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Summers KL, Roseman G, Schilling KM, Dolgova NV, Pushie MJ, Sokaras D, Kroll T, Harris HH, Millhauser GL, Pickering IJ, George GN. Alzheimer's Drug PBT2 Interacts with the Amyloid β 1-42 Peptide Differently than Other 8-Hydroxyquinoline Chelating Drugs. Inorg Chem 2022; 61:14626-14640. [PMID: 36073854 PMCID: PMC9957665 DOI: 10.1021/acs.inorgchem.2c01694] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Although Alzheimer's disease (AD) was first described over a century ago, it remains the leading cause of age-related dementia. Innumerable changes have been linked to the pathology of AD; however, there remains much discord regarding which might be the initial cause of the disease. The "amyloid cascade hypothesis" proposes that the amyloid β (Aβ) peptide is central to disease pathology, which is supported by elevated Aβ levels in the brain before the development of symptoms and correlations of amyloid burden with cognitive impairment. The "metals hypothesis" proposes a role for metal ions such as iron, copper, and zinc in the pathology of AD, which is supported by the accumulation of these metals within amyloid plaques in the brain. Metals have been shown to induce aggregation of Aβ, and metal ion chelators have been shown to reverse this reaction in vitro. 8-Hydroxyquinoline-based chelators showed early promise as anti-Alzheimer's drugs. Both 5-chloro-7-iodo-8-hydroxyquinoline (CQ) and 5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline (PBT2) underwent unsuccessful clinical trials for the treatment of AD. To gain insight into the mechanism of action of 8HQs, we have investigated the potential interaction of CQ, PBT2, and 5,7-dibromo-8-hydroxyquinoline (B2Q) with Cu(II)-bound Aβ(1-42) using X-ray absorption spectroscopy (XAS), high energy resolution fluorescence detected (HERFD) XAS, and electron paramagnetic resonance (EPR). By XAS, we found CQ and B2Q sequestered ∼83% of the Cu(II) from Aβ(1-42), whereas PBT2 sequestered only ∼59% of the Cu(II) from Aβ(1-42), suggesting that CQ and B2Q have a higher relative Cu(II) affinity than PBT2. From our EPR, it became clear that PBT2 sequestered Cu(II) from a heterogeneous mixture of Cu(II)Aβ(1-42) species in solution, leaving a single Cu(II)Aβ(1-42) species. It follows that the Cu(II) site in this Cu(II)Aβ(1-42) species is inaccessible to PBT2 and may be less solvent-exposed than in other Cu(II)Aβ(1-42) species. We found no evidence to suggest that these 8HQs form ternary complexes with Cu(II)Aβ(1-42).
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Affiliation(s)
- Kelly L. Summers
- Molecular and Environmental Sciences Group, Department of Geological Sciences, College of Arts and Science, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada
- Department of Chemistry, College of Arts and Science, University of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N 5C9, Canada
| | - Graham Roseman
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, 1156 High Street, Santa Cruz, California 95064, United States
| | - Kevin M. Schilling
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, 1156 High Street, Santa Cruz, California 95064, United States
| | - Natalia V. Dolgova
- Molecular and Environmental Sciences Group, Department of Geological Sciences, College of Arts and Science, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada
| | - M. Jake Pushie
- Department of Surgery, University of Saskatchewan, 103 Hospital Dr, Saskatoon, Saskatchewan S7N 0W8, Canada
| | - Dimosthenis Sokaras
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States
| | - Thomas Kroll
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States
| | - Hugh H. Harris
- Department of Chemistry, University of Adelaide, South Australia 5005, Australia
| | - Glenn L. Millhauser
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, 1156 High Street, Santa Cruz, California 95064, United States
| | - Ingrid J. Pickering
- Molecular and Environmental Sciences Group, Department of Geological Sciences, College of Arts and Science, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada
- Department of Chemistry, College of Arts and Science, University of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N 5C9, Canada
| | - Graham N. George
- Molecular and Environmental Sciences Group, Department of Geological Sciences, College of Arts and Science, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada
- Department of Chemistry, College of Arts and Science, University of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N 5C9, Canada
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