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Pyrrolo-1,5-benzoxazepines: a new class of apoptotic agents
D M Zisterer1, M M McGee, G Campiani
1Biochemistry Department, Trinity College Dublin, Dublin 2, Ireland. dzistrer@tcd.ie
Abstract:
Some members of a series of novel pyrrolo-1,5-benzoxazepines (PBOXs) potently induce apoptosis in a number of human cancerous cell lines including HL-60 cells and the drug-resistant chronic myelogenous leukaemia cell line, K562. The apoptotic induction seems to be independent of the mitochondrial peripheral-type benzodiazepine receptor (PBR), which binds these PBOXs with high affinity, due to a lack of correlation between their affinities for the receptor and their apoptotic potencies and their high apoptotic activity in PBR-deficient cells. PBOX-6, a potent member of the series, induces a transient activation of c-Jun N-terminal kinase (JNK) in a dose-dependent manner, which correlates with induction of apoptosis. Expression of a cytoplasmic inhibitor of the JNK signal transduction pathway, Jip-1, prevents JNK activity and significantly reduces the extent of apoptosis induced by PBOX-6. This demonstrates the requirement for JNK in the cellular response to this apoptotic agent. In addition, PBOX-6 activates caspase-3-like proteases in K562 and HL-60 cells. The caspase-3 inhibitor, Z-Asp-Glu-Val-Asp-fluoromethylketone (z-DEVD-fmk), blocks caspase-3-like protease activity in both cell types but only prevents PBOX-6-induced apoptosis in HL-60 cells, suggesting that the requirement for caspase-3-like proteases in the apoptotic pathway is dependent on the cell type.
Insights
Novel pyrrolo-1,5-benzoxazepines (PBOXs) induce apoptosis in cancer cells, independent of the peripheral-type benzodiazepine receptor (PBR). JNK activation and caspase-3 proteases play roles in this cell death pathway.
Area of Science:
- Pharmacology
- Molecular Biology
- Cancer Research
Background:
- Novel pyrrolo-1,5-benzoxazepines (PBOXs) are a class of compounds with potential anti-cancer activity.
- Apoptosis, or programmed cell death, is a critical mechanism for eliminating cancerous cells.
- The peripheral-type benzodiazepine receptor (PBR) is known to bind certain PBOXs, but its role in PBOX-induced apoptosis is unclear.
Purpose of the Study:
- To investigate the mechanism of apoptosis induction by novel PBOXs in human cancer cell lines.
- To determine the role of the peripheral-type benzodiazepine receptor (PBR) in PBOX-mediated apoptosis.
- To elucidate the involvement of c-Jun N-terminal kinase (JNK) and caspase-3-like proteases in the apoptotic pathway.
Main Methods:
- Treatment of human cancer cell lines (HL-60, K562) with various PBOX compounds.
- Assessment of apoptosis induction and correlation with PBR binding affinity.
- Analysis of JNK pathway activation using Jip-1 inhibitor.
- Evaluation of caspase-3-like protease activity using specific inhibitors (z-DEVD-fmk).
Main Results:
- Certain PBOXs potently induced apoptosis in HL-60 and K562 cells, including drug-resistant K562 cells.
- Apoptosis induction was independent of PBR affinity, with significant activity observed in PBR-deficient cells.
- PBOX-6 induced transient JNK activation, which was necessary for apoptosis, as demonstrated by Jip-1 inhibition.
- PBOX-6 activated caspase-3-like proteases, but inhibition of these proteases only blocked apoptosis in HL-60 cells, not K562 cells.
Conclusions:
- Novel PBOXs are potent inducers of apoptosis in human cancer cells, irrespective of PBR binding.
- JNK activation is a critical mediator of PBOX-induced apoptosis.
- The requirement for caspase-3-like proteases in PBOX-induced apoptosis is cell-type dependent.