Li S, Deshmukh H M, Huang L
Department of Pharmacology, University of Pittsburgh School of Medicine, Pennsylvania 15261, USA.
Pharm Res. 1998 Oct;15(10):1540-5. doi: 10.1023/a:1011946915209.
Receptors for vitamin folic acid are frequently overexpressed on epithelial cancer cells, especially ovarian cancer cells. In this study, we examined whether this expression might be exploited to specifically deliver antisense oligodeoxynucleotides (ODN) to tumor cells.
A conjugate was prepared by directly coupling folic acid to the 3' terminus of an anti-c-fos ODN and its cellular uptake and tumor inhibitory effect were evaluated using FD2008 cells that overexpress folate receptors.
When a phosphorothioate (PS)/phosphodiester (PO) chimeric ODN was conjugated with folic acid, its uptake by FD2008 cells was increased by about 8-fold (P < 0.01). In contrast, conjugation of folate to the ODN did not increase its uptake by CHO cells that lack the expression of FBP (P > 0.05). Furthermore, the increase in the uptake of conjugated ODN by FD2008 cells could be blocked by adding an excess amount of folic acid. The PS/PO antisense ODN had some inhibitory effect on the growth of FD2008 cells. However, its activity was significantly increased following conjugation with folic acid (P < 0.01). ODN of scrambled sequences with and without conjugation with folic acid failed to inhibit the growth of FD2008 cells. Finally, the antisense effect of the conjugated ODN on FD2008 cells was inhibited by an excess amount of free folic acid, suggesting that the sequence-dependent effect of folate-antisense ODN conjugate was mediated by folate binding protein.
Direct derivatization of ODN with folate significantly improves their targeting efficiency to tumor cells in vitro. The folate-conjugated ODN, due to their small size and possibly efficient extravasation at tumor site, has the potential for treating solid tumors that overexpress folate receptors.
维生素叶酸受体在上皮癌细胞尤其是卵巢癌细胞上常常过度表达。在本研究中，我们检测了这种表达是否可用于将反义寡脱氧核苷酸（ODN）特异性递送至肿瘤细胞。
通过将叶酸直接偶联至抗c-fos ODN的3'末端制备一种偶联物，并使用过表达叶酸受体的FD2008细胞评估其细胞摄取和肿瘤抑制作用。
当硫代磷酸酯（PS）/磷酸二酯（PO）嵌合ODN与叶酸偶联时，FD2008细胞对其摄取增加约8倍（P < 0.01）。相反，叶酸与ODN的偶联并未增加缺乏FBP表达的CHO细胞对其的摄取（P > 0.05）。此外，添加过量叶酸可阻断FD2008细胞对偶联ODN摄取的增加。PS/PO反义ODN对FD2008细胞的生长有一定抑制作用。然而，与叶酸偶联后其活性显著增强（P < 0.01）。有或无叶酸偶联的随机序列ODN均未能抑制FD2008细胞的生长。最后，过量游离叶酸抑制了偶联ODN对FD2008细胞的反义作用，表明叶酸-反义ODN偶联物的序列依赖性作用是由叶酸结合蛋白介导的。
ODN与叶酸的直接衍生化显著提高了其在体外对肿瘤细胞的靶向效率。叶酸偶联的ODN由于其体积小且可能在肿瘤部位有效渗出，具有治疗过度表达叶酸受体的实体瘤的潜力。
