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Inhibitors of ADP-ribose polymerase decrease the resistance of HER2/neu-expressing cancer cells to the cytotoxic
A Lichtenstein1, J F Gera, J Andrews
1Department of Medicine, V.A. Wadsworth-UCLA Medical Center.
Abstract:
Four human ovarian and breast tumor lines expressing the HER2/neu oncogene were resistant to the cytotoxic and DNA-degradative activity of TNF. The resistance was not associated with altered TNF receptor function because Scatchard analysis of 125I-rTNF binding to HER2/neu-expressing target cells revealed receptors with normal binding parameters. Furthermore, the TNF receptors on the resistant lines were capable of signal transduction as evidence by the induction of ADP-ribose polymerase activity and MHC expression. TNF resistance was not reversed by coincubation with drugs that interrupted the glutathione redox cycle. In addition, although coincubation of HER2/neu-expressing targets with cycloheximide resulted in significant TNF-induced lysis, when compared to HER2/neu-nonexpressing targets similarly treated with cycloheximide, a significant relative resistance was still present. To investigate the role of ADP-ribosylation in the resistance of these targets, we used nontoxic concentrations of two inhibitors of ADP-ribose polymerase, 3-aminobenzamide, and nicotinamide. Both inhibitors completely reversed the resistance of HER2/neu-expressing targets to TNF-mediated cytotoxicity and DNA injury in a concentration-dependent fashion. These inhibitors of ADP-ribose polymerase did not act by down-regulating expression of HER2/neu oncogenes. In contrast, aminobenzamide and nicotinamide significantly diminished TNF-induced cytotoxicity of L929 targets. These data suggest that the activity of ADP-ribose polymerase may play a pivotal role in determining the fate of the target cell during exposure to TNF.
Insights
HER2/neu oncogene expression confers resistance to tumor necrosis factor (TNF). Inhibiting ADP-ribose polymerase activity reversed this resistance, suggesting a key role for ADP-ribosylation in TNF-mediated cell death.
Area of Science:
- Oncology
- Molecular Biology
- Immunology
Background:
- HER2/neu oncogene overexpression is common in aggressive breast and ovarian cancers.
- Tumor necrosis factor (TNF) is a cytokine with potent anti-tumor activity.
- Mechanisms of TNF resistance in cancer cells are not fully understood.
Purpose of the Study:
- To investigate the role of HER2/neu oncogene expression in TNF resistance.
- To identify molecular pathways involved in TNF resistance mediated by HER2/neu.
- To explore therapeutic strategies for overcoming TNF resistance in HER2/neu-positive tumors.
Main Methods:
- Utilized human ovarian and breast tumor cell lines expressing HER2/neu.
- Assessed TNF-induced cytotoxicity and DNA degradation.
- Performed Scatchard analysis for TNF receptor binding.
- Measured ADP-ribose polymerase activity and MHC expression.
- Investigated the effect of ADP-ribose polymerase inhibitors (3-aminobenzamide, nicotinamide) and cycloheximide.
Main Results:
- HER2/neu-expressing tumor lines exhibited resistance to TNF's cytotoxic and DNA-degradative effects.
- TNF receptor function and signal transduction (ADP-ribose polymerase activity, MHC expression) were normal in resistant cells.
- Inhibitors of ADP-ribose polymerase (3-aminobenzamide, nicotinamide) completely reversed TNF resistance in HER2/neu-expressing cells.
- These inhibitors did not affect HER2/neu oncogene expression but diminished TNF-induced cytotoxicity in control cells.
Conclusions:
- ADP-ribose polymerase activity plays a critical role in mediating resistance to TNF in HER2/neu-expressing cancer cells.
- Targeting ADP-ribose polymerase represents a potential strategy to sensitize HER2/neu-positive tumors to TNF-based therapies.
- The findings provide insights into the molecular mechanisms underlying cancer cell resistance to immune-mediated cytotoxicity.