肿瘤免疫微环境STING靶向放射性分子探针构建与显像研究

Stimulator of interferon genes (STING) is an adaptor protein that plays an important role in the activation of type I interferons in response to cytosolic nucleic acid ligands. Recent evidence indicates involvement of the STING pathway in the induction of antitumor immune response. Therefore, STING agonists are now being extensively developed as a new class of cancer therapeutics. However, little is known about the consequences of activated STING-mediated signaling in cancer cells on the efficacy of the antitumor treatment. It has been shown that activation of the STING-dependent pathway in cancer cells can result in tumor infiltration with immune cells and modulation of the anticancer immune response. Understanding the function of STING pathway in cancer cells might provide important insights into the development of effective therapeutic strategies. Based on these results, the aims of this project are to develop radiolabeled probes and evaluate their possibility for STING targeted tumor immune microenvironment (TIME) imaging with SPECT/PET. To achieve the objectives, we intend to solve the following key scientific issues: (1) Design and development of several 18F-labeled probes based on STING agonists of cyclic dinucleotide (CDN) and dimeric amidobenzimidazole (diABZI) structures. (2) Development of a series of 18F and 131I-labeled probes based on the small molecular inhibitors of nitrofuran and nitro-fatty acid derivatives for STING targeting. (3) Physico-chemical properties of newly developed radio-probes and in vitro characterization of binding affinity and specificity for STING targeting. (4) The feasibility and advantages of in vivo imaging of TIME via STING targeting will be verified in tumor-bearing mice. The potential value of nuclear imaging with these probes for non-invasive STING quantification in TIME will be discussed. Through the solution of the above problems, it might lay the foundation for establishing STING-target imaging evaluation system of TIME.

STING作为cGAS-STING信号通路关键功能分子参与肿瘤免疫等多种病理生理过程。激活STING促进I型IFN分泌调控肿瘤免疫微环境并诱导肿瘤特异性T细胞的产生，成为免疫治疗新靶点。基于此，本课题首次提出以STING为靶点，构建放射性分子影像探针和成像方法，实现肿瘤免疫微环境的实时动态、在体无创的监测。主要研究内容：（1）分别以环二核苷和胺基苯并咪唑类STING激动剂为先导化合物，构建系列放射性18F标记分子探针。（2）分别以硝基呋喃和硝基脂肪酸类STING抑制剂为先导化合物，构建系列18F和131I标记的分子探针。（3）在体外评价分子探针亲和力和特异性基础上，建立小动物肿瘤模型并验证分子探针用于STING显像的可行性。通过上述研究，开创基于STING的分子影像技术用于肿瘤免疫微环境监测新思路，为探索肿瘤演进中的炎癌转化机制研究提供新途径，为靶向干预和指导肿瘤免疫治疗提供新手段。

STING作为cGAS-STING信号通路关键功能分子参与肿瘤免疫等多种病理生理过程。激活STING促进I型IFN分泌调控肿瘤免疫微环境并诱导肿瘤特异性T细胞的产生，成为免疫治疗新靶点。基于此，本课题首次提出以STING为靶点，构建放射性分子影像探针和成像方法，实现肿瘤免疫微环境的实时动态、在体无创的监测。主要研究内容为分别以STING激动剂氨基苯并咪唑（ABZI）和吖啶酮（Acridone）、抑制剂硝基呋喃（NF）、cGAMP竞争性大环多肽配体（NNK）为母体结构，设计并合成4个系列10种以上放射性标记小分子探针，在蛋白、细胞和活体层面验证评价了放射性探针的理化性质、亲和力和特异性等STING靶向能力。重要结果如下：（1）以ABZI为先导化合物构建系列放射性分子探针，其中以[18F]F-DABI为例在鼠源肿瘤模型中验证了STING蛋白在体可视化的可行性。研究结果表明该探针在肿瘤中的摄取与STING表达正相关，可通过PET显像在活体肿瘤中实现STING定量可视化。（2）合成了3种以吖啶酮为母核结构的18F标记探针，通过标记基团和靶向基团之间聚乙二醇连接的改变优化探针的药代动力学性质，降低非靶部位如肝、肠和胆囊等摄取。进一步以[18F]F-CRI1为例验证了该探针在肿瘤中的摄取与STING表达的相关性，为实现PET成像在体监测肿瘤演进过程中STING实时变化、指导STING相关治疗奠定基础。（3）以硝基呋喃和cGAMP竞争性配体NNK大环肽为先导化合物，构建系列68Ga和131I标记的分子探针并完成了体内外评价。（4）筛选了7种细胞系并进行STING表达定量测定，评价分子探针亲和力和特异性、建立小动物肿瘤模型验证显像可行性。通过上述研究，开创基于STING的分子影像技术用于肿瘤免疫微环境监测新思路，为探索肿瘤演进中的炎癌转化机制研究提供新途径，为靶向干预和指导肿瘤免疫治疗提供新手段。