ABSTRACT
Several cell lines when cultured under proper condition can form three dimensional structures called multicellular tumor spheroids. Tumor spheroids are valuable in vitro models for studying physical and biological behavior of real tumors. A number of previous studies using a variety of techniques have shown no relationship between radiosensitivity and DNA strand breaks in monolayer and spheroid model of cell culture. In the present study, the radiosensitivity of cells grown as monolayer and spheroid were measured with colony assay and the role of DNA strand breaks in this sensitivity was examined using single cell gel electrophoresis assay also known as Comet assay. In the present experiment, spheroids showed more radioresistance than monolayers as judged by the number of colonies which they produced after radiation. Under the same experimental conditions, less level of DNA damage was detected in spheroids using "comet assay" technique. It was concluded that the loss of radioresistance which was observed in monolayer cultures might have been attributed to the higher level of DNA damage occurred in the cells