Department of Radiology and Biomedical Imaging, Center for Molecular and Functional Imaging, University of California at San Francisco, San Francisco, California 94143, USA.
J Nucl Med. 2010 Mar;51(3):427-32. doi: 10.2967/jnumed.109.069492. Epub 2010 Feb 11.
Human antibodies targeting prostate cancer cell surface epitopes may be useful for imaging and therapy. The objective of this study was to evaluate the tumor targeting of an internalizing human antibody fragment, a small-size platform, to provide high contrast in a mouse model of human prostate carcinoma.
A prostate tumor-targeting single-chain antibody fragment (scFv), UA20, along with a nonbinding control scFv, N3M2, were labeled with (99m)Tc and evaluated for binding and rapid internalization into human prostate tumor cells in vitro and tumor homing in vivo using xenograft models. For the in vitro studies, the labeled UA20 scFv was incubated at 37 degrees C for 1 h with metastatic prostate cancer cells (DU145) to assess the total cellular uptake versus intracellular uptake. For the animal studies, labeled UA20 and N3M2 scFvs were administered to athymic mice implanted subcutaneously with DU145 cells. Mice were imaged with small-animal SPECT/CT with concomitant biodistribution at 1 and 3 h after injection.
The UA20 scFv was labeled in 55%-65% yield and remained stable in phosphate buffer within 24 h. The labeled UA20 scFv was taken up specifically by prostate tumor cells. Internalization was rapid, because incubation at 37 degrees C for less than 1 h resulted in 93% internalization of total cell-associated scFvs. In animal studies, SPECT/CT showed significant tumor uptake as early as 1 h after injection. At 3 h after injection, tumor uptake was 4.4 percentage injected dose per gram (%ID/g), significantly greater than all organs or tissues studied (liver, 2.7 %ID/g; other organs or tissues, <1 %ID/g), except the kidneys (81.4 %ID/g), giving tumor-to-blood and tumor-to-muscle ratios of 12:1 and 70:1, respectively. In contrast, the control antibody exhibited a tumor uptake of only 0.26 %ID/g, similar to that of muscle and fat. Tumor-specific targeting was evidenced by reduced tumor uptake of nearly 70% on administration of a 10-fold excess of unlabeled UA20 scFv. Kidney uptake was nonspecific, consistent with the route of excretion by scFvs.
The UA20 scFv showed rapid and specific internalization in prostate tumor cells in vitro and accumulation in prostate tumor xenografts in vivo, demonstrating the potential for future development for prostate cancer imaging and targeted therapy.
针对前列腺癌细胞表面表位的人源抗体可能对成像和治疗有用。本研究的目的是评估一种内化人抗体片段的肿瘤靶向性，该片段是一种小尺寸平台，可在人前列腺癌的小鼠模型中提供高对比度。
用（99m）Tc 标记一种前列腺肿瘤靶向的单链抗体片段（scFv）UA20 和一种非结合对照 scFv N3M2，并在体外评估其与转移性前列腺癌细胞（DU145）的结合和快速内化，以及在异种移植模型中体内肿瘤归巢。对于体外研究，将标记的 UA20 scFv 在 37°C 下孵育 1 小时，以评估总细胞摄取与细胞内摄取。对于动物研究，将标记的 UA20 和 N3M2 scFvs 给予皮下植入 DU145 细胞的无胸腺小鼠。注射后 1 和 3 小时，用小动物 SPECT/CT 进行成像，并同时进行生物分布。
UA20 scFv 的标记产率为 55%-65%，在磷酸盐缓冲液中 24 小时内保持稳定。标记的 UA20 scFv 被前列腺肿瘤细胞特异性摄取。内化迅速，因为在 37°C 孵育不到 1 小时，导致总细胞相关 scFvs 的内化率达到 93%。在动物研究中，SPECT/CT 在注射后 1 小时即可显示出明显的肿瘤摄取。在注射后 3 小时，肿瘤摄取率为 4.4% 注入剂量/克（%ID/g），明显高于所有研究的器官或组织（肝脏，2.7%ID/g；其他器官或组织，<1%ID/g），除了肾脏（81.4%ID/g），分别产生肿瘤-血液和肿瘤-肌肉比为 12:1 和 70:1。相比之下，对照抗体的肿瘤摄取率仅为 0.26%ID/g，与肌肉和脂肪相似。在给予 10 倍过量未标记的 UA20 scFv 后，肿瘤摄取减少近 70%，证明了该 scFv 用于前列腺癌成像和靶向治疗的潜力。
UA20 scFv 在体外前列腺肿瘤细胞中表现出快速和特异性内化，在体内前列腺肿瘤异种移植中积累，为前列腺癌成像和靶向治疗的未来发展提供了潜力。
