In situ radiation response and oxygen enhancement ratio of KHT sarcoma cells in various phases of the cell cycle.

Studies were performed to evaluate the radiation response across the cell cycle of KHT sarcoma cells grown as solid tumours. Centrifugal elutriation, a relatively non-perturbing method for synchronising cells, was used to obtain homogeneous populations of cells with respect to their positions in the cell cycle from suspensions prepared directly from KHT tumours. More than 90% of the non-neoplastic cells were removed and the tumour cells separated into fractions containing 90-95% G1 cells, 70-75% S cells and 70-75% G2M cells. Since survival following in situ irradiation is influenced by the presence and proportion of oxygen-deficient or hypoxic tumour cells, in order to study the radiation response across the cell cycle, KHT sarcoma cells were irradiated under conditions of uniform oxygenation. This was achieved by irradiating the tumour cells either in situ in dead animals or, in vitro, after tumour dissociation and cell separation, while fully oxic or anoxic. Under all these conditions, the most radioresistant portion of the cell cycle was found to be late G1 and early S. G2M were always most radiosensitive. Complete radiation dose-response curves under oxic or anoxic conditions were also obtained for cells in all phases of the cell cycle. From these the oxygen enhancement ratio (OER) was calculated to be 2.4, 2.6 and 2.5 for cells in the G1, S and G2M cell cycle phases respectively.