Insufficient therapeutic effect of auranofin (AF), used in the treatment of rheumatoid arthritis, is found in about 8% of the patients included in clinical trials until now. The mechanisms of resistance to gold-containing drugs are not known, but one reason might be acquired drug resistance. We have studied the relationship between the effects of gold and concentration of the cytoplasmic metal-binding protein metallothionein (MT), in order to evaluate MT as a possible contributing factor to resistance against AF. Different strains of cultured human epithelial cells derived from normal skin, treated with AF, were used as models. The experiments indicate two possible mechanisms for resistance against AF in cells: 1) binding of gold to pre-existent cadmium-induced MT or to de novo AF-induced MT, and 2) the cells' ability to keep the intracellular gold concentration at a low level. AF apparently causes a rapid and pronounced increase of MT-content in these cells. Preliminary results also indicated that AF causes increase of MT-content in human rheumatoid synovial cells, grown as primary cultures. These findings may have two clinical implications: 1) AF-induced MT may decrease therapeutic response, and 2) decrease the toxicity of AF.
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