Brain metastases (BM) are the most common brain tumor in adults and are a leading cause of cancer mortality. Metastatic lesions contain subclones derived from their primary lesion, yet their functional characterization is limited by a paucity of preclinical models accurately recapitulating the metastatic cascade, emphasizing the need for a novel approach to BM and their treatment. We identified a unique subset of stem-like cells from primary human patient brain metastases, termed brain metastasis-initiating cells (BMICs). We now establish a BMIC patient-derived xenotransplantation (PDXT) model as an investigative tool to comprehensively interrogate human BM. Using both in vitro and in vivo RNA interference screens of these BMIC models, we identified SPOCK1 and TWIST2 as essential BMIC regulators. SPOCK1 in particular is a novel regulator of BMIC self-renewal, modulating tumor initiation and metastasis from the lung to the brain. A prospective cohort of primary lung cancer specimens showed that SPOCK1 was overexpressed only in patients who ultimately developed BM. Protein–protein interaction network mapping between SPOCK1 and TWIST2 identified novel pathway interactors with significant prognostic value in lung cancer patients. Of these genes, INHBA, a TGF-β ligand found mutated in lung adenocarcinoma, showed reduced expression in BMICs with knockdown of SPOCK1. In conclusion, we have developed a useful preclinical model of BM, which has served to identify novel putative BMIC regulators, presenting potential therapeutic targets that block the metastatic process, and transform a uniformly fatal systemic disease into a locally controlled and eminently more treatable one.

脑转移瘤（BM）是成人中最常见的脑肿瘤，并且是导致癌症死亡的主要原因。转移性病变包含源自其原发性病变的亚克隆，但由于缺乏能准确概括转移级联反应的临床前模型，它们的功能表征受到限制，从而强调了对BM及其治疗的新颖方法的需求。我们从原发性人类患者脑转移中鉴定出干细胞样细胞的独特子集，称为脑转移起始细胞（BMIC）。我们现在建立一个BMIC患者源性异种移植（PDXT）模型，作为全面询问人类BM的研究工具。使用这些BMIC模型的体外和体内RNA干扰筛选，我们确定SPOCK1和TWIST2是必不可少的BMIC调节剂。SPOCK1特别是BMIC自我更新的新型调节剂，可调节从肺部到脑部的肿瘤起始和转移。一组原发性肺癌标本的前瞻性研究表明，SPOCK1仅在最终发展为BM的患者中过表达。SPOCK1和TWIST2之间的蛋白质-蛋白质相互作用网络图谱鉴定了在肺癌患者中具有重要预后价值的新型途径相互作用物。在这些基因中，INHBA是在肺腺癌中突变的一种TGF-β配体，在SPICK1基因敲低后BMIC中的表达降低。总而言之，我们已经开发了一种有用的BM临床前模型，该模型可用于确定新型的BMIC调节剂，并提供可能阻碍转移过程的治疗靶点，