Dexamethasone, medroxyprogesterone acetate, and vindesine modulation of human malignant melanoma growth in soft agar

We have previously shown biopsies from human malignant melanoma, as well as a cell line (MELUR) derived from human malignant melanoma cells, to contain dexamethasone (DEX) - and medroxyprogesterone acetate (MPA) - binding macromolecules exhibiting properties of glucocorticoid receptors from well-known target organs. In this paper, we demonstrate that the cloning efficiency of MELUR melanoma cells is inhibited by DEX and MPA in a dose-dependent manner. MELUR tumour colony-forming units (MELUR-TCFU) were inhibited more than 40% by either DEX or MPA at 1 X 10(-7) mol/l with concentrations needed to obtain a 50% reduction in TCFU counts for both hormones of 3 X 10(-9) mol/l. MELUR cell growth in soft agar was also modulated by vindesine (VI). At 50 ng/ml, VI produced a 70% reduction of colony formation. The combined drug effects of either DEX or MPA and VI on colony formation were additive. The data indicate that the proliferative activity of MELUR cells is regulated by DEX and MPA, both acting additively to VI.