EGFR Oncogenes Expressed In Glioblastoma Are Activated As Covalent Dimers And Paradoxically Stimulated By Erlotinib

Mutation of both the intracellular catalytic domain and the extracellular domain of the receptor for epidermal growth factor (EGFR) can drive oncogenicity. Despite clinical success with targeting EGFR catalytic site mutations, no drugs have proven effective in patients expressing allosteric extracellular domain EGFR mutations, including glioblastomas (GBM) where these mutations are highly expressed. We define the molecular mechanism for oncogenic activation of families of extracellular EGFR mutations and reveal how this mechanism renders current generation small molecule ATP-site inhibitors ineffective. We demonstrate that a group of commonly expressed extracellular domain EGFR mutants expressed in GBM is activated by disulfide-bond mediated covalent dimerization, collectively referred to as locked dimerization (LoDi) EGFR oncogenes. Strikingly, small molecules binding to the active kinase conformation (Type I), but not those binding to the inactive kinase conformation (Type II), potently inhibit catalytic site mutants, but induce covalent dimerization and activate LoDi-EGFR oncogenes, manifesting in paradoxical acceleration of proliferation. Significance Our data demonstrate how the locked-dimer mechanism of EGFR oncogenesis has a profound impact on the activity of small molecule inhibitors. This provides a mechanistic understanding for the failure of current generation EGFR inhibitors to effectively treat LoDi-EGFR mutants in GBM, and sets guidelines for discovery of selective LoDi-EGFR inhibitors.