A phase IIb, open-label study to assess the efficacy, safety, pharmacodynamics and pharmacokinetics of multiple subcutaneous doses of BMN 045 (previously known as PRO045) in subjects with Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a chromosome X-linked recessive muscle
disorder, affecting 1/3500 newborn boys. Patients experience severe progressive
muscle weakness and wasting, leading to early morbidity and mortality. DMD is
caused by alterations in the gene coding for the protein dystrophin which leads
to little or no dystrophin being produced. Dystrophin is essential for the
integrity and functioning of muscle fibres . Becker muscular dystrophy is also
caused by mutations in the DMD gene, but these maintain the open reading frame,
yield semi-functional dystrophin proteins, and result in a typically much
milder phenotype and longer lifespan.
First signs of muscle weakness typically occur before the age of 4 years and
gradually progress to include skeletal muscles in the arms, legs and trunk.
Over time, heart muscle and respiratory muscles are affected. Even with more
recent clinical interventions, such as glucocorticosteroid treatment and
ventilatory support, DMD patients are usually wheelchair-bound by their
mid-teens and generally die in their twenties/early thirties.
Although glucocorticosteroids and assisted ventilation have altered the natural
course of DMD, there is still no effective treatment for the primary cause of
the disease. A promising therapeutic strategy is treatment with antisense
oligonucleotides that induce specific exon skipping during pre-mRNA splicing,
aimed at reading frame correction and production of a Becker-like transcript.
Although the functionality of the resulting protein may vary, this treatment
could delay or even stop disease progression and improve remaining muscle
function.
Exon skipping provides a mutation-specific, and thus personalized, therapeutic
approach for DMD patients. As mutations cluster around exons 45 to 55, the
skipping of one specific exon may be therapeutic for many patients with
different mutations. The skipping of exon 45 applies to a subset of patients
(~8%). Non-clinical studies on BMN 045 have shown its skipping efficiency,
safety and favourable PK profile, and proof-of-concept for therapeutic exon 45
skipping therapy; inducing novel dystrophin production in cultured muscle cells
from a DMD patient with a relevant mutation.
The aim of BioMarin Pharmaceutical's Inc. therapeutic strategy is to use RNA
modulation (exon skipping) to change the severe form of the disease (DMD) into
a milder form (BMD), in the expectation of a much improved outcome. The
clinical phenotype of BMD is variable and depends on the resulting levels of
dystrophin and/or the functionality of the truncated protein. Cases have been
described that are very severe and similar to DMD, others can be very mild
(muscle cramps only) or even asymptomatic. Remarkably, very mild BMD patients
have been described, who lack up to 67% of the central rod domain. This
suggests, that despite large deletions, a partially functional dystrophin can
be generated.

Primary objective:
To assess the efficacy of BMN 045 after 48 weeks treatment in ambulant subjects
with Duchenne muscular dystrophy.

Secondary objectives:
To assess the safety and tolerability of BMN 045 after 48 weeks of treatment in
all study subjects with Duchenne muscular dystrophy including subjects from the
dose-escalation phase of the study.
To determine the pharmacokinetics of BMN 045 at different dose levels after
subcutaneous administration in subjects with Duchenne muscular dystrophy.
To assess the pharmacokinetics, bioavailability and safety of BMN 045 following
single intravenous dose administration at different dose levels.
To assess the pharmacodynamics of BMN 045 at different dose levels after
subcutaneous administration in subjects with Duchenne muscular dystrophy.
To assess trend in efficacy in all subjects with Duchenne Muscular Dystrophy
not included in the primary objective after 48 weeks of treatment

This is a phase IIb, open-label, multiple-dose study. The study consists of two
phases; a dose-escalation phase (with subsequent dose-titration) and a 48-week
treatment phase.

Dose-escalation phase:
On the assumption that dose-limiting toxicities do not occur, the
dose-escalation phase has the following design
Five groups of three subjects are planned. The BMN 045 starting doses for each
group are 0.15 mg/kg (Group 1), 1 mg/kg (Group 2), 3 mg/kg (Group 3), 6 mg/kg
(Group 4) and 9 mg/kg (Group 5). All doses will be administered by subcutaneous
(SC) injection once per week.
Groups will be started sequentially and all three subjects in each group will
ideally start dosing within the space of one week (the subjects within a group
will each be separated by a minimum of 2 days for safety reasons). The safety
data from at least the first 3 doses of BMN 045 for each subject in Group 1
will be reviewed by a Data and Safety Monitoring Board (DSMB) and assuming
there are no safety concerns, Group 2 may be started (i.e. at a higher dose).
It is anticipated that, due to practical reasons, Group 2 will not start dosing
until Group 1 has received at least 6 doses of BMN 045. Likewise, data from at
least the first 3 doses of BMN 045 in Group 2 (plus all available data from
Group 1) will be reviewed prior to starting Group 3, and similarly for Groups 4
and 5.
In parallel with starting the new dose groups, once a minimum of 12 weeks of
dosing has been completed in Group 2 and assuming acceptable safety data, all
subjects in Group 1 may have their dose increased (up-titrated) to the new dose
level (i.e. from 0.15 mg/kg up to 1 mg/kg). Likewise, once a minimum of 12
weeks of dosing has completed in Group 3 and assuming acceptable safety data,
all subjects in Groups 1 and 2 may have their dose up-titrated to the new dose
level (i.e. from 1 mg/kg up to 3 mg/kg), and similarly for Group 4. It is
therefore anticipated that all subjects will receive at least 18 weeks of
dosing at their initial dose level, followed by at least 6 weeks of dosing at
each subsequent dose level.
Finally, once 12 weeks of dosing has completed in Group 5 and assuming
acceptable safety data, all subjects in Groups 1, 2, 3 and 4 may have their
dose up-titrated to the new dose level (i.e. from 6 mg/kg up to 9 mg/kg).
All efficacy, safety, PD and PK data from all subjects collected up to Week 12
of Group 5 will be reviewed by the Sponsor and DSMB (all subjects will continue
dosing whilst this review is ongoing).

48-week treatment phase:
At the end of the dose-escalation phase, a further 48 weeks of dosing for all
subjects who participated in the escalation phase is planned in the treatment
phase. In addition, a further group of 30 subjects will be recruited to enable
methodologically valid assessment of the primary efficacy endpoint (6MWD) at
the selected dose. The treatment phase will involve all subjects receiving the
same dose regimen (either continuous or intermittent) which will be determined
on the basis of emerging safety, tolerability, pharmacodynamic (PD) and
pharmacokinetic (PK) data from the dose-escalation phase.

All 15 subjects participating in the dose-escalation phase will enter the
48-week treatment phase, but will not be included in the assessment of the
primary efficacy endpoint. Subjects may continue at 9 mg/kg (or the maximum
tolerated dose, if lower) for the 48 weeks, or alternatively the dose and or
dosing regimen in the treatment phase may be chosen for all subjects based on
emerging data as described previously. At the end of the 48 weeks, all subjects
will stop dosing and will have a follow-up period of 21 weeks after the last
administration of BMN 045 . Any subjects who withdraw will also enter the
follow-up period (assuming consent is not withdrawn).


Dose-limiting toxicities:
If dose-limiting toxicities occur, the design will be modified depending on
when the toxicities occur and the nature of the toxicities. Potential changes
include:
If dose-limiting toxicity occurs in 1 of the 3 subjects in Group 1, a further 3
subjects may be recruited to this group (i.e. 6 subjects in total at 0.15 mg/kg
BMN 045). If similar
dose-limiting toxicity occurs in 2 or more subjects at this dose level, the
inclusion of any remaining new subjects planned at that dose level will be
discontinued, and dose-escalation may be stopped after consultation with the
DSMB.
If the dose-limiting toxicity in Group 1 occurs prior to dosing Group 2, then
the start of Group 2 will be delayed until the new subjects in Group 1 have
been dosed for at least the same time period as the original subjects were when
the toxicity occurred. If dosing in Group 2 has already started, then the DSMB
will be consulted to agree continuation of the study as planned, or
down-titration of Group 2, following review of all relevant safety data. The
same principle will apply to subsequent groups.

If dose-limiting toxicity occurs in 1 of the 3 subjects in Group 2 (and
assuming none were observed in Group 1) and depending on the nature and/or
timing of the event, and after discussions with the Medical Monitor and
Sponsor, one of two possible scenarios will be implemented; 1) up to 3 subjects
in Group 1 will be allowed to titrate up to this dose once Group 2 reaches 12
weeks of dosing (whilst any other subjects remain at the lower dose until it is
confirmed that no further dose-limiting toxicities are observed in these new
subjects within the timeframe of the initial dose-limiting toxicity), or 2) up
to 3 new subjects may be recruited to Group 2 prior to escalating Group 1. If
no further dose-limiting toxicities occur in the new subjects within 12 weeks,
then Group 1 may be escalated as initially planned. The same principle will be
applied to any dose-limiting toxicity occurring in 1 of 3 three subjects in
Groups 3, 4 or 5, where either a maximum of 3 subjects from the combined lower
dose group may be allowed to titrate to the higher dose, or 3 new subjects may
be recruited. In the absence of further dose-limiting toxicities, the remaining
subjects may then titrate to the higher dose following the appropriate
time-window.

If more than one subject has a dose-limiting toxicity at any given dose level,
dose-escalation and/or titration will be stopped after consultation with the
DSMB.
If dose-escalation and/or titration is stopped due to dose-limiting toxicities
at the highest dose level, the study may continue with subjects moved to (or
kept at) a lower dose level and/or started on an intermittent dosing regimen,
if deemed appropriate after consultation with the DSMB. The highest dose given,
that was not associated with dose-limiting toxicity will be considered to be
the maximum tolerated dose (MTD).
In the absence of any dose limiting toxicities in any given dose group,
subjects who discontinue for any non-safety related reason prior to completing
5 weeks of dosing, will be replaced.

Doses with the IP, BMN 045, will be administered by subcutaneous (SC) injection
once per week.
Five groups of three subjects are planned in the dose-escalation phase. The
proposed starting doses in each group are as follows:
Group 1: 0.15 mg/kg BMN 045
Group 2: 1 mg/kg BMN 045
Group 3: 3 mg/kg BMN 045
Group 4: 6 mg/kg BMN 045
Group 5: 9 mg/kg BMN 045

Dose groups will be started sequentially, and all three subjects in each group
will ideally start dosing within the space of one week (the subjects within a
group will each be separated by a minimum of two days for safety reasons). The
safety data from at least the first 3 doses of BMN 045 for each subject in
Group 1 will be reviewed by a Data Safety and Monitoring Board (DSMB) and
assuming there are no safety concerns, Group 2 will be started at the dose
recommended by the DSMB (i.e. at a higher dose). This procedure will continue
for all groups.

Prior to moving to the treatment phase (30 patients and 15 patients from
dose-escalation phase), the dose will be determined by examining a number of
parameters from the dose-escalation phase, including:
- Safety and tolerability
- Dystrophin expression
- PK
- Tissue concentration levels
- Additional cellular biomarkers (exploratory)
- MRS (exploratory)

As DMD subjects lose function month on month during the normal course of their
disease, a gap of up to 12 months whilst the next study is initiated is not
felt to be appropriate. Many subjects would no longer be eligible to enter the
treatment phase on the optimal dose and this would impact the available subject
numbers for the treatment phase. All Subjects from the dose-escalation phase
will continue into the treatment phase for safety and secondary efficacy
analysis.

The expected duration of the study is in total:
Screening period: 2 weeks
Dose-escalation phase: Group1 39 weeks up to 1 year
Treatment phase: 48 weeks
Follow-up period: 21 weeks

DMD is a lethal disease for which at present no effective treatment is
available. In view of the observed toxicity profile in non-clinical studies and
the experience obtained with compounds with similar chemistry in clinical
studies, as well as the proposed safety management in the study, it is
considered acceptable to initiate the clinical development of BMN 045.

This is the first time that BMN 045 is studied in humans. The most common side
effects reported with similar oligonucleotides are: injection site reactions,
changes in hepatic and renal protein levels and decrease of platelets in the
blood. Furthermore pro-inflammatory effects have been observed. Other risks are
as follows: a small bleeding at the place of injection or at the place where
the blood is drawn, pain at the place where the biopsies are taken, the site of
the biopsy may feel numb or become infected, a scar at the place of biopsy and
it is possible that the strength of the muscle may be slightly reduced in the
short term, and a reaction to the general anaesthesia.

Patients will receive standard treatment, in addition patients will receive an
injection every week with the study drug.
There are risks involved in joining this study and also the burden is
increased, as patients need an injection every week and blood is drawn
regularly. However, if this treatment is a succes in these patients, there will
be a change in the severity of their disease and it is expected that this will
lead to an improved outcome.