NAD(P)H:Quinone oxidoreductase1 (DT-diaphorase) expression in normal and tumor tissues

Abstract

NAD(P)H:Quinone Oxidoreductase1 (NQO1) also known as DT-diaphorase is a flavoprotein that catalyzes the two-electron reduction of quinones, quinone imines and azo-dyes and thereby protects cells against mutagenicity and carcinogenicity resulting from free radicals and toxic oxygen metabolites generated by the one-electron reductions catalyzed by cytochromes P450 and other enzymes. High levels of NQO1 gene expression have been observed in liver, lung, colon and breast tumors as compared to normal tissues of the same origin. The transcription of the NQO1 gene is activated in response to exposure to bifunctional (e.g. beta-naphthoflavone (beta-NF), 2, 3, 7, 8 tetrachorodibenzo-p-dioxin (TCDD)) and monofunctional (phenolic antioxidants/chemoprotectors e.g. 2(3)-tert-butyl-4-hydroxy-anisole (BHA)) inducers. The high level of expression of the NQO1 gene and its induction by beta-NF and BHA require the presence of an AP1 binding site contained within the human Antioxidant Response Element (hARE) and are mediated by products of proto-oncogenes, Jun and Fos. Induction of NQO1 gene expression involves transfer of a redox signal from xenobiotics to unknown 'redox protein(s)' which in turn, modify the Jun and Fos proteins for greater affinity towards the AP1 site of the NQO1 gene and activates transcription. The expression and regulation of the NQO1 gene is complex as many additional cis-elements have been identified in the promoter region and is a subject of great future interest. In addition to established tumors, NQO1 gene expression is also increased in developing tumors, indicating a role in cellular defense during tumorigenesis. It has been proposed that low molecular weight substance(s) can diffuse from tumor cells into surrounding normal cells and activate the expression of the NQO1 gene. Purification and characterization of such substance(s) may provide important information in regard to the mechanism of activation of NQO1 gene expression and the role of increased NQO1 expression in tumor development. In view of the general consensus that NQO1 is over-expressed in tumor cells and the realization that NQO1 may either activate or detoxify xenobiotics, it is important to establish the role of NQO1 in the activation, and the detoxification of xenobiotics and drugs and in the intrinsic sensitivity of tumors to bioreductive alkylating aziridinyl benzoquinones such as diaziquone (AZQ), mitomycin C (MMC), and indoloquinone EO9, as well as to the dinitrophenyl aziridine, CB1954, and the benzotriazine-di-N-oxide, SR 4233.

Induction of DT-diaphorase by 1,2-dithiole-3-thiones in human tumour and normal cells and effect on anti-tumour activity of bioreductive agents

“…Regulation of expression of DT-diaphorase activity is complex and may include regulation of transcription (Jaiswal, 1991;Belinsky and Jaiswal, 1993;Yao and O'Dwyer, 1995;Wang and Williamson, 1996), altemative splicing of DT-diaphorase mRNA Hu et al, 1996;Yao et al, 1996) and the presence of a polymorphism due to a mutation at position 609 of British Journal of Cancer (1998) 77(8) at 370C with or without 50 gM D3T for 48 h. Cells were then treated with various concentrations of E09 for 1 h. Surviving cell fraction was determined by MUT assay (Johnston et al, 1994). The points represent the mean surviving cell fraction ± standard error of five determinations.…”

“…The enzyme is found in all eukaryotes and is present at varying levels in most tissues (Benson et al, 1980;Belinsky and Jaiswal, 1993). DT-diaphorase is located mainly in the cytosol, but 5-10% is membrane bound in mitochondria, microsomes and Golgi apparatus (Riley and Workman, 1992).…”

“…The enzyme has two identical subunits with individual molecular weights of 32 kDa and requires NADH or NADPH as an electron donor for enzymatic activity (Riley and Workman, 1992). Several DT-diaphorases have been identified in humans (Jaiswal et al, 1990;Jaiswal, 1991), but the NQO, gene has been most extensively studied and appears to be most important for activation of bioreductive anti-tumour agents (Jaiswal, 1991;Riley and Workman, 1992;Belinsky and Jaiswal, 1993). Enzyme levels have been shown to be relatively high in mouse and/or human stomach, bladder, intestine, colon and kidney, but are usually low in liver, lung and haematopoietic cells (Benson et al, 1980;Schlager and Powis, 1990;Smitskamp-Wilms et al, 1995).…”

“…Enzyme levels have been shown to be relatively high in mouse and/or human stomach, bladder, intestine, colon and kidney, but are usually low in liver, lung and haematopoietic cells (Benson et al, 1980;Schlager and Powis, 1990;Smitskamp-Wilms et al, 1995). DT-diaphorase activity is higher in some tumour cells than in the corresponding normal cells, with elevated levels of enzyme activity having been observed in human liver, colon, breast and lung tumour cells (Schlager and Powis, 1990;Malkinson et al, 1992;Belinsky and Jaiswal, 1993;Smitskamp-Wilms et al, 1995).…”

Expression of the prodrug-activating enzyme DT-diaphorase via Ad5 delivery to human colon carcinoma cells in vitro

“…16 DTD is a bioreductive enzyme that can activate a variety of prodrugs, including quinone -based drugs, to DNA alkylating agents. DTD activity has been reported to be elevated in a range of tumor types 30 such as in human non -small cell lung cancer, 13,14 breast, liver, 31 and colon tumors relative to surrounding normal tissue. It has been proposed that various prodrugs that are substrates for DTD could be useful for the treatment of tumors with high DTD activity.…”