Radiation-induced apoptosis in human ovarian carcinoma cells growing as a monolayer and as multicell spheroids

Response to external gamma irradiation was studied in a human ovarian carcinoma cell line (OVCAR 3) growing as a monolayer and as multicell spheroids. Necrosis and apoptosis were documented using Trypan-blue uptake and acridine-orange staining, respectively, and apoptosis was quantified using a terminal deoxynucleotidyl transferase assay. Exposure of OVCAR 3 cells growing as a monolayer to 137Cs gamma radiation at a dose of 10 Gy produced 30-40% apoptosis 72 hr after irradiation. Cell-cycle analysis of irradiated cells showed an accumulation of cells in G2/M phase 24 hr after irradiation and then a decline at 48 hr in conjunction with apoptosis onset. The loss of G0/G1 cells in irradiated cultures suggested a preferential entry into apoptosis. No increase in apoptotic cell number was observed in OVCAR 3 spheroids after irradiation, and the cells probably died as a result of necrosis. When spheroids were disrupted immediately after irradiation to obtain a cell suspension, minor apoptosis was observed in association with a marked increase in TB-positive cell number after 96 hr of incubation following irradiation. Thus, a relationship was found between radiation-induced apoptosis and the cell cycle. Results with spheroids suggested the possible involvement of cell-to-cell interactions in apoptosis regulation.