Germanium oxide enhances the radiosensitivity of cells.

We investigated here the combined effect of GeO(2) and radiation on cell viability. Cells were treated with 0 to 22 mM GeO(2) for 12 h followed by 1 Gy X irradiation. A synergistic cytotoxic effect was observed for the combined treatment with a dose-dependent reduction of cell viability. Complete survival curves showed a 2.3- and 2.75-fold increase in radiosensitivity for 50% cell death in the presence of 5 and 15 mM GeO(2), respectively. The increased radiosensitivity also occurred when GeO(2) was given either 4 h prior to irradiation or immediately after radiation exposure. GeO(2) did not affect the total soluble thiol content or the activities of catalase and glutathione S-transferase. Analysis of the production of reactive oxygen species (ROS) revealed that the combined treatment dramatically increased the synthesis of ROS. Addition of N-acetyl cysteine (NAC, 20 mM) decreased the production of ROS in cells. NAC, however, increased cell viability only slightly after treatment with GeO(2) and radiation. Thus increased production of ROS makes little or no contribution to the observed death. The combination of GeO(2) and X radiation, however, significantly increased the frequency of DNA double-strand breaks (DSBs). Notably, the presence of GeO(2) also reduced the efficiency of DNA repair. We conclude that treatment with GeO(2) followed by X irradiation increases DNA DSBs and cell death.

Germanium oxide inhibits the transition from G2 to M phase of CHO cells.

We report here for the first time that germanium oxide (GeO(2)) blocks cell progression. GeO(2) is not genotoxic to Chinese hamster ovary (CHO) cells and has limited cytotoxicity. However, GeO(2) arrests cells at G2/M phase. The proportion of cells stopped at G2/M phase increased dose-dependently up to 5 mM GeO(2) when treated for 12 h, but decreased at GeO(2) concentration was greater than 5 mM. Analysis of 5-bromodeoxyuridine-labeled cells indicated that GeO(2) delayed S phase progression in a dose-dependent manner, and blocked cells at G2/M phase. Microscopic examination confirmed that GeO(2) treatment arrested cells at G2 phase. Similar to several other events that cause G2 block, the GeO(2)-induced G2 block can also be ameliorated by caffeine in a dose- and time-dependent manner. To explore the mechanism of G2 arrest by GeO(2), cyclin content and cyclin-dependent kinase activity were examined. Cyclin B1 level was not affected after GeO(2) treatment in CHO cells. However, GeO(2) decreased p34(cdc2) kinase (Cdk1) activity. The kinase activity recovered within 9 h after GeO(2) removal and correlated with the transition of G2/M-G1 phase of the cells. This result suggests that GeO(2) treatment reduces Cdk1 activity and causing the G2 arrest in CHO cells.