Distinct metabolic changes in human lung cancer cells with differential radiation sensitivities

Background: Radiotherapy is one of the most important modalities for cancer treatment. However, the radio-resistance of malignant tumor cells is the major cause of radiation treatment failure. Although several biochemical pathways are disturbed in response to radiation, the metabolite profiles related to radio-resistance have not been well investigated in malignant non-small cell lung carcinomas (NSCLCs). Malignant lung cancer cells, CL1-5, were more resistant to radiation than were the parental CL1-0 cells. Therefore, the two cell lines provide a suitable cell model to investigate changes in metabolite profiles related to radiation exposure. Methods: Two human lung cancer cell lines, CL1-5 and CL1-0, with differential radiation sensitivities, were irradiated at a dosage of 10 Gy and harvested at 1, 4, and 24 hr after radiation treatment. Proton nuclear magnetic resonance (1H-NMR) was used to analyze the metabolic profiles of the CL1-0 and CL1-5 cell lines. The metabolite profiles of the cell extracts were subjected to principal component analysis (PCA). Both PCA and specific metabolite data were used to examine metabolic differences between the two cell lines. Results: The colony formation assay results demonstrate that CL1-5 cells are more sensitive than CL1-0 cells to irradiation. The PCA score plots for NMR spectra of CL1-0 and CL1-5 cells identified metabolites such as glutathione, creatine phosphate, glutamate, o-phosphocholine, pyroglutamate, taurine, and trimethylamine n-oxide (TMAO) as key molecules with high correlation in response to different irradiation tolerance. The metabolite profiles of the cell lines were inherent different, but following 24-hr irradiation, common metabolite alterations were induced in both cell lines. Moreover, CL1-0 cells showed a larger difference in the elevation of glutathione levels than CL1-5 cells. Conclusions: Our study demonstrates a clear difference in metabolite profiles between irradiation-resistant and irradiation-sensitive cells. These metabolite profile changes could be used to elucidate the possible mechanism of radio-resistance.