Seattle Genetics Initiates Phase I Trial Of SGN-CD123A For Patients With Relapsed Or Refractory Acute Myeloid Leukemia

-SGN-CD123A, A Novel Antibody-Drug Conjugate (ADC), Represents Seattle Genetics’ Second Clinical ADC Program Focused on AML-

- Preclinical Data Showing Potent Anti-Leukemic Activity of SGN-CD123A Presented at the 2015 American Society of Hematology Annual Meeting-

BOTHELL, Wash.--(BUSINESS WIRE)--Seattle Genetics, Inc. (NASDAQ: SGEN) today announced enrollment of the first patient in a multicenter phase 1 clinical trial of SGN-CD123A for patients with relapsed or refractory acute myeloid leukemia (AML). SGN-CD123A is an investigational antibody-drug conjugate (ADC) targeted to CD123 utilizing Seattle Genetics’ proprietary technology, an engineered cysteine antibody (EC-mAb) stably linked to a highly potent DNA binding agent called a pyrrolobenzodiazepine (PBD) dimer. CD123 is expressed across AML subtypes, including leukemic stem cells, which are difficult to kill and may be responsible for high relapse rates even following intensive therapy. The trial is designed to assess the safety and anti-leukemic activity of SGN-CD123A. SGN-CD123A represents Seattle Genetics’ second clinical-stage program in development for AML, reflecting the company’s commitment to addressing the significant unmet need for these patients.

“AML is an aggressive, life-threatening disease with at least 33,000 newly diagnosed cases in the U.S. and Europe each year, and those patients have few effective treatment options”

“AML is an aggressive, life-threatening disease with at least 33,000 newly diagnosed cases in the U.S. and Europe each year, and those patients have few effective treatment options,” said Jonathan Drachman, M.D., Chief Medical Officer and Executive Vice President, Research and Development at Seattle Genetics. “ADCs are an established treatment modality designed to specifically target cancer cells and minimize toxic side effects. The significant unmet need for AML and frequent expression of the validated target CD123 on leukemic stem cells support initiating this phase 1 clinical trial. Through our SGN-CD123A program, alongside vadastuximab talirine targeted to CD33 and currently in a phase 3 study, we are making a substantial effort to develop novel treatment options for AML patients.”

The study is a phase 1, open-label, multicenter, dose-escalation clinical trial. It will initially evaluate the maximum tolerated dose of SGN-CD123A, followed by an expansion cohort to further define safety and estimate anti-leukemic activity. In addition, the trial will assess pharmacokinetics, remission rate, duration of complete remission and overall survival. The study is designed to evaluate SGN-CD123A administered every three weeks and will enroll up to approximately 100 relapsed or refractory patients at multiple centers in the United States.

Preclinical SGN-CD123A data presented at the 2015 American Society of Hematology (ASH) Annual Meeting demonstrated enhanced anti-leukemic activity across multiple AML disease models, including those typically resistant to chemotherapy. With more than 15 years of experience and innovation, Seattle Genetics is the leader in ADC development. ADCs are designed to selectively deliver cell-killing agents to tumor 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 starts in the bone marrow (the interior part of bones, where new blood cells are made) and quickly moves into the blood. According to the SEER database and Kantar Health Sciences, in 2016 approximately 33,000 new cases of AML (mostly in adults) will be diagnosed in the U.S. and Europe. In the U.S. alone, nearly 10,500 deaths will occur from AML this year.

About SGN-CD123A

SGN-CD123A is a novel ADC targeted to CD123 utilizing Seattle Genetics’ proprietary technology. CD123 is expressed across AML subtypes, including on leukemic stem cells, which are difficult to kill and may be responsible for high relapse rates even following intensive therapy. The CD123 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-CD123 antibody. The ADC is designed to be stable in the bloodstream and to release its potent DNA binding agent upon internalization into CD123-expressing cells.

About Seattle Genetics

Seattle Genetics is an innovative biotechnology company that develops and commercializes novel antibody-based therapies for the treatment of cancer. The company’s industry-leading antibody-drug conjugate (ADC) technology harnesses the targeting ability of antibodies to deliver cell-killing agents directly to cancer cells. ADCETRIS® (brentuximab vedotin), the company’s lead product, in collaboration with Takeda Pharmaceutical Company Limited, is the first in a new class of ADCs commercially available globally in 65 countries for relapsed classical Hodgkin lymphoma (HL) and relapsed systemic anaplastic large cell lymphoma (sALCL). Seattle Genetics is also advancing vadastuximab talirine (SGN-CD33A; 33A), an ADC in a phase 3 trial for acute myeloid leukemia. Headquartered in Bothell, Washington, Seattle Genetics is also advancing a robust pipeline of innovative therapies for blood-related cancers and solid tumors designed to address significant unmet medical needs and improve treatment outcomes for patients. The company has collaborations for its proprietary ADC technology with a number of companies including AbbVie, Astellas, Bayer, Genentech, GlaxoSmithKline and Pfizer. More information can be found at www.seattlegenetics.com

Forward Looking Statements

Certain of the statements made in this press release are forward looking, such as those, among others, relating to the therapeutic potential of SGN-CD123A and planned 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-CD123A advances in clinical trials and regulatory actions. More information about the risks and uncertainties faced by Seattle Genetics is contained under the caption “Risk Factors” included in the company’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2016 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.