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.