Modification of pH induced cellular inactivation by irradiation-glial cells

Human cells of glial origin were examined for clonogenic survival after exposure to subnormal pH of the extracellular fluid for 0 to 5 days at 37°C. The surviving fraction decreased at pH values between 6.7 and 6.4 to 10% within 2 days. Cells that survived irradiation demonstrated a decreased sensitivity to an acid extracellular fluid. The radiation response function was established with and without incubation at pH 6.7 for 66 hours. Doses above 4 Gray resulted in a higher survival at pH 6.7 than at pH 7.4, if pH was reduced 15 hours prior to irradiation. Enhanced clonogenic survival after irradiation under conditions of continuous acidity in the extracellular space may be a further explanation for poor local control of malignant tumors in clinical radiation therapy.