The study shows that blocking a protein called BRD4 can make lung cancer cells that stopped responding to the drug osimertinib become sensitive again, by interfering with a chain of events involving other proteins (YAP1, APT1, and MST1). This work is focused on cancer biology and does not involve the peptide palmitoyl‑dipeptide‑6.

Osimertinib is widely used to treat non-small-cell lung cancer (NSCLC) carrying epidermal growth factor receptor (EGFR) mutations. However, osimertinib resistance inevitably develops in almost all patients. In our study, osimertinib-resistant HCC827/OR and PC-9/OR cells were established from parental osimertinib-sensitive cells, and osimertinib (AZD9291) and NHWD870, a bromodomain and extra-terminal (BET) inhibitor, were used to treat cells and mice. PC-9/OR and HCC827/OR cells were subcutaneously injected into mice to establish a mouse model of NSCLC. Luciferase, electrophoretic mobility shift assay (EMSA), and chromatin immunoprecipitation (ChIP) assays were applied to analyze transcription factors (TFs) binding to the APT1 promoter. MST1 palmitoylation was examined with acyl resin-assisted capture (Acyl-RAC) assays. The interaction of YAP1 and BRD4 was evaluated by co-immunoprecipitation (Co-IP) and GST-pull down assays. Our study showed that YAP1 was highly expressed, and its nuclear translocation was increased in osimertinib-resistant NSCLC cells, and silencing of YAP1 overcame osimertinib resistance. BRD4 was upregulated, and NHWD870 significantly reversed YAP1-mediated osimertinib resistance. Moreover, decreased MST1 palmitoylation at C699 was observed in NSCLC cells that are resistant to osimertinib. Furthermore, knockdown of APT1 reduced YAP1 nuclear translocation and APT1-mediated MST1 depalmitoylation restored osimertinib sensitivity. Inhibition of BRD4 blocked YAP1-mediated APT1 transcription in NSCLC cells. In addition, the BRD4 inhibitor disrupted MST1 depalmitoylation by APT1 and recovered osimertinib sensitivity. In vivo administration of NHWD870 enhanced NSCLC cell sensitivity to osimertinib. These findings indicate that inhibition of BRD4 enhances NSCLC cell sensitivity to osimertinib through the APT1-MST1-YAP1 axis. Inhibition of BRD4 sensitized non-small-cell lung cancer (NSCLC) cells to osimertinib by blocking YAP1-mediated APT1 transcription and disrupting APT1-mediated depalmitoyation of MST1 and YAP1 nuclear translocation, which restores osimertinib sensitivity through the APT1-MST1-YAP1 axis in NSCLC. Our study provides a novel mechanism of osimertinib resistance and suggests potential therapeutic strategies for NSCLC.