Mechanisms of resistance to last generation EGFR inhibitors: hijacking compensatory pathways

EGFR-mutated non-small cell lung cancer (NSCLC) is successfully treated with small molecules TK inhibitors. However, tumor relapse occurs and the underlying mechanisms of drug resistance are related to the insurgence of new mutations or activation of new bypass pathways. The complete abrogation of EGFR axis, achieved through the combination of osimertinib and cetuximab, leads to the activation of the parallel pathways HER2 and HER3 along with the upregulation of the HER3 ligand, NRG1. In line, NRG1 when overexpressed increases proliferation and invasion of cancer cells conferring resistance to EGFR/HER2-targeted therapy. Our hypothesis is that targeting NRG1 will effectively impair ErbB signaling through both HER2, HER3 and HER4 parallel pathways activation. To assess this we employed lung adenocarcinoma cell lines carrying exon 19 deletion in EGFR and an ex vivo model derived from an EGFR-mutated patient but resistant for osimertinib therapy. ScRNAseq revealed the plasticity of lung cancer tumor cells confirming the abundance of the NRG1 driven bypass pathways activation in response to the treatment. Through the use of osimertinib resistant cells (AZDR) we demonstrated the fundamental role of NRG1/HER3 axis in developing resistance and metastasis. Thus, we employed an antibody neutralizing NRG1 in combination with osimertinib and cetuximab to assess the benefit of blocking NRG1 on EGFR neutralization effectiveness. NRG1 neutralization strongly inhibited cell invasion and proliferation in cells and tumor growth in mice, resulting in the dampening of HER3 and RTKs upregulation and activation after TKIs treatment. Collectively, these findings support the hypothesis that NRG1 may represent an escaping mechanism to EGFR inhibition and its neutralization will effectively impair ErbB signaling through both HER2, HER3 and HER4 parallel pathways activation.