Quantitative Analysis of Transferrin Receptor 1 (TfR1) in Individual Breast Cancer Cells by Means of Labeled Antibodies and Elemental (ICP-MS) Detection

Cells are able to precisely control the amount of iron they acquire in the form of transferrin (TF)-bound iron by modulating the synthesis of transferrin receptor 1 (TfR1). In tumor cells, elevated TfR1 seems to be related to poorer outcome for patients. Thus, the direct measurement of this biomarker in breast cancer tissues and cells might serve as a prognosis biomarker. In this work, we have used Nd-labeled antibodies to tag the TfR1 present on the cell surface of two cell models of breast cancer with different malignancy (MCF7 and MDA-MB 231). For this aim, monoclonal antibody anti-TfR1 is first labeled with a polymeric chelator (MAXPAR) with the subsequent incorporation of several isotopic Nd-143 atoms. The characterization of the labeled antibody revealed a stoichiometry of 21 Nd atoms per antibody molecule that can be used for further quantification experiments. This antibody is used for cell tagging followed by single-cell analysis using inductively coupled plasma mass spectrometry (ICP-MS) detection. In this case, cell introduction is conducted using a high-efficiency nebulizer and spray chamber to achieve transport efficiencies of up to 55% for cells. Quantitative results revealed a number of receptors per cell significantly higher in the case of the most malignant phenotype (MDA-MB-231). Absolute and relative TfR1 concentration values are obtained in individual cells for the first time using the proposed system.