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

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.

Redox Proteomic Profile of Tirapazamine-Resistant Murine Hepatoma Cells

“…Our previous studies showed that the murine hepatoma MH22a cells are sufficiently sensitive to TPZ under aerobic conditions [ 7 , 24 ]. The TPZ-resistant MH22a cell subline was obtained as described in the Materials and Methods.…”

“…Thus, according to the available data, among the possible signaling pathways, the relationship between Ahr and the expression of antioxidants and xenobiotics when metabolizing enzymes remains the best elucidated. In this context, the increase in NQO1 levels in TPZ-resistant cells ( Table 1 ) is somehow unexpected since NQO1 promotes Ar N →O cytotoxicity in short-time 24–48 h experiments [ 24 ]. However, it can be assumed that the increase in GST and NQO1 levels ( Table 1 ) is the result of TPZ-induced oxidative stress, which lasts for several months in our conditions, and the cytotoxicity-promoting effect of NQO1 was compensated by other factors.…”

“…In terms of mechanisms, it is almost universally accepted that the most important cellular flavoenzyme performing a single-electron reduction in ArN→O and responsible for both their aerobic and hypoxic cytotoxicity is NADPH: cytochrome P450 reductase (POR) [ 18 , 19 ]. The role of other reductases is debatable (insufficiently characterized nuclear NAD(P)H-dehydrogenases [ 20 , 21 , 22 ]) and is of moderate importance with (NAD(P)H:quinone oxidoreductase (NQO1), catalyzing the mixed single- and two-electron reduction in ArNO [ 23 , 24 ]), or poorly studied (cytochromes P450 [ 25 , 26 ]). The study of TPZ-insensitive A549 cells also partly revealed the role of antioxidant enzymes since, in addition to decreased POR and NQO1 activity, superoxide dismutase (SOD) and glutathione reductase (GR) activity was increased, although catalase (CAT) activity increased modestly [ 27 ].…”

Injectable Living Probiotic Dressing Built by Droplet‐Based Microfluidics and Photo‐Cross‐Linking to Prevent Pathogenic Infection and Promote Wound Repair

“…Probiotic‐mediated therapy has caused widespread concern in recent years owing to its important roles in the treatment of various diseases. [ 8–11 ] In particular, probiotic has been used to prevent bacterial infections. For example, the inactivated Lactobacillus casei biofilm shows antibacterial effectiveness against methicillin‐resistant Staphylococcus aureus (MRSA) owe to the secretion of lactic acid and bacteriocin.…”