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-dead) 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-dead-induced PD-L1 activation and M2 polarization of macrophages.

Conclusion: This pioneering study not only sheds novel light on EV-dead 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-dead-mediated immunosuppressive TME.