Cellular oxygen utilization and radiation response of V-79 spheroids

Chinese hamster V-79-171 cells, when placed in stirred suspension cultures, spontaneously grow as spherical multicell aggregates (spheroids) which eventually contain many thousand tightly-packed cells. These spheroids thus provide a valuable model for the study of oxygen transport, since oxygen concentration at the spheroid periphery can be fairly precisely controlled in the stirred suspension, and the consequences of oxygen diffusion inward through the tissue-like mass can be determined experimentally and compared with theoretical calculations. As in human tumors, appearance of central necrosis can be correlated with severe hypoxia. Additionally, since severely hypoxic cells are considerably more resistant to radiation than are oxygenated cells, determination of the fraction of hypoxic cells by their radioresistance provides a noninvasive technique for monitoring respiratory processes. Using this approach, we have found an excellent correlation between the rate of cellular oxygen utilization by a single cell suspension and the net radio-sensitivity of multicell spheroids when treated with modulating agents, varying from direct control of metabolic activity by changing the ambient temperature, to less direct effects on cellular oxygen consumption induced by exposure of cells to nitroheterocyclic radiosensitizers, chemotherapeutic agents, anesthetics, antibiotics, and even cell growth factors including insulin. Our data from these studies indicate that, at least in the simplistic spheroid system where oxygen delivery to the internal cells is a direct function of the respiratory activity of the external cells, control of cellular oxygen utilization is a convenient and effective method of controlling the net radiosensitivity.