Rhabdomyosarcoma Spheroids with Central Proliferation and Differentiation1

A novel type of multicellular spheroids was established and character ized with regard to growth behavior, proliferation, and differentiation. The spheroids were grown from clonal rat rhabdomyosarcoma cells using the spinner flask technique. The cell aggregates showed several unique properties that were different from those observed in most of the spher oids investigated to date. These properties include a non-Gompertzian volume growth; the coexistence of undifferentiated mononuclear cells and of differentiated, myotube-like giant cells with numerous nuclei; a rela tively homogeneous intraspheroidal distribution of proliferating mononuclear cells with thymidine labeling even in the center of spheroids > 1 mm; the absence of necrosis in such large spheroids, and the accumulation of myotube-like cells in the center of these spheroids instead. There was a decrease in the overall proliferative activity of the mononuclear cells with increasing proportion of giant cells in the rhabdomyosarcoma spheroids.