Synergistic Inhibition of Triple-Negative Breast Cancer by Acetylsalicylic Acid and Recombinant Human APE1/Ref-1 in a Mouse Xenograft Model

<b>Background:</b> Triple-negative breast cancer (TNBC) is a highly aggressive subtype with limited therapeutic options due to the lack of estrogen, progesterone, and HER2 receptors. This study investigated the synergistic anticancer effects of recombinant human apurinic/apyrimidinic endonuclease 1/redox factor-1 (rhAPE1/Ref-1) and acetylsalicylic acid (ASA), a combination that has not been previously tested in vivo. <b>Methods:</b> We treated MDA-MB-231 TNBC cells with rhAPE1/Ref-1, ASA, or their combination to assess cell viability and apoptosis in vitro. In vivo, a murine xenograft model was established to evaluate the efficacy of the combination treatment on tumor growth, tumor-specific biomarkers, and key apoptotic proteins. The safety profile of the combination therapy was also assessed by monitoring hematological parameters. <b>Results:</b> While monotherapy with either rhAPE1/Ref-1 or ASA had minimal effects, their combination significantly reduced cell viability and enhanced apoptosis in vitro by increasing DNA fragmentation. These synergistic cytotoxic effects were significantly inhibited by the receptor for advanced glycation end-products (RAGE) siRNA, suggesting that RAGE acts as an important mediator. In the xenograft model, the combination treatment suppressed tumor growth by approximately 70%, an effect comparable to paclitaxel (PTX). This was confirmed by a significant reduction in the plasma levels of TNBC biomarkers (CEA, CA27-29, and CA15-3) and increased tumor apoptosis via the upregulation of p53 and Bax and downregulation of Bcl-2. Notably, ASA, alone or combined with rhAPE1/Ref-1, induced the expression of RAGE in MDA-MB-231 tumors. In contrast to PTX, the combination of rhAPE1/Ref-1 and ASA did not cause hematological toxicity, such as anemia or thrombocytopenia. <b>Conclusions:</b> The combination of rhAPE1/Ref-1 and ASA represents a promising new therapeutic strategy for TNBC by enhancing apoptosis and significantly inhibiting tumor progression in a mouse xenograft model.