain BPND for LABs was estimated to be 1.4 ± 0.8, which was much lower than that for HABs (4.2 ± 1.3) but about the same as that for HABs with 11C-PBR28 ([methyl-11C]N-acetyl-N-(2-methoxybenzyl)-2-phenoxy-5-pyridinamine)) (∼1.2). CONCLUSION: Obvious in vivo sensitivity to rs6971 was observed in 11C-ER176 that had not been expected from in vitro studies, suggesting that the future development of any improved radioligand for TSPO should consider the possibility that in vitro properties will not be reflected in vivo. We also found that 11C-ER176 has adequately high BPND for all rs6971 genotypes. Thus, the new radioligand would likely have greater sensitivity in detecting abnormalities in patients.
For PET imaging of 18-kDa translocator protein (TSPO), a biomarker of neuroinflammation, most second-generation radioligands are sensitive to the single nucleotide polymorphism rs6971; however, this is probably not the case for the prototypical agent 11C-PK11195 (11C-labeled N-butan-2-yl-1-(2-chlorophenyl)-N-methylisoquinoline-3-carboxamide), which has a relatively lower signal-to-noise ratio. We recently found that 11C-ER176 (11C-(R)-N-sec-butyl-4-(2-chlorophenyl)-N-methylquinazoline-2-carboxamide), a new analog of 11C-(R)-PK11195, showed little sensitivity to rs6971 when tested in vitro and had high specific binding in monkey brain. This study sought, first, to determine whether the sensitivity of 11C-ER176 in humans is similar to the low sensitivity measured in vitro and, second, to measure the nondisplaceable binding potential (BPND, or the ratio of specific-to-nondisplaceable uptake) of 11C-ER176 in human brain. METHODS: Nine healthy volunteers-3 high-affinity binders (HABs), 3 mixed-affinity binders (MABs), and 3 low-affinity binders (LABs)-were studied with whole-body 11C-ER176 PET imaging. SUVs from 60 to 120 min after injection derived from each organ were compared between genotypes. Eight separate healthy volunteers-3 HABs, 3 MABs, and 2 LABs-underwent brain PET imaging. The 3 HABs underwent a repeated brain scan after TSPO blockade with XBD173 (N-benzyl-N-ethyl-2-(7-methyl-8-oxo-2-phenylpurin-9-yl)acetamide) to determine nondisplaceable distribution volume (VND) via Lassen occupancy plotting and thereby estimate BPND in brain. RESULTS: Regional SUV averaged from 60 to 120 min after injection in brain and peripheral organs with high TSPO densities such as lung and spleen were greater in HABs than in LABs. On the basis of VND determined via the occupancy plot, the whole-brain BPND for LABs was estimated to be 1.4 ± 0.8, which was much lower than that for HABs (4.2 ± 1.3) but about the same as that for HABs with 11C-PBR28 ([methyl-11C]N-acetyl-N-(2-methoxybenzyl)-2-phenoxy-5-pyridinamine)) (∼1.2). CONCLUSION: Obvious in vivo sensitivity to rs6971 was observed in 11C-ER176 that had not been expected from in vitro studies, suggesting that the future development of any improved radioligand for TSPO should consider the possibility that in vitro properties will not be reflected in vivo. We also found that 11C-ER176 has adequately high BPND for all rs6971 genotypes. Thus, the new radioligand would likely have greater sensitivity in detecting abnormalities in patients.
Authors: Robert B Innis; Vincent J Cunningham; Jacques Delforge; Masahiro Fujita; Albert Gjedde; Roger N Gunn; James Holden; Sylvain Houle; Sung-Cheng Huang; Masanori Ichise; Hidehiro Iida; Hiroshi Ito; Yuichi Kimura; Robert A Koeppe; Gitte M Knudsen; Juhani Knuuti; Adriaan A Lammertsma; Marc Laruelle; Jean Logan; Ralph Paul Maguire; Mark A Mintun; Evan D Morris; Ramin Parsey; Julie C Price; Mark Slifstein; Vesna Sossi; Tetsuya Suhara; John R Votaw; Dean F Wong; Richard E Carson Journal: J Cereb Blood Flow Metab Date: 2007-05-09 Impact factor: 6.200
Authors: Vincent J Cunningham; Eugenii A Rabiner; Mark Slifstein; Marc Laruelle; Roger N Gunn Journal: J Cereb Blood Flow Metab Date: 2009-09-09 Impact factor: 6.200
Authors: Vassilios Papadopoulos; Mario Baraldi; Tomás R Guilarte; Thomas B Knudsen; Jean-Jacques Lacapère; Peter Lindemann; Michael D Norenberg; David Nutt; Abraham Weizman; Ming-Rong Zhang; Moshe Gavish Journal: Trends Pharmacol Sci Date: 2006-07-05 Impact factor: 14.819
Authors: Paolo Zanotti-Fregonara; Yi Zhang; Kimberly J Jenko; Robert L Gladding; Sami S Zoghbi; Masahiro Fujita; Gianluca Sbardella; Sabrina Castellano; Sabrina Taliani; Claudia Martini; Robert B Innis; Federico Da Settimo; Victor W Pike Journal: ACS Chem Neurosci Date: 2014-08-25 Impact factor: 4.418
Authors: Paolo Zanotti-Fregonara; Mattia Veronese; Belen Pascual; Robert C Rostomily; Federico Turkheimer; Joseph C Masdeu Journal: Eur J Nucl Med Mol Imaging Date: 2019-01-17 Impact factor: 9.236
Authors: Jinsoo Hong; Sanjay Telu; Yi Zhang; William H Miller; H Umesha Shetty; Cheryl L Morse; Victor W Pike Journal: Nat Protoc Date: 2021-08-06 Impact factor: 13.491
Authors: Soumen Paul; Evan Gallagher; Jeih-San Liow; Sanche Mabins; Katharine Henry; Sami S Zoghbi; Roger N Gunn; William C Kreisl; Erica M Richards; Paolo Zanotti-Fregonara; Cheryl L Morse; Jinsoo Hong; Aneta Kowalski; Victor W Pike; Robert B Innis; Masahiro Fujita Journal: J Cereb Blood Flow Metab Date: 2018-05-11 Impact factor: 6.200