Analysis of tridimensional mixed cultures of mouse B16 melanoma cells and 3T3 fibroblasts.

The interactions between invasive malignant cells and normal fibroblastic cells were studied in a cellular spheroid model in vitro. Murine B16 melanoma cells (previously cultured in monolayer for a short period) and 3T3 mouse fibroblasts (greater than or equal to 130 passages in monolayers) were cultured under tridimensional conditions (pure or mixed spheroids). As compared to pure 3T3 or mixed spheroids, B16 spheroids were smaller and characterized by a higher proliferation rate, a lower degree of necrosis, and a less abundant extracellular matrix. Disintegration was observed in some pure 3T3 or mixed spheroids. Melanogenesis progressively increased inside B16 or mixed spheroids. By immunohistochemical methods and electron microscopy, laminin, fibronectin and collagen I, III and IV in extracellular matrix were studied in the three types of spheroids.