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M Delepierre

Publications and source records attributed to M Delepierre.

83 records · Page 5Linked to original sources
PubMed1987

DNA bis-intercalators as new anti-tumour agents: modulation of the anti-tumour activity by the linking chain rigidity in the ditercalinium series.

Ditercalinium (2,2'-([4,4'-bipiperidine-1,1'-diyl] di-2,1-ethane diyl) bis (10-methoxy-7H-pyrido[4,3c] carbazolium) tetra(methyl sulphonate--NSC 366241), a DNA bis-intercalating compound presently under clinical trial, elicits an original mechanism of action and thus appears as the first of a new class of anti-tumour drugs. Previous studies have shown that a reduced flexibility of the linking chain of these dimers is essential for their biological activity. In order to analyze their mechanism of action at the molecular level and to obtain structure-activity relationships in this series, new derivatives with additional methylene groups between the two piperidine rings have been synthesized. Whereas the addition of a single methylene group in the chain preserves the anti-tumour activity of the dimers, the addition of a second methylene diminishes it; the addition of three methylenes completely abolishes it. Lengthening of sonicated DNA and unwinding of supercoiled DNA support a bis-intercalation mechanism for these drugs. In addition, analyses of poly d(A-T) melting curves in the presence of the drugs, and competition experiments with ethidium dimer, show that these compounds bind to DNA with high affinity (10(7)-10(8) M-1). N.m.r. studies of the dimers in aqueous medium show that the introduction of a single methylene group in the linker leads to compounds with a conformationally-induced decrease of intermolecular stacking interactions, which might be related to the DNA affinity enhancement observed for these dimers. Different hypotheses concerning structure-activity relationships in the different series are discussed.

Animals↗
PubMed1987

Rational design of bis-intercalating drugs as antitumour agents: importance of rigidity in the linking chain.

Ditercalinium (NSC 366241), a dimer of 10-methoxy-7H-pyrido[4,3-c]carbazole quaternarized on the pyridine nitrogen by a rigid bis(1,1'-ethyl)-4,4'-bipiperidine linking chain, is endowed with antitumour properties and bis-intercalates with high affinity into DNA. New dimers have been designed in the same series to evaluate the importance of the rigidity of the linking chain for pharmacological activity. The dimers, characterized by one and two additional methylene groups between the two piperidine rings of the linking chain, remain as active as ditercalinium. However, a third additional CH2 group between the two piperidine rings leads to an inactive dimer. Relationships between the different pharmacological activities of the drugs and their intercalation complexes with DNA were investigated using viscosimetry, absorption spectroscopy and NMR analyses.

Animals↗
PubMed1986

Conformational studies of d(m5CpGpm5CpG) and d(CpGpCpG) by 1H and 31P NMR.

Exhaustive conformational studies of d(CpG)2 and d(m5CpG)2, two convenient targets for DNA bisintercalating drugs, have been carried out by 1H and 31P NMR in low salt concentration and in the presence of 30% ethanol. Unambiguous 31P assignments of the B for are obtained with low-power heteronuclear decoupling experiments, while 31P assignments in the Z form are obtained by two-dimensional homonuclear chemical exchange experiments. The 31P chemical shifts and 3JH3'P coupling constants studied at various temperatures in methylated and non-methylated tetranucleotides, are interpreted as resulting from conformational differences between the compounds. These features are corroborated by homonuclear proton nuclear Overhauser effect experiments showing the steric role of the 5-methylcytosine in the induction of an alternating B form in d(m5CpG)2.

Magnetic Resonance Spectroscopy↗
PubMed1985

1H- and 13C-n.m.r. assignments and conformational analysis of some monosaccharide and oligosaccharide substrate-analogues of lysozyme.

The 1H- and 13C-n.m.r. spectra of solutions of GlcNAc, beta-GlcNAc-(1----4)-GlcNAc, and beta-GlcNAc-(1----4)-beta-GlcNAc-(1----4)-GlcNAc in D2O at 50 degrees are interpreted in terms of the conformations, using a combination of 1D- and 2D-n.m.r. spectroscopy and spectra simulation techniques. Two preferred orientations of the hydroxymethyl group were found for each of these saccharides. The conformations have been compared with those found from X-ray crystallographic data and conformational energy calculations.

Animals↗
PubMed1984

Identification using 1H NMR spectroscopy of slowly exchanging amide hydrogens of hen lysozyme in solution.

Resonances of over 20 of the most slowly exchanging amide hydrogens have been identified and assigned in the 1H NMR spectrum of hen lysozyme. This was achieved by combining information about spin-spin coupling patterns with nuclear Overhauser enhancement measurements. A computer-based search program was used to permit the assumptions and constraints in this procedure to be closely defined and to reveal possible ambiguities. In addition, experimental values of coupling constants were compared with values calculated on the basis of the torsion angles found in the crystal structure. The close correlation between these gave further confidence in the assignment procedures and provided information concerning the nature of fluctuations about the average solution structure. The very slowly exchanging amide hydrogens are largely buried in alpha-helical and beta-sheet regions of the protein structure.

Amides↗
PubMed1983

Exchange of individual hydrogens for a protein in a crystal and in solution.

A preliminary comparison of the solvent exchange of individual hydrogens of a protein in solution and in a crystal has been possible by using data for lysozyme from 1H nuclear magnetic resonance and neutron diffraction studies. It is suggested that this approach enables a direct comparison of local dynamical behaviour in the two states. The results indicate markedly similar behaviour for many residues, but significant differences are indicated in several regions of the protein.

Animals↗
PubMed1983

Correlation of hydrogen exchange behaviour and thermal stability of lysozyme.

The solvent exchange rates of individual indole NH hydrogens of tryptophan residues of lysozyme have been measured, by using 1H nuclear magnetic resonance spectroscopy, as a function of temperature in the presence of urea and following chemical modification. The results have been interpreted in terms of a low activation energy process which is not dependent on the thermal stability of the protein, and a higher activation energy process that is directly correlated with the thermal stability. The significance of these observations for an understanding of the dynamics of the protein is discussed.

Hydrogen↗
PubMed1982

Studies of beta-sheet structure in lysozyme by proton nuclear magnetic resonance. Assignments and analysis of spin-spin coupling constants.

Resonances of H alpha, H beta, and HN (amide) protons have been assigned in the NMR spectrum for ten residues in a region of beta-sheet structure of lysozyme. The assignments were achieved primarily by interpretation of nuclear Overhauser effects in conjunction with spin decoupling. The HN hydrogens involved in main-chain hydrogen bonding were found to exchange slowly with D2O solvent, although one of the most slowly exchanging HN hydrogens is not classified as being involved in a hydrogen bond in the crystal structure. Spin-spin coupling constants between H alpha protons and HN and H beta protons correlated well with values predicted from the crystal structure by means of the Karplus relationship. For no residues are the coupling constant discrepancies greater than 2.5 HZ. This indicates that for the residues studied here the torsion angles phi and chi 1 defined in the crystal structure describe accurately, generally well within 20 degrees, those for the average solution state.

Animals↗
PubMed1982

Mechanisms of hydrogen exchange in proteins from nuclear magnetic resonance studies of individual tryptophan indole NH hydrogens in lysozyme.

The individual rates of solvent exchange of the six tryptophan indole NH hydrogens of lysozyme in 2H2O have been measured over a wide range of temperatures by using 1H NMR. Two distinct mechanisms for exchange have been identified, one characterized by a high activation energy and the other by a much lower activation energy. The high-energy process has been shown to be associated directly with the cooperative thermal unfolding of the protein and is the dominant mechanism for exchange of the most slowly exchanging hydrogen even 15 degrees C below the denaturation temperature. Rate constants and activation for the folding and unfolding reactions were obtained from the experimental exchange rates. At low temperatures, a lower activation energy mechanism is dominant for all hydrogens, and this can be associated with local fluctuations in the protein structure which allows access of solvent. The relative exchange rates and activation energies can only qualitatively be related to the different environments of the residues in the crystal structure. There is provisional evidence that a mechanism intermediate between these two extremes may be significant for some hydrogens under restricted conditions.

Hydrogen↗
PubMedDate not supplied

1H NMR study of the structure of a pyridocarbazole dimer-d[CpGpCpG] complex.

The structure of the complexes formed between a 7H-pyridocarbazole dimer (ditercalinium) or the corresponding monomer and d[CpGpCpG] is analyzed in aqueous solution by 270 MHz 1H NMR. In both cases the strong upfield shifts observed on most aromatic resonances are assigned to the formation of intercalated complexes. Bisintercalation of the dimer in the tetranucleotide minihelix is then observed at pH 5.5. The observation of intermolecular negative NOEs induced to some drug resonances by irradiation of sugar protons confirms these conclusions. The orientation of the ligand in the intercalation site is discussed.

Carbazoles↗