Lipoxygenase modulation to reverse carcinogenesis.

New studies of the relationship between polyunsaturated fatty acid metabolismand carcinogenesis have led to novel molecular targets for cancer chemoprevention research. These targets include procarcinogenic lipoxygenases (LOXs), including 5-, 8-, and 12-LOX, and anticarcinogenic LOXs, including 15-LOX-1 and possibly 15-LOX-2. Recent studies indicate that 15-LOX-1 is down-regulated in colorectal cancer cells and that the ability of nonsteroidal anti-inflammatory drugs, a class of clinically active cancer chemopreventive agents, to induce apoptosis and growth inhibition in these cells was dependent on the induction of 15-LOX-1 and its metabolic product 13-S-hydroxyoctadecadienoic acid. Consistent with the colorectal studies, 15-LOX very recently has shown anticarcinogenic activity in esophageal and prostatic carcinogenesis. Inhibitors of other LOXs (e.g., 5-LOX) have preclinical anticarcinogenic activity and are being developed for clinical chemoprevention study. These and other LOX data led us to propose that the various LOX pathways exist in a dynamic balance that shifts during carcinogenesis toward 5-, 8-, and 12-LOX (and cyclooxygenase-2) and away from 15-LOX. A novel approach for cancer chemoprevention would involve LOX modulators, i.e., agents that can induce the anticarcinogenic and/or inhibit the procarcinogenic LOXs, thereby shifting the balance of LOX activities from procarcinogenic to anticarcinogenic metabolism of polyunsaturated fatty acids.