Onda Nobuhiko, Kimura Masayuki, Yoshida Toshinori, Shibutani Makoto
R&D Group, Olympus Corporation, 2-3 Kuboyama-Cho, Hachioji, Tokyo, 192-8512, Japan.
Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-Cho, Fuchu, Tokyo, 183-8509, Japan.
Int J Cancer. 2016 Aug 1;139(3):673-82. doi: 10.1002/ijc.30102. Epub 2016 Apr 4.
Indocyanine green (ICG) is a fluorescent agent approved for clinical applications by the Food and Drug Administration and European Medicines Agency. This study examined the mechanism of tumor imaging using intravenously administered ICG. The in vivo kinetics of intravenously administered ICG were determined in tumor xenografts using microscopic approaches that enabled both spatio-temporal and high-magnification analyses. The mechanism of ICG-based tumor imaging was examined at the cellular level in six phenotypically different human colon cancer cell lines exhibiting different grades of epithelioid organization. ICG fluorescence imaging detected xenograft tumors, even those < 1 mm in size, based on their preferential cellular uptake and retention of the dye following its rapid tissue-non-specific delivery, in contrast to its rapid clearance by normal tissue. Live-cell imaging revealed that cellular ICG uptake is temperature-dependent and occurs after ICG binding to the cellular membrane, a pattern suggesting endocytic uptake as the mechanism. Cellular ICG uptake correlated inversely with the formation of tight junctions. Intracellular ICG was entrapped in the membrane traffic system, resulting in its slow turnover and prolonged retention by tumor cells. Our results suggest that tumor-specific imaging by ICG involves non-specific delivery of the dye to tissues followed by preferential tumor cellular uptake and retention. The tumor cell-preference of ICG is driven by passive tumor cell-targeting, the inherent ability of ICG to bind to cell membranes, and the high endocytic activity of tumor cells in association with the disruption of their tight junctions.
吲哚菁绿（ICG）是一种经美国食品药品监督管理局和欧洲药品管理局批准用于临床的荧光剂。本研究探讨了静脉注射ICG进行肿瘤成像的机制。采用能够进行时空和高倍分析的显微镜方法，在肿瘤异种移植模型中测定了静脉注射ICG的体内动力学。在六种表型不同、上皮样组织分级不同的人结肠癌细胞系中，在细胞水平上研究了基于ICG的肿瘤成像机制。ICG荧光成像能够检测到异种移植肿瘤，即使是那些大小小于1毫米的肿瘤，这是基于在染料快速进行非组织特异性递送后，肿瘤细胞对染料的优先摄取和保留，与之形成对比的是正常组织对染料的快速清除。活细胞成像显示，细胞摄取ICG是温度依赖性的，且发生在ICG与细胞膜结合之后，这种模式表明内吞摄取是其机制。细胞摄取ICG与紧密连接的形成呈负相关。细胞内的ICG被困在膜运输系统中，导致其周转缓慢并被肿瘤细胞长时间保留。我们的结果表明，ICG的肿瘤特异性成像涉及染料向组织的非特异性递送，随后肿瘤细胞优先摄取和保留。ICG对肿瘤细胞的偏好是由被动肿瘤细胞靶向、ICG与细胞膜结合的固有能力以及肿瘤细胞的高内吞活性与其紧密连接的破坏共同驱动的。
