Inhibitors of sterol synthesis. Chemical synthesis of 7 alpha-ethyl and 16 alpha-ethyl derivatives of delta 8(14)-15-oxygenated sterols and their effects on 3-hydroxy-3-methylglutaryl coenzyme A reductase in CHO-K1 cells

The enolate of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one (II), formed upon treatment of II with potassium tert-butoxide in tert-butanol, was alkylated with ethyl iodide. In addition to the major products, 3 beta-hydroxy-14 alpha-ethyl-5 alpha-cholest-7-en-15-one and its 3 beta-ethyl ether, small amounts of 3 beta-hydroxy-7 alpha-ethyl-5 alpha-cholest-8(14)-en-15-one (V), 3 beta-hydroxy-16 alpha-ethyl-5 alpha-cholest-8(14)-en-15-one (VI) and the 3 beta-ethyl ether of VI were isolated. When the enolate of II was formed by treatment with lithium diisopropylamide in tetrahydrofuran, the same alkylation furnished VI as the major product. Reduction of VI with lithium aluminum hydride gave 16 alpha-ethyl-5 alpha-cholest-8(14)-ene-3 beta, 15 alpha-diol (IX) and its 15 beta epimer X, which were separated by column chromatography. Full 1H and 13C nuclear magnetic resonance (NMR) assignments, augmented by nuclear Overhauser effect difference spectra for VI, established the stereochemistry of these diols at C-15 and C-16. The NMR results indicate that the 16 alpha-ethyl group affects the side-chain conformation. The effects of II, V, VI, IX and X on the levels of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity were studied in CHO-K1 cells. With the exception of IX, each of the compounds reduced the levels of HMG-CoA reductase activity. The order of potency with respect to suppression of the elevated levels of HMG-CoA reductase activity induced by transfer of the cells to lipid-deficient medium, was II greater than V greater than VI greater than X.

Metabolism and nucleic acid binding of N-hydroxy-4-acetylaminobiphenyl and N-acetoxy-4-acetylaminobiphenyl by cultured human uroepithelial cells

Metabolic activation of N-hydroxy-4-acetylaminobiphenyl (N-OH-AABP) and N-acetoxy-4-acetylaminobiphenyl (N-OAc-AABP), the proximate carcinogenic metabolites of the human bladder carcinogen 4-aminobiphenyl (ABP), was examined in human uroepithelial cells (HUC). Bioconversion was studied by incubating HUC cultures with [3H]N-OAc-AABP or [3H]N-OH-AABP. Three organo-soluble metabolites, N-OH-AABP, 4-acetylaminobiphenyl (AABP), and ABP were identified in ethyl acetate extracts from cultures exposed to N-OAc-AABP. Similarly, AABP and ABP were characterized as the major metabolites from cultures treated with N-OH-AABP. Incubation of N-OAc-AABP with HUC microsomes in vitro yielded primarily the O-deacetylation product N-OH-AABP. The HUC microsomes also catalyzed the N-deacetylation of N-OAc-[14C]AABP, N-OH-[14C]AABP, and [3H]AABP. The O- and N-deacetylase activities for N-OAc-AABP were 55.9 and 38.2 nmol/mg/min, respectively. These O- and N-deacetylase activities were both blocked by paraoxon. Incubation of [3H]N-OAc-AABP or [3H]N-OH-AABP with HUC microsomes and tRNA or DNA showed that 23.0 and 8.0 nmol of N-OAc-AABP and 74.5 and 25.2 pmol of N-OH-AABP were bound per mg protein/mg RNA or DNA, respectively. In comparison, the acetyl CoA-dependent HUC cytosol-mediated bindings of [3H]N-OH-ABP to RNA and DNA were 801 and 447 pmol/mg nucleic acid/mg protein. The HUC microsome-mediated bindings of N-OAc-AABP and N-OH-AABP to nucleic acids were inhibited by paraoxon, whereas the cytosol-mediated binding of N-OH-ABP was insensitive to paraoxon inhibition. Chromatography of the DNA hydrolysate obtained from the in vitro incubation of [3H]N-OAc-AABP or [3H]N-OH-AABP with HUC microsomes showed N-(deoxyguanosine-8-yl)-4-aminobiphenyl as the major adduct, based on comparison with authentic synthetic standard. These results show that human uroepithelia contain microsomal acetyl transferases that are capable of converting the proximate metabolites N-OAc-AABP and N-OH-AABP of the human bladder carcinogen ABP, to reactive electrophiles that bind to DNA. The occurrence of these acetyl transferases in the target organ of the human bladder carcinogen ABP suggests that metabolic activation of some proximate metabolites of ABP could occur directly in HUC and could play a pivotal role in susceptibility to aryl-amine/acetamide induced human bladder cancers.

Acetyl transferase-mediated metabolic activation of N-hydroxy-4-aminobiphenyl by human uroepithelial cells

Metabolism and nucleic acid binding of N-hydroxy-4-aminobiphenyl (N-OH-ABP), a proximate carcinogenic metabolite of the human bladder carcinogen 4-aminobiphenyl (ABP), was investigated using cultured normal human uroepithelial cells (HUC). HPLC and TLC of the ethyl acetate extract of the media from cultured HUC after 4 h exposure to N-OH-ABP revealed the formation of two major metabolites, ABP and 4-acetylaminobiphenyl (AABP), suggesting the presence of N-acetyl transferase(s) in HUC. This was further confirmed by the formation of AABP, during the incubation of ABP with acetyl coenzyme A (AcCoA) and HUC cytosol. To test whether these enzymes also catalyze the AcCoA-dependent O-acetylation, we examined the metabolic activation of N-OH-ABP using cytosolic preparations. Cytosol from HUC catalyzed AcCoA-dependent binding of [3H]N-OH-ABP to RNA; the amount of binding was 757 pmol/mg RNA/mg protein. Binding with DNA was quantitatively similar to RNA. HPLC and TLC analyses of the enzymatic hydrolysate of [3H]N-OH-ABP-bound DNA revealed the major adduct to be N-(deoxyguanosine-8-yl)-4-aminobiphenyl, based on mobility of the radioactivity in comparison with the authentic synthetic standard. 32P-Post-labeling analysis of the DNA from the cytosol-mediated binding of N-OH-ABP revealed four radioactive spots. In contrast, post-labeling analysis of the DNA from intact HUC exposed to N-OH-ABP showed five adducts, including two of the adducts observed with HUC cytosols, suggesting the possible involvement of additional activation pathway(s) in intact HUC. These results suggest that bioactivation of N-OH-ABP could occur within the HUC, the target organ for ABP, and that cytosolic acetyl transferase(s) may play a critical role in susceptibility to arylamine-induced bladder carcinogenesis.

Purification and properties of the L-amino acid oxidase from monocellate cobra (Naja naja kaouthia) venom

1. The L-amino acid oxidase of the monocellate cobra (Naja naja kaouthia) venom was purified to electrophoretic homogeneity. The molecular weight of the enzyme was 112,200 as determined by Sephadex G-200 gel filtration chromatography, and 57,400 as determined by SDS-polyacrylamide gel electrophoresis. 2. The enzyme had an isoelectric point of 8.12 and a pH optimum of 8.5. It showed remarkable thermal stability, and, unlike many venom L-amino acid oxidase, was also stable in alkaline medium. The enzyme was partially inactivated by freezing. 3. The enzyme was very active against L-phenylalanine and L-tyrosine, moderately active against L-tryptophan, L-methionine, L-leucine, L-norleucine, L-arginine and L-norvaline. Other L-amino acids were oxidized slowly or not oxidized. 4. Kinetic studies suggest the presence of a side-chain binding site in the enzyme, and that the binding site comprises of at least four hydrophobic subsites.

Inhibitors of sterol synthesis. Chemical synthesis and spectral properties of (25R)-5 alpha-cholest-8(14)-ene-3 beta,15 beta,26-triol, a potential metabolite of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one and its effects on 3-hydroxy-3-methylglutaryl-coenzyme A reductase in CHO-K1 cells

(25R)-5 alpha-Cholest-8(14)-ene-3 beta,15 beta,26-triol (III) was prepared by reduction of (25R)-3 beta,26-diacetoxy-5 alpha-cholest-8(14)-en-15-one with sodium borohydride followed by treatment of the crude product with lithium aluminium hydride. The trihydroxysterol III, a potential metabolite of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one, was characterized by the results of mass spectral studies and by nuclear magnetic resonance (NMR) spectroscopy. Full 1H and 13C NMR assignments for III and 5 alpha-cholest-8(14)-ene-3 beta,15 beta-diol are given and used to establish the structure of III. The triol was found to be very potent in lowering the levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in Chinese hamster ovary cells.

Electrostatic properties of 1-methyluracil from diffraction data

1-Methyluracil (1-methyl-2,4-dioxopyrimidine), C5H6-N2O2, M(r) = 126.12, orthorhombic, Ibam, a = 13.188 (6), b = 13.175 (5), c = 6.214 (3) A, V = 1079.7 (8) A3, Z = 8, Dx = 1.552 g cm-3, lambda (Mo K alpha) = 0.7107 A, mu = 1.317 cm-1, F(000) = 528, T = 123 K, R(F2) = 0.068 for 2996 reflections with sin theta/lambda less than 1.08 A-1. The electronic charge-density distribution has been analyzed in terms of Stewart's rigid pseudoatom model, using restricted Slater radial functions and angular multipole terms extending to octapoles for C, N and O, and quadrupoles for H pseudoatoms. Three different structure refinements have been carried out based on two X-ray diffraction data sets from different crystals collected at temperatures differing by about 20 K. The molecular dipole moment is 6.4 (27) D. Maps of the electrostatic potential for a molecule isolated from the crystal show that atoms O2 and O4 confer overall electro-negativity on one side of the molecule while the CH groups and the C1 methyl group confer electropositivity on the other. For the centrosymmetric hydrogen-bonded dimer (N3-H3...O4'; H...O distances 1.77 A) the electrostatic potential shows electropositive bridges between the molecules. These features are lacking for the C-H...O interactions (distances H6...O2, 2.37; H11...O4, 2.34 A). The electron density and its Laplacian have been determined at the intramolecular bond-critical points and also for the intermolecular H...O interactions. Values for the former are characteristic of covalent bonds. Values of the electron density and Laplacian for the C-H...O interactions are very small and have little or no significance in terms of their e.s.d.'s. The electrostatic energy of interaction for the N-H...O hydrogen-bonded dimer is -10 (12) kJ mol-1. The attractive electrostatic energy increases to -67 (33) kJ mol-1 for a centrosymmetric planar tetramer in which the C-H...O interactions are also formed.

Inhibitors of sterol synthesis. A highly efficient and specific side-chain oxidation of 3 beta-acetoxy-5 alpha-cholest-8(14)-en-15-one for construction of metabolites and analogs of the 15-ketosterol

As part of a program directed towards the chemical syntheses of potential metabolites and analogs of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one (I), a potent regulator of cholesterol metabolism, several routes have been explored for the preparation of 3 beta-hydroxy-15-keto-5 alpha-chol-8(14)-en-24-oic acid (IV). These investigations led to a remarkably specific and efficient side-chain oxidation of I. For example, treatment of the acetate of I with a mixture of trifluoroacetic anhydride, hydrogen peroxide, and sulfuric acid for 3.5 h at -2 degrees C gave a crude product consisting of 3 beta-acetoxy-24-trifluoroacetoxy-5 alpha-chol-8(14)-en-15-one (XI), 3 beta-acetoxy-24-hydroxy-5 alpha-chol-8(14)-en-15-one (XII), and 3 beta, 24-diacetoxy-5 alpha-chol-8(14)-en-15-one (XIII) in yields of 58%, 8%, and 3%, respectively, by HPLC analysis. XI was readily hydrolyzed to XII upon treatment with triethylamine in methanol at room temperature. Oxidation of XII with Jones reagent gave 3 beta-acetoxy-15-keto-5 alpha-chol-8(14)-en-24-oic acid (XVIII) from which its methyl ester (IX) was prepared by treatment with diazomethane. Mild alkaline hydrolysis of XVIII gave the 3 beta-hydroxy-delta 8(14)-15-keto C24 acid (IV). Hydrolysis of the crude product of the side-chain oxidation with K2CO3 in methanol gave 3 beta,24-dihydroxy-5 alpha-chol-8(14)-en-15-one (XIV) which was oxidized with Jones reagent to yield 3,15-diketo-5 alpha-chol-8(14)-en-24-oic acid (XV). Treatment of XV with diazomethane gave its methyl ester (XVI) which, upon controlled reduction with NaBH4, yielded methyl 3 beta-hydroxy-15-keto-5 alpha-chol-8(14)-en-24-oate (XVII). Compound IX was also prepared by an independent route. Full 1H and 13C NMR assignments are presented for 12 new compounds. IV caused a approximately 56% reduction of the level of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in CHO-K1 cells at a concentration of 2.5 microM. In contrast, the corresponding 3,15-diketo acid XV had no detectable effect on reductase activity under the same conditions.

Refined structure of rat Clara cell 17 kDa protein at 3.0 A resolution

The rat Clara cell 17 kDa protein (previously referred to as the rat Clara cell 10 kDa protein) has been reported to inhibit phospholipase A2 and papain, and to also bind progesterone. It has been isolated from rat lung lavage fluid and crystallized in the space group P6(5)22. The structure has been determined to 3.0 A resolution using the molecular replacement method. Uteroglobin, whose amino acid sequence is 55.7% identical, was used as the search model. The structure was then refined using restrained least-squares and simulated annealing methods. The R-factor is 22.5%. The protein is a covalently bound dimer. Two disulfide bonds join the monomers together in an antiparallel manner such that the dimer encloses a large internal hydrophobic cavity. The hydrophobic cavity is large enough to serve as the progesterone binding site, but access to the cavity is limited. Each monomer is composed of four alpha-helices. The main-chain structure of the Clara cell protein closely resembles that of uteroglobin, but the nature of many of the exposed side-chains differ. This is true, particularly in a hypervariable region between residues 23 and 36, and in the H1H4 pocket.

Induction of thioguanine-resistant mutations in human uroepithelial cells by 4-aminobiphenyl and its N-hydroxy derivatives

The mutagenic potentials of the human bladder carcinogen 4-amino-biphenyl (ABP) and three of its proximate carcinogenic metabolites, N-hydroxy-4-aminobiphenyl (N-OH-ABP), N-hydroxy-4-acetylaminobiphenyl (N-OH-AABP) and N-acetoxy-4-acetylaminobiphenyl (N-OAc-AABP) were tested on a prime human target cell type for carcinogenesis, human uroepithelial cells (HUC). SV-HUC (PC), a near diploid, clonally derived, nontumorigenic SV40-immortalized human uroepithelial cell line that is transformable to tumorigenicity after exposure to ABP and its metabolites, was used for quantitative mutation assays. The end point used was the induction of mutations in the hypoxanthine-guanine phosphoribosyltransferase (HGPRT) locus, selected using 6-thioguanine resistance (TGr). A single, 24-h exposure of SV-HUC to ABP, N-OH-ABP, N-OH-AABP, or N-OAc-AABP caused a statistically significant, dose-dependent increase in mutation frequency resulting in a 2-30-fold increase in the number of TGr mutants in carcinogen-exposed groups compared to untreated controls. These chemicals were similarly mutagenic towards MC-T11, an SV-HUC-derived low grade tumor cell line that was also shown to be responsive to transformation (in a separate study) by ABP, N-OH-ABP, or N-OH-AABP as judged by the generation of higher grade tumors. In contrast, the mutagenic potencies of ABP and N-OH-ABP were lower when tested on a subclone of SV-HUC (BC) that is refractory to transformation by these chemicals. Thus, these data support a model of transformation in which ABP as well as its metabolites contribute to tumorigenic transformation and neoplastic progression of HUC by inducing mutations in susceptible target cell genes.

Tumorigenic transformation and neoplastic progression of human uroepithelial cells after exposure in vitro to 4-aminobiphenyl or its metabolites

A multistep in vitro/in vivo transformation system was used to test the transforming effect(s) of the human bladder procarcinogen 4-amino-biphenyl (ABP) and two putative proximate carcinogenic metabolites, N-hydroxy-4-aminobiphenyl (N-OH-ABP) and N-hydroxy-4-acetylamino-biphenyl (N-OH-AABP), on a clonally derived nontumorigenic SV40-immortalized human uroepithelial cell line, SV-HUC. SV-HUC were exposed in vitro to concentrations of ABP, N-OH-ABP, or N-OH-AABP that caused a range of cytotoxicity from 5 to 76%. Tumorigenic transformation of SV-HUC, as assessed by the ability of the exposed cells to form carcinomas when inoculated s.c. into athymic nude mice, was achieved after a single exposure to ABP, N-OH-ABP, or N-OH-AABP. In the tumorigenic transformation experiments, 28 of 45 mice representing all 15 carcinogen-exposed observation groups formed carcinomas, whereas none of 9 mice from control groups formed carcinomas (P = 0.001). Neoplastic progression of a low grade regressive squamous cell carcinoma, MC-T11, was also achieved in this system after in vitro exposure to ABP, N-OH-ABP, or N-OH-AABP. In these progression experiments, 11 of 33 mice representing 7 of 12 carcinogen-exposed observation groups formed persistent, high grade nongressing tumors, while only 1 of 19 untreated MC-T11 controls spontaneously progressed on reinoculation (P = 0.022). Forty independent carcinomas generated in athymic nude mice recapitulated diverse cancer phenotypes (including different growth kinetics and histopathological subtypes and grades) represented in clinical bladder cancers. These results demonstrate for the first time the transforming effects of the potent human carcinogen ABP and two of its proximate N-hydroxy metabolites on a prime human target cell type, HUC.

Toward a dynamical structure of DNA: comparison of theoretical and experimental NOE intensities

Comparisons of experimental and calculated interproton nuclear Overhauser effect (NOE) buildup curves for duplex d(CGCGAATTCGCG)2 have been made. The calculated NOEs are based on molecular dynamics simulations including counterions and water and on the single-structure canonical A, B, and crystal forms. The calculated NOE effects include consideration of the motions of individual interproton vectors and the anisotropic tumbling of the DNA. The effects due to inclusion of anisotropic tumbling are much larger than those due to the local motion, and both improve the agreement between calculated and experimental results. The predictions based on the dynamical models agree significantly better with experiment than those based on either of the canonical forms or the crystal structure.

Binding of the adenovirus VAI RNA to the interferon-induced 68-kDa protein kinase correlates with function

In human cells infected with adenovirus, the virus-associated RNA VAI blocks the activation of the interferon-induced double-stranded-RNA-dependent 68-kDa protein kinase (p68) and maintains normal levels of protein synthesis at late times after infection. VAI antagonizes the kinase activity by binding to p68. The structure of VAI consists of two long, base-paired stems connected by a complex short stem-loop structure. Previous work using a series of adenovirus mutants showed that the structural determinants of the VAI RNA that are essential for function reside in the central complex short stem-loop structure and adjacent base-paired regions (functional domain); the long duplex regions were found to be dispensable for function. To determine whether binding of VAI to p68 correlates with function and whether the structural determinants that are essential for function are also essential for binding, we studied the interaction of wild-type and several mutant VAI RNAs with p68 in whole cells. The p68-VAI complexes from mutant- and wild-type-infected cells were immunoprecipitated by an anti-p68 monoclonal antibody. The mutant RNAs that functioned efficiently in the cells bound to p68 efficiently in the cells, whereas functionally impaired mutants failed to bind to p68, indicating that the binding of the VAI RNA to p68 correlates well with function. In vitro binding assays with immunopurified p68 confirmed these observations. Secondary-structure analysis of several mutant VAI RNAs suggests that the binding does not depend on the long duplex regions but requires all the elements of the functional domain. We propose that the functional domain and the p68-binding domain of the VAI RNA are identical.

Recombinant Epstein-Barr virus with small RNA (EBER) genes deleted transforms lymphocytes and replicates in vitro

Strains of Epstein-Barr virus (EBV) with deletions of the small RNA (EBER) genes were made by homologous recombination using the EBV P3HR-1 strain, which has undergone deletion of the essential transforming gene that encodes the EBV nuclear antigen, EBNA-2, and a DNA fragment that was wild type at the EBNA-2 locus but from which the EBER genes had been deleted. Even though the EBER and EBNA-2 genes are separated by 40 kilobases, selection for transforming P3HR-1 recombinants that required a restored EBNA-2 gene resulted in 20% cotransfer of the EBER deletion. EBER-deleted recombinants transformed primary B lymphocytes into lymphoblastoid cell lines (LCLs), which were indistinguishable form LCLs transformed by wild-type EBV in their proliferation, in latency-associated EBV gene expression, and in their permissiveness for EBV replication cycle gene expression. EBER-deleted virus from infected LCL clones could infect and growth-transform primary B lymphocytes. These procedures should be applicable to the construction of other EBV recombinants within 40 kilobases of the EBNA-2 gene. The EBER-deleted EBV recombinants should be useful in further evaluating the role of EBERs in EBV infection.

Glycolysis and Entner-Doudoroff pathways in Halobacterium halobium: some new observations based on 13C NMR spectroscopy

13C NMR was used to study glucose metabolism in intact cells of Halobacterium halobium. Spectra of glucose grown cells incubated with [1-13C] glucose indicate the presence of gluconate as the initial product. The existence of glycolytic pathway is also indicated. In the extracts of these cells an NADP dependent glucose dehydrogenase was detected. Galactose grown cells failed to metabolise glucose but exhibited glucose dehydrogenase activity although about 20-50% less than that for glucose grown cells. Possible explanations of these experiments are discussed.

Domain communication in the dynamical structure of human immunodeficiency virus 1 protease

A dynamical model for the structure of the human immunodeficiency virus 1 (HIV-1) protease dimer in aqueous solution has been developed on the basis of molecular dynamics simulation. The model provides an accurate account of the crystal geometry and also a prediction of the structural reorganization expected to occur in the protein in aqueous solution compared to the crystalline environment. Analysis of the results by means of dynamical cross-correlation coefficients for atomic displacements indicates that domain-domain communication is present in the protein in the form of a molecular "cantilever" and is likely to be involved in enzyme function at the molecular level. The dynamical structure also suggests information that may ultimately be useful in understanding and further development of specific inhibitors of HIV-1 protease.

Preliminary crystallographic data for the thiamin diphosphate-dependent enzyme pyruvate decarboxylase from brewers' yeast

Single crystals of the thiamin diphosphate (the vitamin B1 coenzyme)-dependent enzyme pyruvate decarboxylase (EC 4.1.1.1) from brewers' yeast have been grown using polyethylene glycol as a precipitating agent. Crystals of the homotetrameric version alpha 4 of the holoenzyme are triclinic, space group P1, with cell constants a = 81.0, b = 82.4, c = 116.6 A, alpha = 69.5 beta = 72.6, gamma = 62.4 degrees. The crystals are reasonably stable in a rotating anode x-ray beam and diffract to at least 2.5 A resolution. The Vm value of 2.55 A/dalton is consistent with a unit cell containing four subunits with mass of approximately 60 kDa each. Rotation function results with native data indicate strong non-crystallographic 222 symmetry relating the four identical subunits, thus density averaging methods are likely to play a role in the structure determination.

Theoretical account of the 'spine of hydration' in the minor groove of duplex d(CGCGAATTCGCG)

The hydration of B-form DNA involves a novel sequence of ordered water molecules in the minor groove known as the spine of hydration. The positions of the ordered waters in the AATT region have been determined and indicate water bridges between the A-N3 and T-O2 acceptor sites. Theoretical calculation on hydration based on Monte Carlo simulation show that the water bridges are more sensitive to the prescription for intermolecular potentials than the choice of canonical vs. crystallographic geometry. The GROMOS force field and the SPC model for water are shown to give an accurate theoretical account of the experimental data.

Crystallization and preliminary X-ray study of rat Clara cell 10,000 Mr protein

Single crystals of Clara cell 10,000 Mr protein have been grown by vapour diffusion in the presence of ammonium sulphate. The space group is P4(1)32 or P4(3)32 with unit cell dimension a = 156.9 A. Crystals diffract to about 3.8 A resolution.