ARID1a as a marker of prognosis and increased sensitivity to CDK4/6, mTOR 1/2 and Src homology region 2 phosphatase (SHP 1/2) inhibitors in breast cancer (BC).

Abstract

1082 Background: ARID1a (AT Rich Interactive Domain 1A) is part of the SWI/SNF complex, which regulates gene transcription, and is believed to be a tumor suppressor gene. Low ARID1a expression has been associated with poor prognosis in BC. The aim of this study was to explore the clinical significance of ARID1a mutation and expression loss, and its potential as a therapeutic target in BC. Methods: We analyzed publicly available genomic databases to study the clinical implication of ARID1a mutations and gene expression in BC. Results: ARID1a was mutated in ~5-7 % of BCs within TCGA/METABRIC/MSK (5511 samples), but did not show differences in frequency between histology, grade, or estrogen receptor (ER)/HER2 receptor status. MSK metastatic tissue samples had higher incidence of ARID1a mutation compared to primary tumor samples (7.6% vs 4.4%, χ2 P = 0.0073). Analysis of ARID1a in KMPLOT showed that lower gene expression was associated with worse relapse-free survival and overall survival across all BCs, but the difference was primarily in molecularly classified luminal A tumors. Mutations in ARID1a did not show an association with outcomes in TCGA/METABRIC/MSK datasets. Pathway analysis of ARID1a showed it is involved in regulating ER ligand driven signaling and interacts with targets regulated by CDK4 and mTOR activity. CancerRxgene drug sensitivity analyses on BC cell lines revealed that ARID1a mutated BC cell lines were significantly more sensitive to palbociclib, SHP1/2, and mTOR1/2 inhibitors compared to ARID1a wildtype cell lines. Conclusions: Reduced activity of ARID1a in luminal BC cells may negatively affect prognosis by altering ER signaling leading to activation of druggable resistance mechanisms, particularly in metastatic tissue. Loss of function ARID1a mutations may sensitize cancer cells to CDK4/6, mTOR1/2, and SHP1/2 inhibitors in vitro. Further research in ARID1a mutated ER+ BCs using combinations of these inhibitors is warranted.