Fatty acid signaling in the pancreatic tumor microenvironment

项目摘要/摘要 尽管最近在精确医学方面取得了重大进展，但胰腺导管腺癌(PDAC)仍然 几乎一致致命。虽然目前PDAC中最常见的基因组改变是不可用药的， 常规疗法通常对这种疾病无效，免疫调节疗法有望 有意义地改善PDAC患者的预后。这种疗法的发展需要改进 了解具有PDAC微环境特征的免疫逃避机制，包括 经常排除抗肿瘤T细胞和大量免疫抑制的髓系细胞。我们最近 发现癌细胞固有的谷草转氨酶2(GOT2)塑造免疫 抑制抗肿瘤免疫的微环境。从机制上讲，我们发现GOT2的功能超出了它的范围 在苹果酸-天冬氨酸穿梭中确立作用并促进核受体的转录活性 PPARd，通过直接与PPARd配体花生四烯酸结合而促进。而PDAC细胞中的GOT2是不必要的 对于体内癌细胞的增殖，GOT2缺失会导致T细胞依赖的肿瘤生长抑制，并且 基因或药物上的PPARd激活可在GOT2缺失的情况下恢复PDAC进展。这种癌症 细胞固有的GOT2-PPARd轴促进来自肿瘤的CD4和CD8T细胞的空间限制 微环境，并促进肿瘤浸润性髓系细胞的免疫抑制表型。我们的结果 到目前为止证明了已建立的线粒体酶在转录中的非规范功能 免疫逃避的调节，在这里，我们建议利用这个新的GOT2-PPARd轴来促进 具有以下特定目的的高效抗肿瘤免疫反应。目标1：评估治疗方法 在已建立的PDAC中靶向GOT2-PPARd轴的可能性。我们将进行临床前评估 GOT2/PPARd通路抑制与旨在提高抗肿瘤T细胞活性的治疗方法相结合 在不同的小鼠模型中，在已知临床结果和突变的患者样本中验证我们的发现 状态，并评估患者群体中关于GOT2之间的关联的异质性 信号与T细胞空间调节。目的2：分析癌症驱动的免疫逃避机制 细胞固有的GOT2。我们将应用体外共培养系统，体内检测一组GOT2突变体 具有不同的脂肪酸信号传递能力，并进行无偏见的转录分析，以了解逐步 调节旁分泌调节免疫逃避的机制。目的3：询问脂肪酸介导的基因 GOT2和PPARd的监管。我们将分析PPARd和其他基因的全基因组结合模式 推测受GOT2调控的免疫调节转录因子，并表征细胞中的染色质状态 防止或允许抗肿瘤免疫反应的脂肪酸信号扰动的背景。这项工作将 利用我们最近在PDAC中发现的一种新的免疫抑制机制，有可能 告知准备用于临床翻译的新的治疗组合。

PROJECT SUMMARY/ABSTRACT Despite significant recent advances in precision medicine, pancreatic ductal adenocarcinoma (PDAC) remains near-uniformly lethal. While the most frequent genomic alterations in PDAC are not presently druggable and conventional therapies are often ineffective in this disease, immune-modulatory therapies hold promise to meaningfully improve outcomes for PDAC patients. Development of such therapies requires an improved understanding of the immune evasion mechanisms that characterize the PDAC microenvironment, including frequent exclusion of antineoplastic T cells and abundance of immune-suppressive myeloid cells. We recently found that cancer cell-intrinsic glutamic-oxaloacetic transaminase 2 (GOT2) shapes the immune microenvironment to suppress antitumor immunity. Mechanistically, we found that GOT2 functions beyond its established role in the malate-aspartate shuttle and promotes the transcriptional activity of nuclear receptor PPARd, facilitated by direct binding to PPARd ligand arachidonic acid. While GOT2 in PDAC cells is dispensable for cancer cell proliferation in vivo, GOT2 loss results in T cell-dependent suppression of tumor growth, and genetic or pharmacologic PPARd activation restores PDAC progression in the GOT2-null context. This cancer cell-intrinsic GOT2-PPARd axis promotes spatial restriction of both CD4 and CD8 T cells from the tumor microenvironment, and fosters the immune-suppressive phenotype of tumor-infiltrating myeloid cells. Our results to date demonstrate a non-canonical function for an established mitochondrial enzyme in transcriptional regulation of immune evasion, and here we propose to exploit this novel GOT2-PPARd axis to promote a productive antitumor immune response with the following specific aims. Aim 1: Assess the therapeutic potential of targeting the GOT2-PPARd axis in established PDAC. We will perform preclinical evaluation of GOT2/PPARd pathway inhibition together with therapeutic approaches aimed to increase antitumor T cell activity in diverse mouse models, validate our findings in patient specimens with known clinical outcomes and mutational status, and assess heterogeneity across the patient population with respect to the association between GOT2 signaling and T cell spatial regulation. Aim 2: Analyze the immune evasion mechanisms driven by cancer cell-intrinsic GOT2. We will apply in vitro co-culture systems, in vivo assays testing a suite of GOT2 mutants with varying fatty acid signaling capacity, and unbiased transcriptional analyses to understand the stepwise mechanisms mediating paracrine regulation of immune evasion. Aim 3: Interrogate fatty acid-mediated gene regulation by GOT2 and PPARd. We will analyze the genome-wide binding patterns of PPARd and additional immune-modulatory transcription factors putatively regulated by GOT2, and characterize chromatin states in the context of fatty acid signaling perturbations that prevent or permit antitumor immune responses. This work will leverage our recent identification of a novel immune suppression mechanism in PDAC, with the potential to inform on new therapeutic combinations poised for clinical translation.