Human Malignant Melanoma In Vivo and In Vitro 2

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Abstract
A human malignant melanoma cell line (KHm-1) was established in vitro and has been maintained in culture continuously for 2 1/2 years with more than 80 passages. Cells grew well in soft agar and produced black tumors in animals. From chromosome studies, two distinct marker chromosomes were identified. The KHm-1 cell line showed “morphologic differentiation” after treatment with N6,02′-dibutyryl adenosine 3′,5′-cyclic monophosphate, theophylline, or serum-free medium in vitro. The melanoma cells, spindle-shaped in the normal culture condition, became dendritic after treatment. The dendritic cells then became round immediately after they were changed to a normal culture medium, and the rounded cells returned to the spindle shape in 24 hours. The ultrastructural studies revealed changes in the quantity of actin-like microfilaments in these round, spindle, and dendritic cells; the quantity of the microfllaments progressively decreased in this sequence. Human benign melanocytic tumor cells (cellular blue nevus) were highly dendritic in vitro, and the microfilaments in these benign cells were similar to those observed in the dendritic-shaped melanoma cells. In in vivo studies, microfilaments of malignant melanoma, cellular blue nevus, and epidermal melanocytes had the same pattern of variations: A large quantity of microfilaments was observed in malignant melanoma (cuboid in shape); the least, in benign dendritic epidermal melanocytes. These observations suggested that the amount of actin-like microfilaments in melanocytic cells is inversely correlated to the differentiation of the cells in vivo and in vitro.

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