Sakurai Fuminori, Mizuguchi Hiroyuki
Department of Biochemistry and Molecular Biology, Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan.
Yakugaku Zasshi. 2010 Nov;130(11):1497-504. doi: 10.1248/yakushi.130.1497.
Target tissue-specific delivery and transcription of foreign genes are desirable for safe and effective gene therapy. Two approaches for this purpose, "Targeted Delivery" and "Targeted Expression", have been mainly reported. Among "Targeted Expression" approaches, microRNA (miRNA)-mediated "post-transcriptional de-targeting" has been recently demonstrated, and much attention has been focused on this approach. MiRNAs are an approximately 22-nt length non-coding RNA, and bind to imperfectly complementary sequences in the 3'-untranslated region (UTR) of target mRNA, leading to suppression of gene expression via post-transcriptional regulation. First, in order to reduce the hepatic transduction by Ad vectors, complementary sequences of liver-specific miRNA, miR-122a, were inserted into the 3'-UTR of the transgene expression cassette. Intratumor injection of this Ad vector resulted in approximately 100-fold lower hepatic expression than that of the conventional Ad vector, without reducing gene expression in the tumor. Second, complementary sequences for miRNAs selectively down-regulated in tumor cells were inserted into the E1 gene expression cassette in oncolytic Ads, which exhibit tumor cell-specific replication and antitumor effects. Recent studies demonstrated that expression of several miRNAs is exclusively reduced in tumor cells. Oncolytic Ads containing the miRNA complementary sequences showed reduced replication in the normal cells, without altering the antitumor effects. MiRNA-regulated gene expression system mediates "post-transcriptional de-targeting", in which translation of transgene is suppressed in a tissue-specific manner; however, tissue-specific transgene expression can be achieved by taking tropism of gene delivery vehicles into consideration and reducing the transgene expression in untargeted organs via miRNA-regulated gene expression system.
对于安全有效的基因治疗而言，外源基因的靶向组织特异性递送和转录是十分必要的。主要报道了两种用于此目的的方法，即“靶向递送”和“靶向表达”。在“靶向表达”方法中，最近已证明微小RNA（miRNA）介导的“转录后去靶向”，并且该方法已受到广泛关注。miRNA是一种长度约为22个核苷酸的非编码RNA，它与靶mRNA的3'-非翻译区（UTR）中不完全互补的序列结合，通过转录后调控导致基因表达受到抑制。首先，为了减少腺病毒（Ad）载体对肝脏的转导，将肝脏特异性miRNA miR-122a的互补序列插入到转基因表达盒的3'-UTR中。瘤内注射这种Ad载体导致肝脏表达比传统Ad载体低约100倍，而不会降低肿瘤中的基因表达。其次，将在肿瘤细胞中选择性下调的miRNA的互补序列插入到溶瘤性Ad的E1基因表达盒中，溶瘤性Ad具有肿瘤细胞特异性复制和抗肿瘤作用。最近的研究表明，几种miRNA的表达在肿瘤细胞中专门降低。含有miRNA互补序列的溶瘤性Ad在正常细胞中的复制减少，而不改变其抗肿瘤作用。miRNA调控的基因表达系统介导“转录后去靶向”，其中转基因的翻译以组织特异性方式受到抑制；然而，通过考虑基因递送载体的嗜性并通过miRNA调控的基因表达系统降低非靶向器官中的转基因表达，可以实现组织特异性转基因表达。
