Raman Spectroscopy Detects Biochemical Changes Due to Proliferation in Mammalian Cell Cultures

Raman spectra of cells and nuclei from cultures in the plateau (nonproliferating) and exponential (proliferating) phases of growth were measured and show that Raman spectroscopy can monitor changes due to cell proliferation. A simple fitting routine was developed using a basis set (lipid, protein, DNA, RNA) to estimate the relative amounts of biochemical components in cells and nuclei. Using relative amounts and ratios of biochemical components, reproducible differences can be detected and quantified that are not readily apparent by visual analysis of vibrational bands in the spectra. These differences, due to cell proliferation, can be assigned to specific biochemical changes. They include a decrease in the relative lipid and increases in the relative protein and RNA for both nontumorigenic exponential cells and nuclei, and an increase in the relative RNA for tumorigenic exponential cells. The lipid/RNA ratio decreases for nontumorigenic exponential cells and nuclei and tumorigenic exponential cells. The protein/lipid ratio increases for both tumorigenic and nontumorigenic exponential cells and nuclei. Finally, the lipid/DNA ratio decreases for tumorigenic exponential nuclei. This knowledge will be important for Raman detection of rapidly dividing populations of cancer cells in vivo.