Clinical studies with non-iressa EGFR tyrosine kinase inhibitors

During the last five years there has been interest in developing non-cytotoxic, targeted cancer treatments. This phenomenon has occurred as a result of increased information regarding factors which regulate tumor proliferation, survival, angiogenesis, invasiveness, and metastatic potential. In non-small cell lung cancer many investigators have focused their attention on the epidermal growth factor receptor (EGFR) because this membrane protein, which has an extracellular ligand binding domain, as well as, tyrosine kinase activity on the intracellular portion of the molecule, is expressed in a relatively high proportion of non-small cell lung cancers. Gefitinib which was the first EGFR specific tyrosine kinase inhibitor to be extensively tested in non-small cell lung cancer has shown single agent activity in non-small cell lung cancer. Subsequently, erlotinib, another EGFR specific tyrosine inhibitor, has also demonstrated single agent activity in non-small cell lung cancer. Phase III trials of erlotinib alone or in combination with chemotherapy have been completed, and data are being analyzed. Several dual inhibitors of erb B1 and erb B2 (PKI 166, GW 572016, EKB 569) have been or are being tested in phase I trials. In addition, CI 1033, a pan-erb inhibitor, is also being tested in phase I studies. Diarrhea and rash have been the predominant side effects of these agents. Life threatening toxicity has been rare. Although the erb tyrosine kinase inhibitors are attrative agents to use in treating non-small cell lung cancer because of their relatively benign toxicity profile, more data are needed to define the role of these agents in non-small cell lung cancer.