Non-Invasive <em>In Vivo</em> Imaging of Tumor-Associated CD133/Prominin

BackgroundCancer stem cells are thought to play a pivotal role in tumor maintenance, metastasis, tumor therapy resistance and relapse. Hence, the development of methods for non-invasive in vivo detection of cancer stem cells is of great importance. Methodology/Principal FindingsHere, we describe successful in vivo detection of CD133/prominin, a cancer stem cell surface marker for a variety of tumor entities. The CD133-specific monoclonal antibody AC133.1 was used for quantitative fluorescence-based optical imaging of mouse xenograft models based on isogenic pairs of CD133 positive and negative cell lines. A first set consisted of wild-type U251 glioblastoma cells, which do not express CD133, and lentivirally transduced CD133-overexpressing U251 cells. A second set made use of HCT116 colon carcinoma cells, which uniformly express CD133 at levels comparable to primary glioblastoma stem cells, and a CD133-negative HCT116 derivative. Not surprisingly, visualization and quantification of CD133 in overexpressing U251 xenografts was successful; more importantly, however, significant differences were also found in matched HCT116 xenograft pairs, despite the lower CD133 expression levels. The binding of i.v.-injected AC133.1 antibodies to CD133 positive, but not negative, tumor cells isolated from xenografts was confirmed by flow cytometry. Conclusions/SignificanceTaken together, our results show that non-invasive antibody-based in vivo imaging of tumor-associated CD133 is feasible and that CD133 antibody-based tumor targeting is efficient. This should facilitate developing clinically applicable cancer stem cell imaging methods and CD133 antibody-based therapeutics.背景 肿瘤干细胞被认为在肿瘤维持、转移、治疗抵抗及复发过程中发挥关键作用。因此，开发用于非侵入性体内检测肿瘤干细胞的方法具有重要意义。 研究方法与主要结果 本研究成功实现了多种肿瘤实体的肿瘤干细胞表面标志物CD133/膜突蛋白（prominin）的体内检测。我们使用CD133特异性单克隆抗体AC133.1，对基于CD133阳性与阴性细胞系同基因配对的小鼠异种移植模型开展定量荧光光学成像。第一组模型为不表达CD133的野生型U251胶质母细胞瘤细胞，以及经慢病毒转染的过表达CD133的U251细胞；第二组模型则采用HCT116结肠癌细胞——该细胞系均匀表达CD133且其表达水平与原代胶质母细胞瘤干细胞相当，以及CD133阴性的HCT116衍生细胞系。不出所料，过表达CD133的U251异种移植瘤的CD133可视化与定量检测均获得成功；更重要的是，尽管CD133表达水平较低，配对的HCT116异种移植瘤组间仍存在显著差异。通过流式细胞术证实，静脉注射的AC133.1抗体可与从异种移植瘤中分离的CD133阳性肿瘤细胞结合，而无法结合CD133阴性肿瘤细胞。 结论与意义 综上，本研究结果表明，基于抗体的肿瘤相关CD133非侵入性体内成像是可行的，且基于CD133抗体的肿瘤靶向治疗具有高效性。该研究将有助于开发可应用于临床的肿瘤干细胞成像方法及基于CD133抗体的治疗手段。