The positron emission tomography ligand DAA1106 binds with high affinity to activated microglia in human neurological disorders.

Abstract

Chronic microglial activation is an important component of many neurological disorders, and imaging activated microglia in vivo will enable the detection and improved treatment of neuroinflammation. 1-(2-chlorphenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinoline-carbox-amide (PK11195), a peripheral benzodiazepine receptor ligand, has been used to image neuroinflammation, but the extent to which PK11195 binding distinguishes activated microglia and reactive astrocytes is unclear. Moreover, PK11195 may lack sufficient sensitivity for detecting mild neuroinflammation. We hypothesized that N-(2,5-dimethoxybenzyl)-N-(4-fluoro-2-phenoxyphenyl) acetamide (DAA1106), a new ligand that binds specifically to peripheral benzodiazepine receptor, binds to activated microglia in human neurological diseases with higher affinity than does PK11195. We therefore compared the pharmacological binding properties of [3H](R)-PK11195 and [3H]DAA1106 in postmortem tissues from patients with cerebral infarcts, amyotrophic lateral sclerosis, Alzheimer disease, frontotemporal dementia, and multiple sclerosis (n=10 each). In all diseases, [3H]DAA1106 showed a higher binding affinity as reflected by lower dissociation constant (KD) values than that of [3H](R)-PK11195. Moreover, specific binding of both ligands correlated with the presence of activated microglia identified by immunohistochemistry in situ. We conclude that 1) ligands that bind peripheral benzodiazepine receptor mainly label activated microglia in human neurological disorders and that 2) DAA1106 may possess binding characteristics superior to those of PK11195, which may be beneficial for in vivo positron emission tomography imaging.

• Authors: Sriram Venneti, Guoji Wang, Jason Nguyen, Clayton A Wiley
• Journal: Journal of neuropathology and experimental neurology (J Neuropathol Exp Neurol) Vol. 67 Issue 10 Pg. 1001-10 (Oct 2008) ISSN: 0022-3069 [Print] England
• PMID: 18800007 (Publication Type: Comparative Study, Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Acetamides
• DAA 1106
• Isoquinolines
• Phenyl Ethers
• Radiopharmaceuticals
• PK 11195

Topics

• Acetamides (pharmacokinetics)
• Aged
• Aged, 80 and over
• Autoradiography
• Brain (pathology)
• Female
• Humans
• Inflammation (diagnostic imaging, pathology)
• Isoquinolines (pharmacokinetics)
• Male
• Microglia (diagnostic imaging, metabolism)
• Middle Aged
• Nervous System Diseases (diagnostic imaging, metabolism)
• Phenyl Ethers (pharmacokinetics)
• Positron-Emission Tomography
• Radiopharmaceuticals (pharmacokinetics)