Tyrosine kinase inhibitor NVP-BGJ398 functionally improves FGFR3-related dwarfism in mouse model

Abstract

Achondroplasia (ACH) is the most frequent form of dwarfism and is caused by gain-of-function mutations in the fibroblast growth factor receptor 3-encoding (FGFR3-encoding) gene. Although potential therapeutic strategies for ACH, which aim to reduce excessive FGFR3 activation, have emerged over many years, the use of tyrosine kinase inhibitor (TKI) to counteract FGFR3 hyperactivity has yet to be evaluated. Here, we have reported that the pan-FGFR TKI, NVP-BGJ398, reduces FGFR3 phosphorylation and corrects the abnormal femoral growth plate and calvaria in organ cultures from embryos of the Fgfr3Y367C/+ mouse model of ACH. Moreover, we demonstrated that a low dose of NVP-BGJ398, injected subcutaneously, was able to penetrate into the growth plate of Fgfr3Y367C/+ mice and modify its organization. Improvements to the axial and appendicular skeletons were noticeable after 10 days of treatment and were more extensive after 15 days of treatment that started from postnatal day 1. Low-dose NVP-BGJ398 treatment reduced intervertebral disc defects of lumbar vertebrae, loss of synchondroses, and foramen-magnum shape anomalies. NVP-BGJ398 inhibited FGFR3 downstream signaling pathways, including MAPK, SOX9, STAT1, and PLCγ, in the growth plates of Fgfr3Y367C/+ mice and in cultured chondrocyte models of ACH. Together, our data demonstrate that NVP-BGJ398 corrects pathological hallmarks of ACH and support TKIs as a potential therapeutic approach for ACH.

Meckel’s and condylar cartilages anomalies in achondroplasia result in defective development and growth of the mandible

“…We then observed that the number of Fgfr3-positive cells in this cartilage was increased in Fgfr3 Y367C/+ embryos (+151%, P < 0.0001; Fig. 2A and D) as reported in the growth plate of the same mouse model (11,35) and ACH and TD fetuses (6). FGFR3 exhibits a specific pattern of expression during chondrocyte differentiation (5,36), and in the growth plate, its expression is mostly limited to the resting, proliferating and pre-hypertrophic chondrocytes (37).…”

“…We hypothesized that Fgfr3 activation disturbs chondrocytes homeostasis in MC, as it was shown in other cartilages, such as the growth plate (10), the inner ear (10), the cranial base synchondroses (3) or vertebral bodies (11), and that these defects could be responsible for the mandibular hypoplasia and dysmorphogenesis observed in Fgfr3 Y367C/+ mice. We therefore collected embryos at gestational day E16.5 and E18.5 and analyzed markers of chondrocyte proliferation and differentiation on histological sections.…”

“…We first developed an ex vivo system of mandible explant cultures, similar to the femur explant cultures we used to test pharmacological approaches of FGFR inhibition (11,32,35). We isolated the mandible from WT and Fgfr3 Y367C/+ embryos at E16.5, dissected the mandibles into two hemi-mandibles and cultured those separately for 6 days.…”

“…We performed daily subcutaneous injection of either NVP-BGJ398 (2 mg/kg) or vehicle on 1-day-old mice from P0 to P15 (11). The mandibles of P16 mice were then imaged by micro-CT. As in the ex vivo experiments, we observed phenotypic changes of the condylar neck in Fgfr3 Y367C/+ mice treated with NVP-BGJ398 compared to Fgfr3 Y367C/+ littermates treated with DMSO.…”

“…FGFR3 over-activation disturbs the proliferation and differentiation of chondrocytes in the growth plate of long bones (6–8) and synchondroses of the cranial base (3,9). Other cartilaginous structures are affected in ACH, such as the inner ear (10), vertebral bodies and intervertebral disc (11) and joints (7). …”