Distinct tumor architectures for metastatic colonization of the brain [scRNA-seq]

Brain metastasis is a dismal complication of cancer that hinges on the initial survival and outgrowth of disseminated cancer cells. To better understand these crucial early stages of brain metastatic colonization, we investigated two prevalent sources of cerebral relapse in the clinic, triple-negative breast cancer (TNBC) and HER2+ breast cancer (HER2BC). We elucidated distinctive early tumor architectures, physical and functional stromal interfaces, and autocrine growth programs employed by these two tumor types to colonize the brain. TNBC cells form extensive perivascular sheath colonies with diffusive contact with astrocytes and microglia. In striking contrast, heightened autonomous deposition of several extracellular matrix components prompts HER2BC cells to colonize the brain as compact, spheroidal colonies, segregating stromal cells to the periphery of the colony. Single-cell dissection of the spatially resolved tumor microenvironment (TME) reveals that brain metastases activate – to different degrees – the canonical stages of the disease-associated microglia (DAM) response previously defined in Alzheimer's disease. Differential engagement of paracrine tumor-DAM signaling through the receptor AXL suggests specific pro-metastatic functions of the tumor architecture in both TNBC perivascular and HER2BC spheroidal colonies. Collectively, our findings illuminate the distinct stereospatial features of two different yet highly efficient modes of brain colonization, and the relevance of these features in future efforts to leverage the TME to treat brain metastasis. Overall design: Xenograph model mice were injected with MDA231-BrM or HCC1954-BrM cells and brains were harvested after 30 days of growth for scRNA-seq. Additional processed data files required to run the code uploaded to GitHub (https://github.com/dpeerlab/Brain-metastasis-TME) are deposited in Zenodo (https://doi.org/10.5281/zenodo.13863738).

脑转移瘤是癌症的一类预后极差的并发症，其发生依赖于播散性癌细胞的初始存活与增殖。为更深入解析脑转移定植的关键早期阶段，本研究针对临床中两种常见的脑复发来源——三阴性乳腺癌（triple-negative breast cancer, TNBC）与HER2阳性乳腺癌（HER2+ breast cancer, HER2BC）展开探究。我们阐明了这两类肿瘤用于脑定植的独特早期肿瘤结构、物理与功能基质界面，以及其所采用的自分泌生长程序：三阴性乳腺癌细胞会形成广泛的血管周鞘状集落，与星形胶质细胞和小胶质细胞呈弥散性接触；与之形成鲜明对比的是，HER2阳性乳腺癌细胞可通过多种细胞外基质成分的自主性大量沉积，以紧凑的球形集落形式定植于脑内，并将基质细胞隔离至集落外围。对空间分辨的肿瘤微环境（tumor microenvironment, TME）进行单细胞解析后发现，脑转移瘤会在不同程度上激活阿尔茨海默病中已明确界定的疾病相关小胶质细胞（disease-associated microglia, DAM）应答经典阶段。肿瘤与疾病相关小胶质细胞通过受体AXL介导的旁分泌信号存在差异化参与，这提示两类肿瘤结构分别具备特定的促转移功能。综上，本研究揭示了两种截然不同却均高效的脑定植模式所具有的独特立体空间特征，以及这些特征在未来利用肿瘤微环境治疗脑转移瘤研究中的重要意义。

总体实验设计：将MDA231-BrM与HCC1954-BrM细胞注射至异种移植模型小鼠体内，待细胞生长30天后收获脑组织，用于单细胞RNA测序（single-cell RNA sequencing, scRNA-seq）。上传至GitHub（https://github.com/dpeerlab/Brain-metastasis-TME）的代码运行所需的额外处理后数据文件，已存储于Zenodo数据库（https://doi.org/10.5281/zenodo.13863738）。