2548 - Chemoradiotherapy Integrated Tumor Cell Microparticles Elicit Ferroptosis and Immune Remodeling in Malignant Pleural Effusion

Purpose/Objective(s): Current clinical management of malignant pleural effusion (MPE) predominantly relies on intrapleural chemotherapy, yet its efficacy remains suboptimal due to insufficient activation of antitumor immunity. Although radiotherapy is an established immunomodulatory intervention, its clinical application in MPE is precluded by associated risks. Irradiated tumor cell-derived microparticles (RT-MPs) mimic immune priming effects of radiotherapy, yet show attenuated cytotoxic efficacy against malignant cells. To combine the advantages of RT-MPs and chemotherapy, we developed a chemo-radiotherapy integrated microparticles (CR-MPs) by loading chemotherapeutic agents onto RT - MPs, providing a novel modality for MPE treatment.

Materials/Methods: CR-MPs were generated by incubating irradiated tumor cells with chemotherapy drugs, followed by gradient centrifugation. Drug loading efficiency was detected by HPLC. In vitro cytotoxicity was assessed via CCK-8 and 7-AAD flow cytometry. In vivo efficacy was validated in an MPE mouse model. TME remodeling was assessed via flow cytometry and multiplex immunofluorescence.

Results: HPLC analysis confirmed that RT-MPs encapsulated various chemotherapeutic agents (MTX, DOX, MMAE) with consistent drug-loading efficiency and broad applicability across tumor cell types. Compared to equivalent doses of free drugs or RT-MPs alone, CR-MPs showed dose-dependent tumor cell killing efficacy against homologous cells or heterologous counterparts. Notably, RT-MPs@MTX (RT-MPs loaded with MTX) induced immunogenic cell death, enabling effective phagocytosis by macrophages and enhancing their activation. Transcriptomic profiling revealed that RT-MPs@MTX induce ferroptosis in tumor cells. Mechanistically, the drug - loaded vesicles were significantly enriched in mitochondria after internalization, triggering mitochondrial oxidative stress and elevating levels of cellular reactive oxygen species. Furthermore, RT-MPs@MTX directly activated DC cells via the cGAS-STING axis pathway, upregulating expression of co-stimulatory signals and promoting antigen presentation. In vivo experiments indicated that RT-MPs@MTX significantly prolonged the survival of MPE-bearing mice and remodeled the TME, marked by increased infiltration of IFN?+ and Granzyme B+ cytotoxic T cells. Combined with anti-PD-1 immunotherapy, RT-MPs@MTX achieved a 70% cure rate, with cured mice developing durable immune memory and complete resistance to tumor rechallenge. This treatment demonstrated remarkable biosafety, characterized by its negligible impact on blood cell ratio, hepatic and renal function.

Conclusion: This study established a novel CR-MPs platform that showed significant therapeutic efficacy in controlling MPE both as monotherapy and in combination with immunotherapy. Our findings highlighted its translational potential as a precision concurrent chemoradiotherapy strategy for MPE management in clinical settings.