Raman hyperspectral imaging of transferrin-bound iron in cancer cells

Iron is an essential element required for human life. Iron is highly regulated in the body, as iron deficiency leads to many adverse health effects, such as anemias. Ferric iron (Fe3+) bound to serum transferrin (Tf) is internalized into cells via the transferrin receptor (TfR). Since the exact mechanisms of iron release in cells are not well known, a technique that allows detection of Tf bound iron inside intact human cells has been developed. Methods to determine when and where Tf releases iron inside a cell are required to better understand disease progression, including cancer. We have previously shown that Raman micro-spectroscopy is able to detect and quantify the Tf-bound iron in epithelial cells. In this work, we applied hyperspectral Raman imaging to visualize the spatial distribution of Tf-bound iron in human breast cancer T47D cells internalized with iron-loaded Tf, oxalate-Tf, a chemical Tf mutant unable to release iron, and iron-depleted Tf. We have also shown that Raman imaging can quantify the amount of iron under different times of Tf internalization (Tf uptake time), prior to fixation. Raman micro-spectroscopy provides a unique way to determine the amount of iron under different Tf internalization times by employing the Raman metric, which was used to quantify iron content in oxa, apo-, and holo-Tf samples. Importantly, Raman microspectroscopy can be used to follow iron release from Tf in breast cancer cells. Determining the kinetics and location of iron release in cancer cells is key to further our understanding of iron metabolism during cancer progression.