Molecular Imaging Program, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA.
Bioconjug Chem. 2009 Nov;20(11):2177-84. doi: 10.1021/bc900362k.
Multimodality molecular imaging should have potential for compensating the disadvantages and enhancing the advantages of each modality. Nuclear imaging is superior to optical imaging in whole body imaging and in quantification due to good tissue penetration of gamma rays. However, target specificity can be compromised by high background signal due to the always signal ON feature of nuclear probes. In contrast, optical imaging can be superior in target-specific imaging by employing target-specific signal activation systems, although it is not quantitative because of signal attenuation. In this study, to take advantage of the mutual cooperation of each modality, multimodality imaging was performed by a combination of quantitative radiolabeled probe and an activatable optical probe. The monoclonal antibodies, panitumumab (anti-HER1) and trastuzumab (anti-HER2), were labeled with 111In and ICG and tested in both HER1 and HER2 tumor bearing mice by the cocktail injection of radiolabeled and optical probes and by the single injection of a dual-labeled probe. The optical and nuclear images were obtained over 6 days after the conjugates injection. The fluorescence activation properties of ICG labeled antibodies were also investigated by in vitro microscopy. In vitro microscopy demonstrated that there was no fluorescence signal with either panitumumab-ICG or trastuzumab-ICG, when the probes were bound to cell surface antigens but were not yet internalized. After the conjugates were internalized into the cells, both conjugates showed bright fluorescence signal only in the target cells. These results show that both conjugates work as activatable probes. In in vivo multimodality imaging by injection of a cocktail of radio-optical probes, only the target specific tumor was visualized by optical imaging. Meanwhile, the biodistribution profile of the injected antibody was provided by nuclear imaging. Similar results were obtained with radio and optical dual-labeled probes, and it is confirmed that pharmacokinetic properties did not affect the results above. Here, we could characterize the molecular targets by activatable optical probes and visualize the delivery of targeting molecules quantitatively by radioactive probes. Multimodality molecular imaging combining activatable optical and radioactive probes has great potential for simultaneous visualization, characterization, and measurement of biological processes.
多模态分子成像应该有潜力弥补每种模态的缺点并发挥其优势。由于伽马射线具有良好的组织穿透性，核成像在全身成像和定量方面优于光学成像。然而，由于核探针的信号始终开启的特点，靶特异性可能会因背景信号高而受到影响。相比之下，光学成像可以通过采用靶特异性信号激活系统在靶特异性成像中具有优势，尽管由于信号衰减它不是定量的。在这项研究中，为了利用每种模态的相互协作，通过定量放射性标记探针和可激活光学探针的组合进行了多模态成像。单克隆抗体帕尼单抗（抗 HER1）和曲妥珠单抗（抗 HER2）用 111In 和 ICG 标记，并通过放射性和光学探针的鸡尾酒注射以及双标记探针的单次注射，在 HER1 和 HER2 肿瘤荷瘤小鼠中进行了测试。在注射缀合物后 6 天获得了光学和核图像。还通过体外显微镜研究了 ICG 标记抗体的荧光激活特性。体外显微镜研究表明，当探针与细胞表面抗原结合但尚未内化时，panitumumab-ICG 或 trastuzumab-ICG 既没有荧光信号。缀合物内化到细胞中后，两种缀合物仅在靶细胞中显示出明亮的荧光信号。这些结果表明，两种缀合物都可以作为可激活的探针。在通过注射放射性-光学探针混合物进行的体内多模态成像中，仅通过光学成像可视化靶特异性肿瘤。同时，通过核成像提供了注射抗体的生物分布概况。使用放射性和光学双标记探针获得了类似的结果，并证实药代动力学特性不会影响上述结果。在这里，我们可以通过可激活的光学探针对分子靶标进行特征描述，并通过放射性探针对靶向分子的递送进行定量可视化。结合可激活光学和放射性探针的多模态分子成像具有同时可视化、特征描述和测量生物过程的巨大潜力。
