Breast cancer brain metastases (BCBM) develop when cells spread from the primary breast tumor to the brain. Breast cancer is the second most frequent cause of brain metastasis after lung cancer, with metastases occurring in 10-16% of patients1. Unfortunately, brain metastases remain incurable as >80% of patients die within a year after their brain-metastasis diagnosis, and their quality of life is impaired due to neurological dysfunctions2. There is an urgent need to identify more effective treatment options. Monolayer two-dimensional or three-dimensional culture models are the most commonly used methods in testing therapeutic agents in the laboratory. However, they do not mimic the complex BCBM microenvironment, a major driver of tumor phenotype and growth. Although these models are useful, they do not capture the complex tumor-stromal interactions, the unique metabolic requirements, and the heterogeneity of the tumors3. To more faithfully recapitulate tumor-stromal interactions and microenvironment heterogeneity, our group and others have begun to generate organotypic brain metastasis "slice" cultures with patient-derived tumor cells (primary or metastatic) or cancer cell lines4,5,6. Compared to classical in vitro systems, this short-term ex vivo model may provide more relevant conditions for screening new therapeutics prior to preclinical assessment in large animal cohorts.
Ex vivo models have been constructed and successfully used primarily for the identification of successful treatments of various cancers. They require few days of assessment and additionally can be tailored to patient-specific drug screening. For example, human bladder and prostate cancer ex vivo tissues have shown a dose-dependent anti-tumor response of docetaxel and gemcitabine7. Similar colorectal carcinoma ex vivo tissues were developed to screen chemotherapeutic drugs Oxaliplatin, Cetuximab, and Pembrolizumab8. This application has been widely used in pancreatic cancer, considering the essential interaction between the stromal environment and the genotypic and phenotypic characteristics of pancreatic ductal adenocarcinoma9,10. Furthermore, such organotypic models have been developed for similar screenings in head, neck, gastric, and breast tumors11,12.
Here, an ex vivo brain slice model of xenografted breast cancer brain metastatic tumor cells in their microenvironment is being generated. Mice were intracranially injected with breast cancer brain metastatic brain trophic MDA-MB-231BR cells13 in the cerebral cortex parietal lobe- a common site of TNBC metastasis14,15 and allowed to develop tumors. Brain slices were generated from these xenografted animals and maintained ex vivo as organotypic cultures as described16,17. This novel ex vivo model allows for the analysis of BCBM cell's growth within the brain parenchyma and can be used to test therapeutic agents and radiation effects on tumor cells within the brain microenvironment.