Phase 1 Dose Escalation Study of Seribantumab (MM-121), an anti-HER3 Monoclonal Antibody, in Patients with Advanced Solid Tumors

Abstract BACKGROUND: Overactivation of human epidermal growth factor receptor 3 (HER3) triggers multiple intracellular pathways resulting in tumor cell survival. This Phase 1 study assessed the safety, efficacy, and pharmacokinetics (PK) of seribantumab, a fully human anti-HER3 monoclonal antibody.METHODS: Adult patients with advanced or refractory solid tumors were treated in six dose cohorts of seribantumab: 3.2, 6, 10, 15, or 20 mg/kg weekly, or 40 mg/kg loading dose followed by 20 mg/kg weekly maintenance dose (40/20 mg/kg) using a modified 3+3 dose escalation strategy with cohort expansion. Primary objectives were identification of a recommended Phase 2 dose (RP2D) and determination of objective response rate. Secondary objectives were assessment of safety, dose-limiting toxicities, and PK.RESULTS: Forty-four patients (26 dose escalation; 18 dose expansion) were enrolled. Seribantumab monotherapy was well tolerated with most adverse events being transient and mild to moderate (grade 1 or 2) in severity; maximum tolerated dose was not reached. The highest dose, 40/20 mg/kg, was identified as RP2D. Best response was stable disease, achieved by 24% and 39% of patients during the dose escalation and expansion portions of the study, respectively. Seribantumab terminal half-life was ≈100 hours; steady state concentrations were reached after 3–4 weekly doses. CONCLUSIONS: Seribantumab monotherapy was well tolerated across all dose levels. Safety and PK data from this study support further seribantumab investigations in genomically defined populations. CLINICAL TRIAL REGISTRATION: NCT00734305.DATE OF REGISTRATION: August 12, 2008.