Abstract A49: Verification of two novel phytochemical inducers of phase II metabolic enzyme NQO1 in human lung cells

Abstract

Abstract One strategy for lung cancer chemoprevention focuses on the use of agents to modulate the metabolism and disposition of tobacco, environmental and endogenous carcinogens through up-regulation of detoxifying phase II enzymes. However, in studies to date, most candidate agents are not active in human lung cells. Therefore we previously applied a gene expression-based high-throughput screening approach to investigate n=800 plant-derived polyphenolic- and flavenoid- predominant compounds in the MicroSource Natural Products Library as to their effect on inducing the phase II metabolic enzymes glutathione S-transferases (GSTP1) and NAD(P)H:quinone oxidoreductase 1 (NQO1) in primary normal human bronchial epithelial (NHBE) cells and immortalized human bronchial epithelial cells (HBEC). We had identified 2, 3-dihydroxy-4-methoxy-4’-ethoxybenzophenone (DMEBP, putative source arctic sponge) and triacetylresveratrol (TRES, putative source plant myrtle) as new inducers for NQO1 mRNA expression. In the current study, in order to confirm our results, NHBE and HBEC cells in culture were exposed to diet-achievable levels of TRES and DMEBP (0.5, 1.0, 2.0 µM), as well as a panel of conventionally-recognized phytopreventive agents [epigallocatechin gallate (EGCG), resveratrol (RES) and sulforaphane (SFN)] for 24 h, 48 h, and 6 d, respectively. Quantitative RNA-specific RT-PCR showed an up-regulation of NQO1 mRNA expression of up to 10.8 fold in DMEBP-treated NHBE cells and an up-regulation of up to 4.6 fold in TRES-treated NHBE cells. NQO1 protein expression increased up to 3.4 fold in DMEBP-treated and up to 1.8 fold in TRES-treated NHBE cells. HBEC cells showed similar results for mRNA expression — an up-regulation of NQO1 mRNA expression of up to 9.7 fold in DMEBP-treated HBEC cells and an up-regulation of up to 3.1 fold in TRES-treated HBEC cells — whereas none of the tested compounds had an effect on protein expression in HBEC cells. DMEBP had a narrow therapeutic window, and was notably toxic to lung cells at 1-2 µM. We then measured accumulation of reactive oxygen species (ROS) in NHBE cell using DFA, and total GSH assays. Our ROS data so far show a slight anti-oxidant effect for DMEBP, but no effect yet found for TRES. Our data show two new agents have some effect on the up-regulation of the detoxifying enzyme NQO1 at mRNA and protein levels, but the effect was modest, and none was observed for GSTP1. Among the newly discovered agents, TRES is the most plausible candidate resulting from this search, and compares favorably, to conventional plant-derived polyphenolics/flavenoids tested. Citation Information: Cancer Prev Res 2010;3(12 Suppl):A49.