CXCL1 is critical for pre-metastatic niche formation and metastasis in colorectal cancer

Emerging evidence suggests that the primary tumor influences the development of supportive metastatic microenvironments, referred to as pre-metastatic niches, in certain distant organs before arrival of metastatic cells. However, the mechanisms underlying the contributions of the primary tumor to pre-metastatic niche formation are not fully understood. Here we demonstrate that colorectal carcinoma cells secrete VEGF-A, which stimulates tumor-associated macrophages to produce CXCL1 in the primary tumor. Elevation of CXCL1 in pre-metastatic liver tissue recruited CXCR2-positive myeloid-derived suppressor cells (MDSC) to form a pre-metastatic niche that ultimately promoted liver metastases. Importantly, pre-metastatic liver-infiltrating MDSC induced tumor cell survival without involvement of innate or adaptive immune responses. Our study provides the first evidence that primary malignant cell-secreted VEGF-A stimulates tumor-associated macrophages to produce CXCL1, which recruits CXCR2-positive MDSC to form a pre-metastatic niche to promote liver metastases. Our findings not only shed light on how the tumor microenvironment contributes to pre-metastatic niche formation at distant sites, but they also provide comprehensive insights into how MDSC are recruited to other organs where they contribute to metastatic spread of disease. Moreover, our work also provides a rational for development of CXCR2 antagonists to inhibit or prevent metastatic spread of disease.

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