Factors influencing human tumor radioresistance

The first part of this paper reviews factors which modulate intrinsic radioresistance including free radical scavengers, chemical and enzymatic repair of DNA, chromatin conformation, cell cycle checkpoints and signal transduction processes. In the second part a sub-set of radioresistant cells which have been identified from among cell lines cross-resistant to alkylating agents are described. Radioresistance is associated with a reduction in the value of α in the linear-quadratic model and these cell lines are radiosensitized under aerated conditions by GSH depletion with sensitization involving an increase in α