Englerin A induces an acute inflammatory response and reveals lipid metabolism and ER stress as targetable vulnerabilities in renal cell carcinoma

Renal cell carcinoma (RCC) is among the top ten most common forms of cancer and is the most common malignancy of the kidney. Clear cell renal carcinoma (cc-RCC), the most common type of RCC, is one of the most refractory cancers with an incidence that is on the rise. Screening of plant extracts in search of new anti-cancer agents resulted in the discovery of englerin A, a guaiane sesquiterpene with potent cytotoxicity against renal cancer cells and a small subset of other cancer cells. Though a few cellular targets have been identified for englerin A, it is still not clear what mechanisms account for the cytotoxicity of englerin A in RCC, which occurs at concentrations well below those used to engage the targets previously identified. Unlike any prior study, the current study used a systems biology approach to explore the mechanism(s) of action of englerin A. Metabolomics analyses indicated that englerin A profoundly altered lipid metabolism by 24 h in cc-RCC cell lines and generated significant levels of ceramides that were highly toxic to these cells. Microarray analyses determined that englerin A induced ER stress signaling and an acute inflammatory response, which was confirmed by quantitative PCR and Western Blot analyses. Additionally, fluorescence confocal microscopy revealed that englerin A at 25 nM disrupted the morphology of the ER confirming the deleterious effect of englerin A on the ER. Collectively, our findings suggest that cc-RCC is highly sensitive to disruptions in lipid metabolism and ER stress and that these vulnerabilities can be targeted for the treatment of cc-RCC and possibly other lipid storing cancers. Furthermore, our results suggest that ceramides may be a mediator of some of the actions of englerin A. Lastly, the acute inflammatory response induced by englerin A may mediate anti-tumor immunity.肾细胞癌（Renal cell carcinoma, RCC）是全球十大常见癌症之一，亦是最常见的肾脏恶性肿瘤。透明细胞肾细胞癌（Clear cell renal carcinoma, cc-RCC）作为RCC最常见的亚型，属于难治性癌症之一，且发病率呈逐年上升趋势。研究团队通过筛选植物提取物以发掘新型抗癌候选药物，最终发现了恩格林林A（englerin A）——一种愈创木烷型倍半萜，对肾癌细胞与少量其他癌细胞亚型展现出强效细胞毒性。尽管已有少量细胞靶点被证实与恩格林林A相关，但其介导肾细胞癌产生细胞毒性的具体机制仍未阐明，且其起效浓度远低于此前已确认的靶点结合所需浓度。 与以往所有研究不同，本研究采用系统生物学方法探究恩格林林A的作用机制。代谢组学分析显示，恩格林林A可在24小时内显著改变透明细胞肾细胞癌细胞系的脂质代谢，并诱导产生大量对该类细胞具有高度毒性的神经酰胺。基因芯片分析发现，恩格林林A可激活内质网应激（ER stress）信号通路与急性炎症反应，该结果经定量聚合酶链反应与蛋白质印迹实验得到验证。此外，荧光共聚焦显微镜观察显示，25 nM浓度的恩格林林A可破坏内质网形态，进一步证实其对内质网的损伤作用。 综上，本研究结果表明透明细胞肾细胞癌对脂质代谢紊乱与内质网应激高度敏感，这些脆弱靶点可用于治疗cc-RCC及其他可能存在脂质储存异常的癌症。此外，神经酰胺可能介导了恩格林林A的部分生物学功能。最后，恩格林林A诱导的急性炎症反应或可介导抗肿瘤免疫应答。