Phenotypic Knockout of CXCR4 Expression by a Novel Intrakine Mutant hSDF-1α/54/KDEL Inhibits Breast Cancer Metastasis.

Many malignant tumors express high levels of the chemokine receptor CXCR4, and the interaction between CXCR4 and its ligand, SDF-1, promotes migration, invasion, and metastasis of breast cancer cells. Therefore, blocking the interaction between CXCR4 and SDF-1 could alter the tumor's metastatic phenotype and control the development and progression of cancers. We used a cellular phenotypic knockout strategy and developed a novel recombinant gene, AdSDF-1α/54/KDEL, which contains an adenovirus vector, a mutant form of SDF-1 that lacks a C-terminal α-helix, and a KDEL tetrapeptide sequence that promotes retention at the endoplasmic reticulum (ER). We hypothesized that SDF-1α/54/KDEL could efficiently block metastasis of breast cancer cells with less inflammatory side effects than SDF-1α/KDEL. Using the MCF-7 cell line, which expresses a stable, high level of CXCR4, we found that SDF-1α/54/KDEL efficiently becomes localized at the ER of tumor cells, where it specifically binds to newly synthesized CXCR4 and prevents it from reaching the cell surface. Chemotaxis and invasion assays revealed that the cells treated with SDF-1α/54/KDEL failed to migrate toward SDF-1. We also found that SDF-1α/54/KDEL impaired lung metastasis of metastatic breast cancer by decreasing CXCR4 on the cell surface. The novel recombinant gene, SDF-1α/54/KDEL, played an instrumental role in blocking SDF-1/CXCR4-mediated cell migration, and we found that this gene-based strategy for targeting the SDF-1/CXCR4 axis offers a very effective alternative method for preventing metastasis of breast cancer and other cancers expressing high levels of CXCR4.