OXYGEN-CONSUMPTION RATE AND MITOCHONDRIAL DENSITY IN HUMAN-MELANOMA MONOLAYER-CULTURES AND MULTICELLULAR SPHEROIDS

Rate of oxygen consumption per cell has been shown in previous studies to decrease with increasing depth in the viable rim of multicellular spheroids initiated from rodent cells, human colon-carcinoma cells, an d human glioma cells, due to progressive accumulation of quiescent cel ls during spheroid growth. The purpose of our work was to determine ox ygen-consumption profiles in human melanoma spheroids. Monolayer cultu res of lines (BEX-c, COX-c, SAX-c, and WIX-c) and spheroid cultures of 2 lines (BEX-c and WIX-c) were subjected to investigation. Spheroids were initiated from monolayer cell cultures and grown in spinner flask s. Rate of oxygen consumption was measured with a Clarke-type electrod e. Mitochondrial density was determined by stereological analysis of t ransmission electron micrographs. Thickness of viable rim and cell pac king density were assessed by light microscopy of central spheroid sec tions. Cell-cycle distribution was determined by analysis of DNA histo grams measured by flow cytometry. Cell volume was measured by an elect ronic particle counter. Rate of oxygen consumption per cell differed b y a factor of approximately 1.8 between 4 cell lines and was positivel y correlated to total volume of mitochondria per cell. Rate of oxygen consumption per cell and total volume of mitochondria per cell were eq ual for monolayer cell cultures, 600-mu m spheroids and 1,200-mu m sph eroids of the same line. Mitochondrial density and location int he cel l did not differ between cells at the spheroid surface, in the middle of the viable rim and adjacent to the central necrosis. Cell-cycle dis tribution, cell volume, and cell-packing density in the outer and inne r halves of the viable rim were not significantly different. Consequen tly, the rate of oxygen consumption per cell in inner regions of the v iable rim was probably equal to that at the spheroid surface, suggesti ng that oxygen diffusion distances may be shorter in some melanomas th an in many other tumor types. (C) 1994 Wiley-Liss, Inc.