Anticarcinogenic Effects of Citrus Auraptene Against Breast Cancer.
Breast cancer remains a major health problem to women across the world. The state of Louisiana ranks 4th among the states in the United States based on the number of deaths in women from breast cancer. We wanted to identify the expression of key proteins dysregulated in the breast cancer proteins that are regulated by eIF4E, in the patients. We also wanted to develop a method to analyze the expression of these proteins in a TMA format. Our analysis showed that cyclin D1, ODC, TLK1B, VEGF and c-Myc, all downstream of eIF4E, were upregulated in cancer specimens. Many natural products have been studied for their chemopreventive property against breast cancer. Citrus auraptene has been shown to be chemopreventive against many rodent models of cancer like colon, skin, prostate etc. However auraptene has never been tested against breast cancer. Our initial studies with MDA-MB-231 showed that auraptene reduced the proliferatin of these cells. Our further studies with MCF-7 cells showed that auraptene possessed antiproliferative effect in these cells also along with reduction of cyclin D1. Based on the in vitro data we tested auraptene in the MNU-rat mammary model. We found that auraptene significantly increased the median time to tumor at 500 ppm dose in the diet. There was no significant reduction in the incidence and multiplicity at the end of the study. Auraptene at 200 ppm did not increase the median time to tumor. There was no reduction in tumor incidence and multiplicity at this dose. The HPLC analysis of the mammary glands and tumors showed that auraptene is bioavailable in these tissues in micromolar concentrations. In the western blot analysis of the tumors, we found that the expression of cyclin D1 protein has been significantly reduced in the 500 ppm treated animals. This might have subsequently delayed the median time to tumor. The mechanism of cancer prevention by natural compounds are many and suppression of cell cycle is one among them. The qRT-PCR array was done to study the changes in mRNA of cyclin D1 along with other cell cycle regulators after auraptene treatment. We found that there was no change in the mRNA of cyclin D1 among the various groups. This suggests that effect of auraptene on cyclin D1 was post-transcriptional. However, several other genes were modulated by auraptene, many of which are involved in cell cycle. Cell cycle analysis using flow cytometry indicated that auraptene significantly reduced the percentage of cells in the S-phase in IGF-1 treated cells, after 24h of IGF-1 treatment. Thus, we conclude that auraptene may delay mammary carcinogenesis through suppression of cyclin D1 and cell cycle. This study has helped in understanding the chemopreventive potential of auraptene against breast cancer. The inhibitory effect of auraptene on cyclin D1 protein expression in vivo and S phase of the MCF-7 cells in vitro has provided more insights into the mechanism of action of auraptene against breast cancer. Thus the findings of this study will help in the future study of auraptene and include it in our arsenal of chemopreventive agents against breast cancer.