The Sensitization by Iododeoxyuridine of Cultured Human Cells to the Lethal Effect of X-rays and Heavy Ions

Abstract

A long-term line of cultured cells of human-kidney origin grown for at least one doubling time in iododeoxyuridine (IUdR) is characterized by a reduction in growth-rate and plating efficiency. For these IUdR-treated cells, the in vitro sensitivity to the lethal effects of radiation is increased for x-rays and for 26·3 mev ⁴He ions, but not for 79·0 mev ¹²C ions. The extent of sensitization appears to be independent of oxygen-tension. The results are interpreted theoretically in terms of injury analogous to sub-lethal radiation damage, but induced by incorporation of IUdR: the ability of the cell to reverse the effects of sub-lethal radiation events is impaired. It remains to be seen whether the uptake of IUdR by human tumours in vivo could be sufficient to render them more sensitive to radiation therapy.