Confocal Raman spectroscopic analysis of the cytotoxic response to cisplatin in nasopharyngeal carcinoma cells

Apoptosis of nasopharyngeal carcinoma cells (C666 cell line) induced by an anticancer drug cisplatin was investigated by confocal Raman micro-spectroscopy using near-infrared laser (785 nm) excitation in this study. The Raman spectra of C666 cells treated with different concentrations of cisplatin (0.5, 1, 5 and 10 μg mL−1) for 24 h and different treatment times (6, 12, 18 and 24 h) with 5 μg mL−1 cisplatin were collected separately. Difference in the intensities of Raman peaks assigned to the DNA band (783 cm−1, 1338 cm−1, 1523 cm−1 and 1576 cm−1) between the cells treated with cisplatin and control cells becomes greater as the concentration of cisplatin increases, indicating that the cytotoxicity of cisplatin for NPC cells is likely related to its concentration. The major difference between the apoptotic C666 cells incubated with cisplatin and the non-treated cells is the reduction in intensities of vibration bands generated by cellular nucleic acids, proteins and lipids. Large intensity reduction in nucleic vibrations at 783, 1523 and 1576 cm−1 was observed upon apoptosis of the C666 cells. In particular, up to 14.1% and 49.6% reduction in the magnitude of the peaks at 783 cm−1 and 1523 cm−1 respectively in Raman spectra of the apoptotic cells was observed after 24 h of cisplatin treatment, which suggests the breakdown of phosphodiester bonds and DNA bases. Moreover, the intensity of peaks at 1002 and 1447 cm−1 respectively fell to 40.9% and 43.1% of the original value, which indicates that cisplatin could induce apoptosis of C666 cells and reduce the amount of nucleic acid and protein in the cells. These results demonstrate that Raman spectroscopy is a novel, nondestructive mean for studying the anticancer-treated carcinoma cells, which could also provide abundant information about the changes in biochemical properties of cells and serve as an effective method for real time measurement of apoptosis.