Diphenyl ditelluride anticancer activity and DNA topoisomerase I poisoning in human colon cancer HCT116 cells.

Diphenyl ditelluride (DPDT) is an organotellurium (OT) compound with pharmacological properties, including antioxidant, antigenotoxic and antimutagenic activities when applied at low concentrations. However, DPDT as well as other OT compounds also show cytotoxicity against mammalian cells when treatments occur at higher drug concentrations. Considering that the underlying mechanisms of toxicity of DPDT against tumor cells have been poorly explored, the objective of our study was to investigate the effects of DPDT against both human cancer and non-tumorigenic cells. As a model, we used the colonic HCT116 cancer cells and the MRC5 fibroblasts. Our results showed that DPDT preferentially targets HCT116 cancer cells when compared to MRC5 cells with IC50 values of 2.4 and 10.1 µM, respectively. This effect was accompanied by the induction of apoptosis and a pronounced G2/M cell cycle arrest in HCT116 cells. Furthermore, DPDT induces DNA strand breaks at concentrations below 5 µM in HCT116 cells and promotes the occurrence of DNA double strand breaks mostly during S-phase as measured by γ-H2AX/EdU double staining. Finally, DPDT forms covalent complexes with DNA topoisomerase I, as observed by the TARDIS assay, with a more prominent effect observed in HCT116 than in MRC5 cells. Taken together, our results show that DPDT preferentially targets HCT116 colon cancer cells likely through DNA topoisomerase I poisoning. This makes DPDT an interesting molecule for further development as an anti-proliferative compound in the context of cancer.

Influence of nucleotide excision repair on mitoxantrone cytotoxicity.

Mitoxantrone (MXT) is an anticancer drug structurally related to anthracyclines, such as doxorubicin (DOX). Here we report that cells deficient in nucleotide excision repair (NER) are very sensitive to MXT. However, cells deficient in each of the NER sub-pathways - transcription coupled repair (deficient in CSB protein) and global genome repair (deficient in XPC protein) - demonstrate a difference in sensitivity from each other and also show different responses in cell cycle profile, DNA synthesis and topo II DNA complex formation upon MXT treatment. XPC-deficient cells are slightly more resistant than CSB-deficient cells, and in the same way as MRC5 NER-proficient cells, show G2/M arrest, normal DNA synthesis rate and a pattern of formation of complexes similar to proficient cells, whereas CSB-deficient cells show accumulation in S phase, reduced DNA synthesis and a more intense signal of topo II DNA complexes, indicating that they remain longer in these cells. Complementation of CSB mutant cells with CSB rescue MXT-induced sensitivity and also a decrease in the signal intensity of the complexes, suggest that resolution of these lesions would take place. Taken together, our results indicate that NER proteins are implicated in the response to MXT and that CSB protein has a key role in processing MXT-induced topo II DNA complexes.

Antioxidant and anti-mutagenic effects of ebselen in yeast and in cultured mammalian V79 cells.

Ebselen has a wide spectrum of interesting therapeutic actions including antioxidant, cytoprotective, neuroprotective and anti-inflammatory activities. Since its antioxidant effect is very well known, this paper links the effects of ebselen in redox cellular status to its possible involvement in the maintenance of the integrity of genomic information by using Saccharomyces cerevisiae strains proficient and deficient in antioxidant defences and the mammalian V79 cell line. Using the alkaline comet assay, we showed that 5-10 microM ebselen does not induce DNA damage in V79 cells. Similarly, these same concentrations diminished the extent of the DNA damage induced by hydrogen peroxide (H(2)O(2)). The modified comet assay using DNA glycosylases (formamidopyrimidine-DNA glycosylase and endonuclease II) showed that after pre-treatment with ebselen followed by exposure to H(2)O(2), oxidative damage as recognized by these enzymes was significantly lower. In the same way, ebselen showed strong activity against H(2)O(2)-induced oxidative damage in the anti-mutagenic assay using S. cerevisiae N123 strain and in the antioxidative assay by using S. cerevisiae strains lacking antioxidant defences. This antioxidant effect was more pronounced for the gpx3 delta mutant, which indicated that ebselen acts by mimicking the GPx3 catalytic activity. The results confirm that ebselen is involved in antioxidant defence and that its antioxidant ability contributes to its anti-mutagenic and anti-genotoxic action.