Article

Dose response of bone-targeted enzyme replacement for murine hypophosphatasia

Sanford Children's Health Research Center, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA.
Bone (Impact Factor: 4.46). 03/2011; 49(2):250-6. DOI: 10.1016/j.bone.2011.03.770
Source: PubMed

ABSTRACT Hypophosphatasia (HPP) features rickets or osteomalacia from tissue-nonspecific alkaline phosphatase (TNSALP) deficiency due to deactivating mutations within the ALPL gene. Enzyme replacement therapy with a bone-targeted, recombinant TNSALP (sALP-FcD(10), renamed ENB-0040) prevents manifestations of HPP when initiated at birth in TNSALP knockout (Akp2(-/-)) mice. Here, we evaluated the dose-response relationship of ENB-0040 to various phenotypic traits of Akp2(-/-) mice receiving daily subcutaneous (SC) injections of ENB-0040 from birth at 0.5, 2.0, or 8.2mg/kg for 43days. Radiographs, μCT, and histomorphometric analyses documented better bone mineralization with increasing doses of ENB-0040. We found a clear, positive correlation between ENB-0040 dose and prevention of mineralization defects of the feet, rib cage, lower limbs, and jaw bones. According to a dose-response model, the ED(80) (the dose that prevents bone defects in 80% of mice) was 3.2, 2.8 and 2.9mg/kg/day for these sites, respectively. Long bones seemed to respond to lower daily doses of ENB-0040. There was also a positive relationship between ENB-0040 dose and survival. Median survival, body weight, and bone length all improved with increasing doses of ENB-0040. Urinary PP(i) concentrations remained elevated in all treatment groups, indicating that while this parameter is a good biochemical marker for diagnosing HPP in patients, it may not be a good follow up marker for evaluating response to treatment when administering bone-targeted TNSALP to mice. These dose-response relationships strongly support the pharmacological efficacy of ENB-0040 for HPP, and provide the experimental basis for the therapeutic range of ENB-0040 chosen for clinical trials.

Download full-text

Full-text

Available from: Esther Cory, Jul 11, 2014
1 Follower
 · 
127 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Craniosynostosis, the premature fusion of cranial bones, has traditionally been described as a disease of increased bone mineralization. However, multiple mouse models of craniosynostosis display craniosynostosis simultaneously with diminished cranial bone volume and/or density. We propose an alternative hypothesis that craniosynostosis results from abnormal tissue mineralization through the downregulation of tissue-non-specific alkaline phosphatase (TNAP) enzyme downstream of activating mutations in FGFRs. Neonatal Crouzon (FGFR(C) (342Y/+) ) and wild-type (FGFR(+/+) ) mice were injected with lentivirus to deliver a recombinant form of TNAP. Mice were sacrificed at 4 weeks postnatal. Serum was collected to test for alkaline phosphatase (AP), phosphorus, and calcium levels. Craniofacial bone fusion and morphology were assessed by micro-computed tomography. Injection with the TNAP lentivirus significantly increased serum AP levels (increased serum AP levels are indicative of efficient transduction and production of the recombinant protein), but results were variable and dependent upon viral lot and the litter of mice injected. Morphological analysis revealed craniofacial form differences for inferior surface (p = 0.023) and cranial height (p = 0.014) regions between TNAP lentivirus-injected and vehicle-injected Crouzon mice. With each unit increase in AP level, the odds of lambdoid suture fusion decreased by 84.2% and these results came close to statistical significance (p = 0.068). These results suggest that TNAP deficiency may mediate FGFR2-associated craniosynostosis. Future studies should incorporate injection of recombinant TNAP protein, to avoid potential side effects and variable efficacy of lentiviral gene delivery. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.
    Orthodontics and Craniofacial Research 04/2015; 18 Suppl 1:196-206. DOI:10.1111/ocr.12080 · 1.29 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Hypophosphatasia (HPP) results from ALPL gene mutations, which lead to a deficiency of tissue-nonspecific alkaline phosphatase (TNAP), and accumulation of inorganic pyrophosphate, a potent inhibitor of mineralization that is also a natural substrate of TNAP, in the extracellular space. HPP causes mineralization disorders including soft bones (rickets or osteomalacia) and defects in teeth and periodontal tissues. Enzyme replacement therapy using mineral-targeting recombinant TNAP has proven effective in preventing skeletal and dental defects in TNAP knockout (Alpl(-/-)) mice, a model for life-threatening HPP. Here, we show that the administration of a soluble, intestinal-like chimeric alkaline phosphatase (ChimAP) improves the manifestations of HPP in Alpl(-/-) mice. Mice received daily subcutaneous injections of ChimAP at doses of 1, 8 or 16mg/kg, from birth for up to 53days. Lifespan and body weight of Alpl(-/-) mice were normalized, and vitamin B6-associated seizures were absent with 16mg/kg/day of ChimAP. Radiographs, μCT and histological analyses documented improved mineralization in cortical and trabecular bone and secondary ossification centers in long bones of ChimAP16-treated mice. There was no evidence of craniosynostosis in the ChimAP16-treated mice and we did not detect ectopic calcification by radiography and histology in the aortas, stomachs, kidneys or lungs in any of the treatment groups. Molar tooth development and function improved with the highest ChimAP dose, including enamel, dentin, and tooth morphology. Cementum remained deficient and alveolar bone mineralization was reduced compared to controls, though ChimAP-treated Alpl(-/-) mice featured periodontal attachment and retained teeth. This study provides the first evidence for the pharmacological efficacy of ChimAP for use in the treatment of skeletal and dental manifestations of HPP. Copyright © 2014. Published by Elsevier Inc.
    Bone 11/2014; DOI:10.1016/j.bone.2014.11.017 · 4.46 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Tissue-nonspecific alkaline phosphatase (TNAP) is an enzyme present on the surface of mineralizing cells and their derived matrix vesicles that promotes hydroxyapatite crystal growth. Hypophosphatasia (HPP) is an inborn-error-of-metabolism that, dependent upon age of onset, features rickets or osteomalacia due to loss-of function mutations in the gene (Alpl) encoding TNAP. Craniosynostosis is prevalent in infants with HPP and other forms of rachitic disease but how craniosynostosis develops in these disorders is unknown.
    Bone 10/2014; 67. DOI:10.1016/j.bone.2014.06.040 · 4.46 Impact Factor