Azoreductases in drug metabolism

Abstract

Azoreductases are flavoenzymes that have been characterised in a range of prokaryotes and eukaryotes. Bacterial azoreductases are associated with the activation of two classes of drug, azo drugs for the treatment of inflammatory bowel disease and nitrofuran antibiotics. The mechanism of reduction of azo compounds is presented that requires tautomerisation of the azo compound to a quinoneimine and provides a unifying mechanism for the reduction of azo and quinone substrates by azoreductase. The importance of further work in characterisation of azoreductases from enteric bacteria is highlighted to aid in the development of novel drugs for the treatment of colon related disorders.Human azoreductases are known to play a crucial role in the metabolism of a number of quinone containing cancer chemotherapeutic drugs. The mechanism of hydride transfer to quinones, which is shared not only between eukaryotic and prokaryotic azoreductases but the wider family of NAD(P)H quinone oxidoreductases, is outlined. The importance of common SNPs in human azoreductases is described not only in cancer prognosis but also due to their effects on the efficacy of quinone drug based cancer chemotherapeutic regimens. This highlights the need to screen patients for azoreductase SNPs ahead of treatment with these regimens. Non-approved abbreviations5-ASA: 5-aminosalicylate, AcpD: acyl carrier protein phosphodiesterase, ecAzoR: E. coli azoreductase, FAD: flavin adenine dinucleotide, FMN: Flavin mononucleotide, hNQO1/2: human NAD(P)H quinone oxidoreductase 1 and 2, IBD: inflammatory bowel disease, MdaB: Modulator of drug activity B, NAD(P)H: Nicotinamide adenine dinucleotide (phosphate) reduced, NfsB: Nitrofurazone sensitivity protein B, NRH: (Wu et al., 1997) Introduction to azoreductasesAzoreductases are a group of diverse enzymes found in many bacterial and eukaryotic organisms (Fig 1 (Ryan et al., 2014)). The azoreductases discussed in this review are flavin-dependent (typically FMN) enzymes that are able to reductively cleave compounds containing an azo bond. Azo compounds are defined as those that contain an R 1 -N=N-R 2 group, where R 1 and R 2 are typically aromatic groups. Azoreductases are primarily cytosolic enzymes, however they have been shown to be secreted during exposure of bacteria to azo dyes (Morrison et al., 2015). The physiological role of these enzymes in the bacteria remains unclear, however they are constitutively expressed during growth in vitro (Chen et al., 2005;Wang et al., 2007) which suggests a role in homeostasis. The majority of azoreductase research is focused on their use in bioremediation where they can be used for the treatment of waste water contaminated with azo dyes from the textile and cosmetics industries (Singh et al., 2015). This review is unique in focusing on their role in the activation of several classes of drug.To date the majority of studies on azoreductases have been performed on enzymes from aerobic bacteria (Crescente et al., 2016;Nakanishi et al., 2001), in contrast only a single ...

Azoreductase: a key player of xenobiotic metabolism

“…The quinone reduction activities of azoreductase from different microorganisms and their dependence on NAD(P)H cofactor need to be classified as NAD(P)H quinone oxidoreductases (NQOs) (Liu et al 2008(Liu et al , 2009Ryan et al 2010a, b;Hervas et al 2012). As reviewed by Ryan (2017) and Koppel et al (2017), there are very few NQOs characterized from human gut bacterial strains. Recently, Ryan et al (2014) identified the NAD(P)H quinone oxidoreductase activity in azoreductase from P. aeruginosa and demonstrated that the azoreductases and the NAD(P)H quinone oxidoreductases belong to the same FMN-dependent azoreductase superfamily.…”

Drug metabolism and antibiotic resistance in micro‐organisms

“…Ryan is also an author of a review (Ryan, 2017) and a co-author of the paper by Da Silva et al 2017.…”

“…There are two classes of drug-metabolizing enzymes in bacteria discussed in this themed section: the azoreductases (Ryan, 2017) and the arylamine N-acetyltransferases (Kubiak et al, 2017). The azoreductases, which are found in gut bacteria, activate azo prodrugs, such as balsalazide, used in inflammatory bowel disease and also the nitrofuran group of antibiotics.…”

“…The azoreducatse flavoenzymes use the same mechanism to catalyse the release of the active component 5-aminosalicylate from the azo compound balsalazide or the formation of a highly reactive hydroxyamino group in nitrofurazone. The review (Ryan, 2017) also highlights the human equivalent of the azoreductases and the role of Single Nucleotide Polymorphisms in controlling its activity. The other bacterial drug-metabolizing enzymes discussed are the arylamine N-acetyltransferases, which acetylate arylamine and hydrazine drugs.…”

“Turn‐On” Activatable AIE Dots for Tumor Hypoxia Imaging

“…No fluorescencec ould be observed before the reduction reactiondue to the FRET-mediated quenching. After the enzyme treatment, the emission peak at 465 nm was observed when excited with 760 nm light, which is consistentwith the fluorescence emission of the TPE dots.As the azoreductases are reportedly over-expressedi nh ypoxic cancer cells, [38][39][40][41] we further tested whether PEG-Azo-TPE aggregates can be reducedt or estore TPE fluorescencei nh ypoxic tumor cell cultures. Figure 3s hows the fluorescence images of adherent A549 cells after the incubation with PEG-Azo-TPE under different oxygen concentrations.…”