Radiology & Nuclear Medicine, Cancer Center Amsterdam, Amsterdam UMC, Vrije Universiteit Amsterdam, De Boelelaan, 1117, Amsterdam, The Netherlands.
Genentech Inc., 1 DNA Way, South San Francisco, CA, 94080, USA.
Eur J Nucl Med Mol Imaging. 2021 Mar;48(3):694-707. doi: 10.1007/s00259-020-05002-7. Epub 2020 Sep 5.
Almost all radiolabellings of antibodies with Zr currently employ the hexadentate chelator desferrioxamine (DFO). However, DFO can lead to unwanted uptake of Zr in bones due to instability of the resulting metal complex. DFO*-NCS and the squaramide ester of DFO, DFOSq, are novel analogues that gave more stable Zr complexes than DFO in pilot experiments. Here, we directly compare these linker-chelator systems to identify optimal immuno-PET reagents.
Cetuximab, trastuzumab and B12 (non-binding control antibody) were labelled with Zr via DFO*-NCS, DFOSq, DFO-NCS or DFOSq. Stability in vitro was compared at 37 °C in serum (7 days), in formulation solution (24 h ± chelator challenges) and in vivo with N87 and A431 tumour-bearing mice. Finally, to demonstrate the practical benefit of more stable complexation for the accurate detection of bone metastases, [Zr]Zr-DFO-NCS and [Zr]Zr-DFO-NCS-labelled trastuzumab and B12 were evaluated in a bone metastasis mouse model where BT-474 breast cancer cells were injected intratibially.
[Zr]Zr-DFO*-NCS-trastuzumab and [Zr]Zr-DFOSq-trastuzumab showed excellent stability in vitro, superior to their [Zr]Zr-DFO counterparts under all conditions. While tumour uptake was similar for all conjugates, bone uptake was lower for DFO conjugates. Lower bone uptake for DFO* conjugates was confirmed using a second xenograft model: A431 combined with cetuximab. Finally, in the intratibial BT-474 bone metastasis model, the DFO* conjugates provided superior detection of tumour-specific signal over the DFO conjugates.
DFO*-mAb conjugates provide lower bone uptake than their DFO analogues; thus, DFO* is a superior candidate for preclinical and clinical Zr-immuno-PET.
目前，几乎所有使用 Zr 对抗体进行放射性标记的研究都采用了六齿螯合剂去铁胺（DFO）。然而，由于所形成的金属络合物不稳定，DFO 会导致 Zr 不必要地在骨骼中摄取。DFO*-NCS 和 DFO 的 squaramide 酯，DFOSq，是新型的类似物，在初步实验中，它们比 DFO 产生更稳定的 Zr 络合物。在这里，我们直接比较这些连接子-螯合剂系统，以确定最佳的免疫 PET 试剂。
通过 DFO*-NCS、DFOSq、DFO-NCS 或 DFOSq 将西妥昔单抗、曲妥珠单抗和 B12（非结合对照抗体）与 Zr 标记。在 37°C 下，在血清中（7 天）、制剂溶液中（24 小时±螯合剂挑战）以及 N87 和 A431 荷瘤小鼠体内比较稳定性。最后，为了证明更稳定的络合对于准确检测骨转移的实际益处，我们在 BT-474 乳腺癌细胞经胫骨内注射的骨转移小鼠模型中评估了 [Zr]Zr-DFO-NCS 和 [Zr]Zr-DFO-NCS 标记的曲妥珠单抗和 B12。
[Zr]Zr-DFO*-NCS-曲妥珠单抗和 [Zr]Zr-DFOSq-曲妥珠单抗在体外表现出极好的稳定性，在所有条件下均优于其 [Zr]Zr-DFO 对应物。虽然所有缀合物的肿瘤摄取相似，但 DFO缀合物的骨摄取较低。在另一个 A431 联合西妥昔单抗的异种移植模型中，确认了 DFO缀合物的较低的骨摄取。最后，在 BT-474 胫骨内骨转移模型中，DFO缀合物提供了优于 DFO 缀合物的肿瘤特异性信号检测。
DFO*-mAb 缀合物的骨摄取低于其 DFO 类似物；因此，DFO*是临床前和临床 Zr-免疫 PET 的理想候选物。
