Brain tissue contains the highest number of perivascular pericytes compared to other organs. Pericytes are known to regulate brain perfusion and to play an important role within the neurovascular unit (NVU). The high phenotypic and functional plasticity of pericytes make this cell type a prime candidate to aid physiological adaptations but also propose pericytes as important modulators in diverse pathologies in the brain. This review highlights known phenotypes of pericytes in the brain, discusses the diverse markers for brain pericytes, and reviews current in vitro and in vivo experimental models to study pericyte function. Our current knowledge of pericyte phenotypes as it relates to metastatic growth patterns in breast cancer brain metastasis is presented as an example for the crosstalk between pericytes, endothelial cells, and metastatic cells. Future challenges lie in establishing methods for real-time monitoring of pericyte crosstalk to understand causal events in the brain metastatic process.

Brain metastasis occurs in about 50% of all women with metastatic HER2+ breast cancer and confers poor prognosis for patients. Despite effective HER2-targeted treatments of peripheral HER2+ breast cancer with trastuzumab and HER2 inhibitors, limited brain permeability renders these treatments inefficient for HER2+ breast cancer brain metastasis. The scarcity of suitable patient-derived in vivo models for HER2+ breast cancer brain metastasis has curtailed the study of molecular mechanisms that promote growth and therapeutic resistance in brain metastasis. In this study, we generated and characterized a luminal B HER2+ breast cancer brain metastasis cell model (BCBM94) isolated from a patient with HER2+ brain metastasis. Repeated hematogenic xenografting of BCBM94 consistently generated breast cancer brain metastasis in mice. The clinical receptor tyrosine kinase inhibitor (RTKi) lapatinib blocked phosphorylation of all ERBB receptors (ERBB1–4) and induced the intrinsic apoptosis pathway in BCBM94. Neuregulin 1 (Nrg1), an ERBB3/ERBB4 ligand that is abundantly expressed in the brain, abrogated lapatinib-induced apoptosis in HER2+ BCBM94 and BT474 models. ErbB3 signaling pathways that involved PI3K–AKT and the phosphorylation of BAD at serine 136 to prevent apoptosis were essential for Nrg1-induced survival. High-throughput RTKi screening identified the brain-penetrant pan-ErbB inhibitor poziotinib as a highly potent compound that reduced cell viability in HER2+ breast cancer brain metastasis in the presence of NRG1. Two weeks of poziotinib treatment successfully ablated BCBM94 and BT474 HER2+ brain tumors in vivo. In conclusion, this study established a patient-derived HER2+ breast cancer brain metastasis model and identified poziotinib as a highly efficacious RTKi with excellent brain penetrability that eliminated HER2+ breast cancer brain metastasis. Significance: Development of a preclinical patient-derived model to study HER2+ breast cancer brain metastasis enabled the identification of the irreversible pan-ERBB inhibitor poziotinib as highly efficacious in treating brain metastatic tumors.

The study was carried out with the aim to evaluate the effects of continuous lightning (CL) and subsequent circadian rhythm disruption on CD4⁺/CD8⁺ populations of adaptive cell immunity. For further understanding of underlying processes that affect CD4⁺/CD8⁺ proliferation and differentiation, the expression levels of CD3⁺ and CD95⁺ cell receptors were evaluated. Chinchilla rabbits were exposed to shift work simulation - 24 hours of CL. We organized 5 time-related groups: 2, 4, 6, 12 months of CL respectively. The 5th group – corresponding control. Thymus derived slides were examined using immunofluorescence assay. A decrease in the expression of CD3⁺ and CD8⁺ and an increase in the expression of CD4⁺ lymphocytes, which was accompanied by an increase in the ratio of CD4⁺/CD8⁺ were found after 2 months of the experiment. After 4 and 6 months of CL, there was an increase in CD3⁺ expression and a decrease in CD4⁺ and CD8⁺ expression. The lowest levels of CD3⁺, CD4⁺ and CD8⁺ were recorded after 12 months of the experiment, which is a manifestation of significant immunosuppression due to premature aging of the thymus. The level of CD95⁺ lymphocytes was higher in the group after 12 months of CL, indicating the activation of apoptosis in thymocytes caused by circadian rhythms disruption under the influence of chronic light stress.

Supplemental figures and legends

Comparison ErbB inhibitor response in BCBM94 and NGN2 neurons

ErbB inhibitor response in the presence of rhNRG1