5-Methoxy-1,2-dimethyl-3-[(4-nitrophenoxy)methyl]indole-4,7-dione, a mechanism-based inhibitor of NAD(P)H:quinone oxidoreductase 1, exhibits activity against human pancreatic cancer in vitro and in vivo

Abstract

The enzyme NAD(P)H:quinone oxidoreductase 1 (NQO1) has been found to be up-regulated in pancreatic cancer as well as many other solid tumors. A recent study showed that inhibition of NQO1 in pancreatic cancer cells using the nonselective inhibitor dicumarol suppressed the malignant phenotype. The authors suggested that inhibition of cell growth might result from an increase in intracellular superoxide production due to inhibition of NQO1. We have recently shown that NQO1 can directly scavenge superoxide and this effect may become physiologically relevant in cells containing high NQO1 levels. We therefore tested the hypothesis that 5-methoxy-1,2-dimethyl-3-[(4-nitrophenoxy)methyl]indole-4,7-dione (ES936), a specific mechanism-based inhibitor of NQO1, would be an effective agent for the treatment of pancreatic tumors. The human pancreatic tumor cell lines BxPC-3 and MIA PaCa-2 contain high levels of NQO1 activity and protein as verified by immunoblot and immunocytochemical staining of human pancreatic tumor cells. ES936 treatment inhibited NQO1 activity by >98% in MIA PaCa-2 and BxPC-3 cells. In addition, ES936 treatment induced growth inhibition [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay] in MIA PaCa-2 and BxPC-3 cells with an IC 50 of 108 and 365 nmol/L, respectively. Treatment of MIA PaCa-2 cells with ES936 also inhibited the ability of these cells to form colonies and grow in soft agar in a dose-dependent manner. Treatment of mice carrying MIA PaCa-2 xenograft tumors with ES936 resulted in a significant difference in growth rates in ES936-treated and DMSO-treated (control) tumors. Our data did not show an increase in either intracellular superoxide production or oxygen consumption after treatment of cells with ES936, contrary to the effects seen with dicumarol. In summary, mechanism-based inhibitors of NQO1, such as ES936, may be useful therapeutic agents for the treatment of pancreatic cancer, although the underlying mechanism seems to be independent of superoxide generation. [Mol Cancer Ther 2006;5(7):1702 -9]

Potent Activity of Indolequinones against Human Pancreatic Cancer: Identification of Thioredoxin Reductase as a Potential Target

“…After reduction to the hydroquinone form by NQO1, ES936 loses the p-nitrophenol leaving group from the indole 3-position, and the iminium ion generated subsequently reacts with tyrosine residues in the active site of NQO1, resulting in the inhibition of enzymatic activity (Winski et al, 2001). ES936 and analogs were found to be active against human pancreatic cancer (Dehn et al, 2006); however, the antitumor activity of ES936 and analogs did not correlate with their ability to inhibit NQO1 Reigan et al, 2007). We corroborated this finding in the current study using three different classes of indolequinone analogs.…”

“…We have reported previously the development of an indolequinone, 5-methoxy-1,2-dimethyl-3-[(4-nitrophenoxy)methyl]-indole-4,7-dione (ES936, 1), that exhibited potent growth inhibition effects against human pancreatic cancer cell lines (Dehn et al, 2006). The antitumor activity of ES936 was originally attributed to its role as a mechanism-based inhibitor of human NQO1 [NAD(P)H:quinone oxidoreductase 1 (DT-diaphorase; EC 1.6.99.2)] (Winski et al, 2001).…”

“…Current treatment options of radiation therapy, chemotherapy, and surgery have been ineffective at improving the survival rate (Ghaneh et al, 2007). Development of novel targeted therapeutic approaches is desperately needed.We have reported previously the development of an indolequinone, 5-methoxy-1,2-dimethyl-3-[(4-nitrophenoxy)methyl]-indole-4,7-dione (ES936, 1), that exhibited potent growth inhibition effects against human pancreatic cancer cell lines (Dehn et al, 2006). The antitumor activity of ES936 was originally attributed to its role as a mechanism-based inhibitor of human NQO1 [NAD(P)H:quinone oxidoreductase 1 (DT-diaphorase; EC 1.6.99.2)] (Winski et al, 2001).…”

“…Tumor volume was calculated by the formula (L ϫ W 2 )/2, where L is the longer measurement of the tumor and W is the smaller tumor measurement. Ratios of tumor volumes of treated and control tumors as an indicator of drug efficacy were calculated as described previously (Dehn et al, 2006).…”

Synthesis and Evaluation of 3-Aryloxymethyl-1,2-dimethylindole-4,7-diones as Mechanism-Based Inhibitors of NAD(P)H:Quinone Oxidoreductase 1 (NQO1) Activity

“…The compound is also effective in vivo; MIA PaCa-2 xenografts in mice grow significantly slower after treatment with 1. 19 However, in the case of 1, our studies showed that the cytotoxicity was independent of superoxide generation, and therefore raises the question of whether NQO1 inhibition is the only mechanism operating in pancreatic cancer cells.…”