Wiener E C, Konda S, Shadron A, Brechbiel M, Gansow O
Biomedical Magnetic Resonance Laboratory, College of Medicine, University of Illinois, Urbana-Champaign, USA.
Invest Radiol. 1997 Dec;32(12):748-54. doi: 10.1097/00004424-199712000-00005.
The authors developed a new method for delivering contrast agents to tumors and tumor cells. Gadolinium complexes of folate-conjugated dendrimer-chelates increased the longitudinal relaxation rate of tumor cells expressing the high-affinity folate receptor, hFR. The coupling of folate to polymeric chelates, composed of a dendrimer backbone, targets these chelates to endogenous folate binding proteins. These proteins exist in both the serum of patients with cancer and on the cell surface of many human cancers of epithelial origin.
The authors attached folic acid to a generation four ammonia core polyamidoamine dendrimer. The folate-dendrimer was reacted with 2-(4-isothiocyanatobenzyl)-6-methyl-diethylenetriaminepentaacetic acid to form the polymeric chelate f-PAMAM-TU-DTPA. For fluorescent studies, the generation four dendrimer was reacted with fluorescein-5-isothiocyanate and carboxytetramethylrhodamine succinimidyl ester, followed by capping the remaining amines with succinic anhydride.
The study results show that cells accumulate the folate-conjugated dendrimer in a receptor specific manner. Tumor cells expressing the high-affinity folate receptor showed a 650% increase in the mean fluorescence. This increase occurred with a rapid rise to 325%, followed by a slow increase to 650%. It required both the expression of the hFR and the coupling of folic acid to the dendrimer. Excess free folic acid inhibited the binding of the folate conjugated polymer. Fluorescent microscopic study showed that the folate-conjugated dendrimer binds to the cell surface and is accumulated within the cells. Treatment of tumor cells that express the hFR with gadolinium complexes of the folate-conjugated polymeric chelate increases the longitudinal relaxation rate by 110%. This increase was inhibited by an excess of free folic acid.
These data demonstrate that folate-conjugated magnetic resonance imaging contrast agents represent a promising new approach to tumor targeting.
作者开发了一种将造影剂递送至肿瘤和肿瘤细胞的新方法。叶酸共轭树枝状螯合物的钆配合物提高了表达高亲和力叶酸受体（hFR）的肿瘤细胞的纵向弛豫率。叶酸与由树枝状主链组成的聚合物螯合物的偶联，将这些螯合物靶向至内源性叶酸结合蛋白。这些蛋白存在于癌症患者的血清中以及许多上皮源性人类癌症的细胞表面。
作者将叶酸连接到第四代氨核聚酰胺胺树枝状大分子上。叶酸树枝状大分子与2-(4-异硫氰酸苄基)-6-甲基二乙三胺五乙酸反应，形成聚合物螯合物f-PAMAM-TU-DTPA。对于荧光研究，第四代树枝状大分子与异硫氰酸荧光素和羧基四甲基罗丹明琥珀酰亚胺酯反应，然后用琥珀酸酐封闭剩余的胺。
研究结果表明，细胞以受体特异性方式积累叶酸共轭树枝状大分子。表达高亲和力叶酸受体的肿瘤细胞平均荧光增加了650%。这种增加先是迅速上升至325%，随后缓慢上升至650%。这既需要hFR的表达又需要叶酸与树枝状大分子的偶联。过量的游离叶酸会抑制叶酸共轭聚合物的结合。荧光显微镜研究表明，叶酸共轭树枝状大分子与细胞表面结合并在细胞内积累。用叶酸共轭聚合物螯合物的钆配合物处理表达hFR的肿瘤细胞，纵向弛豫率提高了110%。这种增加被过量的游离叶酸抑制。
这些数据表明，叶酸共轭磁共振成像造影剂是一种有前景的肿瘤靶向新方法。
