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

由于发病率不断上升和缺乏有效的长期治疗方案，肝细胞癌（HCC）正在成为西方社会的一个主要健康问题。HCC的特点是治疗耐药性强，导致不能手术的肿瘤患者预后很差。详细的HCC发病机制分子生化分析对确定新的治疗靶点至关重要。不受控制的能量学和细胞代谢的改变代表了癌症的新特征。在之前的工作中，我们和其他人获得了在人类HCC和小鼠模型系统中激活糖酵解的实验证据。在此背景下，我们决定表征已建立的化学糖酵解抑制剂2-脱氧-d -葡萄糖（2-DG）对HCC生长的影响。虽然2-DG在体外确实能够抑制HCC的生长，但该物质在两种小鼠HCC模型中未能发挥显著的生长抑制作用。葡萄糖摄取增强已被描述为介导对2-DG的抗性。事实上，将细胞培养基中的葡萄糖水平降低75%，可显著增强2-DG的抗增殖功效。为了在体内分析这种影响，我们给含hcc的小鼠喂食了碳水化合物含量降低的饮食（15%，而标准食物为50%）。虽然饮食没有改变2-DG的体内疗效，但碳水化合物限制本身导致肿瘤进展和生存显著降低。这些结果特别有趣，因为所应用的小鼠HCC模型对传统化疗（例如依托泊苷和阿霉素）和索拉非尼完全耐药。鉴于糖酵解被激活，我们假设饮食干预会通过降低葡萄糖可用性来抑制肿瘤生长。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（通过基于质谱的代谢组学测定）都没有显著降低。碳水化合物的消耗是胰岛素分泌最重要的决定因素，而胰岛素在HCC中是一种确定的促肿瘤生长因子。事实上，我们能够证明，在限制碳水化合物的情况下，胰岛素受体/Akt/mTOR通路的激活显著降低。综上所述，我们的研究结果支持常量营养素组成，特别是碳水化合物含量在HCC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，因此这些结果的临床应用似乎是可行的。综上所述，出现了以下关键问题：饮食干预的肿瘤抑制作用是否可在其他啮齿动物HCC模型中重现？限制碳水化合物对肝纤维化相关的hcc安全有效吗？限制碳水化合物与索拉非尼（不能手术的HCC的标准治疗）联合使用效果如何？这些问题将在概述的项目建议书中详细讨论。

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.