Arrowhead Begins Phase 1 Trial of RNAi Therapeutic ARC-520 for Treatment of Chronic Hepatitis B Infection

  Arrowhead Begins Phase 1 Trial of RNAi Therapeutic ARC-520 for Treatment of
  Chronic Hepatitis B Infection

Business Wire

PASADENA, Calif. -- July 23, 2013

Arrowhead Research Corporation (NASDAQ: ARWR), a biopharmaceutical company
developing targeted RNAi therapeutics, today announced that it has initiated
dosing in a Phase 1 clinical trial of ARC-520, the Company’s candidate for the
treatment of chronic hepatitis B virus infection. Trial initiation followed
successful completion of the Clinical Trial Notification (CTN) regulatory
process in Australia. The objectives of the study are to characterize the
safety profile of ARC-520, determine maximum tolerated dose, and evaluate
pharmacokinetics in healthy volunteers. ARC-520 is the first candidate to use
Arrowhead’s proprietary Dynamic Polyconjugate (DPC) delivery platform and
includes two distinct siRNA sequences that have pan-genotypic coverage for
99.6% HBV GenBank sequences.

The Phase 1 trial is a single-center, randomized, double-blind,
placebo-controlled, single dose-escalation, first-in-human study of ARC-520
administered intravenously to healthy adult volunteers and is being conducted
in Melbourne, Australia. Each dose cohort includes 6 subjects randomized at
ratio of 1:2 (placebo:active) to receive a single intravenous injection of
either placebo or ARC-520. Arrowhead expects to complete this Phase 1 trial in
the fourth quarter of 2013 and begin a Phase 2a trial in chronic HBV patients
in 2014.

“This Phase 1 study will establish a safety profile for ARC-520 as well as
provide the first human data for our DPC delivery platform. This is an
important step forward as we seek to advance ARC-520 into HBV patients and
build additional RNAi therapeutics based on what we believe is the most potent
delivery system in the industry,” said Dr. Christopher Anzalone, President and
Chief Executive Officer.

Hepatitis B is the world’s most common serious liver infection. It is
estimated that 350 million people worldwide are chronically infected with HBV,
representing approximately 1 in 20 people on the planet. No currently
available treatment methods can reliably achieve meaningful cure rates.
ARC-520 is designed to reduce the production of new viral particles and viral
proteins. Many experts believe that reducing key viral proteins can revive
patients’ adaptive immune response and potentially lead to a functional cure
of chronic HBV infection with a finite treatment regimen. Arrowhead previously
presented data generated in rodent models and in a chimpanzee chronically
infected with HBV, showing that ARC-520 induces rapid, deep, and durable
knockdown of both circulating HBV DNA and key viral proteins, including
hepatitis B s-antigen, e-antigen, and the core protein that forms the capsid.

About ARC-520

Approximately 350 million people worldwide are chronically infected with the
hepatitis B virus. Chronic HBV infection can lead to cirrhosis of the liver
and is responsible for 80% of primary liver cancers globally. Arrowhead’s
RNAi-based candidate ARC-520 is designed to treat chronic HBV infection by
reducing the expression and release of new viral particles and key viral
proteins. The goal is to achieve a functional cure, which is an immune
clearant state characterized by hepatitis B s-antigen negative serum with or
without sero-conversion. The siRNAs in ARC-520 intervene at the point of DNA
transcription, upstream of where nucleotide and nucleoside analogues act. In
transient and transgenic mouse models of HBV infection, a single co-injection
of Arrowhead’s DPC delivery vehicle with cholesterol-conjugated siRNA
targeting HBV sequences resulted in multi-log knockdown of HBV RNA, proteins
and viral DNA with long duration of effect. In a chimpanzee chronically
infected with HBV and high viremia and antigenemia, ARC-520 induced rapid
reductions of 90-95% in HBV DNA, e-antigen, and s-antigen. Arrowhead is
conducting a Phase 1 single-ascending dose study in normal volunteers, which
the company expects to follow with a Phase 2a study in chronic HBV patients.

About Arrowhead Research Corporation

Arrowhead Research Corporation is a biopharmaceutical company developing
targeted RNAi therapeutics. The company is leveraging its proprietary drug
delivery technologies to develop targeted drugs based on the RNA interference
(RNAi) mechanism that efficiently and specifically silence target genes.
Arrowhead technologies also enable partners to create peptide-drug conjugates
(PDCs) that specifically home to cell types of interest while sparing
off-target tissues. Arrowhead’s pipeline includes programs in chronic
hepatitis B virus, obesity, and cancer.

For more information please visit http://www.arrowheadresearch.com, or follow
us on Twitter @ArrowRes. To be added to the Company's email list to receive
news directly, please send an email to ir@arrowres.com.

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.

Contact:

Arrowhead Research Corporation
Vince Anzalone, CFA
626-304-3400
or
The Trout Group
Lauren Glaser
646-378-2972
ir@arrowres.com