Growth factor receptors in cancer cells
Greater understanding of the spatial distribution of transmembrane receptor tyrosine kinases may provide new insights into signaling mechanisms controlling cell growth. Our research aims to study the role of these receptors in cancer cells using the unique characterization possibilities provided by liquid-phase electron microscopy, capable of studying tens of cells in their native liquid environment with nanometer resolution as needed to resolve the individual constituents of protein complexes. Our recent research involved members of the epidermal growth factor receptor (EGFR) family. HER2, one of the EGFR family members, is overexpressed in certain types of breast cancer. Although HER2 is considered an orphan receptor because it has no ligand, it can form homodimers, thereby contributing significantly to a dysregulation of intracellular signaling and of cell growth. In our latest research, we have studied the intra- and intercellular variation of HER2 at the single-molecule level in intact SKBR3 breast cancer cells. The unique experimental capabilities of liquid-phase electron microscopy (LP-EM) allowed quantifying the stoichiometry of HER2 complexes, distinguishing between monomers, dimers, and higher order clusters, while mapping its location in the cell. Compared to biochemical methods providing information about the average of many cells in pooled cellular material, our methodology provides unique information at the molecular level.
Figure from: Peckys, D.B., Korf, U. & de Jonge, N., Local variations of HER2 dimerization in breast cancer cells discovered by correlative fluorescence- and liquid electron microscopy. Science Advances 1:e1500165, 2015. link
Drug resistance development in HER2 overxpressing of breast cancer
Of key interest is to analyze differences in protein function between individual cancer cells (cancer cell heterogeneity) and between distinct functional membrane regions within the same cell. With our approach it is possible to study the effect of cancer drugs on small sub-populations of cells, aiming to developing predictive markers for increasing the effectiveness of HER2 targeting drugs in personalized medicine. Small sub-populations of breast cancer cells were found to respond differently to the prescription drug trastuzumab than bulk cancer cells, see Peckys et al., Mol. Biol. Cell 28, 3193-3202, 2017.
This research is funded by the Else Kröner-Fresenius-Stiftung in the project entitled “Investigation of the Influence of Breast Cancer Drugs on HER2 Dimerization at the Molecular Level in Individual Cells Aiming to Find Clues for Causes of Drug Resistance: HERe” with projects partners Prof. Stefan Wiemann of the Deutsches Krebsforschungszentrum in Heidelberg, Dr. Diana Peckys, Biophysics Department, Saarland University, and Dr. Gilda Schmidt and Prof. Erich-Franz Solomayer of the Universitätsklinikum des Saarlandes.
Figure from: Peckys, D.B., Korf, U., Wiemann, S. & de Jonge, N., Liquid-phase electron microscopy of molecular drug response in breast cancer cells reveals irresponsive cell subpopulations related to lack of HER2 homodimers. Mol. Biol. Cell 28, 3193-3202, 2017. link
Role of HER2 in drug resistance development of gastric cancer
We also examine the role of HER2 in drug resistance development in gastric cancer by analyzing biopsy samples in a project funded by the Deutsche Krebshilfe: MetGaP “long-term response in Trastuzumab-treated metastatic gastric- or gastroesophageal junction cancer patients via molecular HER2 surface and pathway analyses” with project partner Prof. Timo Gaisery, Institute for Pathology, Medical Center Mannheim.
Figure from: Peckys, D.B., Hirsch, D., Gaiser, T. & de Jonge, N., Visualization of HER2 homodimers in single cells from HER2 overexpressing primary formalin fixed paraffin embedded tumor tissue. Mol. Med. 25, 42:1-12 (2019). link