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ICRF-193 modifies etoposide-induced apoptosis in thymocytes
C Tanimoto1, S Hirakawa, H Kawasaki
1Third Department of Internal Medicine, Okayama University Medical School, Japan.
Abstract:
Etoposide (VP-16), one of the topoisomerase II (TopoII) inhibitors, interferes with TopoII by inducing the formation of and stabilizing a cleavable enzyme-DNA complex. VP-16 has been demonstrated to induce apoptosis in murine thymocytes. To clarify the mechanism of action of VP-16, we examined the in vitro effect of a non-cleavable-complex-forming type TopoII inhibitor, ICRF-193 which inhibits the DNA strand breakage induced by VP-16, on murine thymocytes in which apoptosis had been induced with VP-16. DNA fragmentation is characteristic of apoptosis. In the early stages, ICRF-193 decreased DNA fragmentation induced by VP-16, although this inhibitory effect decreased in the later. These data suggest that TopoII inhibitors induce apoptosis in murine thymocytes in two ways: with DNA-strand breaks in the early stage or without them. ICRF-193 itself induced apoptosis in murine thymocytes. The time course of DNA fragmentation caused by ICRF-193 was different from that of VP-16.
Insights
Etoposide (VP-16), a topoisomerase II inhibitor, induces apoptosis in mouse thymocytes. Another inhibitor, ICRF-193, partially blocked VP-16
Area of Science:
- Molecular Biology
- Cell Biology
- Pharmacology
Background:
- Etoposide (VP-16) is a topoisomerase II (TopoII) inhibitor that induces apoptosis.
- VP-16 stabilizes a cleavable enzyme-DNA complex, leading to DNA damage.
- The precise mechanism of VP-16-induced apoptosis requires further elucidation.
Purpose of the Study:
- To investigate the role of DNA-strand breaks in VP-16-induced apoptosis.
- To clarify the mechanism of action of VP-16 using a non-cleavable complex-forming TopoII inhibitor, ICRF-193.
- To compare the apoptotic effects of VP-16 and ICRF-193 in murine thymocytes.
Main Methods:
- In vitro treatment of murine thymocytes with VP-16 and/or ICRF-193.
- Assessment of DNA fragmentation as a marker of apoptosis.
- Analysis of the time course of DNA fragmentation induced by each inhibitor.
Main Results:
- ICRF-193 partially inhibited VP-16-induced DNA fragmentation in early stages.
- The inhibitory effect of ICRF-193 diminished over time.
- ICRF-193 alone induced apoptosis in murine thymocytes, with a distinct time course compared to VP-16.
Conclusions:
- TopoII inhibitors can induce apoptosis through pathways involving DNA-strand breaks (early stage) and potentially independent of them.
- VP-16 and ICRF-193 exhibit distinct mechanisms and kinetics in inducing thymocyte apoptosis.
- These findings provide insights into the complex mechanisms of TopoII inhibitor-mediated cell death.