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Cyclooxygenase inhibitors block cell growth, increase ceramide and inhibit cell cycle
Namita Kundu1, Miriam J Smyth, Leigh Samsel
1Department of Pathology, University of Maryland School of Medicine, Baltimore 21201, USA.
Abstract:
We have shown previously in a model of metastatic breast cancer that murine mammary tumor cells express both cyclooxygenase-1 (Cox-1) and Cox-2 isoforms. Growth and metastasis of these tumors in syngeneic hosts are inhibited by either selective Cox-1 (SC560) or selective Cox-2 (celecoxib) inhibitors. To gain insight into the relevant mechanisms involved in the therapeutic response, we determined the effect of Cox inhibitors on tumor cell behavior in vitro. We now report that either selective Cox-1 or Cox-2 drugs inhibited cell replication, but only at concentrations that are no longer selective for either isoform. Growth delay by either nonselective or selective inhibitors was associated with changes in cell morphology including cell rounding; these changes were reversed upon removal of drug. Unlike many other cell types examined, treatment of these mammary tumor cells with Cox inhibitors was not associated with detectable apoptosis. Growth inhibition, induced by either selective or nonselective Cox inhibitors, was accompanied by increased intracellular levels of the sphingolipid ceramide by 1.7-2.6-fold in comparison to vehicle-treated cells. Ceramide changes are associated with cell cycle arrest and we observed that all the Cox inhibitors examined increased significantly the number of cells in G0/G1 and reduced the S phase fraction. Likewise, addition of a cell-permeable form of ceramide (C6-ceramide) could mimic the effect of Cox inhibitors on both cell cycle and cell growth inhibition. Thus, mammary tumor cells are growth restricted by Cox inhibitors. These effects are associated with changes in ceramide levels and a block in cell cycle progression.
Insights
Cyclooxygenase (Cox) inhibitors restrict mammary tumor cell growth by increasing ceramide levels, leading to cell cycle arrest. These findings reveal a novel mechanism for Cox inhibitor efficacy in breast cancer models.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- Murine mammary tumor cells express both cyclooxygenase-1 (Cox-1) and Cox-2 isoforms.
- Tumor growth and metastasis are inhibited by selective Cox-1 or Cox-2 inhibitors in preclinical models.
- The precise mechanisms underlying the therapeutic response to Cox inhibitors require further elucidation.
Purpose of the Study:
- To investigate the in vitro effects of Cox inhibitors on mammary tumor cell behavior.
- To identify the molecular mechanisms responsible for growth inhibition induced by Cox inhibitors.
Main Methods:
- Treatment of murine mammary tumor cells with selective and nonselective Cox inhibitors.
- Assessment of cell replication, morphology, and apoptosis.
- Quantification of intracellular ceramide levels and cell cycle analysis (G0/G1 and S phase).
- Evaluation of the effects of cell-permeable ceramide on cell growth and cell cycle.
Main Results:
- Cox inhibitors, at non-selective concentrations, inhibited cell replication and induced morphological changes.
- Growth inhibition was associated with a 1.7-2.6-fold increase in intracellular ceramide levels.
- Cox inhibitors induced cell cycle arrest at the G0/G1 phase and reduced the S phase fraction.
- Exogenous ceramide mimicked the inhibitory effects of Cox inhibitors on cell growth and cell cycle.
Conclusions:
- Mammary tumor cell growth is restricted by Cox inhibitors through mechanisms involving ceramide accumulation.
- Increased ceramide levels and subsequent cell cycle arrest are key mediators of Cox inhibitor efficacy.
- These findings provide insights into the therapeutic potential of targeting the Cox pathway in breast cancer.