Pharmacokinetics and Exposure-Response of Vosoritide in Children with Achondroplasia.

BACKGROUND AND OBJECTIVE: Vosoritide, an analog of C-type natriuretic peptide, has been developed for the treatment of children with achondroplasia. The pharmacokinetics of vosoritide and relationships between plasma exposure and efficacy, biomarkers, and safety endpoints were evaluated in a phase II, open-label, dose-escalation study (N = 35 patients aged 5-14 years who received daily subcutaneous injections for 24 months) and a phase III, double-blind, placebo-controlled study (N = 60 patients aged 5-18 years randomized to receive daily subcutaneous injections for 52 weeks). METHODS: Pharmacokinetic parameters for both studies were obtained from non-compartmental analysis. Potential correlations between vosoritide exposure and changes in annualized growth velocity, collagen type X marker (CXM; a biomarker of endochondral ossification), cyclic guanosine monophosphate (cGMP; a biomarker of pharmacological activity), heart rate, and systolic and diastolic blood pressures were then evaluated. RESULTS: The exposure-response relationships for changes in both annualized growth velocity and the CXM biomarker saturated at 15 µg/kg, while systemic pharmacological activity, as measured by urinary cGMP, was near maximal or saturated at exposures obtained at the highest dose studied (i.e. 30 µg/kg). This suggested that the additional bioactivity was likely in tissues not related to endochondral bone formation. In the phase III study, following subcutaneous administration at the recommended dose of 15 µg/kg to patients with achondroplasia aged 5-18 years, vosoritide was rapidly absorbed with a median time to maximal plasma concentration (Cmax) of 15 minutes, and cleared with a mean half-life of 27.9 minutes after 52 weeks of treatment. Vosoritide exposure (Cmax and area under the concentration-time curve [AUC]) was consistent across visits. No evidence of accumulation with once-daily dosing was observed. Total anti-vosoritide antibody (TAb) responses were detected in the serum of 25 of 60 (42%) treated patients in the phase III study, with no apparent impact of TAb development noted on annualized growth velocity or vosoritide exposure. Across the exposure range obtained with 15 µg/kg in the phase III study, no meaningful correlations between vosoritide plasma exposure and changes in annualized growth velocity or CXM, or changes from predose heart rate, and systolic or diastolic blood pressures were observed. CONCLUSIONS: The results support the recommended dose of vosoritide 15 µg/kg for once-daily subcutaneous administration in patients with achondroplasia aged ≥ 5 years whose epiphyses are not closed. CLINICAL TRIALS REGISTRATION: NCT02055157, NCT03197766, and NCT01603095.

Inhibición del receptor FGFR3 por ARNs de interferencia para la acondroplasia / Fibroblast growth factor receptor 3 inhibition by small interfering RNAs in achondroplasia

Achondroplasia is a short-limbed dwarfism resulting frommutation and gain-of-function in fibroblast growth factor receptor 3(FGFR3). Effective therapy for this condition has not as yet beenestablished. We have tested the efficiency of three different smallinterference RNAs (siRNAs) to abrogate the FGFR3 expression in humanimmortalized chondrocytes carrying the achondroplasia mutation(G380R). Two siRNA sequences induced markedly decrease of FGFR3mRNA (up to 75% reduction) and protein levels (up to 61% reduction).Furthemore, siRNA-mediated knockdown of FGFR3 blocked theactivation of the downstream signal transduction ERK pathway(AU)

Inhibición del receptor FGFR3 por ARNs de interferencia para laacondroplasiaLa acondroplasia es un tipo de enanismo caracterizado porextremidades cortas resultante de una mutación en el receptor decrecimiento de fibroblastos de tipo 3 (FGFR3). Aún no se ha establecidouna terapia efectiva para esta enfermedad. Nosotros hemos testado laeficiencia de tres diferentes small interference RNAs (siRNAs) parabloquear la expresión del receptor FGFR3 en condrocitos humanosinmortalizados portadores de la mutación acondroplásica (G380R). Dossecuencias de siRNAs indujeron un marcado descenso de la expresión deARN mensajero del receptor FGFR3 (hasta un 75%) así como de losniveles de proteína (hasta un 61%). Además, el bloqueo de la expresióndel receptor FGFR3 mediado por los siRNAs redujo la activación de lacascada de transducción de las ERK(AU)

An avian model for comparative studies of insulin teratogenicity.

This study was designed to explore the effects of purified insulin during early stages of chick embryo development, and to search for variations between different molecular structures of the hormone. Chicken embryos were treated in ovo with a single dose of insulin (porcine or bovine), in only one stage of development between day 0 and day 9. Two susceptible periods were found. The earliest period (day 0 to day 3), characterized by abnormalities in the caudal vertebrae and a high mortality rate, was followed by a period with a different set of malformations, a syndrome classified as achondroplasia. The rate of achondroplastic embryos was significantly higher with porcine rather than with bovine insulin. Paradoxically, insulin at physiological doses has stimulatory effects in growth and development but, in contrast, has inhibitory effects at higher doses. The precise signalling cascade of events in the target cells is still unclear. The possible interpretations of our results are discussed. The similarity between the insulin-induced abnormalities in the chicken embryos and the caudal regression syndrome, the most common malformation found in infants of diabetic women, suggests a common mechanism. This circumstance offers the chicken embryos as an excellent in vivo model for research on the mechanism of action of insulin during normal and abnormal development.

Thallium chondrodystrophy in chick embryos: ultrastructural changes in the epiphyseal plate.

Using the transmission electron microscope, we sought to describe the morphology of thallium sulfate-induced chondrodystrophy in chick embryos. There was cell death and degeneration in all zones of growth cartilage, but the cells and matrix of the hypertrophic zone were the most severely affected. Ultrastructural changes of the hypertrophic chondrocytes consisted of alteration of the cytoplasmic contents and of the intercellular matrix; the cell membrane was smooth and without cytoplasmic extensions. The cytoplasm was filled with dilated rough endoplasmic reticulum, vacuoles of varying sizes and contents, and lipidlike bodies with electron-dense granules; mineral crystals, collagen, and degenerating mitochondria were present. The matrix showed only spotty calcification and a reduced number of dense bodies, vesicles, and granules. The cells appeared to have failed to exteriorize cell products across the plasmalemma. Failure to exteriorize cell products and to form cytoplasmic processes reduced the number of potential nucleation sites for calcification. The ultrastructure of osteocytes was much less affected.

The effect of a single injection of papain on growth of the limb bones of the mouse.

The chondrodystrophic mouse mutant stumpy (stm) shortens proximal limb bones more than distal ones and acts late in development (circa 14 days post partum). It was thought that a late disturbance in bone growth might cause more damage to epiphyses of proximal than distal bones. This was investigated using a single injection of papain on days 8, 10 and 12: shortening of proximal and distal bones was demonstrated, but was similar in all three experimental groups.

Thallium-induced achondroplasia in chicken embryos and the concept of critical periods during development.

Achondroplasia was induced in chicken embryos by in ovo application of 0.6 mg/egg thallium sulfate. The critical (sensitive) period for production of achondroplasia began on day 5 of incubation and ended at the start of HH stage 35 (8.5 days). The end of the critical period was accurately timed and found to be 205-207 hours of incubation and to coincide with a 66% decrease in growth rate of the embryos. Treatment resulted in reduced tibial growth one day later, tibial angulation two days later, and chrondrocytic necrosis four days later. The last was therefore not the cause of the angulation. Tibias were taken from thallium-treated and control donor embryos of various ages and grafted to the chorioallantoic membranes of treated and control host embryos of various ages during and outside the critical period and achondroplastic changes induced in grafted tibias exposed to thallium while on the chorioallantoic membrane. The critical period was extended into day 10 of incubation in such grafted tibias. Tibias maintained for seven days in organ culture were achondroplastic if pretreated with thallium at seven or eight days of incubation but not at ten days. Exposure of as little as 0.5 hour was sufficient to elicit micromelia when the tibias were grafted or organ cultured. Thallium therefore rapidly binds to skeletal tissues during a critical period of embryonic development but this critical period may be extended when tibias are removed from the embryo.