Brain endothelial cells promote breast cancer cell extravasation to the brain via EGFR-DOCK4-RAC1 signalling

The role of endothelial cells in promoting cancer cell extravasation to the brain during the interaction of cancer cells with the vasculature is not well characterised. We show that brain endothelial cells activate EGFR signalling in triple-negative breast cancer cells with propensity to metastasise to the brain. This activation is dependent on soluble factors secreted by brain endothelial cells, and occurs via the RAC1 GEF DOCK4, which is required for breast cancer cell extravasation to the brain in vivo. Knockdown of DOCK4 inhibits breast cancer cell entrance to the brain without affecting cancer cell survival or growth. Defective extravasation is associated with loss of elongated morphology preceding intercalation into brain endothelium. We also show that brain endothelial cells promote paracrine stimulation of mesenchymal-like morphology of breast cancer cells via DOCK4, DOCK9, RAC1 and CDC42. This stimulation is accompanied by EGFR activation necessary for brain metastatic breast cancer cell elongation which can be reversed by the EGFR inhibitor Afatinib. Our findings suggest that brain endothelial cells promote metastasis through activation of cell signalling that renders breast cancer cells competent for extravasation. This represents a paradigm of brain endothelial cells influencing the signalling and metastatic competency of breast cancer cells.

Hematopoietic Stem Cell Gene Therapy for Brain Metastases Using Myeloid Cell-Specific Gene Promoters

BACKGROUND

Brain metastases (BrM) develop in 20-40% of cancer patients and represent an unmet clinical need. Limited access of drugs into the brain because of the blood-brain barrier is at least partially responsible for therapeutic failure, necessitating improved drug delivery systems.

METHODS

Green fluorescent protein (GFP)-transduced murine and nontransduced human hematopoietic stem cells (HSCs) were administered into mice (n = 10 and 3). The HSC progeny in mouse BrM and in patient-derived BrM tissue (n = 6) was characterized by flow cytometry and immunofluorescence. Promoters driving gene expression, specifically within the BrM-infiltrating HSC progeny, were identified through differential gene-expression analysis and subsequent validation of a series of promoter-green fluorescent protein-reporter constructs in mice (n = 5). One of the promoters was used to deliver tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to BrM in mice (n = 17/21 for TRAIL vs control group).

RESULTS

HSC progeny (consisting mostly of macrophages) efficiently homed to macrometastases (mean [SD] = 37.6% [7.2%] of all infiltrating cells for murine HSC progeny; 27.9% mean [SD] = 27.9% [4.9%] of infiltrating CD45+ hematopoietic cells for human HSC progeny) and micrometastases in mice (19.3-53.3% of all macrophages for murine HSCs). Macrophages were also abundant in patient-derived BrM tissue (mean [SD] = 8.8% [7.8%]). Collectively, this provided a rationale to optimize the delivery of gene therapy to BrM within myeloid cells. MMP14 promoter emerged as the strongest promoter construct capable of limiting gene expression to BrM-infiltrating myeloid cells in mice. TRAIL delivered under MMP14 promoter statistically significantly prolonged survival in mice (mean [SD] = 19.0 [3.4] vs mean [SD] = 15.0 [2.0] days for TRAIL vs control group; two-sided P = .006), demonstrating therapeutic and translational potential of our approach.

CONCLUSIONS

Our study establishes HSC gene therapy using a myeloid cell-specific promoter as a new strategy to target BrM. This approach, with strong translational value, has potential to overcome the blood-brain barrier, target micrometastases, and control multifocal lesions.

Comparison of tuberculin activity using the interferon-gamma assay for the diagnosis of bovine tuberculosis

In this study, interferon-gamma (IFN-gamma) responses in whole blood cultures stimulated with tuberculins from different sources were compared with regard to their diagnostic reliability in cattle experimentally and naturally infected with Mycobacterium bovis. The IFN-gamma responses to different concentrations of purified protein derivatives (PPDs) from M bovis and Mycobacterium avium were quantified. Significant differences (P<0.05) between sources and concentrations of PPDs used for stimulation were detected, indicating a need for standardisation of PPDs used in the IFN-gamma assay. Additionally, a tool named'relative potency 30' that allows rapid comparison of batches and sources of PPDs was defined.