a The role of CXCR4, CXCR7 and CCR7 in breast cancer metastatis

Abstract

Breast cancer (BrCa) metastasis is a process mediated by the expression of chemokine receptors by BrCa cells, which migrate towards their chemokine ligands presented by glycosaminoglycans (GAGs) in distant organs. Although this metastatic spread is the cause of most BrCa deaths, there are no effective strategies to target this process. This study was designed to investigate whether BrCa cell migration can be controlled by cross-desensitisation of chemokine receptors or by use of non-GAG binding chemokines. Initial experiments showed that the chemokine receptors CXCR4, CXCR7 and CCR7 were upregulated in primary BrCa and that CXCR4 and CXCR7 could form heterodimers in transfected CHO cells. This co-expression modified CXCR4’s potential to activate Akt but did not affect ERK phosphorylation. To assess this signalling disparity, receptor internalisation was assessed. It was found that CXCR7 was recycled to the surface whilst CXCR4 was degraded, a process that could be partially inhibited with a proteasome inhibitor. Internalisation was also assessed using the CXCR7 agonist VUF11207, which caused both CXCR4 and CXCR7 to be degraded after internalization, highlighting its potential as a dual targeting drug. It was also found that only CXCR4 played a role in metastasis by promoting calcium flux, and CXCR7 co-expression did not significantly reduce CXCR4-mediated cellular migration. The role of GAGs in CCR7-mediated lymph node metastasis was investigated by creating a non-GAG binding CCL21 (mutCCL21). In vitro, mutCCL21 bound CCR7 and triggered diffusion gradient chemotaxis, but failed to induce transendothelial cell migration. This was recapitulated in a murine model of BrCa, where daily injections of mutCCL21 significantly reduced lymph node metastases, highlighting the therapy potential of disrupting GAG-chemokine interactions In summary, these findings suggest that each chemokine receptor has a different but vital role in BrCa metastasis, and should be considered as targets for future therapies.