Cellular association, intracellular distribution, and efflux of auranofin via sequential ligand exchange reactions.

Auranofin (AF), an orally active, antiarthritic agent, modulates the functional activities of macrophages in vivo and in vitro. To better understand the molecular mechanism of action of auranofin with macrophages we have investigated its cellular association, intracellular distribution, and efflux with RAW 264.7 cells using auranofin radiolabeled within the triethylphosphine (Et3P) [3H], the gold [195Au] or the tetraacetylthioglucose (TATG)[14C] moieties of the molecule. Evaluation of the effects of auranofin on RAW 264.7 cells demonstrates that (1) cellular association of this compound was concentration, time and temperature dependent; (2) cellular association of AF was inhibited by N-ethylmaleimide but not by 2,4-dinitrophenol and NaF; (3) cellular association and uptake of Au and Et3P into cells was reduced when the drug was preincubated with increasing concentrations of fetal calf serum and albumin; (4) no tetraacetylthioglucose from the auranofin molecule became cell associated whereas the Au and Et3P moieties were internalized and distributed between the nuclear, cytosolic and membrane fractions of cells; and (5) efflux of Au and Et3P from RAW 264.7 cells was time and temperature dependent. Based on these data we propose a model, a sequential ligand exchange process, that describes the molecular interactions of auranofin and possibly other gold compounds with these cells.