The molecular mechanisms of toxicity and cellular transport of anticancer metallodrugs, including
platinum-based agents, have not yet been fully elucidated. The aim of our study was to investigate the relevance of
copper transporters (CTR1 and ATP7A/B), organic
cation transporters (OCT2) and the multidrug and toxin extrusion
proteins (MATE) in the intracellular accumulation of a novel organometallic cytotoxic Au(III) compound in
cancer cells in comparison to
cisplatin. Specifically, the synthesis and characterization of the
gold complex [Au(pyb-H)(PPh2Ar)Cl]PF6 (PPh2Ar = 3-[4-(diphenylphosphino)phenyl]-7-methoxy-2H-chromen-2-one] (1), featuring a
coumarin ligand endowed with "smart" fluorescence properties, have been achieved. Initially, the cytotoxic effects of both
cisplatin and 1 were studied in a small panel of human
cancer cells, and against a non-tumorigenic cell line in vitro. Thus, the human
ovarian cancer cell line A2780 and its
cisplatin resistant variant A2780cisR, were selected, being most sensitive to the treatment of the
gold complex. Co-incubation of the metallodrugs with
CuCl2 (a CTR1 substrate) increased the cytotoxic effects of both the Au(III) complex and
cisplatin; while co-incubation with
cimetidine (inhibitor of OCT2 and MATE) showed some effect only after 72 h incubation. ICP-MS (Inductively Coupled Plasma Mass Spectrometry) analysis of the
cell extracts showed that co-incubation with
CuCl2 increases Au and Cu accumulation in both
cancer cell lines, in accordance with the enhanced antiproliferative effects. Conversely, for
cisplatin, no increase in Pt content could be observed in both cell lines after co-incubation with either
CuCl2 or
cimetidine, excluding the involvement of CTR1, OCT2, and MATE in drug accumulation and overall anticancer effects. This result, together with the evidence for increased Cu content in A2780 cells after
cisplatin co-treatment with
CuCl2, suggests that
copper accumulation is the reason for the observed enhanced anticancer effects in this cell line. Moreover,
metal uptake studies in the same cell lines indicate that both 1 and
cisplatin are not transported intracellularly by CTR1 and OCT2. Finally, preliminary fluorescence microscopy studies enabled the visualization of the sub-cellular distribution of the
gold compound in A2780 cells, suggesting accumulation in specific cytosolic components/organelles.