Cell proliferation kinetics of six xenografted human cervix carcinomas: comparison of autoradiography and bromodeoxyuridine labelling methods.

Cell kinetic and histologic parameters of six xenografted tumours with volume doubling times ranging from 6 to 43 d were investigated in order to obtain kinetic information on a panel of tumours to be used in radiobiological studies. The six tumours covered a range of histologies and their DNA indices varied from 2.7 to 1.4. The length of the cell cycle (Tc), potential doubling time (Tpot) and labelling index (LI) were determined by continuous labelling with [3H]TdR and autoradiography in three tumours, Tc varied from 30 to 40 h. Determinations of the length of the S phase (Ts) were found to be less reliable by this method. Data on Ts and LI were also determined in all six tumours using bromodeoxyuridine (Brd) labelling and the single sample method: values of Tpot were slightly longer than those obtained via the autoradiographic method. In addition, multiple samples were taken after BrdU labelling. Tc was determined by fitting the data obtained from mid-S, mid-G2 and mid-G1 windows to curves described by a damped oscillator. Data obtained via the mid-S window were found to be most reliable. Generally, cell cycle times obtained by the BrdU method were longer than those observed with the autoradiographic method. Differences between the two methods could be explained by inaccuracies in the determination of Ts, LI and Tc and differences in the experimental approach. We consider the BrdU labelling method to be a suitable alternative for the time-consuming autoradiography, if data on Ts or Tpot are sufficient. Due to difficulties in the reproducibility of the immunofluorescence staining and asynchronization of cells approximately 10 h after labelling, the method of windows analysis was affected by similar problems to those observed in interpretation of percentage labelled mitosis (PLM) curves. However, the method may serve as an alternative to determine cell cycle times in vitro and, if improved technically, in vivo. Careful comparison of the data obtained from mid-S, mid-G1 and mid-G2 windows may increase the reliability of the determination of cell kinetic parameters.

The relationship between radiosensitivity and cell kinetic effects after low- and high-dose-rate irradiation in five human tumors in nude mice.

Radiation-induced synchronization of cells in the radiosensitive G2 phase can, theoretically, be applied to individual tailoring of fractionation schemes, possibly rendering radiotherapy more effective. For that purpose, cell cycle perturbations were studied in five xenografts by flow cytometry. A dose-dependent increase of cells in G2 phase was noticed in all five tumor cell lines after high-dose-rate irradiation, and in four tumor cell lines after low-dose-rate irradiation. The timing of maximum accumulation was not related to dose, but coincided with the cell cycle time of the respective tumors. Furthermore, the increase in the number of cells in G2 phase correlated with the radiosensitivity of the tumors as assessed by measurements of regrowth delays. The observed synchronization provides a basis for further investigations on the relevance of radiation-induced cell cycle synchrony to the effectiveness of fractionated radiotherapy.