Metabolic plasticity is an emerging hallmark of cancer, and increased glycolysis 
is often observed in transformed cells. Small molecule inhibitors that target 
driver oncogenes can potentially inhibit the glycolytic pathway. Osimertinib 
(AZD9291) is a novel EGFR tyrosine kinase inhibitor (TKI) that is potent and 
selective for sensitising (EGFRm) and T790M resistance mutations. Clinical 
studies have shown osimertinib to be efficacious in patients with EGFRm/ T790M 
advanced NSCLC who have progressed after EGFR-TKI treatment. However experience 
with targeted therapies suggests that acquired resistance may emerge. Thus there 
is a need to characterize resistance mechanisms and to devise ways to prevent, 
delay or overcome osimertinib resistance. We show here that osimertinib 
suppresses glycolysis in parental EGFR-mutant lung adenocarcinoma lines, but has 
not in osimertinib-resistant cell lines. Critically, we show osimertinib 
treatment induces a strict dependence on mitochondrial oxidative phosphorylation 
(OxPhos), as OxPhos inhibitors significantly delay the long-term development of 
osimertinib resistance in osimertinib-sensitive lines. Accordingly, growth 
conditions which promote a less glycolytic phenotype confer a degree of 
osimertinib resistance. Our data support a model in which the combination of 
osimertinib and OxPhos inhibitors can delay or prevent resistance in 
osimertinib-naïve tumour cells, and represents a novel strategy that warrants 
further pre-clinical investigation.