Abstract 5258: Inhibition of DNA methyltransferases and histone methyltransferases by plant flavones

Methylation of DNA and histone protein is an epigenetic modification mediated by DNA methyltransferases (DNMTs) and histone methyltransferases (HMTs) critically involved in methylation and regulation of affinity binding between the histones and DNA backbone. HMTs catalyze the transfer of one, two, or three methyl groups to lysine and arginine residues of histone proteins. The HMTs-mediated increase in histone affinity to DNA causes chromatin condensation, preventing transcription; whereas DNMTs methylate cytosine residues within gene promoters resulting in transcriptional repression. DNMT and HMT activities are reported to be associated with signal transduction, cell growth and death, as well as with the pathogenesis of various human diseases including cancer. Dietary plant flavones can affect epigenetic modifications accumulated over time and have shown health-beneficial effects. However, the epigenetic response on DNMT and HMT elicited by plant flavones has not been elucidated. Through in silico protein-ligand docking studies and molecular studies with plant flavones viz. chrysin, apigenin and luteolin and their effect on DNA and histone methylation was assessed. The ligands were individually docked into the pocket of DNMT and EZH2 using Glide in XP (extra precision) mode (Schrodinger, LLC). Binding of ligands with proteins were evaluated using GlideScore, which is an empirically derived scoring function. Virtual screening approach using the model of the catalytic site of DNMT and EZH2 demonstrated that plant flavones tethered at both ends inside the catalytic pocket of DNMT and EZH2 by means of hydrogen bonding. Flavones exhibited a high docking rank (Glide score) in the order of chrysin (-5.8), apigenin (-6.4), luteolin (-7.4) compared with the pharmacological inhibitor, 5-Aza-2′-deoxycytidine (-4.2). Notably, all three flavones inhibited EZH2, having a high docking rank compared to the known pharmacological inhibitor, 3-Deazaneplanocin A (DZNep). The docking rank for chrysin was -10.07, apigenin -9.73 and luteolin -11.23, compared to -7.62 for DZNep. Epigenetic studies performed with plant flavones demonstrated reversal of hypermethylation of cytosine bases in the DNA and prevented methylation of cytosine in the GC-rich promoter sequence incubated with MSsI enzyme. Furthermore, decrease protein expression of EZH2 and trimethylation of H3K27 was noted in prostate cancer cells treated with these plant flavones. Taken together, our results suggest that plant flavone can alter DNMT and HMT activities and methylation of DNA and histone proteins that regulate epigenetic modifications providing significant health-effects and prevent various pathological processes involved in the development of cancer. Citation Format: Rajnee Kanwal, Manish Datt, Sanjay Gupta. Inhibition of DNA methyltransferases and histone methyltransferases by plant flavones. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5258.