On July 8, 2009, we entered into an underwriting agreement (the "Underwriting Agreement") with Piper Jaffray & Co. (the "Underwriter") relating to the issuance and sale of 12,500,000 of our common stock, par value $0.0001 per share. The price to the public is $4.17 per share and the Underwriter has agreed to purchase the shares from us pursuant to the Underwriting Agreement at a price of $4.00 per share.

The offering is being made pursuant to a shelf registration statement we filed with the Securities and Exchange Commission on November 25, 2008, which became effective on December 3, 2008 (File No. 333-155660). The closing of the offering is expected to take place on July 13, 2009. A copy of the Underwriting Agreement is attached as Exhibit 1.1 and is incorporated herein by reference, and the foregoing description of the Underwriting Agreement does not purport to be complete and is qualified in its entirety by reference to such exhibit. A prospectus supplement relating to the offering has been filed with the Securities and Exchange Commission. A copy of the opinion of Cooley Godward Kronish LLP relating to the legality of the issuance and sale of the securities in the offering is attached as Exhibit 5.1 hereto.

On July 8, 2009, we also issued a press release announcing the pricing of the offering. A copy of the press release is attached as Exhibit 99.1 hereto.

(d) Exhibits.

Exhibit No.    Description
1.1            Underwriting Agreement, dated July 8, 2009, by and between Arena and
               Piper Jaffray & Co.

5.1            Opinion of Cooley Godward Kronish LLP

23.1           Consent of Cooley Godward Kronish LLP (included in Exhibit 5.1)

99.1           Press release announcing pricing of offering

Forward-Looking Statements

Certain statements in this report are forward-looking statements that involve a number of risks and uncertainties. Such forward-looking statements include statements about the expected closing of the sale and purchase of common stock described. For such statements, we claim the protection of the Private Securities Litigation Reform Act of 1995. Actual events or results may differ materially from our expectations. Factors that could cause actual results to differ materially from the forward-looking statements include, but are not limited to, our ability to satisfy applicable closing conditions under the Underwriting Agreement and the Underwriter's compliance with its obligations to purchase the shares of common stock. Additional factors that could cause actual results to differ materially from those stated or implied by our forward-looking statements are disclosed in our filings with the Securities and Exchange Commission. These forward-looking statements represent our judgment as of the time of this report. We disclaim any intent or obligation to update these forward-looking statements, other than as may be required under applicable law.