Arrowhead Prices $36 Million Private Offering

Approximately 14.3 million shares of common stock and 9,900 shares of series B convertible preferred stock are expected to be issued at closing. The series B preferred shares are priced at $1,000 per share, are convertible into shares of common stock at a conversion price of $1.83 per share of common stock and include no dividends or liquidation preferences. The offering is expected to close on or about May 3, 2013, subject to the satisfaction of customary closing conditions.

This press release shall not constitute an offer to sell or the solicitation of an offer to buy these securities, nor shall there be any sale of these securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to the registration or qualification under the securities laws of any such jurisdiction.

The securities sold in the private placement have not been registered under the Securities Act of 1933, as amended, or state securities laws and may not be offered or sold in the United States absent registration with the Securities and Exchange Commission (SEC) or an applicable exemption from such registration requirements. The Company has agreed to file a registration statement with the SEC registering the resale of the shares of common stock and the shares of common stock issuable upon conversion of the series B preferred.