Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.2 (topoisomerase)
 9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Topoisomerase was extracted from L-1210 nuclei by 0.35 M sodium chloride Extract fractionation by molecular weight revealed two activities. The activities were quantitatively determined using a technique based on the electrophoretic separation of 3H-labelled DNA product from substrate. This technique enables the determination of topoisomerase activity in extracts where nuclease activity is also present.
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PMID:Topoisomerase I activities in L-1210 cell nuclei. 631 33

The gammaH2AX focus assay, based on phosphorylation of the variant histone protein H2AX, was evaluated as a genotoxicity test in immortalised wild-type mouse embryonic fibroblasts (MEFs) treated for 4h with a panel of reference compounds routinely used in genotoxicity testing. The topoisomerase II poison etoposide (0.006-60 microg/ml), the alkylating agent methyl methanesulfonate (1.3-65 microg/ml) and the direct DNA-damaging agent bleomycin (0.1-10 microg/ml) all produced a positive concentration-response relationship. The non-genotoxic compounds ampicillin (0.035-3500 microg/ml) and sodium chloride (0.058-580 microg/ml) showed no such response with increased concentrations. The H2AX phosphorylation results were compared with the outcome of two standard in vitro genotoxicity tests, namely the micronucleus and comet assays. Compounds that produced measurable DNA damage in the focus assay generated micronuclei at comparable concentrations. In this study, the focus assay identified genotoxic agents with the same specificity as the comet assay. These results were substantiated when H2AX phosphorylation was analysed using flow cytometry in the murine cell line L5178Y, growing in suspension. The data were in concordance with the manual scoring focus assay. To further this investigation, the gammaH2AX flow cytometry was compared to the in vitro micronucleus flow cytometry and mouse lymphoma assay using the same cell population after MMS treatment. The median gammaH2AX value increased significantly above the control at all four MMS concentrations tested. The percentage of micronucleus events in the in vitro micronucleus flow test and the mutation frequency in the mouse lymphoma assay were also significantly increased at each MMS concentration. The current data indicate that H2AX phosphorylation could be used as a biomarker of genotoxicity, which could predict the outcome of in vitro mammalian cell genotoxicity assays.
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PMID:H2AX phosphorylation as a genotoxicity endpoint. 1962 53

Irinotecan is an anticancer agent that stabilizes topoisomerase I/DNA complexes. So far, no test system has been reported for directly determining irinotecan-induced stabilization of topoisomerase I/DNA complexes in organs in vivo. We adapted an 'in vivo complexes of enzyme to DNA' (ICE) bioassay to assess irinotecan activity in the stomach, duodenum, colon and liver of male Wistar rats after a single treatment with irinotecan (100 mg/kg body weight, intraperitoneally). This was compared to the control group receiving 0.9% sodium chloride intraperitoneally. In addition, the DNA strand breaking properties of irinotecan were measured in mucosal cells from the distal colon by single-cell gel electrophoresis (comet assay) to investigate the association of topoisomerase poisoning and DNA damage in vivo. A single dose of irinotecan significantly increased amounts of topoisomerase I covalently bound to DNA in stomach, duodenum, colon and liver. Concomitantly, the irinotecan-treated group showed significantly higher amounts of DNA strand breaks in colon mucosa cells compared to the control group. The ICE bioassay and the comet assay represent two test systems for investigating the impact of topoisomerase I poisons on DNA integrity in colon tissues of Wistar rats.
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PMID:In vivo bioassay to detect irinotecan-stabilized DNA/topoisomerase I complexes in rats. 2021 47