PubMed trend for published papers on siRNA
Gene therapy is a hot topic in both genetics and pharmacology. It involves exploiting genetic pathways to treat disease by replacing a mutated gene, integrating a new gene, knocking a gene out, or silencing a gene. "This allows for an entirely new platform of drug targets outside of traditional small molecule targets such as enzymes and receptors. Among the most prominent of these methods is gene silencing, a field in research and medicine that has started to come into its own and show results clinically. The method I will be discussing here - gene silencing via the use of small interfering RNA (siRNA) - requires small pieces of RNA that complement the mRNA transcript of the targeted gene in order to disable or "silence" expression of the gene.
Figure 1: "Gene Silencing by Design" Chemical and Engeering News, November 18, 2013 https://cen.acs.org/articles/91/i46/Gene-Silencing-Design.html
siRNAs
are administered as double-stranded RNAs, and then cleaved by endonucleases
into single-stranded RNAs (Fig. 1). One of these strands is simply a
"passenger" strand that is released and plays no further role. The
other strand is the siRNA itself, a fragment of 21-25 nucleotides engineered to
be complimentary to the messenger RNA (mRNA) of the targeted gene (Gavrilov
& Saltzman, 2012). The siRNA interacts with key proteins such as DICER (an
RNA-cleaving endoribonuclease) and Ago-2 (an RNA-binding protein which can
mediate RNA degradation) to form a complex called the RNA-Induced Silencing
Complex (RISC). When the siRNA, as part of the RISC complex, binds the target
mRNA, the mRNA is cleaved. The cleaved mRNA is thus incomplete and
non-functional, and will not be translated into protein (Lam, Chow, Zhang,
& Leung, 2015). The transcription of the gene, therefore, does not serve
its biological purpose and is functionally "silenced".
Figure 2. The growth of siRNA-based therapeutics: Updated clinical studies" Biochemical Pharmacology, July 2021 (https://www.sciencedirect.com/science/article/abs/pii/S0006295221000289?via%3Dihub)
The
clinical applications of siRNA-based treatments are extensive. As of July of
2021, there are three siRNA-based drugs which have been approved by FDA with several
being tested in clinical trials (Fig. 2). The first to be approved was
Patisiran, an siRNA drug approved to treat transthyretin-mediated amyloidosis
(hATTR). hATTR is caused by mutations in the gene coding for the transthyretin
protein, which causes amyloid deposition in the central nervous system (CNS),
heart, kidneys, and GI tract, leading to severe neuropathy, heart disease, and
ulimately death. The siRNA drug disrupts expression of this protein, and
significantly alleviates symptoms. The second siRNA drug approved for clinical
use by the FDA was Givosiran. Givosiran is used as a treatment for acute
hepatic porphyria (AHP), which causes accumulation of neurotoxic metabolites,
leading to symptoms such as seizures, muscle weakness, tachycardia, and
paralysis. Givosiran disrupts expression of the ALAS1 gene, reducing
AHP-related "attacks" by 74% in clinical trials. Finally, the most
recent FDA-approved drug was Lumasiran, which hit the market in November of
2020. Lumasiran is used to treat primary hyperoxaluria type 1 (PH1), a disease
associated with hepatic enzyme deficiency and toxic metabolite accumulation.
The primary symptom of the disease is excessive calcium oxalate forming kidney
stones, leading to severe damage of the renal system and potential death due to
systemic accumulation of oxalate. Lumasiran targets the gene transcript
associated with a protein which synthesizes the precursor to oxalate, providing
a 53-65% reduction in oxalate levels. Several drugs are currently being tested
in clinical trials for their potential to treat a variety of diseases,
including other hepatic diseases, familial hypercholesterolemia, hemophilia,
kidney disease, glaucoma, and others (Zhang, Bahal, Rasmussen, Manautou, &
Zhong, 2021).
Figure 3. RNA Therapy: Current Status and Future Potential" Chonnam Medical Journal, May 2020
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7250668/
Clearly,
siRNA therapeutics are a promising avenue in pharmacological research which
have begun to realize their potential after gaining the interest of the
biomedical research community in the late 1990's/early 2000's (Fig. 3). The
results are impressive, and even more so is the fact that many of these
treatments exhibit effects lasting months following a single treatment, due to
the ability of the RISC to protect siRNAs from degradation (Kim, 2020). The
merits of siRNA drugs are beginning to yield great advancements in gene
therapy, and the number of siRNA- based products on the market is expected to
grow significantly in the next decade. Clinical use of siRNA therapeutics is
still in its infancy, but its role in the future of medicine is sure to be
prominent.
By
Henry Snider, A Master’s of Medical Science Student at the University of
Kentucky
References
Borman, S. (2013). Gene Silencing by Design. Chemical & Engineering News, 91(46).
Gavrilov, K., & Saltzman, W. M. (2012). Therapeutic siRNA: principles, challenges, and strategies. Yale J Biol Med, 85(2), 187-200.
Kim, Y. K. (2020). RNA Therapy: Current Status and Future Potential. Chonnam Med J, 56(2), 87-93. doi:10.4068/cmj.2020.56.2.87
Lam, J. K., Chow, M. Y., Zhang, Y., & Leung, S. W. (2015). siRNA Versus miRNA as Therapeutics for Gene Silencing. Mol Ther Nucleic Acids, 4, e252. doi:10.1038/mtna.2015.23
Zhang, M. M., Bahal, R., Rasmussen, T. P., Manautou, J. E., & Zhong, X. B. (2021). The growth of siRNA-based therapeutics: Updated clinical studies. Biochem Pharmacol, 189, 114432. doi:10.1016/j.bcp.2021.114432
This was a very interesting topic and very important to target many of health issues we face in today's society. One thing I was curious about are the negative effects that can come with siRNA gene therapy. One of the hurdles some drugs face when working with siRNA is the lack of specificity which can cause them to target sequences known as off-target sequences leading to a sequence of effects like silencing of genes that were not meant to be targeting. Other things that seemed to happen is sometimes siRNAS or their delivery system stimulate an innate immune response causing for an inflammatory signal which can produce unwanted toxicities that can be harmful to a patient. But of course almost all medicines do have negative side effects!
ReplyDeleteThe delivery system is actually a burning topic in the siRNA field of research. There are a lot of researchers working on better delivery systems to not only increase efficacy and specificity, but also reduce immune response as you mentioned.
DeleteVery intriguing! I know very little about genetics myself, so I definitely learned something new from your blog. The examples you provided in your last paragraph sound very promising, especially for people who are suffering from symptoms of poorly understood/treatable diseases who do not benefit much from other existing medications. Also, I was so captivated by the positive results that I didn't think about the possible negative side effects until I read Sarah's comment. I know that earlier in our class we were discussing nanoparticle medicine. Perhaps lipid nanoparticles could serve as a potential vehicle for these siRNA therapies?
ReplyDeleteThis is so fascinating! I don't know a lot about genetics other than siRNAs are being used to knockout certain genes in animal models for in vivo experiments. I thought you brought up a lot of interesting topics and possibilities for treatment. I was especially interested in Givosiran, the drug used to possibly prevent seizures and muscle weakness due to AHP. This siRNA targets an enzyme critical for making heme. I am wondering about the side effects for this; how could you only focus this to the liver as opposed to heme all over the body? It is given by subcutaneous intravenous injection, so it does pass through the live first (it's site of action). While this is FDA approved, I have to wonder about the side effects of such a drug. I do agree with Madison's comment that maybe lipid nanoparticles could be a better vehicle for the drug? Overall, I would like to see more research being done on this, maybe for more neuropathic diseases.
ReplyDeleteI think that this is a very interesting topic, as it is such a new technique for treatment. I definitely agree with Sarah's comment, as there could be issues with the delivery system as other genes could be silenced that should not be. Also, since this is a therapeutic involved in editing the genome, an ethical concern is also bound to be involved in the discussions surrounding this therapeutic target. Have there been any further studies regarding the long-term efficacy or maybe adverse side-effects of using siRNA as a therapeutic? I feel like that could be a very big topic of research and concern regarding therapies involving siRNA.
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ReplyDeleteAwesome post, I was unaware of this particular mode of gene therapy and enjoyed learning about it. You mentioned the drug Lumisarian produces a 33-65% reduction in its target which leads me to believe this therapy can produce less drastic phenotype changes and be potentially less dangerous than complete gene knockouts like CRISPR or TALEN. I could see this as a potential benefit to "knockdown" a gene at the mRNA level vs a complete knockout of a gene at the level of DNA. I am interested to see if they discover any implements that could be used to ensure binding with more certain complementarity to the target sequence. Since this therapy acts on the mRNA level, I can assume that experiments using siRNA might be a bit less complex/work intensive than other gene therapies acting on DNA since all you need to know is the complementary mRNA sequence. Similar to the concerns Sarah mentioned; I wonder if high amounts of exogenous siRNA would have potential to displace endogenous miRNAs from the RISC and result in adverse effects.
ReplyDeleteThis is a very timely topic especially since researchers have been trying to come up with an effective way to treat diseases with not as many adverse side effects. As Noah said before this may be a great alternative to CRISPR or TALEN which could be less dangerous since your not doing a total gene knockout. However, I feel that this would still be quite an expensive therapy. I wonder if this will end up being a therapy accessible to all classes or will be so expensive that only upper class people could afford it.
ReplyDeleteI think siRNAs are a novel answer to the question of how do we stop production in cells when the blueprints are wrong. The technology seems to work best when there is an identifiable unique marker of disease that can be targeted. As other have mentioned, off target effects seem to be the biggest concern, as turning off a dysfunctional gene may be beneficial in one system, but devastating in another system. Additionally, in regards to Madison's comment, Patisiran is already administered in an LNP formulation, though this makes it more likely to non-specifically enter cells rather than be more targeted, due to the lipophilicity of the compound created
ReplyDeletesiRNA’s seem to be a promising option for future medicine. It is something that seems like it could be a fix for many terminal diseases. This science however, like we have discussed, is a very dangerous science that needs to be safeguarded. I would love to see all the avenues siRNA can take in treating illness.
ReplyDeleteI thought this topic was super interesting. As many diseases come from genetic abnormalities, this therapy has so many potential applications. However, because this therapy involves altering gene expression, it sound like it would be really complicated to regulate. How do we make sure we don't silence the wrong genes? This is also in agreement with other people's comments that the delivery system would be a big hurdle to overcome.
ReplyDeleteThis was a very captivating blog to read especially since there are many conditions that are gene based. I think gene therapy is a growing market with a lot of potential. However, I do agree with Sarah's comment that delivery could be an issue along with off-target effects resulting in complications for developing and getting the therapy approved. This led me to wonder how does one determine who is eligible for gene therapy and do the benefits outweigh the cost?
ReplyDeleteThis is a really interesting topic. I think there is a lot of things we'll be able to do in the future with genetic therapy using these new techniques. Given the high number of diseases that come from genetic abnormalities, this could prove to be a good investment of research resources to find more applicable therapeutics in the future.
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