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Determinants of drug response in camptothecin-11-resistant glioma cell lines
Y Matsumoto1, T Fujiwara, S Nagao
1Department of Neurological Surgery, Kagawa Medical School, Japan.
Abstract:
Camptothecin-11 (CPT-11) is a new derivative of camptothecin, a plant alkaloid antitumor agent. Previous studies indicated that antitumor activity of CPT-11 was mediated through interaction of the drug with its target enzyme, DNA topoisomerase I (topo I). To elucidate the mechanisms of CPT-11 resistance, we have characterized glioma cell lines (T98G/CPT-11, C6/CPT-11) selected from the wild types (T98G. C6) for acquired resistance to CPT-11. T98G/CPT-11 and C6/CPT-11 cells demonstrated 5.4- and 7.3-fold increases, respectively, in resistance to CPT-11. Total glutathione S-transferase (GST) and GST-p activities were similar in CPT-11-sensitive and -resistant cells. No difference in intracellular accumulation of CPT-11 was observed between CPT-11-resistant and parental cells, indicating that an alteration in the uptake was not responsible for resistance. In addition, CPT-11-resistant cell lines showed no change in the total activity of Topo I, indicating an alteration in total Topo I was not responsible for resistance. In contrast, significantly increased intracellular glutathione (GSH) levels levels were found in T98G/CPT-11 and C6/CPT-11 cells (4.3- and 2.1-fold). Furthermore, Topo I samples from T98G/CPT-11 and C6/CPT-11 cells were at least 4- and 2-fold more resistant to the inhibitory effect of the CPT-11 on the relaxation activity of Topo I than were Topo I samples from their respective parent lines. The resistance of the enzyme itself to the effects of CPT-11 may be responsible for the resistance to CPT-11. Thus, at least two distinct mechanisms have been selected for the CPT-11-resistant cells.
Insights
This study investigated resistance to chemotherapy drug CPT-11 in glioma cells. Increased glutathione levels and a more resistant DNA topoisomerase I enzyme were identified as key mechanisms contributing to CPT-11 resistance.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- Camptothecin-11 (CPT-11) is a derivative of camptothecin, an alkaloid antitumor agent.
- CPT-11 exerts its antitumor activity by interacting with DNA topoisomerase I (topo I).
- Understanding CPT-11 resistance mechanisms is crucial for improving cancer therapy.
Purpose of the Study:
- To elucidate the mechanisms underlying acquired resistance to CPT-11 in glioma cell lines.
- To characterize the differences between CPT-11-sensitive and CPT-11-resistant glioma cells.
- To identify specific molecular alterations responsible for CPT-11 resistance.
Main Methods:
- Selected and characterized CPT-11-resistant glioma cell lines (T98G/CPT-11, C6/CPT-11) from wild-type parental lines (T98G, C6).
- Assessed intracellular accumulation of CPT-11, total glutathione S-transferase (GST) and GST-p activities.
- Measured intracellular glutathione (GSH) levels and topo I relaxation activity in response to CPT-11.
Main Results:
- Resistant cells showed 5.4- to 7.3-fold increased resistance to CPT-11.
- No significant differences in GST activity or CPT-11 intracellular accumulation were observed.
- Significantly elevated intracellular GSH levels (4.3- and 2.1-fold) were found in resistant cells.
- Topo I from resistant cells exhibited 4- and 2-fold greater resistance to CPT-11 inhibition.
Conclusions:
- Acquired CPT-11 resistance in glioma cells involves at least two distinct mechanisms.
- Increased intracellular glutathione (GSH) levels contribute to CPT-11 resistance.
- Alterations in DNA topoisomerase I (topo I) rendering it less sensitive to CPT-11 are a primary resistance mechanism.