The Screening Of DNA Topoismerase Inhibitor And Inhibiting DNA Topoismerase Mechanisms And Antineoplasmic Activity Of Two Chemical Compounds

Firstly in vitro screening model of DNA topoismerase inhibitors was set up and 34 chemical compounds from different resources were screened by means of DNA topoisomerase model. Vanadium compounds (2#,7#,15#,22#), camptothecin derivants cpt,cpt-0, marine natural product SAD inhibit DNA topoisomerseⅠ(Topo-Ⅰ) notablely. how vanadium compounds 2#(LMC) and 7# inhibit Topo-Ⅰwas further investigated.The IC50 (50%inhibiting concentration) of LMC and 7# is 16.5μM and 8.6μM respectively, lower than that of hydroxycamptothecin (OPT). In comet assay and Measurement of Drug-DNA-Topo-Ⅰcleavable complexes experiment, neither LMC nor 7# was able to generate cleavable complexes, thereby indicating that the inhibition of LMC and 7# occurs upstream of the endonuclease activity of Topo-Ⅰ.The electrophoretic mobility shift assay (EMSA) between supercoiled pBR322 DNA and Topo-Ⅰwere performed. OPT was used as a control, which inhibits the ligase activity without interfering with the binding of the enzyme to DNA. Results clearly indicated that both two compounds hampered the binding of the enzyme to DNA, whereas, as anticipated, this did not occur with OPT. Displacement of ethidium bromide from DNA with concomitant reduction in ethidium fluorescence was used to examine whether LMC and 7# binds to DNA. It appears that LMC and 7# intercalate into DNA, but they don't inhibit DNAaseⅠ, which cuts DNA and generate oligonucleotide with 3'hydroxide radical and 5'...