RNAi-based functional pharmacogenomics

Cell-Penetrating Peptides Delivering siRNAs: An Overview

Cell-Penetrating Peptides (CPP) are valuable tools capable of crossing the plasma membrane to deliver therapeutic cargo inside cells. Small interfering RNAs (siRNA) are double-stranded RNA molecules capable of silencing the expression of a specific protein triggering the RNA interference (RNAi) pathway, but they are unable to cross the plasma membrane and have a short half-life in the bloodstream. In this overview, we assessed the many different approaches used and developed in the last two decades to deliver siRNA through the plasma membrane through different CPPs sorted according to three different loading strategies: covalent conjugation, complex formation, and CPP-decorated (functionalized) nanocomplexes. Each of these strategies has pros and cons, but it appears the latter two are the most commonly reported and emerging as the most promising strategies due to their simplicity of synthesis, use, and versatility. Recent progress with siRNA delivered by CPPs seems to focus on targeted delivery to reduce side effects and amount of drugs used, and it appears to be among the most promising use for CPPs in future clinical applications.

Update on the clinical utility of an RNA interference-based treatment: focus on Patisiran

RNA interference (RNAi) is a naturally existing endogenous mechanism for post-transcriptional gene regulation, nowadays commonly utilized for functional characterization of genes and development of potential treatment strategies for diseases. RNAi-based studies for therapy, after being examined for over a decade, are finally in the pipeline for developing a potential treatment for the mutated transthyretin (TTR) gene, which gives rise to a dysfunctional TTR protein. This dysfunctional protein causes TTR amyloidosis (ATTR), an inherited, progressively incapacitating, and often fatal genetic disorder. TTR is a protein produced in the liver, and functions as a carrier for retinol-binding protein and also thyroxine. This protein facilitates the transport of vitamin A around the human body. A mutation or misprint in the code of this protein results in an abnormal folding of the protein. Therefore, not only does the transportation of the vitamin A become disabled, but also there will be formation of clusters called amyloid deposits, which attack the heart and the nerves causing some patients to be unconditionally bound to bed. ATTR is a hereditary autosomal dominant disease with a 50% chance of inheritance by offspring, even with just one of the parents having a single defective allele of this gene. Alnylam Pharmaceuticals worked on the concept of RNAi therapy for years, which led to the introduction of lipid nanoparticles encircling small interfering RNAs. The drug showed extremely positive results since the first trial, and a great percentage of defective protein reduction. This drug was later named Patisiran.

Generation of stable 3'-mRNA cleavage fragments induced by siRNA in cells with high-levels of duck hepatitis B virus replication

Therapeutic small interfering RNAs (siRNAs) have attracted a lot of interest both in basic biomedical sciences as well as in translational medicine. Apart from their therapeutic efficacy adverse effects of siRNAs must be addressed. The generation of stable mRNA cleavage fragments and the translation of N-truncated proteins induced by antisense oligodeoxynucleotides (ASOs) have been reported. Similar to ASOs, siRNAs are considered to function via an antisense mechanism that promotes the cleavage of the target mRNA. To further investigate whether the stable mRNA cleavage fragments also occur in siRNA we constructed a short hairpin RNA (shRNA) expression plasmid, pshRNA794, containing the same sequence reported in experiments using ASOs which directly targeted the overlapping region of the pre-genomic mRNA (pgmRNA) and sub-genomic mRNA (sgmRNA) of duck hepatitis B virus (DHBV). The shRNA resulted in a 70.9% and 69.9% reduction of the DHBV mRNAs in LMH and HuH-7 cells, respectively. In addition a 70% inhibition of the DHBV DNA level was observed. Interestingly, 3'-mRNA cleavage fragments were detected in LMH but not in HuH-7 cells. Taken together, our findings demonstrate that the ASO sequence was also effective in siRNA. Importantly, our results provide direct evidence that stable 3'-mRNA fragments were generated by siRNA in cells with high levels of DHBV replication. Whether these can cause adverse RNAi effects needs to be explored further.