XTEN Data From Amunix and Versartis Featured in Nature Biotechnology as a Novel Platform for Increasing Serum Half-Life

REDWOOD CITY, CA and MOUNTAIN VIEW, CA, Nov 15 (MARKET
WIRE) --
Amunix, Inc. and Versartis, Inc. announced today that the scientific
journal Nature Biotechnology has published a comprehensive paper entitled
"A recombinant polypeptide extends the in vivo half-life of peptides and
proteins in a tunable manner." The paper
(http://dx.doi.org/10.1038/nbt.1588) describes the design of Amunix's
polypeptide sequence XTEN and presents preclinical data for Versartis'
product candidates VRS-859 as a monthly-dosed treatment for type 2
diabetes and VRS-317 as a monthly-dosed treatment for growth hormone
deficiency.

The published data demonstrate that XTEN, a technology for half-life
extension, can provide an effective means for prolonging the in vivo
half-life of therapeutic peptides and proteins. With a longer half-life,
patients have improved convenience and compliance with comparable efficacy
to the drug without XTEN. XTEN is an unstructured recombinant polypeptide
that is genetically fused to a peptide or protein. The XTEN sequence has
been specifically designed to have low immunogenicity and good
manufacturability, making it a generic platform technology applicable to a
wide variety of peptide and protein therapeutics. The publication
presents, for the first time, the example case of the exenatide peptide
fused to XTEN, with a projected human half-life of 139 hours, and
preclinical data on human growth hormone fused to XTEN with a half-life
in monkeys of 110 hours.

"Based on data from several peptides and proteins fused to XTEN, we expect
that XTEN will enable dosing of otherwise rapidly cleared protein drugs at
up to monthly intervals in humans," commented Willem 'Pim' Stemmer, Ph.D.,
Amunix Chief Executive Officer.

"These peer-reviewed results further validate that the monthly-dosed
exenatide (VRS-859) and human growth hormone (VRS-317) products provide
significant advantages over other approaches on the market or in clinical
trials," noted Jeffrey L. Cleland, Ph.D., Versartis Chief Executive
Officer.

XTEN has now been successfully fused to more than ten different protein
payloads with sizes ranging from small peptides such as exenatide to
larger proteins such as growth hormone and Factor VII. Depending on the
length of the attached XTEN sequence, data have demonstrated that the
serum half-life of a given compound may be tuned to fit its clinical
indication. In the case of some payloads, glucagon in particular,
extremely long serum half-life may exacerbate toxic side-effects. In
addition, extremely long serum half-life can be undesirable in the case
where toxicities manifest during treatment, since drug treatment cannot
be rapidly withdrawn. Therefore, it is expected that the versatility of
various truncations of the XTEN sequence will enable rapid development of
precisely tuned therapeutic agents. Although extremely long serum
half-life is a concern for some payloads, a large number of payloads
benefit significantly from reduced injection frequency, including
improvements in patient compliance and expense.

The recombinant nature of XTEN provides several advantages over
traditional PEGylation. Genetic fusion of a defined amino acid sequence
results in a homogeneous drug compound relative to chemically PEGylated
proteins. The overall cost and yield of the final product are also
significantly improved for XTEN products, since the need for chemical
coupling and purification from multiply PEGylated species, inactive
species, and free PEG has been removed. The nonimmunogenic and
biodegradable properties of XTEN are expected to yield a significantly
improved safety profile relative to PEG.

In addition to the reduced dosing frequency, XTEN products enable room
temperature stability and low cost manufacturing. The XTEN properties
allow for co-formulation and co-administration of proteins and peptides
that are normally incompatible. Versartis and Amunix are also conducting
research on combination products for metabolic disease to further exploit
these novel properties.

About Amunix

Amunix is focused on the application of its proprietary XTEN protein
polymer technology to create a broad spectrum of protein pharmaceutical
products with improvements in dosing frequency, compliance and ease of use
(via serum half-life increase); safety potential (biodegradability
resulting in reduced kidney vacuolation as well as reduced payload
immunogenicity); cost of goods (by elimination of chemical conjugation
steps); manufacturability (through E. coli soluble cytoplasmic expression,
universal purification processes including heat lysis); and formulation
(payload stabilization allowing liquid formulation and increased
concentration through hydrophilicity). Amunix, Inc. has 28 employees and
is located in Mountain View, California. See www.amunix.com for more
details.

About Versartis

Versartis, Inc., a Redwood City, California biotechnology company, is
developing new therapeutic compounds for the treatment of metabolic
diseases and endocrine disorders using XTEN, a novel hydrophilic amino
acid sequence that prolongs the half-life of proteins and peptides.
Versartis products are designed to provide enhanced stability and less
frequent dosing requirements with potentially fewer patient side effects
than currently available treatments.

Versartis, a joint venture company between Amunix, Inc. and Index
Ventures, owns and develops three novel drug candidates in metabolic
diseases and endocrinology that it has licensed from Amunix. Versartis
has preclinical proof-of-concept for exenatide and IL-1ra for diabetes,
and hGH for growth hormone deficiency. Further information on Versartis
can be found at www.versartis.com.

Contacts:
Corporate
Jeffrey L. Cleland, Ph.D.
CEO
650 632-4410
Email Contact

Pim Stemmer, Ph.D.
CEO
650-428-1800
Email Contact

Media
Debra Bannister
530 676-8001
Email Contact

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