Abstract
Expression of the transforming oncogene bcr-abl in chronic myelogenous leukemia (CML) cells is reported to confer resistance against apoptosis induced by many chemotherapeutic agents such as etoposide, ara-C, and staurosporine. In the present study some members of a series of novel pyrrolo-1,5-benzoxazepines potently induce apoptosis, as shown by cell shrinkage, chromatin condensation, DNA fragmentation, and poly(ADP-ribose) polymerase (PARP) cleavage, in three CML cell lines, K562, KYO.1, and LAMA 84. Induction of apoptosis by a representative member of this series, PBOX-6, was not accompanied by either the down-regulation of Bcr-Abl or by the attenuation of its protein tyrosine kinase activity up to 24 h after treatment, when approximately 50% of the cells had undergone apoptosis. These results suggest that down-regulation of Bcr-Abl is not part of the upstream apoptotic death program activated by PBOX-6. By characterizing the mechanism in which this novel agent executes apoptosis, this study has revealed that PBOX-6 caused activation of caspase 3-like proteases in only two of the three CML cell lines. In addition, inhibition of caspase 3-like protease activity using the inhibitor z-DEVD-fmk blocked caspase 3-like protease activity but did not prevent the induction of apoptosis, suggesting that caspase 3-like proteases are not essential in the mechanism by which PBOX-6 induces apoptosis in CML cells. In conclusion, this study demonstrates that PBOX-6 can bypass Bcr-Abl-mediated suppression of apoptosis, suggesting an important potential use of these compounds in the treatment of CML.
Footnotes
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Send reprint requests to: Margaret Mc Gee, Biochemistry of Department, Trinity College, Dublin 2, Ireland. E-mail: mmcgee{at}tcd.ie
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This study was supported by BioResearch Ireland, National Pharmaceutical Biotechnology Centre.
- Abbreviations:
- CML
- chronic myeloid leukemia
- abl, Abelson
- bcr, breakpoint cluster region
- PARP
- poly(ADP-ribose) polymerase
- PBOX
- pyrrolo-1,5-benzoxazepine
- NAC
- N-acetylcysteine
- AMC
- amino-4-methyl coumarin
- fmk
- fluoromethyl ketone
- ROI
- reactive oxygen intermediate
- PAGE
- polyacrylamide gel electrophoresis
- Received July 13, 2000.
- Accepted September 13, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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