siRNA drugs are a promising class of therapeutic agents that leverage RNA molecules to silence disease-causing genes. This innovative approach holds potential for treating a wide range of illnesses resulting from overexpressed or dysfunctional genes, including but not limited to hereditary diseases, viral infections, and cancer. The development of siRNA drugs has been a major focus of research in the RNA therapeutics field, and has encountered several technical challenges since its inception. Nonetheless, ongoing efforts have led to significant progress in this area.

Evolution of siRNA Drugs: From Discovery to FDA Approval

The history of siRNA drug development can be traced back to the early 1990s when RNA interference (RNAi) was first discovered in plants. However, it wasn’t until 1998, when Andrew Fire and Craig Mello revealed the RNAi phenomenon in C. elegans, that the field of molecular biology experienced a paradigm shift. The duo’s discovery earned them the Nobel Prize in Medicine and set the stage for a global surge in the research and development of small nucleic acid drugs.

In 2002, siRNA-mediated gene silencing in vivo was first reported, demonstrating the potential of siRNA to target the expression of specific genes in mice. Despite this breakthrough, the clinical translation of siRNA drugs was initially hindered by several technical challenges, including poor stability, off-target effects, and inefficient delivery.

However, significant progress has been made in recent years, leading to the approval of several siRNA drugs by the US Food and Drug Administration (FDA). In 2018, Onpattro (Patisiran) became the world’s first FDA-approved siRNA drug delivered by lipid nanoparticle (LNP), targeting TTR to treat peripheral polyneuropathy caused by hereditary transthyretin-mediated amyloidosis (hATTR). This approval marked a significant milestone in the development of siRNA drugs.

In 2019, Givlaari (Givosiran) became the second siRNA drug approved by the FDA and the first siRNA drug marketed using GalNAc conjugation technology. The drug targets ALA synthetase ALAS and is used to treat acute hepatic porphyria in adults.

The year 2020 witnessed the approval of two siRNA drugs by the FDA. The first was Oxlumo (Lumasiran), which targets glycolate oxidase HAO1 for the treatment of primary hyperoxaluria type 1. The second was Leqvio (Inclisiran), which targets Pcsk9 for the treatment of hypercholesterolemia in adults.

In 2022, the FDA approved the fifth siRNA drug, Amvuttra (Vutrisiran), which is an upgraded version of Patisiran. The drug uses ESC-GalNAc conjugation technology to target TTR, enhancing the stability of siRNA through chemical modification.

Overall, the development of siRNA drugs has come a long way, with significant progress made in overcoming technical challenges and improving drug delivery. With the approval of several siRNA drugs by the FDA, the future of RNA therapeutics looks promising, and the potential for treating a wide range of diseases continues to grow.

siRNA Drugs Clinical Application

The following are some applications of current and potential siRNA drugs in clinical medicine and the results of clinical trials to date:

• Treatment of Hereditary Transthyretin-Mediated Amyloidosis (hATTR): hATTR is a rare genetic disorder that causes the accumulation of amyloid proteins in various tissues and organs, leading to organ dysfunction and eventually death. Vutrisiran and Patisiran are two siRNA drugs that have been approved by FDA for the treatment of hATTR. Both drugs target the transthyretin (TTR) gene and reduce the production of TTR protein, which forms the amyloid deposits.
• Treatment of Hypercholesterolemia and mixed dyslipidemia: PCSK9 is a protein that regulates the level of low-density lipoprotein (LDL) cholesterol in the blood. Inclisiran is a siRNA drug that targets the PCSK9 gene and reduces the production of PCSK9 protein, thereby lowering the LDL cholesterol level. Compared with other PCSK9 inhibitors, the advantage of Incisiran is that after the first injection, patients only need to receive subcutaneous injection twice a year to control the cholesterol level, which is a very convenient treatment option.
• Treatment of acute porphyria hepatica (AHP): AHP is a genetic disease that results in the formation of toxic porphyrin molecules in the blood during heme production. Givosiran adopted the ESC-GalNAc delivery platform, taking ALAS1 as the target, to reduce the accumulation of neurotoxic heme intermediates, aminolevulinic acid (ALA), porphyrin bilirubin (PBG) and other intermediate products by continuously reducing the level of liver ALAS1.
• Treatment of primary hyperoxaluria type I (PH1): PH1 is a super rare disease, which causes renal failure due to excessive oxalic acid production (oxalic acid is mainly excreted from urine, so the kidney is the main target organ for its deposition), with significant incidence rate and mortality. Lumasiran carries the ESC-GalNAc delivery platform, targeting the HAO1 gene encoding glycolate oxidase (GO) in the liver, and reducing hepatic overproduction of oxalate by reducing GO expression.
• Treatment of acute kidney injury (AKI): AKI is a common clinical acute, critical and severe disease. Among patients who have undergone major cardiovascular surgery, AKI will occur due to ischemia within a few hours to days after surgery. This is due to the reduction of local blood flow during the operation and the reperfusion injury after the recovery of blood flow. QPI-1002 is the first systemic siRNA drug to enter human clinical trials, which aims to inhibit the expression of pro-apoptosis gene p53 to protect normal cells from death due to acute tissue injury. Clinical trials have shown that QPI-1002 can reduce the incidence of AKI in patients undergoing cardiac surgery and improve renal function.
• Treatment of cancer: siRNA drugs can specifically target cancer genes and have effects on the proliferation, angiogenesis and metastasis of cancer cells. They can avoid adverse reactions caused by radiotherapy and chemotherapy without producing drug resistance. At present, a variety of anti-cancer siRNA drugs have entered clinical trials, including liver cancer, lung cancer and ovarian cancer.

Overall, the therapeutic field of siRNA drugs has gradually expanded from rare diseases to common diseases. With its high specificity and efficiency, it has attracted more and more attention. The continuous emergence of siRNA clinical drugs has also made its development path gradually clear. However, it is still necessary to further study the targeted delivery strategy and chemical modification of siRNA drugs.

Mechanism of siRNA Drugs: Targeted Gene Silencing with High Specificity

The specificity of siRNA drugs is due to the complementary base pairing between the siRNA and the target mRNA molecule, allowing them to target almost any gene of interest as long as the target mRNA sequence is known. The RNAi pathway’s strict regulation and tight control in cells further enhance the specificity of siRNA drugs. This ensures that only target mRNA molecules are degraded, minimizing off-target effects. This mechanism has revolutionized the field of molecular biology, opening up new avenues for the treatment of various genetic diseases.

Limitations and Improvement Strategies of siRNA Drugs

Despite the advantages of siRNA drugs, such as high gene silencing efficiency, specificity, and controllable adverse reactions, they still face certain limitations. Poor stability, off-target effects, and inefficient drug delivery are the main challenges that researchers are addressing.

Improving drug delivery is a primary area of focus for researchers. LNP and GalNAc have become mature delivery systems and are widely used, and new systems such as conjugated molecules, exosomes, and CPPs are under development. Enhancing specificity is another area of focus to reduce off-target effects. Chemical modifications like GNA, LNA, and 2′-MOE can improve the immunogenicity of siRNA, reduce off-target toxicity, and increase effectiveness.

Researchers are also targeting previously undruggable genes with siRNA drugs, and combination therapies with chemotherapy or immunotherapy are being explored to enhance efficacy and reduce the risk of resistance. Gene editing technologies such as CRISPR-Cas9 are also being combined with siRNA drugs to achieve precise and targeted gene editing, potentially leading to a cure for genetic diseases.

In the coming years, we can expect to see new breakthroughs in the field of siRNA drug development as researchers continue to explore these promising areas of research. Ultimately, these advances could lead to new and more effective treatments for a wide range of diseases.

Customizable siRNA Products and Services from Synbio Technologies

At Synbio Technologies, we understand that the development of siRNA drugs is a complex and evolving field, which is why we offer a range of customizable siRNA products and services to support researchers in their work. Our siRNA products can be tailored to meet specific research needs, including different lengths, specifications, modifications, and labels.

Moreover, we are proud to offer a free siRNA design service to our customers, where we can design three siRNAs based on gene sequence, Gene ID, or Access Number. The deliverables of this service ensure that at least one pair can effectively inhibit the expression of the corresponding genes, with an mRNA inhibition efficiency of over 70% and a transfection efficiency of at least 90%.

Our expertise in siRNA design and synthesis allows us to provide efficient and reliable solutions for researchers to accelerate progress in the field of RNA therapeutics. With our high-quality siRNA products and services, researchers can confidently pursue their research goals and achieve meaningful results.

References

[1]Ra al F, Kallend D, Ray K, et al. Inclisiran for Heterozygous Familial Hypercholesterolemia. N Engl J Med. 2020;382(16):1520–1530.

[2]Hu B, Zhong LP, Weng YH, Peng L, Huang YY, Zhao YX, Liang XJ. Therapeutic siRNA: state of the art. Signal Transduction and Targeted Therapy, 2020, 5: 101-124.

[3]Alshaer W, Zureigat H, Al Karaki A, et al. siRNA: Mechanism of action, challenges, and therapeutic approaches[J]. European Journal of Pharmacology, 2021, 905: 174178.