Abstract 539: Secretory EMT fuels ERBB3 axis activation in resistance to EGFR inhibitors

Abstract Non-small cell lung cancer (NSCLC) patients with activating EGFR mutations, such as exon 19 deletions (del746-750) and the L858R point mutation in exon 21, respond well to third-generation tyrosine kinase inhibitors (TKIs) like osimertinib. However, resistance inevitably emerges, limiting the long-term efficacy of these therapies. In this study, we investigated non-genomic mechanisms contributing to TKI resistance, focusing on the activation of bypass pathways that facilitate drug tolerance. These pathways enable drug tolerant persister cells to survive EGFR inhibition by exploiting alternative signaling routes. Among these, the upregulation of HER3 has been identified as a key mechanism. Clinical evidence has demonstrated the therapeutic potential of targeting HER3, notably with antibody-drug conjugates (ADCs) like patritumab deruxtecan. However, the precise molecular and cellular basis for HER3 dependency in NSCLC patients who progress on TKI therapy remains poorly understood. To address this gap, we employed a combination of immortalized and patient-derived cell lines, alongside advanced single-cell sequencing technologies, to elucidate the underlying biology. Our findings reveal that HER3 dependency post-TKI treatment is specifically enriched in pulmonary alveolar type I and II cells. This dependency is driven and maintained by paracrine signaling involving secreted factors, with neuregulin-1 (NRG1) playing a central role. NRG1 is primarily secreted by the tumor stroma and by cancer cells undergoing epithelial-to-mesenchymal transition (EMT) or dedifferentiation. Prolonged drug exposure further amplifies NRG1 secretion, which not only sustains HER3 activation but also promotes genetic and phenotypic plasticity. This is accompanied by EMT-associated morphological changes that enhance invasiveness and metastatic potential. Notably, our preclinical models demonstrated that the combination of an NRG1-neutralizing antibody with a dual EGFR blockade—achieved through a TKI and an anti-EGFR antibody—completely eradicated tumors in vivo. These results highlight the critical role of HER3 signaling and its interplay with the tumor microenvironment in mediating TKI resistance and suggest a compelling therapeutic strategy for overcoming resistance in NSCLC. Citation Format: Alessandra Morselli, Donatella Romaniello, Chiara Miroglio, Martina Mazzeschi, Michela Sgarzi, Federica Pagano, Cinzia Girone, Francesca Ambrosi, William Kothalawala, Gyorffy Balázs, Andrea De Giglio, Michelangelo Fiorentino, Andrea Ardizzoni, Yosef Yarden, Mattia Lauriola. Secretory EMT fuels ERBB3 axis activation in resistance to EGFR inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 539.