Dietary Flavones as Dual Inhibitors of DNA Methyltransferases and Histone Methyltransferases

Abstract

Methylation of DNA and histone proteins are mutually involved in the epigenetic regulation of gene expression mediated by DNA methyltransferases (DNMTs) and histone methyltransferases (HMTs). DNMTs methylate cytosine residues within gene promoters, whereas HMTs catalyze the transfer of methyl groups to lysine and arginine residues of histone proteins, thus causing chromatin condensation and transcriptional repression, which play an important role in the pathogenesis of cancer. The potential reversibility of epigenetic alterations has encouraged the development of dual pharmacologic inhibitors of DNA and histone methylation as anticancer therapeutics. Dietary flavones can affect epigenetic modifications that accumulate over time and have shown anticancer properties, which are undefined. Through DNA binding and in silico protein-ligand docking studies with plant flavones viz. Apigenin, Chrysin and Luteolin, the effect of flavones on DNA and histone methylation was assessed. Spectroscopic analysis of flavones with calf-thymus DNA revealed intercalation as the dominant binding mode, with specific binding to a GC-rich sequence in the DNA duplex. A virtual screening approach using a model of the catalytic site of DNMT and EZH2 demonstrated that plant flavones are tethered at both ends inside the catalytic pocket of DNMT and EZH2 by means of hydrogen bonding. Epigenetic studies performed with flavones exhibited a decrease in DNMT enzyme activity and a reversal of the hypermethylation of cytosine bases in the DNA and prevented cytosine methylation in the GC-rich promoter sequence incubated with the M.SssI enzyme. Furthermore, a marked decrease in HMT activity and a decrease in EZH2 protein expression and trimethylation of H3K27 were noted in histones isolated from cancer cells treated with plant flavones. Our results suggest that dietary flavones can alter DNMT and HMT activities and the methylation of DNA and histone proteins that regulate epigenetic modifications, thus providing a significant anticancer effect by altering epigenetic processes involved in the development of cancer.

The dietary flavone luteolin epigenetically activates the Nrf2 pathway and blocks cell transformation in human colorectal cancer HCT116 cells

“…Previous reports have demonstrated that LUT can inhibit DNMT enzyme activity and reverse the CpG hypermethylation of DNA. 35 In our study, hypermethylation of the three CpGs (59.2% methylation) was observed in HCT116 cells without LUT treatment. Treatment with a combination of 5-Aza and TSA, a positive control of demethylation, significantly decreased the CpG methylation level to 41%.…”

Plant Flavone Apigenin: an Emerging Anticancer Agent

“…As such, apigenin acts on HDAC1 and HDAC3 and increases the global histone acetylation and the localized hyperacetylation of histone H3 on the p21/Waf1 promoter [132]. A study by Kanwal et al [133] demonstrated that apigenin could also function as a dual epigenetic inhibitor having ability to alter the DNA methyltransferase and histone deacetylase activity. It does so by reversing both DNA methylation and the trimethylation of lysine 27 at the H3 histone in cultured cells and in an artificial in vitro system [133].…”

“…A study by Kanwal et al [133] demonstrated that apigenin could also function as a dual epigenetic inhibitor having ability to alter the DNA methyltransferase and histone deacetylase activity. It does so by reversing both DNA methylation and the trimethylation of lysine 27 at the H3 histone in cultured cells and in an artificial in vitro system [133]. This study further supported an investigation on apigenin and its role as a chemopreventive agent.…”

Dietary phytochemical PEITC restricts tumor development via modulation of epigenetic writers and erasers

“…However, HDACs and DNMTs are also essential for the downstream maintenance of chromatin structure in the steady-state, hence non-selective inhibition of these enzymes can induce serious adverse effects that disrupt normal cell function1718. Recently, dietary phytochemicals such as indicaxanthin (Ind), genistein, and several flavones such as apigenin, chrysin, and luteolin, have been reported to decrease DNA methylation level by inhibiting DNMT activities192021. Interestingly, these flavones and Ind showed a direct interaction with DNMTs, which assessed by molecular modeling, showed possibility as good alternatives instead of chemically synthesized DNMT inhibitors2021.…”

“…Recently, dietary phytochemicals such as indicaxanthin (Ind), genistein, and several flavones such as apigenin, chrysin, and luteolin, have been reported to decrease DNA methylation level by inhibiting DNMT activities192021. Interestingly, these flavones and Ind showed a direct interaction with DNMTs, which assessed by molecular modeling, showed possibility as good alternatives instead of chemically synthesized DNMT inhibitors2021. Therefore, a more promising approach could be to identify how dietary intake of bioactive phytochemicals can promote and maintain ‘anti-tumor’ epigenetic profiles in the consumer, potentially leading to low-cost dietary interventions that protect a large fraction of the global population against cancers.…”