title: Design, synthesis, and evaluation of hydroxamic acid-based molecular probes for in vivo imaging of histone deacetylase (HDAC) in brain.
abstract: Hydroxamic acid-based histone deacetylase inhibitors (HDACis) are a class of molecules with therapeutic potential currently reflected in the use of suberoylanilide hydroxamic acid (SAHA; Vorinostat) to treat cutaneous T-cell lymphomas (CTCL). HDACis may have utility beyond cancer therapy, as preclinical studies have ascribed HDAC inhibition as beneficial in areas such as heart disease, diabetes, depression, neurodegeneration, and other disorders of the central nervous system (CNS). However, little is known about the pharmacokinetics (PK) of hydroxamates, particularly with respect to CNS-penetration, distribution, and retention. To explore the rodent and non-human primate (NHP) brain permeability of hydroxamic acid-based HDAC inhibitors using positron emission tomography (PET), we modified the structures of belinostat (PXD101) and panobinostat (LBH-589) to incorporate carbon-11. We also labeled PCI 34051 through carbon isotope substitution. After characterizing the in vitro affinity and efficacy of these compounds across nine recombinant HDAC isoforms spanning Class I and Class II family members, we determined the brain uptake of each inhibitor. Each labeled compound has low uptake in brain tissue when administered intravenously to rodents and NHPs. In rodent studies, we observed that brain accumulation of the radiotracers were unaffected by the pre-administration of unlabeled inhibitors. Knowing that CNS-penetration may be desirable for both imaging applications and therapy, we explored whether a liquid chromatography, tandem mass spectrometry (LC-MS-MS) method to predict brain penetrance would be an appropriate method to pre-screen compounds (hydroxamic acid-based HDACi) prior to PET radiolabeling. LC-MS-MS data were indeed useful in identifying additional lead molecules to explore as PET imaging agents to visualize HDAC enzymes in vivo. However, HDACi brain penetrance predicted by LC-MS-MS did not strongly correlate with PET imaging results. This underscores the importance of in vivo PET imaging tools in characterizing putative CNS drug lead compounds and the continued need to discover effect PET tracers for neuroepigenetic imaging.
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School Charlestown, MA 02129, USA.
authors.forename: Changning
authors.initials: C
authors.lastname: Wang
authors.affiliation: Eli Lilly & Co. Indianapolis, IN 46285, USA.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Eessalu
authors.affiliation: Eli Lilly & Co. Indianapolis, IN 46285, USA.
authors.forename: Vanessa N
authors.initials: VN
authors.lastname: Barth
authors.affiliation: Eli Lilly & Co. Indianapolis, IN 46285, USA.
authors.forename: Charles H
authors.initials: CH
authors.lastname: Mitch
authors.affiliation: Stanley Center for Psychiatric Research, Broad Institute of Harvard and MIT 7 Cambridge Center, Cambridge, MA 02142, USA.
authors.forename: Florence F
authors.initials: FF
authors.lastname: Wagner
authors.affiliation: Department of Molecular and Cell Biology, University of California Berkeley, CA 94720, USA.
authors.forename: Yijia
authors.initials: Y
authors.lastname: Hong
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School Charlestown, MA 02129, USA.
authors.forename: Ramesh
authors.initials: R
authors.lastname: Neelamegam
authors.affiliation: Chemical Neurobiology Laboratory, Departments of Neurology and Psychiatry, Center for Human Genetic Research, Massachusetts General Hospital 185 Cambridge Street, Boston, MA 02114, USA.
authors.forename: Frederick A
authors.initials: FA
authors.lastname: Schroeder
authors.affiliation: Stanley Center for Psychiatric Research, Broad Institute of Harvard and MIT 7 Cambridge Center, Cambridge, MA 02142, USA.
authors.forename: Edward B
authors.initials: EB
authors.lastname: Holson
authors.affiliation: Chemical Neurobiology Laboratory, Departments of Neurology and Psychiatry, Center for Human Genetic Research, Massachusetts General Hospital 185 Cambridge Street, Boston, MA 02114, USA.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Haggarty
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School Charlestown, MA 02129, USA.
authors.forename: Jacob M
authors.initials: JM
authors.lastname: Hooker
keywords: HDAC inhibitors; Hydroxamic acid; PET; brain; epigenetic; imaging