A First-In-Human Phase 1 Study Of The Antibody-Drug Conjugate SGN-CD19A In Relapsed Or Refractory B-Lineage Acute Leukemia and Highly Aggressive Lymphoma

CD19, a member of the immunoglobulin superfamily, is a B-cell specific marker that is found on B cells as early as the pro-B cell stage. CD19 is maintained upon malignant transformation and is expressed in the majority of patients with B-lineage leukemia and non-Hodgkin lymphoma (NHL). SGN-CD19A is a novel antibody-drug conjugate composed of a humanized anti-CD19 monoclonal antibody conjugated to the microtubule-disrupting agent monomethyl auristatin F (MMAF) via a maleimidocaproyl (mc) linker. Upon binding to CD19, SGN-CD19A internalizes and releases cys-mcMMAF, which binds to tubulin and induces G2/M arrest and apoptosis in the targeted cells.

A first-in-human, phase 1, open-label, dose-escalation study has been initiated to investigate the safety, tolerability, pharmacokinetics (PK), and antitumor activity of SGN-CD19A in adult and pediatric patients with relapsed or refractory (R/R) B-cell leukemia or highly aggressive B-cell lymphoma (CT.gov NCT01786096). Eligible patients must have a pathologically confirmed diagnosis of B-cell acute leukemia (B-ALL), Burkitt leukemia or lymphoma, or B-cell lymphoblastic lymphoma (B-LBL), and be R/R to at least 1 (adults) or 2 (pediatric) prior systemic regimens. A modified continual reassessment method is being used for dose allocation and maximum tolerated dose (MTD) estimation. SGN-CD19A is administered IV on Days 1 and 8 of 21-day cycles at up to 7 cohort-specific doses (0.3–2.3 mg/kg).

Thirteen patients (11 adults, 2 pediatric) with R/R leukemia (9 B-ALL) or lymphoma (3 B-LBL, 1 Burkitt lymphoma) have been treated in this ongoing study. Adults (73% female) have a median age of 60 years (range, 26–74) and have received a median of 2 prior systemic therapies (range, 1–6). Four of the 11 adults (36%) have also received an allogeneic stem cell transplant (SCT). The pediatric patients, 2 females 13-and 14-years-old, have each received 3 prior systemic therapies; one of the pediatric patients has also received 2 allogeneic SCTs. To date, patients have been treated at 0.3 mg/kg (2 patients), 0.6 mg/kg (3 patients), 1.0 mg/kg (3 patients), and 1.3 mg/kg (5 patients). The maximum number of cycles received by a patient is 7. Four patients remain on treatment and 9 patients have discontinued treatment (7 due to progressive disease, 1 because of investigator decision, and 1 due to death). One patient with B-ALL treated at 1.0 mg/kg developed cardiac arrest in the setting of pre-existing electrolyte abnormalities and died 7 days after the first dose of SGN-CD19A; although this event was considered unrelated to study drug by the investigator, a possible relationship could not be excluded due to temporal association. Treatment-emergent adverse events reported for ≥10% of adult patients were nausea (64%); fatigue and pyrexia (55% each); chills (36%); headache (27%); and dyspnea, hypertension, oral pain, thrombocytopenia, tumor lysis syndrome, and vomiting (18% each). Drug-related AEs in adult patients were pyrexia (55%); nausea (45%); chills (36%); fatigue (27%); and headache, oral pain, and blurred vision (9% each). Drug-related AEs reported for the pediatric patients were abdominal pain, cough, diarrhea, dyspepsia, hyperuricemia, nausea, peripheral neuropathy, pruritus, pyrexia, tachycardia, and urticaria (all Grade 1 or 2, each in one patient). Preliminary data demonstrate rapid clearance of antibody-drug conjugate at low doses in patients with leukemia, suggesting target-mediated drug disposition. To date, best responses for patients with lymphoma are stable disease (2 patients) and progressive disease (2 patients). Best responses for the 8 leukemia patients with available response assessments are complete remission (1 adult at 1.3 mg/kg); resistant disease with clinical benefit, i.e., improvement in leukemia-related symptoms (4 patients); and progressive disease (3 patients).

MTDs have not yet been identified for adult or pediatric patients and dose-escalation continues in both populations. Antitumor activity has been observed, including 1 complete remission in a heavily pretreated B-ALL patient. Nonlinear clearance of the antibody-drug conjugate in leukemia patients suggests target-mediated disposition. Updated safety, PK, and response data will be presented at the meeting. A second trial is evaluating SGN-CD19A every 3 weeks in aggressive B-cell NHL (CT.gov NCT01786135).

Borate:Seattle Genetics, Inc.: Research Funding; Genoptix: Consultancy. Fathi:Millennium: Research Funding; Seattle Genetics, Inc.: Advisory/Scientific board membership Other, Research Funding; Agios: Membership on an entity’s Board of Directors or advisory committees; Teva: Membership on an entity’s Board of Directors or advisory committees. Shah:Seattle Genetics, Inc.: Research Funding; NCCN: Membership on an entity’s Board of Directors or advisory committees; SWOG: Membership on an entity’s Board of Directors or advisory committees; Celgene: Speakers Bureau; Janssen/Pharmacyclics: Speakers Bureau. DeAngelo:Seattle Genetics, inc.: Research Funding. Silverman:Seattle Genetics, Inc.: Advisory/scientific board membership Other. Cooper:Seattle Genetics, Inc.: Research Funding. Albertson:Seattle Genetics, Inc.: Employment, Equity Ownership. O'Meara:Seattle Genetics, Inc.: Employment, Equity Ownership. Sandalic:Seattle Genetics, Inc.: Employment, Equity Ownership. Stevison:Seattle Genetics, Inc.: Employment, Equity Ownership. Chen:Seattle Genetics, Inc.: Consultancy, Research Funding, Speakers Bureau, Travel expenses Other.