Seattle Genetics Provides Update on SGN-30 and SGN-40 Clinical Program

    Business Editors/Health Editors
    ASCO 2005 Annual Meeting

    BOTHELL, Wash.--(BUSINESS WIRE)--May 16, 2005--Seattle Genetics, Inc. (Nasdaq:SGEN) today reported data from its SGN-30 and SGN-40 clinical programs, which are being presented at the American Society of Clinical Oncology (ASCO) 2005 Annual Meeting being held in Orlando. SGN-30 is well tolerated and demonstrates objective antitumor activity in systemic anaplastic large cell lymphoma (ALCL). SGN-40 has shown evidence of biological activity in multiple myeloma, and the company has modified the dose and schedule of SGN-40 administration in the ongoing phase I clinical trials to minimize first dose effects that are potentially attributable to cytokine release.
    "We have seen multiple objective responses with SGN-30 in systemic ALCL and continue to accrue patients at sites in both the United States and Europe," commented Clay B. Siegall, Ph.D., President and Chief Executive Officer of Seattle Genetics. "We are also evaluating new clinical trial designs for SGN-30 in Hodgkin's disease, such as combinations with chemotherapy based on preclinical data showing synergistic effects. In our SGN-40 clinical trials, we have seen preliminary indications of activity, including decreasing serum M-protein, urine protein and B-cell levels during treatment of several patients with multiple myeloma."

    SGN-30 Phase II Clinical Trials

    SGN-30 is a monoclonal antibody that targets CD30, which is highly expressed on T-cell lineage hematologic malignancies and Hodgkin's disease. Seattle Genetics is reporting at ASCO on its ongoing phase II systemic ALCL study and on its completed single-agent phase II study in Hodgkin's disease.
    The clinical evaluation of SGN-30 for relapsed or refractory systemic ALCL is ongoing at more than 40 sites in the United States and Europe. Patients in the study receive 6 milligrams per kilogram (mg/kg) of SGN-30 administered weekly for six consecutive weeks followed by a four-week observation period. The study is designed to assess antitumor activity, tolerability and pharmacokinetics of a multi-dose regimen of SGN-30.
    Fifteen patients have been enrolled in the systemic ALCL study to date. At the time of analysis, nine out of ten patients from the U.S.-based trial were evaluable for efficacy. Three patients exhibited objective responses, including one complete response and two partial responses. Two patients had stable disease and four patients had progressive disease. Multiple doses of SGN-30 have been well tolerated. Drug-related adverse events have been typically mild and consistent with antibody administration.
    SGN-30 was also evaluated as a single-agent therapy for patients with refractory or recurrent Hodgkin's disease. In this study, a total of 38 patients received treatment. Fifteen patients received SGN-30 at a dose of 6 mg/kg and 23 patients received a dose of 12 mg/kg, in each case on a weekly basis for six consecutive weeks followed by a four-week evaluation period. Patients enrolled in the study were heavily pretreated, having received a median of four prior therapies. Seventy-one percent of the patients had received prior bone marrow transplant. The study protocol precluded use of concomitant steroids, chemotherapy or other agents known to affect patient response to treatment with SGN-30. Of the 35 evaluable patients, nine patients had stable disease with an average duration of 3.5 months. Twenty-six patients experienced disease progression. SGN-30 was well tolerated. Seattle Genetics is currently evaluating alternate trial designs for SGN-30 in Hodgkin's disease, including accruing less heavily pretreated patients and/or combining SGN-30 with chemotherapy.

    SGN-40 Phase I Clinical Trials

    SGN-40 is a humanized monoclonal antibody that targets the CD40 antigen, which is expressed on most B-cell lineage hematologic malignancies, including multiple myeloma, non-Hodgkin's lymphoma and chronic lymphocytic leukemia. Seattle Genetics is conducting open-label, multi-dose, single-arm phase I studies designed to evaluate the safety, antitumor activity and pharmacokinetic profile of escalating doses of SGN-40 in patients with relapsed or refractory multiple myeloma or non-Hodgkin's lymphoma.
    In the multiple myeloma study, 16 patients have been treated with SGN-40 at dose levels of 0.5, 1, 2 or 4 mg/kg. Patients were heavily pretreated with a median of 5.5 prior therapies, median time from initial diagnosis of 6.5 years and median age of 60 years. Repeated infusions of SGN-40 at doses of 0.5, 1 and 2 mg/kg were well tolerated. At 4 mg/kg, two of three patients experienced grade 3 headaches and were diagnosed with aseptic meningitis, from which both patients fully recovered. Seattle Genetics has amended the original protocol, including dose and schedule modifications, to attenuate potential cytokine release following the first infusion. Several patients demonstrated disease stabilization and decreasing M-protein in the blood and urine during treatment with SGN-40. The study is open for accrual and continued dose escalation.
    In December 2004, Seattle Genetics initiated a single-agent, open label, dose escalation clinical trial of SGN-40 in relapsed or refractory non-Hodgkin's lymphoma patients. This study is designed to evaluate the tolerability, pharmacokinetic profile and antitumor activity of a multi-dose regimen of SGN-40. To date, six patients with a median of 3.5 prior therapies have received SGN-40 at a dose of 2 mg/kg. Although headaches were not seen in the non-Hodgkin's lymphoma study, the company has amended the administration schedule in accordance with the changes made to the multiple myeloma clinical trial.

    About Seattle Genetics

    Seattle Genetics is a biotechnology company focused on the development of monoclonal antibody-based therapies for the treatment of cancer and immunologic diseases. The company is conducting clinical and preclinical development of a diverse portfolio of product candidates in a variety of oncology and immunology settings. In addition, Seattle Genetics has developed proprietary antibody-drug conjugate (ADC) technology comprised of highly potent synthetic drugs and stable linkers for attaching the drugs to monoclonal antibodies. The company currently has license agreements for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Genentech, Bayer, CuraGen and MedImmune. More information about Seattle Genetics' pipeline and technologies can be found at www.seattlegenetics.com.

    Certain of the statements made in this press release are forward-looking. Actual results or developments may differ materially from those projected or implied in these forward-looking statements. Specifically, statements regarding ongoing and planned clinical trials of SGN-30 and SGN-40 are forward-looking and actual results may differ materially from these statements for various reasons. Factors that may cause such a difference include risks related to adverse clinical results as our product candidates move into and advance in clinical trials, risks that our drug candidates do not provide improved response rates for cancer patients and failure by Seattle Genetics to secure collaborators necessary for the advancement of our drug candidates and technologies. More information about the risks and uncertainties faced by Seattle Genetics is contained in the Company's filings 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.

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CONTACT: Seattle Genetics, Inc. Corporate Communications Peggy Pinkston, 425-527-4160 ppinkston@seagen.com

KEYWORD: WASHINGTON FLORIDA INDUSTRY KEYWORD: PHARMACEUTICAL MEDICAL BIOTECHNOLOGY TRADESHOW PRODUCT SOURCE: Seattle Genetics, Inc.

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