Abstract
Some, but not all, of a series of novel pyrrolo-1,5-benzoxazepines (PBOXs) induce apoptosis as shown by cell shrinkage, chromatin condensation, and DNA fragmentation in three human cell lines, HL-60 promyelocytic, Jurkat T lymphoma, and Hut-78 s.c. lymphoma cells. This chemical selectivity, together with the lack of apoptotic activity against rat Leydig cells, argues against a general cell poisoning effect. PBOX-6, a potent member of the series, caused activation of a member of the caspase-3 family of proteases. In addition, the caspase-3-like inhibitor z-DEVD-fmk, but not the caspase-1-like inhibitor z-YVAD-fmk prevented PBOX-6-induced apoptosis, suggesting that caspase 3-like proteases are involved in the mechanism by which PBOX compounds induce apoptosis. The release of cytochromec into the cytosol in HL-60 cells in response to PBOX-6 suggests that this cellular response may be important in the mechanism by which PBOX-6 induces apoptosis. However, reactive oxygen intermediates do not play a key role in PBOX-6-induced apoptosis because neither the free radical scavenger TEMPO nor the antioxidantN-acetylcysteine had any effect on PBOX-6-induced apoptosis. The apoptotic induction seems independent of the mitochondrial peripheral-type benzodiazepine receptor (PBR) that binds these pyrrolobenzoxazepines with high affinity, due to the lack of correlation between their affinities for the receptor and their apoptotic potencies, their high apoptotic activity in PBR-deficient cells such as Jurkats, and their lack of apoptotic induction in PBR-rich rat Leydig cells. These PBOXs also can overcome nuclear factor-κB-mediated resistance to apoptosis. This suggests an important potential use of these compounds in drug-resistant cancers.
Footnotes
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Send reprint requests to: Dr. Daniela M. Zisterer, Biochemistry Department, Trinity College Dublin, Ireland. E-mail:dzistrer{at}tcd.ie
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↵1 This study was supported by BioResearch Ireland, National Pharmaceutical Biotechnology Center.
- Abbreviations:
- PBR
- peripheral-type benzodiazepine receptor
- ROI
- reactive oxygen intermediate
- NAC
- N-acetylcysteine
- NF-κB
- nuclear factor-κB
- TNF
- tumor necrosis factor
- AMC
- amino-4-methyl coumarin
- PAGE
- polyacrylamide gel electrophoresis
- VDAC
- voltage-dependent anion channel
- TEMPO
- 2,2,6,6-tetramethyl-1-piperidinyloxy
- PBOX
- pyrrolo-1,5-benzoxazepine
- fmk
- fluoromethyl ketone
- Received July 9, 1999.
- Accepted November 8, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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