Abstract 3683: Plant flavonoid apigenin preferentially binds with GC-rich DNA sequences and inhibits DNA methylation
Authors: Kanwal Rajnee , Sharma Haripaul , Gupta Sanjay 
Published: June 2012

Abstract
Epigenetic modifications result in heritable changes in gene expression without changes to the DNA sequence. The most common forms of epigenetic regulation of gene expression are DNA methylation and histone modification, all of which are associated with chromatin remodeling. It is well established that DNA is the central target for both chemical carcinogens and anticancer drugs. Agents that target epigenetic regulators may represent an attractive target for drug development. In recent years, several studies have focused on small molecule interaction with DNA. Flavonoids are natural polyphenolic compounds with major antioxidant activity that exert a multitude of beneficial effects on human health. Apigenin (4’,5,7 trihydroxyflavone), an important bioactive common flavonoid present in a variety of plants, vegetables, fruits, and herbs is well known for its cancer preventive activity. Studies from our group have shown that apigenin preferentially retains in nuclear matrix with possibility of binding to nucleic acid bases. Although apigenin has shown its presence in the nucleus however it's binding with nucleic acid bases and mode of action has not been elucidated. In present study we explored the binding of apigenin with DNA bases, especially with GC versus AT rich sequences. We designed two different sets of 100 bp oligonucleotides probes with GC- and AT- rich sequences and the absorption spectrum changes were recorded by UV-VIS spectrophotometer at 230-450 nm range. UV-VIS spectral studies demonstrated that apigenin possesses high affinity for poly-ds-GC oligonucleotides compared to poly-ds-AT oligonucleotide sequence. Since DNA methylation primarily at the C5 position of cytosine affects gene expression at the promoter CpG islands, therefore, we next studied the effect of apigenin in reversing hypermethylation of cytosine bases in the DNA. For these studies we generated 100 bp highly GC-rich sequences from the CpG island of GSTP1 promoter, a gene which has been shown to be frequently silenced in prostate cancer due to promoter hypermethylation. Spectral studies exhibited that apigenin possess high affinity with CpG island of GSTP1 promoter sequence compared to randomly picked GSTP1 gene sequence. Furthermore, apigenin prevented the methylation of cytosine in the GC-rich promoter sequence incubated with MSsI enzyme. Similar results were obtained with transformed human prostate epithelial RWPE1 cells, where MSsI enzyme-mediated hypermethylation was reduced by apigenin pre-treatment, compared to the control group without apigenin. Taken together, our studies suggest that apigenin binds preferentially to the GC-rich sequence primarily positioned in the promoter region of various tumor suppressor genes and might prevent promoter hypermethylation, at least in part, accountable for its chemopreventive activity.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3683. doi:10.1158/1538-7445.AM2011-3683