APE1–SOX9 Axis Drives Chemoresistance in Esophageal Cancer : Gastroenterology | June 2026

Introduction:

Esophageal Adenocarcinoma is an aggressive malignancy strongly associated with chronic gastroesophageal reflux disease and exposure to acidic bile reflux. Despite advances in multimodal therapy, chemotherapy resistance remains a major barrier to durable disease control and survival.

Problem Statement:

Resistance to platinum-based chemotherapy in esophageal adenocarcinoma is poorly understood, particularly the molecular pathways linking reflux-induced injury to tumour stemness and treatment failure. The transcription factor SOX9 has emerged as a key regulator of tumour plasticity and chemoresistance, but direct therapeutic targeting has remained difficult because of its “undruggable” nature.

Summary:

This translational study identified activation of the SOX9 pathway as a central driver of chemoresistance in esophageal adenocarcinoma and demonstrated that targeting the redox function of APE1 can reverse this resistant phenotype.

RNA sequencing analyses revealed strong enrichment of SOX9-associated transcriptional signatures in esophageal adenocarcinoma tissues, particularly in patients with poor relapse-free survival.

Using reflux-mimicking acidic bile salt exposure models, the investigators demonstrated that APE1-dependent redox signaling activates and stabilizes SOX9 protein expression. This effect persisted during oxaliplatin exposure, suggesting a direct mechanistic link between reflux biology and chemotherapy resistance.

Importantly, both genetic knockdown and pharmacologic inhibition of APE1 redox activity suppressed SOX9 signaling. The study identified the APE1 redox-specific inhibitor APX2009 as a potential therapeutic strategy capable of disrupting this pathway.

Mechanistically, SOX9 activation promoted expression of ALDH1A1, a stemness-associated marker linked to chemoresistance and tumour persistence.

The biological findings were consistently validated across multiple advanced experimental systems, including organotypic cultures, tumour spheroids, patient-derived organoids, genetically engineered mouse models and patient-derived xenografts.

Clinically relevant co-overexpression of APE1 and SOX9 was confirmed in both murine and human esophageal adenocarcinoma specimens, strengthening the translational significance of the pathway.

Most importantly, combining APX2009 with oxaliplatin in patient-derived xenograft models significantly enhanced chemotherapy response and reduced SOX9 expression, supporting the therapeutic feasibility of this approach.

The study is highly relevant because it provides a biologically coherent explanation for why reflux-associated esophageal adenocarcinoma develops profound resistance to systemic therapy.

Rather than attempting to directly inhibit SOX9 itself, the investigators successfully targeted an upstream regulatory mechanism controlling SOX9 stability and activation.

This represents an attractive therapeutic paradigm because transcription factors involved in stemness and lineage plasticity are frequently difficult to inhibit directly.

The work also highlights the broader importance of redox biology in gastrointestinal carcinogenesis and treatment resistance.

Clinically, these findings may ultimately support biomarker-driven therapeutic stratification using APE1/SOX9 signatures to identify patients likely to benefit from combination redox-targeted therapy.

Future studies will need to validate APX2009 in larger clinical settings and determine whether APE1 inhibition can synergize with immunotherapy or radiation therapy in esophageal adenocarcinoma.

Overall, this study identifies the APE1–SOX9 signaling axis as a critical mediator of reflux-driven chemoresistance in esophageal adenocarcinoma and introduces APE1 redox inhibition as a promising strategy to overcome treatment resistance and improve therapeutic response.