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Comparison of [(11)C]-(R)-PK 11195 and [(11)C]PBR28, Two Radioligands for Translocator Protein (18 kDa) in Human and Monkey: Implications for Positron Emission Tomographic Imaging of This Inflammation Biomarker

Comparison of [(11)C]-(R)-PK 11195 and [(11)C]PBR28, Two Radioligands for Translocator Protein (18 kDa) in Human and Monkey: Implications for Positron Emission Tomographic Imaging of This Inflammation Biomarker

William C Kreisl, Masahiro Fujita, Yota Fujimura, Nobuyo Kimura, Kimberly J Jenko, Pavitra Kannan, Jinsoo Hong, Cheryl L Morse, Sami S Zoghbi, Robert L Gladding, Steven Jacobson, Unsong Oh, Victor W Pike, etc.

Neuroimage. 2010 Feb 15;49(4):2924-32.

PMID: 19948230

Abstract:

Ten percent of humans lack specific binding of [(11)C]PBR28 to 18 kDa translocator protein (TSPO), a biomarker for inflammation. "Non-binders" have not been reported using another TSPO radioligand, [(11)C]-(R)-PK 11195, despite its use for more than two decades. This study asked two questions: (1) What is the cause of non-binding to PBR28? and (2) Why has this phenomenon not been reported using [(11)C]-(R)-PK 11195?
Methods:
Five binders and five non-binders received whole-body imaging with both [(11)C]-(R)-PK 11195 and [(11)C]PBR28. In vitro binding was performed using leukocyte membranes from binders and non-binders and the tritiated versions of the ligand. Rhesus monkeys were imaged with [(11)C]-(R)-PK 11195 at baseline and after blockade of TSPOs.
Results:
Using [(11)C]PBR28, uptake in all five organs with high densities of TSPO (lung, heart, brain, kidney, and spleen) was 50% to 75% lower in non-binders than in binders. In contrast, [(11)C]-(R)-PK 11195 distinguished binders and non-binders in only heart and lung. For the in vitro assay, [(3)H]PBR28 had more than 10-fold lower affinity to TSPO in non-binders than in binders. The in vivo specific binding of [(11)C]-(R)-PK 11195 in monkey brain was approximately 80-fold lower than that reported for [(11)C]PBR28.
Conclusions:
Based on binding of [(3)H]PK 11195 to leukocyte membranes, both binders and non-binders express TSPO. Non-binding to PBR28 is caused by its low affinity for TSPO in non-binders. Non-binding may be differentially expressed in organs of the body. The relatively low in vivo specific binding of [(11)C]-(R)-PK 11195 may have obscured its detection of non-binding in peripheral organs.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP85532758	PK 11195		85532-75-8	Price

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