First-in-human evaluation of the human monoclonal antibody vantictumab (OMP-18R5; anti-Frizzled) targeting the WNT pathway in a phase I study for patients with advanced solid tumors.

Abstract

2540 Background: The WNT pathway is a key oncologic pathway in numerous tumor types. Vantictumab is a first-in-class anti-Cancer Stem Cell (CSC) antibody that interacts with the extracellular domain of 5 Frizzled receptors (1, 2, 5, 7, 8) and blocks canonical Wnt signaling (PNAS 109, 11717). In patient-derived xenograft models, vantictumab inhibits growth of many tumor types, reduces CSC frequency, promotes differentiation of tumor cells, and synergizes with many chemotherapeutic agents. Methods: Using a 3+3 design, vantictumab was given intravenously, first every 1 week (q1w) or q2w, and, ultimately, q3w. Objectives were determination of maximum tolerated dose, safety, pharmacokinetics (PK), pharmacodynamics (PD), and efficacy. Results: 18 patients have been treated in 5 dose-escalation cohorts (0.5 & 1 mg/kg q1w; 0.5 mg/kg q2w; 1 & 2.5 mg/kg q3w). Most common related adverse events (AEs) included Grade 1 and 2 fatigue, vomiting, abdominal pain, constipation, diarrhea and nausea. Only related Grade ≥3 AEs were dose-limiting toxicities of Grade 3 diarrhea and vomiting in 1 patient at 1 mg/kg q1w. Vantictumab clearance was dose-dependent, consistent with target-mediated drug disposition, with the half-life ranging from 1.5 (0.5 mg/kg) to 3 days (2.5 mg/kg). Exposure at highest dosed cohorts correlates with efficacy in preclinical tumor models. PD biomarkers indicate manipulation of WNT pathway in patient tumors and surrogate tissue. 1 patient at 0.5 mg/kg q1w had a bone fracture on Day 110 with an ~4-fold increase by Day 28 of β-C-terminal telopeptide (β-CTX), a marker for bone degradation. A revised safety plan and less frequent dosing enabled further dose escalation. Upon β-CTX doubling, 2 patients received zoledronic acid, and β-CTX returned to baseline. 3 patients with neuroendocrine tumors (NETs) had stable disease (SD) for 7+, 3.5, and 9+ months; ~2-, 4- and 7-fold longer, respectively, than on prior therapy. Conclusions: Vantictumab is well tolerated up to 2.5 mg/kg q3w. Bone toxicity appears manageable and reversible. Prolonged SD in 3 patients with NETs may represent single-agent activity. Dose escalation continues. Clinical trial information: NCT01345201.