A First-in-Human Phase I Study of the Anticancer Stem Cell Agent Ipafricept (OMP-54F28), a Decoy Receptor for Wnt Ligands, in Patients with Advanced Solid Tumors.

Wnt signaling is implicated in tumor cell dedifferentiation and cancer stem cell function. Ipafricept (OMP-54F28) is a first-in-class recombinant fusion protein with the extracellular part of human frizzled 8 receptor fused to a human IgG1 Fc fragment that binds Wnt ligands. This trial evaluated ipafricept in patients with solid tumors. A 3+3 design was used; ipafricept was given intravenously every 3 weeks. The objectives were determination of dose-limiting toxicities (DLTs), recommended phase 2 dose (RP2D), safety, pharmacokinetics (PK), immunogenicity, pharmacodynamics (PD), and preliminary efficacy. 26 patients were treated in seven dose-escalation cohorts (0.5, 1, 2.5, 5, 10, 15, and 20 mg/kg). No further dose escalation was pursued as PK modeling indicated that the target efficacious dose was reached at 10 mg/kg, and fragility fractures occurred at 20 mg/kg. Most common related grade 1 and 2 adverse events (AEs; ≥20% of patients) were dysgeusia, decreased appetite, fatigue, and muscle spasms. Ipafricept-related grade 3 TEAEs included hypophosphatemia and weight decrease (1 subject each, 3.8%). Ipafricept half-life was ∼4 days and had low incidence of antidrug antibody formation (7.69%) with no impact on drug exposure. Six patients had β-C-terminal telopeptide (β-CTX) doubling from baseline, which was reversible. PD modulation of Wnt pathway genes in hair follicles occurred ≥2.5 mg/kg. Two desmoid tumor and a germ cell cancer patient experienced stable disease for >6 months. Ipafricept was well tolerated, with RP2D of 15 mg/kg Q3W. Prolonged SD was noted in desmoid tumor and germ cell cancer patients. .