Hyperthermic enhancement of chromosome damage and lack of effect on sister-chromatid exchanges induced by bleomycin in Chinese hamster cells in vitro.

Chinese hamster cells, M-3, were treated with BLM (1--4 micrograms/ml) for 30 min to 1 h at 37 degrees or 43 degrees C. After treatment, the cells were reincubated at 37 degrees until recovery. The material treated at 43 degrees showed increased damage expressed as chromosome and chromatid-type breaks and exchanges. Since the amount of BLM entering the cell at 37 degrees is supposedly similar to that which enters the cell at 43 degrees, the enhanced damage is the result of true synergism, and not the facilitation of the drug's entry into the cell.