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Increased experimental metastatic capacity of a murine melanoma following induction of differentiation.

Because of the interest in possible links between defective differentiation and cellular malignancy, the effects were examined of induced cell differentiation upon the experimental metastatic potential of the sublines F1 and F10 of the B16 mouse melanoma. These cell lines normally have low and high rates, respectively, of colonization of the lungs of mice after i.v. injection. Cellular differentiation was assessed by pigmentation and tyrosinase activity. In both cell lines, low and high levels of differentiation could reproducibly be generated by culture, respectively, at a low extracellular pH and at a higher pH in the presence of a melanocyte-stimulating hormone. Surprisingly, in both lines the cells grown under conditions promoting differentiation showed a markedly higher rate of experimental metastasis, despite their slower proliferation in culture and in subcutaneous tumor implants, than the poorly differentiated cells. Radiolabeled well- and poorly pigmented cells were not initially deposited at significantly different rates in the lungs of mice after i.v. injection. However, subsequent retention in the lungs fell more quickly for the poorly differentiated cells. As indicated by tests in vitro, this difference appears not to be due to differential cytotoxicity by either host macrophages or natural killer cells, and it is under further study.