The EGF receptors and their cognate ligands that belong to the epidermal growth factor (EGF) family of peptides are involved in the pathogenesis of different types of cancers. In fact, the ErbB receptors and the EGF-like growth factors are frequently expressed in human tumors. These proteins form a complex system that regulates the proliferation and the survival of cancer cells. Therefore, ErbB receptors and their ligands might represent suitable targets for novel approaches in human cancer treatment.
In this regard, different target-based agents that are directed against the EGF receptors have been developed in the past two decades. One of these compounds, the humanized anti-ErbB-2 monoclonal antibody trastuzumab has been approved for the treatment of patients with metastatic breast cancer. The anti-EGF receptor (EGFR) antibody C225, as well as EGFR tyrosine kinase inhibitors ZD1839 and OSI-774 are currently in phase III clinical development. Several other ErbB tyrosine kinase inhibitors are in phase I/II studies. These compounds have generally been shown to have an acceptable toxicity profile and promising anti-tumor activity in heavily pretreated patients.
Human carcinomas frequently express high levels of receptors in the EGF receptor family, and overexpression of at least two of these receptors, the EGF receptor (EGFr) and closely related ErbB2, has been associated with a more aggressive clinical behavior. Further, transfection or activation of high levels of these two receptors in nonmalignant cell lines can lead to a transformed phenotype. For these reasons therapies directed at preventing the function of these receptors have the potential to be useful anti-cancer treatments.
In the last two decades monoclonal antibodies (MAbs) which block activation of the EGFr and ErbB2 have been developed. These MAbs have shown promising preclinical activity and 'chimeric' and 'humanized' MAbs have been produced in order to obviate the problem of host immune reactions. Clinical activity with these antibodies has been documented: trastuzumab, a humanized anti-ErbB2 MAb, is active and was recently approved in combination with paclitaxel for the treatment of patients with metastatic ErbB2-overexpressing breast cancer; IMC-C225, a chimeric anti-EGFr MAb, has shown impressive activity when combined with radiation treatment and reverses resistance to chemotherapy. In addition to antibodies, compounds that directly inhibit receptor tyrosine kinases have shown preclinical activity and early clinical activity has been reported. A series of phase III studies with these antibodies and direct tyrosine kinase inhibitors are ongoing or planned, and will further address the role of these active anti-receptor agents in the treatment of patients with cancer.