The two sides of resistance: aggressiveness and mitotic instability as the Achilles heel of Osimertinib-resistant NSCLC

Non-small cell lung cancer (NSCLC) represents majority of lung cancer cases and remains a leading cause of cancer mortality worldwide. Tumors carrying activating mutations in the epidermal growth factor receptor (EGFR) are highly sensitive to EGFR tyrosine kinase inhibitors (TKIs), with third-generation inhibitors such as Osimertinib now established as standard of care. However, acquired resistance to Osimertinib inevitably develops, involving both genetic and non-genetic mechanisms, the latter playing a major role in sustaining cellular plasticity and promoting tumor aggressiveness. Among regulators of adaptive programs, the Polycomb protein BMI1 has emerged as a key factor driving stemness, epithelial-to-mesenchymal transition (EMT), and therapy resistance in multiple cancers, yet its role in Osimertinib resistance remains poorly defined. Here, we show that Osimertinib-resistant H1975 cells, which display greater aggressiveness than their parental counterparts, are enriched in BMI1 target genes and mitotic cell-cycle pathways, establishing a dependency on microtubule dynamics and mitotic control. Functionally, BMI1 drives migration, invasiveness, and tumor progression in resistant cells. This mitotic dependency creates a therapeutic vulnerability that can be exploited with Unesbulin (PTC596), a BMI1 inhibitor that destabilizes microtubules and induces mitotic catastrophe, thereby effectively suppressing tumor growth in vitro and in vivo. Our findings establish BMI1 as a central mediator of Osimertinib resistance and provide a mechanistic and therapeutic rationale for targeting BMI1 and mitotic weaknesses in refractory EGFR-mutant NSCLC.