Mechanisms of BET bromodomain metabolic reprogramming in triple negative breast cancer

在三阴性乳腺癌(TNBC)中，一种可能适合免疫治疗的肿瘤类型， 转移中的恶性细胞的生物学决定了死亡率，而不是原发肿瘤的生物学。这个 意识到只有大约五分之一的患者对免疫疗法有真正的反应，这表明更多的努力 应致力于了解肿瘤微环境中的基本机制。新陈代谢计划在 原发肿瘤和远处转移都会影响对免疫治疗的反应，但许多重要因素 新陈代谢的分子开关仍未被研究。BET溴域蛋白，包括BRD2， 在体细胞中，BRD3和BRD4是新的代谢关键调节因子，可能是 TNBC的免疫治疗。这些转录辅助调节因子是众所周知的肿瘤细胞增殖的参与者。 但直到最近才被发现对新陈代谢和转移至关重要。正如我们在这里所展示的，个人 BET蛋白也控制着PD-L1的表达，这是免疫治疗的核心。小分子PAN-BET抑制剂 (Beti)，如JQ1，在几个临床前癌症模型中显示出希望。个别投注的操控 蛋白质还通过转录上调代谢基因和反式激活来增加脂肪酸氧化。 Vates PPARγ以像pgc-1α这样的基因为靶点，以驱动肿瘤转移的方式。新陈代谢重新编程是 兴趣，而2型糖尿病是一个有用的起点。这些机制在以下方面至关重要 TNBC微环境的代谢。我们的初步数据显示，BRD2和BRD4相互对立 其他代谢功能：Brd2共同抑制PPARγ靶基因和OXPHOS基因转录，但 BRD4反对TNBC中的糖酵解代谢。这表明，适当的选择性BET抑制可能 提高免疫疗法的疗效。我们的长期目标是了解BET溴域蛋白是如何 重新编程代谢以调节TNBC的进展和转移，以及免疫治疗反应。这个 这里的目标是解决每个BET家族成员的个别功能选择性敲除和 下一代Beti，定义调节新陈代谢、转移和检查点功能的基因网络。 中心假设是，BET蛋白控制着TNBC代谢中的代谢开关，这对 转移，并可重新编程为免疫治疗的好处。强劲的初步数据支持三个方面 具体目标：1.确定BET蛋白如何控制代谢可塑性以驱动TNBC的进展。2. 确定BET蛋白如何通过PD-1/PD-L1轴调节乳腺肿瘤免疫逃逸。3. 确定BET蛋白调节的代谢可塑性如何促进抗PD-1/PD-L1策略。我们会 对接受和不接受2型糖尿病和二甲双胍治疗的TNBC患者进行观察性研究。 我们期望发现BET蛋白代谢开关调节TNBC的进展和转移， 将代谢重新编程与检查点功能结合起来。这些见解将有助于定制下一代Beti 目的：最大限度地提高联合免疫治疗的疗效，最大限度地减少TNBC的转移风险。

In triple negative breast cancer (TNBC), a tumor type that may be amenable to immune-based treatment, the biology of malignant cells in metastases drives mortality, rather than the biology of primary tumors. The realization that only about a fifth of patients really respond to immunotherapies suggests that more effort should be dedicated to understanding basic mechanism in the tumor microenvironment. Metabolic programs in both primary tumor and distant metastasis affect responsiveness to immunotherapy, but many important molecular switches of metabolism remain unexplored. The BET bromodomain proteins, comprising BRD2, BRD3 and BRD4 in somatic cells, are new critical regulators of metabolism and could be important targets in immunotherapy for TNBC. These transcriptional co-regulators are well known players in tumor cell prolifer- ation, but are only recently identified as critical for metabolism and metastasis. As we show here, individual BET proteins also control PD-L1 expression, central to immunotherapy. Small molecule pan-BET inhibitors (BETi), such as JQ1, show promise in several pre-clinical cancer models. Manipulation of individual BET proteins also increases fatty acid oxidation by transcriptional upregulation of metabolic genes and transacti- vates PPARγ target genes like PGC-1α, in ways that drive TNBC metastasis. Metabolic reprogramming is of interest, and Type 2 diabetes is a useful place to start. These mechanisms are critically important in metabolism of the TNBC microenvironment. Our preliminary data show that BRD2 and BRD4 oppose each other in metabolic functions: BRD2 co-represses PPARγ target genes and OXPHOS gene transcription, but BRD4 opposes glycolytic metabolism in TNBC. This suggests that properly selective BET inhibition could improve efficacy of immunotherapies. Our long term goal is to understand how BET bromodomain proteins reprogram metabolism to regulate progression and metastasis in TNBC, and immunotherapy responses. The objective here is to resolve the individual functions of each BET family member with selective knockdown and next-generation BETi, to define gene networks that regulate metabolism, metastasis and checkpoint function. The central hypothesis is that BET proteins control a metabolic switch in TNBC metabolism that is critical for metastasis, and can be reprogrammed for immunotherapy benefit. Strong preliminary data support three Specific Aims: 1. Determine how BET proteins control metabolic plasticity to drive progression of TNBC. 2. Determine how BET proteins regulate breast tumor immune escape through the PD-1/PD-L1 axis. 3. Determine how BET protein-regulated metabolic plasticity facilitates anti-PD-1/PD-L1 strategies. We will undertake an observational study of TNBC patients with and without Type 2 diabetes and metformin treatment. We expect to find that a BET protein metabolic switch regulates progression and metastases in TNBC, coupling metabolic reprogramming to checkpoint function. These insights will help tailor next generation BETi to maximize therapeutic efficacy of immunotherapy combinations and minimize metastasis risk in TNBC.