Di-2-pyridylketone-4,4,-dimethyl-3-thiosemicarbazone (
Dp44mT) is a potential candidate in
chelation therapy as an
iron chelator. This study showed that a combined treatment with 2μM easily available Fe(II), Cu(II) and Zn(II) each and 5μM
Dp44mT on eight different
cancer cell lines resulted in a 10-40-fold increase in the intracellular Cu content compared to control samples. The uptake of Cu and Cu-dependent cytotoxicity strictly depend on the Cu concentration of the culture medium. Even as low concentration of
Dp44mT as 0.1μM can transport high amounts of
copper inside the cells. The Cu accumulation and toxicity through
Dp44mT can hardly be influenced by Fe.
Copper uptake and toxicity triggered by 2μM extracellular Cu(II) and 5μM
Dp44mT could not be influenced by Fe(II) extracellular concentrations even 50-times higher than that of Cu(II). A 50-times higher Co(II) extracellular concentration hindered the Cu(II) uptake almost completely and a 10-times higher Co(II) concentration already decreased the Dp44mT-mediated Cu toxicity. Conditional complex stability constant determinations for
Dp44mT with Cu(II), Co(II), Fe(II), Ni(II) and Zn(II) revealed that the
metal-to-
ligand ratio is 1:1 in [Cu(II)
Dp44mT] complex, while for Co(II), Fe(II) and Ni(II) is 1:2. The highest stability constant was obtained for Cu(II) (lg β=7.08±0.05) and Co(II) (lg β2=12.47±0.07). According to our results,
Dp44mT in combination with Cu is highly toxic in vitro. Therefore, the use of
Dp44mT as an
iron chelator is limited if biologically available Cu is also present even at low concentrations.