Cell–cell contact increases radioresistance in head and neck carcinoma cell lines

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Abstract
Purpose : To investigate the in vitro radiosensitivity of microcolonies from head and neck cancers of varying degrees of diÚerentiation. Materials and methods : The location of individual squamous-cell carcinoma (SCC) cells in tissue culture flasks was recorded using computerized microscopy. This allowed the positions of the cells to be continually revisited, which enabled manual sizing of individual microcolonies, both at the time of irradiation (0-5 Gy) and following a post-irradiation incubation period during which the microcolonies were assessed for clonogenic survival. Results : When irradiated as microcolonies with 0-3 Gy, malignant cells had plating eÝciencies (PE; applying multiplicity corrections) that were lower than expected when compared with the PE of cells irradiated individually. However, at between 2 Gy and 3Gy the PE values became similar and at higher doses the 'corrected PE' of microcolonies became higher than that of individually irradiated cells. Conclusion : These data show that cell-cell interactions can occur in malignant cells in a manner similar to that demonstrated previously in non-malignant cells. Cells within microcolonies demonstrate increased radioresistance compared with cells irradiated singly.