Seattle Genetics Initiates Phase 1b Trial of SGN-CD33A in Combination with Frontline Standard of Care and as Consolidation Therapy for Acute Myeloid Leukemia

-SGN-CD33A is an Antibody-Drug Conjugate (ADC) Utilizing Seattle Genetics’ Newest ADC Technology-

BOTHELL, Wash.--()--Seattle Genetics, Inc. (Nasdaq: SGEN) today announced initiation of a phase 1b clinical trial of SGN-CD33A in combination with standard of care chemotherapy, including cytarabine and daunorubicin, for patients with newly diagnosed acute myeloid leukemia (AML). The trial will also evaluate SGN-CD33A in the consolidation setting for AML, both in combination with cytarabine and as a single-agent maintenance regimen. SGN-CD33A is a novel antibody-drug conjugate (ADC) targeted to CD33 utilizing Seattle Genetics’ newest technology. CD33 is expressed on most AML cells regardless of subtype, cytogenetic abnormality or underlying mutational heterogeneity. SGN-CD33A is also under evaluation in an ongoing phase 1 dose escalation trial as a single-agent or in combination with hypomethylating agents for the treatment of patients who have relapsed AML or have declined intensive frontline therapy.

“There have been few therapeutic advances for the treatment of AML in the past three decades, and there is a significant need to identify more efficacious treatment options that result in durable remissions for patients,” said Clay B. Siegall, Ph.D., President and Chief Executive Officer of Seattle Genetics. “We are encouraged by the single-agent activity of SGN-CD33A in AML patients from our ongoing phase 1 trial, as well as the preclinical data in AML models supporting combination regimens, both of which were recently presented at the American Society of Hematology Annual Meeting. Based on these data, we are expanding the evaluation of SGN-CD33A to include combination with standard of care chemotherapy in frontline and consolidation AML settings.”

The study is a phase 1b, open-label, multi-center, dose-escalation clinical trial designed to evaluate SGN-CD33A administered in combination with frontline standard of care regimens for induction (cytarabine and daunorubicin) and/or consolidation (cytarabine). In addition, the study will evaluate single-agent SGN-CD33A as a maintenance regimen. The primary endpoints are determination of the maximum tolerated dose and safety profile of SGN-CD33A in these settings. In addition, the trial will evaluate anti-leukemic activity, pharmacokinetics, progression-free survival and overall survival. The phase 1b trial will enroll approximately 90 patients at multiple centers in the United States.

Clinical data from an ongoing phase 1 trial of SGN-CD33A in AML were presented in an oral session at the 2014 American Society of Hematology (ASH) Annual Meeting (Abstract #623). In this dose-escalation study, 56 patients had been enrolled. Patients were primarily older (median age 75 years) with relapsed AML, predominantly with intermediate or adverse cytogenetic risk and 55 percent had underlying myelodysplasia. Single-agent SGN-CD33A induced bone marrow blast clearance in 44 percent of evaluable patients treated across all dose levels, including 21 percent with a complete remission or complete remission with incomplete recovery (CR/CRi). A dose-response relationship is evolving, with 77 percent of patients treated at doses greater than or equal to 40 micrograms per kilogram achieving at least 50 percent blast reduction. Adverse events were generally manageable and associated with underlying myelosuppression.

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.

SGN-CD33A is comprised of three parts: A cysteine-engineered anti-CD33 antibody enabling uniform site-specific conjugation, a cleavable dipeptide linker that is highly stable in circulation, and a pyrrolobenzodiazepine (PBD) dimer that binds DNA with high intrinsic affinity. PBD dimers are a class of DNA-crosslinking agents significantly more potent than systemic chemotherapeutic drugs. Seattle Genetics has selected and optimized specific PBD molecules for its proprietary use in ADCs. In addition, SGN-CD33A employs a novel linker system and proprietary, site-specific conjugation technology (EC-mAb) that allows uniform drug-loading of the cell-killing PBD dimer to the anti-CD33 antibody. The ADC is designed to be stable in the bloodstream and to release its cytotoxic agent upon internalization into CD33-expressing cells.

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 2014 more than 18,500 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 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 45 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-CD19A, SGN-CD33A, SGN-LIV1A, SGN-CD70A, 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.

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. 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. More information about the risks and uncertainties faced by Seattle Genetics is contained in the company’s 10-Q for the quarter ended September 30, 2014 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.

Contacts

Seattle Genetics, Inc.
Investors:
Peggy Pinkston, 425-527-4160
ppinkston@seagen.com
or
Media:
Tricia Larson, 425-527-4180
tlarson@seagen.com

Contacts

Seattle Genetics, Inc.
Investors:
Peggy Pinkston, 425-527-4160
ppinkston@seagen.com
or
Media:
Tricia Larson, 425-527-4180
tlarson@seagen.com