Bleomycin enhances the tyrosinase activity of human malignant melanoma cells in culture

Abstract

By application of bleomycin fine pigmentations on basalcell layers will appear in irritated parts of the skin. Therefore we investigated the effect of bleomycin on the tyrosinase activity. Bleomycin was determined to exhibit a strong cytostatic activity on human melanoma cells in culture (ED 50 concentration = 0.21 μg/ml) whereas the viability of the cells was not affected. Incubation of pigmented human melanoma cells in the presence of bleomycin containing culture medium (1–100 ng/ml) at 37°C for different periods of time resulted in a marked increase of tyrosinase activity. The level of enzyme activity reached 140% if the controls were set to 100%. Direct addition of bleomycin to the crude cell extract produced no detectable stimulatory effect. There were no significant stimulation if the cells were grown with bleomycin in serum-free culture medium. The serum content influences the activity of tyrosinase in a marked degree. The serum concentration for half-maximal stimulation of tyrosinase was calculated to be 14.2%. Furthermore the inflammatory mediator histamine was found to stimulate tyrosinase in melanoma cells. There were no additional stimulatory effect if cells were incubated in the presence of both histamine and bleomycin. These results suggest that bleomycin is able to enhance tyrosinase activity in intact cell systems. Further a possible role of serum and/or inflammatory factors in the stimulatory process must be considered.