Often described as the next frontier in gene therapy, siRNA has moved from the realm of the quirky biological oddity to applied therapy very quickly. I have asked the Tox1401 students to describe what they see as potential toxicological problems with this approach.
We used this paper as a description of the possible delivery approaches. The paper is freely (and fully) available from pubmed central.
Read on through the comments to see what they came up with.
Gillespie Lab 
siRNA is a controversal and new study that is being researched all around the world currently. It is a hot topic and can lead to amazing clincal discoveries such as curing genetic diseases, some viral diseases,and possibly even HIV. siRNA is bascailly a type of RNA that can silence gene expression and even re-arrange chromatin. siRNa can also interfere in the RNA pathway which will stop the production of certain RNA. If we could completely control siRNA and what it effects it would be one of the biggest break throughs in toxicology history. A major issue with the new type of therapy is that it effects untargeted areas. The way it works is that the siRNA binds to its complementary strain and turns off the gene, but it also attches to other genes that are healthy and they should not be disabled. This is called off-targeting and can cause serious side effects, serious enought to the point where it makes no sense to administer it to patients. One example of it failing was when Dr. Novina who worked for the Center for Cancer Research in Massachusetts tried to use the drug to cure HIV-1.The study ended with proving that HIV-1 cannot currently be treated by siRNA, but there are still hopes for other virus’s Dr. Novina thinks. It will just take more time to produce the right siRNA and to avoid off targeting. siRNA can be a revolutionary medical treatment in the future but more research needs to be done before it is released for human usage. But the therapy has the potential to cure genetic diseases such as Hugintons disease. Which is autosomal Dominate and a terrible chronic disease, even the chance to cure diseases such as Hugintons should be researched. Hopefully in time we can control the off targeting effect and be able to use siRNA therapy.
What would happen if a siRNA were to silence a gene it wasn’t intended to? I just wonder what would happen if the siRNA were to turn off the gene for eye color or something like that. That would never happen because eye color is controlled by so many genes, but what really is controlled by only one gene these days? Do siRNAs have the possibility of turning off more than one gene? Just wondering.
The siRNA seem to replace a similar segment of our own DNA acting recessive to a fine tuned “dominant” in a way that region is becoming (3n) momentarily until a transformation (friendly way of saying mutation) can change enough of the sequence for differentiation now what is normally expressed is sitting at the sidelines and i do not know if there is the previous recessive “next” to this sequence or if that was the actual target to modify and use and intron segment to make it more evolutionarily favorable and luckily the body sees the better “hardware” and swaps them out ….. The closest thing to a thought i can put on this is that we are dumping our own cells with a “desired” sequence back into a recombination like tumbler and hoping for the best of the following three: the change is so intense it is seen as a drastic mutation and to fix the body undergoes mass repair and a resulting immune response can be severe, the change is so miniscule that the body just sees this as some form of minute point mutation and eventually will go about fixing it as our body is designed to, or the (hopefully targeted) area will start using this sequence as exon as described above [kinda]. With the second opstion here i would like to just add that i believe thats where the true dosing issue lies in a way we are making these mutations occur and our body is designed to find fix and prevent these, maybe we need to find a way of shutting those “defenses off” without horrendously increasing our changes of cancer.
—Some of this is from ideas presented from work done by the Centre for Genome-based Therapeutics with much of my irrational thoughts sprinkled in between whilst i read them
siRNA are used for what is called gene therapy, the use of DNA (or RNA) as a pharmaceutical agent to treat disease. The genetic material is used to replace a mutated gene. siRNA is used to turn off and silence mutated genes. This method seems promising, but it brings up many toxicological implications, mainly the safety of using this method. Through my research, I have found that experiments have shown that siRNA can have negative effects on the body, namely toxicity of the liver. In the Nature International Weekly Journal of Science, a paper was published that was conducted by Mark A. Kay and his associates at Stanford University titled Fatality in mice due to oversaturation of cellular microRNA/short hairpin RNA pathways. Kay’s team found that within a few weeks of injecting experimental RNAi therapy for hepatitis B virus into mice, most animals began to die of liver toxicity. What was surprising was not that the RNAi was toxic, because that was always a possibility, it was that the dose of the RNAi was the source of toxicity. The source of the toxicity doesn’t seem to be the RNA sequence or the virus, but rather the amount injected into the mice. The original promoter sequence used for driving production of shRNA created large amounts of RNA that overwhelmed the RNAi system, but wwitching to a promoter that made fewer RNA molecules reduced toxicity dramatically. John Rossi, Chairman and Professor of the Division of Molecular Biology at the City of Hope’s Beckman Research Institute in Duarte, California had similar findings. He found that high levels of shRNAs are toxic in tissue culture cells. Irvin Chen, Professor of Microbiology, Immunology & Molecular Genetics at the University of California, Los Angeles, has also found toxicity with an shRNA for HIV therapy. These results do not mean that siRNA cannot be used for gene therapy, but rather that careful tests must be done to find the right balance between potency and toxicity for each siRNA being tested, as different RNAi’s can have different levels of toxicity at different saturations.
siRNA therapy is currently being researched as a major breakthrough in clinical gene therapies. siRNA interferes with specific genes. This may be used to turn off overactive genes within the human body or turn off genes from foreign invaders in the body to cure disease. However, there are many toxicological obstacles that must be overcome before siRNA is used in clinical therapy settings. One major issue is that siRNAs may affect genes other than their target gene. These are off-target effects. This can cause detrimental effects if important genes in the human body are accidentally silenced by siRNAs. Another potential problem comes from the delivery systems being tested for siRNA delivery. Many delivery systems that were originally deemed safe, such as lipophilic siRNA conjugates, have been shown to be unsafe either because the delivery system itself silences off-target genes or even cancels out the effects of the siRNA by upregulating the target gene. One major potential potential problem is the accumulation of siRNAs in the liver and kidneys. There has been shown to be significant amounts of hepatotoxicity related to systemic siRNA injection. This, however, has promising solutions, firstly because the hepatotoxicity only arises at a certain dose (in the Zimmermann et. al. studies, 2 mg siRNA/kg is considered to be a dangerous dose for the liver), and because scientists can synthesize an siRNA delivery system that is large enough to escape filtration by the liver and kidneys and will therefore not accumulate in these organs.
This is really interesting how this does-response relationship turns out. The problem I find after reading about administering siRNA to the kidney is that although they have found a way for it not to accumulate in these target organs with potent half-life makes it tricky in determining the proper amounts required for its proper expression. I like your response especially how you emphasize the problematic factor of targeting a gene.
The SiRNA, also known as the small interfering RNA is a prized technology that has been used in the silencing of sequence-specific genes. Many scientists have been evaluating the therapeutic effects of SiRNA’s in clinical trial. It is currently being researched as a potential therapy for certain genetic diseases. Many trials have been conducted on animals such as lab rats. However, more recently, trials have been conducted on humans. The first ever clinical trial to be conducted occurred in the year 2004, where patients suffering from Age-related Macular Degeneration (AMD). Clinical trials with SiRNA have also been conducted to treat cancer and respiratory diseases. In order to have effective gene silencing by the SiRNA, there are several challenges which need to be overcome in order to for it to prove worthy. First and foremost the SiRNA has to be designed in such a way that it targets the proper genes so that it does not target the wrong gene causing many deleterious effects to the body. Another important factor is the biological stability of the SiRNA. SiRNA that are not genetically modified cannot reside in the blood and serum. There, due to their short half lives, they will be degraded. Several routes used for systemically delivering the SiRNA include intravitreal, intrathecal, and intravaginal. One advantage of systemic delivery is that it is more applicable to clinical treatment. Scientists are still investigating whether the SiRNA can be delivered orally. However, speculations have been made regarding that the SiRNA would degrade much faster orally and there would be poor bioavailability in the GI tract. The use of SiRNA in genetics is quickly being spread as an efficient gene-silencing strategy. There is still a lot to be learned about these SiRNA and their effects on human genetics.
Good description of siRNAs problems with bioavailability, but aren’t there ways to package siRNA so that it is more bioavailable and less likely to be degraded? Is there a dose of siRNA that is unsafe for the human body?
The siRNA is undergoing extensive research due to its brilliant resilience in the use of science and advancement. This approach is a revolutionary stepping-stone. Although it has many beneficial facets siRNA has also posed new questions and complicated toxicological problems. As the major targeted organs systemically siRNA is administered to the kidney to moderate interest of the therapeutics of siRNA delivery. Research conducted by the Department of Toxicology, Leiden Amsterdam Center for Drug Research, Leiden Unversity in the Netherlands which specifically published work in regard to the Application of siRNA in targeting protein expression in kidney disease. The recent approaches to target renal protein expression under normal and pathological conditions is just an example of application of siRNA using a specific delivery system. In this case a cationic delivery system was applied to enhance immune stimulation of siRNA. More recently, gene expression array analyses have highlighted the ability of delivery systems to induce a “gene signature” of their own that could increase the off-target effects of siRNA (Stokman et al.) It is detrimental to understand that inappropriate selection of a delivery vector can reduce gene-silencing activity and even enhance off-target effects. Delivery systems can also alter the pharmacokinetics of siRNA by altering their molecular and physical size so as to reduce excretion via the kidneys and thus, prolong in vivo half-life. Primarily, it is the off-target effects of siRNA that has been exponentially been brought to the spot light by scientists since as a factor that seems to curtail the use of siRNA clinically. Off-target effects include induction of an inflammatory response thus, activating anti-angiogenetic responses or down regulation of non-target proteins inducing an immune response. Although research has proven for siRNA to be a new breakthrough it is not safe enough until all aspects and have been fully evaluated and off-target mechanisms are fully understood.
http://dx.doi.org/10.1016/j.addr.2010.07.005
I agree that it is not safe yet. Anything new that turns up in science shouldn’t be considered safe. Like you said, no one knows what will happen if you don’t understand what is going on. You have a lot of good support to show how SiRNA’s can be used in real life.
Some of the studies done with siRNA does prove that they are safe, In just few years we will know if siRNA drug therapy silence disease-causing genes with specificity without the toxicity. I want to find out how harmful the siRNA Therapeutics clinical toxicity can be.
After reading about SiRNA we can ask this question: is it safe? To decide whether it is safe or not, we first have to understand what siRNA is. SiRNA is a type of double-stranded RNA that can cause specific genes in our body to be expressed by means of degradation of mRNA during translation. It comes from vectors such as viruses, and is used in the process gene therapy where it is used to block certain pathways so that some genes are expressed and some are not. Xavier de Mollrat du Jeu, senior staff scientist at Life Technologies says, “We’ve added chemical modifications that improve their stability and potency, and reduce the immunogenic response and off-target effects.” SiRNA is used in the treatment of cancer. I personally think that siRNA is a good concept but, because the subject is so new, I am not completely sure if it is 100% safe or not. It is shown that excess siRNA may affect the liver.
I agree it is a fairly new topic and not that much evidence is present to deem it unsafe however moderation should be used when this is being administer. I think people who receive these therapies even if its experiment should be placed in a place where they can be constantly monitored and have immediate medical attention and an antidote should be created just in case things start going wrong.
I think it’s hard to differentiate if it is safe or not. I feel more studies should be conducted to prove if SiRNA is hazardous or safe. The utilization of SiRNA may be useful in treating Huntington’s disease in the future. Scientists are trying to develop a safe effective way to reduce levels of harmful mutant protein, siRNA is being used to prevent the mutant protein from being produced in the cell.
Viral diseases/infections are more common than one may think and the only way to get rid of it is by acquiring immunity to it via your immune system. In some cases such as HIV there is no way the body can natural acquire immunity and the outcome is fatal. With advances in technology and siRNA research therapies have been developed to aid in prolonging the affects of viral and some genetic diseases such as HIV however it is questionable as to whether these treatments are safe to use.
The way these treatments are conducted is that siRNA is synthesis outside of the human body and then injected into the affected individual. The goal of the siRNA is to stop the gene causing the deficiency from causing the problem. However the siRNA is not specific to one gene and thus it ends up suppressing the ability of other genes that are perfectly normal.
One example can be shown in the use of this gene therapy on lab mice to test the effects this gene suppressor would have on hepatitis B. hepatitis B is a disease of the liver that is transmitted through direct contact with body fluids such as saliva, and tears as well as others. In the experiment conducted by Dr. Kay and his team at the Stanford University they found that the therapy used proved to be lethal as within weeks of injecting these mice with these therapies the mice died.
Further testing’s proved that the therapy itself was not lethal but the dosage which cause suppression of the genes was what killed these mice. The conclusion of the experiment was that it is not the therapy that was dangerous but how much was given. This gives rise to the hypothesis how much is enough and shows that care and caution must be taken when administering these therapies especially in humans
This is pretty interesting. Just to clarify HIV/AIDS is a retrovirus thus, it is autoimmune thats why we are not able to find a cure so, this research is extensive. It tends to attack our own immune system so, how does do you know how the siRNA is manipulated to help mechanistically ?
siRNA are used for gene therapy, it is used to turn off and silence mutated genes. The genetic material is used for the replacement of a mutated gene. The problem arises when using this method, because siRNA can provide negative effects on body. It replaces similar segment of our own DNA acting recessive into a dominant transformation. SiRNA also have been used to cure cancer as well respiratory diseases. For SiRNA research to be more effective it has to be biologically stable and it has to be designed so that it only targets the correct genes or else it would cause toxic effects on the body. A study conducted on gene therapy by D M Dykxhoorn at Harvard Medical School, Boston, MA, USA says that “To use siRNAs as a systemic drug, more efficient delivery strategies are necessary to improve in vivo half-life.” SiRNA has short half live therefore it has to be genetically modified because if it is not it won’t exist in the blood and serum and will degrade. Scientist have been more focused on the off-target effects of siRNA that has induction of an inflammatory response and activating anti-angiogenetic responses or sometime down regulation of non-target proteins including an immune response. It is still unclear whether siRNA-based agents can be a safe and effective therapy for diseases, however in few years it might be clear whether siRNA drug therapy to silence disease-causing genes is without toxicity.
This study is published in Nature.com “gene therapy”
You stated some very good points and i agree that siRNA gene therapy isn’t safe yet. Since it is fairly new, we don’t know all the toxicological implications that it can come with. Some research has actually showed that siRNA gene therapy is safe but we need to conduct more research. We should be concerned with the harmful affects it can have on our bodies.
SiRNA, or small interfering RNA, is currently being researched to use in gene therapy. Gene therapy is the use of DNA or RNA as a pharmaceutical agent to treat disease. SiRNA can silence gene expression, re-arrange chromatin, and even interfere with RNA pathways. If we can fully control SIRNA and its affects, we can cure many diseases. Of course with tempering “the natural state,” toxicological implications will occur. One implication is the off-target affects. SiRNA can accidently attack a RNA with the complementary base. This can cause harmful effects if important genes are accidently silenced by the siRNA. Another implication is the dose. How much of the actual siRNA do we have to give to show us the results we want? How can giving too little or too much of the siRNA affect the rest of the body? Through my research I actually found examples of siRNA working in our favor. A paper published by P.A. Campochiaro at the Department of Ophthalmology and Neuroscience in The John Hopkins University School of Medicine explains that siRNA can be used to suppress corneal neovascularization and it has showed to help with ocular scarring. It has been used to identify genes that promote apoptosis or oxidative damage in retinal cells. The eye is a relatively isolated organ, which makes it an ideal target organ for gene therapy. SiRNA injected into the vitreous cavity readily diffuses throughout the eye and as siRNA gets out of the eye it is diluted and is difficult to detect. This allows local silencing of a gene with little chance for an effect on the same gene outside the eye.
Even though this study has found that SiRNA gene therapy can work they are still a lot of toxicological implications that need to be looked upon when dealing with other parts of the body, and even the eye too.
Good point. My suggestion is that to get a highly potent siRNA and use a very low dose might help to overcome this toxicity in the eyes. But we might need to do more studies on the “faultless” dose of siRNA to ensure their safe use.
The therapeutic use of siRNA has become one of the most effective developing trends in biomedicine. And this biotechnology has been combined with nanoparticles for treatment of cancer. The produced nanoparticles delivery system prevents the RNA molecules from being destroyed by the body before reaching their target gene diminished protein expression. On the other hand, the siRNA can enter cell membranes and merge themselves into larger molecules due to their small size. In this regard, although siRNAs can be cellular defense systems, they are large enough to interfere with cell processes. In the other word, it is risky to use siRNAs/nanoparticles because as we make them useful they might be case to have effect. The delivery system-induced gene expression can lead to “enhance siRNA gene-slicing activity” as it also needs “to be balanced against any increase in off-target effects due to the delivery system”. For instance, researchers at the University of Massachusetts studied two types of nanoparticles, in MCF-7 and breast cancer cells, and found an increase in DNA damage. Therefore, more studies need to address and determined on both nanoparticle toxicity when synthetic siRNAs exist in vivo, and their potential toxicity to our human body.
SiRNA therapy at one time considered to be an extreme and last resort therapy is now being more widely used. There are many clinical trials that are being suggested and being performed. One example of this is using SiRNA therapy to help discourage neovascularization after glaucoma surgery. After the surgery there usually is a risk of choroidal neovascularization, which is when new blood cells stem from the vascular layer of the eye containg the connective tissue or the choroid and into the subretinal space that leads to eventual vision loss. SiRNA are recently being used in therapy to help activate genes that promote apoptosis and oxidative damage in order to stop the growth of these new blood vessels. For this to work, the SiRNA is directed towards vascular endothelial growth factor (VEGF) or VEGF receptor 1 which has been shown to signal genes to to suppress corneal neovascularization. Some delivery problems to this could be that the SiRNA affects untargeted genes near the area, which may cause the genes to activate apoptosis in unwanted areas around the eye.
You did a great job in describing a real clinical trial and breaking it down. However, if this therapy is suppose to help prevent the loss of vision I am concerned about siRNA and its off target affects. If the siRNA affects genes other than targeted genes and cause apoptosis in unwanted area around the eyes, could this lead to vision loss as well?
SiRNA is a small interfering RNA, it interferes with the expression of a specific gene. It can silence a specific gene. RNA interference strategy is being used to prevent the mutant protein from being produced in the cell in patients that suffer from Huntington’s disease. This strategy proved to be effective in animal models. If we can control the function of siRNA, there will be many cures. The problem is, we don’t know how much siRNA we should measure to receive the desired results we want. Future research will hopefully give us the answers to proper measurements of siRNAs. The problem with siRNA is that it may affect other genes that are turned on, rather than their targeted genes. This might have profound effects on the human body. SiRNA have short half lives meaning they cannot be fully sustained in the blood stream unless they are modified. Researchers are still conducting research to find out if SiRNA can be taken orally. SiRNA’s can be broken down if taken orally, for that reason, the routes it takes to be delivered are by intravitreal,intravaginal and intrathecal
SiRNA seems to be a large issue that many may agree on while many others do not agree with it. Some people feel that its not an equal efficient type study, because of the many cons people have found. siRNAs are a sort of gene therapy that can treat a disease, what could one possibly find wrong with that? But along the process of it doing so it causes many problems such as binding to the wrong strand perhaps which can cause a big problem within a research. Also when this is performed the immune system doesnt always recognize what is happening so it acts as if it should fight back ans rejects it. I think the more experiments done to fix this problem the better it can get and then eventually siRNA therapy will actually not be such a bad thing to others. We need our RNA so improving it won’t hurt the situation at all.
I agree with you that their are many benefits to using SiRNA especially for gene therapy. However, the cons cannot be overlooked either, just because they may help in gene therapy. This risks for untargeted responses is still very high and needs to be taken into consideration as well.
Small interfering RNA (siRNA), also known as silencing RNA is currently being tested in clinical trials for use in gene therapy. Gene therapy is the use of DNA or RNA as a pharmaceutical agent to treat disease. The most notable role of siRNA is its involvement in the RNA interference (RNAi) pathway, where it interferes with the expression of a specific gene. RNAi is the process by which a specific mRNA is targeted for degradation. This process inhibits the synthesis of the encoded protein and therefore interferes with gene expression. siRNA may be able to cure certain diseases by turning off overactive genes within the human body or turning off genes from foreign invaders in the body. However, there are many toxicological obstacles that go along with siRNA therapy. One of them is off target effects. siRNA may affect other genes other than their target gene, which may have detrimental effects if a critical gene is silenced. Another obstacle is the delivery of siRNA. An appropriate biocompatible delivery system is necessary for the uptake and efficiency of siRNA. An inappropriate selection of a delivery vector for siRNA can reduce the gene-silencing activity and even enhance off target effects. The pharmacokinetics of siRNA can also be altered by the delivery system. The delivery system may be able to alter the molecular and physical size of siRNA, reducing the excretion via the kidneys and causing accumulation. Accumulation of siRNA may also occur in the liver, lung, and spleen. The biological stability of siRNA is also an important factor. siRNAs that are unmodified are unstable in blood and serum and are rapidly degraded by endo- and exonucleases, resulting in short half-lives in vivo. Currently there are several routes used for systemically delivering siRNA. These include intravitreal, intrathecal, and intravaginal. However, the optimal delivery method is orally. This is a major hurdle due to siRNA degradation and the poor bioavailability from the gastrointestinal tract. siRNA seems like great candidate for gene therapy, but a lot more research needs to be done before we can deem it “safe.”
siRNA otherwise known as small interfering RNA or the silencing RNA are double stranded RNA molecules. siRNA is able to turn off or interfere with the expression of certain genes. siRNA is made from RNA, and the RNA gets processed in the cytoplasm. It is sequence specific and compliments certain base pairs. It wanders out of the nucleus and is processed in the cytoplasm where it recruits nucleosomes after it compliments base pairs in the nucleus and silences genes or turns off expression. siRNA is being used as an upcoming cancer therapy. However the only problem with this is, it has poor intracellular uptake, limited blood stability, and non specific immune stimulation. Any thing that is recent in science will take many years before it can be proven safe or effective.