Some properties of Bomirski Ab amelanotic melanoma cells, which underwent spontaneous melanization in primary cell culture. Growth kinetics, cell morphology, melanin content and tumorigenicity.

Four types of the Bomirski Ab amelanotic melanoma primary cell culture, differing in the presence of calf serum in the medium and in the cell number used for starting the culture, were employed in the study. In all types of cell culture, rapid melanization occurred in the cytoplasm of the cultured cells. Calf serum in the culture medium stimulated both melanization and proliferation of the Ab melanoma cells. The process of melanin synthesis occurred during the logarithmic phase of growth and was over when the cells reached the plateau phase. Heavily melanized cells changed their adhesive properties, lost the ability to divide in vitro, and showed decreasing tumorigenicity down to complete absence, though they retained some parameters of viability. The rate of melanin synthesis was lower in the cells cultured at high cell density than in those at low cell density. Highly melanized cells that did not divide in vitro but were still tumorigenic in vivo caused the growth of tumors whose morphology was typical for the amelanotic melanoma, melanin being absent. In conclusion, it may be stated that the present findings suggest the persistence of a highly anaplastic and malignant phenotype of Bomirski amelanotic melanoma, being a result of the regulatory action of the host, while the change in the phenotype in vitro does not rule out autoregulatory influences of the tumor itself on its differentiation level and malignancy.