The epidermal growth factor receptor pathway and its inhibition as anticancer therapy

Epidermal growth factor receptor (EGFR) is commonly overexpressed in a number of epithelial malignancies and is often associated with an aggressive phenotype [e.g., non-small cell lung cancer (NSCLC) and bladder cancer]. EGFR is present in over 50% of cases of NSCLC, head and neck squamous cell carcinomas (HNSCC) and colon cancer. Several EGFR-targeting agents have been recently developed (C225, ABX-EGF, E7.6.3, EMD 55900, ICR62, ZD1839, CP358774, PD168393, CGP75166/PKI166, CGP59326A, BIBX1382). The two most advanced EGFR inhibitors in development are C225 and ZD1839. C225 is an antibody directed against the ligand-binding domain of human EGFR, which competes for receptor binding with EGF and other ligands. In vitro, C225 inhibits EGFR tyrosine kinase activity and proliferation of EGFR-overexpressing squamous cell carcinoma cell lines. Synergy was observed with doxorubicin, cisplatin and radiation in preclinical models. In phase I trials, major toxicity has been dermatological (rash and acneic skin reactions); allergic reactions have also been observed in about 3% of cases. This agent, administered intravenously once weekly, is presently in phase III trials in HNSCC and colon cancer. ZD1839, a synthetic molecule which targets the EGFR ATP binding site, is a very specific inhibitor of EGFR tyrosine kinase activity. Synergy has been observed with paclitaxel and cisplatin. In phase I trials, responses were seen in advanced NSCLC, and cutaneous toxicity and diarrhea were the most important side effects. Oral chronic daily administration is feasible. Two large randomized trials have been completed in advanced NSCLC in combination with chemotherapy. A large phase II study in second and third line has demonstrated a single agent activity of 18.5%. Another large phase II study in patients who received prior platinum and docetaxel obtained a response rate of 11%. There was no difference in response rate between the 250 and the 500 mg/day doses, but side effects were higher in patients who received the 500 mg dose. A very similar small molecule, OSI-774, has also shown activity in this setting. Two large randomized phase III studies of ZD1839 have recently been completed and analyzed in which two doses of ZD1839 (250 or 500 mg/day) or placebo were given in combination with two different chemotherapy regimens (carboplatin-paclitaxel or carboplatin-gemcitabine). These studies failed to demonstrate an increase in survival by adding ZD1839 together with chemotherapy in patients with advanced NSCLC.