Seattle Genetics Initiates Phase I/II Clinical Trial Of SGN-CD33A (Vadastuximab Talirine) Before Or After Allogeneic Stem Cell Transplant In Patients With Relapsed Or Refractory Acute Myeloid Leukemia

-Trial Based on Anti-Leukemic Activity Observed in Ongoing Phase 1 Clinical Trials Evaluating SGN-CD33A in AML-

BOTHELL, Wash.--(BUSINESS WIRE)--Seattle Genetics, Inc. (Nasdaq: SGEN) today announced initiation of a phase 1/2 clinical trial of SGN-CD33A (vadastuximab talirine) in patients with relapsed or refractory acute myeloid leukemia (AML). The trial will evaluate SGN-CD33A monotherapy as a pre-conditioning regimen prior to an allogeneic stem cell transplant (alloSCT) and also for use as maintenance therapy following transplant. SGN-CD33A is a novel antibody-drug conjugate (ADC) targeted to CD33 utilizing Seattle Genetics’ newest ADC technology. CD33 is expressed on almost all AML cells regardless of subtype, cytogenetic abnormality, or underlying mutations.

“Relapsed and refractory acute myeloid leukemia, or AML, remains among the most challenging unmet needs in cancer, and there continues to be little success in treating AML patients utilizing conventional salvage therapies”

“Relapsed and refractory acute myeloid leukemia, or AML, remains among the most challenging unmet needs in cancer, and there continues to be little success in treating AML patients utilizing conventional salvage therapies,” said Jonathan Drachman, M.D., Chief Medical Officer and Executive Vice President, Research and Development at Seattle Genetics. “Our strategy with this trial is to evaluate the potential for SGN-CD33A to increase the percentage of patients who have no detectable leukemic cells prior to allogeneic transplant. Data suggest that patients who test negative for minimal residual disease prior to transplant are less likely to relapse. Separately, we will evaluate the potential for SGN-CD33A to maintain remissions after allogeneic transplant.”

The phase 1/2, open-label, multi-center, clinical trial is a two-part (A and B) study designed to evaluate the safety and activity of SGN-CD33A administered in patients with relapsed chemotherapy-resistant AML. Part A of the study will examine SGN-CD33 as cytoreduction pre-conditioning and Part B will evaluate SGN-CD33A in post-alloSCT as a maintenance regimen. Each part will consist of a phase 1 safety evaluation followed by a phase 2 expansion for activity. Parts A and B will enroll concurrently.

The primary endpoints in phase 1 are determination of the maximum tolerated dose (MTD) and the safety and tolerability profiles of SGN-CD33A in both pre- and post-alloSCT settings. The primary endpoints in phase 2 are to evaluate the one-year survival rates of patients treated with SGN-CD33A at the recommended dose pre- and post-alloSCT; to assess the rate of minimal residual disease negativity; and to further assess the safety and tolerability of SGN-CD33A at the recommended dose. The secondary endpoints include assessments of best response on study treatment, duration of response and overall survival. The two-part, phase 1/2 trial will enroll approximately 100 patients at multiple centers in the United States.

SGN-CD33A is also under evaluation in two other ongoing clinical trials including a phase 1 dose escalation trial as a single-agent or in combination with hypomethylating agents (HMAs) for the treatment of patients who have relapsed AML or have declined intensive frontline therapy; and a phase 1b clinical trial in combination with standard of care intensive chemotherapy, including cytarabine and daunorubicin, for younger fit patients with newly diagnosed AML. The phase 1 clinical data for SGN-CD33A in AML as monotherapy and in combination with HMAs will be presented in two oral sessions (Abstracts #324 and #454) and preclinical data supporting HMA combination strategy will be presented in a poster session (Abstract #3785) at the upcoming American Society of Hematology Annual Meeting from December 5-8, 2015.

With more than 15 years of experience and innovation, Seattle Genetics is the leader in developing ADCs. ADCs are monoclonal antibodies that are designed to selectively deliver cell-killing agents to tumor cells. This approach is intended to spare non-targeted cells and thus reduce many of the toxic effects of traditional chemotherapy while enhancing antitumor activity.

For more information about the trial, including enrolling centers, please visit www.clinicaltrials.gov.

About Acute Myeloid Leukemia

Acute myeloid leukemia, also called acute myelocytic leukemia or AML, is an aggressive type of cancer of the bone marrow and blood that progresses rapidly without treatment. AML is a cancer that starts in the cells that are supposed to mature into different types of blood cells. AML starts in the bone marrow (the soft inner part of the bones, where new blood cells are made) and quickly moves into the blood. According to the American Cancer Society, in 2015 more than 20,500 new cases of AML (mostly in adults) will be diagnosed and nearly 10,500 deaths will occur from AML (almost all will be in adults).

About SGN-CD33A (Vadastuximab Talirine)

SGN-CD33A (vadastuximab talirine) is a novel investigational ADC targeted to CD33 utilizing Seattle Genetics’ newest ADC technology. CD33 is expressed on almost all AML cells. The CD33 antibody is attached to a highly potent DNA binding agent, a pyrrolobenzodiazepine (PBD) dimer, via a proprietary site-specific conjugation technology to a monoclonal antibody with engineered cysteines (EC-mAb). PBD dimers are significantly more potent than systemic chemotherapeutic drugs and the site-specific conjugation technology (EC-mAb) allows uniform drug-loading of the cell-killing PBD agent to the anti-CD33 antibody. The ADC is designed to be stable in the bloodstream and to release its potent DNA binding agent upon internalization into CD33-expressing cells. SGN-CD33A is being evaluated in ongoing phase 1 and phase 1/2 clinical trials for patients with AML.

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 a CD30-targeted ADC that, in collaboration with Takeda Pharmaceutical Company Limited, is commercially available in more than 55 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 in CD30-expressing malignancies. Seattle Genetics is also advancing a robust pipeline of clinical-stage programs, including SGN-CD33A (vadastuximab talirine), SGN-CD19A (denintuzumab mafodotin), SGN-LIV1A, SGN-CD70A, ASG-22ME, ASG-15ME and SEA-CD40. 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.

Certain of the statements made in this press release are forward looking, such as those, among others, relating to the therapeutic potential of SGN-CD33A and anticipated clinical trials including potential patient and site enrollment. 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 the inability to show sufficient activity in this recently initiated clinical trial and the risk of adverse events as SGN-CD33A advances in clinical trials and regulatory actions. More information about these and other risks and uncertainties faced by Seattle Genetics is contained under the heading “Risk Factors” in the company’s quarterly report on Form 10-Q for the quarter ended September 30, 2015 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.