6-thio-2'-deoxyguanosine in GBM: Pre-clinical Evaluation of Mechanism of action, Efficacy and Biomarker identification

项目概要-项目1 神经胶质瘤是成人中最常见的原发性恶性脑肿瘤， 每年在美国。胶质母细胞瘤（GBM）是最常见的胶质瘤类型， 尽管进行了积极的治疗，但生存期不到21个月。GBM和其他人类癌症一样， 一种叫做端粒酶的酶，它可以重建染色体的末端，也就是端粒， 使细胞能够复制永生。事实上，大约90%的GBM病例在组织中存在遗传改变。 TERT基因激活端粒酶。不幸的是，迄今为止，直接靶向端粒酶活性的努力 由于缺乏能穿过血脑屏障的有效小分子， 效果，并在GBM中显示有效性和特异性。因此，迫切需要开发安全、 端粒酶靶向疗法对端粒酶激活的胶质母细胞瘤患者的疗效 基因改变 我们先前使用嘌呤类似物前药6-硫代-2 '-脱氧鸟苷（6-硫代-dG），其用于治疗中。 在20世纪70年代的人类临床试验中，开发了快速诱导端粒酶介导的细胞毒性DNA的策略 端粒损伤而不是抑制端粒酶和允许端粒越来越短，6- 硫代-dG被癌细胞吸收并转化为6-硫代-dGTP，然后将其掺入新的 合成端粒重复序列。一旦这些修饰的片段在端粒中积累，端粒DNA 损伤迅速产生，最终导致细胞死亡。在肺、结肠和黑色素瘤的临床前模型中， 用6-硫代-dG处理导致癌细胞的快速杀伤，而对正常细胞和组织的毒性很小。 重要的是，由6-硫代-dG诱导的端粒DNA损伤也增强了抗肿瘤先天免疫。建筑 根据这些数据，我们将临床前分析扩展到GBM，并获得了6-硫代-dG交叉的证据， 血脑屏障项目1的总体目标是将6-硫代-dG推向临床试验， 由项目2负责。我们提出以下具体目标：1）表征临床前疗效， 单独或与替莫唑胺（TMZ）组合的6-硫代-dG治疗的药效学生物标志物 患者来源的细胞系、PDX和类器官模型的扩展组; 2）测试抗肿瘤功效和 单独的6-硫代-dG和与TMZ或免疫检查点阻断（ICB）组合的炎性潜力 在GBM的免疫活性鼠模型中的治疗;和3）定义细胞毒性和先天性炎性 6-硫代-dG在离体神经胶质瘤组织框架和患者来源的类器官中的潜力。这些研究将 确定6-硫代-dG在GBM中的临床前疗效，并确认将指导治疗的疗效生物标志物。 临床试验设计，包括入组标准。该项目将与拟议的行政管理部门密切合作。 核心，分子生物标志物核心资源和项目2，以实现我们推进6-硫代-dG的共同目标 用于GBM的临床应用。

PROJECT SUMMARY – Project 1 Gliomas are the most common primary malignant brain tumor in adults and account for over 14,000 deaths annually in the United States. The most common type of glioma, glioblastoma (GBM) has a median overall survival of less than 21 months in spite of aggressive therapy. GBMs, like other human cancers, have activated an enzyme called telomerase that rebuilds the ends of the chromosomes – regions known as telomeres – to enable the cell’s replicative immortality. Indeed, roughly 90% of GBM cases harbor genetic alterations in the TERT gene that activate telomerase. Unfortunately, efforts to directly target telomerase activity to date have been hindered by lack of effective small molecules that cross the blood-brain-barrier, demonstrate on-target effects, and show efficacy and specificity in GBMs. Therefore, there is a critical need to develop safe and efficacious telomerase-targeted therapies for patients with GBM whose tumors harbor telomerase activating genetic alterations. We previously used the purine analog pro-drug 6-thio-2’-deoxyguanosine (6-thio-dG), which was used in human clinical trials in the 1970s, to develop a strategy for rapidly inducing telomerase-mediated cytotoxic DNA damage at telomeres. Rather than inhibiting telomerase and allowing telomeres to get progressively shorter, 6- thio-dG is taken up by cancer cells and converted into 6-thio-dGTP, which is then incorporated into newly synthesized telomeric repeats. Once these modified segments accumulate in the telomeres, telomeric DNA damage rapidly results, ultimately leading to cell death. In pre-clinical models of lung, colon, and melanoma, treatment with 6-thio-dG led to rapid killing of the cancer cells with little toxicity to normal cells and tissues. Importantly, telomeric DNA damage induced by 6-thio-dG also enhanced anti-tumor innate immunity. Building on these data, we have extended our pre-clinical analysis to GBMs and obtained evidence that 6-thio-dG crosses the blood-brain-barrier. The overall objective for Project 1 is to advance 6-thio-dG toward a clinical trial to be conducted by Project 2. We propose the following Specific Aims: 1) Characterize the pre-clinical efficacy and pharmacodynamic biomarkers of 6-thio-dG treatment alone or in combination with Temozolomide (TMZ) in an extended panel of patient-derived cell lines, PDX and organoid models; 2) Test the anti-tumor efficacy and inflammatory potential of 6-thio-dG alone and in combination with TMZ or immune checkpoint blockade (ICB) therapies in immune competent murine models of GBM; and 3) Define cell toxicity and innate inflammatory potential of 6-thio-dG in an ex vivo glioma tissue framework and patient-derived organoids. These studies will determine the pre-clinical efficacy of 6-thio-dG in GBM and confirm biomarkers of efficacy that will guide the design of clinical trials including enrollment criteria. This Project will work closely with the proposed Administrative Core, Molecular Biomarker Core Resource, and Project 2 to achieve our shared goal of advancing 6-thio-dG toward clinical application in GBM.