X-ray Inactivation of Human Cells in Tissue Culture under Aerobic and Extremely Hypoxic Conditions in the Presence and Absence of TMPN

Abstract

A technique is described which permits irradiation of suspensions of human cells in tissue culture either aerobically (equilibrated with air) or under extremely hypoxic conditions (flushed with a mixture of 97 per cent N₂ and 3 per cent CO₂, the oxygen content of which was less than 15 p.p.m.). An established cell-line, NHIK 3025, originally derived from an early stage of human cancer of the cervix, was used. The D₀ value of these cells under aerobic conditions was 130 rads and the extrapolation number about 3. Under extremely hypoxic conditions, the dose-effect curve was exponential with a D₀ value of 600 rads. The o.e.r. derived from the ratio of the D₀ values was therefore 4·6. 2,2,6,6tetramethyl-4-piperidinol-N-oxyl (TMPN) at a concentration of 10⁻² M exerted a pronounced sensitizing effect under extremely hypoxic conditions (TMPN e.r. = 2·5), and yielded dose-effect curves with an extrapolation number of 3. The high radio-resistance of the cell under extremely hypoxic conditions in the absence of TMPN may be relevant to the evaluation of the radio-curability of tumours such as squamous cell carcinoma of the cervix uteri.