Li Miao, Ehlerding Emily B, Jiang Dawei, Barnhart Todd E, Chen Weiyu, Cao Tianye, Engle Jonathan W, Cai Weibo
Department of Radiology, The First Affiliated Hospital of Xi'an Jiaotong University 277 West Yanta Road, Xi'an 710061, Shaanxi, China.
Departments of Radiology and Medical Physics, University of Wisconsin-Madison 1111 Highland Avenue, Madison 53705, Wisconsin, United States.
Am J Transl Res. 2020 May 15;12(5):1862-1872. eCollection 2020.
Programmed death protein 1 and programmed death-ligand 1 (PD-1/PD-L1) have been widely studied as one of the most critical immune check-point pairs in the cancer microenvironment. In breast cancer (BrCa), the expression of PD-L1 is regarded as a determinant biomarker for patient stratification and prediction of inhibition response. Quantitative positron emission tomography (PET) imaging of PD-L1 expression in tumors using a therapeutic antibody in the clinic seems to be a promising approach that can complement conventional histopathological methods and overcome several issues, such as the tumor heterogeneities, sampling representativeness and clear differentiation of positive and negative results. In this study, we synthesized and evaluated Zr-labeled avelumab (Ave) for the in vivo characterization of PD-L1 expression in BrCa. Confocal imaging of BrCa cells and flow cytometry were employed to evaluate PD-L1 expression in MDA-MB-231 cells. The intact human monoclonal antibody targeting PD-L1, i.e., Ave, was conjugated to p-SCN-Deferoxamine (Df) and labeled with Zr. After intravenous injection of Zr-Df-avelumab (Zr-Df-Ave), PET imaging of MDA-MB-231 tumor-bearing mice, with or without blocking, was performed. High PD-L1 expression of MDA-MB-231 cells was confirmed by in vitro immuno-fluorescent staining and flow cytometry. PET imaging indicated the peak uptake of Zr-Df-Ave in the tumor (6.4±1.0 %ID/g), spleen (10.2±0.7 %ID/g) and lymph nodes (6.9±1.0 %ID/g) at 48 h after injection (n=4). Blocking study using unlabeled Ave could reduce the tracer uptake in these tissues (5.2±1.0 %ID/g in the tumor, 4.9±0.5 %ID/g in the spleen and 5.8±1.1 %ID/g in lymph nodes at 48 h, n=4), which demonstrated the specificity of Zr-Df-Ave. Biodistribution study and immuno-fluorescent staining were consistent with the quantitative data from PET imaging. Herein, we offer the evidence supporting the value of immuno-PET imaging using Zr-Df-Ave for non-invasive characterization of PD-L1 expression in BrCa and the applicability of this tracer in BrCa for treatment evaluation after immunotherapy.
程序性死亡蛋白1和程序性死亡配体1（PD-1/PD-L1）作为癌症微环境中最关键的免疫检查点对之一，已得到广泛研究。在乳腺癌（BrCa）中，PD-L1的表达被视为患者分层和预测抑制反应的决定性生物标志物。在临床上，使用治疗性抗体对肿瘤中PD-L1表达进行定量正电子发射断层扫描（PET）成像似乎是一种很有前景的方法，它可以补充传统的组织病理学方法，并克服一些问题，如肿瘤异质性、取样代表性以及阳性和阴性结果的明确区分。在本研究中，我们合成并评估了锆标记的阿维鲁单抗（Ave）用于体内表征BrCa中PD-L1的表达。采用BrCa细胞的共聚焦成像和流式细胞术来评估MDA-MB-231细胞中PD-L1的表达。将完整的靶向PD-L1的人单克隆抗体，即Ave，与对氨基硫脲去铁胺（Df）偶联并用锆标记。静脉注射锆-去铁胺-阿维鲁单抗（Zr-Df-Ave）后，对有或没有阻断的荷MDA-MB-231肿瘤小鼠进行PET成像。通过体外免疫荧光染色和流式细胞术证实了MDA-MB-231细胞中PD-L1的高表达。PET成像显示，注射后48小时，Zr-Df-Ave在肿瘤（6.4±1.0 %ID/g）、脾脏（10.2±0.7 %ID/g）和淋巴结（6.9±1.0 %ID/g）中的摄取达到峰值（n = 4）。使用未标记的Ave进行的阻断研究可以降低这些组织中的示踪剂摄取（48小时时肿瘤中为5.2±1.0 %ID/g，脾脏中为4.9±0.5 %ID/g，淋巴结中为5.8±1.1 %ID/g，n = 4），这证明了Zr-Df-Ave的特异性。生物分布研究和免疫荧光染色与PET成像的定量数据一致。在此，我们提供了证据，支持使用Zr-Df-Ave进行免疫PET成像对BrCa中PD-L1表达进行无创表征的价值，以及该示踪剂在BrCa中用于免疫治疗后治疗评估的适用性。
