A phase I study of olaratumab, an anti-platelet-derived growth factor receptor alpha (PDGFRα) monoclonal antibody, in patients with advanced solid tumors

The platelet-derived growth factor receptor (PDGFR) has an important role in tumorigenesis and tumor progression. Olaratumab (IMC-3G3) is a fully human monoclonal antibody that selectively binds human PDGFR alpha and blocks ligand binding. This phase I study assessed the safety, maximum tolerated dose (MTD), recommended phase II dose (RP2D), pharmacokinetics, and preliminary antitumor activity of olaratumab in patients with advanced solid tumors. Patients were enrolled into five dose-escalating cohorts of 3-6 patients each. Olaratumab was administered intravenously weekly at 4, 8, or 16 mg/kg (cohorts 1-3) or once every other week at 15 or 20 mg/kg (cohorts 4-5), with 4 weeks/cycle. Nineteen patients were treated in five cohorts. There were no dose-limiting toxicities; the MTD was not identified with the doses studied. The most common olaratumab-related adverse events (AE) were fatigue and infusion reactions (10.5 % each). With the exception of 1 patient (20 mg/kg) experiencing two grade 3 drug-related AEs after the dose-limiting toxicity assessment period, all drug-related AEs were grade 1 or 2. The trough concentrations (C (min)) for 16 mg/kg weekly and 20 mg/kg biweekly were higher than 155 mu g/mL, and the concentration found to be efficacious in preclinical xenograft models. Twelve patients (63.2 %) had a best response of stable disease [median duration of 3.9 months (95 % CI 2.3-8.7)]. Olaratumab was well tolerated and showed preliminary antitumor activity. RP2Ds are 16 mg/kg weekly and 20 mg/kg biweekly. Phase II studies of olaratumab as monotherapy and in combination are ongoing in several tumor types.