ONWARD Phase II Trial Will Assess Therapeutic Benefit of Oral Cladribine
   Added-on to New Formulation of Rebif(R) in Multiple Sclerosis Patients

    GENEVA, Switzerland, January 24 /PRNewswire-FirstCall/ -- Merck Serono
(virt-x: SERO and NYSE: SRA) announced today that it has begun the ONWARD
(Oral Cladribine Added ON To Rebif New Formulation in Patients With Active
Relapsing Disease) Phase II study. The ONWARD study will evaluate the
safety, tolerability and efficacy of two dose regimens of Merck Serono's
proprietary oral formulation of cladribine when added to the new
formulation of Rebif(R) (interferon beta-1a) in multiple sclerosis (MS)
patients with active disease despite treatment with Rebif(R). Oral
cladribine is currently also evaluated as a monotherapy in a fully enrolled
Phase III pivotal trial (the CLARITY study) for first-line treatment of
relapsing forms of MS. The new formulation of Rebif(R) is under regulatory
review by the European Medicines Agency, the US Food and Drug
Administration and other healthcare authorities.
    "Multiple sclerosis patients with signs of active disease while on
treatment with a disease modifying drug may benefit from adding another
agent with a different mechanism of action, to complement and increase the
overall efficacy while maintaining an acceptable safety and tolerability
profile," said Bruno Musch, Merck Serono's Head of Neurology Clinical
Development. "The different mechanism of action and the oral intermittent
administration of oral cladribine make it a potentially useful add-on
therapy to Rebif(R) at a critical time of disease progression."
    "Oral cladribine is currently being evaluated as a monotherapy in the
CLARITY Phase III pivotal study and is on track to become the first oral
therapy for first-line treatment of multiple sclerosis", said Franck
Latrille, Merck Serono's Head of Product Development. "We are now
initiating the ONWARD study as we believe that oral cladribine also has a
great potential as an add-on therapy, for patients who have signs of active
relapsing disease while on a treatment."
    The ONWARD study is a two-year (96 weeks), randomized, double-blind,
placebo-controlled, international trial. The trial will be conducted in 40
sites located in the United States and in Europe. It will involve 260 MS
patients who have experienced at least one relapse while taking Rebif(R)
during the year prior to study enrollment. Study participants will be
randomized in one of the three arms of the study to receive one of two
different dose regimens of oral cladribine or matching placebo tablets, in
addition to the new formulation of Rebif(R) 44 micrograms subcutaneous
three times a week. In the study, oral cladribine is given in two or four
treatment cycles in the first year, with each cycle consisting of daily
administration for four or five consecutive days, which means study
patients take oral cladribine therapy for only 8 to 20 days during that
year. In the second year, two treatment cycles are administered in all dose
regimens.
    The primary safety endpoints of the ONWARD study consist of a wide
range of safety and tolerability parameters measured during 96 weeks of
treatment. The primary efficacy endpoint is the mean change in the number
of new T1 gadolinium-enhanced lesions per subject per magnetic resonance
imaging (MRI) scan from baseline to 96 weeks.
    About oral cladribine
    Merck Serono's proprietary oral formulation of cladribine is currently
being evaluated in Phase III as a treatment for patients with relapsing
forms of multiple sclerosis (MS). Cladribine is a small molecule that
interferes with the behavior and the proliferation of certain white blood
cells, particularly lymphocytes, which are involved in the pathological
process of MS. Through its differentiated mechanism of action, oral
cladribine may offer a safe and effective new option to patients with MS.
    About Rebif(R)
    Rebif(R) (interferon beta-1a) is a disease-modifying drug used to treat
relapsing forms of multiple sclerosis (MS) and is similar to the interferon
beta protein produced by the human body. Interferon helps modulate the
body's immune system, fight disease and reduce inflammation.
    Rebif(R), which was approved in Europe in 1998 and in the US in 2002,
is registered in more than 80 countries worldwide. In the United States,
Rebif(R) is co-marketed by EMD Serono, Inc. (the US affiliate of Merck
Serono) and Pfizer Inc. Rebif(R) has been proven to delay the progression
of disability, reduce the frequency of relapses and reduce MRI lesion
activity and area[1]. Rebif(R) is not approved for treatment of chronic
progressive MS. Rebif(R) is available in a 22 mcg and 44 mcg ready-to-use
pre-filled syringe and a titration pack, and can be stored at room
temperature for up to 30 days if a refrigerator is not available.
    Most commonly reported side effects are injection site disorders,
flu-like symptoms, elevation of liver enzymes and blood cell abnormalities.
Patients, especially those with depression, seizure disorders, or liver
problems, should discuss treatment with Rebif(R) with their doctors.
    About Merck Serono and multiple sclerosis
    Merck Serono is a leader in multiple sclerosis (MS) with Rebif(R)
(interferon beta-1a), a disease-modifying drug used to treat relapsing
forms of MS, which is registered in more than 80 countries worldwide. In
addition to Rebif(R), the Company also offers a second therapy within its
US portfolio of MS therapies: Novantrone(R) (mitoxantrone for injection
concentrate) for worsening forms of MS. Full prescribing information for
these products can be obtained by contacting the Company or visiting its
website. Additional therapeutic options are currently under development at
Merck Serono, including oral cladribine, currently in Phase III and
potentially the first oral therapy for MS, as well as several products in
early stage development including: osteopontin, an MMP-12 inhibitor, a JNK
inhibitor and interferon beta:Fc. Merck Serono also is taking a leading
role in developing an understanding of the role of genetics in MS, with a
whole genome scan currently underway.
    About multiple sclerosis
    Multiple sclerosis (MS) is a chronic, inflammatory condition of the
nervous system and is the most common, non-traumatic, neurological disease
in young adults. The World Health Organization estimates that up to 2.5
million people suffer from MS worldwide. While symptoms can vary, the most
common symptoms of MS include blurred vision, numbness or tingling in the
limbs and problems with strength and coordination. The relapsing forms of
MS are the most common. Forward-looking statements
    Some of the statements in this press release are forward looking. Such
statements are inherently subject to known and unknown risks, uncertainties
and other factors that may cause actual results, performance or
achievements of Merck Serono S.A. and affiliates to be materially different
from those expected or anticipated in the forward-looking statements.
Forward-looking statements are based on Merck Serono's current expectations
and assumptions, which may be affected by a number of factors, including
those discussed in this press release and more fully described in Serono's
Annual Report on Form 20-F filed with the U.S. Securities and Exchange
Commission on February 28, 2006. These factors include any failure or delay
in Merck Serono's ability to develop new products, any failure to receive
anticipated regulatory approvals, any problems in commercializing current
products as a result of competition or other factors, our ability to obtain
reimbursement coverage for our products, the outcome of any government
investigations and litigation. Merck Serono is providing this information
as of the date of this press release, and has no responsibility to update
the forward-looking statements contained in this press release to reflect
events or circumstances occurring after the date of this press release.
    About Merck Serono
    Merck Serono is a global biotechnology leader, with sales in over 90
countries. The Company is the world leader in reproductive health, with
Gonal-f(R), Luveris(R) and Ovidrel(R)/Ovitrelle(R). It has strong market
positions in neurology, with Rebif(R), as well as in metabolism and growth,
with Saizen(R), Serostim(R) and Zorbtive(TM). The Company has recently
entered the psoriasis area with Raptiva(R). Merck Serono's research
programs are focused on growing these businesses and on establishing new
therapeutic areas, including oncology and autoimmune diseases.
    Bearer shares of Merck Serono S.A., the holding company, are traded on
the virt-x (SERO) and its American Depositary Shares are traded on the New
York Stock Exchange (SRA).
    About Merck
    Merck is a global pharmaceutical and chemical company with sales of EUR
6.3 billion in 2006, a history that began in 1668, and a future shaped by
about 35,000 employees (including Merck Serono) in 56 countries. Its
success is characterized by innovations from entrepreneurial employees.
Merck's operating activities come under the umbrella of Merck KGaA, in
which the Merck family holds a 73% interest and free shareholders own the
remaining 27%. In 1917 the U.S. subsidiary Merck & Co. was expropriated and
has been an independent company ever since.
    [1] The exact correlation between MRI findings and the current or
future clinical status of patients, including disability progression, is
unknown.

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