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PubMed2006

Antitumor effects of a novel phenylbutyrate-based histone deacetylase inhibitor, (S)-HDAC-42, in prostate cancer.

PURPOSE: To assess the antitumor effects of a novel phenylbutyrate-derived histone deacetylase (HDAC) inhibitor, (S)-HDAC-42, vis-à-vis suberoylanilide hydroxamic acid (SAHA) in in vitro and in vivo models of human prostate cancer. EXPERIMENTAL DESIGN: The in vitro effects of (S)-HDAC-42 and SAHA were evaluated in PC-3, DU-145, or LNCaP human prostate cancer cell lines. Cell viability, apoptosis, and indicators of HDAC inhibition were assessed. Effects on Akt and members of the Bcl-2 and inhibitor of apoptosis protein families were determined by immunoblotting. Immunocompromised mice bearing established s.c. PC-3 xenograft tumors were treated orally with (S)-HDAC-42 (50 mg/kg q.o.d. or 25 mg/kg q.d.) or SAHA (50 mg/kg q.d.) for 28 days. In vivo end points included tumor volumes and intratumoral changes in histone acetylation, phospho-Akt status, and protein levels of Bcl-xL and survivin. RESULTS: (S)-HDAC-42 was more potent than SAHA in suppressing the viability of all cell lines evaluated with submicromolar IC50 values. Relative to SAHA, (S)-HDAC-42 exhibited distinctly superior apoptogenic potency, and caused markedly greater decreases in phospho-Akt, Bcl-xL, and survivin in PC-3 cells. The growth of PC-3 tumor xenografts was suppressed by 52% and 67% after treatment with (S)-HDAC-42 at 25 and 50 mg/kg, respectively, whereas SAHA at 50 mg/kg suppressed growth by 31%. Intratumoral levels of phospho-Akt and Bcl-xL were markedly reduced in (S)-HDAC-42-treated mice, in contrast to mice treated with SAHA. CONCLUSIONS: (S)-HDAC-42 is a potent orally bioavailable inhibitor of HDAC, as well as targets regulating multiple aspects of cancer cell survival, which might have clinical value in prostate cancer chemotherapy and warrants further investigation in this regard.

Administration, Oral↗

PubMed1975

Generation of adenosine triphosphate in cytochrome-deficient mutants of Neurospora.

The fungus Neurospora crassa is known to possess a branched respiratory system consisting of the standard cytochrome chain and a cyanide-insensitive alternate oxidase. In the present experiments, the physiological function of the alternate oxidase has been analyzed by taking advantage of a number of cytochrome-deficient mutants, particularly poky f. Respiration, cellular ATP levels, and growth have been examined under the influence of three classes of inhibitors: inhibitors of the cytochrome chain (antimycin, cyanide), an inhibitor of the laternate oxidase (salicyl hydroxamic acid), and an uncoupling agent (carbonyl cyanide m-chlorophenylhydrazone). The results indicate that the over-all efficiency of the alternate oxidase in producing ATP and supporting growth is much less than that of the cytochrome chain. Depending upon the amount of oxidative phosphorylation at Sites II and III in the cytochrome chain, which varies from strain to strain, the efficiency of the alternate oxidase relative to that of the cytochrome chain ranges from 13% in wild type Neurospora to 18 to 21% in poky f, 35% in mi-3, and 57% in cyt-2. A comparison of the short term effects of cyanide and carbonyl cyanide m-chlorophenylhydrazone on cellular ATP in poky f suggests that, during respiration through the alternate oxidase, ATP can be produced both by substrate-level phosphorylation (accompanying glycolysis and the oxidation of alpha-ketoglutarate) and by oxidative phosphorylation at Site I. When cells are grown on sucrose, as much as 22% of ATP synthesis in the presence of cyanide occurs at Site I. When cells are grown on acetate to diminish the rate of glycolysis, the contribution of Site I becomes proportionately larger. Both the growth experiments and the short term inhibitor experiments reveal that ATP levels in Neurospora are kept high be a feedback process which depresses ATP breakdown (and growth) very quckly after ATP synthesis is inhibited. Thus, poky f grows more slowly that wild type Neurospora and is inhibited still further when either the cytochrome chain or the alternate oxidase is blocked. Under all of these conditions, however, cellular ATP in poky f is maintained at a high level (about 3 mmol per kg of cell water, slightly above the values measured in the wild type strain). Continue.

Acetates↗

PubMed2006

A study to determine the effects of food and multiple dosing on the pharmacokinetics of vorinostat given orally to patients with advanced cancer.

PURPOSE: This phase I study, conducted in advanced-stage cancer patients, assessed the safety and tolerability of oral vorinostat (suberoylanilide hydroxamic acid), single-dose and multiple-dose pharmacokinetics of vorinostat, and the effect of a high-fat meal on vorinostat pharmacokinetics. EXPERIMENTAL DESIGN: Patients (n = 23) received single doses of 400 mg vorinostat on day 1 (fasted) and day 5 (fed) with 48 hours of pharmacokinetic sampling on both days. Patients received 400 mg vorinostat once daily on days 7 to 28. On day 28, vorinostat was given (fed) with pharmacokinetic sampling for 24 hours after dose. RESULTS: The apparent t(1/2) of vorinostat was short (approximately 1.5 hours). A high-fat meal was associated with a small increase in the extent of absorption and a modest decrease in the rate of absorption. A short lag time was observed before detectable levels of vorinostat were observed in the fed state, and T(max) was delayed. Vorinostat concentrations were qualitatively similar following single-dose and multiple-dose administration; the accumulation ratio based on area under the curve was 1.21. The elimination of vorinostat occurred primarily through metabolism, with <1% of the given dose recovered intact in urine. The most common vorinostat-related adverse experiences were mild to moderate nausea, anorexia, fatigue, increased blood creatinine, and vomiting. CONCLUSIONS: Vorinostat concentrations were qualitatively similar after single and multiple doses. A high-fat meal increased the extent and modestly decreased the rate of absorption of vorinostat; this effect is not anticipated to be clinically meaningful. Continued investigation of 400 mg vorinostat given once daily in phase II and III efficacy studies is warranted.

Administration, Oral↗

PubMed2003

Histone deacetylase inhibitors promote STI571-mediated apoptosis in STI571-sensitive and -resistant Bcr/Abl+ human myeloid leukemia cells.

Interactions between the Bcr/Abl kinase inhibitor STI571 (Gleevec, imatinib mesylate) and histone deacetylase inhibitors (HDIs) have been examined in STI571-sensitive and -resistant Bcr/Abl(+) human leukemia cells (K562 and LAMA 84). Cotreatment of K562 cells with 250 nM imatinib mesylate and 2.0 micro M suberoylanilide hydroxamic acid (SAHA) for 24 h, exposures that were minimally toxic alone, resulted in a marked increase in mitochondrial damage (e.g., cytochrome c, Smac/DIABLO, and apoptosis-inducing factor release), caspase activation, and apoptosis. Similar events were observed in other Bcr/Abl(+) cells (i.e., LAMA 84), and in cells exposed to STI571 in combination with the HDI sodium butyrate. Coexposure of cells to HDIs in conjunction with STI571 resulted in multiple perturbations in signaling and cell cycle-regulatory proteins, including down-regulation of Raf, phospho-mitogen-activated protein kinase kinase (MEK), phospho-extracellular signal-regulated kinase (ERK), phospho-Akt, phospho-signal transducers and activators of transcription 5, cyclin D1, and Mcl-1, accompanied by dephosphorylation and cleavage of retinoblastoma protein and a striking increase in phosphorylation of c-Jun NH(2)-terminal kinase. Coexposure of Bcr/Abl(+) cells to STI571 also blocked SAHA-mediated induction of p21(CIP1) and resulted in down-regulation of Bcr/Abl protein expression. STI571 and SAHA also interacted synergistically to induce apoptosis in STI571-resistant K562 and LAMA 84 cells that display increased Bcr/Abl protein expression. Lastly, inducible expression of a constitutively active MEK1/2 construct significantly attenuated SAHA/STI571-mediated apoptosis in K562 cells, implicating disruption of the Raf/MEK/ERK axis in synergistic antileukemic effects of this drug combination. Together, these findings indicate that combined exposure of Bcr/Abl(+) cells to the kinase inhibitor STI571 and HDIs leads to diverse perturbations in signaling and cell cycle-regulatory proteins, associated with a marked increase in mitochondrial damage and cell death. They also raise the possibility that this strategy may be effective in some Bcr/Abl(+) cells that are resistant to STI571 through increased Bcr/Abl expression.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed2003

Histone deacetylase inhibitor LAQ824 down-regulates Her-2 and sensitizes human breast cancer cells to trastuzumab, taxotere, gemcitabine, and epothilone B.

Histone deacetylase inhibitors induce hyperacetylation of the amino-terminal lysine residues of the core nucleosomal histones, which results in chromatin remodeling and altered gene expression. Present studies demonstrate that exposure to a novel hydroxamic acid analogue histone deacetylase inhibitor, LAQ824, induced p21WAF1 and p27KIP1 and caused growth arrest and apoptosis of human breast cancer SKBR-3 and BT-474 cells that possess amplification and overexpression of Her-2/neu. Treatment with LAQ824 depleted the mRNA and protein levels of Her-2/neu-encoded Her-2, which was associated with attenuation of pAKT, c-Raf-1, and phosphorylated mitogen-activated protein kinase levels. LAQ824 also induced the acetylation of heat shock protein (hsp) 90, resulting in inhibition of its binding to ATP, which has been shown to impair the chaperone association of hsp 90 with its client proteins, Her-2, AKT, and c-Raf-1. Consistent with this, treatment with LAQ824 shifted the binding of Her-2 from hsp 90 to hsp 70, promoting proteasomal degradation of Her-2. Thus, LAQ824 depletes Her-2 through two mechanisms: attenuation of its mRNA levels and promotion of its degradation by the proteasome. Following LAQ824 treatment, the cell membrane association, autotyrosine phosphorylation, and colocalization of Her-2 with HER-3 also declined. Cotreatment with LAQ824 significantly increased trastuzumab-induced apoptosis of BT-474 and SKBR-3 cells. This was associated with greater attenuation of Her-2, c-Raf-1, and pAKT levels. LAQ824 also enhanced taxotere-induced, epothilone B-induced, and gemcitabine-induced apoptosis of BT-474 and SKBR-3 cells. These findings suggest that LAQ824 is active against human breast cancer cells and has the potential to improve the efficacy of trastuzumab, taxotere, gemcitabine, and epothilone B against breast cancer with Her-2/neuamplification.

Annexin A5↗

PubMed2005

Modulation of radiation response by histone deacetylase inhibition.

PURPOSE: Histone deacetylase (HDAC) inhibitors, which modulate chromatin structure and gene expression, represent a class of anticancer agents that hold particular potential as radiation sensitizers. In this study, we examine the capacity of the HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) to modulate radiation response in human tumor cell lines and explore potential mechanisms underlying these interactions. METHODS AND MATERIALS: Cell proliferation: Exponentially growing tumor cells were incubated in medium containing 0-10 microM of SAHA for 72 h. Cells were fixed/stained with crystal violet to estimate cell viability. Apoptosis: Caspase activity was analyzed by fluorescence spectroscopy using a fluorescein labeled pan-caspase inhibitor. Cells were harvested after 48 h of exposure to SAHA (1.0 microM), radiation (6 Gy), or the combination. Whole cell lysates were evaluated for poly(ADP-ribose) polymerase (PARP) cleavage by western blot analysis. Radiation survival: Cells were exposed to varying doses of radiation +/- 3 days pretreatment with SAHA (0.75-1.0 microM). After incubation intervals of 14-21 days, colonies were stained with crystal violet and manually counted. Immunocytochemistry: Cells were grown and treated in chamber slides. At specified times after treatment with SAHA, cells were fixed in paraformaldehyde, permeabilized in methanol, and probed with primary and secondary antibody solutions. Slides were analyzed using an epifluorescent microscope. RESULTS: SAHA induced a dose-dependent inhibition of proliferation in human prostate (DU145) and glioma (U373vIII) cancer cell lines. Exposure to SAHA enhanced radiation-induced apoptosis as measured by caspase activity (p < 0.05) and PARP cleavage. The impact of SAHA on radiation response was further characterized using clonogenic survival analysis, which demonstrated that treatment with SAHA reduced tumor survival after radiation exposure. We identified several oncoproteins and DNA damage repair proteins (epidermal growth factor receptor, AKT, DNA-PK, and Rad51) that show differential expression after exposure to SAHA. These proteins may contribute to mechanistic synergy between HDAC inhibition and radiation response. CONCLUSION: These preclinical results suggest that treatment with the HDAC inhibitor SAHA can enhance radiation-induced cytotoxicity in human prostate and glioma cells. We are examining the capacity of HDAC inhibitors to modulate radiation response and tumor control in animal xenograft model systems to strengthen the rationale for future clinical trial exploration.

Apoptosis↗

PubMed2002

Reactivity and selectivity of the N-acetyl-Glu-P-1, N-acetyl-Glu-P-2, N-acetyl-MeIQx, and N-acetyl-IQx nitrenium ions: comparison to carbocyclic N-arylnitrenium ions.

The model ultimate carcinogens 1a-d, related to the metabolites of the food-derived carcinogenic heterocyclic amines Glu-P-1, Glu-P-2, MeIQx, and IQx, spontaneously decompose in neutral aqueous solution to generate the heterocyclic nitrenium ions, 2a-d. The less reactive esters 1a and 1b also undergo acid-catalyzed ester hydrolysis to generate the corresponding hydroxamic acids at pH <2, while the more reactive 2c and 2d are prone to rearrangement in nonaqueous solvents. The reactions of the nitrenium ions with AcO(-), HPO(4)(2-), N(3)(-), and 2'-deoxyguanosine (d-G) were characterized in aqueous solution by using a combination of competitive trapping methods and product isolation and identification. The reactions with N(3)(-) and d-G generally follow patterns previously established for carbocyclic nitrenium ions, but the reactions with AcO(-) and HPO(4)(2-) are unusual. Similar reactions have previously only been reported for heterocyclic 1-alkyl-2-imidazolium ions. The N(3)(-)/solvent selectivities of these ions (5.1 x 10(6) M(-1) for 2a, 2.3 x 10(6) M(-1) for 2b, 1.2 x 10(5) M(-1) for 2c, and 5.2 x 10(4) M(-1) for 2d) are comparable to those of highly selective carbocyclic nitrenium ions. If k(az) for these ions is diffusion limited at ca. 5 x 10(9) M(-1) s(-1) the aqueous solution lifetimes of these ions range from 10 micros (2d) to 1 ms (2a). These ions are also highly selective for trapping by d-G, but comparisons to other nitrenium ions show that they are 10- to 50-fold less selective for trapping by d-G than they would be if both the N(3)(-) and d-G reactions were diffusion limited. This is not a consequence of their heterocyclic structures. Several carbocyclic ions show similar behavior. The relatively inefficient trapping of 2c and 2d by d-G may account for the observation of the unusual minor N-2 d-G adduct that is isolated for both of these nitrenium ions, but has not previously been observed for the reactions of other nitrenium ions with monomeric d-G.

Acetylation↗

PubMed1999

Evaluation of the inhibition of other metalloproteinases by matrix metalloproteinase inhibitors.

Two series of compounds synthesized as specific matrix metalloproteinase (MMP) inhibitors have been evaluated for their inhibition of non-MMPs. In a series of substituted succinyl hydroxamic acids, some were found to be significant (IC50 < 1 microM) inhibitors of leucine (microsomal) aminopeptidase, neprilysin (3.4.24.11), and thermolysin. Macrocyclic compounds in which the alpha carbon of the succinyl hydroxamate is linked to the side chain of the P2' amino acid were found to be good inhibitors of aminopeptidase, but not of neprilysin or thermolysin. Compounds of neither series were found to be significant inhibitors of angiotensin converting enzyme or carboxypeptidase A.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2000

Lipase and esterase-catalyzed acylation of hetero-substituted nitrogen nucleophiles in water and organic solvents.

The lipase- and esterase-catalyzed acylations of hydroxylamine and hydrazine derivatives with octanoic acid and ethyl octanoate are described. The influence of solvent and nucleophile on the initial reaction rate was investigated for a number of free and immobilized enzymes. Initial rates were highest in water, but the overall productivity was optimal in dioxane. Octanoic acid (250 g/L) was converted for 93% into the hydroxamic acid in 36 h with only 1% (w/w) Candida antarctica lipase B (Novozym 435) in dioxane at 40 degrees C. This translates to a catalyst productivity of 68.5 g. g(-1). day(-1) and a space time yield of 149 g. L(-1). day(-1), unprecedented figures in the direct reaction of an acid with a nitrogen nucleophile in an organic solvent.

Acylation↗

PubMed1993

Purification and characterization of salicylhydroxamic acid reductase from rat liver.

Salicylhydroxamic acid reductase, which catalyzes the reduction of salicylhydroxamic acid to salicylamide, was purified from rat liver cytosol. The purification procedure consisted of fractionation with ammonium sulfate, chromatography with Phenyl-Toyopearl 650, DEAE-cellulose, hydroxyapatite, and Sephadex G-200, and chromatofocusing with PBE94. The molecular weight of the enzyme was estimated to be about 140,000 by Sephadex G-200 gel filtration and 152,000 by polyacrylamide gel electrophoresis. The enzyme was dissociated into two different subunits with estimated molecular weights of 41,000 and 32,000, respectively, by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These facts suggested that the enzyme is a heterotetramer consisting of two pairs of two nonidentical polypeptide chains. The Km value of the enzyme for salicylhydroxamic acid was estimated to be 91.5 or 88.7 microM in the presence of NADH or NADPH, respectively. The isoelectric point of the enzyme is pH 5.4. The enzyme was highly specific for salicylhydroxamic acid, but it also showed some activity with other hydroxamic acids such as nicotinohydroxamic acid and N-hydroxy-2-acetylaminofluorene. The enzyme activity was inhibited by allopurinol, oxipurinol, dicumarol, menadione, p-chloromercuribenzoic acid, sodium arsenite, potassium cyanide, cupric sulfate, and disulfiram, but little inhibition was observed with oxygen.

Animals↗

PubMed2002

Dimerumic acid as an antioxidant from the mold, Monascus anka: the inhibition mechanisms against lipid peroxidation and hemeprotein-mediated oxidation.

This study aimed to investigate the antioxidant mechanism of dimerumic acid isolated as the active component with a radical scavenging action from the mold Monascus anka, traditionally used for the fermentation of foods. Dimerumic acid inhibited NADPH- and iron(II)-dependent lipid peroxidation (LPO) of rat liver microsomes at 20 and 200 microM, respectively. When ferrylmyoglobin was incubated with dimerumic acid, the myoglobin was scavenged and an electron spin resonance (ESR) signal with nine peaks was observed. The spin adduct was identified as a nitroxide radical by analysis of hyperfine structure. Similar ESR signal was also detected by incubation of dimerumic acid with peroxyl radicals. Thus, it was clarified that the antioxidant action of dimerumic acid is due to one electron donation of the hydroxamic acid group in the dimerumic acid molecule toward oxidants resulting in formation of nitroxide radical.

Animals↗

PubMed2000

Design and synthesis of piperazine-based matrix metalloproteinase inhibitors.

A new generation of cyclic matrix metalloproteinase (MMP) inhibitors derived from dl-piperazinecarboxylic acid has been described. The design involves: incorporation of hydroxamic acid as the bidentate chelating agent for catalytic Zn(2+), placement of a sulfonamide group at the 1N-position of the piperazine ring to fill the S1' pocket of the enzyme, and finally attachment of diverse functional groups at the 4N-position to optimize potency and peroral absorption. A unique combination of all three elements produced inhibitor 20 with high affinity for MMPs 1, 3, 9, and 13 (24, 18, 1.9, and 1.3 nM, respectively). X-ray crystallography data obtained for MMP-3 cocrystallized with 20 gave detailed information on key binding interactions defining an overall scaffold geometry for piperazine-based MMP inhibitors.

Animals↗

PubMed1981

Trypanosoma brucei brucei: a systematic screening for alternatives to the salicylhydroxamic acid-glycerol combination.

Salicylhydroxamic acid (SHAM) and glycerol, when administered together, cause destruction of bloodstream forms of Trypanosoma brucei brucei, both in vitro and in vivo, but the dose required is exceedingly high. In an attempt to improve the efficacy of this drug combination, we examined the ability of various polyols and hydroxamic acids to substitute for glycerol and SHAM, respectively. No satisfactory substitute for glycerol was found. The inhibition of the trypanosomal alpha-glycerophosphate oxidase system (GPO) by SHAM (Ki 21 microM) was uncompetitive. Only primary and secondary aromatic hydroxamates were inhibitory. Among a series of 19 benzhydroxamates, no correlation existed between their acidity or their affinity for iron and their inhibition of the GPO in a cell free preparation. The Ki's of most of the primary hydroxamates ranged from 10 to 24 microM, with the more lipophilic derivatives being slightly more active. The Ki's of secondary hydroxamates were more variable, the best having Ki's of about 10 microM. Several other classes of iron chelators were also evaluated. Tropolones were active with 3-bromo-4,5-benzotropolone being as active as SHAM. 3,4-Dihydroxybenzaldehyde (Ki 15 microM) also inhibited the GPO. On the other hand, diphenylamine and 8-hydroxyquinoline, known inhibitors of the GPO, were 30 to 50 times less active. The results suggest that a lipophilic aromatic iron-chelating agent may be useful as a substitute for SHAM in combination therapy.

Animals↗

PubMed1991

Potent collagenase inhibitors prevent interleukin-1-induced cartilage degradation in vitro.

The matrix metalloproteinases (MMPs) collagenase, gelatinase and stromelysin, contribute to the destruction of articular cartilage which occurs during rheumatoid and osteoarthritis. Ro 31-4724, a substrate analogue containing a hydroxamic acid function, is a potent but non-selective inhibitor of all three MMPs (I50, collagenase = 10 nM), whereas Ro 31-7467, a phosphinic acid transition-state analogue, shows 14-fold and 12-fold selectivity for collagenase (I50 = 17 nM) over gelatinase and caseinase (stromelysin) respectively. The effects of these inhibitors on interleukin-1-induced bovine nasal cartilage degradation were examined. The hydroxamate Ro 31-4724 inhibits proteoglycan and collagen loss, whereas the phosphinic acid Ro 31-7467 selectively inhibits collagen breakdown in this model. This represents the first demonstration of potent and selective inhibition of IL1-induced cartilage degradation in vitro by MMP inhibitors. These results suggest that collagenase is responsible for collagen loss and that a different enzyme, possibly stromelysin, is responsible for proteoglycan degradation in this model.

Animals↗

PubMed1995

An in vivo model for screening peptidomimetic inhibitors of gelatinase A.

Gelatinase A, a matrix metalloproteinase, is frequently associated with human solid tumors, and its secretion and activation in the tumor milieu is considered important in the process of angiogenesis, invasion, and metastasis. Consequently, metalloproteinase inhibitors may be of value in the therapy of cancer as well as other disease states involving tissue remodeling and release of biologically active peptide/protein by proteolytic cleavage. Here we describe the development of a rapid screening assay for in vivo activity of peptidomimetic inhibitors of gelatinase A that involves assessment of inhibition of an enzyme-substrate reaction in a circumscribed body compartment, the mouse pleural cavity. As examples of the utility of this assay, in vivo activity of the aryl sulfonamide, sulfamyl urea, morpholino and carboxylic acid functionality at the P3' position of a series of hydroxamic acid inhibitors was examined after administration both intraperitoneally (ip) (to approximate systemic administration) and orally. For up to 2 h after ip administration, all inhibitors tested showed marked activity (> 90% inhibition) at 17 mumol/kg (approximately 10 mg/kg). This activity declined in a dose-responsive manner to insignificant levels at 0.67 mumol/kg (approximately 0.4 mg/kg). Aryl sulfonamides showed significant inhibition (> 50%) for up to 7 h after administration. A higher dosage (136 mumol/kg, approximately 80 mg/kg) was required to reveal oral activity, which was observed only with morpholino compounds (> 50% inhibition). Thus, the model described may be of value in the identification of orally active gelatinase A inhibitors.

Administration, Oral↗

PubMed1980

Chloramphenicol-induction of a second cyanide-and azide-insensitive mitochondrial pathway in Ustilago maydis.

Growth of wild type Ustilago maydis in presence of chloramphenicol results in increased resistance of cyanide-insensitive respiration to hydroxamic acid derivatives. The biphasic nature of the Dixon plots for hydroxamate inhibition of mitochondrial alternative respiration suggested involvement of two cyanide-sensitive systems. This hypothesis was confirmed by the analysis of kinetic data. One of the two systems exhibits normal sensitivity to hydroxamates and appears similar to that present in mitochondria from cells grown in control medium. In contrast, the inducible system is characterised by resistance to hydroxamates and lower substrate affinity. With excess substrate and AMP in reaction mixutre the two systems have equal participation in the cyanide-insensitive respiration of chloramphenicol-treated mitochondria. In the absence of AMP, however, the inducible oxidase seems to exhibit much higher affinity for oxygen. The new system appears responsible also for changes in sensitivity of alternative respiration to low temperatures. It differs from the hydroxamate resistant systems recently reported for other fungi in its high activity and its complete insensitivity to azide and cyanide.

Adenosine Monophosphate↗

PubMed1982

In vitro inhibition of Pseudomonas aeruginosa elastase by metal-chelating peptide derivatives.

Pseudomonas aeruginosa elastase is a zinc metalloendopeptidase, probably responsible for the tissue destruction observed during infections with this organism. The elastase of a virulent Pseudomonas aeruginosa strain (Habs serotype 1) was isolated and found to have a molecular weight of 35,000; it readily degraded elastin and cartilage proteoglycans. A series of amino acid and peptide derivatives containing the metal-chelating moieties hydroxamate, phosphoryl, or thiol were synthesized and tested as potential inhibitors of the enzyme. Inhibition constants (K(i)s) for the compounds were determined with the chromophoric substrate furylacryloyl-glycyl-l-leucyl-l-alanine. The hydroxamic acid derivatives of benzyloxycarbonyl-glycine, benzyloxycarbonyl-l-leucine and benzyloxycarbonyl-l-phenylalanine had inhibition constants in the range of 11 to 28 muM. The 2-mercaptoacetyl derivatives of l-leucyl-d-phenylalanine and l-leucyl-l-phenylalanine had K(i) values of 34 and 1.5 muM, respectively, demonstrating the stereospecificity of the inhibition. The most potent inhibitors tested were 2- mercaptoacetyl-l-phenylalanyl-l-leucine and phosphoryl-l-leucyl-l-phenylala-nine (K(i) = 0.2 muM). Similar compounds lacking the metal-chelating moiety were about 3 orders of magnitude poorer inhibitors. When the inhibition of the enzyme activity towards azocasein, elastin, or cartilage was examined, inhibitor concentrations approximately 50-fold higher than the respective K(i)s were required to obtain 60 to 90% inhibition. Virtually complete inhibition was achieved with these substrates at inhibitor concentrations 500-fold higher than the respective K(i)s (0.1 to 14 mM). Although, 2-mercaptoacetyl-l-phenylalanyl-l-leucine and phosphoryl-l-leucyl-l-phenylalanine exhibited the same affinity to the enzyme, the latter was inferior in inhibiting cartilage proteoglycan degradation. 2-Mercaptoacetyl-l-phenylalanyl-l-leucine represents a class of potent elastase inhibitors that might prove useful in the management of P. aeruginosa infections.

Cartilage↗

PubMedDate not supplied

Inhibition of aryl sulfotransferase by carboxylic acids.

Aryl sulfotransferase (AST) IV catalyzes the 3'-phosphoadenosine-5'-phosphosulfate-dependent formation of sulfuric acid esters of a wide range of phenols, benzylic alcohols, hydroxamic acids, catecholamines, tyrosine carboxylesters, and peptides with N-terminal tyrosines. The objective of this investigation was to determine whether aryl carboxylic acids could act either as substrates or inhibitors for AST IV. These studies were conducted with AST IV that was purified to homogeneity from male Sprague-Dawley rats. Although none of the carboxylic acids tested were substrates for AST IV, they did competitively inhibit the enzyme with 1-naphthalenemethanol as substrate at pH 7.0. 1-Naphthoic acid, 2-naphthoic acid, and salicylic acid were particularly effective inhibitors of the sulfotransferase. The distance of the carboxyl group from the aromatic ring influenced the inhibitory capability of the carboxylic acids examined. The Kis for 1-naphthylacetic acid and 2-naphthylacetic acid as inhibitors of AST IV-catalyzed sulfation of 1-naphthalenemethanol were approximately 10-fold higher than those of the corresponding naphthoic acids. A substituted 2-naphthylacetic acid derivative, naproxen, also inhibited the aryl sulfotransferase. Preliminary studies indicate that aryl carboxylic acids also inhibit sulfation of phenols catalyzed by AST IV. 2-Naphthoic acid inhibited the sulfation of 2-naphthol catalyzed by AST IV at pH 5.5 with a Ki of 260 microM. In addition to these results with the homogeneous sulfotransferase, inhibition of aryl sulfotransferase activity by carboxylic acids was also observed in rat hepatic 100,000 g supernatant fractions. Thus, aryl carboxylic acids represent a new class of inhibitors for AST IV.

Animals↗