Primary cilia promote resistance to EGFR tyrosine kinase inhibitor, osimertinib, in non–small cell lung cancer

Patients with advanced non-small cell lung cancer (NSCLC) and mutations in epidermal growth factor receptor (EGFR) benefit from EGFR tyrosine kinase inhibitors (TKIs). Osimertinib, a third-generation EGFR TKI, is standard first-line therapy for EGFR-mutated NSCLC, but most patients develop resistance to it. Here, we demonstrate that increased formation of primary cilia, microtubule-based sensory organelles, is associated with osimertinib-refractory NSCLC progression. EGFR-mutated, osimertinib-resistant human NSCLC cells had increased cilia formation and acetylation of α-tubulin and reduced histone deacetylase 6 (HDAC6) activity compared to their osimertinib-sensitive counterparts. HDAC6 inhibition increases cilia formation in osimertinib-sensitive NSCLC cells, and overexpression of exogenous HDAC6 sensitized osimertinib-resistant NSCLC cells to osimertinib's anti-proliferative effects. Because intraflagellar transport (IFT) proteins are essential for primary cilium formation and function, we knocked down IFT88 in osimertinib-resistant NSCLC cells, which reversed osimertinib resistance in orthotopic and subcutaneous mouse models of lung cancer. Mechanistically, increased sodium influx during osimertinib-induced inhibition of EGFR signalling promotes cilia formation through sustained HDAC6 inactivity and greater α-tubulin acetylation. Inhibition of sodium influx with dibutyryl-cAMP decreased cilium formation, increased sensitivity to osimertinib, and reduced tumor progression in mice bearing osimertinib-resistant lung tumors. Collectively, our findings suggest that enhanced primary cilium formation mediates EGFR TKI resistance and that targeted inhibition of ciliogenesis may prevent or overcome osimertinib resistance.