XIAOPI formula inhibits chemoresistance and metastasis of triple-negative breast cancer by suppressing extracellular vesicle/CXCL1-induced TAM/PD-L1 signaling.

BACKGROUND

Triple-negative breast cancer (TNBC) is challenged by the low chemotherapy response and poor prognosis. Emerging evidence suggests that cytotoxic chemotherapy may lead to the pro-metastatic tumor microenvironment (TME) by eliciting pro-tumor extracellular vesicles (EVs) from cancer cells. However, the precise mechanisms and therapeutic approaches remain inadequately understood.

PURPOSE: This study aims to determine whether XIAOPI formula (Chinese name XIAOPI San, XPS), a nationally sanctioned medication for mammary hyperplasia, can chemosensitize TNBC by remodeling the TME via modulating EV signaling, and exploring its underlying mechanisms.

METHODS

Multiple methodologies, such as EV isolation, transmission electron microscope, flow cytometry, dual-luciferase reporter assays, co-immunoprecipitation and in vivo breast cancer xenograft, were employed to elucidate the effect and molecular mechanisms of XPS on paclitaxel-induced EV signaling (EV-dead) of TNBC.

RESULTS

XPS, at non-toxic concentrations, synergized with PTX to inhibit the invasion and chemoresistance of TNBC cells co-cultured with macrophages. Compared to EV-dead, XPS co-treatment-elicited EVs (EV-deadXPS) exhibited a decreased capacity to promote the invasion, chemoresistance and cancer stem cell subpopulation of the co-cultured TNBC cells. Mechanistically, XPS administration led to a reduction in CXCL1 cargo in EV-dead, and thereby attenuated its activation effect on macrophage polarization into M2 phenotype through the transcriptional downregulation of PD-L1 expression. Furthermore, XPS effectively reduced the number of EV-dead from TNBC cells by inhibiting CXCL1-mediated intraluminal vesicle (ILV) biogenesis in multivesicular bodies (MVBs). Moreover, molecular explorations revealed that XPS impaired ILV biogenesis by disrupting the RAB31/FLOT2 complex via suppressing the CXCL1/Myc signaling. Importantly, XPS significantly chemosensitized paclitaxel to inhibit TNBC growth and metastasis in vivo by suppressing EV-deadCXCL1-induced PD-L1 activation and M2 polarization of macrophages.

CONCLUSION

This pioneering study not only sheds novel light on EV-deadCXCL1 as a potential therapeutic target to suppress TNBC chemoresistance and metastasis, but also provides XPS as a promising adjuvant formula to chemosensitize TNBC by remodeling EV-deadCXCL1-mediated immunosuppressive TME.