Expression and activity of P-glycoprotein in transplantable hamster melanomas

In the study described here we investigated the possibility of an associati on between the aggressiveness of melanoma and multidrug resistance phenotyp e by analyzing the expression and activity of P-glycoprotein (Pgp) in two g enetically related transplantable hamster melanomas - a melanotic (Ma) and an amelanotic (Ab) form - which differed in aggressiveness and metastatic p otential. Flow cytometric analysis of Pgp activity (using a verapamil-sensi tive rhodamine R123 exclusion test) as well as Western blotting of cellular lysates showed its preferential (although not very marked) expression in t he Ab melanoma cells. The Ab melanoma cells also exhibited a higher proport ion of tumor-infiltrating lymphocytes (TIL), mostly of T cell phenotype, th at may have reflected a higher immunogenicity of the tumor. In conclusion, Pgp activity appeared to be associated with less-differentiated more aggres sively metastasizing melanoma (the Ab variant) although its role in maintai ning this phenotype remains to be established.