CULTURE-MEDIUM INDUCED MORPHOLOGICAL-CHANGES OF MELANOMA-CELLS ASSOCIATED WITH CHANGE IN SENSITIVITY TO LYSIS BY LYMPHOKINE-ACTIVATED KILLER-CELLS

Three sublines (Clones 1, 2 and 7) of the human melanoma CaCL 73-36 ce ll line with different cellular morphology, growth patterns, melanin c ontent and surface antigenic profile were maintained in RPMI-1640 medi um plus 10% fetal bovine serum (abbreviated as RPMI). Each subline was divided into two groups: one grown in RPMI and the other in Dulbecco' s modified Eagle's medium plus 10% fetal bovine serum (abbreviated as DMEM) for 96 h. Phenotypically, Clone 2 expressed Class I and II MHC a nd ICAM-1 on the surface and in the cytoplasm, while Clones 1 and 7 fa iled to express these antigens in both the cytoplasm and on the cell s urface. Melanotic Clones 1 and 7 cells became even more pigmented, had slower growth rates, and exhibited lower saturation densities when in cubated in DMEM than when they were incubated in RPMI. On the other ha nd, Clone 2 cells maintained in RPM7 were grossly amelanotic, containe d defective-like melanosomes detected ultrastructurally, and had disti nct clusters of microvilli polarly located in most of the cells. Such specialized ultrastructures were not affected by medium conditions. An alysis of sensitivity of the clonal sublines to cytolysis by allogenei c effector cells revealed that in spite of low levels of natural kille r (NK) cytotoxicity noted, DMEM produced a 2- to 14-fold increase in s ensitivity to NK cells, irrespective of which medium was used. Differe nt levels of lymphokine-activated killer (LAK) cytolytic activity were clearly observed in sublines maintained in RPMI with Clone 2 being th e most sensitive and both Clones 1 and 7 being less sensitive. Cells g rown in DMEM exhibited significantly higher levels of sensitivity to L AK cytolysis than cells grown in RPMI as revealed by their differences in lytic units (p < 0.05). This was likely due to the high levels of surface ICAM-1 expression in cells incubated in DMEM vs little express ion of this adhesion molecule by cells grown in RPMI. Taken together t hese results demonstrate the presence of heterogeneous subpopulations within the CaCL 73-36 melanoma cell line regarding their pigmentary st atus, antigenic profile, growth pattern and responsiveness to NK/LAK c ytolysis. The results also call attention to the importance of utilizi ng a same medium in short-and long-term cultures of melanomas for biol ogical studies and response evaluations of therapeutic agents such as LAK cells, when multiple cell targets from different patients or multi -metastatic cell lines from individual patients are to be compared Fin ally, these melanoma sublines may be valuable for further elucidation of the relationship between MHC expression, and increased sensitivity to LAK cytolysis, and the role of the components of DMEM in the mechan ism for the observed induction of cell differentiation and enhanced LA K cytolysis.