124I标记的工程化抗癌胚抗原微型抗体和双抗体可实现无胸腺小鼠体内异种移植瘤的高对比度、抗原特异性小动物正电子发射断层显像。
124I-labeled engineered anti-CEA minibodies and diabodies allow high-contrast, antigen-specific small-animal PET imaging of xenografts in athymic mice.
作者信息
Sundaresan Gobalakrishnan, Yazaki Paul J, Shively John E, Finn Ronald D, Larson Steven M, Raubitschek Andrew A, Williams Lawrence E, Chatziioannou Arion F, Gambhir Sanjiv S, Wu Anna M
机构信息
Crump Institute for Molecular Imaging, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at UCLA, Los Angeles, California 90095, USA.
出版信息
J Nucl Med. 2003 Dec;44(12):1962-9.
UNLABELLED
Prolonged clearance kinetics have hampered the development of intact antibodies as imaging agents, despite their ability to effectively deliver radionuclides to tumor targets in vivo. Genetically engineered antibody fragments display rapid, high-level tumor uptake coupled with rapid clearance from the circulation in the athymic mouse/LS174T xenograft model. The anticarcinoembryonic antigen (CEA) T84.66 minibody (single-chain Fv fragment [scFv]-C(H)3 dimer, 80 kDa) and T84.66 diabody (noncovalent dimer of scFv, 55 kDa) exhibit pharmacokinetics favorable for radioimmunoimaging. The present work evaluated the minibody or diabody labeled with (124)I, for imaging tumor-bearing mice using a high-resolution small-animal PET system.
METHODS
Labeling was conducted with 0.2-0.3 mg of protein and 65-98 MBq (1.7-2.6 mCi) of (124)I using an iodination reagent. Radiolabeling efficiencies ranged from 33% to 88%, and immunoreactivity was 42% (diabody) or >90% (minibody). In vivo distribution was evaluated in athymic mice bearing paired LS174T human colon carcinoma (CEA-positive) and C6 rat glioma (CEA-negative) xenografts. Mice were injected via the tail vein with 1.9-3.1 MBq (53-85 microCi) of (124)I-minibody or with 3.1 MBq (85 microCi) of (124)I-diabody and imaged at 4 and 18 h by PET. Some mice were also imaged using (18)F-FDG 2 d before imaging with (124)I-minibody.
RESULTS
PET images using (124)I-labeled minibody or diabody showed specific localization to the CEA-positive xenografts and relatively low activity elsewhere in the mice, particularly by 18 h. Target-to-background ratios for the LS174T tumors versus soft tissues using (124)I-minibody were 3.05 at 4 h and 11.03 at 18 h. Similar values were obtained for the (124)I-diabody (3.95 at 4 h and 10.93 at 18 h). These results were confirmed by direct counting of tissues after the final imaging. Marked reduction of normal tissue activity, especially in the abdominal region, resulted in high-contrast images at 18 h for the (124)I-anti-CEA diabody. CEA-positive tumors as small as 11 mg (<3 mm in diameter) could be imaged, and (124)I-anti-CEA minibodies, compared with (18)F-FDG, demonstrated highly specific localization.
CONCLUSION
(124)I labeling of engineered antibody fragments provides a promising new class of tumor-specific probes for PET imaging of tumors and metastases.
未标记
尽管完整抗体能够在体内有效地将放射性核素递送至肿瘤靶点，但其延长的清除动力学阻碍了其作为显像剂的发展。在无胸腺小鼠/LS174T异种移植模型中，基因工程抗体片段显示出快速、高水平的肿瘤摄取以及从循环中快速清除的特点。抗癌胚抗原（CEA）T84.66微型抗体（单链Fv片段[scFv]-C(H)3二聚体，80 kDa）和T84.66双体（scFv的非共价二聚体，55 kDa）表现出有利于放射免疫显像的药代动力学。本研究评估了用（124）I标记的微型抗体或双体，使用高分辨率小动物PET系统对荷瘤小鼠进行成像。
方法
使用碘化试剂，用0.2 - 0.3 mg蛋白质和65 - 98 MBq（1.7 - 2.6 mCi）的（124）I进行标记。放射性标记效率范围为33%至88%，免疫反应性为42%（双体）或>90%（微型抗体）。在携带成对的LS174T人结肠癌（CEA阳性）和C6大鼠胶质瘤（CEA阴性）异种移植瘤的无胸腺小鼠中评估体内分布。通过尾静脉给小鼠注射1.9 - 3.1 MBq（53 - 85 μCi）的（124）I - 微型抗体或3.1 MBq（85 μCi）的（124）I - 双体，并在4小时和18小时通过PET成像。一些小鼠在使用（124）I - 微型抗体成像前2天也使用（18）F - FDG进行成像。
结果
使用（124）I标记的微型抗体或双体的PET图像显示，在CEA阳性异种移植瘤处有特异性定位，而在小鼠其他部位的活性相对较低，尤其是在18小时时。使用（124）I - 微型抗体时，LS174T肿瘤与软组织的靶本底比值在4小时时为3.05，在18小时时为11.03。（124）I - 双体也获得了类似的值（4小时时为3.95，18小时时为10.93）。最终成像后对组织进行直接计数证实了这些结果。正常组织活性明显降低，尤其是在腹部区域，使得（124）I - 抗CEA双体在18小时时形成了高对比度图像。小至11 mg（直径<3 mm）的CEA阳性肿瘤可以成像，并且与（18）F - FDG相比，（124）I - 抗CEA微型抗体显示出高度特异性定位。
结论
工程化抗体片段的（124）I标记为肿瘤和转移灶的PET成像提供了一类有前景的新型肿瘤特异性探针。
Zotero 插件