谷氨酰胺代谢在乳腺癌脑转移中的促进作用及分子机制研究

Brain metastasis is a common disease in the end stage of breast cancer progression, which is devastating to the survival and life quality of patients. Sadly, patients with brain metastasis are refractory to almost all currently available treatments, experiencing a traumatic deterioration of quality of life and a devastating <20% one-year survival. There is NO effective treatment available besides radiotherapy that prolongs patients’ lives by merely a few months. To meet the unmet challenge patients face every day in the clinic, we urgently need to better understand the mechanism of brain metastasis and develop novel therapies based on that understanding. The microenvironment of the brain plays a key role in the development of therapeutic resistance of brain metastases. Brain interstitial space contains high levels of glutamine, but its role in the survival/growth of brain metastatic breast cancer cells is unknown. The c-MYC oncogene has perhaps been most associated with upregulated glutamine metabolism. In our previous study, we found that, unlike parental cancer cells, brain metastatic cells survive and proliferate depend on glutamine in the medium with low glucose and animal acid concentration, and exhibited upregulation of c-MYC. We hypothesize that c-MYC promote breast cancer brain metastasis through regulating glutamine metabolism. We have demonstrated the importance of c-MYC in BCBM through overexpression and knockdown of c-MYC. We found that mice intracarotidly injected with cells overexpressing c-MYC developed brain metastasis significantly faster than control mice, and died significantly faster than the control mice. And knockdown c-MYC in brain seeking cell line via shRNA led to a slower brain metastasis growth and prolonged survival. In this application, we will 1) determine the functional roles of c-MYC signaling in BCBM; 3) dissect the mechanisms of c-MYC mediated glutamine metabolism signaling in BCBM by metabolite set enrichment analysis and RNA-seq, and found the key pathways and molecules; 3) determine the clinical relevance of c-MYC and its key downstream regulator with BCBM via analyzing publicly available cancer data base and patient samples; 4) determine the efficacy of targeting c-MYC and glutamine metabolism pathway for the treatment and/or prevention of BCBM. This application will shed light on the function and molecular mechanism of c-MYC mediated glutamine metabolism in BCBM, which can be a potential therapeutic target of in treating this devastating disease.

10-16%的乳腺癌病人会发生脑转移。乳腺癌脑转移（BCBM）缺乏有效治疗方法，病人一年生存率<20%。其治疗耐药的重要原因在于大脑微环境的影响。谷氨酰胺是脑内含量最高的氨基酸，其在BCBM代谢中的作用及机制不明确。c-MYC是调节谷氨酰胺代谢的最重要蛋白。我们前期发现BCBM肿瘤细胞依赖谷氨酰胺存活和增殖，且c-MYC表达增高。因此推测乳腺癌细胞转移到脑后可在c-MYC调节下利用谷氨酰胺作为营养物质存活和增殖。我们初步研究了c-MYC对BCBM的重要性：过表达c-MYC能促进小鼠BCBM生长，降低生存；敲除c-MYC能逆转上述现象。本项目旨在确定c-MYC在BCBM不同阶段的生物功能；通过代谢组学、RNA-Seq阐明c-MYC在BCBM中调控谷氨酰胺代谢的机制和关键蛋白，并确定其表达与BCBM的临床相关性；最后找到靶向c-MYC及其调控的谷氨酰胺代谢通路治疗/预防BCBM的策略。

乳腺癌脑转移（BCBM）缺乏有效治疗方法，其治疗耐药的重要原因在于大脑微环境的影响。谷氨酰胺是脑内含量最高的氨基酸，其在BCBM代谢中的作用及机制不明确。c-MYC是调节谷氨酰胺代谢的最重要蛋白。本项目发现BCBM肿瘤细胞依赖谷氨酰胺存活和增殖，且c-MYC表达增高。在细胞和动物水平上，我们发现过表达c-MYC能够促进BCBM的生长，敲除c-MYC能够降低BCBM的生长，表明其是治疗BCBM的一个潜在靶点。我们发现c-MYC对乳腺癌细胞穿过血脑屏障没有影响，但是能够促进脑内早期微转移的生长；c-MYC可以促进乳腺癌细胞在模拟大脑环境的培养基中线粒体的量，减少活性氧造成的损伤；c-MYC可以通过谷氨酰胺酶GLS1促进BCBM的生长，靶向GLS1可以有效降低BCBM的生长。我们在多个数据库中研究了人样本、小鼠样本中c-MYC基因的表达与BCBM的相关性。虽然没有发现c-MYC的mRNA含量与BCBM的发生发展、病人的生存有相关性，但是已有文献报道一个包括125个 c-MYC调控的基因集 “c-MYC brain metastasis gene set”的表达与乳腺癌发生脑转移成正相关，印证了c-MYC与BCBM的相关性。通过分子生物学手段、小分子抑制剂治疗，我们找到了靶向c-MYC及其调控的谷氨酰胺代谢来治疗BCBM的策略。在本项目的支持下，我们在其他相关工作上也取得了一些研究成果，我们发现抗精神病药物盐酸三氟拉嗪和盐酸氟奋乃静具有治疗三阴性乳腺癌脑转移的效果，并且对其作用机制进行了研究，为老药新用治疗BCBM提供了思路。在本项目的支持下，申请人以第一作者/通讯作者（含并列）在Cell Death & Disease和Pharmacological Research等SCI杂志上发表了第一标注本基金的论文4篇，申请1项相关的专利，指导了一位硕士研究生毕业。