The structural requirements of histone deacetylase inhibitors: suberoylanilide hydroxamic acid analogs modified at the C6 position

Advances in dual-targeting inhibitors of HDAC6 for cancer treatment

Histone Deacetylase 6 (HDAC6) is an essential regulator of histone acetylation processes, exerting influence on a multitude of cellular functions such as cell motility, endocytosis, autophagy, apoptosis, and protein trafficking through its deacetylation activity. The significant implications of HDAC6 in diseases such as cancer, neurodegenerative disorders, and immune disorders have motivated extensive investigation into the development of specific inhibitors targeting this enzyme for therapeutic purposes. Single targeting drugs carry the risk of inducing drug resistance, thus prompting exploration of dual targeting therapy which offers the potential to impact multiple signaling pathways simultaneously, thereby lowering the likelihood of resistance development. While pharmacological studies have exhibited promise in combined therapy involving HDAC6, challenges related to potential drug interactions exist. In response to these challenges, researchers are investigating HDAC6 hybrid molecules which enable the concomitant targeting of HDAC6 and other key proteins, thus enhancing treatment efficacy while mitigating side effects and reducing the risk of resistance compared to traditional combination therapies. The published design strategies for dual targeting inhibitors of HDAC6 are summarized and discussed in this review. This will provide some valuable insights into more novel HDAC6 dual targeting inhibitors to meet the urgent need for innovative therapies in oncology and other related fields.

Small Change, Big Impact: Reversal of Diastereoselection in Cuprate Conjugate Additions to α,β-Unsaturated Lactams and Identification of a Competing Mechanism

A seemingly minor change to a reactant is shown to cause a change in reaction mechanisms. Conjugate addition of organocopper reagents to bicyclic α,β-unsaturated lactams derived from pyroglutaminol is determined by the nature of the aminal group. Aminals derived from aldehydes give anti addition; those from ketones give syn addition. Divergence in diastereoselection occurs because the substrates react by different mechanisms, ultimately due to a small but significant difference in pyramidalization of the aminal nitrogen.

Targeting the epigenome in malignant melanoma: Facts, challenges and therapeutic promises

Malignant melanoma is the most lethal type of skin cancer with high rates of mortality. Although current treatment options provide a short-clinical benefit, acquired-drug resistance highlights the low 5-year survival rate among patients with advanced stage of the disease. In parallel, the involvement of an aberrant epigenetic landscape, (e.g., alterations in DNA methylation patterns, histone modifications marks and expression of non-coding RNAs), in addition to the genetic background, has been also associated with the onset and progression of melanoma. In this review article, we report on current therapeutic options in melanoma treatment with a focus on distinct epigenetic alterations and how their reversal, by specific drug compounds, can restore a normal phenotype. In particular, we concentrate on how single and/or combinatorial therapeutic approaches have utilized epigenetic drug compounds in being effective against malignant melanoma. Finally, the role of deregulated epigenetic mechanisms in promoting drug resistance to targeted therapies and immune checkpoint inhibitors is presented leading to the development of newly synthesized and/or improved drug compounds capable of targeting the epigenome of malignant melanoma.

Isolation, Structure Characterization, Total Synthesis and Biological Evaluation of Cinnamic Acid Derivatives from Tinospora sagittata

Thirteen cinnamic acid derivatives (1-13), including six formerly unreported hybrids incorporating different short-chain fatty acid esters (1-6), have been obtained and structurally elucidated from an ethnological herb Tinospora sagittata. The structures of them have been established by spectroscopic data analyses and NMR comparison with known analogs, while those of 1, 2, 4 and 6 have been further supported by total synthesis, and it is the first report of this type of metabolites from the title species. All the isolates have been assessed in an array of bioassays encompassing cytotoxic, antibacterial, anti-inflammatory, antioxidant, as well as α-glucosidase and HDAC1 inhibitory models. Compound 7 showed significant inhibitory activity against α-glucosidase, and half of the isolates also displayed moderate antiradical effect.

A Therapeutic Perspective of HDAC8 in Different Diseases: An Overview of Selective Inhibitors

Histone deacetylases (HDACs) are epigenetic enzymes which participate in transcriptional repression and chromatin condensation mechanisms by removing the acetyl moiety from acetylated ε-amino group of histone lysines and other non-histone proteins. In recent years, HDAC8, a class I HDAC, has emerged as a promising target for different disorders, including X-linked intellectual disability, fibrotic diseases, cancer, and various neuropathological conditions. Selective HDAC8 targeting is required to limit side effects deriving from the treatment with pan-HDAC inhibitors (HDACis); thus, many endeavours have focused on the development of selective HDAC8is. In addition, polypharmacological approaches have been explored to achieve a synergistic action on multi-factorial diseases or to enhance the drug efficacy. In this frame, proteolysis-targeting chimeras (PROTACs) might be regarded as a dual-targeting approach for attaining HDAC8 proteasomal degradation. This review highlights the most relevant and recent advances relative to HDAC8 validation in various diseases, providing a snapshot of the current selective HDAC8is, with a focus on polyfunctional modulators.

Alternative Therapeutic Interventions: Antimicrobial Peptides and Small Molecules to Treat Microbial Keratitis

Microbial keratitis is a leading cause of blindness worldwide and results in unilateral vision loss in an estimated 2 million people per year. Bacteria and fungus are two main etiological agents that cause corneal ulcers. Although antibiotics and antifungals are commonly used to treat corneal infections, a clear trend with increasing resistance to these antimicrobials is emerging at rapid pace. Extensive research has been carried out to determine alternative therapeutic interventions, and antimicrobial peptides (AMPs) are increasingly recognized for their clinical potential in treating infections. Small molecules targeted against virulence factors of the pathogens and natural compounds are also explored to meet the challenges and growing demand for therapeutic agents. Here we review the potential of AMPs, small molecules, and natural compounds as alternative therapeutic interventions for the treatment of corneal infections to combat antimicrobial resistance. Additionally, we have also discussed about the different formats of drug delivery systems for optimal administration of drugs to treat microbial keratitis.

Synthesis and Investigation of Therapeutic Potential of Isoform-Specific HDAC8 Inhibitors for the Treatment of Cutaneous T Cell Lymphoma

BACKGROUND

The available treatment option for any type of cancer including CTCL is chemotherapy and radiation therapy which indiscriminately persuade on the normal cells. One way out for selective destruction of CTCL cells without damaging normal cells is the use of histone deacetylase inhibitors (HDACi). Despite promising results in the treatment of CTCL, these HDACi have shown a broadband inhibition profile, moderately selective for one HDAC class but not for a particular isotype. The prevalence of drug-induced side effects leaves open a narrow window of speculation that the decreased therapeutic efficacy and observed side effects may be most likely due to non specific HDAC isoform inhibition. The aim of this paper is to synthesis and evaluates HDAC8 isoform specific inhibitors.

METHODS

Based on the preliminary report on the design and in silico studies of 52 hydroxamic acid derivatives bearing multi-substituent heteroaromatic rings with chiral amine linker, five compounds were shortlisted and synthesized by microwave assisted approach and high yielding synthetic protocol. A series of in vitro assays in addition to HDAC8 inhibitory activity was used to evaluate the synthesised compounds.

RESULTS

Inhibitors 1e, 2e, 3e, 4e and 5e exerted the anti-proliferative activities against CTCL cell lines at 20- 100 µM concentrations. Both the pyrimidine- and pyridine-based probes exhibited μM inhibitory activity against HDAC8. The pyrimidine-based probe 1e displayed remarkable HDAC8 selectivity superior to that of the standard drug, SAHA with an IC50 at 0.1µM.

CONCLUSION

Our study demonstrated that simple modifications at different portions of pharmacophore in the hydroxamic acid analogues are effective for improving both HDAC8 inhibitory activity and isoform selectivity. Potent and highly isoform-selective HDAC8 inhibitors were identified. These findings would be expedient for further development of HDAC8-selective inhibitors.

1-Arylsulfonyl indoline-benzamides as a new antitubulin agents, with inhibition of histone deacetylase

We report structure-activity relationships of 1-arylsulfonyl indoline based benzamides. The benzamide (9) exhibits striking tubulin inhibition with an IC₅₀ value of 1.1 μM, better than that of combretastain A-4 (3), and substantial antiproliferative activity against a variety of cancer cells, including MDR-positive cell lines with an IC₅₀ value of 49 nM (KB), 79 nM (A549), 63 nM (MKN45), 64 nM (KB-VIN10), 43 nM (KB-S15), and 46 nM (KB-7D). Dual inhibitory potential of compound 9 was found as it demonstrated significant inhibitory potential against HDAC1, 2 and 6 in comparison to MS-275 (6). Some key interactions of 9 with the amino acid residues of the active site of tubulin and with amino acid residues of HDAC 1 isoform have been figured out by molecular modeling. Compound 9 also demonstrated significant in vivo efficacy in the human non-small cell lung cancer A549 xenograft model as well as B-cell lymphoma BJAB xenograft tumor model.

The structural requirements of histone deacetylase inhibitors: C4-modified SAHA analogs display dual HDAC6/HDAC8 selectivity

Histone deacetylase (HDAC) enzymes govern the post-translational acetylation state of lysine residues on protein substrates, leading to regulatory changes in cell function. Due to their role in cancers, HDAC proteins have emerged as promising targets for cancer treatment. Four HDAC inhibitors have been approved as anti-cancer therapeutics, including SAHA (Suberoylanilide hydroxamic acid, Vorinostat, Zolinza). SAHA is a nonselective HDAC inhibitor that targets most of the eleven HDAC isoforms. The nonselectivity of SAHA might account for its clinical side effects, but certainly limits its use as a chemical tool to study cancer-related HDAC cell biology. Herein, the nonselective HDAC inhibitor SAHA was modified at the C4 position of the linker to explore activity and selectivity. Several C4-modified SAHA analogs exhibited dual HDAC6/8 selectivity. Interestingly, (R)-C4-benzyl SAHA displayed 520- to 1300-fold selectivity for HDAC6 and HDAC8 over HDAC1, 2, and 3, with IC₅₀ values of 48 and 27 nM with HDAC6 and 8, respectively. In cellulo testing of the inhibitors was consistent with the observed in vitro selectivity. Docking studies provided a structural rationale for selectivity. The C4-SAHA analogs represent useful chemical tools to understand the role of HDAC6 and HDAC8 in cancer biology and exciting lead compounds for targeting of both HDAC6 and HDAC8 in various cancers.

The structural requirements of histone deacetylase inhibitors: SAHA analogs modified at the C5 position display dual HDAC6/8 selectivity

Histone deacetylase (HDAC) proteins have emerged as important targets for anti-cancer drugs, with four small molecules approved for use in the clinic. Suberoylanilide hydroxamic acid (Vorinostat, SAHA) was the first FDA-approved HDAC inhibitor for cancer treatment. However, SAHA inhibits most of the eleven HDAC isoforms. To understand the structural requirements of HDAC inhibitor selectivity and develop isoform selective HDAC inhibitors, SAHA analogs modified in the linker at the C5 position were synthesized and tested for potency and selectivity. C5-modified SAHA analogs displayed dual selectivity to HDAC6 and HDAC8 over HDAC 1, 2, and 3, with only a modest reduction in potency. These findings are consistent with prior work showing that modification of the linker region of SAHA can alter isoform selectivity. The observed HDAC6/8 selectivity of C5-modified SAHA analogs provide guidance toward development of isoform selective HDAC inhibitors and more effective anti-cancer drugs.

Structural Requirements of HDAC Inhibitors: SAHA Analogues Modified at the C2 Position Display HDAC6/8 Selectivity

Histone deacetylase (HDAC) proteins are epigenetic regulators that deacetylate protein substrates, leading to subsequent changes in cell function. HDAC proteins are implicated in cancers, and several HDAC inhibitors have been approved by the FDA as anticancer drugs, including SAHA (suberoylanilide hydroxamic acid; Vorinostat and Zolinza). Unfortunately, SAHA inhibits most HDAC isoforms, which limits its use as a pharmacological tool and may lead to side effects in the clinic. In this work SAHA analogues substituted at the C2 position were synthesized and screened for HDAC isoform selectivity in vitro and in cells. The most potent and selective compound, C2-n-hexyl SAHA, displayed submicromolar potency with 49- to 300-fold selectivity for HDAC6 and HDAC8 compared to HDAC1, -2, and -3. Docking studies provided a structural rationale for selectivity. Modification of the nonselective inhibitor SAHA generated HDAC6/HDAC8 dual selective inhibitors, which can be useful lead compounds toward developing pharmacological tools and more effective anticancer drugs.

Inside HDACs with more selective HDAC inhibitors

Inhibitors of histone deacetylases (HDACs) are nowadays part of the therapeutic arsenal mainly against cancers, with four compounds approved by the Food and Drug Administration. During the last five years, several groups have made continuous efforts to improve this class of compounds, designing more selective compounds or compounds with multiple capacities. After a survey of the HDAC biology and structures, this review summarizes the results of the chemists working in this field, and highlights when possible the behavior of the molecules inside their targets.

Structural Requirements of Histone Deacetylase Inhibitors: SAHA Analogs Modified on the Hydroxamic Acid

Histone deacetylase (HDAC) proteins have emerged as targets for anti-cancer therapeutics, with several inhibitors used in the clinic, including suberoylanilide hydroxamic acid (SAHA, vorinostat). Because SAHA and many other inhibitors target all or most of the 11 human HDAC proteins, the creation of selective inhibitors has been studied intensely. Recently, inhibitors selective for HDAC1 and HDAC2 were reported where selectivity was attributed to interactions between substituents on the metal binding moiety of the inhibitor and residues in the 14-Å internal cavity of the HDAC enzyme structure. Based on this earlier work, we synthesized and tested SAHA analogs with substituents on the hydroxamic acid metal binding moiety. The N-substituted SAHA analogs displayed reduced potency and solubility, but greater selectivity, compared to SAHA. Docking studies suggested that the N-substituent accesses the 14-Å internal cavity to impart preferential inhibition of HDAC1. These studies with N-substituted SAHA analogs are consistent with the strategy exploiting the 14-Å internal cavity of HDAC proteins to create HDAC1/2 selective inhibitors.

Lipase-catalyzed synthesis of oxidation-responsive poly(ethylene glycol)-b-poly(β-thioether ester) amphiphilic block copolymers

Lipase-catalyzed one-step synthesis of novel oxidation-responsive poly(ethylene glycol)-b-poly(β-thioether ester) diblock copolymers was reported.

Mutagenesis studies of the 14 Å internal cavity of histone deacetylase 1: insights toward the acetate-escape hypothesis and selective inhibitor design

Histone deacetylase (HDAC) proteins are promising targets for cancer treatment, as shown by the approval of two HDAC inhibitors for the treatment of cutaneous T-cell lymphoma. HDAC1 in particular has been linked to cell growth and cell cycle regulation and is therefore an attractive target for anticancer drugs. The HDAC1 active site contains a hydrophobic 11 Å active-site channel, with a 14 Å internal cavity at the bottom of the active site. Several computational and biochemical studies have proposed an acetate-escape hypothesis where the acetate byproduct of the deacetylation reaction escapes via the 14 Å internal cavity. Selective HDAC inhibitors that bind to the 14 Å cavity have also been created. To understand the influence of amino acids lining the HDAC1 14 Å cavity in acetate escape and inhibitor binding, we used mutagenesis coupled with acetate competition assays. The results indicate that amino acids lining the 14 Å cavity are critical for catalytic activity and acetate competition, confirming the role of the cavity in acetate escape. In addition, these mutagenesis studies will aid in HDAC1-inhibitor design that exploits the 14 Å cavity.

Molecular dynamics simulation of complex Histones Deacetylase (HDAC) Class II Homo Sapiens with suberoylanilide hydroxamic acid (SAHA) and its derivatives as inhibitors of cervical cancer

Cervical cancer is second most common cancer in woman worldwide. Cervical cancer caused by human papillomavirus (HPV) oncogene. Inhibition of histone deacetylase (HDAC) activity has been known as a potential strategy for cancer therapy. SAHA is an HDAC inhibitor that has been used in cancer therapy but still has side effects. SAHA modification proposed to minimize side effects. Triazole attachment on the chain of SAHA has been known to enhance the inhibition ability of SAHA and less toxic. In this study, it will be carried out with molecular dynamic simulations of SAHA modifications consisting ligand 1a, 2a and, 2c to interact with six HDAC in hydrated conditions. To all six HDAC Class II, performed docking with SAHA and a modified inhibitor. The docking results were then carried out molecular dynamics simulations to determine the inhibitor affinities in hydrated conditions. The molecular dynamic simulations results show better affinities of ligand 2c with HDAC 4, 6, and 7 than SAHA itself, and good affinity was also shown by ligand 2a and 1c on HDAC 5 and 9. The results of this study can be a reference to obtain better inhibitors.