Since diethyl dithiocarbamate (DEDTC) forms complexes with either
zinc or
copper, and
8-hydroxyquinoline (8-OHQ) also complexes with
copper, we now compared the cytotoxic activity of Cu[DEDTC]2, Zn[DEDTC]2 and Cu[8-OHQ]2. This report shows that at nanomolar levels, only
copper-[DEDTC]2, suppresses proliferation and clonogenicity of SKBR3 human
breast carcinoma, concurrently with induction of apoptosis-associated PARP fragmentation. Susceptibility to these agents was paralleled by reactive
oxygen generation (ROS) and greater expression of
anti-oxidant enzymes like MnSOD and
catalase, with no comparable effect on
Cu/Zn superoxide dismutase. The lethal effects of Cu[DEDTC]2 manifested when adding the two separate aqueous components or the preformed synthetic complexes in
DMSO, was prevented by N-acetyl
cysteine or
glutathione, with no comparable protection afforded by non-
thiol anti-oxidants like
mannitol or
DMSO. Exogenously added
catalase also protected cells from Cu[DEDTC]2, suggesting that this complex may kill after the levels of
superoxide anion [O2*-] dismutated by MnSOD increase
hydrogen peroxide-related stress. Cu[DEDTC]2 also induced p21WAF1, a cdk inhibitor usually not inducible in mutant p53
tumors like SKBR3
carcinoma, correlating with dephosphorylation of the
Sp1 transcription factor. Concentrations of Cu[DEDTC]2 cytotoxic for SKBR3
carcinoma did not induce comparable damage versus normal diploid human WI-38 fibroblasts. In contrast to the cytotoxic effect of nM levels of Cu[DEDTC]2 against SKBRR3 cells, no response was seen in the same cells exposed to 20 microM cis-platin. Since neither DEDTC bound to
zinc, nor
copper bound to 8-OHQ showed comparable cytotoxicity, our results suggest that the greater activity of
copper-DEDTC reflects a specific structure-activity relationship for the active complex. Since Cu[DEDTC]2 shows more effectiveness than other
metal-
chelator complexes, it may be worth further investigation as an alternative to
cancer therapies.