In vitro modulation of the metastatic phenotype. I. Analysis of differentiation forms of the B16 melanoma expressing Met-72 determinants and metastatic activity.

In vitro cultures of a highly metastatic B16 melanoma clone (BL6-10) were found to undergo dramatic changes in morphology and differentiation upon transfer to another culture medium. Specifically, BL6-10 melanoma cells which had been originally selected and adapted for growth in Eagles' Hanks' amino acid supplemented media with 10 per cent newborn calf serum were amelanotic and epitheliod in shape. When these cells were shifted into Dulbecco's modified Eagles medium with 10 per cent fetal calf serum, they became highly melanotic and of spindle/dendritic morphology within 4 days of culture. These morphological changes as well as other parameters were all characteristic of established criteria of melanoma differentiation. Alterations in the differentiation state of our highly metastatic variant, BL6-10, did not result in any change in tumorigenicity but did have profound effects on metastatic potential. All of the morphological and functional characteristics of the differentiated melanoma were found to be reversible by re-plating the cells in their original growth medium and 4 days of in vitro growth. These studies have allowed us to follow and more firmly establish Met-72 antigen expression as a surface marker for metastatic cells of the B16 melanoma, and have provided direct experimental evidence that the less differentiated, Met-72 positive melanoma form is the dominant cell type capable of metastatic potential.