Demonstration of multiple phenotypic diversity in a murine melanoma of recent origin.

The purpose of these studies was to examine whether the metastatic heterogeneity that is frequently found in serially transplanted neoplasms could be observed in a murine melanoma of recent origin. The primary K-1735 melanoma that arose in an inbred C3H/HeN murine mammary tumor virus-negative (C3H-) mouse was transplanted once into an immunosuppressed recipient and then established in culture. Cells from the fifth in vitro passage were used to produce clones. The parent K-1735 and 22 cloned lines were tumorigenic in syngeneic and outbred N:NIH(S) nude mice. Metastatic properties were assessed by observing the ability of the cells to produce pulmonary and extrapulmonary lesions after they were injected iv into 6-week-old C3H- mice. The number of metastases produced, their relative size, and pigmentation varied dramatically among the clones. Only 2 of 22 clones were indistinguishable from the parent tumor. Most of the nonmetastatic (but tumorigenic clones) were also nonmetastatic in 3-week-old nude mice, which suggests that the absence of metastasis formation was not merely due to their immunologic rejection by the normal C3H- mouse. Control subcloning experiments demonstrated that the procedure of cloning in vitro was not responsible for the variability among the clones. The clones did not differ in their karyotype or cell size, but they did differ in their growth rate in vitro. These phenotypes, however, did not correlate with metastatic propensity. In conclusion, the K-1735, a murine melanoma of most recent origin, is heterogeneous and contains subpopulations of cells with diverse biologic behavior.