Oxygen Diffusion Distance and Development of Necrosis in Multicell Spheroids

Abstract

The multicell spheroid in vitro tumor model was used to study the effects of diffusion limitations of metabolites on the development of necrosis in a tumor-like environment. Chinese hamster [lung] V79-171b cells were grown in suspension as multicellular spheroids in different O2 or glucose concentrations to diameters where they developed central necrosis surrounded by an outer rim of viable cells. The range of O2 concentrations used in the gas phase was 1-20.3%, in equilibrium with complete nutrient medium. For each O2 concentration the thickness of the rim of viable cells was determined from measurements of histological sections. The square of the thickness of the viable rims of spheroids grown at different O2 concentrations between 5-20.3% increased linearly with the theoretically derived O2 diffusion distance, showing that the O2 diffusion distance is a main factor controlling, directly or indirectly, the development of necrosis in this concentration range. Spheroids grown at > 5% O2 contained a very small proportion of cells which were severely hypoxic or anoxic. The viable rim thickness was relatively less affected during growth at < 5% O2; an unknown mechanism may control the formation of necrosis when the O2 diffusion distance is less than approximately 80 .mu.m. Although alterations in the glucose concentration had some effect on viable rim thickness at these low O2 concentrations, the effect was much less than expected if glucose alone were responsible for controlling viability in this outer region.