Brain meninges tumor formation byin vivo-selected metastatic B16 melanoma variants in mice

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Abstract
The murine melanoma subline B16-F1 of low brain- and lung-colonizing potential has been used to obtain brain-colonizing variant sublines by sequential selectionin vivo for their abilities to form brain meningeal tumors. After fourteen and fifteen selections in syngeneic C57BL/6 mice sublines B16-B14b and B16–B15b, respectively, were established in culture. These were then assayedin vivo by injection of single tumor cell suspensions into the tail vein (i.v.), left ventricle of the heart (i.c.) or left common carotid artery (i.a.), and the resulting tumors were examined histologically. Injection of subline B16-B14b or B16–B15b resulted in brain meningeal tumor formation in the dura mater and leptomeninges with invasion into underlying brain parenchyma and also some brain ventricular tumors at the sites of i.a. injection. Lung colonization ability remained in the brain-selected sublines, although it was remarkably reduced in i.a. tumor cell-injected animals. The brain meningeal tumors that formed were of three types: intravascular, nodular or infiltrative. Injection of tumor cells i.v. resulted mainly in the establishment of the intravascular type of brain meningeal tumors with eventual perivascular invasion, while injection i.a. or i.c. resulted mostly in nodular or infiltrative type brain meningeal tumors. The B16–B14b brain meningeal tumors formed were small (< 1 mm in diameter) and usually non-pigmented, while B16–B15b tumors were generally large (up to 7mm in diameter) and pigmented. Host reactions towards B16–B14b and B16–B15b tumors at meningeal sites differed. The former B16 subline was characterized by extensive fibrosis with some immunocytic cell infiltration in and around the meningeal tumors, while the latter subline did not elicit such host reactions. In contrast, tumors in brain parenchyma failed to evoke observable host reactions, and there was little evidence of immunocyte cell infiltration or glial cell alterations.