Relationship of Arachidonic Acid Metabolizing Enzyme Expression in Epithelial Cancer Cell Lines to the Growth Effect of Selective Biochemical Inhibitors

Arachidonic acid (AA) metabolizing enzymes are emerging as significant mediators of growth stimulation for epithelial cells. The relative contribution of the various family members of AA metabolizing enzymes to epithelial cancer cell growth is not known. To study this question, we first analyzed a series of epithelial cancer cells to establish the relative frequency of expression for the various enzymes. We analyzed the expression of five AA metabolizing enzymes as well as 5-lipoxygenase activating protein (FLAP) in a panel of human epithelial cancer cell lines (n = 20) using reverse transcription-PCR. From this analysis, we found that cyclooxygenase-1 (COX-1), 5-lipoxygenase (5-LOX), and FLAP were universally expressed in all cancer cell lines tested. For the remaining enzymes, the expression of COX-2, 12-LOX, and 15-LOX varied among cell lines, 60, 35, and 90%, respectively. Although the pattern of expression varied among the different cell types, all of the enzymes were expressed in all major cancer histologies. Using a panel of selective biochemical AA metabolizing enzyme inhibitors, we then evaluated the effect of these agents on cell lines with known expression status for the AA metabolizing enzymes. For the enzymes that were not universally expressed, growth inhibition by selective biochemical inhibitors did not closely correlate with the expression status of specific enzymes (P > 0.05). For the universally expressed enzymes, the LOX inhibitors were more potent growth inhibitors than the COX inhibitors. The frequent expression of the AA metabolizing enzymes suggests that AA metabolism pathway may be modulated in response to xenobiotic exposure during carcinogenesis. Although establishing a priori AA metabolizing enzyme status was not consistently informative about what AA metabolizing enzyme inhibition would be most growth inhibitory, the frequent inhibition of many epithelial cancers by these biochemical inhibitors opens a new avenue for cancer therapy and intervention in carcinogenesis.