Seattle Genetics Presents Preclinical Data on Antibody-Drug Conjugate Programs

BOTHELL, Wash.--(BUSINESS WIRE)--Oct. 24, 2008 - Seattle Genetics, Inc. (NASDAQ:SGEN), today announced data highlighting preclinical findings on two of its antibody-drug conjugate (ADC) programs, SGN-35 and SGN-19A, as well as research advances with its proprietary ADC technology. The data are being presented at the European Organization for Research and Treatment of Cancer-National Cancer Institute-American Association for Cancer Research (EORTC-NCI-AACR) International Conference on Molecular Targets and Cancer Therapeutics being held in Geneva, Switzerland.

"Our ADC technology is gaining substantial momentum, demonstrated by the four empowered antibodies now in clinical trials between us and our collaborators, as well as progress with multiple preclinical programs," said Clay B. Siegall, Ph.D., President and Chief Executive Officer at Seattle Genetics. "Data presented on SGN-19A, our anti-CD19 ADC, suggest it may represent a promising addition to the treatment options for non-Hodgkin lymphoma and other hematologic malignancies, including acute lymphoblastic leukemia (ALL). In addition, preclinical research with SGN-35 demonstrates its utility in a variety of Hodgkin lymphoma settings, including in combination with upfront and salvage chemotherapy regimens, complementing our clinical data on its ability to induce objective responses as a single agent."

ADCs utilize the targeting ability of monoclonal antibodies to deliver potent, cell-killing payloads to specific cells. Seattle Genetics has developed proprietary technology employing synthetic, highly potent drugs that can be attached to antibodies through proprietary linker systems. The linkers are designed to be stable in the bloodstream but to release the drug payload once inside target cells, thereby sparing non-target cells many of the toxic effects normally observed with traditional chemotherapy.

Data Summary

Preclinical data presented on SGN-35 highlight its enhanced activity when combined with chemotherapeutic agents in models of Hodgkin lymphoma, including the most common frontline therapy, ABVD (doxorubicin, bleomycin, vinblastine and dacarbazine) as well as Gemzar(R) (gemcitabine). (Abstract #523). Seattle Genetics is conducting phase I clinical trials of SGN-35 in patients with relapsed or refractory Hodgkin lymphoma and other CD30-positive hematologic malignancies. In a single-agent phase I trial, 45 percent of evaluable patients treated at doses of 1.2 milligrams per kilogram and higher achieved an objective response, including 23 percent with a complete response. Additionally, 81 percent of the 37 patients treated across all dose levels who had at least one post-baseline assessment achieved reductions in tumor volume. Seattle Genetics expects to finalize its SGN-35 development plans, including registration pathway, during 2008 and begin pivotal trials in the first half of 2009. Future trials of SGN-35 in frontline lymphoma are also planned.

SGN-19A is an ADC targeting CD19, which is expressed in a variety of hematologic malignancies, including non-Hodgkin lymphoma (NHL), chronic lymphocytic leukemia (CLL) and ALL. In preclinical models, SGN-19A was shown to internalize rapidly into CD19-expressing tumor cells and release its potent drug payload. Complete tumor regressions were observed in multiple tumor models, including lymphoma cell lines resistant to treatment with Rituxan(R) (rituximab). High levels of CD21 expression, which have previously been shown by others to interfere with CD19 targeted therapies, did not reduce the antitumor activity of SGN-19A. (Abstract #507)

Data were also presented describing novel linkers attached to auristatins that demonstrate the potential to enhance the potency and tolerability of ADCs (Abstract #527).

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 has four product candidates in ongoing clinical trials: dacetuzumab (SGN-40), lintuzumab (SGN-33), SGN-35 and SGN-70. Dacetuzumab is being developed under a worldwide collaboration with Genentech. In addition, the company has developed proprietary antibody-drug conjugate (ADC) technology comprising highly potent synthetic drugs and stable linkers for attaching the drugs to monoclonal antibodies. Seattle Genetics has collaborations for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including Genentech, Bayer, CuraGen, Progenics, Daiichi Sankyo and MedImmune, a subsidiary of AstraZeneca, as well as an ADC co-development agreement with Agensys, a subsidiary of Astellas Pharma. More information can be found at www.seattlegenetics.com.

Certain of the statements made in this press release are forward-looking, such as those, among others, relating to the therapeutic potential of Seattle Genetics' product candidates and ADC technology, and the timing of initiating pivotal trials of SGN-35. 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 adverse clinical results as our product candidates move into and advance in clinical trials, risks inherent in early-stage development and failure by Seattle Genetics' collaborators to advance product candidates incorporating its technology. 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.

Contact

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

Posted: October 2008

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