Robert M. Sutherland

Abnormal vascularization of malignant tumors is associated with the development of microregions of heterogeneous cells and environments. Experimental models such as multicell spheroids and a variety of new techniques are being used to determine the characteristics of these microregions and to study the interactions of the cells and microenvironments. The special cellular microecology of tumors influences responsiveness to therapeutic agents and has implications for future directions in cancer research.

Journal Article Growth of Multicell Spheroids in Tissue Culture as a Model of Nodular Carcinomas Get access Robert M. Sutherland, Robert M. Sutherland The Ontario Cancer Treatment and Research Foundation, London Clinic, and the Departments of Therapeutic Radiology and Surgery, University of Western Ontario, London, Ontario, Canada Search for other works by this author on: Oxford Academic PubMed Google Scholar John A. McCredie, John A. McCredie The Ontario Cancer Treatment and Research Foundation, London Clinic, and the Departments of Therapeutic Radiology and Surgery, University of Western Ontario, London, Ontario, Canada Search for other works by this author on: Oxford Academic PubMed Google Scholar W. Rodger Inch W. Rodger Inch The Ontario Cancer Treatment and Research Foundation, London Clinic, and the Departments of Therapeutic Radiology and Surgery, University of Western Ontario, London, Ontario, Canada Search for other works by this author on: Oxford Academic PubMed Google Scholar JNCI: Journal of the National Cancer Institute, Volume 46, Issue 1, January 1971, Pages 113–120, https://doi.org/10.1093/jnci/46.1.113 Published: 01 January 1971 Article history Received: 29 June 1970 Accepted: 28 September 1970 Published: 01 January 1971

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.

To investigate the effects of glucose and oxygen on spheroid growth, EMT6/Ro mouse mammary carcinoma cell spheroids were cultured in suspension in either 0.28 mM (20%) or 0.07 mM (5%) oxygen and 16.5, 5.5, 1.7, and 0.8 mM glucose. The spheroids initially grew at the same exponential rate in all culture conditions, with spheroid volume and cell number doubling times of 20-24 h. The growth rates slowed as the spheroids grew, and the maximum volume and cell number attained at growth saturation were proportional to the oxygen and glucose concentrations in the medium. There was a 500-fold difference in saturation sizes comparing spheroids cultured in the highest oxygen and glucose concentrations to those grown in the lowest. The thickness of the viable cell rims was also positively correlated with the oxygen and glucose concentrations in the medium. Comparison of the growth saturation and viable cell rim data showed an excellent correlation between the onset of central necrosis and the cessation of spheroid growth. A model is presented to explain the observed spheroid growth characteristics by proposing a competition between externally supplied growth and viability-promoting factors and internally generated inhibitory factors produced by the process of necrosis. This model has critical implications for the use of spheroids as models of cellular growth in tumors.

Knowledge about the oxygenation of human tumors and its importance in the response to radiotherapy is crucial to the effort to develop improved treatment methods for radiotherapy. The measurement of oxygenation of human tumors and correlations with response to radiotherapy were the subjects of a recent workshop sponsored by the National Cancer Institute. The following methods for measuring oxygen or hypoxia, or a parameter related to either, were presented: polarographic oxygen electrodes, the comet and alkaline elution assays for radiation-induced DNA damage, nitroimidazole binding assays, hemoglobin saturation assays, magnetic resonance spectroscopy, electron spin resonance spectroscopy, phosphorescence imaging, and an assay for tumor interstitial pressure. The electron spin resonance, alkaline elution, and phosphorescence imaging methods have not been used in human tumors. The comet assay, nitroimidazole binding assays, magnetic resonance spectroscopy, cryospectroscopy, and near-infrared spectroscopy have been employed in human tumors, but correlations to treatment response have not been made. Polarographic measurements have indicated that the presence of hypoxia correlates with a poor response to radiotherapy in cervical cancers, but additional data are needed on early-stage disease, and with long-term follow-up on local control and survival. If these confirm the correlation between hypoxia and poor response to radiotherapy, additional tumor sites should be studied. Future clinical trials of treatments that sensitize, exploit, or kill hypoxic cells should identify and include the individual patients with hypoxic tumors. Fundamental unanswered questions regarding the assessment of tumor oxygenation concern the need for invasive procedures, the spatial resolution needed for prediction of response to radiotherapy, the importance of reoxygenation, differences between tumors in rates and degrees of reoxygenation, whether measurements made during a course of therapy are of value, and correlations among methods and with other predictive assays such as intrinsic radiosensitivity and potential doubling time.