New strategies to overcome limitations of reversible EGFR tyrosine kinase inhibitor therapy in non-small cell lung cancer

The epidermal growth factor receptor (EGFR), a member of the HER family of receptors, has become a well-established target for the treatment of patients with non-small cell lung cancer (NSCLC). Several EGFR-targeted agents produce objective responses in a minority of unselected patients, but a majority of those with EGFR-activating mutations; however, all responders eventually develop resistance. The modest activity of agents that target only EGFR may be due, in part, to the complexity and interdependency of HER family signaling. The interdependent signaling that occurs between EGFR and HER2 provides a rationale for the simultaneous inhibition of these receptors with reversible and irreversible inhibitors. Several agents with activity against both EGFR and HER2 are currently under development. Irreversible EGFR/HER2 tyrosine kinase inhibitors (TKIs) (e.g., BIBW 2992, HKI-272) and pan-HER TKIs (e.g., PF00299804) comprise a novel class of agents in clinical development that may prevent and overcome inherent and acquired resistance to first-generation reversible EGFR TKIs. Other agents in development include the monoclonal antibody pertuzumab, and XL-647, which inhibits EGFR and HER2, as well as multiple vascular endothelial growth factor receptor family members. Here we briefly review the currently available EGFR-targeted agents, discuss the rationale for extending inhibition to other HER family members, weigh the merits of irreversible HER family inhibition, and summarize preclinical and clinical data with EGFR/HER2 and pan-HER inhibitors under clinical development.