Arrowhead Announces Licensing by Subsidiary of RNAi Delivery Technology to Benitec

PASADENA, California – (BUSINESS WIRE) – June 21, 2005 – Arrowhead Research Corporation (NASDAQ:ARWR) announced today that its majority-owned subsidiary, Calando Pharmaceuticals Inc., has granted an exclusive worldwide license to Benitec Ltd. (ASX:BLT) for the combination of Calando's polymeric nucleic acid delivery technology with Benitec's RNA interference (RNAi)-based therapeutic for hepatitis C virus (HCV). The new technology created by this partnership represents an entirely new therapeutic approach to treating HCV, presently largely incurable and resistant to treatment. HCV is the most common blood-borne infection and the biggest cause of liver transplants in the United States. Calando will receive an upfront payment, milestone payments and royalties on revenue from this HCV therapeutic.

We are pleased to be working with Benitec," said R. Bruce Stewart, Arrowhead's President. "It has been estimated that the market for HCV therapeutics could approach $4 billion, and this collaboration represents the first step in executing our strategy in the RNAi therapeutics marketplace."

About Arrowhead Research Corporation

Arrowhead Research Corporation (www.arrowheadresearch.com) is a publicly-traded nanotechnology company commercializing new technologies in the areas of life sciences, electronics, and energy. Arrowhead is building value for shareholders through the progress of majority owned subsidiaries founded on nanotechnologies originally developed at universities. The company works closely with universities to source early stage deals and to generate rights to intellectual property covering promising new nanotechnologies. Currently, Arrowhead has four subsidiaries commercializing nanotech products and applications, including anti-cancer drugs, RNAi therapeutics, carbon-based electronics and compound semiconductor materials.

Safe Harbor Statement under the Private Securities Litigation Reform Act of 1995:

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 the recent economic slowdown affecting technology companies, the future success of our scientific studies, our ability to successfully develop products, rapid technological change in our markets, changes in demand for our future products, legislative, regulatory and competitive developments and general economic conditions. Our Annual Report on Form 10-K and 10-K/A, recent and forthcoming Quarterly Reports on Form 10-Q and 10-Q/A, recent Current Reports on Forms 8-K and 8-K/A, our Registration Statement on Form S-3, and other SEC filings discuss some of the important risk factors that may affect our business, results of operations and financial condition. We undertake no obligation to revise or update publicly any forward-looking statements for any reason.

Contacts

R. Bruce Stewart, President
Telephone: 626.792.5549
Email: bruce@arrowres.com