Patients with metastatic cancer commonly have increased serum galectin-3 concentrations, but it is not known whether this has any functional implications for cancer progression. We report that MUC1, a large transmembrane mucin protein that is overexpressed and aberrantly glycosylated in epithelial cancer, is a natural ligand for galectin-3. Recombinant galectin-3 at concentrations (0.2-1.0 μg/ml) similar to those found in the sera of patients with metastatic cancer increased adhesion of MUC1-expressing human breast (ZR-75-1) and colon (HT29-5F7) cancer cells to human umbilical vein endothelial cells (HUVEC) by 111% (111 ± 21%, mean ± S.D.) and 93% (93 ± 17%), respectively. Recombinant galectin-3 also increased adhesion to HUVEC of MUC1 transfected HCA1.7+ human breast epithelial cells that express MUC1 bearing the oncofetal Thomsen-Friedenreich antigen (Galβ1,3 GalNAc-α (TF)) but did not affect adhesion of MUC1-negative HCA1.7-cells. MUC1-transfected, Ras-transformed, canine kidney epithelial-like (MDE9.2+) cells, bearing MUC1 that predominantly carries sialyl-TF, only demonstrated an adhesive response to galectin-3 after sialidase pretreatment. Furthermore, galectin-3-mediated adhesion of HCA1.7+ to HUVEC was reduced by O-glycanase pretreatment of the cells to remove TF. Recombinant galectin-3 caused focal disappearance of cell surface MUC1 in HCA1.7+ cells, suggesting clustering of MUC1. Co-incubation with antibodies against E-Selectin or CD44H, but not integrin-β1, ICAM-1 or VCAM-1, largely abolished the epithelial cell adhesion to HUVEC induced by galectin-3. Thus, galectin-3, by interacting with cancer-associated MUC1 via TF, promotes cancer cell adhesion to endothelium by revealing epithelial adhesion molecules that are otherwise concealed by MUC1. This suggests a critical role for circulating galectin-3 in cancer metastasis and highlights the functional importance of altered cell surface glycosylation in cancer progression.

Background: Formation of tumour cell aggregation/emboli prolongs the survival of circulating tumour cells in the circulation, enhances their physical trapping in the micro-vasculature and thus increases metastatic spread of the cancer cells to remote sites. Results: It shows here that the presence of the galactoside-binding galectin-3, whose concentration is markedly increased in the blood circulation of cancer patients, increases cancer cell homotypic aggregation under anchorage-independent conditions by interaction with the oncofetal Thomsen-Friedenreich carbohydrate (Galβ1,3GalNAcα-, TF) antigen on the cancer-associated transmembrane mucin protein MUC1. The galectin-3-MUC1 interaction induces MUC1 cell surface polarization and exposure of the cell surface adhesion molecules including E-cadherin. The enhanced cancer cell homotypic aggregation by galectin-MUC1 interaction increases the survival of the tumour cells under anchorage-independent conditions by allowing them to avoid initiation of anoikis (suspension-induced apoptosis). Conclusion: These results suggest that the interaction between free circulating galectin-3 and cancer-associated MUC1 promotes embolus formation and survival of disseminating tumour cells in the circulation. This provides new information into our understanding of the molecular mechanisms of cancer cell haematogenous dissemination and suggests that targeting the interaction of circulating galectin-3 with MUC1 in the circulation may represent an effective therapeutic approach for preventing metastasis.

Purpose: Adhesion of disseminating tumor cells to the blood vascular endothelium is a pivotal step in metastasis. Previous investigations have shown that galectin-3 concentrations are increased in the bloodstream of patients with cancer and that galectin-3 promotes adhesion of disseminating tumor cells to vascular endothelium in vitro and experimental metastasis in vivo. This study determined the levels of galectin-1, -2, -3, -4, -8, and -9 in the sera of healthy people and patients with colon and breast cancer and assessed the influence of these galectins on cancer-endothelium adhesion. Experimental Design: Serum galectins and auto–anti-MUC1 antibodies were assessed using ELISA and mucin protein (MUC1) glycan microarrays, and cancer-endothelium adhesion was determined using monolayers of human microvascular lung endothelial cells. Results: The levels of serum galectin-2, -3, -4, and -8 were significantly increased up to 31-fold in patients with cancer and, in particular, those with metastases. As previously shown for galectin-3, the presence of these galectins enhances cancer-endothelium adhesion by interaction with the Thomsen-Friedenreich (TF; Galβ1,3GalNAcα-) disaccharide on cancer-associated MUC1. This causes MUC1 cell surface polarization, thus exposing underlying adhesion molecules that promote cancer-endothelium adhesion. Elevated circulating galectin-2 levels were associated with increased mortality in patients with colorectal cancer, but this association was suppressed when anti-MUC1 antibodies with specificity for the TF epitope of MUC1 were also present in the circulation. Conclusions: Increased circulation of several members of the galectin family is common in patients with cancer and these may, like circulating galectin-3, also be involved in metastasis promotion. Clin Cancer Res; 17(22); 7035–46. ©2011 AACR.

Adhesion of circulating tumor cells to the blood vessel endothelium is a critical step in cancer metastasis. We show in this study that galectin-3, the concentration of which is greatly increased in the circulation of cancer patients, increases cancer cell adhesion to macrovascular and microvascular endothelial cells under static and flow conditions, increases transendothelial invasion, and decreases the latency of experimental metastasis in athymic mice. These effects of galectin-3 are shown to be a consequence of its interaction with cancer-associated MUC1, which breaks the “protective shield” of the cell-surface MUC1 by causing MUC1 polarization, leading to exposure of smaller cell-surface adhesion molecules/ligands including CD44 and ligand(s) for E-selectin. Thus, the interaction in the bloodstream of cancer patients between circulating galectin-3 and cancer cells expressing MUC1 bearing the galectin-3 ligand TF (Galβ1,3GalNAc-) promotes metastasis. This provides insight into the molecular regulation of metastasis and has important implications for the development of novel therapeutic strategies for prevention of metastasis. [Cancer Res 2009;69(17):6799–806]

Purpose: Cytokines such as interleukin (IL)-6 and granulocyte colony-stimulating factor (G-CSF) are important metastasis promoters. This study has investigated the functional significance of the increased circulation of galectin-3, a common feature in patients with cancer and in particular those with metastasis, on cytokine secretion from the blood vascular endothelium in cancer. Experimental Design: The effects of galectin-3 on secretion of cytokines from human microvascular lung endothelial cells were assessed in vitro by cytokine array and in vivo in mice. The consequences of galectin-3–induced cytokine secretion on endothelial cell behaviors were determined, and the relationship between the levels of circulating galectin-3 and cytokines in patients with colorectal cancer with and without metastasis was investigated. Results: Galectin-3 at pathologic concentrations found in patients with cancer induces secretion of IL-6, G-CSF, sICAM-1, and granulocyte macrophage colony-stimulating factor from blood vascular endothelial cells in vitro and in mice. These cytokines autocrinely/paracrinely interact with the vascular endothelium to increase the expressions of endothelial cell surface adhesion molecules integrinα_vβ₁, E-selectin, ICAM-1, and VCAM-1, resulting in increased cancer cell–endothelial adhesion and increased endothelial cell migration and tubule formation. In patients with metastatic colon cancer, higher serum galectin-3 levels correlated significantly with increased serum G-CSF, IL-6, and sICAM1 concentrations. Conclusion: The increased circulation of galectin-3 in patients with cancer induces secretion of several metastasis-promoting cytokines from the blood vascular endothelium that enhances endothelial cell activities in metastasis. Targeting the actions of circulating galectin-3 in patients with cancer therefore represents a promising therapeutic strategy to reduce metastasis and improve survival. Clin Cancer Res; 19(7); 1693–704. ©2013 AACR.