CYTOTOXICITY OF BLEOMYCIN AND EXTERNAL RADIATION IN SQUAMOUS-CELL CANCER CELL-LINES OF HEAD AND NECK

Bleomycin, a natural antibiotic toxic to dividing cells, has been succ essfully used in combinations for treatment of recurrent head and neck cancer. In this study, we investigated five recently established head and neck squamous cell cancer lines (UT-SCC-2, UT-SCC-8, UT-SCC-9, UT -SCC-12A, UT-SCC-19A) in terms of response to bleomycin and radiation treatment. Experiments were carried out using the 96-well plate clonog enic assay for concentration determinations causing 20% (IC20), 50% (I C50), and 90% (IC90) inhibition of clonogenic survival and dose-respon se calculations for bleomycin. Survival fraction after a radiation dos e of 2 Gy (SF2) was used as a measure for radiation sensitivity. The s ensitivity for bleomycin was in good accordance with radiation sensiti vity except for cell line UT-SCC-9. This was the cell line most sensit ive to radiation (SF2 = 0.25 +/- 0.03) but was fairly resistant to che motherapy (IC50 = 11.5M). Sensitivity patterns may suggest partly diff erent mechanisms of action.