The Decade of RNA Delivery – Beyond the Liver

Pictured: Iris Grossman, Ph.D., chief therapeutics officer, Eleven Therapeutics/company courtesy 

With the opportunity to treat spades of infectious diseases, cancers and single gene disorders, there is enormous potential in RNA therapeutics. To realize it, however, researchers will need to optimize delivery to on-target cells, minimize exposure to off-target cells and move beyond the liver.   

Yogev Debbi is co-founder and CEO of Israel-based Mana.bio, which specializes in “building the space shuttle” for RNA and DNA delivery. 

“The RNA is the astronaut that needs to get to the space station in order to fix it. But they can’t just walk there. They need a space shuttle with oxygen and seatbelts that can get past the atmosphere. We build space shuttles," he told BioSpace.

The past two decades were all about nucleic acid reading and writing, Debbi said. The next is about delivering DNA and RNA.

Eleven Therapeutics, tri-located in Tel Aviv, Cambridge, U.K. and Boston, marries the oligonucleotide therapeutics revolution and the AI revolution, Iris Grossman, Ph.D., chief therapeutics officer, told BioSpace.

In order for RNA therapeutics to make it to the clinic, and eventually the market, Grossman said three properties need to be mastered: potency, durability and delivery. 

Most Effective Route of Delivery?

The conjugate class is the ideal route of delivery for RNA, Grossman said.

“It’s one and the same backbone of your main moiety. As you think about the CMC and all the characterization efforts, you have a single entity as opposed to multiple entities.”

Conjugates also tend to work via a selective receptor mechanism, often composed of small molecules, antibodies and/or aptamers. 

Grossman pointed to N-acetylgalactosamine (GalNAc) short interfering RNA (siRNA) conjugates as a prime example. According to a 2018 review in Nucleic Acid Therapeutics, Tris-GalNAc binds to the asialoglycoprotein receptor highly expressed on hepatocytes, resulting in rapid endocytosis. While the exact mechanism is unknown, “Sufficient amounts of siRNAs enter the cytoplasm to induce robust, target selective RNAi responses in vivo,” the authors wrote.

The problem, Grossman said, is that very few of these have been discovered. “We have yet to identify something that is parallel to GalNAc for other tissues.”   

In the absence of conjugates, she said LNPs work fine, but there are immunogenicity and cytotoxicity concerns, particularly in the context of frequent repeat dosing for chronic treatment.

In terms of expanding the delivery toolbox, Grossman highlighted antibodies and polymers. Another strategy is to add targeting moieties to LNPs to deliver selectively to a certain cell type.

Lungs: The Next Frontier?

The lung has become a hot target of late for RNA therapeutics.

Using its AI/ML-based engine, Mana.bio designed a lipid nanoparticle (LNP)-based delivery system that is able to selectively target the lung, completely bypassing the liver. 

This system could effectively deliver mRNA to appropriate cells to treat a single-gene disease like cystic fibrosis (CF). To Debbi’s knowledge, this is the first time an LNP delivery system for mRNA has been designed using AI.

Mana.bio is currently looking to collaborate with partners to leverage this delivery technology for the right payload and the right indication, he said. In addition, the company is focused on unlocking the delivery of RNA to other organs.  

Grossman spoke specifically about RNA interference modalities, such as antisense oligonucleotides (ASOs) and siRNAs.

“All of them show sometimes exquisite genomic selectivity, specificity and effect size, but the biggest barrier is we don’t know how to get them to the target organ,” she said. “Virtually only the liver has been successfully targeted.”

Grossman will lead a session devoted to this challenge at the upcoming Biomed Israel conference entitled, “Facts and Myths on Ex-Liver Delivery of Nucleic Acid Therapeutics and New Horizons to Cure Rare Disorders”.

Eleven is leveraging its AI-based platform to map the chemical space and uncover the structure-activity relationship of RNA molecules.

The company’s proprietary DELiveri platform inserts a genetic circuit into the cell of interest. 

“It allows you to both amplify the intensity of the signal but also reduce the background [noise] because it is so selective.” This makes for a very efficient screening engine, she said.

The company then runs a DNA-encoded library within these cells, allowing it to screen hundreds of thousands of entities at once.  

In partnership with the Bill & Melinda Gates Foundation, Eleven is developing broad-acting prophylactics against COVID-19 and the flu. A third indication targets a yet-to-be-named chronic respiratory disease, which is more in-line with the company’s primary focus.

45 minutes away, in Jerusalem, SpliSense is leveraging its proprietary technology to deliver an ASO directly to the lungs via inhalation for CF.

The company’s lead asset, SPL84, is intended to treat CF patients carrying the 3849+10 kilobase (Kb) C->T splicing mutation in the CFTR gene.    

SPL84 is a “very small, short, single strand RNA that can enter the cell very easily, very elegantly with no multiplications, with no need for a carrier, no need for any lipid nanoparticles,” Gili Hart, Ph.D., CEO, told BioSpace in a previous interview.

Stateside, Vertex is developing VX-522, an mRNA therapy designed to treat the underlying cause of CF lung disease. Part of a research collaboration with Moderna, VX-522 is delivered to the lung through inhalation of a CFTR mRNA encapsulated by a lipid nanoparticle.

Targeting the Brain

Beyond the lung, RNA therapeutics have potential to treat several neurological diseases.

The blood-brain barrier stands as the greatest challenge to delivery in this space. But progress is being made. Currently approved RNA-based therapeutics for neurological diseases include Sarepta Therapeutics’ Exondys 51 (eteplirsen) for Duchenne muscular dystrophy and Biogen’s Spinraza (nusinersen) for spinal muscular atrophy.

Several others are currently in development. Amsterdam-based uniQure is developing AMT-130, which uses a microRNA to reduce the production of mutant HTT in Huntington’s disease. Wave Life Sciences is developing oligonucleotide therapies for Huntington’s, ALS and frontotemporal dementia. 

RNA therapeutics also have potential in diseases like Parkinson’s or Alzheimer’s, where part of the biology is clear.

As Debbi said, “You first need to design the astronaut." 

 *The Biomed Israel conference facilitated meetings with the aforementioned companies at their labs and offices.