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Topoisomerase II-mediated alterations of K562 drug resistant sublines
1Department of Oncology-Pathology at Radiumhemmet , Uppsala University Hospital, Sweden. Rong.Zhou@cck.ki.se
Abstract:
In order to further elucidate the roles of DNA topoisomerase II (topo II) subtypes, alpha and beta, as drug targets in chemotherapy, we have determined the enzyme levels in K562 cells selected for resistance to mitoxantrone (K562/Mxn), daunorubicin (K562/Dnr) and idarubicin (K562/Ida 20 and K562/Ida 60), as well as topo II-DNA complex formation, DNA damage and cytotoxicity, induced by topo II interactive agents, for example etoposide, teniposide, mitoxantrone and amsacrine. As compared to the parental cells, topo IIalpha/beta protein levels in K562/Mxn, K562/Dnr, K562/Ida 20 and 60 lines, measured with Western blot, were 17/67%, 85/88, 24/31% and 10/7% respectively. DNA damage, determined by DNA unwinding technique, induced by teniposide and amsacrine correlated with both topo IIalpha/beta protein levels (r2 = 0.8/0.9, P = 0.03/0.01 and r2 = 0.8/0.9, P = 0.04/0.01, respectively). Topo II-DNA complex formation induced by all studied drugs correlated with topo IIbeta protein levels (r2-range 0.8-0.9, P-range 0.01-0.04), while the correlation with topo IIalpha was weaker. Topo IIalpha/beta protein levels tended to show an inverse correlation with the cytotoxicity of etoposide (r2 = -0.9/-0.7, P = 0.01/0.06). The overall topo II-DNA complex formation correlated with drug-induced DNA damage (r2 = 0.9, P = 0.0001), whilst not with the cytotoxicity. Our findings indicate that both topo II isozymes are the targets of the antitumor agents studied, and of potential clinical relevance for prediction of treatment efficacy. They could play a role in tailored chemotherapy.
Insights
This study investigated DNA topoisomerase II (topo II) subtypes alpha and beta in chemotherapy drug resistance. Findings show both topo II isozymes are targets for antitumor agents, potentially aiding tailored chemotherapy and predicting treatment efficacy.
Area of Science:
- Biochemistry
- Molecular Biology
- Pharmacology
Background:
- DNA topoisomerase II (topo II) is crucial for DNA replication and transcription.
- Understanding the roles of topo II subtypes alpha and beta is vital for chemotherapy drug development.
- Drug resistance mechanisms involving topo II subtypes are not fully elucidated.
Purpose of the Study:
- To investigate the roles of DNA topoisomerase II (topo II) subtypes, alpha and beta, as drug targets in chemotherapy.
- To determine enzyme levels, topo II-DNA complex formation, DNA damage, and cytotoxicity in drug-resistant K562 cells.
- To analyze correlations between topo II levels, DNA damage, complex formation, and cytotoxicity induced by anticancer agents.
Main Methods:
- Western blot analysis to quantify topo IIalpha and beta protein levels in parental and drug-resistant K562 cell lines.
- DNA unwinding technique to assess drug-induced DNA damage.
- Measurement of topo II-DNA complex formation.
- Cytotoxicity assays for various topo II-interactive agents (etoposide, teniposide, mitoxantrone, amsacrine).
Main Results:
- Topo IIalpha/beta protein levels varied significantly in drug-resistant cell lines compared to parental cells.
- Drug-induced DNA damage by teniposide and amsacrine correlated strongly with both topo IIalpha and beta levels.
- Topo II-DNA complex formation correlated more strongly with topo IIbeta levels than topo IIalpha.
- Topo IIalpha/beta levels showed an inverse correlation with etoposide-induced cytotoxicity.
- Overall topo II-DNA complex formation correlated with DNA damage but not cytotoxicity.
Conclusions:
- Both DNA topoisomerase II alpha and beta are targets of the studied antitumor agents.
- Topo II isozyme levels and complex formation are relevant for predicting chemotherapy treatment efficacy.
- Findings suggest a role for topo II subtypes in the development of tailored chemotherapy strategies.