XIAOSHUI formula inhibits malignant pleural effusion by targeting the STC1/p65/CXCL5 axis to reprogram tumor-associated macrophages.

[BACKGROUND] Malignant pleural effusion (MPE) is a common and debilitating complication in advanced lung carcinoma, driven by an immunosuppressive tumor microenvironment (TME), where tumor-associated macrophages (TAMs) play a pivotal role. This specialized milieu not only facilitates neoplastic proliferation but also contributes to immune system dysfunction. Preliminary evidence suggests that Xiaoshui Formula (XSF) could inhibit MPE by modulating TAM polarization, a key mechanism underlying T cell dysfunction and compromised tumor surveillance capabilities.

[PURPOSE] This study seeks to elucidate the precise molecular mechanism by which XSF remodels the TME in MPE, with a focus on its regulation of tumor cell signaling and subsequent effects on TAM polarization and T cell function.

[METHODS] We employed a combination of in vivo MPE mouse models and in vitro cell culture systems. Lewis lung carcinoma cells (LLCs) and bone marrow-derived macrophages were used. Techniques included RNA-seq, Western blot, ELISA, flow cytometry, immunohistochemistry, and qPCR to analyze signaling pathways, cytokine secretion, and immune cell populations.

[RESULTS] XSF treatment led to a dose-dependent reduction in pleural effusion volume, marked by a shift in TAM polarization. Transcriptomic and functional analyses revealed that XSF targets tumor cells, inhibiting the expression of Stanniocalcin-1 (STC1), which leads to reduced phosphorylation of the NF-κB subunit p65 and subsequent downregulation of the chemokine CXCL5. This suppression of tumor-derived CXCL5 impaired the recruitment and M2 polarization of TAMs. Consequently, XSF treatment reshaped the TME, leading to an enhancement of anti-tumor T cell function (downregulation of PD-1, CTLA-4, TIM-3 and increased production of IFN-γ and Granzyme B).

[CONCLUSION] Our findings demonstrate that XSF inhibits MPE progression by suppressing the STC1/p65/CXCL5 axis in tumor cells, thereby reprogramming TAMs and potentiating T cell-mediated anti-tumor immunity. This study provides a mechanistic foundation for the clinical application of XSF and highlights the value of targeting tumor cell-intrinsic pathways to modulate the immune TME.