Human colon adenocarcinoma cells WiDr were cultured as monolayers or multicellular spheroids in 5% or 20% (v/v) oxygen and in various external lactate concentrations of 0-20 mM. Doubling times and H-3-thymidine labeling indices of exponential monolayer cells indicated that there was no difference in growth behavior between the two oxygen environments, yet these parameters reflected a growth retardation upon elevation of lactate. Growth of WiDr spheroids was retarded in both low oxygen and high lactate concentrations. There was a tendency towards a decrease in the thickness of the viable cell rim with increasing lactate in 20% O-2, whereas the width of the viable rim increased significantly as a function of external lactate in 5% O-2. Intraspheroidal oxygen tensions (Po-2) measured with microelectrodes were less in 5% O-2 than in 20% O-2, yet did not vary systematically as a function of external lactate. Po-2 values in the spheroid center dropped to 0 mm Hg prior to the emergence of central necrosis under all conditions investigated. Unlike numerous other spheroid types investigated up to now, WiDr spheroids mimic tumor microregions with hypoxia-induced necrosis and with nonproliferating cells at very low oxygen pressure.

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