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.