mRNA, RNAi, circRNA, ASOs: A comparative guide to RNA therapeutics

RNA therapies

Newsletter Signup - Under Article / In Page

"*" indicates required fields

Subscribe to our newsletter to get the latest biotech news!

By clicking this I agree to receive Labiotech's newsletter and understand that my personal data will be processed according to the Privacy Policy.*
This field is for validation purposes and should be left unchanged.

You’ve certainly heard about antibodies, peptides, and even DNA as therapeutics, but what about RNA? In this review, we take a look at what’s happening in a field that some believe may be as big a revolution as monoclonal antibodies.

For a long time after the discovery of nucleic acids, now almost 150 years ago, RNA has been considered an extremely delicate molecule, prone to degradation, and therefore dismissed in therapeutic applications. Today, however, major developments have made RNA a focus of medical research with exciting applications, such as better treatments for hemophilia and cheaper vaccines. Let’s review how the technology works and the latest advancements in the field.

Table of contents

    RNAi therapeutics: interfering with disease

    RNA interference (RNAi) therapeutics are based on a natural process by which RNA sequences can block the expression of DNA into protein. The RNAi molecule binds to specific messenger RNA molecules that code a certain protein and directs it to the RNA-induced silencing complex (RISC), which cleaves the molecule, and therefore, the protein cannot be produced.

    Or, as Massachusetts-based RNAi therapeutics company Alnylam’s former president Barry Greene put it, “If you have a leaking faucet in your kitchen, today’s drugs work by mopping up the floor; we shut off the spigot.”  

    Back in the early 2000s, scientists started to realize the potential of RNAi and its discovery ended up winning a Nobel Prize in 2006. This led to massive investments, such as Merck’s acquisition of Sirna Therapeutics for $1.1 billion. But soon after, several clinical trials showed the young technology could induce severe side effects and most big pharma shied away – including Merck, which sold Sirna for almost a tenth of the acquisition over a decade ago.

    This didn’t seem to worry Greene. “Big pharma is a miserable barometer for innovation. They only got into proteins and antibodies when it was already a $20 billion market,” said Greene, back in 2017.  And while Alnylam suffered some setbacks itself, including an earlier candidate that was pulled after 18 deaths in the clinic and the dosing halt of fitusiran a few years ago, Greene believed that RNAi therapeutics will now be appreciated as much as antibodies or protein drugs. Now, the FDA is set to make a decision on the approval of Sanofi’s fitusiran in two months. 

    In recent years, a number of RNA therapies have been greenlit by the FDA. Being an integral player in RNA therapeutics, Alnylam’s drugs may be the first to come to mind. Patisiran was approved in 2018 for transthyretin amyloidosis (ATTR), a disease that affects multiple organs, particularly the heart and nerves. It is a small interfering RNA (siRNA) therapy that silences the mutant transthyretin (ATTR) gene responsible for producing misfolded proteins that accumulate in tissues, causing ATTR.

    Then, there is givosiran, which was approved a year later, to treat a condition called acute hepatic porphyria, a rare genetic disease that causes severe abdominal pain and other symptoms. As it is caused by the defect in an enzyme that leads to its overproduction and the eventual buildup of toxins, givosiran is designed to suppress the production of the enzyme. Now marketed as Givlaari, it represents a major advancement in the treatment of AHP, significantly reducing the frequency of acute attacks in patients and improving their quality of life.

    Other siRNA treatments include lumasiran for a genetic disorder called primary hyperoxaluria type 1 (PH1) and inclisiran to reduce cholesterol, both approved in 2020 and 2021, respectively. 

    ASO RNA therapy: modifying gene expression

    Another kind of RNA therapy that has been approved by regulators in the U.S. and Europe alike, are antisense oligonucleotides. These work by binding to specific mRNA sequences in order to modify gene expression. By correcting faulty RNA processing through altering splicing – a process that involves the joining together and removal of genetic material – they can modify gene expression. They also help block the translation of harmful proteins by preventing mRNA expression from taking place.

    Several ASOs have been on the market since the first one – fomivirsen for a viral eye infection that affects patients with AIDS – was cleared by the FDA in 1998. For people with Duchenne muscular dystrophy, these drugs have been a significant step towards their care. Golodirsen, known as Vyondys 53, is an exon skipper that targets exon 53 of the dystrophin gene – which contains a mutation that can cause muscle weakness. In 2020, Viltepso was granted the FDA nod, a drug similar in mechanism to Vyondys 53.

    Most recently, Qalsody (tofersen) received a thumbs up from regulators to treat amyotrophic lateral sclerosis (ALS) caused by the SOD1 mutations. It aims to cut down high SOD1 protein levels, which is linked to motor neuron damage. The therapy represents a novel approach to treating ALS as it is a progressive neurodegenerative disease with no cure.

    mRNA: a myriad of possibilities

    Despite the key role of messenger RNA in the translation of DNA into protein has been known since Crick described it in the late 50s, it hadn’t been investigated as a therapeutic product until much later. 

    The idea of mRNA therapeutics is simple. If you deliver an mRNA sequence to a cell, it will use it to create the protein encoded there as if it were its own, removing the need – and issues – of producing it externally. In theory, virtually any protein could be produced using this method.

    But in reality, working with mRNA traditionally came with two big obstacles. First, it is highly immunogenic. Second, RNAse enzymes that degrade it can be found pretty much everywhere life exists. But scientists can now easily get around these problems by playing with the sequences and making chemical modifications to the nucleotide building blocks that form mRNA. Now, the technology leads in the COVID-19 vaccine space.

    The two big names are Comirnaty, which was granted Emergency Use Authorization in 2020 and bagged full approval in 2021, and Spikevax, which was given full approval in 2022. Both vaccines – developed by Pfizer and BioNTech, and Moderna, respectively – use mRNA technology to encode the spike protein of the SARS-CoV-2 virus. Once injected into the body, the mRNA is translated by cells, prompting the production of the spike protein. This stimulates an immune response, allowing the body to recognize and fight the virus even in the future.

    Since then, a number of mRNA vaccines have been tried and tested in the clinic in the race to create highly-effective jabs for people. And now, with the spread of bird flu, the U.S. health service has just awarded Moderna a $590 million contract to advance mRNA vaccines through clinical trials. Moreover, its mRESVIA vaccine grabbed the FDA’s approval to protect people from the respiratory syncytial virus (RSV).

    While this technology shot to fame during the pandemic, it could also be pivotal in cancer care research. Personalized cancer vaccines are tailored to individual patients based on the unique mutations present in their tumors. Sequencing the tumor’s genome allows for the identification of neoantigens, which are mutated proteins that are specific to the tumor. These neoantigens can then be encoded in mRNA and administered as a vaccine. And since the vaccine is personalized, it has the potential to be highly targeted in killing tumors.

    Vaccine developer BioNTech has a potential stake in the game. Its FixVac mRNA cancer vaccine platform is based on activating immune cells that recognize cancer-specific antigens to counter cancer cells. A phase 2 trial of one of its candidates born from the platform proved a success in the clinic after showing statistically significant improvement in the overall response rate (ORR) in patients with advanced melanoma last year. Also in the spotlight are Moderna, Gritstone Bio, and CureVac – all moving their mRNA candidates up the clinic to address solid tumors as well as blood cancers.

    However, the technology is not without its challenges – which mostly have to do with delivery. A major hurdle for mRNA therapies is getting the mRNA into the right cells at the right time. mRNA is a large, negatively charged molecule that does not naturally cross cells easily. Lipid nanoparticles (LNPs) are the most common method used for delivering mRNA into cells, but designing LNPs that are both effective and safe, remains an ongoing area of research.

    Moreover, mRNA vaccines are expensive to manufacture, require cold-chain storage, and can be difficult to transport, making the whole process of getting them to patients complicated. That’s potentially where circular RNA could come in. In fact, rumor is that it could even replace mRNA as it may be more cost-effective to manufacture and is far more durable.

    Circular RNA therapeutics: could it take over mRNA technology?

    Circular RNA is essentially a single-stranded RNA molecule with a closed- loop structure that does not code for any protein. It was initially disregarded when it was discovered back in 1991, when it was thought to represent errors.

    But now, times have changed. Norwegian biotech Circio is pioneering research in the field. Its circVec platform is a genetic cassette designed to create circRNAs in cells. It can be tailored for any DNA or viral vector, enabling protein expression via circRNA. Its lead candidate is aimed at treating patients with alpha-1 antitrypsin (AAT) deficiency, a rare genetic disorder that can result in lung or liver disease.

    Then, there is also Massachusetts-based Orna Therapeutics, which has strengthened its position in the field since it debuted with $100 million in 2021. It is developing its circular RNA technology platform oRNA, which is formed from a linear RNA precursor. Last year, it acquired fellow circular RNA developer ReNAgade Therapeutics and it is also creating an LNP delivery system that is scalable. The two platforms are panCAR, which targets multiple lineages of the immune system at once, and SiTu Editing in the Marrow (STEM), which targets stem cells in the bone marrow.

    Soon, scientists aim to bring this technology to the clinic as young biotechs like Orna focus on treating cancers, autoimmune, and certain genetic diseases.

    What is next for RNA therapeutics?

    At present, RNA therapies are a hot topic across indications. mRNA’s influence during the pandemic has opened the door for broader applications in infectious disease prevention. Apart from RSV and influenza, biopharmas are advancing candidates to treat zika and malaria. Moderna’s phase 2 candidate mRNA-1893 contains an mRNA sequence encoding for the structural proteins of Zika virus and is designed to cause cells to secrete virus-like particles, mimicking the response of the cell after natural infection. However, it might throw in the towel after it announced plans last year to can trials if it doesn’t obtain funding. 

    Meanwhile, genetic and rare disorders are getting the attention they deserve. For the lung disease cystic fibrosis, Vertex Pharmaceuticals has an mRNA medicine, which bagged Investigational New Drug (IND) clearance nearly three years ago.

    Also, trials for sickle cell disease and beta-thalassemia, two genetic blood disorders, are underway. A notable advancement is the University of Pennsylvania’s Perelman School of Medicine’s mRNA gene therapy, which can correct the gene mutation that causes sickle cell in human cells without having to alter cells outside the body. Researchers showed that it can be delivered via LNP, which would reduce cost and increase access to gene therapies, according to a proof-of-concept paper that was published in 2023.

    And that’s not all. RNA technology could also turn the tables for people with autoimmune diseases – many of whom are reliant on immunosuppressants, which have been linked to a higher risk of infections. By changing immune cell behavior, RNA could potentially offer a more targeted approach. Bristol Myers Squibb and Repertoire Immune Medicines struck a deal worth up to $1.8 billion last year to generate tolerizing mRNA vaccines for “resetting the immune system.” It is now in the process of nominating its candidates to treat autoimmune conditions.

    With the rapid success of mRNA therapeutics and the continued breakthroughs in RNAi technology, the field is brimming with potential. Although challenges concerning delivery, among other hurdles, remain, the pace of R&D is only accelerating as researchers turn to create scalable ways to bring treatments to millions of people.

    This article was originally published in 2017 by Clara Rodríguez Fernández and has since been updated by Roohi Mariam Peter.

    inpart logo

    New technologies to RNA therapeutics: