Role of peroxidases, thiols and Bak/Bax in tumor cell susceptibility to Cu[DEDTC]2

Copper and two molecules of diethyl dithiocarbamate [DEDTC] form the Cu[DEDTC]2 complex, which shows cytotoxicity against melanoma and carcinoma cells, making it a potentially useful anti-cancer agent. The differential response to Cu[DEDTC]2 in susceptible human SKBR3 carcinoma and C8161 melanoma cell variants of moderate and high resistance to this organometallic complex was evaluated in this study. Both cell lines underwent apoptosis-associated PARP cleavage, changes in expression of nuclear NFkB p65, p21WAF1 and cyclin A, with loss of clonogenicity in response to this agent. However, a threefold greater concentration [IC50 0.6 μM DEDTC: 0.3 μM Cu] was required to kill moderately resistant C8161 melanoma compared to highly susceptible SKBR3 cells. Decreased susceptibility to Cu[DEDTC]2 in C8161 melanoma correlated with greater levels of glutathione peroxidase and catalase, and a fourfold lower requirement for N-acetyl cysteine (1 mM) to overcome toxicity. Whereas melanoma cells selected for resistance to [0.8 μM DEDTC: 0.4 μM Cu] showed persistent catalase and GPx activity, melanoma cells with moderate susceptibility showed decreased catalase and Gpx when responding to treatment. Cytotoxic response in moderately susceptible C8161 melanoma cells involved an early accumulation of pro-apoptotic Bax in the G2 cell cycle phase, followed by an increased ratio of pro-apoptotic Bak to anti-apoptotic Mcl-1 in mitochondria. Our data suggests that Cu[DEDTC]2 toxicity is mediated through an increase in pro-apoptotic Bak/Bax via disruption of the peroxide and thiol metabolism.