Mode of action assessment of the genotoxic properties of antimony and its compounds evaluated in the ToxTracker assay.

Antimony (Sb) and its compounds are negative in gene mutation assays in bacteria and cultured mammalian cells but positive in some assays for clastogenicity and/or DNA damage. In order to better understand the modes of action for antimony genotoxicity, we assessed reporter gene activation by antimony and antimony compounds in the new expanded ToxTracker assay. ToxTracker evaluates the activation of biomarkers for different cellular defense mechanisms using a series of green fluorescent protein reporters inserted into mouse embryonic stem cell lines. The assay responds to: 1) DNA damage and inhibition of DNA replication; 2) oxidative stress; 3) unfolded protein response (protein damage); and 4) p53-dependent cellular stress. Sb metal powder, six trivalent (Sb(III)) compounds, and five pentavalent antimony (Sb(V)) compounds were assessed. Sb powder and all six Sb(III) compounds activated oxidative stress ToxTracker reporters at non-toxic doses. Of the five Sb(V) compounds, antimony pentachloride and potassium hexahydroantimonate induced a robust oxidative stress response while sodium antimonate induced only a weak oxidative stress response. At higher concentrations (up to either 75 % toxicity or the highest dissolved concentration tested), Sb powder and all Sb(III) compounds except for antimony trichloride induced the unfolded protein response. Of the five Sb(V) compounds tested, only potassium hexahydroantimonate induced weak activation of the unfolded protein response and was also the only pentavalent compound to yield modest (30 %) cytotoxicity. None of the compounds tested activated the DNA damage/inhibition of DNA replication reporters, nor did they activate the p53-dependent response. All Sb(III) compounds, Sb powder, and three of the five Sb(V) compounds activated the oxidative stress reporters, but there was no activation of reporters associated with DNA damage and repair or p53-dependent cellular stress. The consistent activation of reporters for oxidative stress suggests this mode of action may underlie genotoxicity responses for antimony and its compounds.
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