The fractalkine-receptor axis improves human colorectal cancer prognosis by limiting tumor metastatic dissemination

Human colorectal cancer (CRC) is a frequent neoplasia inWestern countries, and its metastatic progression is a major cause of cancerrelated death. In search of specific molecules upregulated in CRC, with possible clinical relevance, we performed a differential geneprofiling analysis in surgery-derived CRC samples and adjacent uninvolved intestinal mucosa. The chemokine CX₃CL1 and its specific receptor CX₃CR1 were significantly upregulated in tumors. Higher expression of CX₃CL1 and CX₃CR1 was confirmed by immunohistochemistry in 100 CRC tumor samples (stages I-III). Unexpectedly, high immune scores of CX₃CL1 did not correlate with the density of tumor-infiltrating CD3+ T cells or CD68+ macrophages. Coexpression of ligand and receptor by tumor cells (axis-positive tumors) significantly associated with longer disease-free (p = 0.01) and disease-specific survival (p = 0.001). Conversely, axis-negative tumors (with low expression of both ligand and receptor) had increased risk of tumor relapse (p = 0.02), and increased likelihood of metachronous metastasis (p = 0.001), including after stage adjustment (p = 0.006). Transduction of CX₃CL1 and CX₃CR1 in CRC tumor cell lines induced cell aggregation that strongly inhibited in vitro migration in chemotaxis assays. In a mouse model of spleen- liver metastases, cancer dissemination to liver was dramatically reduced in CX₃CL1-CX₃CR1-expressing tumors, and ligand- receptor interaction was confirmed in cancer cells in vivo by fluorescence resonance energy transfer analysis. In conclusion, tumoral expression of the CX₃CL1-CX₃CR1 chemokine axis functions as a retention factor, increasing homotypic cell adhesion and limiting tumor spreading to metastatic sites. Lack or low levels of expression of CX₃CL1-CX₃CR1 by tumor cells identifies a group of CRC patients at increased risk of metastatic progression.