Exosome-mediated transfer of lncRNA RP11-838N2.4 promotes erlotinib resistance in non-small cell lung cancer

Currently, resistance to tyrosine kinase inhibitors, such as erlotinib, has become a major obstacle for improving the clinical outcome of patients with metastatic and advanced-stage non-small cell lung cancer (NSCLC). While cell behavior can be modulated by long non-coding RNAs (lncRNAs), the roles of lncRNAs within extracellular vesicles (exosomes) are largely unknown. To this end, in this study, the involvement and regulatory functions of potential lncRNAs wrapped by exosomes during the development of chemoresistance in human NSCLC were investigated. Erlotinib-resistant cell lines were established by grafting HCC827 and HCC4006 cells into mice and which were treated with erlotinib. After one treatment course, xenografted NSCLC cells were isolated and transplanted into nude mice again followed by erlotinib treatment. This process was repeated until 4th generation xenografts were isolated and confirmed to be erlotinib-resistant NSCLC cells. lncRNA microarray assays followed by RT-qPCR were then performed which identified that lncRNA RP11-838N2.4 was upregulated in erlotinib-resistant cells when compared to normal NSCLC cells. Furthermore, bioinformatics analysis and chromatin immunoprecipitation revealed that forkhead box protein O1 (FOXO1) could bind to the promoter region of lncRNA RP11-838N2.4, resulting in its silencing through the recruitment of histone deacetylase. Functional experiments demonstrated that the knockdown of lncRNA RP11-838N2.4 potently promoted erlotinib-induced cytotoxicity. Furthermore, extracellular lncRNA RP11-838N2.4 could be incorporated into exosomes and transmitted to sensitive cells, thus disseminating erlotinib resistance. Treatment-sensitive cells with exosomes containing lncRNA RP11-838N2.4 induced erlotinib resistance, while the knockdown of lncRNA RP11-838N2.4 abrogated this effect. In addition, the serum expression levels of exosomal lncRNA RP11-838N2.4 were upregulated in patients exhibiting resistance to erlotinib treatment. On the whole, exosomal lncRNA RP11-838N2.4 may serve as a therapeutic target for patients with NSCLC.