ARID1A loss drives osimertinib resistance by epigenetically suppressing PTEN and activating the Akt pathway in lung cancer.

BACKGROUND

Osimertinib resistance poses a major therapeutic challenge in lung adenocarcinoma, and the key transcriptional regulators driving this resistance remain largely unclear.

METHODS

Immunohistochemical staining was conducted to assess ARID1A protein levels in lung adenocarcinoma tissues. An osimertinib-resistant lung adenocarcinoma cell line, PC-9 OR, was established. Cell lines with high or low expression of ARID1A or PTEN were constructed to assess the effects of osimertinib treatment or non-treatment on the half-maximal inhibitory concentration (IC50), cell invasive ability, migration, colony-forming ability, and Akt phosphorylation.

RESULTS

ARID1A expression is elevated in lung adenocarcinoma tissues and is correlated with overall survival. Lentiviral knockdown of ARID1A promoted invasive behavior and clonogenic capacity in PC-9 cells. Upon osimertinib treatment, cells with ARID1A knockdown still showed increased invasive and colony-forming abilities compared with those in the control group. Overexpression of ARID1A in the resistant PC-9 OR cell line reduced the invasive and colony-forming abilities. Lentiviral knockdown of PTEN in PC-9 cells also led to increased Akt phosphorylation, while overexpression of PTEN in PC-9 shARID1A cells decreased Akt phosphorylation. Conversely, knockdown of PTEN in PC-9 OR Flag-ARID1A cells increased Akt phosphorylation. IC50 assays showed that inhibition or knockdown of PTEN increased the IC50 of osimertinib in PC-9 cells; overexpression of PTEN in PC-9 shARID1A cells reduced IC50; and knockdown of PTEN in PC-9 OR Flag-ARID1A cells increased IC50. Compared with osimertinib alone, combined treatment with osimertinib and a PTEN inhibitor showed enhanced colony formation in PC-9 cells. With osimertinib treatment, colony formation was significantly increased in the PC-9 shPTEN group compared with that in the PC-9 shCtrl group. Compared with the untreated group, the colony formation ability of PC-9 OR Flag-ARID1A cells was significantly reduced in the osimertinib-treated group. Loss of ARID1A expression in lung adenocarcinoma promotes resistance to osimertinib by enhancing IC50, cell invasive ability, migration, and colony-forming abilities, while overexpression of ARID1A partially reverses the resistant phenotype. CUT&Tag assays suggest a model in which ARID1A binds to upstream elements of PTEN and activates PTEN transcription.

CONCLUSION

ARID1A loss drives osimertinib resistance by downregulating PTEN expression via transcriptional repression, leading to activation of the oncogenic Akt signaling pathway. These findings establish the ARID1A-PTEN-Akt axis as a critical determinant of drug sensitivity and highlight its potential as a therapeutic target for combination strategies to overcome osimertinib resistance in lung cancer.