Comparative in vitro investigation of anticancer copper chelating agents

Abstract

Evaluation of in vitro cytotoxicity of several Cu chelating agents - 2,2′-biquinoline, 8-hydroxyquinoline (oxine), ammonium pyrrolidinedithiocarbamate (APDTC), di-2-pyridylketone-4,4,-dimethyl-3-thiosemicarbazone (Dp44mT), dithizone and neocuproine – on HT-29 human colon adenocarcinoma as well as long term in vitro cytostatic effect were assessed in the presence of Cu(II) ions. Intracellular Cu accumulation was observed for each chelating agent. Cytotoxicity was also investigated on HCT-15 and HCT-116 human colon adenocarcinomas, HT-1080 human fibrosarcoma, A-375 malignant melanoma, MCF-7, MDA-MB-231 and ZR-75-1 human breast adenocarcinomas as well as MeT-5A and P31wt mesothelioma. For both short and long term antiproliferative studies, each chelating agent proved to be much more effective in the presence of Cu(II) ions. Generally, the following cytotoxicity order could be established on each cell line: Dp44mT>neocuproine>APDTC>oxine>2,2′ biquinoline≈dithizone. The IC50 values even showed one order of magnitude difference among the cell lines. Considerable differences were also observed for colony formation and spheroid growth inhibition. Thus, for Dp44mT and neocuproine, practically no resistant cell line could be developed, whereas for the rest of the chelating agents the long term survival was ensured. By raising the Cu(II) concentration from 0.5μM to 50μM, dramatically higher apoptotic processes were induced for Dp44mT and oxine after just 20min. Elevated Cu(II) concentration activated reactive oxygen species generation. The investigated chelating agents restored the DNA damage caused by free Cu(II). Thus, DNA is not the target of the intracellular Cu accumulation. However, DNA intercalation was observed for the Cu(II) and neocuproine combination.