24 November 2015 - - US-based Seattle Genetics, Inc. (NASDAQ: SGEN) has initiated a phase 1/2 clinical trial of SGN-CD33A (vadastuximab talirine) in patients with relapsed or refractory acute myeloid leukemia. 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 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. 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 and the safety and tolerability profiles of SGN-CD33A in both pre- and post-alloSCT settings. According to the company, 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 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 a focused on developing ADCs. ADCs are monoclonal antibodies that are designed to selectively deliver cell-killing agents to tumor cells.