Blocking Interaction of Apurinic/apyrimidinic Endonuclease and DNA Secondary Structure G-quadruplex Suppresses Triple-Negative Breast Cancer Metastasis

Triple-negative breast cancer (TNBC) is the most aggressive and highly metastatic breast cancer. Recent genome-wide analyses have identified significant alterations in non-canonical four-stranded DNA secondary structures, G-quadruplexes (G4), within promoter and enhancer regions of genes linked to metastatic TNBC. The mechanistic link between G4 DNA and TNBC metastasis, however, remains unclear. Using CRISPR to genetically abrogate G4 folding at the endogenous gene promoters in TNBC cells, we demonstrate that loss of G4 structure in CXCL1 gene promoter significantly reduces CXCL1 expression, consequently a significant decrease in cell migration and invasion, as well as in vivo tumorigenesis and lung metastasis. Mechanistically, G4 recruits APE1, a multifunctional protein that enhances transcription factors binding through its redox-effector function and activates key metastasis-associated genes. Further, APE1 deletion or disruption of its binding to G4 with TMPyP4, a G4 ligand, suppresses gene expression, tumor growth, and lung metastasis. Our study provides the first genetic evidence of G4's role in tumor progression and metastasis and identifies the G4:APE1 axis as a novel therapeutic target to target TNBC primary tumor and metastasis.