Radiochemistry Service, Department of Radiology, Memorial Sloan-Kettering Cancer Center, Sloan-Kettering Cancer Center, New York, New York, United States of America.
PLoS One. 2010 Jan 25;5(1):e8859. doi: 10.1371/journal.pone.0008859.
The positron-emitting radionuclide (89)Zr (t(1/2) = 3.17 days) was used to prepare (89)Zr-radiolabeled trastuzumab for use as a radiotracer for characterizing HER2/neu-positive breast tumors. In addition, pharmacodynamic studies on HER2/neu expression levels in response to therapeutic doses of PU-H71 (a specific inhibitor of heat-shock protein 90 [Hsp90]) were conducted.
METHODOLOGY/PRINCIPAL FINDINGS: Trastuzumab was functionalized with desferrioxamine B (DFO) and radiolabeled with [(89)Zr]Zr-oxalate at room temperature using modified literature methods. ImmunoPET and biodistribution experiments in female, athymic nu/nu mice bearing sub-cutaneous BT-474 (HER2/neu positive) and/or MDA-MB-468 (HER2/neu negative) tumor xenografts were conducted. The change in (89)Zr-DFO-trastuzumab tissue uptake in response to high- and low-specific-activity formulations and co-administration of PU-H71 was evaluated by biodistribution studies, Western blot analysis and immunoPET. (89)Zr-DFO-trastuzumab radiolabeling proceeded in high radiochemical yield and specific-activity 104.3+/-2.1 MBq/mg (2.82+/-0.05 mCi/mg of mAb). In vitro assays demonstrated >99% radiochemical purity with an immunoreactive fraction of 0.87+/-0.07. In vivo biodistribution experiments revealed high specific BT-474 uptake after 24, 48 and 72 h (64.68+/-13.06%ID/g; 71.71+/-10.35%ID/g and 85.18+/-11.10%ID/g, respectively) with retention of activity for over 120 h. Pre-treatment with PU-H71 was followed by biodistribution studies and immunoPET of (89)Zr-DFO-trastuzumab. Expression levels of HER2/neu were modulated during the first 24 and 48 h post-administration (29.75+/-4.43%ID/g and 41.42+/-3.64%ID/g, respectively). By 72 h radiotracer uptake (73.64+/-12.17%ID/g) and Western blot analysis demonstrated that HER2/neu expression recovered to baseline levels.
CONCLUSIONS/SIGNIFICANCE: The results indicate that (89)Zr-DFO-trastuzumab provides quantitative and highly-specific delineation of HER2/neu positive tumors, and has potential to be used to measure the efficacy of long-term treatment with Hsp90 inhibitors, like PU-H71, which display extended pharmacodynamic profiles.
正电子发射放射性核素（89）Zr（t(1/2) = 3.17 天）被用于制备（89）Zr 放射性标记曲妥珠单抗，用作 HER2/neu 阳性乳腺癌肿瘤的示踪剂。此外，还进行了针对 HER2/neu 表达水平的药效学研究，以响应治疗剂量的 PU-H71（热休克蛋白 90 [Hsp90] 的特异性抑制剂）。
方法/主要发现：使用改良的文献方法，在室温下用去铁胺 B（DFO）对曲妥珠单抗进行功能化，并使用[（89）Zr]Zr-草酸盐进行放射性标记。在皮下接种 BT-474（HER2/neu 阳性）和/或 MDA-MB-468（HER2/neu 阴性）肿瘤异种移植的雌性无胸腺 nu/nu 小鼠中进行免疫 PET 和生物分布实验。通过生物分布研究、Western blot 分析和免疫 PET 评估高和低特异性活性制剂以及 PU-H71 联合给药后（89）Zr-DFO-曲妥珠单抗组织摄取的变化。（89）Zr-DFO-曲妥珠单抗的放射性标记以高放射化学产率和特定活性 104.3+/-2.1 MBq/mg（2.82+/-0.05 mCi/mg 的 mAb）进行。体外测定显示>99%的放射化学纯度，免疫反应部分为 0.87+/-0.07。体内生物分布实验显示，在 24、48 和 72 小时后，BT-474 的摄取具有高度特异性（64.68+/-13.06%ID/g；71.71+/-10.35%ID/g 和 85.18+/-11.10%ID/g，分别），活性保留时间超过 120 小时。在进行 PU-H71 预处理后，进行（89）Zr-DFO-曲妥珠单抗的生物分布研究和免疫 PET。在给药后 24 和 48 小时内，HER2/neu 的表达水平发生了变化（分别为 29.75+/-4.43%ID/g 和 41.42+/-3.64%ID/g）。到 72 小时，放射性示踪剂摄取（73.64+/-12.17%ID/g）和 Western blot 分析表明，HER2/neu 的表达恢复到基线水平。
结论/意义：结果表明，（89）Zr-DFO-曲妥珠单抗提供了 HER2/neu 阳性肿瘤的定量和高度特异性描绘，并且有可能用于测量 HSP90 抑制剂（如 PU-H71）长期治疗的疗效，其药效学特征具有延长的作用时间。
