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Proffered Abstract (Oral Presentation): Prevention of Estrogen Receptor-Negative Breast Cancer

The triterpenoid, CDDO-methyl ester, and the rexinoid, LG100268, synergize in the prevention of mammary tumors in a mouse model of estrogen receptor-negative breast cancer.

Dartmouth Medical School, Hanover, NH; Dartmouth College, Hanover, NH; Ligand Pharmaceuticals, San Diego, CA

Abstract

PR-08

We have previously reported that the rexinoid, LG100268 (268) and the selective estrogen receptor modulator, Arzoxifene, synergize in the prevention and treatment of estrogen receptor negative (ER-) mammary tumors in MMTV-neu mice. The synthetic triterpenoid CDDO (2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid) inhibits proliferation and induces apoptosis of ER+ and ER- breast cancer cells in vitro and blocks growth of ER- breast cancer cells in immunodeficient mice. CDDO and its methyl ester (CDDO-Me) are currently in Phase I clinical trial for treatment of leukemia and solid tumors, so we tested whether CDDO-Me, alone and in combination with 268, prevents ER- breast cancer. Female MMTV-neu mice were fed powdered control diet or diet containing CDDO-Me (50 mg/kg diet), 268 (20 mg/kg diet), or the combination, beginning at 10 weeks of age. By 40 weeks of age, 100% of control mice (n = 15) had developed mammary gland tumors. In contrast, only 12% of the mice on the CDDO-Me diet and 29% of the mice on the 268 diet had developed tumors, but no tumors were observed in the combination group (n = 8 in each group). After an additional 3 months on diet, 50% of the mice on the CDDO-Me diet and 43% of mice on the 268 diet had developed tumors, but still no tumors were found in the combination group. The concentrations of drugs used in this experiment were well-tolerated, and the mice continued to gain weight throughout the experiment. Neither the individual compounds nor the combination inhibited transgene expression in E18-14C-27 tumor cells derived from the MMTV-neu mice, and analysis of transgene expression in the mammary glands and tumors of mice fed these drugs is ongoing. Moreover, in vitro experiments with human ER- breast cancer cells demonstrate that 268 induces PTEN expression, CDDO-Me decreases constitutive pSTAT3 expression, and the combination blocks the degradation of IKB-alpha in cells treated with TNF-alpha. In summary, these studies demonstrate that CDDO-Me and 268 as individual drugs significantly delay tumor development in vivo. Furthermore, the combination of a triterpenoid and rexinoid are synergistic for prevention of ER- breast cancer and should be considered for future clinical prevention trials. Supported by NIH grant RO1 CA101207 and Reata Pharmaceuticals, Inc.