Antimelanoma activity of the redox dye DCPIP (2,6-dichlorophenolindophenol) is antagonized by NQO1.

Altered redox homeostasis involved in the control of cancer cell survival and proliferative signaling represents a chemical vulnerability that can be targeted by prooxidant redox intervention. Here, we demonstrate that the redox dye 2,6-dichlorophenolindophenol (DCPIP) may serve as a prooxidant chemotherapeutic targeting human melanoma cells in vitro and in vivo. DCPIP-apoptogenicity observed in the human melanoma cell lines A375 and G361 was inversely correlated with NAD(P)H:quinone oxidoreductase (NQO1) expression levels. In A375 cells displaying low NQO1 activity, DCPIP induced apoptosis with procaspase-3 and PARP cleavage, whereas G361 cells expressing high levels of enzymatically active NQO1 were resistant to DCPIP-cytotoxicity. Genetic (siRNA) or pharmacological (dicoumarol) antagonism of NQO1 strongly sensitized G361 cells to DCPIP apoptogenic activity. DCPIP-cytotoxicity was associated with the induction of oxidative stress and rapid depletion of glutathione in A375 and NQO1-modulated G361 cells. Expression array analysis revealed a DCPIP-induced stress response in A375 cells with massive upregulation of genes encoding Hsp70B' (HSPA6), Hsp70 (HSPA1A), heme oxygenase-1 (HMOX1), and early growth response protein 1 (EGR1) further confirmed by immunodetection. Systemic administration of DCPIP displayed significant antimelanoma activity in the A375 murine xenograft model. These findings suggest feasibility of targeting tumors that display low NQO1 enzymatic activity using DCPIP.