Characterization of a differentiated cat melanoma cell line

We have established several long-term cultures of a naturally occurring metastatic melanoma of a domestic cat. The cells are fully differentiated as indicated by the Fontana-Masson staining of the melanin in the perinuclear region and by electron microscopy of the cytoplasmic melanosomes in various stages of development. The melanoma cells do not produce virus particles or the major core proteins (i.e., protein with a molecular weight of 30,000) of the feline leukemia virus or the endogenous cat virus RD-114. Retrovirus is also not induced when melanoma cultures are treated with 5-iodo-2'-deoxyuridine or bromodeoxyuridine and cocultivated with susceptible cells. Treatment of cells with N6,O2'-dibutyryl cyclic adenosine 3' :5'-monophosphate or theophyllin, however, accentuates melanin production and increases the number of pigmented cells. The cultured cells develop melanotic tumors in s.c. inoculated newborn cats and athymic nude mice. As far as we can ascertain, this is the first report of a spontaneous malignant melanoma of a cat which provides an important resource for studying cell differentiation in vitro.