Abstract 5471: Mechanism-based inhibition of NRH: quinone oxidoreductase 2 (NQO2) by a series of aminoalkylamino substituted indolequinones
Authors: Siegel David , Yan Chao , Dufour Marine , Shieh Biehuoy , Reigan Philip , Moody Chris , Ross David 
Published: February 2011

Abstract
NQO2 is an NRH-dependent quinone reductase that catalyzes the two-electron reduction of quinones to their corresponding hydroquinones. Despite structural similarities between NAD(P)H quinone oxidoreductase 1 (NQO1) and NQO2 many compounds have been shown to bind selectively to NQO2. Previous studies have shown that many drugs including resveratrol, quercetin, chloroquine, and imatinib can bind to and inhibit the catalytic activity of NQO2. Whether the binding and inhibition of NQO2 influences the pharmacology of these compounds is currently unknown. In this study we have developed a series of indolequinones as mechanism-based inhibitors of NQO2. These compounds were based on ES936 (5-methoxy-1,2-dimethyl-3-(4-nitrophenoxy)methylindole-4,7-dione) an efficient mechanism-based inhibitor of NQO1. We found that substitution of the 5-methoxy group in ES936 with an aminoalkylamino side chain generated potent mechanism-based inhibitors of NQO2 that do not efficiently inhibit NQO1. Interestingly, MD436 (5-amino-1,2-dimethyl-3-(2,4,6-trifluorophenoxy)methylindole-4,7-dione) a compound that contains only an amino group at the 5-position was a mechanism-based inhibitor of NQO1 and NQO2. Structural requirements for optimal inhibition of NQO2 were examined and found to include an aminoalkylamino side chain at the 5-position. NQO2 inhibition was observed with compounds with alkyl chains that varied from 3 to 8 carbons in length, with maximal inhibition observed with compounds that possessed chain lengths of between 3 to 5 carbons. Compounds where the aminoalkyl chain terminated in either an unsubstituted amino group or a dimethyl substituted amino group were efficient inhibitors of NQO2. Compounds with substitutions at the 6-position were not efficient mechanism-based inhibitors of NQO2 despite molecular docking studies that suggested NQO2 could accommodate either 5 or 6-position aminoalkylamino side chains. Co-crystallization studies are currently underway to more precisely define the physical interactions between compounds substituted at the 5-position and NQO2. As previously observed for a series of NQO1 mechanism-based inhibitors, structural requirements for efficient inhibition of NQO2 also include a methyl group at the 2-position of the indole ring and a substituent at the 3-position capable of leaving to generate a reactive iminium electrophile following enzymatic reduction. MD372 (5-(3-aminopropylamino)-1,2-dimethyl-3-(2,4,6-trifluorophenoxy)methylindole-4,7-dione) was tested for NQO2 inhibition using the human leukemia cell line K562 that has been shown to contain very high levels of NQO2 protein and activity. Treatment of K562 cells with MD372 (100nM) for 15 min resulted in greater than 95% inhibition of NQO2 catalytic activity, confirming that these compounds enter cells and efficiently inhibit NQO2 (Supported by R21 HL095995).
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5471.