Inhibition of hTERT/telomerase/telomere mediates therapeutic efficacy of osimertinib in EGFR mutant lung cancer

The inevitable acquired resistance to osimertinib (AZD9291), an FDA-approved third-generation EGFR tyrosine kinase inhibitor (EGFR-TKI) for the treatment of patients with advanced non-small cell lung cancer (NSCLC) harboring EGFR activating or T790M resistant mutations, limits its long-term clinical benefit. Telomere maintenance via telomerase reactivation is linked to uncontrolled cell growth and is a cancer hallmark and an attractive cancer therapeutic target. Our effort toward understanding the action mechanisms, including resistance mechanisms, of osimertinib has led to the identification of a novel and critical role in maintaining c-Myc-dependent downregulation of hTERT, a catalytic subunit of telomerase, and subsequent inhibition of telomerase/telomere and induction of telomere dysfunction in mediating therapeutic efficacy of osimertinib. Consequently, osimertinib combined with the telomere inhibitor, 6-Thio-dG, which is currently tested in a phase II trial, effectively inhibited the growth of osimertinib-resistant tumors, regressed EGFRm NSCLC patient-derived xenografts, and delayed the emergence of acquired resistance to osimertinib, warranting clinical validation of this strategy to manage osimertinib acquired resistance.