Purpose: Epithelial-to-mesenchymal transition (EMT) confers resistance to a number of targeted therapies and chemotherapies. However, it has been unclear why EMT promotes resistance, thereby impairing progress to overcome it. Experimental Design: We have developed several models of EMT-mediated resistance to EGFR inhibitors (EGFRi) in EGFR mutant lung cancers to evaluate a novel mechanism of EMT-mediated resistance. Results: We observed that mesenchymal EGFR mutant lung cancers are resistant to EGFRi-induced apoptosis via insufficient expression of BIM, preventing cell death despite potent suppression of oncogenic signaling following EGFRi treatment. Mechanistically, we observed that the EMT transcription factor ZEB1 inhibits BIM expression by binding directly to the BIM promoter and repressing transcription. De-repression of BIM expression by depletion of ZEB1 or treatment with the BH3 mimetic ABT-263 to enhance "free" cellular BIM levels both led to re-sensitization of mesenchymal EGFR mutant cancers to EGFR inhibitors. This relationship between EMT and loss of BIM is not restricted to EGFR mutant cancers as it was also observed in KRAS mutant lung cancers and large datasets including different cancer subtypes. Conclusions: Altogether, these data reveal a novel mechanistic link between EMT and resistance to lung cancer targeted therapies.
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