ACCELERATED DISCOVERY 15-LOX-1: a Novel Molecular Target of Nonsteroidal Anti-inflammatory Drug-Induced Apoptosis in Colorectal Cancer Cells

(NSAIDs) appear to act via induction of apoptosis— programmed cell death—as potential colorectal cancer che-mopreventive agents. NSAIDs can alter the production of different metabolites of polyunsaturated fatty acids (linoleic and arachidonic acids) through effects on lipoxygenases (LOXs) and cyclooxygenases. 15-LOX-1 is the main enzyme for metabol iz ing colonic l inole ic ac id to 13-S-hydroxyoctadecadienoic acid (13-S-HODE), which induces apoptosis. In human colorectal cancers, the expression of this enzyme is reduced. NSAIDs can increase 15-LOX enzy-matic activity in normal leukocytes, but their effects on 15-LOX in neoplastic cells have been unknown. We tested the hypothesis that NSAIDs induce apoptosis in colorectal can-cer cells by increasing the protein expression and enzymatic activity of 15-LOX-1. Methods: We assessed 15-LOX-1 pro-tein expression and enzymatic activity, 13-S-HODE levels, and 15-LOX-1 inhibition in association with cellular growth inhibition and apoptosis induced by NSAIDs (primarily su-lindac and NS-398) in two colorectal cancer cell lines (RKO and HT-29). All P values are two-sided. Results: Sulindac and NS-398 progressively increased 15-LOX-1 protein ex-pression in RKO cells (at 24, 48, and 72 hours) in association with subsequent growth inhibition and apoptosis. Increased 13-S-HODE levels and the formation of 15-hydroxy-eicosatetraenoic acid on incubation of the cells with the sub-strate arachidonic acid confirmed the enzymatic activity of 15-LOX-1. Inhibition of 15-LOX-1 in RKO cells by treat-ment with caffeic acid blocked NS-398-induced 13-S-HODE production, cellular growth inhibition, and apoptosis (P =.007, P<.0001, and P<.0001, respectively); growth inhibition and apoptosis were restored by adding exogenous 13-S-HODE (P<.0001 for each) but not its parent compound, lin-oleic acid (P = 1.0 for each). Similar results occurred with other NSAIDs and in HT-29 cells. Conclusions: These data identify 15-LOX-1 as a novel molecular target of NSAIDs for inducing apoptosis in colorectal carcinogenesis. [J Natl Can