Inherent Cellular Differences May Explain the Dissimilar Survival of RIF-1 and KHT Tumour Cells Under Aerobic and Hypoxic Conditions

Abstract

Although previous work has shown striking differences in radiobiological hypoxic fraction between KHT and RIF-1 murine sarcomas, intravascular oxyhaemoglobin (HbO₂ saturations have revealed less substantial variations. Using quantitative histological techniques, we have also found minor differences in the distributions of distances between tumour cells and the nearest bloods vessel for KHT versus RIF-1 sarcomas. We report here, the results of an investigation of the inherent ability of these tumour cells to withstand conditions of hypoxia by in vitro culturing under aerobic and anoxic conditions. Tumours were dissociated, seeded into culture dishes, and placed in air-tight aluminium chambers. These chambers were repeatedly evacuated and refilled with a mixture of 95% N₂ and 5% CO₂ over a 2·5-h period. Following anoxic exposure, cells were removed and replated, and the in vitro plating efficiency (PE) was determined using a colony survival assay. After normalizing to aerobic controls, KHT tumour cells had a significantly lower PE, following a 16-hour exposure to anoxic conditions (0·4), than RIF-1 (0·6). Increasing the hypoxic exposure to 40 h resulted in normalized PEs of 0·07 for KHT versus 0·4 for RIF-1. Although these results support the hypothesis that the two tumour lines have different inherent abilities to withstand hypoxia, they do not explain the failure of direct measures of tumour oxygenation to correlate with the radiobiological hypoxic fraction. Additional factors such as differences in oxygen diffusivity or oxygen consumption rates between tumour lines may also be involved.