Combined chemo- and radiosensitivity testing with ifosfamide and ACNU in human lung cancer cell lines.

The combination of radiotherapy and cytostatic drugs is of interest in the treatment of several solid tumors. In these preclinical investigations we tested whether ifosfamide and ACNU are able to enhance radiation effects. The experiments were performed by using the MTT assay. Two small cell and 2 non small cell lung cancer cell lines were involved. Ifosfamide, ACNU or both drugs together were tested in 6 different concentrations adjusted to the peak blood level. During the 1 hour drug incubation time, the cell lines were either irradiated with a single dose of 4 Gy or not. The main results were that ACNU possessed only little cytostatic activity in the cell lines under examination. In contrast, ifosfamide caused a dose related cytostatic activity in all cell lines. Concentrations of 26 micrograms/ml (NCC-SCLC H 82) or 10-12 micrograms/ml (3 other cell lines) were able to reduce the surviving cell fraction to less than 50% (IC50). While ACNU showed no clear outlined radiosensitizing properties, ifosfamide reinforced the radiation effects in 3 out of 4 cell lines indicating radiosensitizing properties of this drug. Synergistic effects of ifosfamide and ACNU have not been noticed. These preclinical investigations may constitute the basis for combined ifosfamide and irradiation therapy in future clinical trials.