👤 Elena Muslimova

Hypochondroplasia is a rare genetic form of skeletal dysplasia, caused by gain-of-function pathogenic variants in the FGF receptor 3 (FGFR3). It is characterized by disproportionate short stature and has a wide spectrum of clinical features. Currently, there are no precision therapeutic options approved for hypochondroplasia. Infigratinib is an orally bioavailable FGFR1-3 selective tyrosine kinase inhibitor in development for achondroplasia and hypochondroplasia. Infigratinib acts directly at the source of the pathophysiological cause of both conditions by inhibiting the phosphorylation of FGFR3 and attenuating both main downstream signaling pathways that are involved in the conditions. Results from a phase 2 study support the concept that infigratinib has a potential to improve bone growth in achondroplasia. We report results of a step-wise evaluation of the therapeutic relevance of infigratinib for hypochondroplasia: in silico assessment of infigratinib with hypochondroplasia associated FGFR3 variants suggest strong interaction; in vitro, infigratinib showed potent inhibitory effect; in a mouse model of hypochondroplasia (Fgfr3N534K/+), infigratinib resulted in significant improvement in skeletal growth. These data in addition to the clinical results from the phase 2 study conducted in children with achondroplasia provide support for the development of infigratinib in the treatment of hypochondroplasia. Show less

Achondroplasia is a genetic skeletal condition that results in disproportionately short stature and medical complications throughout life. Infigratinib is an orally bioavailable FGFR1-3 selective tyrosine kinase inhibitor in development for achondroplasia. In this phase 2 dose-finding study, we evaluated the safety and efficacy of oral infigratinib in children with achondroplasia between the ages of 3 and 11 years. A total of 72 children were enrolled in five sequential cohorts to receive daily infigratinib at doses of 0.016 mg per kilogram of body weight (cohort 1), 0.032 mg per kilogram (cohort 2), 0.064 mg per kilogram (cohort 3), 0.128 mg per kilogram (cohort 4), and 0.25 mg per kilogram (cohort 5) for 6 months, followed by 12 months of extended treatment in which the dose in cohorts 1 and 2 could be escalated to the next ascending level at months 6 and 12. The primary safety outcome was the incidence of adverse events that led to a decrease in the dose or discontinuation of infigratinib. The primary efficacy outcome was the change from baseline in the annualized height velocity. During treatment, all the children had at least one adverse event, most of which were mild or moderate in severity; none resulted in treatment discontinuation. In cohort 5, an increased annualized height velocity was observed, which persisted throughout the duration of the study, with a mean change from baseline at 18 months of 2.50 cm per year (95% confidence interval [CI], 1.22 to 3.79; P = 0.001). The mean change from baseline in height z score was 0.54 (95% CI, 0.35 to 0.72) relative to an untreated achondroplasia reference population at 18 months; the mean change from baseline in the upper-to-lower body segment ratio was -0.12 (95% CI, -0.18 to -0.06). The administration of oral infigratinib did not result in any apparent major safety signal and increased the annualized height velocity and z score and decreased the upper-to-lower body segment ratio at 18 months of treatment in cohort 5. (Funded by BridgeBio Pharma; PROPEL2 ClinicalTrials.gov number, NCT04265651.). Show less

Achondroplasia (ACH), the most common form of disproportionate short stature, is caused by gain-of-function point mutations in fibroblast growth factor receptor 3 (FGFR3). Abnormally elevated activation of FGFR3 modulates chondrocyte proliferation and differentiation via multiple signaling pathways, such as the MAPK pathway. Using a mouse model mimicking ACH (Fgfr3Y367C/+), we have previously shown that daily treatment with infigratinib (BGJ398), a selective and orally bioavailable FGFR1-3 inhibitor, at a dose of 2 mg/kg, significantly increased bone growth. In this study, we investigated the activity of infigratinib administered at substantially lower doses (0.2 and 0.5 mg/kg, given once daily) and using an intermittent dosing regimen (1 mg/kg every 3 days). Following a 15-day treatment period, these low dosages were sufficient to observe significant improvement of clinical hallmarks of ACH such as growth of the axial and appendicular skeleton and skull development. Immunohistological labeling demonstrated the positive impact of infigratinib on chondrocyte differentiation in the cartilage growth plate and the cartilage end plate of the vertebrae. Macroscopic and microcomputed analyses showed enlargement of the foramen magnum area at the skull base, thus improving foramen magnum stenosis, a well-recognized complication in ACH. No changes in FGF23 or phosphorus levels were observed, indicating that the treatment did not modify phosphate homeostasis. This proof-of-concept study demonstrates that infigratinib administered at low doses has the potential to be a safe and effective therapeutic option for children with ACH. Show less