Citrus auraptene suppresses cyclin D1 and significantly delays N-methyl nitrosourea induced mammary carcinogenesis in female Sprague-Dawley rats

The effects of auraptene on cell proliferation of MCF-7 and MDA-MB-231 human breast carcinoma cells in culture was assessed by measuring metabolism of a substrate to a formazan dye. Dietary effects of auraptene on tumor incidence, multiplicity and latency were studied in the N-methyl nitrosourea (MNU) induced mammary carcinogenesis model in female Sprague Dawley rats. The concentration of auraptene in rat tissues was analyzed by reverse phase HPLC. Cyclin D1 expression in MCF-7 cells and rat tumors was measured by western blot.Auraptene (500 ppm) significantly delayed median time to tumor by 39 days compared to the MNU only group (p < 0.05, n = 24–26). Auraptene (10 μM) reduced Insulin like Growth Factor-1 (IGF-1, 10 ng/mL)-induced cyclin D1 expression by 40% in MCF-7 cells. In comparison, western blot analysis of rat mammary tumors (n = 10 per group) confirmed that auraptene (500 ppm) significantly reduced (p < 0.05) cyclin D1 expression by 49% compared to the MNU only group. Analysis of rat mammary tissue extract by HPLC with fluorescence detection indicated an average concentration (means ± S.E.) of 1.4 ± 0.5 μM and 1.8 ± 0.3 μM in the normal mammary glands of the auraptene 200 ppm and 500 ppm groups, respectively. The concentration (means ± S.E.) of auraptene in the mammary tumors of the auraptene 200 ppm group was 0.31 ± 0.98 μM.Overall, these observations suggest that the predominant effect of auraptene was to delay the development of tumors possibly through the suppression of cyclin D1 expression. These results point to the potential chemopreventive effects of auraptene in mammary carcinogenesis.Breast cancer is a major cause of death in women under the age of 55. In the year 2008, 184,450 new cases of breast cancer (182,460 women and 1990 men) and 40,930 deaths (40,480 women and 450 men) are expected [1]. Breast cancer is second only to lung cancer as the leading cause of cancer deaths in women [1]. Many risk factors have been attributed to breast cancer occ