Validation and humanization of a PET imaging agent that targets PD-L1.

 描述(由申请人提供)：最近有几种策略通过刺激适应性免疫治疗癌症显示了令人信服的临床疗效。例如，免疫检查点抑制物(CPIs)可以重新激活患者自身的T细胞，通过阻止导致肿瘤浸润性淋巴细胞(TIL)耗尽的相互作用来消除肿瘤。CPIs已显示出对转移性黑色素瘤的显著疗效，并正在测试用于治疗许多其他类型的肿瘤，无论是单独治疗还是联合治疗。细胞表面标记PD-L1的表达，无论是在肿瘤边缘的TIL上，还是在肿瘤本身上，似乎与CPI治疗的临床疗效有关，认为它是一个潜在的患者分层和治疗的生物标志物。目前评估这一生物标志物的标准是对原发灶和转移灶进行活组织检查，然后进行免疫组织化学鉴定。活检的局限性包括由于其侵袭性和难以在许多解剖位置接触肿瘤而导致患者和医生接受程度低，以及与肿瘤病灶内和肿瘤之间的标记物分布不均有关的抽样偏差，增加了假阴性结果的可能性。迫切需要一种非侵入性的成像技术，能够在不同解剖位置的原发灶和转移灶的整个表面上显示生物标记物的分布。121 Bio在开发这种非侵入性成像方法方面具有得天独厚的优势。我们正在开发一种正电子发射断层扫描(PET)试剂，它可以非侵入性地成像PD-L1。我们的产品使用特定部位的结合，可控制和可重复地在单域抗体(SdAbs)上安装放射性同位素标记。由于其体积小，所得到的显像剂显示出高组织摄取率和快速的肾脏清除。这一设计允许非常高的PET信噪比，即使在抗原丰度较低的情况下，在注射后2小时内也可以，从而实现高分辨率的当天成像。我们的小鼠概念验证实验使用针对特定免疫细胞和肿瘤标记物的放射性标记sdAbs，显示了异常高分辨率的淋巴和肿瘤成像。121 Bio组建了一支高素质的科学团队，在蛋白质工程、抗体发现和开发、肿瘤免疫学和核医学方面拥有丰富的经验。为了补充内部能力，我们已经获得了更多的外部设施，并招募了一个肿瘤免疫学和PET成像专家小组。我们建议用~(89)Zr或~(18)F标记Pd-L1反应性sdAb。由此产生的成像数据将指导我们为开发我们的放射诊断产品选择最佳的放射标记。我们还将正式演示使用我们的主要候选PD-L1抗体可以可视化显示人类肿瘤。最后，我们将人源化的sdAb，以降低潜在的免疫原性。这种抗PD-L1显像剂有可能成为第一个用于癌症免疫治疗患者选择和管理的非侵入性显像剂。

 DESCRIPTION (provided by applicant): Several strategies have recently shown convincing clinical efficacy by stimulating adaptive immunity for the treatment of cancer. Immune checkpoint inhibitors (CpIs), for example, reactivate a patient's own T cells to eliminate tumors by blocking interactions that cause tumor infiltrating lymphocytes (TILs) to become exhausted. CpIs have shown significant efficacy in metastatic melanoma, and are in testing for the treatment of numerous other tumor types, either alone or in combination. Expression of the cell surface marker PD-L1, either on TILS at the tumor margin or on the tumor itself, appears to be correlated with clinical efficacy in CpI therapy, identifying it as a potential biomarker for patiet stratification and management. The current standard for assessment of this biomarker entails biopsy of primary and metastatic tumor foci, followed by immunohistochemical characterization. Limitations of biopsy include low patient and physician acceptance due to its invasiveness and the difficulty of accessing tumors at many anatomical locations, and sampling bias related to the heterogeneous distribution of markers both within and between tumor foci, increasing the likelihood of false negative results. There is an urgent need for non-invasive imaging techniques that allow visualization of biomarker distribution on the entire surface of primary and metastatic tumor foci at diverse anatomical locations. 121 Bio is uniquely positioned to develop such a non-invasive imaging approach. We are developing a positron emission tomography (PET) agent that can non-invasively image PD-L1. Our product uses site-specific conjugation for controlled and reproducible installation of a radio-isotopic label on single domain antibodies (sdAbs). Due to its small size, the resulting imaging agents show high tissue uptake and rapid renal clearance. This design allows an exceptionally high PET signal to noise ratio, even at low levels of antigen abundance and within 2 hours of injection, enabling same day imaging at high resolution. Our mouse proof of concept experiments using radiolabelled sdAbs to specific immune cell and tumor markers shows exceptionally high resolution imaging of lymph nodes and tumors. 121 Bio has assembled a highly qualified scientific team with broad experience in protein engineering, antibody discovery and development, tumor immunology and nuclear medicine. To supplement internal capabilities, we have gained access to additional outside facilities and have recruited a panel of expert tumor immunology and PET imaging consultants. We propose here to prepare PD-L1-reactive sdAbs radiolabeled with either 89Zr or 18F. The resulting imaging data will guide our selection of the optimal radiolabel for development of our radiodiagnostic product. We will also formally demonstrate that human tumors can be visualized using our lead candidate antibody against PD-L1. Finally, we will humanize the sdAb in order to reduce potential immunogenicity. This anti-PD-L1 imaging agent offers the potential to be the first non-invasive imaging agent to be used in selection and management of patients undergoing cancer immunotherapy.