Chemotherapy Enrichment of ID Family Expression Is Associated with IL-6 Signaling in Ovarian Cancer

Background/Objectives: Ovarian cancer (OC) remains the most lethal gynecologic malignancy, largely due to late-stage diagnosis and high rates of recurrence following platinum-based chemotherapy. Growing evidence implicates cancer stem-like cells (CSCs) in OC relapse, as these cells exhibit enhanced chemoresistance, stemness, epithelial–mesenchymal transition (EMT), and the capacity to remodel the tumor microenvironment. Inhibitors of DNA-binding (ID) 1-4 proteins are transcription factors with known redundancy; however, their collective role in OC chemotherapy response remains poorly defined. Here, we examined how ID family signaling responds to chemotherapy and contributes to CSC-associated features and microenvironment remodeling. Methods: Publicly available patient data, OC cell lines, and a subcutaneous xenograft mouse model were used to correlate changes in ID1-4 expression with CSCs, EMT, and the tumor microenvironment (TME). OC cell lines were used for in vitro assays to evaluate CSC features and IL-6 production in the presence of carboplatin and/or a small molecule inhibitor of ID proteins, AGX51. Results: Analysis of clinical datasets, cell lines, and in vivo models revealed enrichment of ID1-4 following chemotherapy, with additive increases across treatment cycles. In vivo ID2 and ID4 expression was associated with IL-6 secretion and loss of anti-tumoral macrophages. Pan-ID inhibition demonstrated that cumulative ID activity minimally supports CSC maintenance during chemotherapy, while more strongly regulating IL-6 secretion. Conclusions: IL-6 production from cancer cells was at least partially dependent on ID proteins, linking collective ID signaling to microenvironment remodeling and relapse potential in ovarian cancer.