Characterization and tumorigenicity of spheroids composed of pigmented or non pigmented B16 melanoma cells.

A parental line of mouse B16 melanoma cells (B16) and two derived cloned lines, either pigmented (B16P) or non pigmented (B16NP), were cultured in vitro as spheroids. After 48 hrs, the pigmented cells (B16, B16P) formed smaller and looser aggregates, with higher rates of cell proliferation and lower amounts of extracellular matrix as compared to B16NP spheroids. The three lines were more tumorigenic when inoculated subcutaneously as spheroids than as isolated cells. Furthermore, B16P or B16 spheroids developed richly vascularized subcutaneous tumors and metastases more rapidly than B16NP aggregates. After intravenous injection of spheroids, the measurement with an image analyzer of the area of sections in lung colonies indicated that B16P colonies were larger and more numerous than those induced by B16NP cells.