CircSPINT2 confers sensitivity to osimertinib via hsa-miR-1296-3p/RBP1 axis and inhibits NSCLC progression

Lung adenocarcinoma (LUAD) is the most common type of lung cancer. Prolonged treatment of LUAD with 1^st/2^nd generation epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) promotes the emergence of secondary EGFR T790M mutation conferring resistance to these drugs. Patients who acquire EGFR T790M mutation respond to the 3^rd generation EGFR-TKI osimertinib but develop resistance within 12 months. Circular RNAs (circRNAs) are notably associated with cancerogenesis, making them promising biomarkers or therapeutic targets. In this study, we aimed to identify circRNAs that regulate osimertinib resistance and elucidate the functions and mechanisms to reveal potential therapeutic targets and biomarkers for osimertinib-resistant LUAD. The analysis of circRNA transcriptome sequencing identified circSPINT2 to be downregulated in osimertinib-resistant cell lines. The loss-/gain-of-function assays revealed that circSPINT2 sensitizes cells to osimertinib treatment by inducing apoptosis. Functionally, circSPINT2 enhanced the expression of RBP1 by sponging hsa-miR-1296-3p. Osimertinib-resistant xenograft tumor model was established by long-term osimertinib treatment, and the molecular and histologic analysis of subcutaneous xenograft tumors corroborated our <i>in vitro</i> findings. Conclusively, our study demonstrates that circSPINT2 possesses tumor-suppressive functions; the restoration of circSPINT2 expression level confers sensitivity to osimertinib treatment via miR-1296-3p/RBP1 axis. The secreted circSPINT2 may serve as a monitoring biomarker for osimertinib resistance status in LUAD.