Treatment of Pancreatic Cancer Cells with Dicumarol Induces Cytotoxicity and Oxidative Stress

Abstract

Purpose: NAD(P)H:quinone oxidoreductase (NQO₁) catalyzes the two-electron reduction of quinones to hydroquinones. This reaction is believed to prevent the one-electron reduction of quinones that would result in redox cycling with generation of superoxide (O₂^.-). We have recently demonstrated that inhibition of NQO₁ with dicumarol increases intracellular O₂^.- production and inhibits the in vitro malignant phenotype of pancreatic cancer cells (J. Cullen et al., Cancer Res., 63: 5513–5520, 2003). We hypothesized that inhibition of NQO₁ would increase cell killing, induce oxidative stress, and inhibit in vivo tumor growth. Experimental Design and Results: In the human pancreatic cancer cell line MIA PaCa-2, dicumarol decreased cell viability, as measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and decreased clonogenic survival. Dicumarol increased the percentage of apoptotic cells in a time-dependent and dose-dependent manner as measured by 3,3′-diaminobenzidine staining and flow cytometry, which was associated with cytochrome c release and poly(ADP-ribose) polymerase cleavage. Dicumarol also induced oxidative stress as evidenced by increased total glutathione and oxidized glutathione, as well as sensitizing to cell killing mediated by menadione. In established orthotopic pancreatic tumors in nude mice, intratumoral injections of dicumarol slowed tumor growth and extended survival. Conclusions: Inhibition of NQO₁ with dicumarol induces cell killing and oxidative stress in pancreatic cancer cells and speculate that dicumarol may prove to be useful in pancreatic cancer therapeutics.