Targeting Tankyrases to Mitigate Immunosuppression and Enhance Cancer Immunotherapy

项目总结 肝激酶B1(LKB1)是细胞能量平衡的重要调节因子，也是众所周知的肿瘤抑制因子 基因在许多癌症中存在，尤其是肺癌，在约30%的肿瘤中该基因被缺失。LKB1抑制 或耗尽会导致肿瘤形成增强，免疫抑制增加，对 免疫检查点抑制剂。尽管LKB1负性调控对肿瘤生长和 侵袭性，目前还没有已知的LKB1上游调控因子。通过合理设计的药物筛查， 我们鉴定了Tankyrase(TNKS；TNKS1，或PARP5A，和TNKS2，或PARP5B)为上游负向 LKB1的监管机构。Tnks属于聚(ADP-核糖)聚合酶(PARP)的亲缘关系密切的成员。 以β-NAD+为底物将腺苷二磷酸核糖部分添加到目标蛋白上的家族，称为偶联反应。 TnKS对靶蛋白的部分合成通常会导致泛素化和蛋白酶体降解，例如 Axin(在Wnt信号中隔离Apc/β-catenin)、PTEN和端粒酶。然而，PARSYNTING的 LKB1不会导致LKB1的降解，但会抑制LKB1的活性。过表达TNKS刺激肿瘤 细胞在体外的增殖和增强体内肿瘤的形成是依赖于LKB1的。肺肿瘤(两者均为 腺癌和鳞癌)在表达LKB1的肿瘤中过表达TNKS1 预示着预后较差。鉴于LKB1突变的肺癌免疫抑制和 对免疫检查点抑制剂的反应很差，我们假设TNKS可能是阴性的 在LKB1野生型肿瘤中诱导免疫抑制的LKB1调节因子。我们将通过以下方式验证我们的假设： (1)确定TNKS在肿瘤微环境中的免疫抑制作用 使用同基因原位模型和基因工程小鼠模型(GEMM)更好地理解 如果TNKS水平使肿瘤处于免疫抑制状态；以及(2)利用同基因原位肿瘤模型 评价TNKS的表达对免疫治疗产生耐药的能力，并确定 抑制TNKS在增强免疫治疗应答中的作用。在这个项目完成后，我们 将更清楚地了解TNKS通过 LKB1的负性调控。这项研究将把TNKS作为临床翻译改进的目标 目前肺癌的治疗方法。

PROJECT SUMMARY Liver kinase B1 (LKB1) is a key regulator of cellular energy homeostasis and well known tumor suppressor gene in many cancers, particularly lung cancer, where it is deleted in ~30 percent of tumors. LKB1 suppression or depletion leads to enhanced tumorigenesis, increased immunosuppression, and reduced response to immune checkpoint inhibitors. Despite the importance of LKB1 negative regulation on tumor growth and aggressiveness, there is no known upstream regulator of LKB1. Through a rationally designed drug screen, we identified tankyrases (TNKS; TNKS1, or PARP5A, and TNKS2, or PARP5B), as upstream negative regulators of LKB1. TNKS belong to the closely related members of the poly (ADP-ribose) polymerase (PARP) family that adds ADP-ribose moieties to target proteins using β-NAD+ as substrate, termed PARsylation. PARsylation of target proteins by TNKS typically leads to ubiquination and proteasome degradation, such as AXIN (which sequesters APC/β-catenin in Wnt signaling), PTEN, and telomerase. However, PARsylation of LKB1 does not lead to LKB1 degradation, but inhibit LKB1 activity. Overexpression of TNKS stimulates tumor cellular proliferation in vitro and enhances tumorigenesis in vivo that is LKB1-dependent. Lung tumors (both adenocarcinoma and squamous cell carcinoma) that overexpress TNKS1 in LKB1 expressing tumors portended to poorer prognosis. Given the fact that LKB1 mutant lung tumors are immune suppressed and respond poorly to immune checkpoint inhibitors, we hypothesize that TNKS potentially could be the negative regulator of LKB1 that induce immune suppression in LKB1 wild type tumors. We will test our hypothesis by: (1) determining the role of TNKS on conferring immunosuppression in the tumor microenvironment through the use of syngeneic orthotopic models and Genetically-Engineered Mouse Models (GEMMs) to better understand if TNKS levels confers immunosuppressive state in tumors; and (2) utilizing syngeneic orthotopic tumor models to evaluate the ability of TNKS expression to generate resistance to immunotherapy and determine the effectiveness of TNKS inhibition on enhancing immunotherapy response. Upon completion of this project, we will have a clearer understanding of the immunosuppressive state that is conferred by TNKS through the negative regulation of LKB1. This research will implicate TNKS as a target for clinical translation to improve current therapies in lung cancer.