Radiation Recovery Response of Mammalian Tumour Cells in vivo

Abstract

SINCE the original report by Elkind and Sutton¹ that mammalian cells are able to repair sublethal radiation damage in vitro, there have been several reports describing similar results in a variety of mammalian cell systems both in vitro and in vivo². The P-388 murine lymphocytic leukaemia maintained as an ascites tumour in the DBA/2 mouse is ideal material with which to investigate the recovery response of a malignant mammalian cell in vivo. Shortly after intraperitoneal transplantation of 10⁶ cells (24–48 h), the radiation response of this tumour is typical for that of an oxygenated population; after 6–7 days of intraperitoneal growth, this tumour demonstrates anoxic radiation response³. Consequently, it is possible to investigate the radiation recovery response of oxygenated and hypoxic cells depending on the age of the tumour at the time of the conditioning dose. Fig. 1 shows the survival response for 1-day tumours and 6-day tumours irradiated in vivo and assayed for tumour cell viability as previously described³. The dose modifying factor for 6-day tumours with respect to 1-day tumours is ∼3. In addition, while both curves have an initial shoulder, the extrapolation number for 1-day cells is significantly higher than that for 6-day cells.