ASG-5ME Expected to Advance into Phase I Clinical Trials During 2010 for Prostate and Pancreatic Cancers

BOTHELL, WA, USA & SANTA MONICA, CA, USA | April 21, 2010 | Seattle Genetics, Inc. (Nasdaq: SGEN – News) and Agensys, Inc., an affiliate of Tokyo-based Astellas Pharma Inc., today reported preclinical data with ASG-5ME, an antibody-drug conjugate (ADC) that is being co-developed by both companies for the treatment of solid tumors. In models of human prostate and pancreatic cancer, ASG-5ME was found to have potent and long lasting antitumor activity. The findings were presented at the 101st Annual Meeting of the American Association for Cancer Research (AACR) being held in Washington, D.C.

“ASG-5ME is one of the ADC products in Agensys’ pipeline that we are advancing to the clinic. We believe that our ADC products will contribute to Astellas’ growing presence in oncology,” said Aya Jakobovits, Ph.D., Executive Vice President and Chief Scientific Officer at Agensys. “ASG-5ME is directed to AGS-5, an Agensys proprietary target expressed significantly in patients with prostate, pancreatic and gastric cancers, providing multiple clinical development opportunities.”

“We are excited to test the potential of ASG-5ME in patients with prostate and pancreatic cancer,” said Jonathan Drachman, M.D., Vice President, Translational Medicine at Seattle Genetics. “The collaboration between Agensys and Seattle Genetics allowed ASG-5ME to advance rapidly toward clinical trials, and we look forward to evaluating the tolerability and antitumor activity of this ADC in cancer indications that are in need of new therapeutic options.”

ASG-5ME is an ADC composed of a fully human antibody directed to AGS-5, a novel cancer target discovered by Agensys. The antibody is attached to a potent, synthetic drug payload, monomethyl auristatin E (MMAE), via an enzyme-cleavable linker using Seattle Genetics’ proprietary technology. The ADC is designed to be stable in the bloodstream, but to release MMAE upon internalization into AGS-5-expressing tumor cells, resulting in targeted cell-killing.

Data presented at AACR show that AGS-5 is significantly expressed on more than 80 percent of samples derived from patients with prostate, pancreatic and gastric cancers. In preclinical models, ASG-5ME induced long-term regression of established prostate, pancreatic and colon cancer xenografts (Abstracts #2590 and #4393). Seattle Genetics and Agensys expect to initiate phase I clinical trials of ASG-5ME during 2010.

According to the American Cancer Society, more than 192,000 new cases of prostate cancer were diagnosed in the United States during 2009, making it the third most commonly diagnosed form of cancer. More than 27,000 men died of prostate cancer in 2009. The annual incidence of pancreatic cancer is estimated to be greater than 42,000 cases, and more than 35,000 people died from the disease in 2009. The 5-year survival rate for people diagnosed with pancreatic cancer is only five percent.

About Seattle Genetics

Seattle Genetics is a clinical stage biotechnology company focused on the development and commercialization of monoclonal antibody-based therapies for the treatment of cancer and autoimmune disease. The company’s lead product candidate, brentuximab vedotin, is in a pivotal trial under a Special Protocol Assessment with the U.S. Food and Drug Administration. Brentuximab vedotin is being developed in collaboration with Millennium: The Takeda Oncology Company. In addition, Seattle Genetics has four other product candidates in ongoing clinical trials: lintuzumab (SGN-33), dacetuzumab (SGN-40), SGN-70 and SGN-75. Seattle Genetics has collaborations for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Bayer, Celldex Therapeutics, Daiichi Sankyo, Genentech, GlaxoSmithKline, MedImmune, a subsidiary of AstraZeneca, Millennium: The Takeda Oncology Company and Progenics, as well as an ADC co-development agreement with Agensys, an affiliate of Astellas. More information can be found at www.seattlegenetics.com.

About Agensys

Agensys, Inc., an affiliate of Astellas Pharma Inc., is developing a pipeline of therapeutic fully human monoclonal antibodies (MAbs) to treat solid tumor cancers. The MAb product pipeline is being generated to Agensys’ diverse portfolio of proprietary, clinically relevant cancer targets that encompass 14 types of solid tumors. Agensys’ target portfolio and related products are protected by a large patent estate. The Company has full capabilities to generate, develop and manufacture antibody products. Agensys is progressing a pipeline of both naked and antibody-drug conjugated (ADC) therapeutic antibodies, directed at a variety of cancer indications, including those of the prostate, kidney, pancreas, ovary, bladder, lung, colon, breast and skin. ADC products are based on drug platform technologies developed by Seattle Genetics. Agensys is developing a growing pipeline of clinical stage functional MAbs and ADC products.

About Astellas

Astellas Pharma Inc., located in Tokyo, Japan, is a pharmaceutical company dedicated to improving the health of people around the world through the provision of innovative and reliable pharmaceutical products. Astellas has approximately 15,000 employees worldwide. The organization is committed to becoming a global category leader by rapidly establishing a business model in urology, immunology & infectious diseases, neuroscience, DM complications & metabolic diseases and oncology. Astellas has discovered a treatment for functional symptoms of benign prostatic hyperplasia (BPH) , Flomax®, a treatment for over-active bladder (OAB) , Vesicare® and an immunosuppressant, Prograf® (tacrolimus), which have enabled Astellas to become an established leader in both Urology and Transplant. For more information on Astellas Pharma Inc., please visit Astellas’ website at http://www.astellas.com/en.

For Seattle Genetics, Inc.:

Certain of the statements made in this press release are forward looking, such as those, among others, relating to the therapeutic potential indicated by preclinical studies in tumor models. Actual results or developments may differ materially from those projected or implied in these forward-looking statements. Factors that may cause such a difference include risks related to insufficient clinical activity or the observance of unacceptable toxicities as ASG-5ME moves into and advances in clinical trials and failure by Seattle Genetics’ collaborators to advance product candidates incorporating its technology, such as ASG-5ME. More information about the risks and uncertainties faced by Seattle Genetics is contained in the company’s 10-K for the year ended December 31, 2009 filed with the Securities and Exchange Commission. Seattle Genetics disclaims any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.

SOURCE: Seattle Genetics