Abstract B37: Antiproliferative effects of pomegranate are associated with downregulation of homologous recombination pathway: Potential use in cancer prevention

Abstract

Abstract High antioxidant capacity of pomegranate fruit is thought to be responsible for various health benefits, although the link between antioxidant capacity and antiproliferative effects has not been established yet. To better understand this relation we examined growth inhibition by pomegranate extract (PE) in association with antioxidant capacity and analyzed global gene expression changes in breast cancer MCF-7 cells. PE inhibited cell growth by induction of cell cycle arrest in G2/M and the induction of apoptosis. In contrast, antioxidants N-acetylcysteine and Trolox did not affect cell growth at doses containing equivalent antioxidant capacity as PE, suggesting that growth inhibition by PE cannot solely be attributed to its high antioxidant potential. DNA microarray analysis revealed that PE downregulated genes associated with mitosis, chromosome organization, RNA processing, DNA replication and DNA repair, and upregulated genes involved in regulation of apoptosis and regulation of cell proliferation. Of particular interest, both microarray and quantitative RT-PCR indicated that PE downregulated important genes involved in DNA repair by homologous recombination (HR), such as MRE11, RAD50, NBS1, RAD51, BRCA1, BRCA2 and BRCC3. Downregulation of HR genes correlated with increased levels of their predicted microRNAs, miR-183 (predicted target RAD50) and miR-24 (predicted target BRCA1), suggesting that PE may regulate microRNAs involved in DNA repair processes. Further, PE induced DNA double strand breaks (DSBs) that persisted and cells remained growth-inhibited for at least four days after the removal of PE. These data suggest that PE targets HR sensitizing cells to DSBs, cell cycle arrest and apoptosis. Downregulation of HR by PE is expected to specifically affect transformed and other rapidly growing cells because HR pathway is found to be dispensable for quiescent and post-mitotic tissues. HR not only repairs DSBs and replication-associated lesions but also may result in genome rearrangements and loss of heterozygocity, which drives oncogenic transformation. Hyperactive HR, genetic instability and elevated carcinogenesis has been exemplified in both humans and mice deficient in cell cycle control and DNA damage response genes including TP53 and ATM. Thus, these data suggest that downregulation of HR by PE may retard cell growth and prevent genetic instability and carcinogenesis. Citation Format: Prasad Kovvuru, Amit Shirode, Ramune Reliene. Antiproliferative effects of pomegranate are associated with downregulation of homologous recombination pathway: Potential use in cancer prevention. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr B37.