Design and synthesis of novel HDAC8 inhibitory 2,5-disubstituted-1,3,4-oxadiazoles containing glycine and alanine hybrids with anti cancer activity

Oxadiazole is a heterocyclic compound containing an oxygen atom and two nitrogen atoms in a five-membered ring. Of the four oxadiazoles known, 1,3,4-oxadiazole has become an important structural motif for the development of new drugs and the compounds containing 1,3,4-oxadiazole cores have a broad spectrum of biological activity. Herein, we describe the design, synthesis and biological evaluation of a series of novel 2,5-disubstituted 1,3,4-oxadiazoles (10a–10j) as class I histone deacetylase (HDAC) inhibitors. The compounds were designed and evaluated for HDAC8 selectivity using in silico docking software (Glide) and the top 10 compounds with high dock score and obeying Lipinski’s rule were synthesized organically. Further the biological HDAC inhibitory and selectivity assays and anti-proliferative assays were carried out. In in silico and in vitro studies, all compounds (10a–10j) showed significant HDAC inhibition and exhibited HDAC8 selectivity. Among all tested compounds, 10b showed substantial HDAC8 inhibitory activity and better anticancer activity which is comparable to the positive control, a FDA approved drug, vorinostat (SAHA). Structural activity relation is discussed with various substitutions in the benzene ring connected on 1,3,4-oxadizole and glycine/alanine. The study warranted further investigations to develop HDAC8-selective inhibitory molecule as a drug for neoplastic diseases. Novel 1,3,4-oxadizole substituted with glycine/alanine showed HDAC8 inhibition.     

HDAC inhibitors: Targets for tumor therapy,immune modulation and lung diseases

Histone deacetylases (HDACs) are enzymes that play a key role in the epigenetic regulation of gene expression by remodeling chromatin. Inhibition of HDACs is a prospective therapeutic approach for reversing epigenetic alteration in several diseases. In preclinical research, numerous types of HDAC inhibitors were discovered to exhibit powerful and selective anticancer properties. However, such research has revealed that the effects of HDAC inhibitors may be far broader and more intricate than previously thought. This review will provide insight into the HDAC inhibitors and their mechanism of action with special emphasis on the significance of HDAC inhibitors in the treatment of Chronic Obstructive Pulmonary Disease and lung cancer. Nanocarrier-mediated HDAC inhibitor delivery and new approaches for targeting HDACs are also discussed.     

Pimelic diphenylamide 106 is a slow, tight-binding inhibitor of class I histone deacetylases

Histone deacetylase (HDAC) inhibitors, including various benzamides and hydroxamates, are currently in clinical development for a broad range of human diseases, including cancer and neurodegenerative diseases. We recently reported the identification of a family of benzamide-type HDAC inhibitors that are relatively non-toxic compared with the hydroxamates. Members of this class of compounds have shown efficacy in cell-based and mouse models for the neurodegenerative diseases Friedreich ataxia and Huntington disease. Considerable differences in IC(50) values for the various HDAC enzymes have been reported for many of the HDAC inhibitors, leading to confusion as to the HDAC isotype specificities of these compounds. Here we show that a benzamide HDAC inhibitor, a pimelic diphenylamide (106), is a class I HDAC inhibitor, demonstrating no activity against class II HDACs. 106 is a slow, tight-binding inhibitor of HDACs 1, 2, and 3, although inhibition for these enzymes occurs through different mechanisms. Inhibitor 106 also has preference toward HDAC3 with K(i) of approximately 14 nm, 15 times lower than the K(i) for HDAC1. In comparison, the hydroxamate suberoylanilide hydroxamic acid does not discriminate between these enzymes and exhibits a fast-on/fast-off inhibitory mechanism. These observations may explain a paradox involving the relative activities of pimelic diphenylamides versus hydroxamates as gene activators.     

Molecular Modeling Study on Tunnel Behavior in Different Histone Deacetylase Isoforms

Histone deacetylases (HDACs) have emerged as effective therapeutic targets in the treatment of various diseases including cancers as these enzymes directly involved in the epigenetic regulation of genes. However the development of isoform-selective HDAC inhibitors has been a challenge till date since all HDAC enzymes possess conserved tunnel-like active site. In this study, using molecular dynamics simulation we have analyzed the behavior of tunnels present in HDAC8, 10, and 11 enzymes of class I, II, and IV, respectively. We have identified the equivalent tunnel forming amino acids in these three isoforms and found that they are very much conserved with subtle differences to be utilized in selective inhibitor development. One amino acid, methionine of HDAC8, among six tunnel forming residues is different in isoforms of other classes (glutamic acid (E) in HDAC10 and leucine (L) in HDAC 11) based on which mutations were introduced in HDAC11, the less studied HDAC isoform, to observe the effects of this change. The HDAC8-like (L268M) mutation in the tunnel forming residues has almost maintained the deep and narrow tunnel as present in HDAC8 whereas HDAC10-like (L268E) mutation has changed the tunnel wider and shallow as observed in HDAC10. These results explained the importance of the single change in the tunnel formation in different isoforms. The observations from this study can be utilized in the development of isoform-selective HDAC inhibitors.     

Distinct and redundant functions of histone deacetylases HDAC1 and HDAC2 in proliferation and tumorigenesis

Histone deacetylases (HDACs) are negative regulators of gene expression and have been implicated in tumorigenesis and tumor progression. Therefore, HDACs are promising targets for anti-tumor drugs. However, the relevant isoforms of the 18 members encompassing HDAC family have not been identified. Studies utilizing either gene targeting or knockdown approaches reveal both specific and redundant functions of the closely related class I deacetylases HDAC1 and HDAC2 in the control of proliferation and differentiation. Combined ablation of HDAC1 and HDAC2 in different cell types led to a severe proliferation defects or enhanced apoptosis supporting the idea that both enzymes are relevant targets for tumor therapy. In a recent study on the role of HDAC1 in teratoma formation we have reported a novel and surprising function of HDAC1 in tumorigenesis. In this tumor model HDAC1 attenuates proliferation during teratoma formation. In the present work we discuss new findings on redundant and unique functions of HDAC1 and HDAC2 as regulators of proliferation and tumorigenesis and potential implications for applications of HDAC inhibitors as therapeutic drugs.     

Role of metastasis-induced protein S100A4 in human non-tumor pathophysiologies

S100A4, an important member of the S100 family of proteins, is best known for its significant role in promoting cancer progression and metastasis. In addition to its expression in tumors, upregulation of S100A4 expression has been associated with various non-tumor pathophysiology processes. However, the mechanisms underlying the role of S100A4 remain unclear. Activated “host” cells (fibroblasts, immunocytes, vascular cells, among others) secrete S100A4 into the extracellular space in various non-tumor human disorders, where it executes its biological functions by interacting with intracellular target proteins. However, the exact molecular mechanisms underlying these interactions in different non-tumor pathophysiologies vary, and S100A4 is likely one of the cross-linking factors that acts as common intrinsic constituents of biological mechanisms. Numerous studies have indicated that the S100A4-mediated epithelial–mesenchymal transition plays a vital role in the occurrence and development of various non-tumor pathophysiologies. Epithelial–mesenchymal transition can?be?categorized?into?three?general subtypes based on the phenotype and function of the output cells. S100A4 regulates tissue fibrosis associated with the type II epithelial–mesenchymal transition via various signaling pathways. Additionally, S100A4 stimulates fibroblasts to secrete fibronectin and collagen, thus forming the structural components of the extracellular matrix (ECM) and stimulating their deposition in tissues, contributing to the formation of a pro-inflammatory niche. Simultaneously, S100A4 enhances the motility of macrophages, neutrophils, and leukocytes and promotes the recruitment and chemotaxis of these inflammatory cells to regulate inflammation and immune functions. S100A4 also exerts a neuroprotective pro-survival effect on neurons by rescuing them from brain injury and participates in angiogenesis by interacting with other target molecules. In this review, we summarize the role of S100A4 in fibrosis, inflammation, immune response, neuroprotection, angiogenesis, and some common non-tumor diseases as well as its possible involvement in molecular pathways and potential clinical value.     

Design, synthesis and preliminary bioactivity studies of 1,3,4-thiadiazole hydroxamic acid derivatives as novel histone deacetylase inhibitors

Histone deacetylase (HDAC) inhibitors have emerged as a new class of anticancer agents, targeting the biological processes including cell cycle, apoptosis and differentiation. In the present study, a series of 1,3,4-thiadiazole based hydroxamic acids were developed as potent HDAC inhibitors. Some of them showed good inhibitory activity in HDAC enzyme assay and potent growth inhibition in some tumor cell lines. Among them, compound 6i (IC(50) = 0.089 μM), exhibited better inhibitory effect compared with SAHA (IC(50) = 0.15 μM).     

Quantification of Histone Deacetylase Isoforms in Human Frontal Cortex,Human Retina,and Mouse Brain

Histone deacetylase (HDAC) inhibition has promise as a therapy for Alzheimer’s disease (AD) and other neurodegenerative diseases. Currently, therapeutic HDAC inhibitors target many HDAC isoforms, a particularly detrimental approach when HDAC isoforms are known to have different and specialized functions. We have developed a multiple reaction monitoring (MRM) mass spectrometry assay using stable isotope-labeled QconCATs as internal standards to quantify HDAC isoforms. We further determined a quantitative pattern of specific HDACs expressed in various human and mouse neural tissues. In human AD frontal cortex, HDAC1,2 decreased 32%, HDAC5 increased 47%, and HDAC6 increased 31% in comparison to age-matched controls. Human neural retina concentrations of HDAC1, 2, HDAC5, HDAC6, and HDAC7 decreased in age-related macular degeneration (AMD)-affected donors and exhibited a greater decrease in AD-affected donors in comparison to age-matched control neural retinas. Additionally, HDAC concentrations were measured in whole hemisphere of brain of 5XFAD mice, a model of β-amyloid deposition, to assess similarity to AD in human frontal cortex. HDAC profiles of human frontal cortex and mouse hemisphere had noticeable differences and relatively high concentrations of HDAC3 and HDAC4 in mice, which were undetectable in humans. Our method for quantification of HDAC isoforms is a practical and efficient technique to quantify isoforms in various tissues and diseases. Changes in HDAC concentrations reported herein contribute to the understanding of the pathology of neurodegeneration.     

Focal Nature of Neurological Disorders Necessitates Isotype-Selective Histone Deacetylase (HDAC) Inhibitors

Histone deacetylase (HDAC) inhibitors represent a promising new avenue of therapeutic options for a range of neurological disorders. Within any particular neurological disorder, neuronal damage or death is not widespread; rather, particular brain regions are preferentially affected. Different disorders exhibit distinct focal pathologies. Hence, understanding the region-specific effects of HDAC inhibitors is essential for targeting appropriate brain areas and reducing toxicity in unaffected areas. The outcome of HDAC inhibition depends on several factors, including the diversity in the central nervous system expression of HDAC enzymes, selectivity of a given HDAC inhibitor for different HDAC enzymes, and the presence or absence of cofactors necessary for enzyme function. This review will summarize brain regions associated with various neurological disorders and factors affecting the consequences of HDAC inhibition.     

Histone deacetylase 6 and heat shock protein 90 control the functions of Foxp3(+) T-regulatory cells

Foxp3(+) T-regulatory cells (Tregs) are key to immune homeostasis such that their diminished numbers or function can cause autoimmunity and allograft rejection. Foxp3(+) Tregs express multiple histone/protein deacetylases (HDACs) that regulate chromatin remodeling, gene expression, and protein function. Pan-HDAC inhibitors developed for oncologic applications enhance Treg production and Treg suppression function but have limited nononcologic utility given their broad actions and various side effects. We show, using HDAC6-deficient mice and wild-type (WT) mice treated with HDAC6-specific inhibitors, that HDAC6 inhibition promotes Treg suppressive activity in models of inflammation and autoimmunity, including multiple forms of experimental colitis and fully major histocompatibility complex (MHC)-incompatible cardiac allograft rejection. Many of the beneficial effects of HDAC6 targeting are also achieved by inhibition of the HDAC6-regulated protein heat shock protein 90 (HSP90). Hence, selective targeting of a single HDAC isoform, HDAC6, or its downstream target, HSP90, can promote Treg-dependent suppression of autoimmunity and transplant rejection.     

Distinct and redundant functions of histone deacetylases HDAC1 and HDAC2 in proliferation and tumorigenesis

Histone deacetylases (HDACs) are negative regulators of gene expression and have been implicated in tumorigenesis and tumor progression. Therefore, HDACs are promising targets for antitumor drugs. However, the relevant isoforms of the 18 members encompassing HDAC family have not been identified. Studies utilizing either gene targeting or knockdown approaches reveal both specific and redundant functions of the closely related class I deacetylases HDAC1 and HDAC2 in the control of proliferation and differentiation. Combined ablation of HDAC1 and HDAC2 in different cell types led to a severe proliferation defects or enhanced apoptosis supporting the idea that both enzymes are relevant targets for tumor therapy. In a recent study on the role of HDAC1 in teratoma formation we have reported a novel and surprising function of HDAC1 in tumorigenesis. In this tumor model HDAC1 attenuates proliferation during teratoma formation. In the present work we discuss new findings on redundant and unique functions of HDAC1 and HDAC2 as regulators of proliferation and tumorigenesis and potential implications for applications of HDAC inhibitors as therapeutic drugs.Key words: tumor therapy, HDAC inhibitor, teratoma, chromatin, epigenetics, proliferation, histone acetylation, tumorigenesis     

靶向c-Myc的癌症治疗策略

c-Myc是一种转录因子,参与Myc/Max/Mxd信号调控网络。c-Myc不仅调节机体的正常发育,在肿瘤的发生发展过程中也发挥着十分重要的作用。目前的研究显示,超过70%肿瘤中存在c-Myc突变或表达量的变化。因此,c-Myc靶向抑制剂可能成为肿瘤治疗的新策略。目前,临床上尚无针对c-Myc的治疗方法,但是随着靶向c-Myc临床应用研究的不断深入,以Omomyc为代表的抑制剂研究取得了较大的进展,并且c-Myc在肿瘤中的直接抑制可能发展为可行的临床治疗手段。虽然靶向c-Myc在癌症治疗中具有广阔的前景,但c-Myc的直接抑制目前仍存在诸多的风险与挑战。本综述中,首先,对c-Myc在细胞中的调节网络及其生物学功能进行简要的总结;其次,讨论靶向c-Myc及其同系物在肿瘤治疗中的潜在意义;另外,总结c-Myc作为一个潜在的临床治疗靶点应用于临床所面临的诸多挑战。最后,对目前已经发现的一些c-Myc抑制剂,例如小分子抑制剂以及蛋白质和肽类抑制剂的优缺点进行对比与探讨,并就其所存在的问题作出展望,从而为癌症中以c-Myc为靶点的临床治疗提供理论依据。     

Histone Deacetylase (HDAC) 10 Suppresses Cervical Cancer Metastasis through Inhibition of Matrix Metalloproteinase (MMP) 2 and 9 Expression

Aberrant expression of histone deacetylases (HDACs) is associated with carcinogenesis. Some HDAC inhibitors are widely considered as promising anticancer therapeutics. A major obstacle for development of HDAC inhibitors as highly safe and effective anticancer therapeutics is that our current knowledge on the contributions of different HDACs in various cancer types remains scant. Here we report that the expression level of HDAC10 was significantly lower in patients exhibiting lymph node metastasis compared with that in patients lacking lymph node metastasis in human cervical squamous cell carcinoma. Forced expression of HDAC10 in cervical cancer cells significantly inhibited cell motility and invasiveness in vitro and metastasis in vivo. Mechanistically, HDAC10 suppresses expression of matrix metalloproteinase (MMP) 2 and 9 genes, which are known to be critical for cancer cell invasion and metastasis. At the molecular level, HDAC10 binds to MMP2 and -9 promoter regions, reduces the histone acetylation level, and inhibits the binding of RNA polymerase II to these regions. Furthermore, an HDAC10 mutant lacking histone deacetylase activity failed to mimic the functions of full-length protein. These results identify a critical role of HDAC10 in suppression of cervical cancer metastasis, underscoring the importance of developing isoform-specific HDAC inhibitors for treatment of certain cancer types such as cervical squamous cell carcinoma.