Investigating a Novel Glutamine Metabolism Pathway in Pancreatic Cancer

 描述(申请人提供)：胰腺导管腺癌(PDAC)是一种致命疾病，迫切需要新的治疗方法。我们以前的工作表明，PDAC的代谢发生了变化，致癌的Kras在这种代谢重编程中发挥了关键作用。重要的是，我们已经确定了一种新的谷氨酰胺(Gln)依赖的途径，这是PDAC生长所必需的，通过产生NADPH来维持氧化还原平衡(称为Gln-氧化还原途径)。这一途径依赖于致癌的Kras，在体外和体内对PDAC的生长是绝对必要的，而在正常细胞中则是必不可少的。因此，可能会有一个可接近的治疗窗口。我们已经证明致癌的Kras通过调节两种关键代谢酶GOT1和GLUD1的相对表达来控制GLN-氧化还原途径的流量，从而促进GOT1对Gln衍生的天冬氨酸的转氨化，并抑制GLUD1将谷氨酸转化为α-酮戊二酸。最终，NADPH和丙酮酸是由苹果酸酶(ME1)产生的。此外，我们的数据表明，ME1产生的绝大多数谷氨酰胺衍生的丙酮酸不会通过乳酸脱氢酶转化为乳酸。具体地说，同位素分析表明，这一丙酮酸池直接进入线粒体，在那里它可以被丙酮酸羧基酶(PC)作用。总之，这支持了在线粒体丙酮酸转运蛋白(MPC1/2)和PC之间存在复合体的观点。与这一概念一致，我们已经表明，在Gln示踪研究中，抑制MPC1或PC都会导致全标记天冬氨酸的显著积累，这表明Gln-氧化还原途径被抑制。在此背景下，我们提出了一系列深入的机制研究，以阐明：i)致癌Kras对该途径的调控；ii)该途径与PDAC中其他ROS清除途径的整合；iii)丙酮酸最终产物的代谢命运；以及iv)体内PDAC微环境对这种独特的Gln代谢的影响。考虑到开发Kras抑制剂的困难，靶向Kras调节的代谢途径可能为这种毁灭性的癌症提供新的攻击点。因此，完全了解这一新的谷氨酰胺-氧化还原途径将是将这些发现转化为临床的关键。SA1.探讨致癌Kras对谷氨酰胺代谢和氧化还原平衡的调节作用。SA2.探讨苹果酸酶衍生丙酮酸在PDAC谷氨酰胺代谢中的去向。SA3.探讨基础和应激条件下PDAC微环境对体内谷氨酰胺代谢和氧化还原平衡的影响。

 DESCRIPTION (provided by applicant): Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease and new therapies are desperately needed. Our previous work has shown that PDAC have an altered metabolism and that oncogenic Kras plays a key role in this metabolic reprogramming. Importantly, we have identified a novel, glutamine (Gln) -dependent pathway that is necessary for PDAC growth through the generation of NADPH for the maintenance of redox balance (referred to as the Gln-redox pathway). This pathway is dependent on oncogenic Kras and is absolutely essential for PDAC growth both in vitro and in vivo, while being dispensable in normal cells. Thus, there may be an accessible therapeutic window. We have shown that oncogenic Kras controls flux through the Gln-redox pathway by regulating the relative expression of two key metabolic enzymes; GOT1 and GLUD1, thereby promoting the transamination of Gln-derived aspartate by GOT1 and repressing the canonical conversion of glutamate to alpha-ketoglutarate by GLUD1. Ultimately, NADPH and pyruvate are produced by malic enzyme (ME1). Additionally, our data demonstrate that the overwhelming majority of Gln- derived pyruvate produced by ME1 is not converted to lactate via lactate dehydrogenase. Specifically the isotopomer analyses suggest that this pool of pyruvate is directly tunneled into the mitochondria where it can be acted upon by pyruvate carboxylase (PC). Together, this supports the idea that a complex exists between ME1, the mitochondrial pyruvate transporter (MPC1/2), and possibly PC. Consistent with this concept, we have shown that suppression of either MPC1 or PC results in a significant accumulation of fully labeled aspartate in Gln tracing studies, suggesting that the Gln-redox pathway has been inhibited. Against this backdrop, we propose a series of in-depth, mechanistic studies to elucidate: i) the regulation of the pathway by oncogenic Kras; ii) the integration of this pathway with other ROS scavenging pathways in PDAC; iii) the metabolic fate of the pyruvate end product, and iv) the impact of the PDAC microenvironment in vivo on this unique Gln metabolism. Given the difficulties in developing inhibitors to Kras, targeting Kras-regulated metabolic pathways that are required for growth may provide novel entry points of attack in this devastating cancer. Thus, a complete understanding of this novel Gln-redox pathway will be critical to translate these findings to the clinic. SA1. T explore the regulation of glutamine metabolism and redox balance by oncogenic Kras. SA2. To investigate the fate of malic enzyme derived pyruvate in PDAC glutamine metabolism. SA3. To explore how the PDAC microenvironment impacts glutamine metabolism and redox balance in vivo under basal and stress conditions.