Rare Disease Day Feb 28th, 2023—Six mRNA Therapeutics in Development

Rare Disease Day?(Figure 1)?occurs annually on the 28th?of February. In order to raise awareness, this blog highlights research aimed at mRNA-based?protein replacement therapies?for rare diseases. These approaches, which are at either clinical testing or early preclinical stages, involve administration of?in vitro?transcribed (IVT) mRNA to provide therapeutically beneficial proteins. Key advantages of mRNA therapeutics include their transient, non-integrating nature, and ability to deliver multiple mRNAs to encode complex multimeric proteins. In addition, IVT mRNA provides a rapidly deployable platform for accelerating development of therapeutics.?

Nearly 7,000 rare diseases affect 25-30 million Americans. Maybe surprisingly, having a rare disease is not actually so rare. Even though each disease is rare in and of itself, patients with rare diseases are common, accounting for?

~~

4%–6% of the worldwide population or?

~~

260–450 million persons (Shourick et al. 2021). In the United States, this works out to approximately 1 in 10 Americans having a rare disease.?However, the NIH?estimates?that only?

~~

300 rare diseases have any treatment options available.?

This blog post highlights progress made on mRNA-based protein replacement treatments for six rare diseases. These approaches involve administration of?in vitro?transcribed (IVT) mRNA to provide therapeutically beneficial proteins. Protein replacement-based therapy holds significant promise for developing new or improved treatments for the following six rare diseases:?

1. Propionic Acidemia??
2. Methylmalonic Acidemia?
3. Glycogen Storage Disease Type 1a?
4. Ornithine Transcarbamylase Deficiency?
5. Phenylketonuria?
6. Fatal Infantile Cardioencephalomyopathy?

1. Propionic Acidemia (PA)?

PA is a life-threatening, inherited metabolic disorder caused by deficiency of the mitochondrial enzyme propionyl-CoA carboxylase (PCC), which is comprised of six alpha and six beta subunits. Moderna reported an enzyme replacement approach to treat PA using a combination of two mRNAs encoding the alpha and beta subunits separately encapsulated in lipid nanoparticles (LNPs) to produce functional PCC enzyme in liver (Jiang et al.?2020). In each codon-optimized IVT mRNA, uridine was replaced with N1-methylpseudouridine (m1ψ). In long-term 6-month repeat-dose studies in PA-mice the mRNAs reduced primary disease-associated toxins in a dose-dependent manner with no adverse findings.?

A Moderna-sponsored Phase 1/2 clinical trial (NCT04159103) of this dual mRNA therapeutic (mRNA-3927) is currently enrolling an estimated 36 participants 1-year of age and older with genetically confirmed PA. The study is designed to characterize baseline biomarker levels followed by assessment of safety, pharmacokinetics, and pharmacodynamics of different doses of mRNA-3927 as part of the dose optimization.??

2. Methylmalonic Acidemia (MMA)?

MMA is a metabolic disorder caused by complete or partial deficiency of methylmalonyl-coenzyme A mutase (MUT). As a result, patients’ bodies lack the ability to properly digest specific fats and proteins. This leads to a buildup of toxic levels of methylmalonic acid in the blood, causing progressive alteration of brain function or structure.?

In a mouse model of MMA, promising findings used an IVT mRNA encoding MUT (An et al.?2017). In this study, the uridines were replaced with 5-methoxyuridine (5-moU) using TriLink products.?

Currently, Moderna has a therapeutic, mRNA-3705, which encodes MUT. They are enrolling a Phase 1/2 clinical study (NCT04899310) with approximately 33 participants with elevated methylmalonic acid due to MUT deficiency. The main goals of the study are to assess the safety, pharmacokinetics, and pharmacodynamics of mRNA-3705 for dose optimization. Participants who complete the treatment period will be offered participation in the mRNA-3705 extension study.??

3. Glycogen Storage Disease Type 1a (GSD1a)??

GSD1a is an inherited disorder caused by deficiency of the enzyme glucose-6-phosphatase (G6Pase), which normally cleaves glycogen to produce free glucose. When this enzyme is deficient, hypoglycemia and lactic acidosis can result. The liver is the first organ affected since it is the principal site of gluconeogenesis, and there is a life-long risk of liver cancer.?

A Moderna-led collaborative research effort found that m1ψ-substituted IVT mRNA encoding G6Pase delivered repeatedly in a mouse of GSD1a was well-tolerated and resulted in the management of life-threatening hypoglycemia (Cao et al.?2021).??

A Moderna-sponsored Phase 1 trial (NCT05095727) of this potential therapeutic formulation (mRNA-3745) is currently enrolling an estimated 18 adult participants with GSD1a for a dose-escalation study to evaluate safety and tolerability. Pharmacokinetic and pharmacodynamic responses to mRNA-3745 will also be characterized in this study.??

4. Ornithine Transcarbamylase (OTC) Deficiency?

The urea cycle functions to eliminate toxic ammonia by converting it to urea for excretion in urine. The most proximal enzyme in the urea cycle is ornithine transcarbamylase (OTC); partial or complete inactivity of OTC results in episodes of hyperammonemia that cause neurological damage if not fatal. The current standard of care includes daily administration of “ammonia scavengers” and blood dialysis when necessary. Despite these treatments, 60% of surviving children with OTC deficiency have disabling neurological complications. Because the only cure for OTC deficiency to date is a liver transplant, there remains an urgent unmet need for a more effective treatment of this disease (Yu et al.?2022).?

Arcturus Therapeutics has reported full restoration of OTC activity in an OTC-deficient mouse model using an LNP-encapsulated OTC mRNA. Two clinical trials of this therapeutic formulation (ARCT-810) are in progress (Yu et al.?2022). A Phase 1b study (NCT04442347) will assess safety, tolerability, and pharmacokinetics of ascending doses in an estimated 12 adult participants with OTC deficiency. In a Phase 2 study (NCT05526066), approximately 24 OTC deficiency patients will be randomized (3:1) to receive up to 6 doses of ARCT-810 or placebo, each separated by 14 days.?

In September 2022, Moderna announced it also has a candidate for treating OTC deficiency, although no further information was given.??

5. Phenylketonuria (PKU)?

PKU is a genetic disease caused by deficiencies in phenylalanine metabolism resulting from mutations in the phenylalanine hydroxylase (PAH) gene. Indications of PKU are toxic levels of phenylalanine accumulation in plasma and tissues. In the brain, accumulations result in irreversible intellectual disability (Perez-Garcia et al.?2022).?

Arcturus has studied mRNA replacement therapy for PKU in a preclinical mouse model of the disease (Perez-Garcia et al.?2022). A full-length PAH-encoding mRNA was LNP-encapsulated and delivered to mice that carry a missense mutation in the PAH gene and develop toxic levels of phenylalanine. Administration of the LNP-PAH mRNA generated high levels of PAH protein in hepatocytes and restored phenylalanine metabolism in this mouse model. Together, these data were said to establish a proof-of-principle for a novel mRNA replacement therapy to treat PKU.??

However, there is currently no PKU study sponsored by Arcturus in the ClinicalTrials.Gov database. Moderna has announced that they have a candidate treatment for PKU, mRNA-3283, which encodes for human PAH.???

6. Fatal Infantile Cardioencephalomyopathy (FIC)?

Cytochrome c oxidase (COX) is the terminal enzyme complex of the mitochondrial electron transport chain (Tay et al., 2004). One of the genes needed for assembly and function of COX is termed SCO2, which encodes a protein subunit that is imported into mitochondria. Mutations in SCO2 have been described in patients with FIC, a disorder in which the heart muscle is structurally and functionally abnormal.?

Cell penetrating peptides (CPPs) are a class of agents of interest for intracellular delivery of drugs (Xie et al. 2020). CPPs non-covalently complexed to TriLink reporter mRNAs CleanCap? mCherry mRNA (5moU), enhanced green fluorescence protein (EGFP) mRNA, and Ovalbumin (OVA) mRNA have led to intracellular delivery and protein translation?in vitro?(Kim et?al.?2022).?An IVT-mRNA therapeutic approach for treating FIC is based on the covalent conjugation of mRNA-encoded functional SCO2 to a hexapeptide (HEX) CPP (Miliotou et al.?2021). The HEX-SCO2 mRNA conjugate showed significantly higher stability toward degradation by either fetal bovine serum or RNase A compared to non-conjugated SCO2 mRNA control. More importantly, incubation of SCO2/COX-deficient fibroblasts obtained from a patient led to?~~7-fold more SCO2-positive cells compared to non-conjugated SCO2 mRNA control.?

Based on these findings with SCO2 mRNA, and similar results with β-globin mRNA, Miliotou et al. suggested that mRNA conjugation to HEX represents a new and potentially generalizable delivery platform for other IVT mRNA therapeutics.??

Concluding Comments?

The examples presented here indicate positive progress for mRNA therapeutics in the rare diseases space. Information on the importance of rare disease research and how to find clinical trials are provided at the NIH Genetic and Rare Diseases (GARD)?website.??

On Rare Disease Day, the NIH hosts an event to raise awareness about rare diseases, the people they affect, and the NIH-sponsored research on rare diseases. If you want to be involved with this event, you can register to participate in person or virtually at their?website.??

Thousands of other events for Rare Disease Day happen globally. More information can be found at RareDiseaseDay.org.??