Sadri Kayvan, Ren Qing, Zhang Kaijun, Paudyal Bishnuhari, Devadhas Devakumar, Rodeck Ulrich, Thakur Mathew
Department of Radiology, Thomas Jefferson University, Philadelphia, Pennysylvania 19107, USA.
Nucl Med Commun. 2011 Jul;32(7):563-9. doi: 10.1097/MNM.0b013e3283419523.
Cetuximab is a monoclonal antibody that binds to and inhibits the epidermal growth factor receptor (EGFR). EGFR overexpression has been observed in a subset of breast cancers. The purpose of this study was to evaluate 64Cu-labeled cetuximab as an imaging agent using MDA-MB-468 breast cancer cells.
Cetuximab was coupled with an N-sulfosuccinimide ester of DOTA, purified, and labeled with the positron-emitting nuclide, 64Cu. Receptor-binding specificity and affinity of 64Cu-DOTA-cetuximab were studied using human MDA-MB-468 breast cancer cells, which express high levels of EGFR. Micropositron emission tomography and biodistribution studies were performed in athymic nude mice bearing MDA-MB-468 cell xenografts. Blocking studies with cold cetuximab were also performed to determine the specific binding of cetuximab.
The radiochemical yield was 97.1 ± 1.1%. The specific activity was 1.5 Ci/μm cetuximab and the affinity to EGFR-positive MDA-MB-468 cells was high (KD=0.4 nmol/l). Both biodistribution and micropositron emission tomographic imaging studies with 64Cu-DOTA-cetuximab showed higher tumor uptake at 24 h (20.91 ± 2.49% ID/g, standardized uptake values of 9.6) than at 4 h (11.65 ± 3.89% ID/g, standardized uptake values of 4.9). Tumor uptake was significantly reduced from 20.91 ± 2.49% ID/g at 24 h to 14.42 ± 0.85% ID/g in a 1-h blocking study (P=0.00).
Cetuximab can be labeled with 64Cu without compromising its biological activity. The tumor uptake was excellent with high tumor/muscle (7.97 ± 1.78 at 4 h, 15.91 ± 6.04 at 24 h) and reasonable tumor/blood (0.5 ± 0.18 at 4 h, 2.12 ± 0.86 at 24 h) ratios. Blocking studies showed the specific binding of the labeled antibody to tumor tissue.
西妥昔单抗是一种可结合并抑制表皮生长因子受体（EGFR）的单克隆抗体。在部分乳腺癌中观察到EGFR过表达。本研究的目的是使用MDA-MB-468乳腺癌细胞评估64Cu标记的西妥昔单抗作为一种成像剂。
将西妥昔单抗与DOTA的N-琥珀酰亚胺磺酸酯偶联，纯化后用发射正电子的核素64Cu进行标记。使用高表达EGFR的人MDA-MB-468乳腺癌细胞研究64Cu-DOTA-西妥昔单抗的受体结合特异性和亲和力。对携带MDA-MB-468细胞异种移植瘤的无胸腺裸鼠进行微型正电子发射断层扫描和生物分布研究。还进行了冷西妥昔单抗阻断研究以确定西妥昔单抗的特异性结合。
放射化学产率为97.1±1.1%。比活度为1.5 Ci/μm西妥昔单抗，对EGFR阳性的MDA-MB-468细胞的亲和力较高（KD = 0.4 nmol/l）。64Cu-DOTA-西妥昔单抗的生物分布和微型正电子发射断层扫描成像研究均显示，24小时时肿瘤摄取量（20.91±2.49% ID/g，标准化摄取值为9.6）高于4小时时（11.65±3.89% ID/g，标准化摄取值为4.9）。在一项1小时阻断研究中，肿瘤摄取量从24小时时的20.91±2.49% ID/g显著降低至14.42±0.85% ID/g（P = 0.00）。
西妥昔单抗可用64Cu标记而不影响其生物活性。肿瘤摄取良好，肿瘤/肌肉比值高（4小时时为7.97±1.78，24小时时为15.91±6.04），肿瘤/血液比值合理（4小时时为0.5±0.18，24小时时为2.12±0.86）。阻断研究显示标记抗体与肿瘤组织的特异性结合。
