Promising new drug candidates for
Duchenne Muscular Dystrophy
Dominic Wells
Department of Comparative Biomedical Sciences
Royal Veterinary College London
Disclosures
Member of the Scientific Advisory Board for Akashi
Therapeutics.
Grant funding for DMD work from a range of charities,
DoH and research councils.
Have conducted DMD mouse model studies for
Proximagen and AstraZeneca and have consulted for a
number of other companies.
Member of MDUK, Telethon, AFM grant committees.
Duchenne muscular dystrophy
© Imperial College London
Pa
ge
Types of mutations associated with DMD
Large deletions and
duplications
Splice site mutations
Small deletions and
insertions
Nonsense mutations
Missense mutations
From Roberts at al, 1994
Most mutations disrupt the open reading frame leading to a failure
to fully translate the mRNA and produce a functional protein
DMD pathology
Absence of dystrophin
Activity induced damage
Loss of cell signaling
Influx of calcium
Oxidative stress
Nitrosylation
Hypercontraction
Mitochondrial damage
Activation of proteases
Necrosis
Inflammation and fibrosis
Loss of strength
Failure of regeneration
http://neuromuscular.wustl.edu/pathol/dmdpath.htm
Longevity/QoL increased with:
Respiratory assistance with positive pressure ventilation.
Appropriate drug treatment of any developing
cardiomyopathy and potential prevention with presymptomatic treatment.
Corticosteroids can slow the progress of DMD, maintain
ambulation beyond 12, reduce scoliosis and maintain
FVC
However progressive decline in muscle function reduces
independence – so goal of experimental therapies is to
halt or reverse this progressive decline
Loss of reading frame
In frame mutation
X
leads to unstable protein
Duchenne muscular dystrophy
generates an internally deleted protein
Becker muscular dystrophy
Gene Addition
e.g. microdystrophin
via viral vector.
Cell therapy.
DNA
RNA
Modify RNA
e.g. exon-skipping
Protein
Modify translation
e.g. gentamycin
PTC 124 (ataluren)
“Genetic” therapies
Gene therapy
Clinical trials in muscular dystrophy - AAV
2006-2009 Mendell (Ohio)/Asklepios Biopharmaceutical
(Xiao Xiao and Jude Samulski) – AAV2.5-microdystrophin
(Biostrophin) for DMD
• Intramuscular injection in 6 patients at two dose levels, no serious
adverse events. But also no significant microdystrophin expression
and evidence of autoreactive T cells (Mendell et al., 2010).
• However was a safe clinical trial ! (Bowles et al., 2011).
Several other studies have used AAV to transfer
sarcoglycans – e.g. Mendell et al 2010
LGMD2D
Gene
therapy
clinical
trial
Mendell et al, 2010
Follistatin gene transfer
• Mendell lab showed local AAV delivery of follistatin (antagonist to
myostatin) increased muscle mass in non-human primates (Kota
et al., 2009).
• Gene therapy trial run in BMD and IBM patients with evidence of
safety and some functional improvement (Mendell et al., Mol
Ther. 2014).
New gene therapy trials
• Follow on from the previous trials:
• Milo Therapeutics. rAAV1.CMV.huFollistatin344.
Treatment for DMD, Phase 1/2, injections into
gluteals, quadriceps and tibialis anterior.
• SOLID ventures. rAAVrh74MCKmicroDystrophin.
Phase 1 intramuscular injections into the EDB.
Cell therapies
Cell therapy human clinical trials
• Potential to improve muscle regeneration and restore
dystrophin but will not make new muscle per se
• 1990s – myoblast transplants – unsuccessful
• Trembley (Canada) continuing with a Phase 1/2
clinical trials with local delivery to a specific muscle.
• Mesoangioblast trial run by Guilio Cossu in Italy
• Stem cell trials (Phase 1/2) ongoing in Turkey and
India.
• Cardiosphere derived cells delivered via
intracoronary infusion (Capricor, USA, Phase 1/2)
Exon-skipping
Exon skipping as a treatment for DMD
Exon skipping – clinical trials
• Two chemistries taken to clinical trial – 2OmePS and
PMO. Evidence of clinical benefit – arresting the
progression of the disease for boys eligible for exon 51
skipping.
• Other exon targets current in clinical trial (44, 45, 53).
• Other antisense reagents:
– Cell penetrating peptides linked to PMO
– TricycloDNA oligonucleotides
Read-through of premature stop mutations
Read-through of
premature stop mutations
• Approximately 15% of DMD patients have a premature stop
mutation.
• Aminoglycoside antibiotics can “read-through” these mutations but
are too toxic for long-term human use.
• High-throughput screening identified a much less toxic compound
with similar activity (PTC124 – Ataluren).
• EU conditional approval as Translarna for a restricted age range.
Pharmacological approaches to DMD therapy
Up-regulation of utrophin to treat DMD.
Increasing muscle mass.
Inhibiting the pathological process.
Improving the bllod supply to muscles
Nutritional supplements.
All the above use compounds that can be delivered
systemically thus offering the promise of treating
all affected muscles.
Many compounds are already in use in man.
Utrophin as a substitute for dystrophin
Utrophin similar to
dystrophin but does not
localise nNOS
Expression of utrophin
developmentally precedes
dystrophin
Can correct mdx mouse
SMT C1100 : Utrophin Inducer for DMD
Currently in Phase 1b clinical trial (Summit).
Biglycan: Stabilises utrophin at the muscle
membrane (Tivorsan)
Anti-inflammatory / anti-fibrotics
• Corticosteroids
– current standard of care where tolerated but have
significant side effects
• Potential alternatives (most act by inhibiting NFkB):
•
•
•
•
•
Halofugionone (HT-100 Phase ½, Akashi Therapeutics)
CAT-1000 (Phase ½, Catabasis)
VBP-15 (about to enter trial, ReveraGen)
Nemo-binding domain (NBD) peptide
And others……..
Increasing muscle mass
•Myostatin is a negative regulator of muscle mass
•Release of soluble form of the Activin IIB receptor to block myostatin signaling
(Acceleron - ACE-031). Trial stopped because of bleeding.
•Antibody to block myostatin binding. Pfizer PF-06252616 (phase 1/2).
•Adnectin to block myostatin. Bristol-Myers Squib BMS-986089 (Phase 1/2)
•Other strategies: Propeptide blocker, Inhibition of myostatin production (siRNA)
Improving mitochondrial function +/- biogenesis
• Mitochondria are a significant calcium store but get
overwhelmed in DMD.
• Mitochondrial biogenesis stimulated via PGC1a. A number of
different drugs (approved and experimental) can do this. A
variety of drugs will also improve function of existing
mitochondria.
• Phase III Double-Blind, Randomised, Placebo-Controlled Study
of the Efficacy, Safety and Tolerability of Idebenone (Catena®)
in 10-18 Year Old Patients With Duchenne Muscular Dystrophy
showed prevention of respiratory decline (Buyse et al., 2015)
but only in patients not taking corticosteroids
Selected other mitochondrial drugs
• DeBio 025 (Solid Biosciences).
• Metformin (Clinical trials in Basel)
• PGC1alpha activators
Improving blood flow in muscle and heart
• The loss of the membrane associated nNOS means
that muscle blood flow during exercise is impaired.
• Tadalafil and Sildenafil (Cialis and Viagra) – PDE5
inhibitors – have been trialled in DMD. Tadalafil has
shown the most promising results
A new candidate therapeutic
• Simvastatin has shown remarkable effectiveness in
reducing dystrophic pathology and increasing
muscle force in mdx mice treated from 3, 12 and 52
weeks old (Whitehead et al., Oct 2015 PNAS).
Summary
• Exciting time for those working on or affected by a
neuromuscular disease.
• Increasing interest from big and small pharma/biotech.
• Wide range of possibilities, many in or about to enter
clinical trial.
• Vital to have good translational studies in pre-clinical
models
• Clinical trial design is critical for good go/no-go
decisions
• Combination therapies are the likely long-term outcome