Hydroxamate-based histone deacetylase inhibitors (HDACIs) have been approved as therapeutic agents by the US Food and Drug Administration for use in oncology applications. While the potential utility of such HDACIs in other areas of medicinal chemistry is tremendous, there are significant concerns that “pan-HDAC inhibitors” may be too broadly acting and/or toxic for clinical use beyond oncology. In addition to the isozyme selectivity challenge, the potential mutagenicity of hydroxamate-containing HDAC inhibitors represents a major hindrance in their application to other therapeutic areas. Herein we report on the mutagenicity of known hydroxamates, discuss the mechanisms responsible for their genotoxicity, and review some of the current alternatives to hydroxamates. We conclude that the hydroxamate group, while providing high-potency HDACIs, is not necessarily the best zinc-binding group for HDACI drug discovery.

No abstract

Charcot–Marie–Tooth (CMT) disease is a disorder of the peripheral nervous system where progressive degeneration of motor and sensory nerves leads to motor problems and sensory loss and for which no pharmacological treatment is available. Recently, it has been shown in a model for the axonal form of CMT that histone deacetylase 6 (HDAC6) can serve as a target for the development of a pharmacological therapy. Therefore, we aimed at developing new selective and activity-specific HDAC6 inhibitors with improved biochemical properties. By utilizing a bicyclic cap as the structural scaffold from which to build upon, we developed several analogues that showed improved potency compared to tubastatin A while maintaining excellent selectivity compared to HDAC1. Further screening in N2a cells examining both the acetylation of α-tubulin and histones narrowed down the library of compounds to three potent and selective HDAC6 inhibitors. In mutant HSPB1-expressing DRG neurons, serving as an in vitro model for CMT2, these inhibitors were able to restore the mitochondrial axonal transport deficits. Combining structure-based development of HDAC6 inhibitors, screening in N2a cells and in a neuronal model for CMT2F, and preliminary ADMET and pharmacokinetic profiles, resulted in the selection of compound 23d that possesses improved biochemical, functional, and druglike properties compared to tubastatin A.

No abstract

No abstract

S.J. oversaw the experimental design and data analyses of animal studies. University Health Network: D.S. designed and performed the dose-response tubulin acetylation studies in HEK293 cells and assisted in the preparation of the manuscript, and J.H.E. oversaw the experimental design and data analyses of the in vitro tubulin acetylation study. Leuven Research Institute for Neuroscience and Disease: V.B. designed and performed the tubulin/histone acetylation studies in N2a and assisted in the preparation of the manuscript; L.V.D.B. oversaw the experimental design and data analyses of the in vitro tubulin acetylation study. Promega Corporation: C.A.Z. designed and performed the cellular HDAC target engagement assay; M.B.R. oversaw the experimental design and data analyses of target engagement study and assisted in the preparation of the manuscript. Institute of Biotechnology of the Czech Academy of Sciences: Z.K. performed and confirmed the HDAC6 and HDAC11 data for SW-100. C.B. oversaw the experimental design and data analyses of HDAC enzyme studies.

Tubastatin A, a tetrahydro-γ-carboline-capped selective HDAC6 inhibitor (HDAC6i), was rationally designed 10 years ago, and has become the best investigated HDAC6i to date. It shows efficacy in various neurological disease animal models, as HDAC6 plays a crucial regulatory role in axonal transport deficits, protein aggregation, as well as oxidative stress. In this work, we provide new insights into this HDAC6i by investigating the molecular basis of its interactions with HDAC6 through X-ray crystallography, determining its functional capability to elevate the levels of acetylated αtubulin in vitro and in vivo, correlating PK/PD profiles to determine effective doses in plasma and brain, and finally assessing its therapeutic potential toward psychiatric diseases through use of the SmartCube screening platform.

Human ornithine aminotransferase (hOAT), a pyridoxal 5′-phosphate-dependent enzyme, plays a critical role in the progression of hepatocellular carcinoma (HCC). Pharmacological selective inhibition of hOAT has been shown to be a potential therapeutic approach for HCC. Inspired by the discovery of the nonselective aminotransferase inactivator (1R,3S,4S)-3-amino-4-fluoro cyclopentane-1-carboxylic acid (1), in this work, we rationally designed, synthesized, and evaluated a novel series of fluorine-substituted cyclohexene analogues, thereby identifying 8 and 9 as novel selective hOAT time-dependent inhibitors. Intact protein mass spectrometry and protein crystallography demonstrated 8 and 9 as covalent inhibitors of hOAT, which exhibit two distinct inactivation mechanisms resulting from the difference of a single fluorine atom. Interestingly, they share a similar turnover mechanism, according to the mass spectrometry-based analysis of metabolites and fluoride ion release experiments. Molecular dynamics (MD) simulations and electrostatic potential (ESP) charge calculations were conducted, which elucidated the significant influence of the one-fluorine difference on the corresponding intermediates, leading to two totally different inactivation pathways. The novel additionaromatization inactivation mechanism for 9 contributes to its significantly enhanced potency, along with excellent selectivity over other aminotransferases.