Exon-16-skipping HER2 as a novel mechanism of osimertinib-resistance in EGFR L858R/T790M-positive non-small-cell lung cancer.

Abstract

BACKGROUND\nOsimertinib is the current recommended treatment for EGFR T790M-positive NSCLC following EGFR-TKI therapy. However, resistance to osimertinib therapy is inevitably acquired after a period of effective treatment. We had a patient suffering from EGFR L858R/T790M-positive NSCLC who initially responded to osimertinib therapy but eventually developed resistance. Plasma cell-free DNA analysis revealed the occurrence of exon-16-skipping HER2, which may resulted in the HER2 splice variant, HER2D16. HER2D16 has never been reported in lung cancer, and HER2D16-driven signaling was known to be regulated by Src-kinase in breast cancer. We investigated the role of HER2D16 as an osimertinib-resistant mechanism.\n\n\nMETHODS\nWe constructed and established H1975 cells stably expressing HER2D16. The dimeric formation of HER2D16 was tested using non-reducing polyacrylamide gel electrophoresis (PAGE). The effects of drug on signaling transduction were examined using Western blot. The synergistic effect was assessed using Chou-Talalay method.\n\n\nRESULTS\nWe found HER2D16 can form homo-dimer in NSCLC cells. HER2D16-expressing H1975 cells were resistant to osimertinib treatment. We also found mutant EGFR and HER2D16 cooperated to activate downstream signaling for osimertinib-resistance. Besides, co-treatment with osimertinib and Src-kinase inhibitor failed to reverse resistance, indicating that HER2D16-driven signaling in NSCLC was not through canonical pathway. Finally, we revealed that the combination of osimertinib with the pan-HER small molecular inhibitor, afatinib, could synergistically repress cell growth and signaling in H1975-HER2D16 cells.\n\n\nCONCLUSION\nHER2D16 can contribute to osimertinib resistance through Src independent pathway. HER2D16 should be included in the molecular diagnosis panel for lung cancer.