FGF Signaling in the Self-Renewal of Colon Cancer Organoids. FGF Signaling in the Self-Renewal of Colon Cancer Organoids

With their ability to self-renew and simultaneously fuel the bulk tumor mass with highly proliferative tumor cells, cancer stem cells (CSC) are supposedly driving cancer progression. However, the CSC-phenotype in colorectal cancer (CRC) is unstable and dependent on environmental cues. Since FGF2 is essential for adult and embryonic stem cell culture to maintain self-renewal, we investigated its role in advanced CRC using tumor-derived organoids as experimental model. We found that FGF-Receptor (FGFR) inhibition prevents organoid formation in very early expanding cells but induces cyst formation when applied to already established organoids. Comprehensive transcriptome analyses revealed that the induction of the transcription factor activator protein-1 (AP-1) together with a MAPK stimulation was most prominent after FGFR-inhibition. These effects resemble mechanisms of an acquired resistance against other described tyrosine kinase inhibitors such as targeted therapies against the EGF-Receptor. Furthermore, we detected elevated expression levels of several self-renewal and stemness-associated genes in organoid cultures with active FGF2 signaling. The combined data assumes that CSC are a heterogeneous subpopulation while self-renewal is a common feature regulated by many different pathways. Finally, we highlight the effects of FGF2 signaling as one of numerous aspects of the complex regulation of stemness in cancer. Overall design: The transcriptomes of colon cancer organoids with and without FGFR inhibition and human ESC lines were compared by microarray analysis (PrimeView Human Gene Expression Array, Affymetrix, Thermo Fisher Scientific).

癌症干细胞（cancer stem cells, CSC）兼具自我更新能力，并能为肿瘤实体大量补充高增殖性肿瘤细胞，被认为是推动癌症进展的核心群体。然而，结直肠癌（colorectal cancer, CRC）中的CSC表型并不稳定，且依赖于环境信号。
鉴于FGF2对成体与胚胎干细胞培养以维持自我更新至关重要，本研究以肿瘤源性类器官为实验模型，探究了其在晚期结直肠癌中的作用。我们发现，抑制FGF受体（FGF-Receptor, FGFR）可阻止极早期扩增细胞的类器官形成，但在作用于已建立的类器官时则会诱导囊状结构生成。
全转录组分析显示，在FGFR抑制后，转录因子激活蛋白1（activator protein-1, AP-1）的诱导与丝裂原活化蛋白激酶（mitogen-activated protein kinase, MAPK）信号激活最为显著。这些效应与已报道的其他酪氨酸激酶抑制剂（如针对表皮生长因子受体（EGF-Receptor）的靶向治疗）的获得性耐药机制相似。
此外，我们在FGF2信号激活的类器官培养物中，检测到多个自我更新相关与干细胞特性相关基因的表达水平升高。综合所有数据可知，CSC是一类异质性亚群，而自我更新是受多种不同通路调控的共同特征。最后，本研究强调了FGF2信号的作用，这是癌症中干细胞特性复杂调控网络的众多环节之一。
实验整体设计：通过微阵列分析（PrimeView人类基因表达芯片，Affymetrix，赛默飞世尔科技），对比了存在与不存在FGFR抑制的结肠癌细胞类器官，以及人类胚胎干细胞系（human ESC lines）的转录组。