H<sub>6</sub>phospa-trastuzumab: bifunctional methylenephosphonate-based chelator with<sup>89</sup>Zr,<sup>111</sup>In and<sup>177</sup>Lu
作者:Eric W. Price、Brian M. Zeglis、Jason S. Lewis、Michael J. Adam、Chris Orvig
DOI:10.1039/c3dt51940f
日期:——
The acyclic chelator H6phospa and the bifunctional derivative p-SCN–Bn–H6phospa have been synthesized using nosyl protection chemistry and evaluated with 89Zr, 111In, and 177Lu. The p-SCN–Bn–H6phospa derivative was successfully conjugated to trastuzumab with isotopic dilution assays indicating 3.3 ± 0.1 chelates per antibody and in vitro cellular binding assays indicating an immunoreactivity value of 97.9 ± 2.6%. Radiolabeling of the H6phospa-trastuzumab immunoconjugate was achieved with 111In in 70–90% yields at room temperature in 30 minutes, while 177Lu under the same conditions produced more inconsistent yields of 40–80%. Stability experiments in human serum revealed the 111In-phospa-trastuzumab complex to be 52.0 ± 5.3% intact after 5 days at 37 °C, while the 177Lu-phospa-trastuzumab to be only 2.0 ± 0.3% intact. Small animal SPECT/CT imaging using mice bearing subcutaneous SKOV-3 ovarian cancer xenografts was performed, and it was found that 111In-phospa-trastuzumab successfully identified and delineated small (∼2 mm in diameter) tumors from surrounding tissues, despite visible uptake in the kidneys and bone due to moderate chelate instability. As predicted from stability assays in serum, the 177Lu-phospa-trastuzumab conjugate served as a negative control and displayed no tumor uptake, with high uptake in bones indicating rapid and complete radiometal dissociation and suggesting a potential application of H6phospa in transient lanthanide chelation for bone-delivery. Radiolabeling with 89Zr was attempted, but even with elevated temperatures of 37 °C, the maximum observed radiometal incorporation over 18 hours was 12%. It can be concluded from this work that H6phospa is not superior to the previously studied H4octapa for use with 111In and 177Lu, but improvements in 89Zr radiolabeling were observed over H4octapa, suggesting H6phospa to be an excellent starting point for elaboration of 89Zr-based radiopharmaceutical development. To our knowledge, H6phospa is the best desferrioxamine alternative for 89Zr radiolabeling to be studied to date.
合成了非环状螯合剂H6phospa及其双功能衍生物p-SCN–Bn–H6phospa,采用了nosyl保护化学,并对89Zr、111In和177Lu进行了评估。p-SCN–Bn–H6phospa衍生物成功与曲妥珠单抗结合,放射性稀释实验表明每个抗体含有3.3 ± 0.1个螯合物,体外细胞结合实验显示其免疫反应值为97.9 ± 2.6%。H6phospa-曲妥珠单抗免疫偶联物在室温下以70–90%的产率,用111In进行放射性标记,仅需30分钟,而在相同条件下,使用177Lu的产率则不够稳定,范围为40–80%。在人血清中的稳定性实验显示,111In-phospa-曲妥珠单抗复合物在37°C下经过5天后仍保持52.0 ± 5.3%的完整性,而177Lu-phospa-曲妥珠单抗的完整性仅为2.0 ± 0.3%。使用携带皮下SKOV-3卵巢癌异种移植的老鼠进行了小动物SPECT/CT成像,发现111In-phospa-曲妥珠单抗成功识别并勾勒出周围组织中的小肿瘤(约2毫米直径),尽管由于中等的螯合剂不稳定性,肾脏和骨骼出现了明显的摄取。根据血清中的稳定性实验预测,177Lu-phospa-曲妥珠单抗作为阴性对照,没有显示肿瘤摄取,而在骨骼中的高摄取则表明放射性金属迅速完全解离,建议H6phospa可能在短暂的锕类金属螯合用于骨输送方面有潜在应用。进行了89Zr的放射性标记尝试,但即使在37°C的高温下,观察到的最大放射性金属结合率在18小时内也仅为12%。可以从这项研究得出的结论是,H6phospa在与111In和177Lu的应用方面并不优于之前研究的H4octapa,但在89Zr放射性标记方面相比H4octapa有改进,表明H6phospa是89Zr基放射药物开发的优秀起点。根据我们所知,H6phospa是迄今为止针对89Zr放射性标记研究的最佳去铁胺替代物。