Antisense therapy


Antisense therapy is a form of treatment that uses antisense oligonucleotides to target messenger RNA. ASOs are capable of altering mRNA expression through a variety of mechanisms, including ribonuclease H mediated decay of the pre-mRNA, direct steric blockade, and exon content modulation through splicing site binding on pre-mRNA. Several ASOs have been approved in the United States, European Union, and elsewhere.

Nomenclature

The common stem for antisense oligonucleotides drugs is -rsen. The substem -virsen designates antiviral antisense oligonucleotides.

Pharmacokinetics and pharmacodynamics

Half-life and stability

ASO-based drugs employ highly modified, single-stranded chains of synthetic nucleic acids that achieve wide tissue distribution with very long half-lives. For instance, many ASO-based drugs contain phosphorothioate substitutions and 2' sugar modifications to inhibit nuclease degradation enabling vehicle-free delivery to cells.

''In vivo'' delivery

Phosphorothioate ASOs can delivered to cells without the need of a delivery vehicle. ASOs do not penetrate the blood brain barrier when delivered systemically but they can distribute across the neuraxis if injected in the cerebrospinal fluid typically by intrathecal administration. Newer formulations using conjugated ligands greatly enhances delivery efficiency and cell-type specific targeting.

Approved therapies

Batten disease

Milasen was a novel individualized therapeutic agent that was designed and approved by the FDA for the treatment of Batten disease. This therapy serves as an example of personalized medicine.
In 2019, a report was published detailing the development of milasen, an antisense oligonucleotide drug for Batten disease, under an expanded-access investigational clinical protocol authorized by the Food and Drug Administration. Milasen "itself remains an investigational drug, and it is not suited for the treatment of other patients with Batten's disease" because it was customized for a single patient's specific mutation. However it is an example of individualized genomic medicine therapeutical intervention.

Cytomegalovirus retinitis

, was approved by the U.S. FDA in Aug 1998 as a treatment for cytomegalovirus retinitis.

Duchenne muscular dystrophy

Several morpholino oligos have been approved to treat specific groups of mutations causing Duchenne muscular dystrophy. In September 2016 eteplirsen received FDA approval for the treatment of cases that can benefit from skipping exon 51 of the dystrophin transcript. In December 2019 golodirsen received FDA approval for the treatment of cases that can benefit from skipping exon 53 of the dystrophin transcript.

Familial chylomicronaemia syndrome

was approved by the European Medicines Agency for treatment of familial chylomicronaemia syndrome in May 2019.

Familial hypercholesterolemia

In January 2013 mipomersen was approved by the FDA for the treatment of homozygous familial hypercholesterolemia.

Hereditary transthyretin-mediated amyloidosis

received FDA approval for the treatment of hereditary transthyretin-mediated amyloidosis in October 2018. The application for inotersen was granted orphan drug designation. It was developed by Ionis Pharmaceuticals and licensed to Akcea Therapeutics.

Spinal muscular atrophy

In 2004, development of an antisense therapy for spinal muscular atrophy began. Over the following years, an antisense oligonucleotide later named nusinersen was developed byIonis Pharmaceuticals under a licensing agreement with Biogen. In December 2016, nusinersen received regulatory approval from FDA and soon after, from other regulatory agencies worldwide.

Investigational therapies

Current clinical trials

As of 2020 more than 50 antisense oligonucleotides were in clinical trials, including over 25 in advanced clinical trials.

Phase III trials

Amyotrophic lateral sclerosis
Tofersen is currently being tested in a phase 3 trial for amyotrophic lateral sclerosis due to mutations in the SOD1 gene. Results from a phase 1/2 trial have been promising. It is being developed by Biogen under a licensing agreement with Ionis Pharmaceuticals.
Hereditary transthyretin-mediated amyloidosis
A follow-on drug to Inotersen is being developed by Ionis Pharmaceuticals and under license to Akcea Therapeutics for hereditary transthyretin-mediated amyloidosis. In this formulation the ASO is conjugated to N-Acetylgalactosamine enabling hepatocyte-specific delivery, greatly reducing dose requirements and side effect profile while increasing the level of transthyretin reduction in patients.
Huntington's disease
Tominersen is currently being tested in a phase 3 trial for Huntington's disease. It is being developed by Roche under a licensing agreement with Ionis Pharmaceuticals.

Phase I & II trials

Clinical trials are ongoing for several diseases and conditions including:
Acromegaly, age related macular degeneration, Alzheimer's disease, amyotrophic lateral sclerosis, autosomal dominant retinitis pigmentosa, beta thalassemia, cardiovascular disease, centronuclear myopathy, coagulopathies, cystic fibrosis, Duchenne muscular dystrophy, diabetes, epidermolysis bullosa dystrophica, familial chylomicronemia syndrome, frontotemporal dementia, Fuchs' dystrophy, hepatitis B, hereditary angioedema, hypertension, IgA nephropathy, Leber's hereditary optic neuropathy, multiple system atrophy, non-alcoholic fatty liver disease, Parkinson's disease, prostate cancer, Stargardt disease, STAT3-expressing cancers, Usher syndrome.

Preclinical development

Several ASOs are currently being investigated in disease models for Alexander disease, ATXN2 and FUS amyotrophic lateral sclerosis, Angelman syndrome, Lafora disease, lymphoma, multiple myeloma, myotonic dystrophy, Parkinson's disease, Pelizaeus–Merzbacher disease, and prion disease, Rett syndrome, spinocerebellar Ataxia Type 3.