Efferocytosis‐Driven Polyamine Metabolism in Macrophages Enhances Cancer Stem Cell Enrichment after Chemotherapy in Ovarian Cancer

Abstract Chemotherapy‐induced enrichment of cancer stem cells (CSCs) is a key mechanism underlying acquired chemoresistance and recurrence of epithelial ovarian cancer (OC). Although chemotherapy may enrich CSCs through selection or by inducing dedifferentiation, the dynamic changes in the tumor niche and their impact on CSCs during chemotherapy remain unclear. In this study, single‐cell sequencing and multiplex immunohistochemical analysis are used to define microenvironmental changes, and a post‐chemotherapy increase in efferocytotic macrophages that phagocytosed chemotherapy‐induced apoptotic tumor cells is identified. Efferocytotic macrophages are associated with poor prognosis and CSCs in OC. Their conditioned medium facilitates OC stemness in vitro. Meanwhile, targeting efferocytosis suppresses CSC enrichment, chemoresistance, and regrowth in vivo. Mechanistically, it is demonstrated that enhanced expression of ODC1 driven by efferocytosis increases polyamine flux, particularly putrescine, by integrating metabolomics and transcriptomics. The increase in putrescine content leads to the SPP1 and OPN overexpression in macrophages, conferring cancer stemness to OC cells through the OPN‐CD44 axis. Treatment with an ODC1 selector inhibitor mitigates CSC enrichment, sensitizes tumors to cisplatin, and restricts tumor regrowth. Together, the study shows that efferocytosis and associated polyamine metabolic reprogramming support the chemotherapy‐induced enrichment of CSCs, providing new targets for addressing chemoresistance and recurrence of OC.