Nutritive carbohydrates determine tumor progression in murine hepatocellular carcinoma: An innovative approach for therapy?

由于不断上升的发病率和缺乏有效的长期治疗方案，肝细胞癌(HCC)正成为西方社会的一个主要健康问题。肝细胞癌具有强大的治疗抵抗力，导致不能手术的肿瘤患者的预后非常差。对肝细胞癌发病机制进行详细的分子和生化分析对于寻找新的治疗靶点至关重要。解除管制的能量学和细胞新陈代谢的改变是癌症的新特征。在之前的工作中，我们和其他人获得了在人类肝癌和小鼠模型系统中激活糖酵解的实验证据。在此背景下，我们决定对已建立的化学糖酵解抑制剂2-脱氧-D-葡萄糖(2-DG)对肝癌生长的影响进行表征。虽然2-DG在体外确实能够抑制肝癌的生长，但在两种小鼠肝癌模型中，该物质未能发挥显著的生长抑制作用。增强的葡萄糖摄取已被描述为介导对2-DG的抵抗。事实上，将细胞培养上清液中的葡萄糖水平降低75%会显著增强2-DG的抗增殖效果。为了在体内分析这种影响，我们给携带肝癌的小鼠喂食碳水化合物含量较低的饮食(15%，而标准饮食为50%)。虽然饮食没有改变2-DG的体内疗效，但限制碳水化合物本身会显著降低肿瘤的进展和存活率。这些结果特别耐人寻味，因为应用的小鼠肝癌模型对常规化疗(如依托泊苷和阿霉素)以及索拉非尼完全耐药。考虑到激活的糖酵解，我们假设饮食干预将通过减少葡萄糖供应来抑制肿瘤生长。然而，通过限制饮食碳水化合物，血液和肿瘤组织中的葡萄糖水平(通过基于质谱学的代谢组学测定)都没有显著降低。碳水化合物摄入量是影响胰岛素分泌的最重要的决定因素，而胰岛素在肝细胞癌中是公认的促肿瘤生长因子。事实上，我们能够在限制碳水化合物的情况下显示胰岛素受体/Akt/mTOR通路的激活显著减少。综上所述，我们的结果支持了大量营养素的组成，尤其是碳水化合物含量在肝细胞癌发病机制中的关键作用。由于低碳水化合物饮食已经安全使用了近一个世纪，这些结果的临床应用似乎是可行的。综上所述，以下关键问题出现了：饮食干预的肿瘤抑制作用在其他啮齿动物肝细胞癌模型中是否可以重现？在与肝纤维化相关的肝细胞癌中，限制碳水化合物是否安全有效？限制碳水化合物与标准疗法索拉非尼联合治疗不能手术的肝细胞癌的效果如何？这些问题将在概述的项目提案中详细阐述。

Hepatocellular carcinoma (HCC) is becoming a major health problem in Western societies due to constantly rising incidence and lack of effective long-term treatment options. HCC is characterized by robust therapy resistance, resulting in very poor prognosis of patients with inoperable tumors. Detailed molecular and biochemical analysis of HCC pathogenesis is of pivotal importance to identify new therapy targets. Deregulated energetics and alterations of cellular metabolism represent emerging hallmarks of cancer. In previous work, we and others obtained experimental evidence for activation of glycolysis in human HCC and murine model systems. Against this background, we decided to characterize the effect of the established chemical glycolysis inhibitor 2-deoxy-D-gluocse (2-DG) on HCC growth. While 2-DG was indeed able to inhibit HCC growth in vitro, the substance failed to exert significant growth inhibiting properties in two murine HCC models. Enhanced glucose uptake has been described to mediate resistance towards 2-DG. Indeed, reducing glucose levels in cell culture media by 75% resulted in significantly enhanced antiproliferative efficacy of 2-DG. In order to analyze this effect in vivo, we fed a diet with reduced carbohydrate content (15% as compared to 50% in standard chow) to HCC-bearing mice. While the diet did not modify the in vivo efficacy of 2-DG, carbohydrate restriction per se resulted in significantly reduced tumor progression and survival. These results are especially intriguing as the applied murine HCC model is completely resistant towards conventional chemotherapy (e.g. etoposide and doxorubicin) as well as sorafenib. Given the activated glycolysis we hypothesized that the dietary intervention would inhibit tumor growth via reduced glucose availability. However, neither glucose levels in blood nor in tumor tissue (determined via mass spectrometry-based metabolomics) was significantly reduced via dietary carbohydrate restriction. Carbohydrate consumption is the most important determinant of insulin secretion and insulin represents an established pro-tumorigenic growth factor in HCC. Indeed, we were able to show significantly reduced activation of the insulin receptor/Akt/mTOR pathway upon carbohydrate restriction. Taken together, our results support a critical role of macronutrient composition, especially carbohydrate content, for HCC pathogenesis. As low carbohydrate diets have been safely used for almost a century, clinical application of these results seems feasible. Taken together, the following key questions emerge: Are the tumor inhibiting effects of the dietary intervention reproducible in additional rodent HCC models? Is carbohydrate restriction safe and effective in HCCs associated with liver fibrosis? How effective is carbohydrate restriction in combination with sorafenib, the standard therapy of inoperable HCC? These questions will be addressed in detail in the outlined project proposal.