👤 Benoit Demuynck

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 (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