Edgar Filing: CELL GENESYS INC

Filed by BioSante Pharmaceuticals, Inc.

Pursuant to Rule 425 under the

Securities Act of 1933 and deemed filed

pursuant to Rule 14a-6 under the

Securities Exchange Act of 1934

Subject Company: Cell Genesys, Inc.

Commission File No.: 333-161181

The following is a joint press release issued by BioSante Pharmaceuticals, Inc. and Cell Genesys, Inc. on September 17, 2009:

Forward-Looking Statements

This communication contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 about BioSante and Cell Genesys. Such statements include, but are not limited to, statements about the proposed transaction and its potential benefits to the BioSante and Cell Genesys stockholders, the expected timing of the completion of the transaction, the combined company’s plans, objectives, expectations and intentions with respect to future operations and products and other statements that are not historical in nature, particularly those that utilize terminology such as “will,” “potential,” “could,” “can,” “believe,” “intends,” “continue,” “plans,” “expects,” “estimates” or comparable terminology. Forward-looking statements are based on current expectations and assumptions, and entail various known and unknown risks and uncertainties that could cause actual results to differ materially from those expressed in such forward-looking statements. Important factors known to BioSante and Cell Genesys that could cause actual results to differ materially from those expressed in such forward-looking statements include general business and economic conditions; the failure of the BioSante or Cell Genesys stockholders to approve the transaction or the failure of either party to meet any of the other conditions to the closing of the transaction; the failure to realize the anticipated benefits from the transaction or delay in realization thereof; the businesses of BioSante and Cell Genesys may not be combined successfully, or such combination may take longer, be more difficult, time-consuming or costly to accomplish than expected; and operating costs and business disruption following the merger, including adverse effects on employee retention and on business relationships with third parties, BioSante’s need for and ability to obtain additional financing, the difficulty of developing pharmaceutical products, obtaining regulatory and other approvals and achieving market acceptance; the marketing success of BioSante’s licensees or sublicensees and the success of clinical testing. Additional factors that could cause BioSante’s and Cell Genesys’s results to differ materially from those described in the forward-looking statements can be found in BioSante’s recent registration statement on Form S-4 and BioSante’s and Cell Genesys’s most recent annual reports on Form 10-K and subsequent quarterly reports on Form 10-Q and other filings with the Securities and Exchange Commission, which are filed with the SEC and available at the SEC’s web site at www.sec.gov and which discussions also are incorporated herein by reference. The information set forth herein speaks only as of the date hereof, and BioSante and Cell Genesys disclaim any intention and do not assume any obligation to update or revise any forward looking statement, whether as a result of new information, future events or otherwise.

Important Additional Information for Investors and Stockholders

This communication is being made in respect of the proposed business combination involving BioSante and Cell Genesys. In connection with the proposed transaction, BioSante has filed with the SEC, a registration statement on Form S-4, containing a joint proxy statement/prospectus and other relevant materials. The final joint proxy statement/prospectus has been mailed to the stockholders of record as of August 21, 2009, of BioSante and Cell Genesys. INVESTORS AND SECURITY HOLDERS OF BIOSANTE AND CELL GENESYS ARE URGED TO READ THE JOINT PROXY STATEMENT/PROSPECTUS (INCLUDING ANY AMENDMENTS OR SUPPLEMENTS) AND OTHER DOCUMENTS FILED WITH THE SEC CAREFULLY IN THEIR ENTIRETY BECAUSE THEY CONTAIN IMPORTANT INFORMATION ABOUT BIOSANTE, CELL GENESYS AND THE PROPOSED TRANSACTION.

Investors and security holders are be able to obtain free copies of the registration statement and the joint proxy statement/prospectus and other documents filed with the SEC by BioSante and Cell Genesys at the SEC’s web site at www.sec.gov. Free copies of the registration statement and the joint proxy statement/prospectus and other documents filed with the SEC can also be obtained by directing a request to BioSante, Attention: Investor Relations, telephone: (847) 478-0500 or to Cell Genesys, Attention: Investor Relations., telephone (650) 266-3200. In addition, investors and security holders may access copies of the documents filed with the SEC by BioSante on BioSante’s website at www.biosantepharma.com, and investors and security holders may access copies of the documents filed with the SEC by Cell Genesys’s website at www.cellgenesys.com.

BioSante, Cell Genesys and their respective directors and executive officers and other persons may be deemed to be participants in the solicitation of proxies from the stockholders of BioSante and Cell Genesys in respect of the proposed transaction. Information regarding BioSante’s directors and executive officers is available in its annual report on Form 10-K for the year ended December 31, 2008, filed with the SEC on March 16, 2009 and the proxy statement for BioSante’s 2009 annual meeting of stockholders, filed with the SEC on April 27, 2009.

Information regarding Cell Genesys’s directors and executive officers is available in its annual report on Form 10-K for the year ended December 31, 2008, filed with the SEC on March 9, 2009 and the proxy statement for Cell Genesys’s 2009 annual meeting of stockholders, filed with the SEC on March 31, 2009. Investors and stockholders can obtain more detailed information regarding the direct and indirect interests of BioSante’s and Cell Genesys’s directors and executive officers in the merger by reading the definitive joint proxy statement/prospectus.

* * * * *

111 Barclay Boulevard

Lincolnshire, Illinois 60069

www.biosantepharma.com

400 Oyster Point Boulevard #525

South San Francisco, CA 94080

www.cellgenesys.com

FOR IMMEDIATE RELEASE

RiskMetrics Group — ISS Governance Services Recommends Stockholders Vote

“FOR” BioSante and Cell Genesys Merger

LINCOLNSHIRE, Illinois and SOUTH SAN FRANCISCO, California (September 17, 2009) — BioSante Pharmaceuticals, Inc. (NASDAQ: BPAX) and Cell Genesys, Inc. (NASDAQ: CEGE), today jointly announced that RiskMetrics Group — ISS Governance Services, a leading proxy advisory firm, has recommended that BioSante and Cell Genesys stockholders vote “FOR” the adoption of the merger agreement between BioSante and Cell Genesys at their upcoming respective special meeting of stockholders scheduled to be held on September 30, 2009.

BioSante and Cell Genesys encourage all stockholders to vote their shares promptly by phone, Internet or by mailing their proxy card. The boards of directors of both companies unanimously recommend that stockholders vote “FOR” the adoption of the merger agreement.

BioSante stockholders in need of assistance voting their shares can call BioSante’s proxy solicitor, Laurel Hill Advisory Group, LLC, toll-free at (888) 742-1305. Cell Genesys stockholders in need of assistance voting their shares can call Cell Genesys’s proxy solicitor, Innisfree M&A Incorporated, toll-free at (800) 750-5833.

About BioSante Pharmaceuticals, Inc.

BioSante is a specialty pharmaceutical company focused on developing products for female sexual health, menopause, contraception and male hypogonadism. BioSante’s lead products include LibiGel® (transdermal testosterone gel) in Phase III clinical development by BioSante under a U.S. Food and Drug Administration (FDA) SPA (Special Protocol Assessment) for the treatment of female sexual dysfunction (FSD), and Elestrin™ (estradiol gel) developed through FDA approval by BioSante, indicated for the treatment of moderate-to-severe vasomotor symptoms associated with menopause, currently marketed in the U.S. Also in development are Bio-T-Gel™, a testosterone gel for male hypogonadism, and an oral contraceptive in Phase II clinical development using BioSante patented technology. The current market in the U.S. for estrogen and testosterone

products is approximately $2.5 billion and for oral contraceptives approximately $3 billion. The company also is developing its calcium phosphate technology (CaP) for aesthetic medicine (BioLook™), as a vaccine adjuvant, including for an H1N1 (swine flu) vaccine, and drug delivery. Additional information is available online at: www.biosantepharma.com.

About Cell Genesys, Inc.

Cell Genesys is headquartered in South San Francisco, California. For additional information, please visit Cell Genesys’ website at www.cellgenesys.com.

Forward-Looking Statements

This news release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 about BioSante and Cell Genesys. Such statements include, but are not limited to, statements about the proposed transaction and the expected timing of the completion of the transaction and other statements that are not historical in nature, particularly those that utilize terminology such as “will,” “potential,” “could,” “can,” “believe,” “intends,” “continue,” “plans,” “expects,” “estimates” or comparable terminology. Forward-looking statements are based on current expectations and assumptions, and entail various known and unknown risks and uncertainties that could cause actual results to differ materially from those expressed in such forward-looking statements. Important factors known to BioSante and Cell Genesys that could cause actual results to differ materially from those expressed in such forward-looking statements include general business and economic conditions; the failure of the BioSante or Cell Genesys stockholders to approve the transaction or the failure of either party to meet any of the other conditions to the closing of the transaction; the failure to realize the anticipated benefits from the transaction or delay in realization thereof; the businesses of BioSante and Cell Genesys may not be combined successfully, or such combination may take longer, be more difficult, time-consuming or costly to accomplish than expected; and operating costs and business disruption following the merger, including adverse effects on employee retention and on business relationships with third parties, BioSante’s need for and ability to obtain additional financing, the difficulty of developing pharmaceutical products, obtaining regulatory and other approvals and achieving market acceptance; the marketing success of BioSante’s licensees or sublicensees and the success of clinical testing. Additional factors that could cause BioSante’s and Cell Genesys’s results to differ materially from those described in the forward-looking statements can be found in BioSante’s registration statement on Form S-4 and BioSante’s and Cell Genesys’s most recent annual reports on Form 10-K and subsequent quarterly reports on Form 10-Q and other filings with the Securities and Exchange Commission, which are filed with the SEC and available at the SEC’s web site at www.sec.gov and which discussions also are incorporated herein by reference. The information set forth herein speaks only as of the date hereof, and BioSante and Cell Genesys disclaim any intention and do not assume any obligation to update or revise any forward looking statement, whether as a result of new information, future events or otherwise.

Important Additional Information for Investors and Stockholders

In addition, investors and security holders may access copies of the documents filed with the SEC by BioSante on BioSante’s website at www.biosantepharma.com, and investors and security holders may access copies of the documents filed with the SEC by Cell Genesys’s website at www.cellgenesys.com.

For shareholders of record that require an additional copy of the prospectus and proxy

Please contact:

Computershare Trust Company, NA

PO box 43078

Providence Rhode Island 02940-3078

(781) 575-2879

For more information about BioSante, please contact:

McKinney/Chicago

Alan Zachary

(312) 944-6784 ext. 316; azachary@mckinneychicago.com

For more information about Cell Genesys, please contact:

Investor Relations

Victoria Soares

(650) 322-3200