Arrowhead Closes Private Offering with Net Proceeds of $60 Million

  Arrowhead Closes Private Offering with Net Proceeds of $60 Million

       Financing led by RA Capital Management, LLC with a syndicate of
                       healthcare-focused institutions

Business Wire

PASADENA, Calif. -- October 14, 2013

Arrowhead Research Corporation (NASDAQ:ARWR), a biopharmaceutical company
developing targeted RNAi therapeutics, today announced that on October 11,
2013 it closed a previously announced private offering of common and
convertible preferred stock. The financing, which was oversubscribed, had net
proceeds of $60 million, after deducting commissions and other offering
expenses payable by the company. It was led by RA Capital Management, LLC and
included a syndicate of new and existing institutional investors.

“This capital raise enables us to aggressively build on the success of the
ARC-520 Phase 1 study,” said Dr. Christopher Anzalone, Arrowhead’s President
and CEO. “We have the resources to advance ARC-520 through the upcoming Phase
2a study in chronic HBV patients and a multi-national Phase 2b planned for the
second half of 2014. The financing also enables us to expand on the DPC
delivery platform by funding two new candidates through clinical proof of
concept and advancing our pre-clinical pipeline with additional IND-ready
candidates. We see the strong demand from high quality institutions as a vote
of confidence in our technology, strategic plan, and execution.”

3,071,672 shares of common stock were issued at $5.86 per share. 46,000 shares
of Series C convertible preferred stock were issued at $1,000 per share. Each
share of preferred stock is convertible into 170.6 shares of common stock at a
conversion price of $5.86 per share of common stock. The Series C preferred
was issued to those investors who desire to not own in excess of 9.99% of
Arrowhead’s outstanding voting securities following the financing.The Series
C Preferred is non-voting above a beneficial ownership cap of 9.99% and
carries no dividend or liquidation preference.

Jefferies LLC and Piper Jaffray & Co. acted as joint placement agents for the
offering and Trout Capital acted as a financial advisor to the company.

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 mRNA level,
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 has completed enrollment in 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
mechanism that efficiently silence disease-causing genes. Arrowhead
technologies also enable partners to create peptide-drug conjugates that
specifically home to cell types of interest while sparing off-target tissues.
Arrowhead’s pipeline includes clinical programs in chronic hepatitis B virus
and obesity and partner-based programs in oncology.

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