Aerobic Cytotoxicity of Aromatic N-Oxides: The Role of NAD(P)H:Quinone Oxidoreductase (NQO1).

Aušra Nemeikaitė-Čėnienė,Mindaugas Lesanavičius,Lina Misevičienė,Jonas Šarlauskas,Violeta Jonušienė,Narimantas Čėnas,Audronė Marozienė

doi:10.3390/ijms21228754

Abstract

Derivatives of tirapazamine and other heteroaromatic N-oxides (ArN→O) exhibit tumoricidal, antibacterial, and antiprotozoal activities, which are typically attributed to bioreductive activation and free radical generation. In this work, we aimed to clarify the role of NAD(P)H:quinone oxidoreductase (NQO1) in ArN→O aerobic cytotoxicity. We synthesized 9 representatives of ArN→O with uncharacterized redox properties and examined their single-electron reduction by rat NADPH:cytochrome P-450 reductase (P-450R) and Plasmodium falciparum ferredoxin:NADP+ oxidoreductase (PfFNR), and by rat NQO1. NQO1 catalyzed both redox cycling and the formation of stable reduction products of ArN→O. The reactivity of ArN→O in NQO1-catalyzed reactions did not correlate with the geometric average of their activity towards P-450R- and PfFNR, which was taken for the parameter of their redox cycling efficacy. The cytotoxicity of compounds in murine hepatoma MH22a cells was decreased by antioxidants and the inhibitor of NQO1, dicoumarol. The multiparameter regression analysis of the data of this and a previous study (DOI: 10.3390/ijms20184602) shows that the cytotoxicity of ArN→O (n = 18) in MH22a and human colon carcinoma HCT-116 cells increases with the geometric average of their reactivity towards P-450R and PfFNR, and with their reactivity towards NQO1. These data demonstrate that NQO1 is a potentially important target of action of heteroaromatic N-oxides.

Highlights

N-oxides of 1,2,4-benzotriazine, quinoxaline, and phenazine (ArN→O) possess promising antitumor, antiprotozoal, and antibacterial activities, including their potential application as hypoxia-specific antitumor agents ([1,2,3,4,5,6], and references therein)
We examined the relationship between enzymatic redox properties and aerobic cytotoxicity of aromatic N-oxides with a particular emphasis on the role of NQO1
The rate constants of single-electron reduction of ArN→O 1–9 by P-450 reductase (P-450R) and P. falciparum ferredoxin:NADP+ oxidoreductase (Pf FNR) (Table 1) are in line with previous findings [22,27], showing that the reactivity is mostly determined by the electron-accepting potency of ArN→O, and hardly depend on their structural peculiarities

Summary

Introduction

N-oxides of 1,2,4-benzotriazine, quinoxaline, and phenazine (ArN→O) possess promising antitumor, antiprotozoal, and antibacterial activities, including their potential application as hypoxia-specific antitumor agents ([1,2,3,4,5,6], and references therein). In most cases, their action is attributed to the enzymatic reduction and free radical generation. TPZ (a) is enzymatically reduced in a single-electron way to a free radical (b), which forms DNA-damaging species under hypoxic conditions, namely, an oxidizing hydroxyl radical

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