Tamoxifen and the Rafoxifene analog LY117018: their effects on arachidonic acid release from cells in culture and on prostaglandin I2 production by rat liver cells.
BACKGROUND
Tamoxifen is being used successfully to treat breast cancer. However, tamoxifen also increases the risk of developing endometrial cancer in postmenopausal women. Raloxifene also decreases breast cancer in women at high risk and may have a lower risk at developing cancer of the uterus. Tamoxifen has been shown to stimulate arachidonic acid release from rat liver cells. I have postulated that arachidonic acid release from cells may be associated with cancer chemoprevention.


METHODS
Rat liver, rat glial, human colon carcinoma and human breast carcinoma cells were labelled with [3H] arachidonic acid. The release of the radiolabel from these cells during incubation with tamoxifen and the raloxifene analog LY117018 was measured. The prostaglandin I2 produced during incubation of the rat liver cells with microM concentrations of tamoxifen and the raloxifene analog was quantitatively estimated.


RESULTS
Tamoxifen is about 5 times more effective than LY117018 at releasing arachidonic acid from all the cells tested. In rat liver cells only tamoxifen stimulates basal prostaglandin I2 production and that induced by lactacystin and 12-O-tetradecanoyl-phorbol-13-acetate. LY117018, however, blocks the tamoxifen stimulated prostaglandin production. The stimulated prostaglandin I2 production is rapid and not affected either by preincubation of the cells with actinomycin or by incubation with the estrogen antagonist ICI-182,780.


CONCLUSIONS
Tamoxifen and the raloxifene analog, LY117018, may prevent estrogen-independent as well as estrogen-dependent breast cancer by stimulating phospholipase activity and initiating arachidonic acid release. The release of arachidonic acid and/or molecular reactions that accompany that release may initiate pathways that prevent tumor growth. Oxygenation of the intracellularly released arachidonic acid and its metabolic products may mediate some of the pharmacological actions of tamoxifen and raloxifene.
Department of Biochemistry, Brandeis University Waltham, MA 02454, USA. llevine@brandeis.edu
Lawrence
L
Levine
D000818:Animals; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D016718:Arachidonic Acid / Q000378:metabolism*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000378:metabolism; D051546:Cyclooxygenase 2; D011464:Epoprostenol / Q000096:biosynthesis*; D004965:Estrogen Antagonists / Q000494:pharmacology; D006801:Humans; D007527:Isoenzymes / Q000096:biosynthesis; D008099:Liver / Q000378:metabolism*; D008565:Membrane Proteins; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis; D011759:Pyrrolidines / Q000494:pharmacology*; D051381:Rats; D011960:Receptors, Estrogen / Q000378:metabolism; D013629:Tamoxifen / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D013876:Thiophenes / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D018931:Antineoplastic Agents, Hormonal; D004965:Estrogen Antagonists; D007527:Isoenzymes; D008565:Membrane Proteins; D011759:Pyrrolidines; D011960:Receptors, Estrogen; D013876:Thiophenes; D013629:Tamoxifen; D016718:Arachidonic Acid; C025430:LY 117018; D011464:Epoprostenol; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases