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A two-drug model for etoposide action against human topoisomerase IIalpha
Kenneth D Bromberg1, Alex B Burgin, Neil Osheroff
1Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, USA.
Abstract:
The widely used anticancer drug etoposide kills cells by increasing levels of topoisomerase II-mediated DNA breaks. While it is known that the drug acts by inhibiting the ability of topoisomerase II to ligate cleaved DNA molecules, the precise mechanism by which it accomplishes this action is not well understood. Because there are two scissile bonds per enzyme-mediated double-stranded DNA break, it has been assumed that there are two sites for etoposide in every cleavage complex. However, it is not known whether the action of etoposide at only one scissile bond is sufficient to stabilize a double-stranded DNA break or whether both drug sites need to be occupied. An oligonucleotide system was utilized to address this important issue. Results of DNA cleavage and ligation assays support a two-drug model for the action of etoposide against human topoisomerase IIalpha. This model postulates that drug interactions at both scissile bonds are required in order to increase enzyme-mediated double-stranded DNA breaks. Etoposide actions at either of the two scissile bonds appear to be independent of one another, with each individual drug molecule stabilizing a strand-specific nick rather than a double-stranded DNA break. This finding suggests (at least in the presence of drug) that there is little or no communication between the two promoter active sites of topoisomerase II. The two-drug model has implications for cancer chemotherapy, the cellular processing of etoposide-stabilized enzyme-DNA cleavage complexes, and the catalytic mechanism of eukaryotic topoisomerase II.
Insights
Etoposide, a cancer drug, requires two molecules to stabilize DNA breaks by inhibiting topoisomerase II. This two-drug model clarifies etoposide
Area of Science:
- Biochemistry
- Molecular Biology
- Cancer Research
Background:
- Etoposide is a widely used anticancer drug that induces cell death by increasing DNA breaks.
- The drug inhibits topoisomerase II (an enzyme crucial for DNA replication and repair) by preventing the ligation of cleaved DNA molecules.
- The precise mechanism of etoposide's action and the role of its binding sites on DNA are not fully understood.
Purpose of the Study:
- To investigate the mechanism by which etoposide stabilizes DNA breaks mediated by human topoisomerase IIalpha.
- To determine if one or two etoposide molecules are required to stabilize a double-stranded DNA break.
Main Methods:
- Utilized an oligonucleotide system to create a defined substrate for DNA cleavage and ligation assays.
- Performed DNA cleavage and ligation assays to analyze the effect of etoposide on topoisomerase II activity.
Main Results:
- Results support a two-drug model for etoposide's action on human topoisomerase IIalpha.
- Drug interactions at both scissile bonds are necessary to increase enzyme-mediated double-stranded DNA breaks.
- Etoposide binding at each site appears independent, stabilizing strand-specific nicks rather than double-stranded breaks.
Conclusions:
- The findings suggest a two-drug model where both drug molecules are required for etoposide to effectively stabilize DNA breaks.
- This implies limited communication between the active sites of topoisomerase II when bound by etoposide.
- The two-drug model has significant implications for cancer chemotherapy and understanding topoisomerase II function.