Variations in tumor cell growth rates and metabolism with oxygen concentration, glucose concentration, and extracellular pH

Abstract

Tumors and multicellular tumor spheroids can develop gradients in oxygen concentration, glucose concentration, and extracellular pH as they grow. In order to calculate these gradients and assess their impact on tumor growth, it is necessary to quantify the effect of these variables on tumor cell metabolism and growth. In this work, the oxygen consumption rates, glucose consumption rates, and growth rates of EMT6/Ro mouse mammary tumor cells were measured at a variety of oxygen concentrations, glucose concentrations, and extracellular pH levels. At an extracellular pH of 7.25, the oxygen consumption rate of EMT6/Ro cells increased by nearly a factor of 2 as the glucose concentration was decreased from 5.5 mM to 0.4 mM. This effect of glucose concentration on oxygen consumption rate, however, was slight at an extracellular pH of 6.95 and disappeared completely at an extracellular pH of 6.60. The glucose consumption rate of EMT6/Ro cells increased by roughly 40% when the oxygen concentration was reduced from 0.21 mM to 0.023 mM and decreased by roughly 60% when the extracellular pH was decreased from 7.25 to 6.95. The growth rate of EMT6/Ro cells decreased with decreasing oxygen concentration and extracellular pH; however, severe conditions were required to stop cell growth (0.0082 mM oxygen and an extracellular pH of 6.60). Empirical correlations were developed from these data to express EMT6/Ro cell growth rates, oxygen consumption rates, and glucose consumption rates, as functions of oxygen concentration, glucose concentration, and extracellular pH. These empirical correlations make it possible to mathematically model the gradients in oxygen concentration, glucose concentration, and extracellular pH in EMT6/Ro multicellular spheroids by solution of the diffusion/reaction equations. Computations such as these, along with oxygen and pH microelectrode measurements in EMT6/Ro multicellular spheroids, indicated that nutrient concentration and pH levels in the inner regions of spheroids were low enough to cause significant changes in nutrient consumption rates and cell growth rates. However, pH and oxygen concentrations measured or calculated in EMT6/Ro spheroids where quiescent cells have been observed were not low enough to cause the cessation of cell growth, indicating that the observed quiescence must have been due to factors other than acidic pH, oxygen depletion, or glucose depletion.

Energy metabolism in human melanoma cells under hypoxic and acidic conditions in vitro

“…However, the up-regulation was not sufficiently large to compensate for the loss in energy generation resulting from the inhibition of the oxidative pathway. The effects of hypoxia on glycolysis and adenylate energy charge reported here for human melanoma cells are thus consistent with those reported previously for rodent tumour cells and other histological types of human tumour cells (Rotin et al, 1986;Heacock and Sutherland, 1990;Casciari et al, 1992;Gerweck et al, 1992).…”

“…Experimental studies have suggested that the energy status is particularly low in hypoxic tumour cells at PHe in the lower part of this range, because of inhibited glycolysis owing to the low PHe (Halperin et al, 1969;Rotin et al, 1986;Casciari et al, 1992;Gerweck et al, 1993). However, the adenylate energy charge at pHe 6.6 was similar to that at pHe 7.4 and 7.0 in hypoxic cultures of the cell lines studied here, even though the rate of glucose uptake was lower at PHe 6.6, than at PHe 7.4 and 7.0.…”

“…After medium samples had been collected for measurement of glucose and lactate concentrations, the cells were detached from the dishes by trypsinization and counted by using a haemocytometer and a phase-contrast microscope. (1997) 76(4), [421][422][423][424][425][426][427][428] 6., Measurements of rates of glucose uptake and lactate release Cellular rates of glucose uptake and lactate release were determined by using standard enzymatic test kits (Boehringer Mannheim, Mannheim, Germany) and spectrophotometric assays (Casciari et al, 1992). The glucose and lactate concentrations in the media of aerobic and hypoxic cell cultures were measured as a function of time.…”

“…The ATP formation is reduced markedly in tumour cells in a hypoxic microenvironment, mainly because of inhibition of respiration but also because of inhibition of glycolysis by low PHe (Rotin et al, 1986;Gerweck et al, 1993). ATP utilization is subsequently reduced, leading to decreased DNA and protein synthesis and cessation of cell proliferation (Born et al, 1976;Heacock and Sutherland, 1990;Casciari et al, 1992). The rate of energy deprivation during exposure to hypoxia at normal or low PHe might thus differ between tumours because of differences in the capacity of the tumour cells to generate energy and/or to reduce the energy consumption.…”

Necrotic core in EMT6/Ro tumour spheroids: Is it caused by an ATP deficit?

“…The growth characteristics and the metabolism of the EMT6/Ro spheroid (mouse mammary carcinoma cells) have been extensively investigated (Mueller-Klieser and Sutherland, 1982, Mueller-Klieser, 1984, Freyer and Sutherland, 1985, Freyer and Sutherland, 1986a, Casciari et al, 1988, Freyer, 1988, Walenta et al, 1990, Freyer et al, 1991, Casciari et al, 1992, Casciari et al, 1992a. In Freyer and Sutherland (1986a) in particular, the radius of the necrotic core for spheroids of different size and under different oxygen and glucose concentrations in the medium were reported.…”