Nobel Prize awarded for the discovery of microRNA and its role in post-transcriptional gene regulation

Congratulations to Victor Ambros and Gary Ruvkun who were jointly awarded the 2024 Nobel Prize in Physiology or Medicine for their discovery of microRNA in the small worm C. elegans¹. As we’ll discuss in the article, this revealed a new dimension to gene regulation, essential for all complex life forms, and has paved the way for a new class of RNA therapeutics.
 
Before we get into the details of what microRNA is and how it was discovered, it’s interesting to note that this isn’t the first time the humble nematode worm C. elegans has contributed to Nobel Prize-winning work. Back in 2002 Sydney Brenner, John Sulston, and Robert Horvitz were awarded a Nobel Prize for their research using C. elegans to unravel how cell division, differentiation, and cell death are genetically controlled during organ development².
 
This also isn’t the first time a Nobel Prize has been awarded for RNA -based technologies. Looking back over the last 10 years, in 2006 the award in chemistry went to work leading to the discovery of RNA interference - gene silencing by double-stranded RNA³. In 2020 the award in chemistry went to the revolutionary CRISPR/Cas9 technology and the award in physiology and medicine went to the discovery of the hepatitis C RNA virus⁴. Just last year, in 2023, the prize in physiology and medicine went to the research underpinning the effective mRNA vaccines against COVID-19.
 

What is miRNA and how was it discovered?

As the name suggests, microRNAs, or miRNAs, are a class of short, typically around 20-22 nucleotide-long, RNA molecules.
 
Many of us will be familiar with the “central dogma of molecular biology” - DNA makes RNA, and RNA makes protein. The fundamental process remains but scientific advances continue to add further layers of complexity. In 1961 François Jacob and Jacques Monod published their seminal work demonstrating that proteins could regulate gene expression⁵. The discovery of miRNAs unravelled a further dimension. Whereas proteins in the nucleus regulate RNA transcription and splicing, Ambros and Ruvkun showed that miRNAs play a key role in gene regulation by exerting post-transcriptional control over messenger RNA (mRNA) stability and protein translation in the cytoplasm. 
 
The discovery of miRNA and its role in gene regulation began with the identification of the lin-4 and lin-14 mutants of C. elegans, which exhibited opposing developmental timing defects. The Nobel laureates went on to discover that the lin-4 gene did not encode protein, but a 22 nucleotide-long non-coding RNA (subsequently termed lin-4 miRNA). Crucially, Ruvkun showed that lin-4 did not inhibit the production of lin-14 mRNA (unlike known modes of gene regulation). Instead, the lin-4 miRNA was found to regulate lin-14 mRNA via base pairing with multiple elements in the 3’ untranslated region (3’UTR) of lin-14 mRNA, ultimately “turning off” lin-14 mRNA and blocking lin-14 protein production^6;7.
 
It wasn’t until seven years later when a further miRNA was discovered in Ruvkun’s laboratory, that miRNAs garnered significant attention in the scientific community. It was found that let-7 encodes a short 21 nucleotide-long non-coding RNA with complementarity to 3’UTRs of various genes that regulate the timing and sequence of developmental events⁸. A further significant breakthrough came when it was uncovered that let-7 miRNA was highly conserved across diverse animal species, including humans⁹.
 
Ambros and Ruvkun’s seminal discovery, along with subsequent efforts of research groups around the world, has led to today’s understanding of the evolutionarily conserved post-transcriptional regulatory mechanism mediated by miRNA¹⁰.
 

Patent protection for miRNA

As expected, a discovery as groundbreaking as Ambros and Ruvkun’s led to a flurry of patent application filings. The European Patent Office (EPO) has published over 1000 European patent applications referring to “microRNA” or “miRNA” in their title.
 
Perhaps unsurprisingly, the majority of published miRNA patent applications are directed towards cancer therapeutics. Further therapeutic indications include, for example, metabolic disorders, inflammatory disorders and cardiovascular disorders.
 
Patent applications directed towards miRNA therapeutics largely fall into three main categories:

• miRNA mimics – augmenting the impact of endogenous miRNAs

• miRNA inhibitors (or anti-miRs) – suppressing aberrant miRNAs

• delivery systems – to improve and fine tune delivery of miRNA mimics and inhibitors

Beyond therapeutics, we have seen a number of European patent application filings relating to diagnostic uses of miRNAs and methods of modulating stem cell fate.
 

miRNAs in the clinic

The crucial role of miRNAs in regulating gene expression holds great therapeutic potential, as implied by the current patent landscape. miRNA-based therapies are being explored in clinical trials around the world for a variety of diseases such as metabolic disorders, cardiovascular disease, neurodegenerative conditions, and cancer. Some examples include:

• MRX34, a liposomal mir-34a mimic, is one of the first miRNA-based drugs to enter clinical trials for patients with advanced solid tumors and melanoma (NCT01829971; NCT02862145). The tumor suppressor mir-34a downregulates expression of greater than 30 oncogenes, as well as genes involved in tumor immune evasion¹¹.
   

• MesomiR 1, a specific TargomiR (miR-16-based miRNA mimic packaged in non-living bacterial minicells targeting EGFR), entered clinical trials for miRNA replacement therapy in patients with recurrent malignant pleural mesothelioma and non-small cell lung cancer (NCT02369198). This therapy seeks to restore miR-16, which acts as a tumour suppressor in malignant pleural mesothelioma¹².
   

• MRG-106 or Cobomarsen, a locked nucleic acid (LNA)-modified oligonucleotide inhibitor of miR-155, entered clinical trials for patients with mycosis fungoides (NCT03837457). MRG-106 was designed to inhibit the activity of miR-155 as overexpression of miR-155 is associated with poor prognosis in a variety of T-cell lymphomas and several other blood cancers¹³.
   

• Miravirsen, a locked nucleic acid–modified DNA phosphorothioate antisense oligonucleotide inhibitor of miR-122, entered clinical trials for patients with chronic hepatitis C virus (HCV) infection (NCT01200420; NCT02508090). Miravirsen was designed to sequester miR-122, thereby inhibiting its function¹⁴.

Many more miRNA-based clinical trials are already underway and we look forward to many success stories in the coming years.
 
Congratulations again, and thank you, to this year’s Nobel laureates who have revolutionised the RNA therapeutics landscape!
 
Our team has considerable experience advising clients on patent matters in relation to miRNAs, along with other RNA therapeutics including: mRNA, mRNA vaccines, antisense oligonucleotides, non-coding RNA (ASO), CRISPR-based genome editing and LNP chemistry. Please get in touch with Beth Ormrod, Jamie Atkins, or your usual Kilburn & Strode advisor if you have any related queries.