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Prostaglandins and the regulation of tumor growth
David Bishop-Bailey1, Sara Calatayud, Timothy D Warner
1Department of Cardiac, Vascular and Inflammation Research, William Harvey Research Institute, Queen Mary's University, London, UK. d.bishop-bailey@mds.qmw.ac.uk
Abstract:
Increased expression of inducible cyclooxygenase (COX-2) is associated with a wide variety of tumors. In addition, inhibitors of COX have shown a great deal of promise in vitro and in animal models as potential antitumor therapies. COX enzymes use the substrate arachidonic acid to produce prostaglandin (PG)H2, the precursor to all the prostanoids. Therefore, the release of individual prostanoids depends on the abundance and functional coupling to individual PG synthase isoenzymes. Colony stimulating factors (CSFs) are also potential antitumor agents via their ability to augment the immune response. When COX-2 is expressed, the CSF, granulocyte macrophage (GM)-CSF, and granulocyte (G)-CSF are exquisitely sensitive to endogenous PGs. In addition, the ability of COX-2 to suppress GM-CSF release is mediated via traditional IP/EP prostanoid receptors linked to cAMP-dependent pathways. Therefore, inhibition of COX-2 in tumors may have the important side effect of enhancing the immune response. Recently, novel signaling pathways for PG derivatives have been discovered; in particular the PGD2 dehydration product 15-deoxy-delta(12,14)-(15d)-PGJ2 was identified as a ligand for the nuclear receptor/transcription factor, peroxisome proliferator-activated receptor (PPAR)-gamma. PPARgamma is present at high levels in a number of tumors, and is also present in endothelial cells. 15d-PGJ2 as well as other nonprostanoid PPARgamma ligands are antitumor, and antiangiogenic, by dramatically inhibiting the growth of tumor cells and endothelial cells by either causing terminal differentiation, and/or by inducing apoptosis. We have recently found that, in addition to IP and EP ligands generated by COX-2, PPARgamma ligands similarly inhibit GM-CSF release. Effecting individual prostanoid pathways at the level of COX expression, profile of PG products produced or selective PG receptor activation may produce novel therapies, either dependent or independent of CSF release, to target cancers.
Insights
Inhibiting cyclooxygenase-2 (COX-2) in tumors may enhance immune response and offers novel cancer therapies by targeting prostaglandin pathways and PPAR-gamma. This approach impacts tumor cell and endothelial cell growth.
Area of Science:
- Molecular Biology
- Cancer Research
- Immunology
Background:
- Increased cyclooxygenase-2 (COX-2) expression is linked to various tumors.
- COX inhibitors show promise as antitumor therapies by modulating prostaglandin (PG) production.
- Colony-stimulating factors (CSFs) can augment immune responses against cancer.
Purpose of the Study:
- To investigate the role of COX-2 and its products in tumor growth and immune modulation.
- To explore novel signaling pathways involving prostaglandin derivatives, such as 15-deoxy-delta(12,14)-(15d)-PGJ2, and their interaction with nuclear receptors like peroxisome proliferator-activated receptor (PPAR)-gamma.
- To evaluate the potential of targeting these pathways for developing new cancer therapies.
Main Methods:
- Analysis of COX-2 expression in tumors.
- Investigating the effects of COX inhibitors and prostaglandin derivatives on tumor cells and endothelial cells.
- Examining the impact on colony-stimulating factor (CSF) release and immune response modulation.
- Identifying ligands for nuclear receptors such as PPAR-gamma.
Main Results:
- COX-2 inhibition may enhance anti-tumor immune responses by affecting CSF release.
- 15-deoxy-delta(12,14)-(15d)-PGJ2, a PPAR-gamma ligand, demonstrates antitumor and antiangiogenic properties by inhibiting tumor and endothelial cell growth.
- Both COX-2-derived ligands and PPAR-gamma ligands can inhibit GM-CSF release, suggesting converging pathways.
Conclusions:
- Targeting COX-2 expression, prostaglandin production, or selective PG receptor activation presents novel therapeutic strategies for cancer.
- These strategies may offer benefits independent of or dependent on CSF release.
- Modulating prostaglandin pathways, including via PPAR-gamma activation, holds significant potential for cancer treatment.