Fluorescence Polarization of Methylene Blue as a Quantitative Marker of Breast Cancer at the Cellular Level.

A quantitative technique to detect cancer in single cells could transform cancer diagnosis. Current cancer diagnosis utilizes histopathology, which requires tissue acquisition, extensive processing and, in most cases, relies on the qualitative morphological analysis of tissues and cells. Molecular biomarkers are only available for a few specific tumor subtypes. We discovered that the fluorescence polarization (Fpol) of Methylene Blue (MB) is significantly higher in cancer than in normal human breast tissues and cells. We confirmed that fluorescence polarization imaging did not affect the viability of the cells and yielded highly significant differences between cancer and normal cells using MB concentrations as low as 0.05 and 0.01 mg/ml. To explain this phenomenon we examined intracellular localization of MB and its fluorescence lifetime. We determined that higher fluorescence polarization of MB occurs due to its increased accumulation in mitochondria of cancer cells, as well as shorter fluorescence lifetime in cancer relative to normal cells. As quantitative MB Fpol imaging can be performed in vivo and in real time, it holds the potential to provide an accurate quantitative marker of cancer at the cellular level.