Abstract 576: Novel compounds from Allspice (Pimenta dioica) inhibit breast cancer growth by autophagy induction

Abstract

Abstract Background: Breast Cancer (BrCa) ranks second as cause of cancer death in women, causing 40,000 deaths in 2010. Recent studies have shown that novel plant-derived compounds used as dietary chemopreventive agents prolong survival and reduce breast cancer deaths. Lack of mechanism of action and limited bioavailability are the leading concerns for adopting natural dietary compounds as chemopreventive or adjuvant therapeutic agents against breast and other cancers. We identified several likely anti-cancer compounds from water extract of Allspice, the unripe berries of Pimenta dioica (Jamaican pepper). The compounds limit the growth of breast cancer cells by novel mechanism and may synergize with main-stream cancer therapeutics. Methods: An aqueous extract of Certified-organic Allspice (AAE) was prepared and a solution of suitable strength was tested on several BrCa cell lines (MCF-7, T47D, MDA-MB231, SKBr3) for potential inhibition of proliferation, autophagy and estrogen-receptor inactivation using commonly used analytical techniques. Potential effect on estrogen receptor levels and transcriptional activities were determined using quantitative-real time PCR, promoter luciferase assay and immunoblotting. Results: AAE reduced the viability and clonogenic growth of BrCa cells (IC50α100μg/ml) with limited activity (50% less toxicity in quiescent cells). AAE induced cell-death was only associated with several characteristics of autophagy, including increase in acidic vesicular organelle content, levels of GFP-LC3-positive puncta, and LC3-II protein level. Knockdown of ATG-7 gene expression by siRNA partially prevented AAE-induced cell death by 40%. Autophagy was induced by Endoplasmic reticulum (ER) stress but not changes in ATP levels. Further, AAE caused inhibition of mTOR signaling pathway and enhanced cytotoxicity combined with mTOR inhibitor, rapamycin. Furthermore, AAE reduced Estrogen Receptor-α protein as well mRNA levels in ERα positive-BrCa cell lines MCF-7 and T47D. The decrease in ERα protein level was only partially rescued by proteasome inhibitor MG132, indicating AAE accelerates ERα protein degradation. Activity based purification combined with chemical identification strategies resulted in identification of one compound Ericifolin, and several compounds in a highly enriched fraction exhibiting same properties as that of AAE. Conclusion: We showed the anti-cancer effects of aqueous extract of Allspice on BrCa cells, which includes anti-proliferation by inducting autophagy after AAE treatment and ERα downregulation which has promising clinical application for BrCa treatment. [Grant Support: R01 CA156776-01and Sylvester Cancer Center (BLL)]. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 576. doi:1538-7445.AM2012-576