-Sixth Proprietary ADC in Clinical Development for the Treatment of Cancer-
-Second Proprietary ADC Program Utilizing Newest ADC Technology to Advance into Clinical Trials-

BOTHELL, WA, USA I August 12, 2014 I Seattle Genetics, Inc. (SGEN) today announced the initiation of a phase 1 clinical trial evaluating SGN-CD70A for CD70-positive relapsed or refractory non-Hodgkin lymphoma (NHL) and metastatic renal cell carcinoma (RCC). SGN-CD70A is a novel antibody-drug conjugate (ADC) targeted to CD70 utilizing the company’s newest ADC technology. The phase 1 trial is designed to assess the safety and antitumor activity of SGN-CD70A.

“CD70 is a very promising ADC antigen, which is highly expressed in both NHL and RCC, and has minimal expression in healthy tissues,” said Jonathan Drachman, M.D., Chief Medical Officer and Executive Vice President, Research and Development, at Seattle Genetics. “We are building on the single-agent activity we observed with our former SGN-75 candidate and have designed SGN-CD70A with a goal to have enhanced activity by utilizing our next-generation ADC technology. Our preclinical data demonstrate that this novel ADC is extremely potent in RCC and NHL models, and we are enthusiastic about commencing a clinical trial of SGN-CD70A in patients with a clear need for new therapeutic options.”

Seattle Genetics previously observed single-agent activity, including objective responses, in a phase 1 clinical trial with an initial CD70-targeted ADC called SGN-75 but did not observe enough activity to support further clinical development. To build on that experience, the company developed a next-generation anti-CD70 ADC utilizing its newest technology comprising a highly potent cytotoxic agent, called a pyrrolobenzodiazepine (PBD) dimer, stably linked to a CD70-directed antibody via proprietary site-specific conjugation technology. Preclinical data presented at the 2014 American Association of Cancer Research (AACR) annual meeting demonstrate SGN-CD70A induces targeted cell killing via DNA damage to treated tumors in both RCC and NHL models.

The new SGN-CD70A study is a phase 1, open-label, multi-center, dose-escalation clinical trial. The primary endpoints are to estimate the maximum tolerated dose and to evaluate the safety of SGN-CD70A. In addition, the trial will evaluate the antitumor activity and pharmacokinetics in patients with CD70-positive metastatic RCC or relapsed or refractory NHL, including mantle cell lymphoma and diffuse large B-cell lymphoma. The study is designed to evaluate SGN-CD70A administered every three weeks and will enroll approximately 95 patients at multiple centers in the United States.

ADCs are monoclonal antibodies that are designed to selectively deliver cytotoxic agents to tumor cells. This approach is intended to spare non-targeted cells and reduce many of the toxic effects of traditional chemotherapy while enhancing antitumor activity.

About SGN-CD70A

SGN-CD70A is an ADC utilizing PBD dimers, a class of DNA-crosslinking agents that are significantly more potent than standard chemotherapeutic drugs. Seattle Genetics has been working with PBDs since 2009 under an exclusive research and licensing arrangement with Spirogen Ltd. Over the past five years, Seattle Genetics has selected and optimized specific PBD molecules for its proprietary use in ADCs. In addition, SGN-CD70A employs a novel linker system and proprietary, site-specific conjugation technology (EC-mAb) that allows uniform drug-loading of the cell-killing PBD agent to the anti-CD70 antibody. The ADC is designed to be stable in the bloodstream and to release its cytotoxic agent upon internalization into CD70-expressing cells. SGN-CD70A is Seattle Genetics’ second ADC in clinical development employing the novel PBD technology.

More information about the trial, including enrolling centers, will be available by visiting www.clinicaltrials.gov.

About Seattle Genetics

Seattle Genetics is a biotechnology company focused on the development and commercialization of innovative antibody-based therapies for the treatment of cancer. Seattle Genetics is leading the field in developing antibody-drug conjugates (ADCs), a technology designed to harness the targeting ability of antibodies to deliver cell-killing agents directly to cancer cells. The company’s lead product, ADCETRIS® (brentuximab vedotin), is an ADC that, in collaboration with Takeda Pharmaceutical Company Limited, is commercially available for two indications in more than 40 countries, including the U.S., Canada, Japan and members of the European Union. Additionally, ADCETRIS is being evaluated broadly in more than 30 ongoing clinical trials. Seattle Genetics is also advancing a robust pipeline of clinical-stage ADC programs, including SGN-CD70A, SGN-CD19A, SGN-CD33A, SGN-LIV1A, ASG-22ME and ASG-15ME. Seattle Genetics has collaborations for its ADC technology with a number of leading biotechnology and pharmaceutical companies, including AbbVie, Agensys (an affiliate of Astellas), Bayer, Genentech, GlaxoSmithKline and Pfizer. More information can be found at www.seattlegenetics.com.

SOURCE: Seattle Genetics