APX3330 reverses the immunosuppressive tumor microenvironment during colorectal carcinogenesis.

BACKGROUND AND OBJECTIVES: Colorectal cancer (CRC) ranks as the third most common cancer globally and is the second leading cause of cancer-related deaths. While some CRC patients with deficient mismatch repair (dMMR) or high microsatellite instability (MSI-H) respond to immune checkpoint inhibitors (ICIs), many exhibit resistance, partly due to polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs). APE1/Ref-1, a bifunctional protein involved in DNA repair and redox regulation, has an inhibitor, APX3330, which targets its redox function without affecting DNA repair. This study aims to explore the relationship between APE1/Ref-1 and PMN-MDSCs in CRC, assess the impact of APX3330 on the tumor microenvironment (TME), and identify a novel therapeutic target. METHODS: Surgical specimens from 176 CRC patients were analyzed using immunohistochemistry (IHC) and multiplex IHC (mIHC) to evaluate APE1/Ref-1 expression, tumor stage, malignancy grade, and immune cell infiltration. An azoxymethane/dextran sodium sulfate (AOM/DSS) model was established to simulate murine colon cancer. RNA sequencing (RNA-seq) and mIHC were employed to examine the effects of APX3330 on immune cell infiltration. Additionally, MC38 murine colon cancer cells were used to establish subcutaneous tumors in mice to analyze the impact of APX3330 and APE1/Ref-1 on immune cell infiltration. RESULTS: Elevated APE1/Ref-1 expression in CRC was associated with increased PMN-MDSC infiltration. APX3330 modulated the TME by regulating PMN-MDSCs and enhancing the infiltration of CD4(+) and CD8(+) T cells, thereby altering the immune landscape. APX3330 demonstrated enhanced efficacy in tumors with low APE1/Ref-1 expression, and downregulated genes associated with APX3330 were linked to poorer prognosis. CONCLUSIONS: Increased APE1/Ref-1 expression in CRC patients correlates with worse clinical outcomes and heightened PMN-MDSC infiltration. APX3330 effectively reshapes the TME by altering immune cell infiltration, highlighting its potential as a therapeutic agent for CRC. GRAPHICAL ABSTRACT: [Image: see text] SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12935-026-04176-8.