The three-dimensional structures of the extracellular domains of each family member have been determined and widely support the mode of ligand-mediated dimerization activation of the EGFR signaling pathway (5). These receptors are expressed in epithelial, mesenchymal, and neuronal tissues and play fundamental roles in cell proliferation, differentiation, adhesion, survival, migration (6), and in the molecular pathogenesis of cancer. SKOV-3. A simultaneous incubation with Cetuximab (anti-EGFR) and Trastuzumab (anti-HER2) disturbed EGFR/HER2 heterodimers resulting in a 72% reduction. Cetuximab, Trastuzumab or Pertuzumab (anti-HER2) alone induced a 48, 44, or 24% reduction, respectively. In Endothelin-2, human contrast, the tyrosine kinase inhibitors Erlotinib and Lapatinib had very little effect on EGFR/HER2 dimers concentration.In vivo, the combination of Cetuximab and Trastuzumab showed a better therapeutic effect (median survival and percentage of tumor-free mice) than the single mAbs. These results suggest a correlation between the extent of the mAb-induced EGFR/HER2 heterodimer reduction and the efficacy of such mAbs in targeted therapies. In conclusion, quantifying EGFR/HER2 heterodimers using our antibody-based TR-FRET assay may represent a useful method to predict the efficacy and explain the mechanisms of action of therapeutic mAbs, in addition to other commonly used techniques that focus on antibody-dependent cellular cytotoxicity, phosphorylation, and cell proliferation. Keywords:Antibodies, Anticancer Drug, Cancer Therapy, Receptor Endothelin-2, human Regulation, Receptor Tyrosine Kinase, HTRF, Therapeutic Antibodies, Tyrosine Kinase Inhibitors == Introduction == The human ErbB family of receptor tyrosine kinase comprises four members: epidermal growth factor receptor (EGFR),2HER2 (c-erbB-2), HER3 (c-erbB-3), and HER4 (c-erbB-4). These large glycoproteins contain an extracellular ligand binding domain name, a transmembrane region and an intracellular receptor tyrosine kinase (RTK) domain name. The extracellular portion consists of four subdomains referred to as domains I-IV (1). Except for HER2, structural changes in answer (from tethered to untethered conformation) that allow the exposure of the dimerization arm are induced following activation by a subset of potential ligands, including EGF (2,3). Therefore, HERs can form homodimers, heterodimers and possibly higher order Endothelin-2, human oligomers. HER2, which naturally adopt the untethered conformation, is usually described as the preferred heterodimerization partner with other HERs (4). The three-dimensional structures of the extracellular domains of each family member have been decided and widely support the mode of ligand-mediated dimerization activation of the EGFR signaling pathway (5). These receptors are expressed in epithelial, mesenchymal, and neuronal tissues and play fundamental roles in cell proliferation, differentiation, adhesion, survival, migration (6), and in the molecular pathogenesis of cancer. Many modifications of HER expression contribute to generate malignant transformation, such as HER2 overexpression in breast cancer. HERs are, therefore, a key therapeutic target in many types of cancer, including breast and colorectal cancers. Clinically, the prognostic significance of each HER receptor is usually controversial, but generally, HER overexpression is usually correlated with poor prognosis (7,8). Specifically, EGFR and HER2 co-expression is usually reported to occur in the most aggressive carcinomas (9). This association might be explained by the fact that EGFR/HER2 dimers can reduce EGFR endocytosis (10), decrease the dissociation between EGF and EGFR (11), increase EGFR recycling (12) and favor the mobility of cancer cells (13). Finally, HER heterodimers have been reported to be implicated in cancer cell resistance to various drugs by increasing phosphorylation of HER2 (14). Targeted therapies against HER Endothelin-2, human receptors are now one of the most attractive areas of oncology research. Two major classes of HER-targeted treatments are currently available: anti-HER monoclonal antibodies (mAbs), which target the extracellular domain name (15,16), and HER-specific tyrosine kinase inhibitors (TKIs) (1618), which target the tyrosine kinase activity of these receptors. Most TKIs are ATP competitors and consequently inactivate the signal transduction pathways Endothelin-2, human that mediate EGFR functions. The mAb mechanisms of action are multifactor and not completely comprehended. Their effect can be indirect through recruitment of the immune system mediated by the fragment crystallizable region of the antibody (promoting antibody-dependent cellular cytotoxicity, ADCC), or direct around the receptor by, for instance, preventing ligand binding (like in the case of the anti-EGFR mAb Cetuximab). The direct blockade of the binding GADD45A site inhibits phosphorylation of the tyrosine kinase domain name and therefore activation of the downstream signaling pathways (19). However, some other potential effects of anti-HER mAbs should be explored like their ability to modify HER internalization and degradation or to perturb the concentration of homo- and heterodimers. Although, the expression levels of the different HERs can be used as biomarkers.
The three-dimensional structures of the extracellular domains of each family member have been determined and widely support the mode of ligand-mediated dimerization activation of the EGFR signaling pathway (5)
