Abstract
Merbarone (5-[N-phenyl carboxamido]-2-thiobarbituric acid) is an anticancer drug that inhibits the catalytic activity of DNA topoisomerase II (topo II) without damaging DNA or stabilizing DNA-topo II cleavable complexes. Although the cytotoxicity of the complex-stabilizing DNA-topo II inhibitors such as VP-16 (etoposide) has been partially elucidated, the cytotoxicity of merbarone is poorly understood. Here, we report that merbarone induces programmed cell death or apoptosis in human leukemic CEM cells, characterized by internucleosomal DNA cleavage and nuclear condensation. Treatment of CEM cells with apoptosis-inducing concentrations of merbarone caused activation of c-Jun NH2-terminal kinase/stress-activated protein kinase, c-jun gene induction, activation of caspase-3/CPP32-like protease but not caspase-1, and the proteolytic cleavage of poly(ADP-ribose) polymerase. Treatment of CEM cells with a potent inhibitor of caspases, Z-Asp-2.6-dichlorobenzoyloxymethyl-ketone, inhibited merbarone-induced caspase-3/CPP32-like activity and apoptosis in a dose-dependent manner. These results indicate that the catalytic inhibition of topo II by merbarone leads to apoptotic cell death through a caspase-3-like protease-dependent mechanism. These results further suggest that c-Jun and c-Jun NH2-terminal kinase/stress-activated protein kinase signaling may be involved in the cytotoxicity of merbarone.
Footnotes
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Send reprint requests to: Dr. William T. Beck, UIC Cancer Center (M/C 569), College of Medicine, University of Illinois at Chicago, 900 S. Ashland Ave., Chicago, IL. E-mail: wtbeck{at}uic.edu
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This work was supported in part by Research Grant CA-40570 from the National Cancer Institute (WTB), in part by the Cancer Center, University of Illinois at Chicago (WTB, TK), and in part by the Association pour la Recherche sur le Cancer, France (TK).
- Abbreviations:
- ICE
- interleukin 1β-converting enzyme
- CED-3
- Caenorhabditis elegans cell death protein
- PBS
- phosphate-buffered saline
- PARP
- poly(ADP-ribose) polymerase
- DAPI
- 4,6-diamino-2-phenylindole
- JNK/SAPK
- c-Jun NH2-terminal kinase/stress-activated protein kinase
- ERK
- extracellular signal-regulated kinase
- MAP
- mitogen-activated protein
- Ac-DEVD-MCA
- acetyl-Asp-Glu-Val-Asp-methylcoumaryl-7-amide
- Ac-YVAD-MCA
- acetyl-Tyr-Val-Ala-Asp-methylcoumaryl-7-amide
- Z-Asp
- Z-Asp-2,6-dichlorobenzoyloxymethyl-ketone
- topo II
- topoisomerase II
- Received June 25, 1998.
- Accepted December 14, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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