Methimazole, an Effective Neutralizing Agent of the Sulfur Mustard Derivative 2-Chloroethyl Ethyl Sulfide

Sulfur mustard (SM),designated by the military as HD, is a highlytoxic and dangerous vesicant that has been utilized as a chemicalwarfare agent since World War I. Despite SM's extensive history,an effective antidote does not exist. The effects of SM are predominantlybased on its ability to alkylate important biomolecules. Also, withthe potential for a fraction of SM to remain unreacted up to daysafter initial contact, a window of opportunity exists for direct neutralizationof unreacted SM over the days following exposure. In this study, weevaluated the structure-activity relationship of multiple nucleophilicmolecules to neutralize the toxic effects of 2-chloroethyl ethyl sulfide(CEES), a monofunctional analogue of SM, on human keratinocyte (HaCaT)cells. Cell viability, relative loss of extracellular matrix adhesions,and apoptosis caused by CEES were measured via MTT, cell-matrixadhesion (CMA), and apoptosis protein marker assays, respectively.A set of five two-carbon compounds with various functional groupsserved as a preliminary group of first-generation neutralizing agentsto survey the correlation between mitigation of CEES's toxiceffects and functional group nucleophilicity. Apart from thioacids,which produced additive toxicity, we generally observed the trendof increasing protection from cytotoxicity with increasing nucleophilicity.We extended this treatment strategy to second-generation agents whichcontained advantageous structural features identified from the first-generationmolecules. Our results show that methimazole (MIZ), a currently FDA-approveddrug used to treat hyperthyroidism, effectively reduced cytotoxicity,increased CMA, and decreased apoptosis resulting from CEES toxicity.MIZ selectively reacts with CEES to produce 2-(2-(ethylthio)ethylthio)-1-methyl-1H-imidazole (EEMI) in media and cell lysate treatments resultingin the reduction of toxicity. Based on these results, future developmentof MIZ as an SM therapeutic may provide a viable approach to reduceboth the immediate and long-term toxicity of SM and may also helpmitigate slower developing SM toxicity due to residual intact SM.