PRODUCTS

EN101

EN101 FOR MYASTHENIA GRAVIS

INTRODUCTION

In December 2007, Amarin acquired Ester Neurosciences Limited (Ester), a private research and development company based in Israel. As a result of the acquisition, Amarin gained access to EN101 and its underlying platform technology.

EN101 is an orally delivered oligonucleotide with complementary mechanisms of action. As an antisense agent it preferentially suppresses the "read-through" or "R" isoform (AChE-R) of acetylcholinesterase (AChE). This enhances neuromuscular functioning while avoiding the negative cholinergic effects currently observed with conventional, non-selective acetylcholinesterase inhibitors. The following animation depicts the potential role for EN101 in myasthenia gravis as an antisense agent.

EN101 also acts on re-balancing innate immunity features, which are often impaired by conventional acetylcholinesterase inhibitors. By elevating acetylcholine levels EN101 further reduces circulating pro-inflammatory cytokines through the "cholinergic anti-inflammatory reflex".
Myasthenia gravis (MG) is the first target indication for which EN101 is undergoing clinical development. MG is a chronic disease characterized by fatigable weakness of muscles due to autoimmune attack on acetylcholine receptors at the neuromuscular junction, and the resulting interference with nerve-to-muscle signaling. Since acetylcholine action is regulated by AChE, and since MG is characterized by under stimulation of the muscles, drugs blocking the activity of AChE have proven an effective palliative treatment for this disease. The prevalence of myasthenia gravis in the United States is estimated at 14-20 per 100,000 population, approximately 42,000 to 60,000 cases in the United States (more on Myasthenia Gravis).

The current standard of care for MG includes a combination of AChE inhibitors (neostigmine, pyridostigmine, physostigmine), steroids, immunosuppressants, plasmapheresis, intravenous immunoglobulins and thymectomy. However, as EN101 is intended primarily for use as a first line of treatment in MG, direct competition to EN101 is most likely the currently available AChE inhibitors for MG.

According to our research, one of the main drawbacks of the AChE inhibitors is their side effect profile e.g. drooling, loose stools, hypersalivation. Excessive medication of such AChE inhibitors in MG can lead to cholinergic crisis characterized by severe generalized weakness and respiratory failure. Another drawback of current AChE inhibitors is their dosing regimen - require multiple daily dosing (up to 5 pills a day, more in some cases). AChE inhibitors also appear to be only moderately effective, wearing off in the majority of patients after a few months. After this time patients are typically given corticosteroids and / or immunosuppressants, both of which are associated with long term side effects.

For more information on myasthenia gravis please refer to http://www.myasthenia.org/

Intellectual Property

EN101 and its underlying platform messenger RNA silencing technology are protected by a number of granted patents and pending applications in a number of territories worldwide, including the US and Europe. EN101, specifically, is protected by a granted composition of matter patent in the US which extends to 2022.

EN101 has been designated an orphan drug in both the US and Europe, which means it will have seven years marketing exclusivity post its approval in the US, and up to 10 years in Europe. 

DEVELOPMENT TO DATE IN MYASTHENIA GRAVIS

To date, EN101 has demonstrated safety and efficacy in a Phase Ib clinical trial and Phase IIa exploratory trial. Furthermore, the complementary mechanisms of action and data generated in preclinical inflammatory models, suggests steroid sparing and immunosuppressive avoidance properties.

Preclinical Development

In order to evaluate the potential therapeutic use of EN101 in improving muscle activity in MG patients, a set of in-vivo studies with EAMG animal model were designed.

Experimental Autoimmune Myasthenia Gravis (EAMG) shares many characteristic features of human MG: (a) muscle weakness (aggravated by exercise and relieved by cholinesterase inhibitors) (b) decrementing compound muscle action potentials and low amplitude miniature endplate potentials (c) simplification of the postsynaptic membrane at neuromuscular junctions (d) circulating autoantibodies to nicotinic AChR (e) T-cell responding to AChR.

In EAMG, electromyographic (i.e. electrical properties of skeletal muscle) abnormalities were alleviated by nanomolar doses of EN101. Whereas animals treated with placebo or conventional anticholinesterases continued to deteriorate. A four week daily oral administration of EN101 improved survival, neuromuscular strength and clinical status in moribund EAMG rats.1

EN101 Phase Ib Clinical Study

A Phase Ib clinical trial was conducted by Ester in 2002 to assess the safety, efficacy and pharmacokinetics of oral EN101 in MG patients.2,3

This study was a multicenter (Israel and UK), open label, non-placebo controlled trial conducted in 16 patients with stable MG receiving at least 180mg of pyridostigmine daily. For assessment of myasthenia status, the Quantitative MG (QMG) score was used. The QMG score is used commonly in MG studies and measures the strength of 13 different muscle groups. Escalating oral doses of EN101 (10μg/kg, 50μg/kg and 150μg/kg) were given in the first day, followed by a daily dose of 500μg/kg for three days. Patients were monitored for one month thereafter.

Baseline QMG score was 14.9 (±7.25 SD). Of the 15 patients evaluated for efficacy, all showed an improvement in QMG score on day four as compared with baseline. The overall mean QMG change from baseline was 6.13 (±4.5 SD), a mean 46.5% improvement (p< 0.01).

EN101 was well tolerated with no major adverse events. Four patients participated in a four week extension study and no adverse events related to EN101 were reported..

EN101 Phase Ib Clinical Study

A Phase Ib clinical trial was conducted by Ester in 2002 to assess the safety, efficacy and pharmacokinetics of oral EN101 in MG patients.2,3

This study was a multicenter (Israel and UK), open label, non-placebo controlled trial conducted in 16 patients with stable MG receiving at least 180mg of pyridostigmine daily. For assessment of myasthenia status, the Quantitative MG (QMG) score was used. The QMG score is used commonly in MG studies and measures the strength of 13 different muscle groups. Escalating oral doses of EN101 (10μg/kg, 50μg/kg and 150μg/kg) were given in the first day, followed by a daily dose of 500μg/kg for three days. Patients were monitored for one month thereafter.

Baseline QMG score was 14.9 (±7.25 SD). Of the 15 patients evaluated for efficacy, all showed an improvement in QMG score on day four as compared with baseline. The overall mean QMG change from baseline was 6.13 (±4.5 SD), a mean 46.5% improvement (p< 0.01).

EN101 was well tolerated with no major adverse events. Four patients participated in a four week extension study and no adverse events related to EN101 were reported.

EN101 Exploratory Phase IIa Clinical Study

In June 2009, Amarin announced the results of an exploratory Phase 2a multi-centre, dose-ranging, cross-over clinical study of EN101 in patients with myasthenia gravis. The primary objective of the study, for which interim results had previously been announced, was to assess the efficacy and safety of three doses of EN101 each given orally once daily for one week in patients with myasthenia gravis.

The results of the study indicate that 10mg, 20mg and 40mg of EN101 resulted in a statistically significant reduction in Quantitative Myasthenia Gravis (QMG) score from baseline of 11.8% (p=0.001), 16.8% (p<0.001) and 20.3% (p<0.001) respectively. Importantly, EN101 was also shown to be safe and well tolerated.
The 31-patient study was performed in six centers in the U.K., Israel and Serbia. Each dose of EN101 was administered to patients for one week and was separated by a one week wash out on pyridostigmine, often the current first line treatment for myasthenia gravis. Efficacy was assessed by evaluating changes in the QMG score, an established questionnaire that evaluates signs and symptoms of myasthenia gravis.

The results from this exploratory Phase 2a study support the further development of EN101 for myasthenia gravis, for which Amarin is now seeking a partner.

REFERENCES

1. Brenner et al - FASEB J. 17, 214–222 (2003) - “The role of readthrough acetylcholinesterase in the pathophysiology of MG”.
2. Argov et al – Neurology 2007;69:699-700 – “Treatment of Human Myasthenia Gravis with Oral Antisense Suppression of Acetylcholinesterase”;
3. Kaminski – Neurology 2007;69:629-630 – “Restoring the Balance at the Neuromuscular Junction”.

FURTHER READING

• Admec et al – Behavioural Brain Research 2008 - “The Role of the Read Through Variant of Acetylcholinesterase in Anxiogenic Effects of Predator Stress in Mice”
• Evron et al – Neurodegenerative Dis 2005;2:16-27 – “RNA-Targeted Suppression of Stress Induced Allostasis in Primate Spinal Cord Neurons”
• Pollak et al – Ann Neurol 2005;57:741-745 – “Acetylcholinesterase Inhibitors Reduce Brain and Blood Interleukin-1beta Production”
• Soreq et al - J Mol Med 2000;78:228-236 – “Antisense Approach to Isoform Specific Blockade of Acetylcholinesterase”
• Nijholt et al – Molecular Psychiatry 2004;9:174-183 – “Stress Induced Alternative Splicing of Acetylcholinesterase Results in Enhanced Fear Memory and Long-term Potentiation”
• Shohmai et al – J Mol Med 2000;78:228-236 – “Antisense Prevention of Neuronal Damages Following Head Injury in Mice”
• Gillboa-Geffen et al – Blood, 109, 4383-4391 (2007) - “The Thymic Theme of Acetylcholinesterase Splice Variants in Myasthenia Gravis”
• Perry et al – Neoplasia 2004;6:279-286 – “CREB Regulates AChE-R-Induced Proliferation of Human Glioblastoma Cells”