Structural biology for synergistic development of innovative drugs: biostruct-farm

Epidermal growth factor receptors (EGFRs), also called ErbB receptors, are considered the canonical receptor tyrosine kinases (RTKs). ErbB3 is one of these receptor and it is involved in different types of cancers. Its function is to activate kinase signaling by heterodimerization with ErbB1 and ErbB2. ErbB3 is therefore a key player in tumor progression and resistance since it is upregulated in response to inhibitors-based therapies that target ErbB1 and ErbB2. However, ErbB3 lacks tyrosine kinase activity, making tyrosine kinase inhibitors (TKIs) ineffective. To overcome this problem and to provide an alternative anti-cancer therapy, a potential strategy is to prevent the ErbB3-ErbB1/2 heterodimerization with monoclonal antibodies. For this purpose, Takis S.r.l., a biotech company based in Rome, has developed two humanized monoclonal antibodies against ErbB3. The aim of my PhD project, born from a collaboration between Takis (Giuseppe Roscilli’s group) and Sapienza University (Beatrice Vallone’s laboratory), is to structurally and functionally characterize the binding modalities of these antibodies to ErbB3. In this thesis, we demonstrate the high affinity of the two humanized monoclonal antibodies for the ErbB3 receptor by ELISA and BLI assays, and the effective suppression of ligand-dependent stimulation by in vitro experiments. Using X-ray crystallography we identified the epitope residues involved in the binding to one of these antibodies, while single particle cryo-electron microscopy revealed the location of the binding site of both of them in the presence of the ligand NRG1β. In conclusion, these results, arising from an integrative approach of structural biology techniques, functional and binding studies, paves the way towards new anticancer strategies targeting ErbB3 receptor.