Arrowhead Receives Notice of Patent Allowance for New Protease Sensitive Masking Chemistry for DPC siRNA Delivery System

  Arrowhead Receives Notice of Patent Allowance for New Protease Sensitive
  Masking Chemistry for DPC siRNA Delivery System

Business Wire

PASADENA, Calif. -- February 28, 2013

Arrowhead Research Corporation (NASDAQ: ARWR), a targeted therapeutics
company, today announced that it has received a Notice of Allowance from the
U.S. Patent and Trademark Office forU.S. Patent Application Number 13/336,028
entitled, “In Vivo Polynucleotide Delivery Conjugates Having Enzyme Sensitive
Linkages.” This new IP expands the Dynamic Polyconjugate (DPC) platform,
broadly protecting Arrowhead's next generation DPC polymer masking
technology.Using this masking technology, DPCs can be engineered for long
circulation times and improved tissue-targeting characteristics. In addition,
hepatocyte-targeted DPCs formulated using this new masking technology have
shownto be highly potent upon subcutaneous administration. The company has
previously reported target gene knockdown of 99% in monkeys after a single
subcutaneous injection of 1 mg/kg, with >80% knockdown for 3 months.
Additional data will be reported at upcoming scientific conferences and
through peer-reviewed publications.

“This patent protects a new masking chemistry that broadens the reach of
DPC-enabled RNAi therapeutics. It enables efficient subcutaneous delivery of
siRNA and opens up new therapeutic area targets including oncology,” said Dr.
Chris Anzalone, President and CEO of Arrowhead. “Arrowhead scientists continue
to discover innovative solutions for siRNA delivery and we look forward to
providing updates on how these technologies are being deployed to create new
drug candidates.”

About Arrowhead Research Corporation

Arrowhead Research Corporation is a clinical stage targeted therapeutics
company with development programs in oncology, obesity, and chronic hepatitis
B virus infection. The company is leveraging its platform technologies to
design and develop peptide-drug conjugates (PDCs) that specifically home to
cell types of interest while sparing off-target tissues, create targeted drugs
based on the gene silencing RNA interference (RNAi) mechanism, and work with
partners to create improved versions of traditional small molecule drugs.

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Safe Harbor Statement under the Private Securities Litigation Reform Act:

This news release contains forward-looking statements within the meaning of
the "safe harbor" provisions of the Private Securities Litigation Reform Act
of 1995. These statements are based upon our current expectations and speak
only as of the date hereof. Our actual results may differ materially and
adversely from those expressed in any forward-looking statements as a result
of various factors and uncertainties, including our ability to finance our
operations, the future success of our scientific studies, our ability to
successfully develop drug candidates, the timing for starting and completing
clinical trials, rapid technological change in our markets, and the
enforcement of our intellectual property rights. Arrowhead Research
Corporation's most recent Annual Report on Form 10-K and subsequent Quarterly
Reports on Form 10-Q discuss some of the important risk factors that may
affect our business, results of operations and financial condition. We assume
no obligation to update or revise forward-looking statements to reflect new
events or circumstances.


Arrowhead Research Corporation
Vince Anzalone, CFA
The Trout Group
Lauren Glaser, 646-378-2972
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