Inhibition of colon carcinogenesis by post-initiation induction of NQO1 in Sprague-Dawley rats.

Inducers of phase II detoxifying enzymes have been studied as chemopreventive agents for a variety of cancers. Phase II detoxifying enzymes may play a significant role in preventing carcinogen-induced colon cancer at the initiation and post-initiation stage, but the contribution of NAD(P) H:quinone oxidoreductase 1 (NQO1) to this effect remains unclear. Using the carcinogen-induced colon cancer Sprague-Dawley rat model, we previously showed that oltipraz selectively induces NQO1 in the colons of these rats without inducing other phase II detoxifying enzymes.

Delayed sodium thiosulphate administration reduces cisplatin efficacy on mouse EMT6 tumour cells in vitro.

Objective: To determine whether simultaneous and/or delayed administration of sodium thiosulphate (STS) affects the oncologic effect of cisplatin or cisdiaminedichloroplatinum (CDDP) in EMT6 tumour cells in vitro.

Setting: Cell biology research laboratory.

Methods: Clonogenic assays of EMT6 tumour cells with CDDP alone, CDDP plus simultaneous STS, and CDDP plus a 4-hour delay of STS were performed.

A Model for NAD(P)H:Quinoneoxidoreductase 1 (NQO1) Targeted Individualized Cancer Chemotherapy.

NQO1 (NAD(P)H:quinoneoxidoreductase 1) is a reductive enzyme that is an important activator of bioreductive antitumor agents. NQO1 activity varies in individual tumors but is generally higher in tumor cells than in normal cells. NQO1 has been used as a target for tumor specific drug development.

Investigation of an NQO1 polymorphism as a possible risk and prognostic factor for chronic lymphocytic leukemia.

NAD(P)H:quinoneoxidoreductase 1 (NQO1) inhibits some cancers and increases p53 and apoptosis in cells. Due to an inactivating polymorphism, 10% of humans have no NQO1 activity. A case:control study suggested that chronic lymphocytic leukemia (CLL) patients may have an increased incidence of the NQO1 null genotype compared with controls.

Role of NADPH cytochrome P450 reductase in activation of RH1.

Purpose: RH1 is a new bioreductive agent that is an excellent substrate for the two-electron reducing enzyme, NAD(P)H quinone oxidoreductase 1 (NQO1). RH1 may be an effective NQO1-directed antitumor agent for treatment of cancer cells having elevated NQO1 activity. As some studies have indicated that RH1 may also be a substrate for the one-electron reducing enzyme, NADPH cytochrome P450 reductase (P450 Red), P450 Red may contribute to the activation of RH1 where NQO1 activities are low and P450 Red activities are high.

A NAD(P)H:quinone oxidoreductase 1 polymorphism is a risk factor for human colon cancer.

Colon cancer is one of the most common cancers in North America and generally develops from colonic epithelial cells following initiation by carcinogens. We have shown that the phase II detoxifying enzyme, NAD(P)H:quinone oxidoreductase 1 (NQO1) contributes to the inhibition of carcinogen-induced colon cancer in rats at both the initiation and postinitiation stages. An inactivating polymorphism at base 609 of the NQO1 gene, (609)C (NQO1 *1) --> (609)T (NQO1 *2), occurs at high frequency in the human population.

The reductive activation of the antitumor drug RH1 to its semiquinone free radical by NADPH cytochrome P450 reductase and by HCT116 human colon cancer cells.

RH1 (2,5-diaziridinyl-3-(hydroxymethyl)-6-methyl-1,4-benzoquinone), which is currently in clinical trials, is a diaziridinyl benzoquinone bioreductive anticancer drug that was designed to be activated by the obligate two-electron reductive enzyme NAD(P)H quinone oxidoreductase 1 (NQO1). In this electron paramagnetic resonance (EPR) study we showed that RH1 was reductively activated by the one-electron reductive enzyme NADPH cytochrome P450 reductase and by a suspension of HCT116 human colon cancer cells to yield a semiquinone free radical. As shown by EPR spin trapping experiments RH1 was reductively activated by cytochrome P450 reductase and underwent redox cycling to produce damaging hydroxyl radicals in reactions that were both H2O2- and iron-dependent.

Structure-activity studies with cytotoxic anthrapyrazoles.

Anthrapyrazoles have been investigated as cancer chemotherapeutic agents. The mechanism of action of these compounds is thought to involve inhibition of DNA topoisomerase II. A structure-activity study was carried out to determine the in vitro cytotoxic activity of nine novel anthrapyrazoles against human breast carcinoma, head and neck squamous cell carcinoma and leukemia cells, and against Chinese hamster ovary cells.

Sodium thiosulphate impairs the cytotoxic effects of cisplatin on FADU cells in culture.

Objectives: To study the effect of cisplatin (CDDP) on FADU human squamous cell carcinoma cells and to determine if sodium thiosulphate (STS), an agent protective against CDDP ototoxicity, affects the tumoricidal activity of CDDP.

Method: FADU tumour cells were grown in culture. Cells were exposed to varying concentrations of CDDP with and without concomitant STS, and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assays were then performed to determine the effect of treatment on FADU cell growth.

Effect of sodium thiosulphate and cis-diamminedichloroplatinum on FADU tumour cells in nude mice.

Objectives: To study the effect of cis-diamminedichloroplatinum (CDDP) on FADU squamous cell carcinoma cells in a nude mouse model and to determine the effect of sodium thiosulphate (STS) on CDDP activity.

Methods: CD1 nude mice were inoculated with FADU tumour cells to both flanks. They were then randomized to four treatment groups: control, CDDP only, STS only, or CDDP and STS.

Role of NQO1 polymorphisms as risk factors for squamous cell carcinoma of the head and neck.

A case: control study was carried out to determine if inactivating polymorphisms of the NQO1 gene at bases 609 and 465 are associated with altered risk of developing squamous cell carcinoma of the head and neck (SCCHN). Genotyping was carried out by PCR RFLP analysis on whole blood samples. The frequency of the inactive 609T and active 609C forms, and the inactive 465T and active 465C forms, of NQO1 were compared in patient and control groups by a logistic regression analysis and odds ratios (ORs) were calculated.

Structure-activity study of the interaction of bioreductive benzoquinone alkylating agents with DNA topoisomerase II.

Purpose: Quantitative structure-activity studies were performed on a series of benzoquinone mustard (BM) bifunctional alkylating agents to determine whether DNA topoisomerase II (topo II) inhibition was responsible for cell growth inhibition.

Methods: Topo II inhibition was evaluated by decatenation and agarose gel electrophoresis assays.

Results: The BM compounds were shown to potently inhibit the decatenation activity of topo II.

Effect of NQO1 induction on the antitumor activity of RH1 in human tumors in vitro and in vivo.

NQO1 is a reductive enzyme that is important for the activation of many bioreductive agents and is a target for an enzyme-directed approach to cancer therapy. It can be selectively induced in many tumor types by a number of compounds including dimethyl fumarate and sulforaphane. Mitomycin C is a bioreductive agent that is used clinically for treatment of solid tumors.

Structure-activity study with bioreductive benzoquinone alkylating agents: effects on DT-diaphorase-mediated DNA crosslink and strand break formation in relation to mechanisms of cytotoxicity.

Purpose: Structure-activity studies were carried out with the model bioreductive alkylating agent benzoquinone mustard (BM) and its structural analogs. The specific objectives were: (1) to investigate the effects of functional group substitutions to the benzoquinone ring on DNA crosslink and strand break formation subsequent to reduction of the analogs by DT-diaphorase (DTD) in vitro, (2) to correlate DNA crosslink and strand break formation by the analogs with anaerobic reduction of the BM analogs by DTD and their redox cycling in vitro, and (3) to correlate DNA crosslink and strand break formation by the BM analogs with their cytotoxic effects in cancer cells.

Methods: DNA interstrand crosslink and single-strand break formation were assessed using agarose gel assays.

Role of the TRAIL/APO2-L death receptors in chlorambucil- and fludarabine-induced apoptosis in chronic lymphocytic leukemia.

The standard treatments for chronic lymphocytic leukemia (CLL) include the alkylating agent chlorambucil (CLB) and the nucleoside analog fludarabine (F-ara-AMP, Flu). Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a death receptor ligand that induces apoptosis preferentially in tumors. However, CLL cells seem to be resistant to TRAIL-induced apoptosis.

Induction of NAD(P)H quinone: oxidoreductase1 inhibits carcinogen-induced aberrant crypt foci in colons of Sprague-Dawley rats.

Phase II detoxifying enzymes like NAD(P)H (quinone acceptor)oxidoreductase1 (NQO1), glutathione S-transferases (GST), and UDP-glucuronyltransferases (UGT) may play an important role in preventing carcinogen-induced cancers. Inducers of these enzymes have been shown to inhibit carcinogen-induced colon tumors in rat and mouse models. However, it has not been clearly demonstrated that NQO1 contributes to this effect.

Lack of NQO1 induction in human tumor cells is not due to changes in the promoter region of the gene.

DT-diaphorase is a two-electron reducing enzyme that is an important detoxifying enzyme and activator of bioreductive antitumor agents. Expression of the DT-diaphorase gene, NQO1, appears to be transcriptionally regulated, and the gene is induced by a wide variety of compounds. We showed that 1,2-dithiole-3-thione can selectively increase DT-diaphorase activity in human and murine tumors, and that this enhanced the antitumor activity of bioreductive antitumor agents.

The effect of functional groups on reduction and activation of quinone bioreductive agents by DT-diaphorase.

Purpose: Bioreductive antitumor agents are an important class of anticancer drugs that include the clinically used drug, mitomycin C, and new agents such as EO9 and tirapazamine that have recently been tested in clinical trials. These agents require activation by reductive enzymes such as DT-diaphorase or NADPH:cytochrome P450 reductase. A major focus for improving cancer chemotherapy has been to increase the selectivity and targeting of antitumor drugs to tumor cells.