Unraveling the Pathology of the Blood‐Tumor Barrier in an Experimental Model of Brain Metastases of Lung Cancer

Abstract

Lung cancer is the leading cause of cancer‐related deaths worldwide (1.76 million deaths in 2018) and the leading cause of brain metastatic disease among all primary cancers. As tumor cells colonize the neuroparenchyma, they breach the tightest and most effective vascular barrier in the body, the blood‐brain barrier (BBB). The functional components of the BBB include endothelial cells, basement membranes, pericytes and astrocytes. Herein, we hypothesized that dynamic transformation of the BBB to the blood‐tumor barrier (BTB) would correlate with changes in paracellular permeability. An experimental model of lung cancer brain metastases was developed using twelve 6‐week‐old athymic nude mice. Mice were injected with 250,000 brain‐seeking cells, which colonized the brain for 4–6 weeks. Animals were injected with 3 kd Texas Red dextran at the time of euthanasia, and brains were harvested, cryosectioned and prepared for immunofluorescence analysis. Metastatic tumors were characterized as highly or poorly permeable based on the diffusion of Texas Red dextran within and around the tumor parenchyma. Brain metastases were roughly spherical and measured between 50–500 μm in diameter, irrespective of their permeability status. The most striking BTB pathology was identified in tight junctions and associated adapter proteins. Highly permeable tumors exhibited haphazard expression of claudin‐5 and a loss of zona occludens‐1 adapter protein compared to metastases with low paracellular permeability. Understanding the cellular and molecular alterations occurring within the BBB during brain metastatic disease from non‐small cell lung cancer is imperative for the identification of novel therapeutic targets and improved methods of drug delivery. Support or Funding Information Claudine Auld was supported by the Summer Research Opportunities Program, sponsored by the American Society of Investigative Pathology. This research was supported in part by the Showalter Research Trust.