Protocol to generate murine organotypic brain cultures for drug screening and evaluation of anti-metastatic efficacy.

Organotypic brain cultures are short-term assays that phenotypically and functionally recapitulate brain metastatic cells in vivo. Here, we present a protocol to generate murine organotypic brain cultures for drug screening. We describe steps for sectioning of murine brains and plating of organotypic cultures. We then detail evaluation of the anti-metastatic effect of chemical compounds through bioluminescence imaging before and after drug treatment. Combined with downstream applications, this protocol allows comprehensive characterizations of both cancer cells and the tumor-associated microenvironment. For complete details on the use and execution of this protocol, please refer to Zhu et al. (2022).1.

Stratification of radiosensitive brain metastases based on an actionable S100A9/RAGE resistance mechanism.

Whole-brain radiotherapy (WBRT) is the treatment backbone for many patients with brain metastasis; however, its efficacy in preventing disease progression and the associated toxicity have questioned the clinical impact of this approach and emphasized the need for alternative treatments. Given the limited therapeutic options available for these patients and the poor understanding of the molecular mechanisms underlying the resistance of metastatic lesions to WBRT, we sought to uncover actionable targets and biomarkers that could help to refine patient selection. Through an unbiased analysis of experimental in vivo models of brain metastasis resistant to WBRT, we identified activation of the S100A9-RAGE-NF-κB-JunB pathway in brain metastases as a potential mediator of resistance in this organ. Targeting this pathway genetically or pharmacologically was sufficient to revert the WBRT resistance and increase therapeutic benefits in vivo at lower doses of radiation. In patients with primary melanoma, lung or breast adenocarcinoma developing brain metastasis, endogenous S100A9 levels in brain lesions correlated with clinical response to WBRT and underscored the potential of S100A9 levels in the blood as a noninvasive biomarker. Collectively, we provide a molecular framework to personalize WBRT and improve its efficacy through combination with a radiosensitizer that balances therapeutic benefit and toxicity.