<em>In silico</em> identification and biological evaluation of CXCR2 inhibitor naringin to suppress breast cancer premetastatic niche formation and metastasis

Distant metastasis greatly threatens the overall survival of breast cancer patients. C-X-C chemokine receptor 2 (CXCR2) expressed on myeloid-derived suppressor cells (MDSCs) has been proven to be an essential modulator for the formation of premetastatic niche (PMN), which facilitates cancer cell seeding and later metastasis. However, current CXCR2 inhibitors are challenged by serious side effects and toxicities, thus, increasing attention has been paid to discovering CXCR2 antagonists from dietary compounds. Herein, <em>in silico </em>CXCR2<em> </em>pharmacophore models were established and subsequently identified 9'''-methyl lithospermate B<strong>,&nbsp;</strong>thiostrepton, rhoifolin and naringin (NAR) as potential CXCR2 antagonists from the L6020 database of traditional Chinese medicine (TCM) compounds. NAR was further validated to possess the admirable target affinity with CXCR2 by BLI analysis, and DARTS detection also validated CXCR2 as the direct binding target of NAR. Further investigation revealed that NAR could suppress the metastasis of MDSC and reverse its immunosuppressive effects on CD8⁺T cells <em>via</em> CXCR2 inhibition. Subsequent investigations utilizing the zebrafish xenotransplantation model revealed that NAR inhibited the mobilization of MDSCs and the generation of PMNs by targeting CXCR2, ultimately resulting in diminished growth and metastasis of breast cancer. Meanwhile, the mouse breast cancer orthotopic model also validated that NAR could suppress breast cancer PMN formation, growth and metastasis by inhibiting CXCR2. This suppression is evidenced by a reduction in the population of MDSCs in the lung, tumor, and blood, as well as a decrease in CXCR2 phosphorylation within splenic MDSCs.&nbsp; Taken together, our study identifies NAR as a natural CXCR2 antagonist, and sheds novel light on utilizing NAR to prevent PMN formation and breast cancer metastasis <em>via</em> inhibiting MDSC recruitment.