Circulating tumor cells (CTCs) can be isolated via a minimally invasive blood draw and are considered a "liquid biopsy" of their originating solid tumors. CTCs contain a small subset of metastatic precursors that can form metastases in secondary organs and provide a resource to identify mechanisms underlying metastasis-initiating properties. Despite technological advancements that allow for highly sensitive approaches of detection and isolation, CTCs are very rare and often present as single cells, posing an extreme challenge for ex vivo expansion after isolation. Here, using previously established patient-derived CTC lines, we performed a small molecule drug screen to identify compounds that can improve ex vivo culture efficiency for single CTCs. We found that N-acetylcysteine (NAC) and other antioxidants can promote ex vivo expansion of single CTCs, by reducing oxidative and other stress particularly at the initial stage of single cell expansion. RNA-seq analysis of growing clones and non-growing clones confirmed the effect by NAC, but also indicate that NAC-induced decrease in oxidative stress is insufficient for promoting proliferation of a subset of cells with predominant senescent features. Despite the challenge in expanding all CTCs, NAC treatment led to establishment of single CTC clones that have similar tumorigenic features. Implications: Through a small molecule screen and validation study, we found that NAC could improve the success of ex vivo expansion of single CTCs by mitigating the initial stress, with the potential to facilitate the investigation of functional heterogeneity in CTCs.

中文翻译：

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N-乙酰-L-半胱氨酸通过减轻细胞应激反应促进单个循环肿瘤细胞的离体生长和扩增

循环肿瘤细胞 (CTC) 可以通过微创抽血分离，被认为是其起源实体肿瘤的“液体活检”。CTC 包含一小部分转移前体，它们可以在次级器官中形成转移，并提供资源来识别潜在的转移启动特性的机制。尽管技术进步允许高灵敏度的检测和分离方法，但 CTC 非常罕见，并且通常以单细胞形式存在，对分离后的离体扩增提出了极大的挑战。在这里，我们使用先前建立的源自患者的 CTC 系，进行了小分子药物筛选，以确定可以提高单个 CTC 离体培养效率的化合物。我们发现 N-乙酰半胱氨酸 (NAC) 和其他抗氧化剂可以通过减少氧化和其他压力，特别是在单细胞扩增的初始阶段，促进单个 CTC 的离体扩增。生长克隆和非生长克隆的 RNA-seq 分析证实了 NAC 的作用，但也表明 NAC 诱导的氧化应激降低不足以促进具有主要衰老特征的细胞亚群的增殖。尽管在扩展所有 CTC 方面存在挑战，但 NAC 治疗导致建立了具有相似致瘤特征的单个 CTC 克隆。启示：通过小分子筛选和验证研究，我们发现 NAC 可以通过减轻初始压力来提高单个 CTC 离体扩增的成功率，