Microelectrode Measurements of Oxygen Tension Distributions in Multicellular Spheroids Cultured in Spinner Flasks

Abstract

Since multicellular spheroids were introduced into cancer research by Sutherland et al. (1970, 1971), they have been widely used for studying the susceptibility of cancer cells to various treatment modalities. Many of these investigations provided evidence for a major role of oxygen in controlling the metabolic and cell cycle state of the tumor cells, thus modifying the responsiveness of the cells to therapy. Several investigators have measured O₂ tension (PO₂) distributions in spheroids with O₂-sensitive microelectrodes (Carlsson et al. 1979; Kaufman et al. 1981; Mueller-Klieser and Sutherland 1982a, b, 1983; Mueller-Klieser et al. 1983). The measurements produced PO₂ values that varied considerably since different cell lines, culturing methods, and measuring techniques were used. Because of this obvious dependence of spheroid oxygenation on the culturing and measuring conditions thorough standardization of both these conditions is needed. Also, the measuring conditions should match the growth conditions as closely as possible if inferences on growth are to be drawn from the values measured. This certainly holds for all assays with spheroids in which oxygen supply may play a significant role. Similar considerations, however, may also apply to the supply of nutrients and the removal of metabolic waste products during growth and measurements. Since the factors mentioned can determine many growth characteristics of spheroids, such as the amount of necrosis or the fraction of proliferating cells, caution should be exercised in drawing conclusions on solid tumor growth from spheroid data.