High-throughput library screening identifies two novel NQO1 inducers in human lung cells

Many phytochemicals possess antioxidant and cancer-preventive properties, some putatively through antioxidant response element-mediated phase II metabolism, entailing mutagen/oxidant quenching. In our recent studies, however, most candidate phytochemical agents were not potent in inducing phase II genes in normal human lung cells. In this study, we applied a messenger RNA (mRNA)-specific gene expression-based high throughput in vitro screening approach to discover new, potent plant-derived phase II inducing chemopreventive agents. Primary normal human bronchial epithelial (NHBE) cells and immortalized human bronchial epithelial cells (HBECs) were exposed to 800 individual compounds in the Micro- Source Natural Products Library. At a level achievable in humans by diet (1.0 μM), 2,3-dihydroxy-4-methoxy-4′- ethoxybenzophenone (DMEBP), triacetylresveratrol (TRES), ivermectin, sanguinarine sulfate, and daunorubicin induced reduced nicotinamide adenine dinucleotide phosphate:quinone oxidoreductase 1 (NQO1) mRNA and protein expression in NHBE cells. DMEBP and TRES were the most attractive agents as coupling potency and low toxicity for induction of NQO1 (mRNA level, ≥3- to 10.8-fold that of control; protein level,≥two- to fourfold that of control). Induction of glutathione S-transferase pi mRNA expression was modest, and none was apparent for glutathioneS-transferasepiproteinexpression.Measurements of reactive oxygenspecies and glutathione/oxidizedglutathione ratio showed an antioxidant effect for DMEBP, but no definite effect was found for TRES in NHBE cells. Exposure ofNHBE cells to H ₂O ₂ induced nuclear translocationofnuclear factorerythroid2-relatedfactor2,but this translocationwas not significantly inhibited by TRES and DMEBP. These studies show that potency and low toxicity may align for two potential NQO1-inducing agents, DMEBP and TRES.