ICAM1 initiates CTC cluster formation and trans-endothelial migration in lung metastasis of breast cancer

Abstract

Circulating tumor cell (CTC) clusters mediate metastasis at a higher efficiency and are associated with lower overall survival in breast cancer compared to single cells. Combining single-cell RNA sequencing and protein analyses, here we report the profiles of primary tumor cells and lung metastases of triple-negative breast cancer (TNBC). ICAM1 expression increases by 200-fold in the lung metastases of three TNBC patient-derived xenografts (PDXs). Depletion of ICAM1 abrogates lung colonization of TNBC cells by inhibiting homotypic tumor cell-tumor cell cluster formation. Machine learning-based algorithms and mutagenesis analyses identify ICAM1 regions responsible for homophilic ICAM1-ICAM1 interactions, thereby directing homotypic tumor cell clustering, as well as heterotypic tumor-endothelial adhesion for trans-endothelial migration. Moreover, ICAM1 promotes metastasis by activating cellular pathways related to cell cycle and stemness. Finally, blocking ICAM1 interactions significantly inhibits CTC cluster formation, tumor cell transendothelial migration, and lung metastasis. Therefore, ICAM1 can serve as a novel therapeutic target for metastasis initiation of TNBC.

Better together: circulating tumor cell clustering in metastatic cancer

“…In breast cancer, homotypic clustering of CTCs can be directed by CD44 homophilic interactions that upregulate OCT4, epidermal growth factor receptor (EGFR), and p21-activated kinase 2 (PAK2)/focal adhesion kinase (FAK) signaling pathways [ 11 , 37 ] and also by a newly identified stemness-promoting adhesion molecule, intercellular adhesion molecule 1 (ICAM1) [ 45 ] ( Figure 1 ). Other studies characterizing CTC clusters have shown that intratumor hypoxia can trigger cluster formation and that the cell junction protein plakoglobin is overexpressed in CTC clusters compared with single CTCs in breast cancer [ 3 , 46 ] ( Figure 1 ).…”

“…Because CTCs must maintain a level of plasticity to successfully metastasize and CTC clusters promote significantly higher metastatic capacity than single CTCs, this begs the question whether CTC clustering helps promote and/or regulate the necessary stemness signatures. CTC clusters showed an increased expression of stemness-related cell adhesion markers, such as CD44 and ICAM1, compared with single CTCs in patient blood samples [ 11 , 25 , 45 ]. These results, suggesting an increased plasticity in CTC clusters, is also in line with studies showing that, in animal models, tumor cells with a plastic phenotype are much more efficient in forming metastasis than cells blocked in a completely epithelial state [ 65 , 73 – 75 ].…”

“…However, about 20% of CTC clusters and 60% of single CTCs stain negative for CD44, suggesting that CD44-independent mechanisms might also play a role CTC clustering and plasticity in breast cancer [ 11 ]. Recent studies have revealed that ICAM1 is another stemness marker mediating breast CTC clustering as well as tumor cell adhesion to endothelial cells for dissemination to distant organs ( Figure 2 ) [ 45 ]. ICAM1-mediated signaling further promotes self-renewal through upregulation of cell cycle kinases [ 45 ].…”

“…Recent studies have revealed that ICAM1 is another stemness marker mediating breast CTC clustering as well as tumor cell adhesion to endothelial cells for dissemination to distant organs ( Figure 2 ) [ 45 ]. ICAM1-mediated signaling further promotes self-renewal through upregulation of cell cycle kinases [ 45 ]. Additionally, CAFs in primary tumors enhance the formation of CAF–tumor cell hybrid clusters during tumor cell migration, featuring highly epithelial or a hybrid epithelial/mesenchymal protein signature in tumor cells in metastasis [ 82 ].…”

Circulating Tumour Cells (CTCs) in NSCLC: From Prognosis to Therapy Design

“…In addition, some studies suggest that curcumin also repressed cluster formation. Taftaf et al reported that depletion of ICAM-1 in a mouse patient-derived xenograft (PDX) model of triple-negative breast cancer significantly inhibited cluster formation, tumour cell transendothelial migration, and lung metastasis [259]. Yang et al found that curcumin inhibited the IL-6/STAT3 pathway in NCI-H446 and NCI-1688 small carcinoma cells, leading to suppression of VEGF, MMP-2, MMP-7, and ICAM-1 [260].…”