Medical Imaging Laboratories, Robarts Research Institute, London, Ontario.
Department of Medical Sciences, University of Western Ontario, London, Ontario.
Invest Radiol. 2019 May;54(5):302-311. doi: 10.1097/RLI.0000000000000542.
OBJECTIVES: Multimodality reporter gene imaging provides valuable, noninvasive information on the fate of engineered cell populations. To complement magnetic resonance imaging (MRI) measures of tumor volume and 2-dimensional reporter-based optical measures of cell viability, reporter-based MRI may offer 3-dimensional information on the distribution of viable cancer cells in deep tissues. MATERIALS AND METHODS: Here, we engineered human and murine triple-negative breast cancer cells with lentivirus encoding tdTomato and firefly luciferase for fluorescence imaging and bioluminescence imaging (BLI). A subset of these cells was additionally engineered with lentivirus encoding organic anion transporting polypeptide 1a1 (Oatp1a1) for MRI. Oatp1a1 operates by transporting gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) into cells, and it concomitantly improves BLI substrate uptake. After orthotopic implantation of engineered cells expressing or not expressing Oatp1a1, longitudinal fluorescence imaging, BLI, and 3-Tesla MRI were performed. RESULTS: Oatp1a1-expressing tumors displayed significantly increased BLI signals relative to control tumors at all time points (P < 0.05). On MRI, post-Gd-EOB-DTPA T1-weighted images of Oatp1a1-expressing tumors exhibited significantly increased contrast-to-noise ratios compared with control tumors and precontrast images (P < 0.05). At endpoint, tumors expressing Oatp1a1 displayed intratumoral MR signal heterogeneity not present at earlier time points. Pixel-based analysis of matched in vivo MR and ex vivo fluorescence microscopy images revealed a strong, positive correlation between MR intensity and tdTomato intensity for Oatp1a1-expressing tumors (P < 0.05), but not control tumors. CONCLUSIONS: These results characterize Oatp1a1 as a sensitive, quantitative, positive contrast MRI reporter gene for 3-dimensional assessment of viable cancer cell intratumoral distribution and concomitant BLI enhancement. This multimodality reporter gene system can provide new insights into the influence of viable cancer cell intratumoral distribution on tumor progression and metastasis, as well as improved assessments of anticancer therapies.
目的：多模态报告基因成像为工程细胞群体的命运提供了有价值的、非侵入性的信息。为了补充磁共振成像（MRI）对肿瘤体积的测量和基于二维报告基因的细胞活力的光学测量，基于报告基因的 MRI 可能提供关于深层组织中存活癌细胞分布的三维信息。
材料与方法：在这里，我们通过慢病毒将 tdTomato 和萤火虫荧光素酶基因转染到人源和鼠源三阴性乳腺癌细胞中，用于荧光成像和生物发光成像（BLI）。这些细胞的一部分还通过慢病毒转染有机阴离子转运多肽 1a1（Oatp1a1）用于 MRI。Oatp1a1 通过将钆乙氧基苯甲基二乙三胺五乙酸（Gd-EOB-DTPA）转运到细胞内，同时提高 BLI 底物的摄取。在原位植入表达或不表达 Oatp1a1 的工程细胞后，进行纵向荧光成像、BLI 和 3T MRI 检查。
结果：Oatp1a1 表达的肿瘤在所有时间点的 BLI 信号均显著高于对照肿瘤（P < 0.05）。在 MRI 上，Oatp1a1 表达的肿瘤在 Gd-EOB-DTPA 后 T1 加权图像上的对比噪声比显著高于对照肿瘤和预对比图像（P < 0.05）。在终点时，表达 Oatp1a1 的肿瘤显示出肿瘤内 MR 信号异质性，而在早期时间点则没有这种情况。基于体内 MR 和离体荧光显微镜图像的像素分析显示，Oatp1a1 表达的肿瘤的 MR 强度与 tdTomato 强度之间存在强烈的正相关（P < 0.05），但对照肿瘤则没有。
结论：这些结果将 Oatp1a1 描述为一种敏感、定量、正性对比 MRI 报告基因，可用于三维评估存活癌细胞的肿瘤内分布和伴随的 BLI 增强。这种多模态报告基因系统可以为研究存活癌细胞肿瘤内分布对肿瘤进展和转移的影响以及改善抗癌治疗评估提供新的见解。
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