Nearly all human tissues express epidermal growth factor receptors(ErbBs)embedded in the plasma membrane. Four homologous ErbB proteins exert a pivotal function of transmitting proliferative signals by binding their cognate ligands. Binding promotes receptor activation mediated by dimer formation. Due to genetic mutations/deletions, amplification of ErbB2 is associated with aberrant receptor activation leading to malignancy and poor clinical prognosis. Removal of ErbB2 from dimers and subsequently from the cell surface may reduce oncogenicity in cells overexpressing ErbB2. This has been an important focus in this thesis. Two anticancer agents, pertuzumab, targeting ErbB2`s dimerization arm andgeldanamycin, inducing cellular internalization and degradation of ErbB2, were applied as pharmaceutical tools for this purpose. Furthermore, an ErbB2-Ubiquitin chimeric protein is under construction to confirm whether ubiquitin is instrumental inthese processes.
Based on immunological isolation and detection of crosslinked ErbB1-ErbB2, disruption of the ligand-induced heterodimers was evident on pertuzumab stimulation. Consequently, increased ErbB1 internalization was detected by confocal imaging and internalization assays, confirming that ErbB2 inhibits internalization of other ErbB proteins. In the same cellular system where ErbB2 overexpression biases the formation of ErbB2-containing dimers, pertuzumab was additionally shown to completely dissolve ligand-independent heterodimers. Furthermore, the geldanamycin induced effect on ErbB2 was demonstrated in an ovarian carcinoma cell line and further enhanced by a novel combination with pertuzumab. Flow cytometry analysis detected a synergetic reduction of ErbB2 surface levels whileconfocal microscopy visualized intracellular ErbB2-localization when the two agents were added simultaneously. In conclusion, data addressing molecular insight into mechanisms underlying ErbB-protein down-regulation will promote innovative drug design.