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B G Feuerstein

Publications and source records attributed to B G Feuerstein.

65 records · Page 4Linked to original sources
PubMed1989

Molecular dynamics of spermine-DNA interactions: sequence specificity and DNA bending for a simple ligand.

We used molecular dynamics to model interactions between the physiologically important polyamine spermine and two B-DNA oligomers, the homopolymer (dG)10-(dC)10 and the heteropolymer (dGdC)5-(dGdC)5. Water and counterions were included in the simulation. Starting coordinates for spermine-DNA complexes were structures obtained by molecular mechanics modeling of spermine with the two oligomers; in these models, spermine binding induced a bend in the heteropolymer but not in the homopolymer. During approximately 40 psec of molecular dynamics simulation, spermine moves away from the floor of the major groove and interacts nospecifically with d(G)10-d(C)10. In contrast, a spermine-induced bend in the helix of (dGdC)5-(dGdC)5 is maintained throughout the simulation and spermine remains closely associated with the major groove. These results provide further evidence that the binding of spermine to nucleic acids can be sequence specific and that bending of alternating purine-pyrimidine sequences may be a physiologically important result of spermine binding.

Base Sequence↗
PubMed1988

Recognition of Z-RNA and Z-DNA determinants by polyamines in solution: experimental and theoretical studies.

Protonated polyamines are among the most efficient cations that induce the left-handed Z-form in certain polynucleotides. It is not known, however, whether these cations bind to specific sites on Z-sequences in solution. We have studied potential polyamine binding sites by measuring the effects of polyamines on the binding of purified immunoglobulins (IgGs) to different regions of the Z-helix and by molecular mechanics modeling. The specific binding of anti-Z-DNA and anti-Z-RNA IgGs to Z-helices was studied as a function of spermidine or spermine concentration. The effect of polyamines on the antibody-nucleic acid interaction was different for IgGs with different specificities for various determinants on the Z-helix. Polyamines inhibit the binding of certain anti-Z IgGs directed against specific sites probably at or near the interface between the major convex surface and the phosphate backbone, most likely by competing with the antibody binding site(s). In contrast, polyamines have no effect on other anti-Z IgGs directed against sites determined by the phosphate backbone. Furthermore, these cations can enhance the binding of anti-Z IgG directed against bulky groups at the C-5 position on the major convex surface of the helix; the enhancement may be related to charge neutralization. Under these conditions, no direct binding of antibodies with polyamines was observed. These data suggest the existence of a specific binding site(s) for polyamines on both Z-DNA and Z-RNA in solution. These binding sites have some similarity to those observed in oligonucleotide crystals by Quigley (in "Molecular Structure and Biological Activity," J.F. Griffin and W.L. Duax, eds., Elsevier, Amsterdam (1982), pp. 317-331). The experimental evidence for specific spermine binding sites on the helical surface was supported by molecular mechanics modeling of the interaction of spermine with the major groove of (dG-dC)5.(dG-dC)5 in both the Z- and B-forms. The crystal coordinates of spermine-containing oligonucleotides in both the B- and Z-forms were used as the starting points for modeling studies. The potential energy of spermine bound to the major convex surface of the Z-form was much less favorable than that of spermine bound to the major groove of the B-form. In the presence of sodium ions, however, the Z-form-spermine complexes were favored over the B-form. Thus, both theoretical and experimental studies indicate that polyamines can specifically recognize Z-helical determinants in solution as well as in crystals.

Binding Sites↗
PubMed1986

Spermine-DNA interactions: a theoretical study.

Models for the interaction of spermine and DNA were studied by performing conformational energy calculations on spermine and molecular mechanics calculations on major and minor groove complexes of spermine and oligomers of DNA. Docked into the major groove of B-DNA, spermine stabilizes the complex by maximizing interactions between proton acceptors on the oligomer and proton donors on spermine. This is achieved by bending the major groove of DNA over spermine and altering oligomer sugar puckering and interstrand phosphate distances. By comparison, Liquori's minor groove model appears to be less stable than the major groove model. This evidence favors a preferential binding of spermine to certain sites in DNA, which provides a powerful force for the modification of DNA conformation.

DNA↗
PubMed1986

Relationship between heat sensitivity and polyamine levels after treatment with alpha-difluoromethylornithine (DFMO).

Alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, was used to study the effect of polyamine depletion on delayed heat sensitization in Chinese hamster ovary cells (CHO). The cells were treated with 1 or 10 mM DFMO for 8 or 48 h and then given a single heat treatment (43 degrees C, 90 min) at intervals up to 150 h after DFMO addition. Cellular survival, DNA polymerase activity, and polyamine levels were measured. Delayed heat sensitization for cell lethality began 50-55 h (about two cell divisions) after addition of 10 or 1 mM of DFMO for 8 or 48 h, respectively; i.e., cell survival of heated control cells was about 10(-1), but decreased to 10(-4)-10(-5) in heated DFMO-treated cells by 100 h. During this same interval, delayed heat sensitization also was observed for loss of DNA polymerase beta activity (from 20% in cells heated without DFMO treatment to 7% in heated DFMO-treated cells), but none was observed for DNA polymerase alpha activity. Delayed heat sensitization disappeared at 120-130 h after DFMO addition, with survival of heated DFMO-treated cells returning to that for heated control cells. The onset of delayed heat sensitization occurred 30-40 h after intracellular levels of putrescine and spermidine were depleted by more than 95%; however, spermine levels were not lowered, and in some cases even increased. Levels of putrescine and spermidine increased 5-10 h before delayed heat sensitization disappeared. While putrescine reached 25% of control, spermidine exceeded control levels during this time. Furthermore, delayed heat sensitization could be reversed by adding 10(-3) M putrescine or 5 X 10(-5) M spermidine 85-95 h after DFMO addition; in both cases spermidine increased 5-10 h before the decrease in heat sensitization. Finally, neither delayed heat sensitization nor depletion of spermidine was observed in nondividing plateau-phase cells treated with DFMO, although putrescine was depleted. These results lead to the hypothesis that DFMO-induced heat sensitization which occurs after inhibition of the synthesis of putrescine is secondary to the depletion of spermidine in some critical compartment of the cell or to a biochemical alteration. This depletion or biochemical alteration apparently occurs as the cells divide about two times after the intracellular levels of soluble spermidine have been depleted.

Cell Division↗
PubMed1985

New DNA polymorphism: evidence for a low salt, left-handed form of poly(dG-m5dC).

Spectroscopic studies on solutions of poly(dG-m5dC) over a wide range of salt concentration are presented. Low salt solutions [( Na+]) less than 2 mM) of poly(dG-m5dC) produce circular dichroism (CD) spectra typical of the left-handed, Z form at high salt [( Na+] = 1.75 M). Solutions of poly(dG-m5dC) at intermediate salt concentrations, e.g., 142 mM, yield CD spectra characteristic of the right-handed, B conformation. 31p NMR spectra of the low salt form of poly(dG-m5dC) reveal two well separated peaks, split by 1.4 ppm, consistent with a dinucleotide repeat. Kinetic studies show that the transition from the low salt form to teh right-handed B form is slow, as expected for a major conformational change. These results suggest that the Z conformation in poly(dG-m5dC) can be stabilized at very low salt as well as at high salt.

Circular Dichroism↗
PubMed1985

Effects of dicyclohexylamine sulfate, a spermidine synthase inhibitor, in 9L rat brain tumor cells.

Growth characteristics, polyamine levels, and distribution of cells in the cell cycle were determined for 9L rat brain tumor cells treated for various periods with 1 mM dicyclohexylamine sulfate (DCHA). Continuous treatment of cells with DCHA caused growth inhibition at 2 days of treatment. After 2 days of treatment the growth rate of cells increased to approximately the same rate as control cells, even though treatment was continuous. Levels of spermidine were depleted to less than 10% of control levels, spermine levels were essentially unchanged, and putrescine levels were elevated to more than 350% of control levels after 9L cells were treated with DCHA for 2 days. In contrast to results found for the polyamine biosynthesis inhibitor alpha-difluoromethylornithine, treatment of 9L cells with DCHA did not potentiate the cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea. To mimic the effects on polyamine levels caused by treatment with DCHA, 9L cells were treated with 5 mM putrescine alone or with 5 mM putrescine and 1 mM DCHA after treatment with 1 mM alpha-difluoromethylornithine. Results of these experiments suggest that treatment with DCHA alone does not potentiate the cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea because elevated levels of putrescine caused by treatment counteract the effects of decreased spermidine levels.

Animals↗
PubMed1983

Differential potentiation of 1,3-bis(2-chloroethyl)-1-nitrosourea by alpha-difluoromethylornithine in chloroethylnitrosourea-sensitive and -resistant 9L rat brain tumor cells in vitro.

alpha-Difluoromethylornithine, an enzyme-activated, irreversible inhibitor of ornithine decarboxylase, inhibited the growth of both chloroethylnitrosourea-sensitive and -resistant 9L rat brain tumor cells in vitro. After 48 hr of treatment with 10 mM alpha-difluoromethylornithine, the putrescine and spermidine contents of both resistant and sensitive cells were less than 5% of control levels, but the spermine level was slightly elevated. The cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea, as measured by a colony-forming efficiency assay, was significantly increased in alpha-difluoromethylornithine-pretreated sensitive cells but not in resistant cells treated with this polyamine inhibitor. With the sister chromatid exchange assay, we found that alpha-difluoromethylornithine pretreatment increased 1,3-bis(2-chloroethyl)-1-nitrosourea-induced damage to chromosomes in sensitive but not in resistant cells.

Animals↗
PubMedDate not supplied

Effects of the polyamine analogs BE-3-7-3, 3-8-3, and BE-3-8-3 on human brain tumor cell growth and survival.

Based on computer modeling, physicochemical studies of spermine-DNA interactions, and cell culture experiments, we hypothesized that polyamine analogs with hydrocarbon chain lengths differing from natural polyamines and a stronger affinity for nucleic acids than spermine should have a cellular antiproliferative effect. We tested three spermine analogs with long hydrocarbon chains, 1,16-diamino-4,12-diazahexadecane (3-8-3), 1,16-bis(ethyl)amino-4,12-diazahexadecane (BE-3-8-3), and 1,15-bis(ethyl)amino-4,11-diazapentadecane (BE-3-7-3) in human brain tumor cell lines U-251 MG, SF-126, and SF-188. Analog concentrations < or = 5 microM inhibited growth and colony-forming efficiency in each cell line by treatment day 5, with significant decreases in putrescine and spermidine, but not spermine, levels. These findings suggest that potentially cytotoxic polyamine analogs can be specified on the basis of their hydrocarbon chain length and DNA affinity.

Brain Neoplasms↗
PubMedDate not supplied

The ability of polyamine analogues to induce Z-DNA structure in synthetic polynucleotides in vitro inversely correlates with their effects on cytotoxicity of cis-diaminedichloroplatinum (II) (CDDP) in human brain tumor cell lines.

We studied the effects of 72 h pretreatment with five polyamine analogues on the cytotoxicity of cis-diaminedichloroplatinum (II) (CDDP) in U-251 MG and SF-188 human brain tumor cells. A colony forming efficiency assay showed that the pretreatment with clinically important analogues 1,11-bis(ethylamino)-4, 8-diazaundecane (BE-3-3-3), 1,14-bis(ethylamino)-5,10-diazatetradecane (BE-4-4-4), and 1,l9-bis(ethylamino)-5,10,15-triazanonadecane (BE-4-4-4-4) increased the cytotoxicity of CDDP by 1.3 to 2.3-fold; 1,19-diamino-5,10, 15-triazanonadecane (4-4-4-4) did not affect CDDP cytotoxicity, and 1,11-diamino-4,8-diazaundecane (3-3-3) protected cells from the cytotoxic effects of CDDP. An alkaline elution assay detected a small increase in DNA interstrand crosslinks accompanying the enhancement of CDDP cytotoxicity only in cells pretreated with BE-3-3-3. This study is the first to show that the Z-DNA inducing abilities of the polyamine analogues in synthetic polynucleotides in vitro correlates inversely with their effects on CDDP cytotoxicity in human tumor cells in culture.

Antineoplastic Agents↗