NQO1 and cancer: In present study; to further elucidate the potency of tested compounds as inducers of the cancer chemopreventive marker NQO1 at the functional level, we used an assay system at which the NQO1 substrate menadione (MD), a toxic quinone which is known to cause redox cycling and oxidative damage through 1-electron reduction catalyzed by NADH Cytochrome P450 reductase and this results in the formation of unstable toxic semiquinone [23].