Hydroxamic Acid Groups Research Articles

Biosynthetic Origin of the Hydroxamic Acid Moiety of Trichostatin A: Identification of Unprecedented Enzymatic Machinery Involved in Hydroxylamine Transfer.

Trichostatin A (TSA) is widely used in the field of epigenetics because it potently inhibits histone deacetylase (HDAC). In-depth studies have revealed that the hydroxamic acid group in TSA chelates the zinc(II) ion in the active site of HDAC to realize the inhibitory activity. Here we report the first identification of a complete TSA biosynthetic gene cluster from Streptomyces sp. RM72 and the heterologous production of TSA in Streptomyces albus. Biochemical analyses unambiguously demonstrate that unprecedented biosynthetic machinery catalyzes the direct transfer of hydroxylamine from a nonproteinogenic amino acid, l-glutamic acid γ-monohydroxamate, to the carboxylic acid group of trichostatic acid to form the hydroxamic acid moiety of TSA. The present study establishes the biosynthetic pathway of TSA, paving the way toward understanding the biosynthesis of other hydroxamic acid-containing natural products.

Design, synthesis, docking studies and biological evaluation of novel chalcone derivatives as potential histone deacetylase inhibitors

A group of novel chalcone derivatives comprising hydroxamic acid or 2-aminobenzamide group as zinc binding groups (ZBG) were synthesized. The structure of the prepared compounds was fully characterized by IR, NMR and elemental microanalyses. Most of the tested compounds displayed strong to moderate HDAC inhibitory activity. Some of these compounds showed potent anti-proliferative activity against human HepG2, MCF-7 and HCT-116 cell lines. In particular, compounds 4a and 4b exhibited significant anti-proliferative activity against the three cell lines compared to SAHA as reference drug and displayed promising profile as anti-tumor candidates. The results indicated that these chalcone derivatives could serve as a promising lead compounds for further optimization as antitumor agents.

Single Conformation Spectroscopy of Suberoylanilide Hydroxamic Acid: A Molecule Bites Its Tail.

Suberoylanilide hydroxamic acid (SAHA) is a histone deacetylase inhibitor that causes growth arrest and differentiation of many tumor types and is an approved drug for the treatment of cancer. The chemical structure of SAHA consists of formanilide "head" and a hydroxamic acid "tail" separated by an n-hexyl chain, C6H5NH(C═O)-(CH2)6-(C═O)NHOH. The alkyl chain's preference for extended structures is in competition with tail-to-head (T-H) or head-to-tail (H-T) hydrogen bonds between the amide and hydroxamic acid groups. Laser desorption was used to bring SAHA into the gas phase and cool it in a supersonic expansion before interrogation with mass-resolved resonant two-photon ionization spectroscopy. Single conformation UV spectra in the S0-S1 region and infrared spectra in the hydride stretch and mid-IR regions were recorded using IR-UV hole-burning and resonant ion-dip infrared spectroscopy, respectively. Three conformers of SAHA were distinguished and spectroscopically characterized. Comparison of the experimental IR spectra with the predictions of density functional theory calculations (DFT, B3LYP D3BJ/6-31+G(d)) leads to assignments for the three conformers, all of which possess tightly folded alkyl chains that enable formation of a T-H (conformer A) or H-T (conformers B and C) hydrogen bonds. A modified version of the generalized Amber force field was developed to more accurately describe the hydroxamic acid OH internal rotor potential, leading to predictions for the relative energies in reasonable agreement with experiment. This force field was used to generate a disconnectivity graph for the low-energy portion of the potential energy landscape of SAHA. This disconnectivity graph contains more than one hundred minima and maps out the lowest-energy pathways between them, which could then be characterized via DFT calculations. This combination of force field and DFT calculations provides insight into the potential energy landscape and how population was funneled into the three observed conformers.

Ring-opened tetrahydro-γ-carbolines display cytotoxicity and selectivity with histone deacetylase isoforms

This study is focused on modification of the indole moiety and the N1-zinc binding domain of tubastatin A, and the effects of such changes on biological activity. Fourteen N-substituted indoles (5–18) were synthesized and structure-activity relationship studies indicated that the change of the tetrahydro-γ-carboline in tubastatin A led to substituted indoles (compounds 7, 11, and 15) which showed significant improvements of selective inhibition for HDAC6 over HDAC1 and HDAC2 in comparison to ACY1215, a compound undergoing clinical trials. In addition, attachment of different hydroxamic acid groups, the zinc binding motif at the N1 position, contributes to the antiproliferative activity in cancer cells. Several synthetic compounds exhibited potent growth inhibition in a broad spectrum of tumor cell lines, induced irreversible growth arrest capacities by suppressing colony formation ability and activated the apoptosis pathway. The data provide compelling evidence that our newly synthesized compounds with type B to D hydroxamic acid groups as the zinc binding motif at the N1 position are potent selective inhibitors of HDAC6 and could be investigated preclinically as potential anticancer drugs.

Efficient Palladium-Triggered Release of Vorinostat from a Bioorthogonal Precursor.

Bioorthogonal uncaging strategies have recently emerged as an experimental therapeutic approach to control drug release. Herein we report a novel masking strategy that enables to modulate the metal chelating properties of hydroxamic acid groups by bioorthogonal chemistry using Pd-functionalized resins. This novel approach allowed to devise an inactive precursor of the histone deacetylase inhibitor vorinostat that was efficiently uncaged by heterogeneous Pd catalysis in cell culture models of glioma and lung cancer.

Detoxification of VX and Other V-Type Nerve Agents in Water at 37 °C and pH 7.4 by Substituted Sulfonatocalix[4]arenes.

Sulfonatocalix[4]arenes with an appended hydroxamic acid residue can detoxify VX and related V‐type neurotoxic organophosphonates with half‐lives down to 3 min in aqueous buffer at 37 °C and pH 7.4. The detoxification activity is attributed to the millimolar affinity of the calixarene moiety for the positively charged organophosphonates in combination with the correct arrangement of the hydroxamic acid group. The reaction involves phosphonylation of the hydroxamic acid followed by a Lossen rearrangement, thus rendering the mode of action stoichiometric rather than catalytic. Nevertheless, these calixarenes are currently the most efficient low‐molecular‐weight compounds for detoxifying persistent V‐type nerve agents under mild conditions. They thus represent lead structures for novel antidotes that allow treatment of poisonings by these highly toxic chemicals.

Protection mechanism of deacetylase inhibitor on spleen of rats with severe hemorrhagic shock.

To explore the protection and molecular mechanism of histone deacetylase inhibitors (HDACIs) on the spleen of rats with hemorrhagic shock. A total of 60 SPF male SD rats were selected for the modeling of severe hemorrhagic shock using the method of arterial and venous cannulation with the time-divided bleeding. The measurement of mean arterial blood pressure and blood lactic acid was used to verify the modeling. The modeled rats were randomly divided into shock group, shock+suberoylanilide hydroxamic acid (SAHA) group, shock+autogenous transfusion group and shock+SAHA+autogenous transfusion group. Three hours after the treatment, the spleen of rats was collected and TUNEL method was employed to detect the apoptosis of spleen cells in each group. The statistical analysis was performed. Afterwards, real-time PCR and western blot were employed to detect the expression of BCL-2, BAX and caspass3 in the spleen of rats in each group. A total of 53 rats had successful modeling of severe hemorrhagic shock, with success rate of 88%. Cell apoptosis in the severe hemorrhagic model group was the most serious. After the intervention of HDACIs and the autogenous transfusion, the tissue injury was a bit recovered. Cell apoptosis was least in the shock+SAHA+autogenous transfusion group (P<0.05). After the intervention of HDACIs and the autogenous transfusion, the relative expression of BCL-2 was significantly increased (P<0.05), with highest relative expression of BCL-2 in shock+SAHA+autogenous transfusion group (P<0.05). After the intervention of HDACIs and the autogenous transfusion, the relative expression of BAX was significantly decreased (P<0.05), with lowest relative expression of BAX in the intervention group of single HDACIs. The change in the expression of caspass3 was similar to BAX, namely the relative expression of caspass3 was significantly decreased after the intervention of HDACIs and the autogenous transfusion (P<0.05). HDACIs and autogenous transfusion can all protect the spleen injury because of the severe hemorrhagic shock. Its molecular mechanism may be related to the regulation on the expression of BCL-2/BAX and caspass3, which may affect the apoptosis process of cells.

Selective non-zinc binding MMP-2 inhibitors: Novel benzamide Ilomastat analogs with anti-tumor metastasis

Novel Ilomastat analogs with substituted benzamide groups, instead of hydroxamic acid groups, were designed, synthesized and evaluated against MMP-2 and MMP-9. Among these analogs, the most potent compound 10a exhibited potent inhibitory activity against MMP-2 with IC50 value of 0.19nM, which is 5 times more potent than that of Ilomastat (IC50=0.94nM). Importantly, 10a exhibited more than 8300 fold selectivity for MMP-2 versus MMP-9 (IC50=1.58μM). Molecular docking studies showed that 10a bond to the catalytic active pocket of MMP-2 by a non-zinc-chelating mechanism which was different from that of Ilomastat. Furthermore, the invasion assay showed that 10a was effective in reducing HEY cells invasion at 84.6% in 50μM concentration. For 10a, the pharmacokinetic properties had been improved and especially the more desirable t1/2z was achieved compared with these of the lead compound Ilomastat.

Selective Photorelease of an Organometallic-Containing Enzyme Inhibitor

Histone deacetylases (HDACs) are regarded as promising targets in cancer and a growing number of other diseases due to their crucial involvement in epigenetics and cellular signaling. Many organic HDAC inhibitors are known, and several efficient metal-based analogues have been recently developed. Many of them contain a hydroxamic acid group that binds to the catalytic HDAC zinc center. In this work, a light-activatable organometallic HDAC inhibitor (p-Fc-SAHA) was synthesized and characterized. More specifically, the hydroxamic acid moiety of a known ferrocene-containing HDAC inhibitor (Fc-SAHA) was blocked with a photolabile protecting group (PLPG), namely, 1-(bromomethyl)-4,5-dimethoxy-2-nitrobenzene. Upon UV-A (350 nm) irradiation, Fc-SAHA could be successfully released from p-Fc-SAHA. Importantly, p-Fc-SAHA was significantly less active on HDAC1, HDAC2, and HDAC6 than Fc-SAHA. As expected, the inhibition activity of Fc-SAHA was recovered upon light irradiation. To our knowledge, this is the first stud...

HDAC Inhibitor Oxamflatin Induces Morphological Changes and has Strong Cytostatic Effects in Ovarian Cancer Cell Lines.

Ovarian epithelial carcinoma is the leading cause of deaths from gynecologic malignancy. New reagents with therapeutic potentials against ovarian cancer, especially the drug-resistant cases, are required for better treatment of ovarian cancer patients. Epigenetic events such as changes in DNA methylation and histone modification, through their effects on DNA-protein interaction, chromatin conformation, and gene expression, affect cell function, cancer behavior, clinical manifestations, and outcomes. Previous studies have shown that histone deacetylase (HDAC) inhibitors have strong cytostatic and apoptotic activities in hematologic and some solid cancer cells. Oxamflatin, a compound containing the aromatic sulfonamide and hydroxamic acid groups, is known to be a potent HDAC inhibitor capable of inhibiting the growth of mouse and human cancer cell lines. In this study we found that oxamflatin in the nM range induced morphological changes in OVCAR-5 and SKOV-3 ovarian cancer cell lines. Treatment with oxamflatin also led to decreased cell viability. Moreover, results of BrdU incorporation assay, cell counting, and Ki-67 immunostaining indicated that oxamflatin was able to significantly inhibit DNA synthesis and cell proliferation. Using real-time PCR and Western blot analyses we demonstrated that oxamflatin was capable of downregulating the expression of c-Myc, CDK4, E2F1, and the phosphorylation levels of Rb protein, but upregulating p21. These findings pave the way to examine if oxamflatin along with or in combination with other reagents could deliver anticancer effects against ovarian cancers in vivo.

Measuring benzohydroxamate complexation with Mg2+, Mn2+, Co2+, and Ni2+ using isothermal titration calorimetry

Isothermal titration calorimetry has been used to determine the stoichiometry and first (K1) and second (K2) conditional stability constants, where applicable, for the formation of complexes of benzohydroxamate (BzH) with Mg2+, Mn2+, Co2+, and Ni2+ ions, and benzoylphosphonate with Ni2+ ions. Binding determinations were conducted in HEPES buffer (0.1 mol L−1, pH 7.5) at 25.0 °C by titration of the ligand with metal ion. BzH and Mg2+, and benzoylphosphonate and Ni2+, formed complexes with a 1:1 stoichiometry; however, BzH formed complexes with Mn2+, Co2+, and Ni2+ ions in a step-wise binding model with a stoichiometry of 2:1 (BzH:M2+). In addition, the Gibbs energy change accompanying the binding of BzH to each of the divalent metal ions was found to follow the order of the Irving–Williams series (Mg2+ < Mn2+ < Co2+ < Ni2+) and to correlate with the electron affinities of the metal ions. Conditional stability constants, determined in this manner, may be useful for calculating the concentrations of free inhibitor when inhibition studies are conducted with metalloenzymes and enzyme inhibitors containing a hydroxamic acid group.

Synthesis and Biological Evaluation of 3-Aryl Pyrazoles as CDK2/HDAC Inhibitor for Anticancer Agents

A novel series of pyrazole derivatives containing hydroxamic acid group were designed and synthesized as multi-target inhibitors targeting CDK2 (cyclin-dependent kinases 2) and HDAC (histone deacetylase). Compounds 6e and 6f exhibited most potent CDK2 inhibition as well as HDAC inhibition. In vitro antiproliferative assay indicated that several compounds showed better antiproliferative potency compared to olomoucine and SAHA. Docking simulation suggested a common mode of interaction at the active binding sites of CDK2 and HDAC, which demonstrates that compound 6f is a potential agent for cancer therapy deserving further researching.

Discovery of N-hydroxy-4-(1H-indol-3-yl)butanamide as a histone deacetylase inhibitor.

The indoles plant growth hormones have exhibited potentially antitumor activities. However, the targets of these indoles have not been clearly elucidated. By introduction of hydroxamic acid group to the structure of indolebutyric acid, the derived molecule (IBHA) exhibited potent HDAC2 (IC50 value of 0.32 ± 0.02 µM) and HDAC3 (IC50 value of 0.14 ± 0.01 µM) inhibitory activities compared with SAHA (IC50 value of 1.25 ± 0.06 µM and 0.97 ± 0.04 µM against HDAC2 and HDAC3). In the antiproliferative assays, the tested hematologic cell lines (U937 and K562) are more sensitive to IBHA than the solid tumor cell lines (MDA-MB-231 and PC-3). In the docking studies, the derived molecule (IBHA) could bind to the active site of human HDAC2 and HDAC3 by strong H-bond interactions and hydrophobic interactions. Pharmacophore mapping results revealed that properties of IBHA matches the receptor (HDAC3) based pharmacophore model.

Exploration of the labeling of [11C]tubastatin A at the hydroxamic acid site with [11C]carbon monoxide.

We aimed to label tubastatin A (1) with carbon-11 (t1/2 = 20.4 min) in the hydroxamic acid site to provide a potential radiotracer for imaging histone deacetylase 6 in vivo with positron emission tomography. Initial attempts at a one-pot Pd-mediated insertion of [(11)C]carbon monoxide between the aryl iodide (2) and hydroxylamine gave low radiochemical yields (<5%) of [(11) C]1. Labeling was achieved in useful radiochemical yields (16.1 ± 5.6%, n = 4) through a two-step process based on Pd-mediated insertion of [(11)C]carbon monoxide between the aryl iodide (2) and p-nitrophenol to give the [(11)C]p-nitrophenyl ester ([(11)C]5), followed by ultrasound-assisted hydroxyaminolysis of the activated ester with excess hydroxylamine in a DMSO/THF mixture in the presence of a strong phosphazene base P1-t-Bu. However, success in labeling the hydroxamic acid group of [(11)C]tubastatin A was not transferable to the labeling of three other model hydroxamic acids.

Flocculation performance and mechanism of hydroxamate flocculants on synthetic hematite or goethite suspension

Suitable amounts of Al(OH)3, NaOH and synthetic hematite or goethite were taken to be digested under the simulated condition of the Bayer process and subsequently diluted with simulative Bayer red mud lotion, then the synthetic hematite or goethite suspension was obtained. The flocculation effect of self-made modified poly(acrylic acids) flocculants containing hydroxamic acid groups (abbreviated as HPAA) on the synthetic hematite or goethite suspension was studied. The experimental results show that with the increase of the dosages of added flocculants, the average settling rate of the synthetic hematite or goethite suspension in the first 1 min speeds up, the supernatant solids decrease. It could also be found that there is generally a decrease in the average settling rate of the synthetic hematite or goethite suspension in the first 1 min with increasing solid content of the suspension. When the solid content of hematite or goethite of the suspension is 50 g/L with 240 g/t dosage of HPAA, HPAA has a better flocculation effect on the synthetic goethite suspension than on the synthetic hematite suspension. The adsorption mechanism of HPAA on the surface of hematite or goethite was investigated by Fourier transform infrared spectroscopy(FT-IR) and X-ray photoelectron spectroscopy(XPS). All the results suggest that HPAA is adsorbed on the hematite or goethite surface by a chemisorption, and it has a stronger adsorption on the goethite surface than on the hematite surface.

Design and Evaluation of Tumor-Specific Dendrimer Epigenetic Therapeutics.

Histone deacetylase inhibitors (HDACi) are promising therapeutics for cancer. HDACi alter the epigenetic state of tumors and provide a unique approach to treat cancer. Although studies with HDACi have shown promise in some cancers, variable efficacy and off-target effects have limited their use. To overcome some of the challenges of traditional HDACi, we sought to use a tumor-specific dendrimer scaffold to deliver HDACi directly to cancer cells. Here we report the design and evaluation of tumor-specific dendrimer–HDACi conjugates. The HDACi was conjugated to the dendrimer using an ester linkage through its hydroxamic acid group, inactivating the HDACi until it is released from the dendrimer. Using a cancer cell model, we demonstrate the functionality of the tumor-specific dendrimer–HDACi conjugates. Furthermore, we demonstrate that unlike traditional HDACi, dendrimer–HDACi conjugates do not affect tumor-associated macrophages, a recently recognized mechanism through which drug resistance emerges. We anticipate that this new class of cell-specific epigenetic therapeutics will have tremendous potential in the treatment of cancer.

Poly-hydroxamic acid (PHA) matrix for gadolinium pre-concentration and removal

A novel hydrophilic, three dimensionally cross-linked, aliphatic backbones with pendant hydroxamic acid (HA) group as functional moiety has been synthesized and utilized targeting removal of gadolinium [Gd(III)] from laboratory waste aqueous effluent. To understand the nature of sorption, gadolinium solution of various concentrations viz., 20, 10, 5.0, 1.0, 0.5 and 0.1 ppm has been contacted with a dose rate of 1 g/100 mL for 2 h. In this study, ICP-AES has been used for determination of concentration (ppm) of gadolinium in feed, filtrate and elute. EDXRF study also ensures the presence of gadolinium in the respective medium. Loaded gadolinium matrix was eluted with 1 N HCl for determining the elution factor (0.98).

Comparative study of copper complexes with different anchoring groups by molecular modeling and its application to dye-sensitized solar cells

Copper complexes with different anchoring groups (based on biquinoline ligands with acetylacetone, catechol, hydroxamic acid, phosphonic acid and thiocarboxylic acid groups) have been studied by Density Functional Theory and Time-Dependent Density Functional Theory, also the integral equation formalism of the polarizable continuum model has been extended to the calculation of solvent effects. Maximum absorption wavelength reaches the highest value for the complex with hydroxamic acid as anchoring group but a low oscillator strength; the rest of the complexes fulfill both properties. In general, the molecular orbitals energy levels and the schematic representation of them suppose an appropriate electron transfer between the sensitizer and the semiconductor (TiO2), emphasizing more clearly for the copper complex with the thiocarboxylic acid. Chemical reactivity parameters like chemical hardness shows similitude for all molecular systems; but not so in the case of the electrophilicity index and electroaccepting power.

Preparation of a novel chelating resin for the removal of Ni2+ from water

Abstract A new chelating resin DVB-MA-HDA modified with hydroxamic acid groups was prepared for the fast removal of Ni 2+ from water. SEM, BET, elemental analysis, FT-IR spectroscopy and XPS were used to characterize this new adsorbent. Batch adsorption experiment indicated that the equilibrium adsorption capacity of DVB-MA-HD for Ni 2+ was more than 130 mg/g, and the adsorption isotherm can be well fitted by the Langmuir model. The adsorption kinetic curve indicates that more than 60% of the adsorption amount of Ni 2+ at equilibrium occurred within the initial 20 min. 0.1 mol/L EDTA solution could desorb Ni 2+ from DVB-MA-HDA effectively.

ROS and RNS induced apoptosis through p53 and iNOS mediated pathway by a dibasic hydroxamic acid molecule in leukemia cells

Anticancer drugs induce apoptosis to cancer cells and also exhibit undesired toxicity to normal cells. Therefore development of novel agents triggering apoptosis and have low toxicity towards normal cells is most important. Hydroxamic acids suppress tumour cell growth through apoptosis but the underlying mechanism is poorly understood.Herein, we describe the apoptotic potential of a dibasic hydroxamic acid derivative, viz., oxayl bis (N-phenyl) hydroxamic acid (OBPHA), which induces apoptosis through generation of both ROS and NO in doxorubicin resistant T-lymphoblastic leukemia, CEM/ADR5000 cells. Present study discloses that OBPHA selectively kills cancerous cells irrespective of their drug resistant phenotype. We also determined the crystal structure of OBPHA to understand the structural requirements for apoptosis; the study reveals that the presence of substituted hydroxamic acid groups (–CO–NH–OH) favours the generation of NO possibly through auto degeneration. Along with the induction of caspase 3 mediated intrinsic apoptosis; OBPHA also activates p53 dependent signalling cascade and downregulates HDAC3 expression in a time dependent manner possibly due to increased ROS and NO production and simultaneous decrease in cellular GSH level. Thus ROS and NO mediated downstream signalling are essential for the anticancer effect of OBPHA. Therefore OBPHA, having a structurally relevant pharmacophore provides important insight into the development of new ROS and RNS generating chemicals inducing p53 dependent apoptosis.