Sulfur mustard-stimulated protease: A target for antivesicant drugs

One of the mechanisms of the skin blistering effect (vesication) of sulfur mustard (bis-(2-chloroethyl)sulfide, HD) is believed to be via the stimulation of specific protease(s) at the dermal-epidermal junction. Cultured normal human epidermal keratinocytes (NHEK) were used as a model to study and characterize protease stimulated by the mustards 2-chloroethyl ethyl sulfide (CEES), 2-chloro-N-(2-chloroethyl)-N-methylethanamine hydrochloride (nitrogen mustard, HN2) and HD. The results obtained using a chromozym (TRY) peptide substrate protease assay revealed the optimum mustard concentrations and time for protease stimulation to be about 200 muM (CEES), 100 muM (HN2) and 100 muM (HD) and 16 h. The mustardstimulated protease was membrane bound and was inhibited by adding a Ca2+ chelator (either 2 mM EGTA (ethylene glycol-bis(amino ethyl ether) N,N,N',N' tetraacetic acid) or 50 muM BAPTA AM (1,2-bis(z-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, tetraacetoxy methyl ester) alone or in combination), a serine protease inhibitor diisopropyl fluoro-phosphate (DFP, 1 mM), or a protein synthesis inhibitor cycloheximide (35 muM) in the extracellular medium. These results suggest that mustard toxicity may involve the stimulation of trypsin/chymotrypsin-like serine protease, dependent on Ca2+ and new protein synthesis. Protein purification by gel exclusion and hydrophobic chromatography produced a 70-80 kDa protease, which had an amino acid sequence homologous with a mammalian-type bacterial serine endopeptidase. Based on this information, research is in progress to identify the protease stimulated by HD in NHEK and to determine whether its inhibitors are useful as prospective antivesicant drugs. Published in 2002 by John Wiley Sons, Ltd.