Type IA topoisomerase activities are essential for resolving DNA topological barriers via an enzyme-mediated transient single strand DNA break. Accumulation of topoisomerase DNA cleavage product can lead to cell death or genomic rearrangement. Many antibacterial and anticancer drugs act as topoisomerase poison inhibitors that form stabilized ternary complexes with the topoisomerase covalent int...

Observations of cells in culture have demonstrated that, for many antitumor agents, topoisomerase II-mediated DNA damage relates to cytotoxicity. However, there is no evidence in tumor-bearing animals to suggest that such agents induce topoisomerase II-mediated damage of DNA in solid tumors or that such damage reflects inhibition of tumor growth. To address this question, a mouse fibroblast cel...

We have isolated two etoposide (VP16)-resistant cell lines, KB/VP-1 and KB/VP-2, from human cancer KB cells after stepwise exposure to increasing doses of VP16. KB/VP-1 and KB/VP-2 showed 30and 50fold higher resistance to VP16 and also 20and 30-fold higher resistance to teniposide than the parent cell line. Furthermore, both resistant cell lines showed more than 2-fold cross-resistance to Adria...

We have isolated two etoposide (VP16)-resistant cell lines, KB/VP-1 and KB/VP-2, from human cancer KB cells after stepwise exposure to increasing doses of VP16. KB/VP-1 and KB/VP-2 showed 30and 50fold higher resistance to VP16 and also 20and 30-fold higher resistance to teniposide than the parent cell line. Furthermore, both resistant cell lines showed more than 2-fold cross-resistance to Adria...

Increasing the cellular concentration of DNA topoisomerase II in yeast by expressing constitutively a plasmid-borne TOP2 gene encoding the enzyme greatly increases the sensitivity of the cells to amsacrine and etoposide (VP-16). This increased drug sensitivity at a higher intracellular DNA topoisomerase II level is observed in both RAD52+ repair-proficient strains and rad52 mutants that are def...

A complementary DNA fragment of the human DNA topoisomerase II gene was cloned into a T7 expression vector and overproduced in Escherichia coli. Rabbit polyclonal antibodies were raised against the recombinant topoisomerase II polypeptide which corresponds to the C-terminal one-third of human topoisomerase II polypeptide. Using the antiserum, DNA topoisomerase II levels were measured by immunob...

The nuclear distribution of Drosophila DNA topoisomerase II was determined by immunoblot analysis after nuclease digestion and cell fractionation. About 60% of DNA topoisomerase II could be removed from nuclei by RNase A, about 70% by DNase I, and about 90% by incubation with both enzymes together or with micrococcal nuclease. Nuclease treatment of nuclei did not affect the distribution of lami...

Human leukemic HL60 cells were selected for resistance to alkylating agents by stepwise exposure to increasing concentrations of L-phenylalanine mustard (melphalan). The resulting resistant cell line (R-HL60) was 4-fold resistant (melphalan IC50 value, 27.84 +/- 4.2 microM) to melphalan compared with parental HL60 cells (melphalan IC50 value, 6.9 +/- 1.78 microM). Nuclear extracts from R-HL60 c...

BACKGROUND DNA topoisomerase II inhibitors and poisons are among the most efficacious drugs for the treatment of cancer. Sensitivity of cancer cells to the cytotoxic effects of topoisomerase II targeting agents is thought to depend on the expression of the topoisomerase IIalpha isoform, and drug resistance is often associated with loss or mutation of topoisomerase IIalpha. Histone deacetylase i...

Bisdioxopiperazines such as ICRF-159 and ICRF-193 have been shown to inhibit DNA topoisomerase II. To determine the molecular target of these compounds in vivo, we utilized a yeast genetic system in which the topoisomerase II activity can be modulated. To reduce topoisomerase II activity, we used top2-1 mutant yeast cells that have normal DNA topoisomerase II activity at 25 degrees C but greatl...