Chakravarty Rubel, Goel Shreya, Valdovinos Hector F, Hernandez Reinier, Hong Hao, Nickles Robert J, Cai Weibo
Department of Radiology, University of Wisconsin-Madison , Madison, Wisconsin 53792, United States.
Bioconjug Chem. 2014 Dec 17;25(12):2197-204. doi: 10.1021/bc500415x. Epub 2014 Nov 24.
Scandium-44 (t1/2 = 3.9 h) is a relatively new radioisotope of potential interest for use in clinical positron emission tomography (PET). Herein, we report, for the first time, the room-temperature radiolabeling of proteins with (44)Sc for in vivo PET imaging. For this purpose, the Fab fragment of Cetuximab, a monoclonal antibody that binds with high affinity to epidermal growth factor receptor (EGFR), was generated and conjugated with N-[(R)-2-amino-3-(para-isothiocyanato-phenyl)propyl]-trans-(S,S)-cyclohexane-1,2-diamine-N,N,N',N″,N″-pentaacetic acid (CHX-A″-DTPA). The high purity of Cetuximab-Fab was confirmed by SDS-PAGE and mass spectrometry. The potential of the bioconjugate for PET imaging of EGFR expression in human glioblastoma (U87MG) tumor-bearing mice was investigated after (44)Sc labeling. PET imaging revealed rapid tumor uptake (maximum uptake of ∼12% ID/g at 4 h postinjection) of (44)Sc-CHX-A″-DTPA-Cetuximab-Fab with excellent tumor-to-background ratio, which might allow for same day PET imaging in future clinical studies. Immunofluorescence staining was conducted to correlate tracer uptake in the tumor and normal tissues with EGFR expression. This successful strategy for immunoPET imaging of EGFR expression using (44)Sc-CHX-A″-DTPA-Cetuximab-Fab can make clinically translatable advances to select the right population of patients for EGFR-targeted therapy and also to monitor the therapeutic efficacy of anti-EGFR treatments.
钪 - 44（半衰期 = 3.9小时）是一种相对较新的放射性同位素，在临床正电子发射断层扫描（PET）中具有潜在应用价值。在此，我们首次报道了在室温下用（44）Sc对蛋白质进行放射性标记用于体内PET成像。为此，制备了与表皮生长因子受体（EGFR）具有高亲和力的单克隆抗体西妥昔单抗的Fab片段，并将其与N - [（R）-2 - 氨基 - 3 - （对 - 异硫氰酸苯酯）丙基] - 反式 - （S，S） - 环己烷 - 1,2 - 二胺 - N，N，N'，N″，N″ - 五乙酸（CHX - A″ - DTPA）偶联。通过SDS - PAGE和质谱法确认了西妥昔单抗 - Fab的高纯度。在（44）Sc标记后，研究了该生物偶联物用于人胶质母细胞瘤（U87MG）荷瘤小鼠中EGFR表达PET成像的潜力。PET成像显示（44）Sc - CHX - A″ - DTPA - 西妥昔单抗 - Fab在肿瘤中快速摄取（注射后4小时最大摄取量约为12％ID/g），肿瘤与背景比值优异，这可能使未来临床研究中同一天进行PET成像成为可能。进行免疫荧光染色以将肿瘤和正常组织中的示踪剂摄取与EGFR表达相关联。使用（44）Sc - CHX - A″ - DTPA - 西妥昔单抗 - Fab对EGFR表达进行免疫PET成像的这一成功策略可为选择合适的EGFR靶向治疗患者群体以及监测抗EGFR治疗的疗效带来临床上可转化的进展。
