EICOSANOIDS AS MEDIATORS OF LINOLEIC ACID-STIMULATED INVASION AND TYPE-IV COLLAGENASE PRODUCTION BY A METASTATIC HUMAN BREAST-CANCER CELL-LINE

Diets rich in linoleic acid (LA) stimulate the metastasis of MDA-MB-43 5 human breast cancer cells from the mammary fat pads of nude mice, Th is omega-6 fatty acid is metabolized to various cyclo-oxygenase and li poxygenase products, several of which have been previously associated with tumor cell invasion and metastasis. We now report that MDA-MB-435 cells secreted increased levels of prostaglandin E(2) (PGE(2)), and 1 2-hydroxyeicosatetraenoic acid (12-HETE) and 15-HETE when cultured in the presence of 2.7 mu M (0.75 mu g/ml) LA; 5-HETE secretion was uncha nged, The 12-lipoxygenase inhibitor esculetin (20 mu M) completely blo cked the LA-stimulated 12-HETE secretion, Linoleic acid also increased MDA-MB-435 cell invasion in an in vitro assay; this stimulation was a bolished by 20 mu M esculetin, but was unaffected by piroxicam, a sele ctive cyclooxygenase inhibitor, The effect of LA on invasion was repli cated by 0.1 mu M 12-HETE, but not by 5-HETE or PGE(2); 15-HETE was st imulatory only at a concentration of 1.0 mu M. Zymographic and Norther n blot analyses showed that these events are accompanied by the induct ion of 92 kDa isoform type IV collagenase (metalloproteinase-9) enzymi c activity and mRNA expression by exogenous LA and 12-HETE, and their suppression by the 12-lipoxygenase inhibitor, These results suggest th at the effects of dietary LA on breast cancer cell metastasis in the n ude mouse model are due, at least in part, to enhanced 12-HETE biosynt hesis, with an associated increase in proteolytic enzyme activity and tumor cell invasiveness.