Abstract 3477: Dietary polyphenols as epigenetic ‘reader' inhibitors

Abstract

Abstract Introduction: There is continued interest in targeting epigenetic "readers, writers, and erasers" for the treatment of cancer and other pathologies. Bromodomain (BRD)-containing proteins act as epigenetic readers by recognizing lysine acetylation on histone and non-histone proteins and regulating various transcriptional processes. Treatment with the BRD inhibitor JQ1, synergized with the dietary deacetylase inhibitor sulforaphane (SFN) in colon cancer cells and suppressed tumor development in animal models of colorectal cancer1, providing a mechanistic basis for potential new therapeutic avenues involving epigenetic combination treatments. In the current work, we explored dietary compounds to identify potential JQ1-like natural BRD inhibitors that may provide a safer alternative to using JQ1. Methods: Docking of BRD1, BRD2, BRD3 and BRD4 was performed using STRAP, following multiple sequence alignment, and analyzed by AutoDock Vina1. Ligand-protein interactions were analyzed using PDBePISA and LPC/CSU1. The structures of natural molecules were created using Protein Data Bank2. Subsequently, selected compounds were screened at 10 µM, using BROMOscan®-Bromodomain assay panel to identify compounds that bind to BRD1, BRD2(1), BRD2(2), BRD3(1), BRD3(2), BRD4(1) and BRD4(2) active sites and prevent them from binding to the immobilized ligand, using qPCR to detect the associated DNA label3. Results: In silico screening identified several dietary polyphenols, including tea catechins, genistein, luteolin, and resveratrol as BRD inhibitors, with binding energy ≤ -7.0 kcal/mol, mimicking acetyl-lysine interactions. The BROMOscan® screening revealed that some of these dietary polyphenols only moderately inhibited BRD binding to their respective ligands, by less than 40% when tested at 10 µM. However, genistein inhibited BRD4(2) by 80%, and orientin inhibited BRD3(1) by 73%, prioritizing them as candidates for further investigation. Conclusions: In silico docking and BROMOscan® screening implicated natural polyphenols as potential BRD inhibitors. Ongoing investigations will determine their dissociation constant (Kd) via isothermal titration calorimetry and/or surface plasmon resonance for assessing their binding affinity. Natural BRD inhibitors and their metabolites will be further evaluated for the inhibition of cell growth and BRD protein expression in human colon cancer cells. Our results suggest that dietary polyphenols have the potential to recognize epigenetic reader domains by interacting with BRDs, providing new insights in the field of nutrigenomics and precision medicine. Acknowledgements: Research supported by NCI grant CA122959, John S. Dunn Foundation, Texas A&M AgriLife Research, and a Chancellor's Research Initiative.