Infigratinib in Children With Achondroplasia (ACH): Design of PROPEL2 - A Phase 2, Open-Label, Dose-Escalation and Dose-Expansion Study

Background: ACH, the most common non-lethal form of skeletal dysplasia, is characterized by defective endochondral ossification resulting from gain-of-function mutations in the fibroblast growth factor receptor 3 (FGFR3) gene, a negative regulator of endochondral bone formation. Current treatment options are non-targeted, ineffective, or painful interventions aimed at preventing or treating complications. Infigratinib is an orally bioavailable and selective FGFR1-3 tyrosine kinase inhibitor in development for FGFR-related conditions. In vitro data with infigratinib showed inhibition of FGFR1-3 activity with reversal of established growth arrest in chondrocytes. In vivo studies revealed dose-dependent improvements in foramen magnum and long bone length in Fgfr3Y367C/+ mice following treatment with infigratinib. Methods: PROPEL2 is a prospective, phase 2, open-label study of infigratinib in children with ACH. Children 3-11 years of age with ACH who have completed at least 6 months of observation in the observational PROPEL study are eligible to participate. PROPEL2 consists of dose escalation with an extended treatment phase, designed as dose finding, followed by a dose-expansion phase to confirm the selected dose and to provide evidence of efficacy. The primary endpoints of the dose-escalation/extended treatment phase are treatment-emergent adverse events and change from baseline in annualized growth velocity. Subjects (n=40) will be enrolled in ascending dose cohorts of approximately 10 subjects/cohort (4 cohorts planned) and treated for 6 months at their assigned dose, continuing for an additional 12 months with dose modifications as required. Up to 20 new subjects will be enrolled in the dose-expansion phase and receive infigratinib (mini-tablets, administered orally once daily) for 12 months. Secondary objectives include: safety/tolerability of infigratinib; changes from baseline in anthropometric parameters, including body proportions; and the pharmacokinetic/pharmacodynamic profile of infigratinib. An exploratory objective is evaluation of changes in ACH disease burden. Current Status: PROPEL2 is currently enrolling - the first subject was entered in July 2020. The planned total enrollment is 60 children with ACH (n=40 in the dose-escalation/extended treatment phase; n=20 in the dose-expansion phase). Following completion of PROPEL2, subjects have the opportunity to enroll in an open-label long-term extension study to assess the safety and efficacy of long-term administration of infigratinib in children with ACH.