15-lipoxygenase metabolites of gamma-linolenic acid/eicosapentaenoic acid suppress growth and arachidonic acid metabolism in human prostatic adenocarcinoma cells: possible implications of dietary fatty acids.

Although gammalinolenic acid (GLA) and eicosapentaenoic acid (EPA) have independently been reported to suppress growth of cancer cells, their relative potencies are unknown. To determine the possible attenuating efficacies of dietary GLA or EPA on prostate carcinogenesis, we hereby report the in vitro effects of GLA, EPA and their 15-lipoxygenase (15-LOX) metabolites: 15(S)-HETrE and 15(S)-HEPE, respectively, on growth and arachidonic acid (AA) metabolism in human androgen-dependent (LNCaP) and androgen-independent (PC-3) prostatic cancer cells in culture. Specifically, both cells were preincubated respectively with the above PUFAs. Growth was determined by [3H]thymidine uptake and AA metabolism by HPLC analysis of the extracted metabolites. Our data revealed increased biosynthesis of prostaglandin E2 (PGE2) and 5-hydroxyeicosatetraenoic acid (5(S)-HETE) by both cells. Preincubation of the cells with 15(S)-HETrE or 15(S)-HEPE more markedly inhibited cellular growth and AA metabolism when compared to precursor PUFAs. Notably, 15(S)-HETrE exerted the greatest inhibitory effects. These findings therefore imply that dietary GLA rather than EPA should better attenuate prostate carcinogenesis via its in vivo generation of 15(S)-HETrE, thus warranting exploration.