Raman mapping of transferrin and ferritin distributions in breast cancer cells

Understanding cellular iron homeostasis is critical to understanding cancer cell survival and proliferation, as this process includes balancing iron uptake with storage and utilization. Iron-bound transferrin (holo-Tf) will bind to the transferrin receptor (TfR) at the cell surface and undergo endocytosis where iron is released into a mildly acidified endosome. Inside the endosome the iron is reduced for transport across the membrane for utilization or into the cytosol for storage in ferritin (Ft). It remains unclear whether iron uptake and storage regulation remain coordinated processes in breast cancer cells. Normally, it is expected for TfR and Ft protein expression to be inversely related based on their regulation via iron regulatory proteins (IRP1/2); however, increased expression of both TfR and Ft have been expressed in heterogenous breast cancer populations. To address the heterogeneous populations, single-cell analysis with Raman hyperspectral imaging could evaluate the relationship of iron uptake and storage through identification of iron-bound Tf and Ft in unlabeled cells. Raman hyperspectral imaging at 532 nm excitation has facilitated the imaging of iron-bound Tf in unlabeled cells. It indicated disrupted Tf iron-release in triple-negative breast cancer cells (MDAMB231), but not in the luminal A breast cancer line (T47D). Our data suggests that 532 nm excitation of Ft results in unique spectra. Currently we are collecting data on the unlabeled breast cancer cells to determine the relationship of iron-bound Tf and Ft by single-cell Raman hyperspectral imaging. This method will accelerate our understanding of iron homeostasis in breast cancer cells.