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Varlow C, Mathis CA, Vasdev N. In vitro evaluation of [ 3H]PI-2620 and structural derivatives in non-Alzheimer's tauopathies. Nucl Med Biol 2024; 130-131:108891. [PMID: 38458074 DOI: 10.1016/j.nucmedbio.2024.108891] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Revised: 01/28/2024] [Accepted: 02/16/2024] [Indexed: 03/10/2024]
Abstract
Alzheimer's disease (AD) and non-AD tauopathies such as chronic traumatic encephalopathy (CTE), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD) are characterized by the abnormal aggregation of three-repeat (3R) and/or four-repeat (4R) tau isoforms. Several tau-PET tracers have been applied for human imaging of AD and non-AD tauopathies including [18F]PI-2620. Our objective is to evaluate [3H]PI-2620 and two promising structural derivatives, [3H]PI-2014 and [3H]F-4, using in vitro saturation assays and competitive binding assays against new chemical entities based on this scaffold in human AD tissues for comparison with PSP, CBD and CTE tissues. Thin section autoradiography was employed to assess specific binding and distribution of [3H]PI-2620 and [3H]F-4 in fresh-frozen human post-mortem AD, PSP, CBD and CTE tissues. Immunohistochemistry was performed for phospho-tau (AT8) and 4R-tau (RD4). Homogenate filtration binding assays were performed for saturation analysis and competitive binding studies against [3H]PI-2620. All compounds bound with high affinity in AD tissue. In PSP tissue [3H]PI-2620 demonstrated the highest affinity (5.3 nM) and in CBD tissue [3H]F-4 bound with the highest affinity (9.4 nM). Over 40 fluorinated derivatives based on PI-2620 and F-4 were screened in AD and PSP tissue. Notably, compound 2 was the most potent derivative in PSP tissue (Ki = 7.3 nM). By autoradiography, [3H]PI-2620 and [3H]F-4 demonstrated positive signals similar in intensity in AD, PSP and CTE tissues that were displaced by homologous blockade. Binding of both radiotracers aligned with immunostaining for 4R-tau. This work demonstrates that [3H]PI-2620 and [3H]F-4 show promise for imaging 4R-tau aggregates in non-AD tauopathies. PI-2620 continues to serve as a structural scaffold for PET radiotracers with higher affinity for non-AD tau over AD tau.
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Affiliation(s)
- Cassis Varlow
- Institute of Medical Science, University of Toronto, ON M5S 1A8, Canada; Brain Health Imaging Centre, Centre for Addiction and Mental Health, Toronto, ON M5T 1R8, Canada.
| | - Chester A Mathis
- Department of Radiology, University of Pittsburgh, PA 15213, USA
| | - Neil Vasdev
- Institute of Medical Science, University of Toronto, ON M5S 1A8, Canada; Brain Health Imaging Centre, Centre for Addiction and Mental Health, Toronto, ON M5T 1R8, Canada.
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Cao L, Kong Y, Ji B, Ren Y, Guan Y, Ni R. Positron Emission Tomography in Animal Models of Tauopathies. Front Aging Neurosci 2022; 13:761913. [PMID: 35082657 PMCID: PMC8784812 DOI: 10.3389/fnagi.2021.761913] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Accepted: 11/30/2021] [Indexed: 12/18/2022] Open
Abstract
The microtubule-associated protein tau (MAPT) plays an important role in Alzheimer's disease and primary tauopathy diseases. The abnormal accumulation of tau contributes to the development of neurotoxicity, inflammation, neurodegeneration, and cognitive deficits in tauopathy diseases. Tau synergically interacts with amyloid-beta in Alzheimer's disease leading to detrimental consequence. Thus, tau has been an important target for therapeutics development for Alzheimer's disease and primary tauopathy diseases. Tauopathy animal models recapitulating the tauopathy such as transgenic, knock-in mouse and rat models have been developed and greatly facilitated the understanding of disease mechanisms. The advance in PET and imaging tracers have enabled non-invasive detection of the accumulation and spread of tau, the associated microglia activation, metabolic, and neurotransmitter receptor alterations in disease animal models. In vivo microPET studies on mouse or rat models of tauopathy have provided significant insights into the phenotypes and time course of pathophysiology of these models and allowed the monitoring of treatment targeting at tau. In this study, we discuss the utilities of PET and recently developed tracers for evaluating the pathophysiology in tauopathy animal models. We point out the outstanding challenges and propose future outlook in visualizing tau-related pathophysiological changes in brain of tauopathy disease animal models.
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Affiliation(s)
- Lei Cao
- Institute for Regenerative Medicine, University of Zurich, Zurich, Switzerland
- Changes Technology Corporation Ltd., Shanghai, China
| | - Yanyan Kong
- PET Center, Huashan Hospital, Fudan University, Shanghai, China
| | - Bin Ji
- Department of Radiopharmacy and Molecular Imaging, School of Pharmacy, Fudan University, Shanghai, China
| | - Yutong Ren
- Guangdong Robotics Association, Guangzhou, China
| | - Yihui Guan
- PET Center, Huashan Hospital, Fudan University, Shanghai, China
| | - Ruiqing Ni
- Institute for Regenerative Medicine, University of Zurich, Zurich, Switzerland
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
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Seen SB, Gong Y, Ashton M. The application of the Fischer indole synthesis in medicinal chemistry. ADVANCES IN HETEROCYCLIC CHEMISTRY 2022. [DOI: 10.1016/bs.aihch.2022.11.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Kroth H, Oden F, Molette J, Schieferstein H, Gabellieri E, Mueller A, Berndt M, Sreenivasachary N, Serra AM, Capotosti F, Schmitt-Willich H, Hickman D, Pfeifer A, Dinkelborg L, Stephens A. PI-2620 Lead Optimization Highlights the Importance of Off-Target Assays to Develop a PET Tracer for the Detection of Pathological Aggregated Tau in Alzheimer's Disease and Other Tauopathies. J Med Chem 2021; 64:12808-12830. [PMID: 34455780 DOI: 10.1021/acs.jmedchem.1c00861] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The first candidate PI-2014 was tested in healthy controls and subjects with Alzheimer's disease (AD). As PI-2014 displayed off-target binding to monoamine oxidase A (MAO-A), a new lead with improved binding to Tau and decreased MAO-A binding was required. For compound optimization, Tau binding assays based on both human AD brain homogenate and Tau-paired helical filaments were employed. Furthermore, two MAO-A screening assays based on (1) human-recombinant MAO-A and (2) displacement of 2-fluoro-ethyl-harmine from mouse brain homogenate were employed. Removing the N-methyl group from the tricyclic core resulted in compounds displaying improved Tau binding. For the final round of optimization, the cyclic amine substituents were replaced by pyridine derivatives. PI-2620 (2-(2-fluoropyridin-4-yl)-9H-pyrrolo[2,3-b:4,5-c']dipyridine) emerged as a best candidate displaying high Tau binding, low MAO-A binding, high brain uptake, and fast and complete brain washout. Furthermore, PI-2620 showed Tau binding on brain sections from corticobasal degeneration, progressive supranuclear palsy, and Pick's disease.
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Affiliation(s)
- Heiko Kroth
- AC Immune SA, EPFL Innovation Park, Building B, 1015 Lausanne, Switzerland
| | - Felix Oden
- Life Molecular Imaging GmbH, Tegeler Strasse 6-7, 13353 Berlin, Germany
| | - Jerome Molette
- AC Immune SA, EPFL Innovation Park, Building B, 1015 Lausanne, Switzerland
| | | | | | - Andre Mueller
- Life Molecular Imaging GmbH, Tegeler Strasse 6-7, 13353 Berlin, Germany
| | - Mathias Berndt
- Life Molecular Imaging GmbH, Tegeler Strasse 6-7, 13353 Berlin, Germany
| | | | | | | | | | - David Hickman
- AC Immune SA, EPFL Innovation Park, Building B, 1015 Lausanne, Switzerland
| | - Andrea Pfeifer
- AC Immune SA, EPFL Innovation Park, Building B, 1015 Lausanne, Switzerland
| | - Ludger Dinkelborg
- Life Molecular Imaging GmbH, Tegeler Strasse 6-7, 13353 Berlin, Germany
| | - Andrew Stephens
- Life Molecular Imaging GmbH, Tegeler Strasse 6-7, 13353 Berlin, Germany
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