Cell cycle kinetic measurements in an irradiated rat rhabdomyosarcoma using a monoclonal antibody to bromodeoxyuridine

Open Access
Publisher Website
Google Scholar
Abstract
Cell cycle kinetics after X‐irradiation were studied in a solid rat rhabdomosarcoma using a monoclonal antibody to bromodeoxyuricline (BrdUrd) In cells in which the DNA was labeled by BrdUrd. It could be shown that this tumor was composed of about 80% diploid host cells, and only 20% of the cells in the dissociated tumor were actually tetraploid tumor cells. When rats were injected intraperitoneally with BrdUrd to label S‐phase cells in the tumor, only a fraction of both types of cells became labeled with Brdtlrd during s‐phase, even 24 h after injection. The diploid BrdUrd‐labeled cells progressed rapidly into cycle; 4 h after injection of BrdUrd, labeled diploid s‐phase cells could be observed. Only 25% of the tetraploid S‐phase cells could be labeled by a single injection of BrdUrd (160 mg/kg body weight). These labeled tetraploid cells progressed through the cell cycle with similar velocities as did labeled diploid cells. Using a “Mini Osmotic Pump” containing bromodeoxycytidine (BrdCyd) at high concentration (0.3 mol/L) that released BrdCyd continuously into the organism where it was converted to BrdUrd, it could be shown that after 2 days about 60% of cells in S‐phase and 70% of cells in S‐phase were labeled. The fraction of labeled S‐phase cells in irradiated tumors (D = 10 and 20 Gy) was enhanced between 10 and 50 h after irradiation clue to a radiation‐induced G2 block in cycling tetraploid tumor cells. No effect of irradiation on incorporation of BrdUrd in S‐phase could be observed in the continuous labeling experiments in contrast to the pulse labeling with BrdUrd, where a small retardation of DNA synthesis was observed in the irradiated tumors during the first 15 h after irradiation. When dissociated cells of the tumor were plated in medium containing 20 μmol/L BrdUrd, only the tetraploid tumor cells were able to incorporate BrdUrd and to enter cycle.