AMENDMENT TO RIGHTS AGREEMENT

Young Tang Under the CA Transfer to Minors Act, Kevin Tang and Haeyoung Tang Trustees The Tang Family Trust Dated 8-27-02, IRA FBO Kevin Tang DB Securities Inc. Custodian Rollover Account and any Person whose beneficial ownership of Common Shares is by or through any of such Persons; provided that any such Person shall not be an Excluded Stockholder in the event that such Person, together with all Affiliates and Associates of such Person, acquires in the aggregate (together with all other acquisitions of Common Shares by such Person and all Affiliates and Associates of such Person pursuant to this proviso, but excluding any Common Shares acquired by such Person pursuant to the terms of that certain Purchase Agreement, dated as of February 2, 2006, by and among the Company and the other parties thereto or pursuant to the terms of warrants issued to such Person under such Purchase Agreement and excluding, in the case of Special Situations Fund III QP, L.P., Special Situations Fund III, L.P., Special Situations Cayman Fund, L.P., Special Situations Private Equity Fund, L.P., Special Situations Life Sciences Fund, L.P., 709,832 Common Shares acquired from Versant Capital Management LLC and 750,000 Common Shares issuable upon exercise of a warrant originally issued under such Purchase Agreement to Versant Capital Management LLC) more than 1.0% of the then issued and outstanding Common Shares after April 4, 2006.

(b)          The first sentence of Section 3(a) of the Agreement is hereby amended and restated in its entirety as follows:

Until the earlier of the Close of Business on (i) the tenth day after the Shares Acquisition Date or (ii) the tenth Business Day (or such later date as may be determined by action of the Board of Directors prior to such time as any Person becomes an Acquiring Person) after the date of the commencement (determined in accordance with Rule 14d-2 under the Exchange Act) by any Person (other than the Company, any Subsidiary of the Company, any employee benefit plan of the Company or of any Subsidiary of the Company or any entity holding Common Shares for or pursuant to the terms of any such plan) of, or of the first public announcement of the intention of any Person (other than the Company, any Subsidiary of the Company, any employee benefit plan of the Company or of any Subsidiary of the Company or any entity holding Common Shares for or pursuant to the terms of any such plan) to commence, a tender or exchange offer (which intention to commence remains in effect for five Business Days after such announcement), the consummation of which would result in any Person becoming an Acquiring Person (including any such date which is after the date of this Agreement and prior to the issuance of the Rights, the earlier of such dates being herein referred to as the “Distribution Date”), (x) the Rights will be evidenced by the certificates for Common Shares registered in the names of the holders thereof (which certificates shall also be deemed to be Right Certificates) and not by separate Right Certificates, and (y) the Rights (and the right to receive Right Certificates therefor) will be transferable only in connection with the transfer of Common Shares.