Acquired Resistance against Gold(III)-Chloride in Cultured human cells

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Abstract
Acquired resistance against gold(III)-chloride was developed in cultures of human epithelial cells derived from normal skin, by growing them with stepwise increased concentrations of the compound in the medium. Resistance to 350 μmol gold-chloride/l, about twice the commonly tolerated concentration and an otherwise lethal concentration to the cells, was attained after an adaptation period of 2–3 months. These cells had preserved their normal appearance except from small inclusion bodies in the cytoplasm. The effect of 350 μmol gold-chloride/l culture medium on cell growth of the sensitive (HE) and resistant (HEAu350) cell strain, was tested over a period of 9 days. On day 9, 2% of the HE cells and 80% of the HEAu350 cells remained adherent to the flasks compared with their non-treated control cells. The doubling time of the HE cells grown without gold was 24 h, that of the HEAu350 cells grown continuously on 350 μmol/l was 36 h. The HE cells died on prolonged exposure to this concentration. Measurement of the cellular content of Au, Cu and Zn by atomic absorption spectrophotometry revealed that the HEAu350 cells contained 1.8 times as much cellular and cytosolic Au per mg cell protein as the HE cells. Sixty per cent of the cytosolic gold in the HEAu350 cells was bound to high molecular weight proteins; no metallothionein was detected. Both strains contained minor amounts of zinc and copper compared with gold. The HEAu350 cells contained twice as much cellular Cuhg cell protein as the HE cells, whereas the zinc content remained unchanged. The mechanism of acquired resistance against gold-chloride in these cells remains unknown. However, the resistance cannot be due to binding of gold to metallothionein or to factors reducing the intracellular concentration of the toxic substance.