Metabolism of anandamide by COX‐2 is necessary for endocannabinoid‐induced cell death in tumorigenic keratinocytes

Abstract

Nonmelanoma skin cancer is the most prevalent cancer in the United States with approximately 1.25 million new cases diagnosed each year. Cyclooxygenase-2 (COX-2) expression is commonly elevated in these and other epithelial tumors. Cyclooxygenases metabolize arachidonic acid to prostaglandins, which promote growth and survival of tumor cells. COX-2 also metabolizes endocannabinoids forming prostaglandin-ethanolamides (PG-EA); however, the role of these lipid molecules in tumor cell survival is unclear. The goal of this research is to determine if the metabolic products of COX-2 contribute to endocannabinoid-induced cell death. Anandamide [also known as arachidonyl ethanolamide (AEA)] induced cell death in the COX-2 overexpressing squamous carcinoma cell line JWF2. In contrast, AEA did not initiate cell death in HaCaT keratinocytes, which express low basal levels of COX-2. Resistance to AEA-mediated cell death in HaCaT cells was reversed by overexpressing COX-2 in these cells. Next, ELISA assays were carried out to identify prostaglandins involved in AEA-mediated cell death. D-type prostaglandins were predominantly formed in AEA-exposed JWF2 cells although significant increases in E- and F-type prostaglandins were also seen. Cells were then treated with various prostaglandins or PG-EA to determine the contribution of each to AEA-induced cell death. PGD(2) and PGD(2)-EA were found to be cytotoxic to JWF2 keratinocytes and the PGD(2) dehydration products, PGJ(2) and 15-deoxy Delta(12,14) PGJ(2), were also potent inducers of cell death. These results suggest that AEA selectively induces cell death in tumorigenic keratinocytes due to COX-2 overexpression and the resulting metabolism of AEA to cytotoxic prostaglandins.

The endogenous cannabinoid, anandamide, induces COX-2-dependent cell death in apoptosis-resistant colon cancer cells

“…In the current study we have provided direct genetic evidence that establishes sensitivity to anandamide-induced cell death is dependent on COX-2 expression, a finding recently supported by a study in murine squamous carcinoma cells (44). The importance of COX-2 in the response to anandamide is emphasised by the fact that COX-2 is over-expressed in the majority of colorectal carcinomas (85%), and in a large population of colorectal adenomas (40-50%) (29), suggesting that anandamide treatment may be of benefit both in chemoprevention as well as treatment of advanced disease.…”

Endocannabinoid Oxygenation by Cyclooxygenases, Lipoxygenases, and Cytochromes P450: Cross-Talk between the Eicosanoid and Endocannabinoid Signaling Pathways

“…82,88 As noted above, PG-EAs and PG-Gs are resistant to degradation by 15-hydroxyprostaglandin dehydrogenase when compared to their free acid counterparts. Thus, it is conceivable that these compounds could serve as a more metabolically stable pool of PGs that is transported to distant sites prior to hydrolysis and receptor binding.…”

Receptor-dependent and receptor-independent endocannabinoid signaling: A therapeutic target for regulation of cancer growth

“…Recently we showed that AEA-induced cytotoxicity was mediated by the production of proapoptotic, J-series prostaglandins in tumorigenic keratinocytes that overexpress COX-2 (Van Dross, 2009;Kuc et al, 2012). In addition, resistance to AEA-induced cytotoxicity was observed in non-tumorigenic keratinocytes with low basal COX-2 expression however, these cells underwent cell death when transfected with an expression plasmid containing COX-2.…”

“…Blockade of AEA degradation by inhibiting FAAH increased J-series prostaglandin synthesis and apoptosis. Also, the cytotoxic effect of AEA was not blocked by CB1R, CB2R or TRPV1 antagonists (Van Dross, 2009). Thus, AEA-induced cell death in tumor cells which overexpress COX-2 appears to be caused by the conversion of AEA to cytotoxic prostaglandins (Van Dross, 2009;Kuc, Jenkins, and Van Dross, 2012;Patsos et al, 2010; Pastos et al, 2005).…”