Self-assembly of an oligodeoxyribonucleotide harboring the estrogen response element in the presence of polyamines: ionic, structural, and DNA sequence specificity effects

Tamoxifen metabolite endoxifen interferes with the polyamine pathway in breast cancer

Tamoxifen is the most widely used drug to treat women with estrogen receptor α (ERα)-positive breast cancer. Endoxifen is recognized as the active metabolite of tamoxifen in humans. We studied endoxifen effects on ERα-positive MCF-7 breast cancer cells. Estradiol increased the proliferation of MCF-7 cells by two- to threefold and endoxifen suppressed its effects. Endoxifen suppressed c-myc, c-fos and Tff1 oncogene expression, as revealed by RT-PCR. Estradiol increased the activity of ornithine decarboxylase (ODC) and adenosyl methioninedecarboxylase (AdoMetDC), whereas endoxifen suppressed these enzyme activities. Endoxifen increased activities of spermine oxidase (SMO) and acetyl polyamine oxidase (APAO) significantly, and reduced the levels of putrescine and spermidine. These data suggest a possible mechanism for the antiestrogenic effects of tamoxifen/endoxifen, involving the stimulation of polyamine oxidase enzymes. Therefore, SMO and APAO stimulation might be useful biomarkers for the efficacy of endoxifen treatment of breast cancer.

Polyaminooligonucleotide: NMR structure of duplex DNA containing a nucleoside with spermine residue, N-[4,9,13-triazatridecan-1-yl]-2'-deoxycytidine

BACKGROUND

The nature of the polyamine-DNA interactions at a molecular level is not clearly understood.

METHODS

In order to shed light on the binding preferences of polyamine with nucleic acids, the NMR solution structure of the DNA duplex containing covalently bound spermine was determined.

RESULTS

The structure of 4-N-[4,9,13-triazatridecan-1-yl]-2'-deoxycytidine (dCSp) modified duplex was compared to the structure of the reference duplex. Both duplexes are regular right-handed helices with all attributes of the B-DNA form. The spermine chain which is located in a major groove and points toward the 3' end of the modified strand does not perturb the DNA structure.

CONCLUSION

In our study the charged polyamine alkyl chain was found to interact with the DNA surface. In the majority of converged structures we identified the presumed hydrogen bonding interactions between O6 and N7 atoms of G4 and the first internal -NH2(+)- amino group. Additional interaction was found between the second internal -NH2(+)- amino group and the oxygen atom of the phosphate of C3 residue.

GENERAL SIGNIFICANCE

The knowledge of the location and nature of a structure-specific binding site for spermine in DNA should be valuable in understanding gene expression and in the design of new therapeutic drugs.

Preparation of a DNA-bound [Ru(bpy)₂(mbpibH2)]²+ film and its two-mode luminescence tuning by copper(II) ions and EDTA

An imidazophenanthroline-containing ruthenium(II) complex [Ru(bpy)(2)(mbpibH2)](2+) (bpy=2,2'-bipyridine, mbpibH2=1,3-bis([1,10]phenanthroline[5,6-d]imidazol-2-yl)benzene) can bind DNA through groove-binding and/or non-classical intercalation modes, revealed by spectrophotometric methods, viscosity measurements and variable ionic strength experiments. On the basis of binding interactions between cationic [Ru(bpy)(2)(mbpibH2)](2+) and anionic DNA at a molar ratio of 1:1, a yellow transparent cast film has been assembled on an indium-tin oxide (ITO) surface using a solution-based self-standing method. The prepared DNA-[Ru(bpy)(2)(mbpibH2)](2+) film shows a bi-exponential luminescence decay with τ(1)=62.1 ns (8.0%) and τ(2)=594.5 ns (92.0%), whose lifetimes become much shorter than those of DNA-bound [Ru(bpy)(2)(mbpibH2)](2+) in buffer solutions. The Ru(II) complex with a free bi-dentate coordination site in the DNA cast film shows tunable luminescence, quenched dynamically by Cu(2+) and restored by using EDTA to eliminate two modes of Cu(2+)-binding. The results from this study provide a significant foundation for better understanding the fabrication and modulation of a DNA-based solid luminescence device using the Ru(II) complexes as DNA-concentrating and signal-sensing agents.

An investigation of the dynamics of spermine bound to duplex and quadruplex DNA by (13)C NMR spectroscopy

A detailed analysis of the (13)C relaxation of (13)C-labelled spermine bound to duplex and quadruplex DNA is presented. T(1), T(2) and heteronuclear NOE data were collected at four (13)C frequencies (75.4, 125.7, 150.9 and 201.2 MHz). The data were analyzed in terms of a frequency-dependent order parameter, S (2)(omega), to estimate the generalized order parameter and the contributions to the relaxation from different motional frequencies in the picosecond-nanosecond timescale and from any exchange processes that may be occurring on the microsecond-millisecond timescale. The relaxation data was surprisingly similar for spermine bound to two different duplexes and a linear parallel quadruplex. Analysis of the relaxation data from these complexes confirmed the conclusions of previous studies that the dominant motion of spermine is independent of the macroscopic tumbling of the DNA and has an effective correlation time of approximately 50 ps. In contrast, spermine bound to a folded antiparallel quadruplex had faster relaxation rates, especially R (2). As with the other complexes, a fast internal motion of the order of 50 ps makes a substantial contribution to the relaxation. The generalized order parameter for spermine bound to duplex DNA and the linear quadruplex is small but is larger for spermine bound to the folded quadruplex. In the latter case, there is evidence for exchange between at least two populations of spermine occurring on the microsecond-millisecond timescale.

Influence of Spermine on DNA Conformation in a Molecular Dynamics Trajectory of d(CGCGAATTCGCG)2: Major Groove Binding by One Spermine Molecule Delays the A→B Transition

The effect of spermine on the A-DNA to B-DNA transition in d(CGCGAATTCGCG)(2) has been investigated by five A-start molecular dynamics simulations, using the Cornell et al. potential. In the absence of spermine an A-->B transition is initiated immediately and the DNA becomes equidistant from the A- and B-forms at 200ps. In three DNA-spermine simulations, when a spermine is located across the major groove of A-DNA in one of three different initial locations, the time taken to reach equidistance from the A- and B-forms is delayed until 800, 950 or 1000ps. In each case the A-form appears to be temporarily stabilized by spermine's electrostatic interactions with phosphates on both sides of the major groove. The onset of the A-->B transition can be correlated with the spermine losing contact with phosphates on one side of the groove and with A-like --> B-like sugar pucker transitions in the vicinity of the spermine bridge. However in the fifth trajectory, in which the spermine initially threads from the major groove via the backbone into the minor groove, the B-->A transition occurs rapidly once again and the DNA is equidistant between the A- and B-forms within 300ps. This indicates that the mere presence of spermine is insufficient to delay the transition and that major groove binding stabilizes A-DNA.