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

Abstract

Summary DT-diaphorase is a two-electron-reducing enzyme that is an important activator of bioreductive anti-tumour agents, such as mitomycin C (MMC) and E09, and is inducible by many compounds, including 1,2-dithiole-3-thiones (D3Ts). We showed previously that D3T selectively increased DT-diaphorase activity in mouse lymphoma cells compared with normal mouse marrow cells, and also increased MMC or E09 cytotoxic activity in the lymphoma cells with only minor effects in the marrow cells. In this study, we found that D3T significantly increased DT-diaphorase activity in 28 of 38 human tumour cell lines representing ten tissue types with no obvious relationships between the tumour type, or the base level of DT-diaphorase activity, and the ability of D3T to increase the enzyme activity. Induction of DT-diaphorase activity in human tumour cell lines by 12 D3T analogues varied markedly with the D3T structure. D3T also increased DT-diaphorase activity in normal human bone marrow and kidney cells but the increases were small in these cells. In addition, D3T increased the level of enzyme activity in normal human lung cells. Pretreatment of human tumour cells with D3T analogues significantly increased the cytotoxic activity of MMC or E09 in these cells, and the level of enhancement of anti-tumour activity paralleled the level of DT-diaphorase induction. In contrast, D3T did not effect the toxicity of E09 in normal kidney cells. These results demonstrate that D3T analogues can increase DT-diaphorase activity in a wide variety of human tumour cells and that this effect can enhance the anti-tumour activity of the bioreductive agents MMC and E09.

Dietary induction of NQO1 increases the antitumour activity of mitomycin C in human colon tumours in vivo

“…Treatment of HCT116 cells in vitro with DMF for 48 h increased NQO1 activity in these cells by two-fold (Po0.001), and cells that were pretreated with DMF were 1.4-fold more sensitive to MMC than cells that were not pretreated (Po0.001). This result was similar to our previous findings in murine lymphoma cells (Begleiter et al, 1996) and human breast, lung and colon cancer cells (Doherty et al, 1998;Wang et al, 1999) using synthetic inducers of NQO1.…”

“…Cells with elevated NQO1 levels are generally more sensitive to MMC (Begleiter et al, 1989;Marshall et al, 1989;Siegel et al, 1990), and NQO1 can be induced by a wide variety of dietary and synthetic agents (Talalay et al, 1988;Prestera et al, 1993). We have previously shown that NQO1 activity can be selectively increased in tumour cells compared with normal cells, and that this enhances MMC cytotoxicity in human and murine cell lines in vitro (Doherty et al, 1998;Wang et al, 1999). In this study we investigated a novel approach to increasing the antitumour activity of MMC by using a dietary component to selectively induce NQO1 activity in tumour cells compared with normal cells.…”

“…In addition, it should be noted that the potential toxic effects of combining DMF diet with MMC were studied in a mouse model, while the antitumour effects were studied in human tumours. Although we have previously shown that induction of NQO1 in human and murine tumours and in human and murine bone marrow cells is similar (Begleiter et al, 1996;Doherty et al, 1998), induction of NQO1 in other human tissues has not been extensively studied. This suggests that caution should be used in applying this approach to enhancing the antitumour activity of MMC in the clinic.…”

“…NQO1 activity was measured as described previously (Doherty et al, 1998) using menadione as electron acceptor and is reported as nmol MTT reduced min À1 mg protein À1 . Protein was determined with the Bio-Rad DC kit using gamma-globulin as protein standard.…”

“…Thus, selectively increasing the level of NQO1 in tumour cells by gene transfer (Rauth et al, 1998) or by selective induction of NQO1 in tumours may be useful for enhancing the efficacy of bioreductive agents. We showed previously that we could selectively increase NQO1 activity in tumour cells compared with normal cells and that this enhanced MMC antitumour activity in vitro (Doherty et al, 1998;Wang et al, 1999). In this study we investigated whether we could selectively induce NQO1 activity in human tumours implanted in a nude mouse model, and if this would increase the antitumour activity of bioreductive agents without increasing the toxicity of these agents.…”