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  • Articles  (7)
  • Biochemistry  (5)
  • Life and Medical Sciences  (2)
  • 1990-1994  (7)
  • Chemistry and Pharmacology  (7)
  • 1
    Electronic Resource
    Electronic Resource
    Chemoprevention of rat mammary carcinogenesis: Exceptional activity of dietary dehydroepiandrosterone (DHEA) (1993)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 53 (1993), S. 253-254 
    Details
    ISSN: 0730-2312
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: A major determinant of progress in human breast cancer prevention is the identification of agents with significant anticarcinogenic activity and acceptable levels of toxicity in experimental animals. Over the past 20 years, more than 50 experimental regimens have been shown to have significant chemopreventive activity in the rat mammary gland. The most effective approaches to mammary cancer chemoprevention in rats involve surgical endocrine ablations such as bilateral ovariectomy. However, prophylactic surgical ablations are unlikely to be acceptable to the majority of the general public. All chemicals evaluated to date are less effective, and none has been shown to reduce mammary cancer incidence to zero. As a result, efforts continue to identify chemical agents whose protective activity is comparable to that of endocrine ablation. DHEA is an adrenal steroid with chemopreventive activity in several animal models for human cancer. In the present studies, the chemopreventive efficacy of DHEA was evaluated in rats exposed to the mammary gland carcinogen, N-methyl-N-nitrosourea (MNU). Groups of 20 female Sprague-Dawley rats were fed an AIN-76A diet supplemented with 0, 400, or 800 mg DHEA per kg diet; one week later, all rats received a single i.p. injection of 35 mg MNU per kg body weight. Animals were palpated weekly to monitor mammary tumor development, and all mammary tumors were histologically confirmed. When administered at 800 mg/kg diet, DHEA reduced mammary cancer incidence in controls from 95% to 15%; carcinoma multiplicity in rats receiving 800 mg DHEA per kg diet was reduced by more than 85% from control levels. In a separate study, the 400 mg/kg diet dose of DHEA reduced the incidence of mammary cancer to 5% from 80% found in controls fed the basal diet. Reductions in mammary cancer incidence and multiplicity associated with DHEA administration were accompanied by large increases in cancer latency. Evaluation of mammary gland wholemounts from animals fed DHEA demonstrated a massive induction of lobuloalveolar differentiation. These results indicate the dietary supplementation with non-toxic dose levels of DHEA has chemopreventive efficacy approaching that of endocrine ablation. This protection may be mediated by the induction of differentiation in the mammary gland, during which sensitive mammary parenchymal structures (terminal end buds) are stimulated to develop into structures (alveolar buds) less sensitive to carcinogenic insult.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240531154
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  • 2
    Electronic Resource
    Electronic Resource
    Intermediate endpoint biomarkers for chemoprevention (1992)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 50 (1992), S. 93-110 
    Details
    ISSN: 0730-2312
    Keywords: bladder cancer ; chemoprevention ; F-actin ; G-actin ; intermediate biomarker ; intermediate endpoint biomarker ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: The understanding of intermediate endpoint biomarker expression in relation to the sequential events in bladder tumorigensesis establishes a useful approach for evaluating chemopreventive agents. Biomarkers may be genotypic or phenotypic and function as biomarkers of susceptibility, expouser, effect, or disease. This paper reviews serverla years or reserach on biomarkers and their use in monitoring chemoprevention therapy. In initial animal experimnets, mice were doesed with N-butyl-N-(4-hydroxybutyl) nitrosamine(OH-BBN) while co-administering N(4-hydroxyphenyl) retinamide (4-HPR). 4-HPR did not statistically reduce tumor incidence, but did affect tumor dfferentiation and consequently, nuclear size and DNA ploidy. These results suggest that nuclear size and ploidy may function as intermediate endpoint biomarkers of effect for oncogenesis and that epigenetic as well as genetic mechanisms may be primary in the oncogenic proces. Early biomarkers of effect which occur prior to genetic effects or chromosome aberration may portend a higher probability of being modulated by differentiating agents such as retinoids. In vitro studies demonstrated that RPMI-7666 cells cultured with a phorbol ester tumor promoter (12O-tetradecanoyl-phorbol-13-acetate) could be redifferentiatee with 13-cis-retinoic acid and dimethyl sulfoxide (DMSO). F-Actin, A cytoskeltal biomerker with a presumed function in the epigenetic mechanisms of carcinogenesis, could also be normalized in HL-60 cells treated with 4-HPR or DMSO.A clinical evaluation of F-actin in patients whith varying degrees of risk confirmed the value of F-actin as a differentiating biomarker useful for bladder cancer risk assessment. The clarification of when the photypic changes of F-acting occur in biomerker useful for bladder cancer risk assessment. The clarification of when the phenotypic changes of F-actin occur in the oncogenic process was achieved when a variety of biochemical changes were mapped in the patients with bladder cancer. There stuides confirmed that G-acting, a reciprocal form of F-actin, is increased relatively early in bladder cancer oncogenesis when multiple biomarkers are quantiated in the field, adjacent area, and the tumor. Comparison of each individual biomarker's expression from field, adjacent to tumor, and tumor, and subsequent cluster analysis of these biomarkers, indicated that the possible sequences of phenotypic expression of biomarkers in bladder cancer oncogenesis is from G-actin, to p300 antigen, to epidermal growth factor receptor (EGFR), to p185, (neu oncogene product), to DNA aneuploidy and family, finally, to visual morphology. To date, a bettery of three biomarkers, G-actin, M344, and DNA, with routine cytology has been used to monitor eleven patients receiving Bacillus Calmette-Guerin(BCG) immunotherapy and eight patients clinically free of bladder cancer (negative cytology and biopsy) who were treated with differentiation agent, DMSO. These results indicate that G-actin may be useful biomarker for evaluating the efficacy of chemopreventive agents. © 1992 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240501320
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  • 3
    Electronic Resource
    Electronic Resource
    On a proposed radiation-induced polaronic hole in silicon dioxide (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 254-265 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab-initio self-consistent-field molecular-orbital (SCF MO) Hartree-Fock (HF) calculations using the STO-3G, 6-31G, and 6-31G* basis sets, were performed to model quasi-tetrahedral silicon species in silicon dioxide. Mostly nine-atom clusters, [Si(OH)4]qt, with charge number qt = 0 or + 1, were studied. The positions of the Si and O atoms were varied to achieve minimum total energies, while the protons were held fixed in the O-(neighboring)Si direction to simulate the rigid crystal surroundings. The α-quartz-type local symmetry C2 was found to be retained for the neutral cluster, but not for the ionic one. The unrestricted HF calculations indicate that the latter paramagnetic centre, (qt = +1), has its spin population almost entirely on one short-bonded oxygen ion bonded weakly to its neighboring Si, and is quite high in energy (9.55 eV with 6-31G) compared to the diamagnetic centre (qt = 0). The ionization energy is much higher than the self-trapping potential of the polaronic hole, a fact which may account for the failure so far to observe a [SiO4]+1 center in quartz by means of continuous-wave electron paramagnetic resonance spectroscopy. Calculations on the [SiO4]+1 center agree well with ultraviolet spectra, and with the [hole portion of a] proposed radiation-induced exciton in quartz. The hole in [Si(OH)4]+1 can be shifted from a short-bonded to a long-bonded oxygen to give the excited state [Si(OH)4]es+1. Conclusions reached with the nine-atom clusters were confirmed by a series of calculations on the extended model [Si(OSiH3)4]qt. Comparisons with the known isoelectronic species [AlO4]0 were carried out.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120216
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  • 4
    Electronic Resource
    Electronic Resource
    A general approach for atom-type assignment and the interconversion of molecular structure files (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 209-214 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: In molecular modeling projects which require use of several different computer programs, one encounters problems in sharing data between programs. One difficult problem is the conversion of atom types from one program's definition to another. A second problem is the conversion of a polymer, such as a protein or polynucleotide molecule, from a “general” program, which understands molecules as a collection of atoms, to a “polymer” program, which understands molecules as a collection of molecular fragments stored in some library. We describe here a new method by which atom types are deduced from the environment of each atom. We use the Daylight Chemical Information Systems library of programs to deduce the atom types based only on the atomic symbol, connectivity and formal charge of each atom in the molecule. We also describe a method by which the polypeptide nature and sequence of a molecule can be deduced from minimal information about the atoms in the molecule. We have written a computer program which demonstrates this method. This program deduces atom types for AMBER, GRIN/GRID, CHARMm, and ALOGP. It will also produce input files for the AMBER/PREP fragment library preparation program.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120210
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  • 5
    Electronic Resource
    Electronic Resource
    Ab initio calculations on CO4 centers in silicon dioxide (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 12 (1991), S. 446-453 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio SCF-MO Hartree-Fock calculations were performed using the STO-3G, 6-31G, and 6-31G* basis sets to model hypothetical substitutional carbon impurities in silicon dioxide. We utilized nine-atom clusters, [C(OH)4]qt, with charge number qt = 0 and + 1. The positions of the C and O atoms were varied to achieve minimum total energies, while the fixed protons served to simulate the rigid crystal surroundings. In the optimized configuration of the neutral cluster, the C—O bond lengths are appreciably longer than typical C—O bonds, indicating relatively weak bonds for a carbon impurity at a silicon site. For comparison, the relative positions of all nine atoms in the [C(OH)4]0 model were allowed to vary. This unconstrained model yielded more normal bond lengths and was lower in energy than the fixed-proton model by 6.80 eV with the 6-31G* basis set. The free-H model compared favorably with the x-ray diffraction data for an analogous orthocarbonate. Our results are in concert with the lack of reports of any substitutional carbon impurity in α-quartz. In the fixed-H models, the twofold local symmetry was found to be retained when qt is 0 but not when qt is + 1. For the latter ion, the unrestricted H-F calculations indicate that this paramagnetic center has its spin population almost entirely on one oxygen ion and is high in energy (5.31 eV with 6-31G) compared to the diamagnetic neutral one. Conclusions reached with the nine-atom clusters were confirmed by a series of calculations on the extended model [C(OSiH3)4]0.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540120406
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  • 6
    Electronic Resource
    Electronic Resource
    Reversed stereochemical preference in binding of Ro 31-8959 to HIV-1 proteinase: A free energy perturbation analysis (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 15 (1994), S. 1241-1253 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ro 31-8959 is a highly potent inhibitor of HIV-1 proteinase in phase III clinical trials for treatment of AIDS. It is also the first subnanomolar inhibitor that demonstrated reversed stereochemical preference at the central hydroxyl group. Free energy perturbation calculations have been carried out to rationalize the preference for the R-diastereomer by consideration of two models of the (weaker) S-diastereomer. In the first model, the central hydroxyl group makes only one hydrogen bond with the active site aspartates, whereas the hydroxyl group in the second model makes at least three strong hydrogen bonds. Using the first model, the free energy difference in binding of Ro 31-8959 and its S-diastereomer is calculated to be 3.4 kcal/mol, which is in close agreement with the experimental value. Although the second model has a more favorable interaction with the active site aspartates compared to the first model, it has a higher energy N-axial conformation at the decahydroisoquinoline group in P1′. We show here that the two contributions cancel each other and the two models of S-diastereomer are predicted to have equivalent binding. The stereochemical preference in a hydroxyethylamine series of inhibitors appears to be affected by both intermolecular and intramolecular (conformational) energies. The binding data on the proline containing inhibitors are rationalized based on these results. © 1994 by John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540151106
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  • 7
    Electronic Resource
    Electronic Resource
    Conformational analysis of HIV protease inhibitors. I. Rotation of the amide group adjacent to the P′1 decahydroisoquinoline ring system in ro 31-8959 and related systems (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 14 (1993), S. 1446-1453 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Pipecolic acid derivatives have proven to be effective P′1 groups in a series of highly potent inhibitors of the enzyme HIV protease. One such inhibitor, Ro 31-8959, contains the saturated bicyclic ring system decahydroisoquinoline (DIQ) in the P′1 position. The binding orientation of Ro 31-8959 is known from X-ray crystallography. However, the bound conformation of the S-hydroxy diastereomer has not been studied, and for this molecule there are at least two different possible binding conformations. Specifically, the N-alkyl substituents may be equatorial or axial and the 3-carboxamide may be rotated into several different orientations. To gain a better understanding of the relative energies of these various conformations, ab initio molecular orbital calculations have been carried out on a series of pipecolic acid and DIQ derivatives. The results indicate that the lowest-energy N-equatorial rotamer is always at least 3 kcal/mol more stable than the lowest-energy N-axial rotamer. The presence of the second ring, as in the DIQ system, considerably raises the equatorial-axial difference to nearly 7 kcal/mol. Also, the preferred rotation angle of the amide group is different for the N-equatorial and N-axial cases. When the molecular dynamics-averaged conformation of the bound S-hydroxy inhibitor is considered, the energy difference between the N-equatorial and N-axial conformers drops to 4-5 kcal/mol. The preferred amide rotations in these systems are compared to those found in proline-containing peptides. Finally, some observations are made with respect to the large conformational energy penalty necessary for binding Ro 31-8959. © John Wiley & Sons, Inc.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540141206
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