Biomedical subjects

F Leteurtre

Publications and source records attributed to F Leteurtre.

23 records · Page 2Linked to original sources

PubMed1993

Specific interaction of camptothecin, a topoisomerase I inhibitor, with guanine residues of DNA detected by photoactivation at 365 nm.

Camptothecin-induced DNA photolesions were examined after UVA irradiation at 365 nm. DNA single-strand breaks were induced both in supercoiled and in relaxed SV40 DNA. In uniquely end-labeled human c-myc DNA, camptothecin-induced cleavage occurred exclusively at guanines and was markedly enhanced by hot piperidine treatment. Runs of polyguanines were the most cleaved, especially in their 5' flank. Primer extension experiments in the absence of piperidine treatment confirmed these results and did not show additional lesions. We found that synthetic single-stranded oligonucleotides were more reactive than duplex oligonucleotides. In addition, an excess of dideoxyguanosine triphosphates competed for camptothecin-induced DNA photolesions. Therefore, camptothecin stacking in DNA grooves is more likely than genuine drug intercalation. Groove shielding with sodium or magnesium reduced camptothecin-induced photodamage while minor groove occupancy with spermine extended damages. Photolesion mechanisms were investigated using scavengers. In aerobic conditions, the most effective scavengers were thiourea, sodium azide, and catalase. Protection by superoxide dismutase was weak, and mannitol was ineffective. In anaerobic conditions, lesions were more extensive. Taken together, these results show that photoactivated camptothecin interacts specifically and intimately with guanines. This finding is consistent with preferential stimulation of topoisomerase I cleavage at sites that bear a guanine at their 5'-DNA terminus [Jaxel, C., et al. (1991) J. Biol. Chem. 266, 1465-1469] and with the camptothecin stacking model at topoisomerase I DNA cleavage sites.

Animals↗

PubMed1993

Dual inhibition of topoisomerase II and tubulin polymerization by azatoxin, a novel cytotoxic agent.

Azatoxin (NSC 640737) is a synthetic molecule that was rationally designed as a topoisomerase II inhibitor (Leteurtre et al., Cancer Res 52: 4478-4483, 1992). The present study was undertaken in order to investigate the molecular pharmacology and the cytotoxic activity of azatoxin in human tumor cells. Alkaline elution experiments performed in HL-60 cells demonstrated that: (1) azatoxin induces DNA-protein cross-links and protein-linked DNA single- and double-strand breaks characteristics of topoisomerase II inhibition in HL-60 cells; and (2) the potency of azatoxin is comparable to that of etoposide (VP-16). Testing of azatoxin in 45 human cell lines in the National Cancer Institute (NCI) in vitro Drug Screening Program indicated that azatoxin was potent (mean IC50 = 0.13 microM), but that its cell line sensitivity profile was correlated with that of tubule inhibitors rather than that of topoisomerase II inhibitors. These data led us to investigate the anti-tubulin activity of azatoxin. We found that azatoxin inhibited tubulin polymerization in vitro and was a mitotic inhibitor at 1 microM and above in the human colon cancer cell line KM20L2. In these cells topoisomerase II inhibition, as detected by the induction of protein-linked DNA strand breaks, required azatoxin concentrations of at least 10 microM. In summary, azatoxin is a potent cytotoxic agent that inhibited both tubulin and topoisomerase II. At lower azatoxin concentrations the former activity prevailed whereas at higher concentrations topoisomerase II inhibition became prominent.

Cell Death↗

PubMed1993

Inhibitors of human immunodeficiency virus integrase.

In an effort to further extend the number of targets for development of antiretroviral agents, we have used an in vitro integrase assay to investigate a variety of chemicals, including topoisomerase inhibitors, antimalarial agents, DNA binders, naphthoquinones, the flavone quercetin, and caffeic acid phenethyl ester as potential human immunodeficiency virus type 1 integrase inhibitors. Our results show that although several topoisomerase inhibitors--including doxorubicin, mitoxantrone, ellipticines, and quercetin--are potent integrase inhibitors, other topoisomerase inhibitors--such as amsacrine, etoposide, teniposide, and camptothecin--are inactive. Other intercalators, such as chloroquine and the bifunctional intercalator ditercalinium, are also active. However, DNA binding does not correlate closely with integrase inhibition. The intercalator 9-aminoacridine and the polyamine DNA minor-groove binders spermine, spermidine, and distamycin have no effect, whereas the non-DNA binders primaquine, 5,8-dihydroxy-1,4-naphthoquinone, and caffeic acid phenethyl ester inhibit the integrase. Caffeic acid phenethyl ester was the only compound that inhibited the integration step to a substantially greater degree than the initial cleavage step of the enzyme. A model of 5,8-dihydroxy-1,4-naphthoquinone interaction with the zinc finger region of the retroviral integrase protein is proposed.

Antibiotics, Antineoplastic↗

PubMed1992

Rational design and molecular effects of a new topoisomerase II inhibitor, azatoxin.

Azatoxin [NSC 640737-M; 5.R,11aS-1H,6H,3-one-5,4,11,11a-tetrahydro-5-(3,5-dimethoxy-4-hydr oxyphenyl) oxazolo (3',4':1,6)pyrido-(3,4-b)indole] was rationally designed from a model for the pharmacophore of drugs with topoisomerase II inhibition activity. This pharmacophore has at least 2 domains: a quasiplanar polycyclic ring system proposed to bind between the DNA base pairs and a pendant substituent proposed to interact with the enzyme and/or to the DNA grooves. The present study shows that, in cell free systems, azatoxin induces a large number of double strand-breaks in linear Simian virus 40 and human c-myc DNA. These breaks yield cleavage patterns that are different from those of well established topoisomerase II inhibitors (epipodophyllotoxins, amsacrine, mitoxantrone). Azatoxin also inhibits the catalytic activity of purified topoisomerase II, and is a nonintercalator. The structure-activity relationship of 3 isomers and 6 derivatives of azatoxin shows a stringent stereochemical requirement for activity. The effects of azatoxin pendant ring substitution on topoisomerase II mediated DNA cleavage activity were similar to the relationship observed for etoposide.

DNA↗

PubMed1991

pH dependence of 5-fluorouracil uptake observed by in vivo 31P and 19F nuclear magnetic resonance spectroscopy.

Multinuclear nuclear magnetic resonance spectroscopy was used to follow the metabolism and kinetics of 5-fluorouracil (5FU) after i.v. administration at a dose of 100 mg/kg on Wistar rats. 31P spectra allow one to determine both the energetic status and the pH of the tissues under investigation, while serial 19F spectra reveal the drug clearance. Analyses of 5FU kinetics show that the half-life of 5FU elimination is about 35 min in tissue with a pH of 7.3. However, this half-life increases 2.5-fold when the local pH decreases below 6.9. Thus, acidification seems to induce a local retention of 5FU, which tends to prove the existence of active transport. This retention of the drug may have significant clinical implications for assessing and improving chemotherapy alone or in combination.

9,10-Dimethyl-1,2-benzanthracene↗