Lewisite is a potent arsenic-based chemical warfare agent known to induce painful cutaneous inflammation and blistering. Only a few modestly effective antidotes have so far been described in the literature. However, the discovery of effective antidotes for lewisite was hampered by the paucity of the exact molecular mechanism underlying its cutaneous pathogenesis. We investigated the molecular mechanism underlying lewisite-induced cutaneous blistering and inflammation and describe its novel antidotes. On the basis of our initial screening, we used a highly sensitive murine model that recapitulates the known human pathogenesis of arsenicals-induced cutaneous inflammation and blistering. Topically administered lewisite induced potent acute inflammation and microvesication in the skin of Ptch1 þ/À /SKH-1 mice. Even at a very low dose, lewisite up-regulates unfolded protein response signaling, inflammatory response, and apoptosis. These cutaneous lesions were associated with production of reactive oxygen species and extensive apoptosis of the epidermal keratinocytes. We confirmed that activation of reactive oxygen speciesedependent unfolded protein response signaling is the underlying molecular mechanism of skin damage. Similar alterations were noticed in lewisitetreated cultured human skin keratinocytes. We discovered that chemical chaperone 4ephenyl butyric acid and antioxidant N-acetylcysteine, which significantly attenuate lewisite-mediated skin injury, can serve as potent antidotes. These data reveal a novel molecular mechanism underlying the cutaneous pathogenesis of lewisite-induced lesions. We also identified novel potential therapeutic targets for lewisite-mediated cutaneous injury.

Here, we report on the organic arsenical darinaparsin (ZIO-101, S-dimethylarsino-glutathione) and its anti-myeloma activity compared with inorganic arsenic trioxide. Darinaparsin induced apoptosis in multiple myeloma cell lines in a dose-dependent manner, and the addition of N-acetylcysteine, which increases intracellular glutathione (GSH), blocked cytotoxicity of both darinaparsin and arsenic trioxide. In contrast to arsenic trioxide, intracellular GSH does not appear to be important for darinaparsin metabolism, as an inhibitor of GSH synthesis, buthionine sulfoximine, had little effect on drug activity. This discrepancy was resolved when we determined the effects of thiols on drug uptake. The addition of exogenous GSH, L-cysteine, or D-cysteine prevented darinaparsin cellular uptake and cell death but had no effect on the uptake or activity of arsenic trioxide, suggesting a difference in the transport mechanism of these two drugs. In addition, gene expression profiling revealed differences in the signaling of protective responses between darinaparsin and arsenic trioxide. Although both arsenicals induced a transient heat shock response, only arsenic trioxide treatment induced transcription of metal response genes and anti-oxidant genes related to the Nrf2-Keap1 pathway. In contrast to the protective responses, both arsenicals induced up-regulation of BH3-only proteins. Moreover, silencing of BH3-only proteins Noxa, Bim, and Bmf protected myeloma cells from darinaparsin-induced cell death. Finally, treatment of an arsenic trioxide-resistant myeloma cell line with darinaparsin resulted in dose-dependent apoptosis, indicating that cross-resistance does not necessarily develop between these two forms of arsenic in multiple myeloma cell lines. These results suggest darinaparsin may be useful as an alternative treatment in arsenic trioxide-resistant hematologic cancers.