Synthesis and cancer antiproliferative activity of new histone deacetylase inhibitors: hydrophilic hydroxamates and 2-aminobenzamide-containing derivatives

Targeting histone deacetylases for heart diseases

Histone deacetylases (HDACs) are responsible for the deacetylation of lysine residues in histone or non-histone substrates, leading to the regulation of many biological functions, such as gene transcription, translation and remodeling chromatin. Targeting HDACs for drug development is a promising way for human diseases, including cancers and heart diseases. In particular, numerous HDAC inhibitors have revealed potential clinical value for the treatment of cardiac diseases in recent years. In this review, we systematically summarize the therapeutic roles of HDAC inhibitors with different chemotypes on heart diseases. Additionally, we discuss the opportunities and challenges in developing HDAC inhibitors for the treatment of cardiac diseases.

Computer-Driven Development of an in Silico Tool for Finding Selective Histone Deacetylase 1 Inhibitors

Histone deacetylases (HDACs) are a class of epigenetic modulators overexpressed in numerous types of cancers. Consequently, HDAC inhibitors (HDACIs) have emerged as promising antineoplastic agents. Unfortunately, the most developed HDACIs suffer from poor selectivity towards a specific isoform, limiting their clinical applicability. Among the isoforms, HDAC1 represents a crucial target for designing selective HDACIs, being aberrantly expressed in several malignancies. Accordingly, the development of a predictive in silico tool employing a large set of HDACIs (aminophenylbenzamide derivatives) is herein presented for the first time. Software Phase was used to derive a 3D-QSAR model, employing as alignment rule a common-features pharmacophore built on 20 highly active/selective HDAC1 inhibitors. The 3D-QSAR model was generated using 370 benzamide-based HDACIs, which yielded an excellent correlation coefficient value (R² = 0.958) and a satisfactory predictive power (Q² = 0.822; Q²_F3 = 0.894). The model was validated (r²_{ext_ts} = 0.794) using an external test set (113 compounds not used for generating the model), and by employing a decoys set and the receiver-operating characteristic (ROC) curve analysis, evaluating the Güner-Henry score (GH) and the enrichment factor (EF). The results confirmed a satisfactory predictive power of the 3D-QSAR model. This latter represents a useful filtering tool for screening large chemical databases, finding novel derivatives with improved HDAC1 inhibitory activity.

Synthesis, molecular packing and anti-cholinesterase activity of some new C-2 N-substituted anthranilamide derivatives

Synthesis of C-2 N-substituted anthranilamide derivatives was carried out in a straight forward manner, utilizing 2-aminobenzamide and benzyl chloride as starting materials. Their crystal structures have been established by single crystal X-ray crystallographic method. In the molecules of 2-benzylamino-benzamide (3a), intramolecular hydrogen bonding b/w O atom and proton of –NH and classical intermolecular hydrogen bonding of the type N–H · · · O forming eight membered rings in R4 2(8) pattern. In both molecules of 2-(dibenzylamino)benzamide (3b), unlike the molecule in 3a, each H atoms is pointed towards N atom causing intramolecular hydrogen bonding interactions, resulting in S(6) motifs. However, it is interesting to note that both molecules in 3b are lying about inversion centres and form dimers in R4 2(8) motifs; the two dimers are linked via non-classical intermolecular hydrogen bonds C–H · · · O resulting in clusters of four molecules in the structure. In vitro assay results revealed that molecule 3b with IC50 values of 3.8 ± 0.08 μM (AChE) and 17.6 ± 1.10 μM (BChE) possessed better cholinesterase (AChE and BChE) inhibition potential as compared to standard drug galantamine. Preliminary in silico studies showed that more biological active derivatives were also having good pharmacokinetic profile with no AMES toxicity and carcinogenicity.

Identification of N-Hydroxycinnamamide analogues and their bio-evaluation against breast cancer cell lines

The present study demonstrates the identification of N-hydroxycinnamamide derivatives and their anticancer potential against human triple-negative breast cancer cell line MDA-MB‑231, MCF-7 and non-malignant origin cell line, HEK-293 (human embryonic kidney). MTT assay was studied with HEK-293 cell line. Anticancer potential of the N-hydroxycinnamamide derivatives were compared with marked drug Tamoxifen through in vitro study. The compound numbers 3b and 3h exhibit most potent activity against antagonistic breast cancer cells (MDA-MB-231) with IC₅₀13μM and 5μM respectively. Compound 3h promotes DNA fragmentation and induction of apoptosis. Furthermore, loss of mitochondrial membrane potential induced by compound 3h. The major mechanism of compound 3h for anti-breast cancer activity was probably initiation of reactive oxygen species (ROS) in cancer cells thereby persuading apoptotic cell deaths in cancer cells.

A hydroxamic acid–methacrylated collagen conjugate for the modulation of inflammation-related MMP upregulation

The selective covalent coupling of hydroxamic acid functions on to methacrylated type I collagen led to UV-cured networks with inherent MMP-modulating capability and enhanced proteolytic stability.

One-pot preparation of labelled mannan-peptide conjugate, model for immune cell processing

An efficient method for preparation of fluorescently labelled mannan-peptide glycoconjugates has been developed. After selective Dess-Martin periodinane oxidation of mannan, it was conjugated to the fluorescent label alone and a peptide with the label via reductive amination. Prepared glycoconjugates were characterised by HPSEC, FTIR-ATR and UV-VIS spectroscopy. Finally, the fluorescently labelled mannan and mannan-peptide conjugate were used for microscopic visualization of their accumulation in intracellular organelles of RAW 264.7 cells.

Design, spectral characterization, DFT and biological studies of transition metal complexes of Schiff base derived from 2-aminobenzamide, pyrrole and furan aldehyde

A series of two biologically active Schiff base ligands L(1), L(2) have been synthesized in equimolar reaction of 2-aminobenzamide with pyrrol-2-carboxaldehyde and furan-2-carboxaldehyde. The synthesized Schiff bases were used for complexation with different metal ions like Co(II), Ni(II) and Cu(II) by using a molar ratio of ligand: metal as 2:1. The characterization of newly formed complexes was done by (1)H NMR, UV-Vis, TGA, IR, mass spectrophotometry, EPR and molar conductivity studies. The thermal studies suggested that the complexes are more stable as compared to ligand. In DFT studies the geometries of Schiff bases and metal complexes were fully optimized with respect to the energy using the 6-31+g(d,p) basis set. On the basis of the spectral studies an octahedral geometry has been assigned for Co(II) and Ni(II) complexes and distorted octahedral geometry for Cu(II) complexes. All the synthesized compounds, were studied for their in vitro antimicrobial activities, against four bacterial strains and two fungal strains by using serial dilution method. The data also revealed that the metal complexes showed better activity than the ligands due to chelation/coordination.

Ni(II) and Zn(II) complexes of 2-((thiophen-2-ylmethylene)amino)benzamide: synthesis, spectroscopic characterization, thermal, DFT and anticancer activities

The paper presents the synthesis of Ni(II) and Zn(II) complexes of general composition M(L)X₂ and M(L)₂X₂ (M=Ni(II), Zn(II), X=Cl(-1), OAc(-1)) with Schiff base obtained through the condensation of 2-aminobenzamide with thiophene-2-carbaldehyde. The characterization of newly formed complexes was done by (1)H NMR, UV-VIS, TGA, IR, mass spectrophotometry and molar conductivity studies. The thermal studies suggested that the complexes are more stable as compared to ligand. In DFT studies the geometries of Schiff's base and metal complexes were fully optimized with respect to the energy using the 6-31+g(d,p) basis set. On the basis of the spectral studies a distorted octahedral geometry has been assigned for Ni(II) complexes and tetrahedral geometry for Zn(II) complexes. The effect of these complexes on proliferation of human breast cancer cell line (MCF-7) and human hepatocellular liver carcinoma cell line (HepG2) were studied and compared with those of free ligand.

Di-μ-chlorido-bis-[(2-amino-benzamide-κ(2) N (2),O)chlorido-copper(II)]

The title compound, [Cu2Cl4(C7H8N2O)2], crystallizes as discrete [CuLCl2]2 (L = 2-amino-benzamide) dimers with inversion symmetry. Each Cu(II) ion is five-coordinated and is bound to two bridging chloride ligands, a terminal chloride ligand and a bidentate 2-amino-benzamide ligand. The crystal structure exhibits alternating layers parallel to (010) along the b-axis direction. In the crystal, the components are linked via N-H⋯Cl hydrogen bonds, forming a three-dimensional network. These inter-actions link the mol-ecules within the layers and also link the layers together and reinforce the cohesion of the structure.

Design, synthesis and biological evaluation of hydroxamic acid derivatives as potential high density lipoprotein (HDL) receptor CLA-1 up-regulating agents

Trichostatin A (TSA) and suberoylanilide hydroxamic acid (SAHA) were reported in our recent publication as novel human high density lipoprotein (HDL) receptor CD36 and Lysosomal integral membrane protein-II Analogous-1 (CLA-1) up-regulators. As part of a broader effort to more fully explore the structure-activity relationships (SAR) of CLA-1 up-regulators, we synthesized a series of hydroxamic acid derivatives and evaluated their CLA-1 up-regulating activities in HepG2 cells. Some compounds exhibited over 10-fold up-regulation of CLA-1 expression in HepG2 cells at 10 μg/mL concentration. The compound 1g showed the best potency, with a lower EC₅₀ than TSA (EC₅₀ = 0.32 μM versus 1.2 μM). These compounds provide early new CLA-1 up-regulators with potential for treating atherosclerosis.

The synthesis and evaluation of N1-(4-(2-[18F]-fluoroethyl)phenyl)-N8-hydroxyoctanediamide ([18F]-FESAHA), a PET radiotracer designed for the delineation of histone deacetylase expression in cancer

INTRODUCTION

Given the significant utility of suberoylanilide hydroxamic acid (SAHA) in chemotherapeutic protocols, a PET tracer that mimics the histone deacetylase (HDAC) inhibition of SAHA could be a valuable tool in the diagnosis, treatment planning and treatment monitoring of cancer. Here, we describe the synthesis, characterization and evaluation of N(1)-(4-(2-[(18)F]-fluoroethyl)phenyl)-N(8)-hydroxyoctanediamide ([(18)F]-FESAHA), a PET tracer designed for the delineation of HDAC expression in cancer.

METHODS

FESAHA was synthesized and biologically characterized in vivo and in vitro. [(18)F]-FESAHA was then synthesized in high radiochemical purity, and the logP and serum stability of the radiotracer were determined. In vitro cellular uptake experiments and acute biodistribution and small-animal PET studies were performed with [(18)F]-FESAHA in mice bearing LNCaP xenografts.

RESULTS

[(18)F]-FESAHA was synthesized in high radiochemical purity via an innovative one-pot procedure. Enzymatic inhibition assays illustrated that FESAHA is a potent HDAC inhibitor, with IC(50) values from 3 nM to 1.7 μM against the 11 HDAC subtypes. Cell proliferation experiments revealed that the cytostatic properties of FESAHA very closely resemble those of SAHA in both LNCaP cells and PC-3 cells. Acute biodistribution and PET imaging experiments revealed tumor uptake of [(18)F]-FESAHA and substantially higher values in the small intestine, kidneys, liver and bone.

CONCLUSION

The significant non-tumor background uptake of [(18)F]-FESAHA presents a substantial obstacle to the use of the radiotracer as an HDAC expression imaging agent. The study at hand, however, does present a number of lessons critical to both the synthesis of hydroxamic acid containing PET radiotracers and imaging agents aimed at delineating HDAC expression.

New orally bioavailable 2-aminobenzamide-type histone deacetylase inhibitor possessing a (2-hydroxyethyl)(4-(thiophen-2-yl)benzyl)amino group

New 2-aminobenzamide-type histone deacetylase (HDAC) inhibitors were synthesized. They feature a sulfur-containing bicyclic arylmethyl moiety-a surface recognition domain introduced to increase in cellular uptake-and a substituted tert-amino group which affects physicochemical properties such as aqueous solubility. Compound 22 with a (2-hydroxyethyl)(4-(thiophen-2-yl)benzyl)amino group reduced the volume of human colon cancer HCT116 xenografts in nude mice to T/C 67% by oral administration at 45mg/kg, which was comparable to the rate (T/C 62%) for a positive control, MS-275. Western blot analyses as well as cell cycle and TUNEL assays by flow cytometry suggested that the two compounds inhibited the growth of cancer cells via similar mechanisms.

Modified cap group suberoylanilide hydroxamic acid histone deacetylase inhibitor derivatives reveal improved selective antileukemic activity

A series of SAHA cap derivatives was designed and prepared in good-to-excellent yields that varied from 49% to 95%. These derivatives were evaluated for their antiproliferative activity in several human cancer cell lines. Antiproliferative activity was observed for concentrations varying from 0.12 to >100 microM, and a molecular modeling approach of selected SAHA derivatives, based on available structural information of human HDAC8 in complex with SAHA, was performed. Strikingly, two compounds displayed up to 10-fold improved antileukemic activity with respect to SAHA; however, these compounds displayed antiproliferative activity similar to SAHA when assayed against solid tumor-derived cell lines. A 10-fold improvement in the leukemic vs peripheral blood mononuclear cell therapeutic ratio, with no evident in vivo toxicity toward blood cells, was also observed. The herein-described compounds and method of synthesis will provide invaluable tools to investigate the molecular mechanism responsible for the reported selectively improved antileukemic activity.

Histone deacetylase inhibitors (HDACIs). Structure--activity relationships: history and new QSAR perspectives

Histone deacetylase (HDAC) inhibition is a recent, clinically validated therapeutic strategy for cancer treatment. HDAC inhibitors (HDACIs) block angiogenesis, arrest cell growth, and lead to differentiation and apoptosis in tumor cells. In this article, a survey of published quantitative structure-activity relationships (QSARs) studies are presented and discussed in the hope of identifying the structural determinants for anticancer activity. Secondly a two-dimensional QSAR study was carried out on biological results derived from various types of HDACIs and from different assays using the C-QSAR program of Biobyte. The QSAR analysis presented here is an attempt to organize the knowledge on the HDACIs with the purpose of designing new chemical entities with enhanced inhibitory potencies and to study the mechanism of action of the compounds. This study revealed that lipophilicity is one of the most important determinants of activity. Additionally, steric factors such as the overall molar refractivity (CMR), molar volume (MgVol), the substituent's molar refractivity (MR) (linear or parabola), or the sterimol parameters B(1) and L are important. Electronic parameters indicated as σ(p), are found to be present only in one case.

Hydroxamates: relationships between structure and plasma stability

Hydroxamates are valuable tools for chemical biology as well as interesting leads for medicinal chemistry. Although many hydroxamates display nanomolar activities against metalloproteases, only three hydroxamates have reached the market, among which is the HDAC inhibitor vorinostat. Failures in development are generally attributed to lack of selectivity, toxicity, or poor stability. To help medicinal chemists with respect to plasma stability, we have performed the first and preliminary study on structure-plasma stability for hydroxamates. We define some structural rules to predict or improve the plasma stability in the preclinical stage.

Polyaminohydroxamic acids and polyaminobenzamides as isoform selective histone deacetylase inhibitors

A series of polyaminohydroxamic acids (PAHAs) and polyaminobenzamides (PABAs) were synthesized and evaluated as isoform-selective histone deacetylase (HDAC) inhibitors. These analogues contain a polyamine chain to increase affinity for chromatin and facilitate cellular import. Seven PAHAs inhibited HDAC >50% (1 microM), and two PABAs inhibited HDAC >50% (5 microM). Compound 17 increased acetylated alpha-tubulin in HCT116 colon tumor cells 253-fold but only modestly increased p21 (waf1) and acetylated histones 3 and 4, suggesting that 17 selectively inhibits HDAC 6. PABA 22 alone minimally increased p21 (waf1) and acetylated histones 3 and 4 but caused dose-dependent increases in p21 (waf1) in combination with 0.1 microM 5-azadeoxycytidine. Finally, 22 appeared to be a substrate for the polyamine transport system. None of these compounds were cytotoxic at 100 microM. PAHAs and PABAs exhibit strikingly different cellular effects from SAHA and have the potential for use in combination antitumor therapies with reduced toxicity.

Effects of a novel histone deacetylase inhibitor, N-(2-aminophenyl) benzamide, on a reversible hypertrophy induced by isoproterenol in in situ rat hearts

The aim of the present study was performed to determine whether a novel histone deacetylase (HDAC) inhibitor, N-(2-aminophenyl)-4-{[benzyl(2-hydroxyethyl)amino]methyl} benzamide (K-183), prevents a reversible cardiac hypertrophy induced by isoproterenol and improves left ventricular (LV) dysfunction in rats. Either isoproterenol or vehicle was infused for 3 days by osmotic minipump. One hour prior to the implantation of isoproterenol, K-183 or trichostatin A (TSA) was injected twice a day for 3 days. We recorded continuous LV pressure-volume (P-V) loops of in situ hearts one hour after removal of the osmotic minipump. LV work capability (systolic P-V area at midrange LV volume: PVA(mLVV)) and hemodynamics were evaluated. K-183 per se induced neither cardiac hypertrophy nor collagen production. Although K-183 did not prevent the hypertrophy, where PVA(mLVV) remained decreased, K-183, differently from TSA, significantly attenuated the decrease of cardiac output and the increase of effective arterial elastance in the hypertrophied heart. These results indicate that the novel HDAC inhibitor K-183 has some beneficial effects on hemodynamics, although K-183 has no effects of anti-hypertrophic modalities.

Novel Selective Inhibitors of the Zinc Plasmodial Aminopeptidase PfA-M1 as Potential Antimalarial Agents

Proteases that are expressed during the erythocytic stage of Plasmodium falciparum are newly explored drug targets for the treatment of malaria. We report here the discovery of potent inhibitors of PfA-M1, a metallo-aminopeptidase of the parasite. These compounds are based on a malonic hydroxamic template and present a very good selectivity toward neutral aminopeptidase (APN-CD13), a related protease in mammals. Structure-activity relationships in these series are described. Further optimization of the best inhibitor yielded a nanomolar, selective inhibitor of PfA-M1. This inhibitor displays good physicochemical and pharmacokinetic properties and a promising antimalarial activity.

Structural requirements of HDAC inhibitors: SAHA analogs functionalized adjacent to the hydroxamic acid

Inhibitors of histone deacetylase (HDAC) proteins such as suberoylanilide hydroxamic acid (SAHA) have emerged as effective therapeutic anti-cancer agents. To better understand the structural requirements of HDAC inhibitors, a small molecule library with a variety of substituents attached adjacent to the metal binding hydroxamic acid of SAHA was synthesized. The presence of a substituent adjacent to the hydroxamic acid led to an 800- to 5000-fold decrease in inhibition compared to SAHA. The observed results have implications for drug design, suggesting that HDAC inhibitors with substituents near the metal binding moiety will have inhibitory activities in the micromolar rather than nanomolar range.