Abstract
We compared the cellular responses to three different forms of germanium compounds, i.e. inorganic-Ge (germanium oxide, GeO2), organic-Ge (Ge-132), and nano-Ge particle. Treating Chinese hamster ovary K1 cells with 5 mM Ge-132 did not alter the growth rate as compared to those of untreated cells within 48 hours. On the contrary, 5 mM GeO2 treatment delayed the cell growth through arresting the cells at G2/M phase. The same effect was observed in cells treated with nano-Ge. However, the population of cells in G2/M phase remained unchanged when receiving Ge-132. Moreover, treating cells with GeO2 and nano-Ge enhanced radiosensitivity, whereas the effect was not observed in Ge-132 treated cells. The cellular uptake rate of Ge-132 was slower than that of GeO2, which resulted in a less accumulation of Ge content in Ge-132 treated cells. However, the Ge content was similar when cell received 5 mM Ge-132 or 1 mM GeO2 for 12 hours. In this condition, a different radiosensitizing effect was still observed. GeO2 and nano-Ge enhanced radiosensitivity through elevating DNA damage as analyzed by alkaline comet assay and the quantity of □-H2AX. After exposing to the X-ray, a prolonged G2/M arrest was found in cells treated with GeO2 and nano-Ge. The presence of inorganic Ge compounds also affects the efficiency of DNA repair after X-irradiation. Enhancement of DNA break and reduction of DNA repair efficiency concurrently cause the increase of radiosensitivity.