Search PubMed⌕ Search

Biomedical subjects

V Favaudon

Publications and source records attributed to V Favaudon.

At least 37 records · Page 2Linked to original sources
PubMed1993

DNA repair and cell cycle interactions in radiation sensitization by the topoisomerase II poison etoposide.

The interactions between ionizing radiation and etoposide were probed using asynchronous growing V-79 fibroblasts. Synergistic cell kill was observed as gamma-rays were applied prior to or concomitantly with the drug. Three major determinants of enhanced cytotoxicity in combined treatment were identified. The kinetic analysis of radiation recovery bore evidence of two repair interaction mechanisms. First, rapidly repairable radiation-induced DNA damage was fixed into lethal lesions by etoposide, thus giving rise to marked supra-additive interaction under concomitant radiation-drug exposure. Second, cells arrested in G2 phase following radiation proved hypersensitive to the cytotoxic effect of etoposide. It is proposed that either topoisomerase II alpha is closely involved in some rapid DNA repair pathway operating during all phases of the cell cycle, and even further involved in DNA repair acting within the radiation-induced G2 block, or that the lesions induced by etoposide are able to impair these processes. The shoulder of the radiation survival curve was abolished as gamma-rays and drug were applied at 1-h intervals. This effect, corresponding to mode II additivity from isobologram determinations, appeared to be correlated with a differential sensitivity of the various phases of the cell cycle to drug and radiation.

Animals↗
PubMed1992

Three-dimensional solution structure of apo-neocarzinostatin from Streptomyces carzinostaticus determined by NMR spectroscopy.

The three-dimensional solution structure of apo-neocarzinostatin has been resolved from nuclear magnetic resonance spectroscopy data. Up to 1034 constraints were used to generate an initial set of 45 structures using a distance geometry algorithm (DSPACE). From this set, ten structures were subjected to refinement by restrained energy minimization and molecular dynamics. The average atomic root mean square deviations between the final ten structures and the mean structure obtained by averaging their coordinates run from 0.085 nm for the best defined beta-sheet regions of the protein to 0.227 nm for the side chains of the most flexible loops. The solution structure of apo-neocarzinostatin is closely similar to that of the related proteins, macromomycin and actinoxanthin. It contains a seven-stranded antiparallel beta-barrel which forms, together with two external loops, a deep cavity that is the chromophore binding site. It is noteworthy that aromatic side chains extend into the binding cleft. They may be responsible for the stabilization of the holo-protein complex and for the chromophore specificity within the antitumoral family.

Amino Acid Sequence↗
PubMed1991

Additive and supraadditive interaction between ionizing radiation and pazelliptine, a DNA topoisomerase inhibitor, in Chinese hamster V-79 fibroblasts.

The cytotoxic effect of the 9-azaellipticine derivative pazelliptine in combination with gamma-ray irradiation was investigated using Chinese hamster V-79 cells in culture. gamma-ray irradiation and drug treatment (1-h drug exposure) were applied at 1-h intervals for partial DNA damage recovery in growth medium. Isobologram analysis of the clonogenic potential gave evidence of supraadditive interaction in the radiation----drug sequence with 10% survival as an endpoint. No synergistic potentiation was observed at higher survival or as pazelliptine was applied first. Pazelliptine abolished the low-dose shoulder characteristic of asynchronous cell response to gamma-rays. Although rejoining of radiation-induced DNA strand breaks was completed at the time of drug exposure, pazelliptine brought about a larger amount of DNA strand breaks in preirradiated than in nonirradiated cells. The time and dose dependencies of DNA strand break formation and repair with radiation and/or pazelliptine were analyzed by neutral and alkaline filter elution. Pazelliptine in the micromolar range showed the same pattern of double-stranded cleavable complex formation as expected of a DNA topoisomerase II-targeting agent. At a low concentration of pazelliptine, however, protein-concealed breaks were mostly in the form of single-stranded adducts. Such single-stranded complexes have been reported to occur with some topoisomerase II-targeting drugs; their properties are also reminiscent of those induced by the topoisomerase I poison, camptothecin. It is proposed that topoisomerase poisoning interacts with the repair of radiation-induced lesions.

Animals↗
PubMed1990

CO2.- radical induced cleavage of disulfide bonds in proteins. A gamma-ray and pulse radiolysis mechanistic investigation.

Disulfide bond reduction by the CO2.- radical was investigated in aponeocarzinostatin, aporiboflavin-binding protein, and bovine immunoglobulin. Protein-bound cysteine free thiols were formed under gamma-ray irradiation in the course of a pH-dependent and protein concentration dependent chain reaction. The chain efficiency increased upon acidification of the medium, with an apparent pKa around 5, and decreased abruptly below pH 3.6. It decreased also at neutral pH as cysteine accumulated. From pulse radiolysis analysis, CO2.- proved able to induce rapid one-electron oxidation of thiols and of tyrosine phenolic groups in addition to one-electron donation to exposed disulfide bonds. The bulk rate constant of CO2.- uptake by the native proteins was 5- to 10-fold faster at pH 3 than at pH 8, and the protonated form of the disulfide radical anion, [symbol: see text], appeared to be the major protein radical species formed under acidic conditions. The main decay path of [symbol: see text] consisted of the rapid formation of a thiyl radical intermediate [symbol: see text] in equilibrium with the closed, cyclic form. The thiyl radical was subsequently reduced to the sulfhydryl level [symbol: see text] on reaction with formate, generating 1 mol of the CO2.- radical, thus propagating the chain reaction. The disulfide radical anion [symbol: see text] at pH 8 decayed through competing intramolecular and/or intermolecular routes including disproportionation, protein-protein cross-linking, electron transfer with tyrosine residues, and reaction with sulfhydryl groups in prereduced systems. Disproportionation and cross-linking were observed with the riboflavin-binding protein solely. Formation of the disulfide radical cation [symbol: see text], phenoxyl radical Tyr-O. disproportionation, and phenoxyl radical induced oxidation of preformed thiol groups should also be taken into consideration to explain the fate of the oxygen-centered phenoxyl radical.

Carbon Dioxide↗
PubMed1990

Proton NMR studies of apo-neocarzinostatin from Streptomyces carzinostaticus. Sequence-specific assignment and secondary structure.

The sequence-specific resonance assignment of apo-neocarzinostatin from Streptomyces carzinostaticus was carried out from two-dimensional proton-NMR spectra. The assignments were obtained for the backbone protons of 111 of the 113 residues of the protein, missing the two C alpha H of one glycine but including 3 of the 4 prolines. The majority of side chain protons were also assigned. The secondary structure derived from the analysis of sequential connections corresponds to ten beta-strands separated by clearly identified loops and turns. Inter-strand connectivities and slowly exchanging amide protons confirm the presence of the two disulfide bridges from Cys37 to Cys47 and from Cys88 to Cys93 and indicate a global folding similar to that of the similar proteins, actinoxanthin and macromomycin, for which crystallographic data are available.

Alanine↗
PubMed1989

Radiation-induced crosslinking between poly(deoxyadenylic-deoxythymidylic acid) and tripeptides containing aromatic residues.

OH.-induced covalent peptide-nucleotide adducts have been isolated by reverse-phase chromatography from the enzymic hydrolyzates of gamma-ray irradiated solutions containing double-stranded poly(deoxyadenylic-deoxythymidylic acid) and one of the tripeptides, lysyl-tryptophyl-lysine or lysyl-tyrosyl-lysine. Numerous compounds were formed, resulting presumably from different modes of radical addition. All isomers appeared to have the same general structure peptide-d(ApTpA), based mostly on double-labelling experiments of bases and phosphate groups in DNA. The major adduct fraction obtained from Lys-Trp-Lys and poly(dA-dT) was purified to homogeneity by sequential reverse-phase and ion-exchange chromatography, and characterized spectrally. The pattern of acid and alkaline hydrolysis suggests that thymine is the site of peptide-nucleotide binding in this particular adduct fraction.

Cobalt Radioisotopes↗
PubMed1987

Covalent and non-covalent interaction of chymotrypsin with alpha 2-macroglobulin.

The pattern of covalent crosslinking between human alpha 2-macroglobulin (alpha 2M) and chymotrypsin has been investigated by chromatography and polyacrylamide gel electrophoresis in denaturing medium. Reaction with a single mol of chymotrypsin per mol alpha 2M results in the formation of a 95% covalent 1:1 chymotrypsin-alpha 2M complex and in the proteolytic cleavage of both 180 kDa monomers in one alpha 2M subunit. Proteolytic cleavage in the other alpha 2M subunit requires the presence of a second mol of chymotrypsin; part (20%) of the protease in the 2:1 chymotrypsin-alpha 2M complex thus formed appears to be non-covalently bound to the alpha 2M chains. Covalent binding is abolished when the reaction of alpha 2M with the protease is carried out in the presence of hydroxylamine. A single mol of the protease is then able to cleave all four 180 kDa monomers in alpha 2M.

Binding Sites↗
PubMed1987

The reaction of human alpha 2-macroglobulin with alpha-chymotrypsin. A stopped-flow kinetic investigation.

The kinetics of the conformational changes of human alpha 2-macroglobulin (alpha 2M) induced by reaction with pure alpha-chymotrypsin, have been analyzed using three fluorescent probes, namely protein tryptophan groups and the dye 6-(4-toluidino)-2-naphthalenesulfonate, to monitor alterations of the alpha 2M structure, and a covalent conjugate of chymotrypsin and fluorescein isothiocyanate (Chy-FITC). The main reaction sequence exhibits a triphasic time course with any of the labels used. Each phase is first-order. The fixation of a single molecule of chymotrypsin to one protease-binding site of alpha 2M (site A) initiates the whole process and determines the access to the second site (site B). Of the three exponential phases of the reaction (20 degrees C), phase I (k1 approximately 19.6 min-1) and phase II (k2 approximately 5.3 min-1) belong to site A. Phase III is related to site B transformation. It contains two steps with different responses from tryptophan (k3 approximately 0.77 min-1) and Chy-FITC (k3 approximately 0.19 min-1) fluorescence measurements. The point to be stressed is that site A and site B, while presumably identical in the native form, are not equivalent with regard to their fluorescence and kinetic properties. However, the activation energy (E = 30.1 +/- 2.7 kJ mol-1) is the same for the three phases of the reaction. When present in sufficient excess, free chymotrypsin or native alpha 2M is able to form reversible complexes with the above-related chymotrypsin-alpha 2M adducts. Only the alpha 2M site A core seems to be involved in this parallel process. In addition the conformational state of the chymotrypsin-alpha 2M complexes is shown to depend on the pH, with a pKa of 6.4.

Chymotrypsin↗
PubMed1985

Poly(deoxyadenylic-deoxythymidylic acid) damage by radiolytically activated neocarzinostatin.

The anaerobic reaction of poly(deoxyadenylic-deoxythymidylic acid) with neocarzinostatin activated by the carboxyl radical CO2-, an electron donor generated from gamma-ray radiolysis of nitrous oxide saturated formate buffer, has been characterized. DNA damage includes base release and strand breaks. Few strand breaks are formed prior to alkaline treatment; they bear 3'-phosphoryl termini. In contrast, most (66%) of the base release occurs spontaneously. DNA damage is highly (95%) specific for thymidine sites. Neither DNA-drug covalent adduct nor nucleoside 5'-aldehyde, which are major products in the DNA-nicking reaction initiated by mercaptans and oxygen, is formed in this reaction. Data are presented to show that the CO2(-)-activated neocarzinostatin intermediate is a short-lived free radical able to abstract hydrogen atoms from the C-1' and C-5' positions of deoxyribose. Attack occurs mostly (68%) at the C-1' position, producing a lesion whose properties are consistent with those of (oxidized) apyrimidinic sites.

Antibiotics, Antineoplastic↗
PubMed1983

Study of the Hansenula anomala yeast flavocytochrome-b2--cytochrome-c complex 1. Characterization of fluorescent Zn(II)-substituted cytochrome c.

Substitution of Fe2+ for the Zn2+ ion in Hansenula anomala cytochrome c provides a luminescent derivative suitable as a probe for the determination of the interaction of cytochrome c with H. anomala flavocytochrome b2; its light absorption and fluorescence properties have been characterized. H. anomala Zn-cytochrome c appears to be in the form of a stable though non-covalent dimer from molecular weight determinations performed using gel filtration, polyacrylamide gel electrophoresis under denaturing conditions, and ultracentrifugation methods. By contrast, metal-free porphyrin-cytochrome c, the precursor of Zn-cytochrome c obtained upon removal of iron from cytochrome c in cold anhydrous fluorhydric acid, had the same partition coefficient as native cytochrome c through conventional gel filtration. Significant conformational perturbations of H. anomala cytochrome c should therefore follow from Zn2+ incorporation into the porphyrin c moiety. Titrations at low ionic strength with native, tetrameric H. anomala flavocytochrome b2 in the lactate-reduced state showed a simple binding equilibrium (Kd = 0.1 microM at I = 0.03 M, 10 degrees C) with a stoichiometry of one Zn-cytochrome c dimer per protomer of flavocytochrome b2. Quenching of the Zn-porphyrin c fluorescence within this complex was much larger (43%) than reported by other authors using cytochrome c and flavocytochrome b2 from different sources.

Ascomycota↗
PubMed1983

Study of the Hansenula anomala yeast flavocytochrome-b2-cytochrome-c complex 2. Localization of the main association area.

The reversible association of the Zn2+-substituted Hansenula anomala cytochrome c dimer (Thomas et al., preceding paper in this issue) to flavocytochrome b2 in oxidized or lactate-reduced state has been investigated by fluorimetry. The same method has been used for the determination of Zn-cytochrome c complexing to defined proteolytic fragments of flavocytochrome b2, either heme-b2-containing monomers or a flavin-linked tetramer. All these fragments but the isolated cytochrome b2 core showed binding stoichiometries, Kd values and ionic strength dependences quite similar to those found for native flavocytochrome b2. These data allowed localization of the single high-affinity binding site of cytochrome c on a particular globule in the dehydrogenase domain of the flavocytochrome b2 protomers. Quenching of the Zn-porphyrin c fluorescence in the various complexes occurred with only minor changes of the fluorescence lifetime and did not show any direct relationship to the presence or the redox state of the heme b2 group.

Ascomycota↗
PubMed1983

Localization of the proteinase-induced thiol groups in alpha 2-macroglobulin.

Free thiol groups released on proteolytic attack of alpha 2-macroglobulin by trypsin or chymotrypsin bind covalently to thiopropyl-Sepharose, indicating that they are located at the surface of the complexes. These cysteine sulfhydryl groups appear to be in contact with the alpha 2M-bound proteases from singlet-singlet energy transfer measurements between fluorescein isothiocyanate-labeled proteinases and N-(iodoacetylaminoethyl)-5-naphtylamine-1-sulfonic acid-labeled thiols in alpha 2-macroglobulin.

Binding Sites↗
PubMed1983

Likelihood of the new antitumoral drug 10-[gamma-diethylaminopropylamino]-6-methyl-5H-pyrido[3',4':4,5]pyrrolo [2,3-g]isoquinoline (BD-40), a pyridopyrroloisoquinoline derivative, to induce DNA strand breaks in vivo and its nonmutagenicity in yeast.

BD-40, a pyridopyrroloisoquinoline analogue of ellipticines, has dose-dependent cytostatic and cytotoxic effects on cultures of Saccharomyces cerevisiae. These inhibitory effects take place only in growing cells and are enhanced in the presence of oxygen. Among the different repair-deficient mutants examined, a mutant defective in DNA strand break repair (rad52-1) was found to be the most sensitive to such a toxic effect. A triple mutant blocked in the excision (rad2), the mutagenic (rad6), and the recombinogenic (rad52) repair pathways demonstrated the same sensitivity as the single rad52 mutant. Nuclear reversion and forward mutations as well as mitochondrial "petite" mutation were not induced by BD-40. These results indicate that: (a) the lesions induced in vivo by BD-40 are likely to be DNA strand breaks; (b) such damage is repairable in the wild type and is not of the mutagenic type; and (c) the excision pathway is not involved in such a repair of BD-40-induced lesions, and the mutagenic pathway plays a minor role. Since DNA strand breaks were not detected in vitro whether exposure of DNA to BD-40 was achieved in the presence or the absence of microsomal S-9 mix, it is suggested that an oxygen-dependent enzymatic processing, not linked to the microsomal monooxygenase complex, is required for the development of the cytotoxic activity of BD-40.

Aerobiosis↗
PubMed1982

On the mechanism of reductive activation in the mode of action of some anticancer drugs.

Bioactivation of a number of DNA-specific antitumor drugs depends on oxidoreduction. Bleomycin, neocarzinostatin and anthracycline glycosides are the best known among such drugs in terms of reductive activation processes. Their reduction results in short-lived radical or electrophilic intermediates attacking DNA stereospecifically. The physico-chemical properties of these drugs and the nature of DNA damage are reviewed. Models for DNA-intercalation, electron-donor systems involved in drug metabolisation, and the role of oxygen in radical reactions, are discussed in the light of recent reports.

Animals↗
PubMed1981

Localization of the two protease binding sites in human alpha 2-macroglobulin.

The distance between the two protease binding sites in human plasma alpha 2-macroglobulin has been estimated using singlet-singlet energy transfer experiments. alpha-Chymotrypsin was labeled covalently with donor (dansyl chloride) or acceptor (fluorescein isothiocyanate) groups, and the efficiency of transfer between these dyes was measured within the alpha 2-macroglobulin . (alpha-chymotrypsin)2 complex. The distance between the surface exterior of the protease molecules was calculated to be 4 to 11 A, depending on the assumption made about the equivalence of the binding sites. A catalytically active dimer of alpha-chymotrypsin was prepared using the heterobifunctional reagent N-succinimidyl-3-(2-pyridyldithio)propionate. In contrast with the alpha-chymotrypsin monomer, it binds to alpha 2-macroglobulin with a 1:1 stoichiometry. However, the 1:1 alpha 2-macroglobulin . dimeric alpha-chymotrypsin complex is still able to bind 1 mol of the alpha-chymotrypsin monomer. Energy transfer experiments performed with this ternary complex showed that the distance between the alpha 2-macroglobulin-bound alpha-chymotrypsin molecules is not higher than 4 A, i.e. the two protease binding sites in alpha 2-macroglobulin should be about 44 A apart (center to center) if the anhydrous radius of alpha-chymotrypsin is 20 A.

Animals↗
PubMed1981

The interaction of the membrane binding segment of cytochrome b5 with phospholipid vesicles. A pulse-radiolysis investigation.

The reactions of the radical anions Br2- and (SCN)2- produced by pulse-radiolysis have been used to study the interaction of dipalmitoyl phosphatidyl choline vesicles with the membrane binding segment (MBS) of cytochrome b5. Tryptophan oxidation by Br2- at neutral pH was characterized spectrophotometrically in detergent-solubilized solutions of MBS; the attack of tyrosine by (SCN)2- under alkaline conditions could also be observed directly. The incorporation of MBS into the lipid bilayer protected the tryptophan, tyrosine and methionine residues from oxidation by Br2- or (SCN)2-. Some structural implications of these results are discussed.

Cytochromes↗