Nucleic acid aptamers, often termed “chemical antibodies”, are functionally comparable to traditional antibodies, but offer several advantages including their relatively small physical size, flexible structure, quick chemical production, versatile chemical modification, high stability, and lack of immunogenicity. In addition, many aptamers internalize upon binding to cellular receptors making them useful targeted delivery agents for siRNAs, microRNAs and conventional drugs. However,Ge several crucial factors, such as their inherent physicochemical characteristics and lack of safety data, have delayed the clinical translation of therapeutic aptamers. This review discusses these challenges, highlighting recent clinical developments and technological advances that have revived impetus for this promising class of therapeutics.

The discovery that gene expression can be controlled by the Watson–Crick base-pairing of small RNAs with messenger RNAs containing complementary sequence — a process known as RNA interference — has markedly advanced our understanding of eukaryotic gene regulation and function. The ability of short RNA sequences to modulate gene expression has provided a powerful tool with which to study gene function and is set to revolutionize the treatment of disease. Remarkably, despite being just one decade from its discovery, the phenomenon is already being used therapeutically in human clinical trials, and biotechnology companies that focus on RNA-interference-based therapeutics are already publicly traded.

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Key features of diabetic nephropathy (DN) include the accumulation of extracellular matrix proteins such as collagen 1-␣ 1 and -2 (Col1a1 and -2). Transforming growth factor ␤1 (TGF-␤), a key regulator of these extracellular matrix genes, is increased in mesangial cells (MC) in DN. By microarray profiling, we noted that TGF-␤ increased Col1a2 mRNA in mouse MC (MMC) but also decreased mRNA levels of an E-box repressor, ␦EF1. TGF-␤ treatment or short hairpin RNAs targeting ␦EF1 increased enhancer activity of upstream E-box elements in the Col1a2 gene. TGF-␤ also decreased the expression of Smad-interacting protein 1 (SIP1), another E-box repressor similar to ␦EF1. Interestingly, we noted that SIP1 is a target of microRNA-192 (miR-192), a key miR highly expressed in the kidney. miR-192 levels also were increased by TGF-␤ in MMC. TGF-␤ treatment or transfection with miR-192 decreased endogenous SIP1 expression as well as reporter activity of a SIP1 3 UTR-containing luciferase construct in MMC. Conversely, a miR-192 inhibitor enhanced the luciferase activity, confirming SIP1 to be a miR-192 target. Furthermore, miR-192 synergized with ␦EF1 short hairpin RNAs to increase Col1a2 E-box-luc activity. Importantly, the in vivo relevance was noted by the observation that miR-192 levels were enhanced significantly in glomeruli isolated from streptozotocin-injected diabetic mice as well as diabetic db/db mice relative to corresponding nondiabetic controls, in parallel with increased TGF-␤ and Col1a2 levels. These results uncover a role for miRs in the kidney and DN in controlling TGF-␤-induced Col1a2 expression by down-regulating E-box repressors.diabetic nephropathy ͉ mesangial cells ͉ small noncoding RNA ͉ transforming growth factor ␤1 D iabetic nephropathy (DN) is the most common cause of kidney failure in patients with diabetes mellitus. The major characteristics of DN include glomerular basement-membrane thickening, mesangial expansion and hypertrophy, and an accumulation of extracellular matrix (ECM) proteins (1). Evidence shows that transforming growth factor ␤1 (TGF-␤) levels are increased under diabetic conditions in renal cells, including mesangial cells (MC), can up-regulate ECM proteins such as collagens (2, 3), and also can promote MC survival and oxidant stress (4).To date, Smad transcription factors have been shown to be the major effectors of TGF-␤ signaling (5, 6). Collagen 1-␣ 1 and -2 (Col1a1 and -2) and other ECM genes are regulated in MC by TGF-␤ via Smads (7,8). The regulation of collagen by TGF-␤ in MC also is mediated by mitogen-activated protein kinases (MAPKs) such as p38 and ERKs (9-11). However, the molecular mechanisms by which TGF-␤ regulates ECM genes still are not understood fully. The collagen gene has E-box elements in the far upstream enhancer region (12, 13). An E-box repressor, ␦EF1, is a key inhibitor of E-cadherin (14) and E2-box transcription factors such as Nkx2.5 (12). Moreover, it is a known repressor of collagen type 1 and type 2 genes in other cells (12, 13), but its role in MC is ...

The discovery of RNA interference (RNAi) may well be one of the transforming events in biology in the past decade. RNAi can result in gene silencing or even in the expulsion of sequences from the genome. Harnessed as an experimental tool, RNAi has revolutionized approaches to decoding gene function. It also has the potential to be exploited therapeutically, and clinical trials to test this possibility are already being planned.

Since the first description of RNA interference (RNAi) in animals less than a decade ago, there has been rapid progress towards its use as a therapeutic modality against human diseases. Advances in our understanding of the mechanisms of RNAi and studies of RNAi in vivo indicate that RNAi-based therapies might soon provide a powerful new arsenal against pathogens and diseases for which treatment options are currently limited. Recent findings have highlighted both promise and challenges in using RNAi for therapeutic applications. Design and delivery strategies for RNAi effector molecules must be carefully considered to address safety concerns and to ensure effective, successful treatment of human diseases.

RNA interference (RNAi) is the process of sequence-specific post-transcriptional gene silencing triggered by double-stranded RNAs. In attempts to identify RNAi triggers that effectively function at lower concentrations, we found that synthetic RNA duplexes 25-30 nucleotides in length can be up to 100-fold more potent than corresponding conventional 21-mer small interfering RNAs (siRNAs). Some sites that are refractory to silencing by 21-mer siRNAs can be effectively targeted by 27-mer duplexes, with silencing lasting up to 10 d. Notably, the 27-mers do not induce interferon or activate protein kinase R (PKR). The enhanced potency of the longer duplexes is attributed to the fact that they are substrates of the Dicer endonuclease, directly linking the production of siRNAs to incorporation in the RNA-induced silencing complex. These results provide an alternative strategy for eliciting RNAi-mediated target cleavage using low concentrations of synthetic RNA as substrates for cellular Dicer-mediated cleavage.

RNA interference (RNAi) was discovered less than a decade ago and already there are human clinical trials in progress or planned. A major advantage of RNAi versus other anti-sense based approaches for therapeutic applications is that it utilizes cellular machinery that efficiently allows targeting of complementary transcripts, often resulting in highly potent down-regulation of gene expression. Despite the excitement about this remarkable biological process for sequence specific gene regulation, there are a number of hurdles and concerns that must be overcome prior to making RNAi a real therapeutic modality, which include off-target effects, triggering of type I interferon responses, and effective delivery in vivo. This review discusses mechanistic aspects of RNAi, the potential problem areas and solutions and therapeutic applications. It is anticipated that RNAi will be a major therapeutic modality within the next several years, and clearly warrants intense investigation to fully understand the mechanisms involved.