Common stock offered by us

5,000,000 shares (or 5,750,000 shares if the underwriters exercise their over-allotment option in full)

Common stock to be outstanding after this offering

19,272,409 shares (or 20,022,409 shares if the underwriters exercise their over-allotment option in full), based on the number of shares outstanding as of June 30, 2007.

Initial public offering price per share

$12.00 per share

Potential purchases by existing stockholders:

Certain of our principal stockholders and/or their affiliates have indicated an interest in purchasing shares of our common stock in this offering as follows:

Matthew V. McPherron is a member of our board of directors and is a managing director of Brookside Capital Partners Fund, L.P. Steven A. Elms is the chairman of our board of directors and is a managing director of Perseus-Soros Biopharmaceutical Fund, L.P. John G. Freund is a member of our board of directors and is a managing director of Skyline Ventures, an affiliate of Skyline Partners. Certain of our other current stockholders have indicated an interest in purchasing up to 400,000 shares of our common stock in this offering. Assuming such purchases are completed in full, our current executive officers and directors as a group will beneficially own approximately 62.4% of our outstanding common stock after this offering. The number and percentage of shares beneficially owned is based on 19,399,234 shares of common stock outstanding after this offering as of June 30, 2007 (this number includes 928,318 shares to be issued to holders of our preferred stock upon the closing of this offering as a cumulative dividend accumulated through September 14, 2007, at which time further accumulation ended, pursuant to the terms of our certificate of incorporation), and assumes no exercise of the underwriters’ over-allotment option.

However, because indications of interest are not binding agreements or commitments to purchase, these stockholders may decide not to purchase shares in this offering.

Net proceeds:

We estimate that we will receive net proceeds of approximately $53.7 million from the sale of the shares of common stock in this offering, based on the initial public offering price of $12.00 per share and after deducting the underwriting discounts and commissions and estimated offering expenses payable by us. If the underwriters’ over-allotment option is exercised in full, we estimate that our net proceeds will be approximately $62.1 million.

Pro forma as adjusted balance sheet data:

Based on the initial public offering price of $12.00 per share, as of June 30, 2007, on a pro forma as adjusted basis, cash, cash equivalents and short-term investments would have been approximately $108.1 million, working capital would have been approximately $99.7 million, total assets would have been approximately $113.1 million and total stockholders’ equity would have been approximately $96.3 million.

Pro forma as adjusted capitalization:

Based on the initial public offering price of $12.00 per share, as of June 30, 2007, on a pro forma as adjusted basis, cash, cash equivalents and short-term investments would have been approximately $108.1 million, additional paid-in capital would have been approximately $173.1 million, total stockholders’ equity would have been approximately $96.3 million and total capitalization would have been approximately $104.4 million.

Dilution:

After giving effect to our sale in this offering of 5,000,000 shares of our common stock at the initial offering price of $12.00 per share and after deducting underwriting discounts and commissions and estimated offering expenses payable by us, our pro forma as adjusted net tangible book value as of June 30, 2007 would have been approximately $96.3 million, or $5.00 per share of our common stock. This represents an immediate increase of net tangible book value of $2.02 per share to our existing stockholders and an immediate dilution of $7.00 to investors purchasing shares in this offering. If the underwriters exercise their over-allotment option in full, the pro forma as adjusted net tangible book value per share after giving effect to this offering would be $5.23 per share, and the dilution in pro forma net tangible book value per share to investors in this offering would be $6.77 per share. Investors purchasing shares of common stock in this offering will have purchased approximately 26% of our outstanding common stock immediately following the completion of this offering and will have contributed approximately 36% of the total consideration paid for our common stock.