Chemotherapy induces an IL1β-dependent neutrophil recruitment and activation that promote chemoresistance in metastatic ovarian cancer

Background: High-grade serous carcinoma (HGSC) of the ovary acquires chemoresistance through diverse cancer cell-intrinsic and cell-extrinsic mechanisms, culminating in treatment-refractory intraperitoneal metastasis. Previous work suggests that chemotherapy induces immunological changes in the tumor microenvironment (TME). However, experimental evidence for how such chemotherapy-induced TME remodeling modulates the response to ongoing chemotherapy remains poorly documented in HGSC. Methods: We analyzed paired pre-chemotherapy and post-chemotherapy HGSC bulk transcriptomic and single-cell RNA sequencing (scRNA-seq) datasets to identify chemotherapy-induced tumor-extrinsic factors and their cellular sources in the TME. To test causality, we used chemoresistant, homologous recombination-proficient murine metastatic HGSC models with deficiencies in the interleukin 1 beta (IL1β) pathway (IL1β-interleukin 1 receptor type 1 (IL1R1) axis). Flow cytometry and scRNA-seq of omental tumors were used to define cellular interactions. Contributions of neutrophils and neutrophil extracellular traps (NETs) were assessed by antibody-mediated depletion and immunofluorescence. Direct effects of IL1β and NETs on cancer cell chemosensitivity were tested in vitro. Finally, paired pre-chemotherapy and post-chemotherapy omental HGSC specimens from patients were analyzed for neutrophil infiltration and NET formation. Results: In HGSC datasets, post-chemotherapy tumors exhibited increased IL1β expression with myeloid cells identified as the primary source. In chemoresistant murine models, chemotherapy increased neutrophils and NETs in omentum tumors in wild-type mice. These increases were abrogated in IL1β-deficient mice, which showed a shift toward an effector-like CD8+ T-cell state and improved tumor control. Neutrophil depletion in wild-type mice recapitulated the chemosensitive phenotype of IL1β-deficient mice. In vitro, IL1β did not alter cancer cell-intrinsic chemosensitivity, whereas NETs reduced the chemosensitivity of cancer cells. Furthermore, scRNA-seq and flow cytometry revealed that IL1R1 was predominantly expressed by tumor-associated fibroblasts. Consistently, IL1R1-deficient mice exhibited increased chemosensitivity, with decreased neutrophil accumulation and increased IFNγ+TNF+CD8+ T cells. Additionally, we found that chemotherapy upregulated the neutrophil chemoattractant C-X-C motif chemokine ligand 2 (CXCL2), and disruption of the IL1β-IL1R1 axis decreased CXCL2 levels in tumor-associated fibroblasts. Finally, residual human HGSC tumors after chemotherapy showed increased neutrophils and a trend toward increased NETs. Conclusions: We demonstrate that chemotherapy-induced IL1β-dependent neutrophil accumulation drives chemoresistance in HGSC. This study provides experimental evidence that chemotherapy-induced inflammation contributes to chemoresistance and highlights the potential of targeting this pathway to overcome chemoresistance in HGSC.