Increased radioresistance of cells in cultured multicell spheroids. I. Dependence on cellular interaction.

Monolayers of six different cell lines were investigated with respect to ionic coupling using micro-electrode techniques. In parallel, survival after Co-gamma-irradiation of monolayer- and spheroid cultures of these lines was compared. It was found that spheroids of coupled cell lines were more radioresistant than monolayers ("contact effect"). however, cell coupling did not enhance the survival of monolayers over single cells. This suggests that the contact effect is a "tissue phenomenon" requiring cellular interaction but is expressed only under conditions of three-dimensional growth.