Histone deacetylase inhibitors: a survey of recent patents

Structure-activity relationship and mechanistic studies for a series of cinnamyl hydroxamate histone deacetylase inhibitors

Histone deacetylases (HDACs) are a family of enzymes that modulate the acetylation status histones and non-histone proteins. Histone deacetylase inhibitors (HDACis) have emerged as an alternative therapeutic approach for the treatment of several malignancies. Herein, a series of urea-based cinnamyl hydroxamate derivatives is presented as potential anticancer HDACis. In addition, structure-activity relationship (SAR) studies have been performed in order to verify the influence of the linker on the biological profile of the compounds. All tested compounds demonstrated significant antiproliferative effects against solid and hematological human tumor cell lines. Among them, 11b exhibited nanomolar potency against hematological tumor cells including Jurkat and Namalwa, with IC₅₀ values of 40 and 200 nM, respectively. Cellular and molecular proliferation studies, in presence of compounds 11a-d, showed significant cell growth arrest, apoptosis induction, and up to 43-fold selective cytotoxicity for leukemia cells versus non-tumorigenic cells. Moreover, compounds 11a-d increased acetylated α-tubulin expression levels, which is phenotypically consistent with HDAC inhibition, and indirectly induced DNA damage. In vitro enzymatic assays performed for 11b revealed a potent HDAC6 inhibitory activity (IC₅₀: 8.1 nM) and 402-fold selectivity over HDAC1. Regarding SAR analysis, the distance between the hydroxamate moiety and the aromatic ring as well as the presence of the double bond in the cinnamyl linker were the most relevant chemical feature for the antiproliferative activity of the series. Molecular modeling studies suggest that cinnamyl hydroxamate is the best moiety of the series for binding HDAC6 catalytic pocket whereas exploration of Ser568 by the urea connecting unity (CU) might be related with the selectivity observed for the cinnamyl derivatives. In summary, cinnamyl hydroxamate derived compounds with HDAC6 inhibitory activity exhibited cell growth arrest and increased apoptosis, as well as selectivity to acute lymphoblastic leukemia cells. This study explores interesting compounds to fight against neoplastic hematological cells.

Neuropharmacological potentials of β-carboline alkaloids for neuropsychiatric disorders

Neuropsychiatric disorders are diseases of the central nervous system (CNS) which are characterised by complex pathomechanisms that including homeostatic failure, malfunction, atrophy, pathology remodelling and reactivity anomaly of the neuronal system where treatment options remain challenging. β-Carboline (βC) alkaloids are scaffolds of structurally diverse tricyclic pyrido[3,4-b]indole alkaloid with vast occurrence in nature. Their unique structural features which favour interactions with enzymes and protein receptor targets account for their potent neuropharmacological properties. However, our current understanding of their biological mechanisms for these beneficial effects, especially for neuropsychiatric disorders is sparse. Therefore, we present a comprehensive review of the scientific progress in the last two decades on the prospective pharmacology and physiology of the βC alkaloids in the treatment of some neuropsychiatric conditions such as depression, anxiety, Alzheimer's disease, Parkinson's disease, brain tumour, essential tremor, epilepsy and seizure, licking behaviour, dystonia, agnosia, spasm, positive ingestive response as demonstrated in non-clinical models. The current evidence supports that βC alkaloids offer potential therapeutic agents against most of these disorders and amenable for further drug design.

Design and development of sulfonylurea derivatives as zinc metalloenzyme modulators

Sulfonylurea derivatives are zinc metalloenzyme modulators.

Current trends in the development of histone deacetylase inhibitors: a review of recent patent applications

Histone deacetylases (HDACs) have become an important target for the treatment of cancer and other diseases. Currently, more than ten HDAC inhibitors have entered clinical studies and two of them have already reached the market. The hydroxamic acid derivative SAHA (also known as vorinostat or Zolinza®) and the cyclic depsipeptide FK228 (romidepsin or Istodax®) have gained approval from the US FDA for the treatment of cutaneous T-cell lymphoma. Nevertheless, there has been a continuous effort aimed at discovering a new generation of clinical candidates with improved pharmaceutical properties. This review provides a summary of the most recent patents published from mid-2009 to mid-2011.

Histone deacetylase inhibitors: a chemical genetics approach to understanding cellular functions

There are eleven zinc dependent histone deacetylases (HDAC) in humans which have histones and many non-histone substrates. The substrates of these enzymes include proteins that have a role in regulation of gene expression, cell proliferation, cell migration, cell death, immune pathways and angiogenesis. Inhibitors of HDACs (HDACi) have been developed which alter the structure and function of these proteins, causing molecular and cellular changes that induce transformed cell death. The HDACi are being developed as anti-cancer drugs and have therapeutic potential for many non-oncologic diseases.

New patented histone deacetylase inhibitors

IMPORTANCE OF THE FIELD

Following FDA approval of vorinostat in 2006, several novel HDAC inhibitors (HDACis) have entered clinical trials, and there are numerous published patent applications claiming novel HDACis which were optimized as potential drug candidates, designed for regional or systemic release, and created as dual or multifunctional inhibitors. Given the breadth and depth of recent reporting of novel HDACis, there has emerged a need to review the field from a chemist's perspective in one compact article.

AREAS COVERED IN THIS REVIEW

This review provides a summary of published patent applications claiming novel HDACis from 2007 until mid-2009, covering mainly classes I, II and IV anticancer HDACis including those that have recently advanced to the clinic.

WHAT THE READER WILL GAIN

Readers will rapidly gain an overview of the majority of HDACi scaffolds with representative structure-activity relationships; they will learn how these new compounds were created, how their drug like properties were improved and which companies are the main players in the field.

TAKE HOME MESSAGE

Although competition in this field is intense, the future application of HDACis to treat human disease either as single agents or in combination with existing drugs holds real promise.

Histone deacetylase inhibitors--turning epigenic mechanisms of gene regulation into tools of therapeutic intervention in malignant and other diseases

Histone deacetylase inhibitors reside among the most promising targeted anticancer agents that are potent inducers of growth arrest, differentiation, and/or apoptotic cell death of transformed cells. In October 2006, the US Food and Drug Administration approved the first drug of this new class, vorinostat (1, Zolinza, Merck). Several histone deacetylase (HDAC) inhibitors more are in clinical trials. HDAC inhibitors have shown significant activity against a variety of hematological and solid tumors at doses that are well tolerated by patients, both in monotherapy as well as in combination therapy with other drugs. This paper reviews the most recent developments in HDAC inhibitor design, particularly in the context of anticancer therapy, and other possible pharmaceutical applications.

Identification and optimisation of a series of substituted 5-pyridin-2-yl-thiophene-2-hydroxamic acids as potent histone deacetylase (HDAC) inhibitors

Further investigation of a series of thienyl-based hydroxamic acids that included ADS100380 and ADS102550 led to the identification of the 5-pyridin-2-yl-thiophene-2-hydroxamic acid 3c, which possessed modest HDAC inhibitory activity. Substitution at the 5- and 6-positions of the pyridyl ring of compound 3c provided compounds 5a-g, 7a, b, 9, and 13a. Compound 5b demonstrated improved potency, in vitro DMPK profile, and rat oral bioavailability, compared to ADS102550. Functionalisation of the pendent phenyl group of compounds 5b, 5e and 13a provided analogues that possessed excellent enzyme inhibition and anti-proliferative activity.

Identification and optimisation of a series of substituted 5-(1H-pyrazol-3-yl)-thiophene-2-hydroxamic acids as potent histone deacetylase (HDAC) inhibitors

Optimisation of ADS100380, a sub-micromolar HDAC inhibitor identified using a virtual screening approach, led to a series of substituted 5-(1H-pyrazol-3-yl)-thiophene-2-hydroxamic acids (6a-i), that possessed significant HDAC inhibitory activity. Subsequent functionalisation of the pendent phenyl group of compounds 6f and 6g provided analogues 6j-w with further enhanced enzyme and anti-proliferative activity. Compound 6j demonstrated efficacy in a mouse xenograft experiment.

Highly Potent and Selective Histone Deacetylase 6 Inhibitors Designed Based on a Small-Molecular Substrate

To find novel histone deacetylase 6 (HDAC6)-selective inhibitors and clarify the structural requirements for HDAC6-selective inhibition, we prepared thiolate analogues designed based on the structure of an HDAC6-selective substrate and evaluated the histone/alpha-tubulin acetylation selectivity by Western blot analysis. Aliphatic compounds 17b-20b selectively caused alpha-tubulin acetylation over histone H4 acetylation. In enzyme assays using HDAC1, HDAC4, and HDAC6, compounds 17a-19a exhibited HDAC6-selective inhibition over HDAC1 and HDAC4.