Abstract
Although chordoma, a rare bone cancer, has been treated with surgery and/or radiation including heavy ions, no in vitro characterizations of chordoma cells are available. The main reason for this is the extremely long doubling time associated with the only recognized cell line, U-CH1. Here, we derived a cell line (designated as U-CH1-N) from U-CH1 and made the in vitro characterization, and results with U-CH1-N were compared with those with HeLa (cervical cancer) and U87-MG (glioblastoma) cells in the following.
1) Cellular doubling time, DNA content
The cell doubling times for HeLa, U87-MG and U-CH1-N were 18 h, 24 h and 3 days respectively. U-CH1-N had the most DNA content among the three, was near tetraploid, and showed an abnormal karyotype.
2) Cellular Radiosensitivity
U-CH1-N and U87-MG were more sensitive to x-irradiation than HeLa cells. Heavy ion irradiation more efficiently killed all three cell lines than x-rays did. Relative biological effectiveness (RBE) at 10% survival for U87-MG and HeLa cells was about 2.5 for 70keV/μm carbon ions and 3 for 200keV/μm iron ions, while for U-CH1-N it was 2.5 for carbon and 4 for iron ions. We proceeded the RBE evaluation with neon ions, argon ions and silicon ions, and the RBE curve of U-CH1-N had a peak value, 5.3 for 150keV/μm silicon ions.
3) Sensitivity to Genotoxic Chemical Agents
Four different chemical agents producing various DNA lesions were used for further characterization of these cells. Although camptothecin, mitomycin C or cisplatin did not reveal strong cytotoxity to U-CH1-N compared with other cells, bleomycin, which produces DNA strand breaks, showed marked cytotoxic effect on U-CH1-N.
Our data provide the first chronological cell survival information using cells of chordoma origin and also help explain the successful chordoma treatment by heavy ions.
