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-435 human breast cancer cells from the mammary fat pads of nude mice. This omega-6 fatty acid is metabolized to various cyclo-oxygenase and lipoxygenase 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 E₂ (PGE₂), and 12-hydroxyeicosatetraenoic acid (12-HETE) and 15-HETE when cultured in the presence of 2.7 μM (0.75 μg/ml) LA; 5-HETE secretion was unchanged. The 12-lipoxygenase inhibitor esculetin (20 μM) completely blocked the LA-stimulated 12-HETE secretion. Linoleic acid also increased MDA-MB-435 cell invasion in an in vitro assay; this stimulation was abolished by 20 μM esculetin, but was unaffected by piroxicam, a selective cyclooxygenase inhibitor. The effect of LA on invasion was replicated by 0.1 μM 12-HETE, but not by 5-HETE or PGE₂; 15-HETE was stimulatory only at a concentration of 1.0 μM. Zymographic and Northern blot analyses showed that these events are accompanied by the induction of 92 kDa isoform type IV collagenase (metalloproteinase-9) enzymic activity and mRNA expression by exogenous LA and 12-HETE, and their suppression by the 12-lipoxygenase inhibitor. These results suggest that the effects of dietary LA on breast cancer cell metastasis in the nude mouse model are due, at least in part, to enhanced 12-HETE biosynthesis, with an associated increase in proteolytic enzyme activity and tumor cell invasiveness.