Abstract
Glioblastomas commonly (40%) exhibit epidermal growth factor receptor (EGFR) amplification, half of these tumors carry the EGFRvIII deletion variant characterized by an in-frame deletion of exons 2–7, resulting in constitutive EGFR activation. Although EGFR tyrosine kinase inhibitors had only modest effects in glioblastoma, novel therapeutic agents targeting amplified EGFR or EGFRvIII continue to be developed. Depatuxizumab mafodotin (ABT-414) is an antibody drug conjugate consisting of the monoclonal antibody 806 and, as its toxic payload, monomethyl auristatin F, designed to target EGFR-overexpressing tumor cells. Since long-term glioma cell lines and patient-derived glioma-initiating cell lines appeared to express too little EGFR in vitro to be sensitive to ABT-414, we generated glioma sublines overexpressing EGFR or EGFRvIII to explore the determinants of ABT-414-induced glioma cell death. Overexpression of EGFRvIII induces sensitization to ABT-414 more readily than overexpression of EGFR. There is no bystander killing of cells devoid of EGFR or EGFRvIII expression. Surprisingly, either exposure to EGF or to EGFR tyrosin kinase inhibitors reduce EGFR protein levels and are thus no strategies to promote ABT-414-induced cell killing. Furthermore, glioma cells overexpressing kinase-dead EGFR or EGFRvIII retain binding of mAb 806 and sensitivity to ABT-414, allowing to dissociate EGFR phosphorylation from the emergence of the “active” EGFR conformation required for ABT-414 binding. The combination of EGFR-targeting antibody drug conjugates with EGFR tyrosine kinase inhibitors carries a high risk of failure. Promoting mere EGFR expression rather than phosphorylation should result in glioblastoma cell sensitization to ABT-414 or related agents.
High-throughput screening uncovers miRNAs enhancing glioblastoma cell susceptibility to tyrosine kinase inhibitors