Dose response of bone-targeted enzyme replacement for murine hypophosphatasia

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-FcD10, 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 8.2 mg/kg for 43 days. 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 ED80 (the dose prevents the bone defects in 80% of mice) was 3.2, 2.8 and 2.9 mg/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 PPi concentrations remained elevated in all treatment groups, indicating that while this parameter is a good biochemical marker for diagnosing HPP, it may not be a good follow up marker for evaluating response to treatment when administering bone-targeted TNSALP. 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.

Failure of Teriparatide in Treatment of Bone Complications of Adult Hypophosphatasia

“…At treatment discontinuation, serum calcium was 2.70 mmol/L, serum phosphorus 1.40 mmol/L, 24-hour urinary calcium 6.5 mmol/day, 25OHD 38 ng/mL, PTH 27 pg/mL, ALP 18 IU/L, bALP \2 mg/L, osteocalcin 43 ng/mL, and serum CTX 560 pg/mL. Spinal bone mineral density (BMD) was 1.05 g/cm 2 (T score -1.1) and whole-body BMD 0.945 g/cm 2 before treatment (femoral neck BMD could not be measured because of osteosynthesis), while spinal BMD was 1.04 and whole-body BMD was 0.920 after treatment.In the cases reported in the literature, teriparatide led to increased bALP levels and fracture healing [1][2][3]. However, although bone remodeling was stimulated in our patient, as shown by increased osteocalcin and CTX, teriparatide did not modify bALP levels or BMD and did not improve fracture healing.…”

“…In the cases reported in the literature, teriparatide led to increased bALP levels and fracture healing [1][2][3]. However, although bone remodeling was stimulated in our patient, as shown by increased osteocalcin and CTX, teriparatide did not modify bALP levels or BMD and did not improve fracture healing.…”

“…In our patient, the N461L mutation led to complete disappearance of the bone isoenzyme, which was not modified by PTH treatment, whereas the level has been reported to increase in patients presenting the D378V [1] and the G339R, E191K, A176T, and V423A [2] mutations. The solution of the future could be treatment with recombinant ALP [3].…”

Cellular function and molecular structure of ecto-nucleotidases

“…Similarly, TNAP knockout mice (Akp2−/−) accumulate extracellular PP i , reveal hypomineralization [488][489][490][491], and can serve as a model for the infantile form of hypophosphatasia [492]. The defect can be eliminated by subcutaneous injections of soluble TNAP targeted to mineralizing tissue [493,494] or by lentiviral application of a bone-targeted form of TNAP [495].…”

Improvement of Bone and Dental Phenotype of Murine Hypophosphatasia Mediated by a Single Injection of Lentiviral Gene Therapy

“…In 2008, reports indicated that enzyme replacement therapy (ERT) using daily injections of bone-targeted TNAP (TNAP-D 10 ) is effective in preventing all the skeletal and dental manifestations of HPP in TNAP knockout (Alpl −/− ) mice [6] [7] [8]. Recently ERT has been approved for pediatric-onset HPP in Japan [9].…”