Dicer-substrate siRNA inhibits tumor necrosis factor alpha secretion in Kupffer cells in vitro: in vivo targeting of Kupffer cells by siRNA-liposomes

Design, mechanism, delivery and therapeutics of canonical and Dicer-substrate siRNA

Upon the discovery of RNA interference (RNAi), canonical small interfering RNA (siRNA) has been recognized to trigger sequence-specific gene silencing. Despite the benefits of siRNAs as potential new drugs, there are obstacles still to be overcome, including off-target effects and immune stimulation. More recently, Dicer substrate siRNA (DsiRNA) has been introduced as an alternative to siRNA. Similarly, it also is proving to be potent and target-specific, while rendering less immune stimulation. DsiRNA is 25–30 nucleotides in length, and is further cleaved and processed by the Dicer enzyme. As with siRNA, it is crucial to design and develop a stable, safe, and efficient system for the delivery of DsiRNA into the cytoplasm of targeted cells. Several polymeric nanoparticle systems have been well established to load DsiRNA for in vitro and in vivo delivery, thereby overcoming a major hurdle in the therapeutic uses of DsiRNA. The present review focuses on a comparison of siRNA and DsiRNA on the basis of their design, mechanism, in vitro and in vivo delivery, and therapeutics.

Therapeutic approaches for the delivery of TNF-α siRNA

Immune-mediated diseases are emerging as a major healthcare concern in the present era. TNF-α, a proinflammatory cytokine, plays a major role in the manifestation of these diseases by mediating different pathways and inducing the expression of other cytokines. In last decades, monoclonal antibodies and extracellular portion of human TNF-α receptors are explored in this area; however, the risk of immunological response and undesired effects urge a need to develop more effective therapies to control TNF-α levels. siRNA therapeutic strategies are emerging for the treatment of myriad of diseases, but the delivery challenges associated with siRNA require the development of suitable delivery vectors. For delivery of TNF-α siRNA, both viral and nonviral vectors are explored. This review attempts to describe different delivery approaches for TNF-α siRNA with special focus on nonviral delivery vectors.

Functional inhibition of chemokine receptor CCR2 by dicer-substrate-siRNA prevents pain development

BACKGROUND

Accumulating evidence suggests that the C-C chemokine ligand 2 (CCL2, or monocyte chemoattractant protein 1) acts as a neuromodulator in the central nervous system through its binding to the C-C chemokine receptor 2 (CCR2). Notably, it is well established that the CCL2/CCR2 axis plays a key role in neuron-glia communication as well as in spinal nociceptive transmission. Gene silencing through RNA interference has recently emerged as a promising avenue in research and drug development, including therapeutic management of chronic pain. In the present study, we used 27-mer Dicer-substrate small interfering RNA (DsiRNA) targeting CCR2 and assessed their ability to reverse the nociceptive behaviors induced by spinal CCL2 injection or following intraplantar injection of complete Freund's adjuvant.

RESULTS

To this end, we first developed high-potency DsiRNAs designed to target different sequences distributed across the rat CCR2 (rCCR2) messenger RNA. For optimization, methyl groups were added to the two most potent DsiRNA candidates (Evader and M7 2'-O-methyl modified duplexes) in order to improve in vivo duplex stability and to reduce potential immunostimulatory activity. Our results demonstrated that all modified candidates formulated with the cell-penetrating peptide reagent Transductin showed strong RNAi activity following intrathecal delivery, exhibiting >50% rCCR2 knockdown in lumbar dorsal root ganglia. Accordingly, we found that these DsiRNA duplexes were able to reduce spinal microglia activation and were effective at blocking CCL2-induced mechanical hypersensitivity. Along with similar reductions of rCCR2 messenger RNA, both sequences and methylation patterns were similarly effective in inhibiting the CCL2 nociceptive action for the whole seven days testing period, compared to mismatch DsiRNA. DsiRNAs against CCR2 also reversed the hypernociceptive responses observed in the complete Freund's adjuvant-induced inflammatory chronic pain model.

CONCLUSION

Altogether, these results validate CCR2 as a an appropriate molecular target for pain control and demonstrate that RNAi-based gene therapy represent an highly specific alternative to classical pharmacological approaches to treat central pathologies such as chronic pain.

Evaluation of canonical siRNA and Dicer substrate RNA for inhibition of hepatitis C virus genome replication--a comparative study

Hepatitis C virus (HCV) frequently establishes persistent infections in the liver, leading to the development of chronic hepatitis and, potentially, to liver cirrhosis and hepatocellular carcinoma at later stages. The objective of this study was to test the ability of five Dicer substrate siRNAs (DsiRNA) to inhibit HCV replication and to compare these molecules to canonical 21 nt siRNA. DsiRNA molecules were designed to target five distinct regions of the HCV genome - the 5' UTR and the coding regions for NS3, NS4B, NS5A or NS5B. These molecules were transfected into Huh7.5 cells that stably harboured an HCV subgenomic replicon expressing a firefly luciferase/neoR reporter (SGR-Feo-JFH-1) and were also tested on HCVcc-infected cells. All of the DsiRNAs inhibited HCV replication in both the subgenomic system and HCVcc-infected cells. When DsiRNAs were transfected prior to infection with HCVcc, the inhibition levels reached 99.5%. When directly compared, canonical siRNA and DsiRNA exhibited similar potency of virus inhibition. Furthermore, both types of molecules exhibited similar dynamics of inhibition and frequencies of resistant mutants after 21 days of treatment. Thus, DsiRNA molecules are as potent as 21 nt siRNAs for the inhibition of HCV replication and may provide future approaches for HCV therapy if the emergence of resistant mutants can be addressed.

Voltage-gated Ca2+ influx and mitochondrial Ca2+ initiate secretion from Aplysia neuroendocrine cells

Neuroendocrine secretion often requires prolonged voltage-gated Ca(2+) entry; however, the ability of Ca(2+) from intracellular stores, such as endoplasmic reticulum or mitochondria, to elicit secretion is less clear. We examined this using the bag cell neurons, which trigger ovulation in Aplysia by releasing egg-laying hormone (ELH) peptide. Secretion from cultured bag cell neurons was observed as an increase in plasma membrane capacitance following Ca(2+) influx evoked by a 5-Hz, 1-min train of depolarizing steps under voltage-clamp. The response was similar for step durations of ≥ 50 ms, but fell off sharply with shorter stimuli. The capacitance change was attenuated by replacing external Ca(2+) with Ba(2+), blocking Ca(2+) channels, buffering intracellular Ca(2+) with EGTA, disrupting synaptic protein recycling, or genetic knock-down of ELH. Regarding intracellular stores, liberating mitochondrial Ca(2+) with the protonophore, carbonyl cyanide-p-trifluoromethoxyphenyl-hydrazone (FCCP), brought about an EGTA-sensitive elevation of capacitance. Conversely, no change was observed to Ca(2+) released from the endoplasmic reticulum or acidic stores. Prior exposure to FCCP lessened the train-induced capacitance increase, suggesting overlap in the pool of releasable vesicles. Employing GTP-γ-S to interfere with endocytosis delayed recovery (presumed membrane retrieval) of the capacitance change following FCCP, but not the train. Finally, secretion was correlated with reproductive behavior, in that neurons isolated from animals engaged in egg-laying presented a greater train-induced capacitance elevation vs quiescent animals. The bag cell neuron capacitance increase is consistent with peptide secretion requiring high Ca(2+), either from influx or stores, and may reflect the all-or-none nature of reproduction.