Pharmacokinetics in rats of a long-acting human parathyroid hormone-collagen binding domain peptide construct

The Relationship between the Drug Delivery Properties of a Formulation of Teriparatide Microneedles and the Pharmacokinetic Evaluation of Teriparatide Administration in Rats

PURPOSE

Teriparatide is an effective drug for the treatment of osteoporosis. This study examines the relationship between the drug delivery properties of the solid formulation with teriparatide and the pharmacokinetic properties of teriparatide in vivo.

METHODS

Teriparatide microneedles with different dissolution rates were prepared using sucrose and carboxymethylcellulose (CMC). There were three aspects of this study: (1) The dissolution rate of teriparatide from both formulations (sucrose and CMC) was measured in vitro. (2) After administration into porcine skin ex vivo, the diffusion rate of FITC-dextran was observed using a confocal microscope. (3) Pharmacokinetic studies were performed in rats and pharmacokinetic data compared with the release rate and the diffusion pattern.

RESULTS

In the in vitro dissolution experiment, 80% of teriparatide was released within 30 min from the CMC MNs, whereas 80% of teriparatide was released within 10 min from the sucrose MNs. After 30 min, the fluorescence intensity on the surface of the MNs was 40% of the initial intensity for sucrose MNs and 90% for CMC MNs. In the pharmacokinetic study, the C_max values of the CMC and sucrose MNs were 868 pg/mL and 6809 pg/mL, respectively, and the AUC_last values were 6771 pg*hr/mL for the CMC MNs and 17,171 pg*hr/mL for the sucrose MNs.

CONCLUSIONS

When teriparatide is delivered into the skin using microneedles, the release rate from the solid formulation determines the drug's pharmacokinetic properties. The diffusion pattern of fluorescence into the skin can be used to anticipate the pharmacokinetic properties of the drug.

Development of a Hypoparathyroid Male Rodent Model for Testing Delayed-Clearance PTH Molecules

CONTEXT

Parathyroid hormone (PTH) replacement is a promising approach in the management of hypoparathyroidism but long-acting analogues need to be developed. To date, animal models for testing PTH required parathyroidectomy by surgery. We have developed a nonsurgical rodent hypoparathyroid model and tested a delayed-clearance PTH molecule (DC-PTH).

OBJECTIVE

The aim of this study was to use cinacalcet to suppress calcium levels in normal rats and to reverse these effects with the administration of PTH or PTH analogues.

METHODS

Male Wistar rats were gavaged with either 30 mg/kg cinacalcet-HCl (cinacalcet) or vehicle only. Animals were then dosed with either single or repeated subcutaneous doses of PTH 1-34 or a DC-PTH at 20 nmol/kg. Control animals received vehicle only. Serum samples were analyzed for ionized calcium (iCa), phosphate, PTH, and DC-PTH. A pharmacokinetic-pharmacodynamic (PK-PD) model was built for cinacalcet, PTH 1-34, and DC-PTH using Phoenix64.

RESULTS

Cinacalcet reduced iCa levels between 2 and 24 hours, returning to baseline by 72 hours post dose with nadir at 8 hours (analysis of variance P < .001), associated with a fall in rat PTH. For phosphate there was a variable biphasic response. Single-dose PTH abrogated the cinacalcet-induced fall in iCa for up to 2 hours. DC-PTH prevented the fall in iCa from 4 hours post dose and gave a prolonged response, with iCa levels quicker to return to baseline than controls. DC-PTH has a half-life of 11.5 hours, approximately 44 times longer than human PTH 1-34. The PK-PD models defined the reproducible effect of cinacalcet on iCa and that DC-PTH had prolonged biological activity.

CONCLUSION

The administration of cinacalcet provides a robust and reproducible nonsurgical animal model of hypoparathyroidism. DC-PTH holds promise for the treatment of hypoparathyroidism in the future.

Novel bone-targeted parathyroid hormone-related peptide antagonists inhibit breast cancer bone metastases

Patients with advanced breast cancer often develop bone metastases. Treatment is limited to palliative care. Parathyroid hormone (PTH)/parathyroid hormone-related peptide (PTHrP) antagonists for bone metastases failed clinically due to short half-life and inadequate concentration in bone. We synthesized two novel PTHrP antagonists fused to an inert bacterial collagen binding domain (CBD) that directs drugs to bone. PTH(7-33)-CBD is an N-terminal truncated PTHrP antagonist. [W2]PTH(1-33)-CBD is an PTHrP inverse-agonist. The aim of this study was to assess PTH(7-33)-CBD to reduce breast cancer bone metastases and prevent osteolytic destruction in mice and to assess both drugs for apoptosis of breast cancer cells in vitro and inhibition of PTH receptor (PTHR1). PTH(7-33)-CBD (1000 µg/kg, subcutaneous) or vehicle was administered 24 h prior to MDA-MB-231 breast cancer cell inoculation into the tibia marrow. Weekly tumor burden and bone density were measured. Pharmacokinetic analysis of PTH(7-33)-CBD in rat serum was evaluated. Drug effect on cAMP accumulation in SaOS-2 osteosarcoma cells and apoptosis of MDA-MB-231 cells was assessed. PTH(7-33)-CBD reduced MDA-MB-231 tumor burden and osteolytic destruction in mice 4-5 weeks post-treatment. PTH(7-33)-CBD (1000 μg/kg i.v. and subcutaneous) in rats was rapidly absorbed with peak concentration 5-min and terminal half-life 3-h. Bioavailability by the subcutaneous route was 43% relative to the i.v. route. PTH(7-33)-CBD was detected only on rat periosteal bone surfaces that stained positive for collagen-1. PTH(7-33)-CBD and [W2]PTH(1-33)-CBD (10-8M) blocked basal and PTH agonist-induced cAMP accumulation in SaOS-2 osteosarcoma cells. Both drugs induced PTHR1-dependent apoptosis of MDA-MB-231 cells in vitro. Novel bone-targeted PTHrP antagonists represent a new paradigm for treatment of breast cancer bone metastases.

Computational model of the dual action of PTH - Application to a rat model of osteoporosis

This paper presents a pharmacokinetic/pharmacodynamic (PK/PD) model of the action of PTH(1-34) on bone modelling and remodelling, developed for quantitatively investigating the dose- and administration pattern-dependency of the bone tissue response to this drug. Firstly, a PK model of PTH(1-34) was developed, accounting for administration via subcutaneous injections. Subsequently, the PK model was coupled to a (mechanistic) bone cell population model of bone modelling and remodelling, taking into account the effects of PTH(1-34) on the differentiation of lining cells into active osteoblasts, on the apoptosis of active osteoblasts, and on proliferation of osteoblast precursors, as well as on the key regulatory pathways of bone cell activities. Numerical simulations show that the coupled PK/PD model is able to distinguish between continuous and intermittent administration patterns of PTH(1-34), in terms of yielding both catabolic bone responses (if drug administration is carried out continuously) and anabolic bone responses (if drug administration is carried out intermittently). The model also features a non-linear relation between bone gain and drug dose (as known from experiments); doubling the dose from 80 μg/kg/day to 160 μg/kg/day induced a 1.3-fold increase of the bone volume-to-total volume ratio. Furthermore, the model presented in this paper confirmed that bone modelling represents an essential mechanism of the anabolic response of bone to PTH(1-34) administration in rat models, and that the large amount of bone formation observed in such models cannot be explained via remodelling alone.

Sub-picomolar quantification of PTH 1-34 in plasma by UHPLC-MS/MS after subcutaneous injection of teriparatide and identification of PTH 1-33, its degradation product

Teriparatide (PTH 1-34, Forsteo^®) is a bioactive N-terminal fragment of the native endogenous parathyroid hormone (PTH 1-84) recommended for the treatment of osteoporosis in patients with high risk of fracture. Since PTH 1-34 may undergo proteolysis we have validated an ultra-high pressure liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method for unambiguously measuring intact PTH 1-34 with the same sensitivity as ELISA, at subpicomolar level (LLOQ at 0.4 pM). The full chromatographic run was achieved in 16.5 min. The method validation showed satisfactory intra- and inter-assay precision (CV < 13%) and excellent trueness (<5%), and almost no matrix effect (recoveries 78-92%). We found that after subcutaneous injection in two volunteers, PTH 1-34 half-life was shorter with UHPLC-MS/MS and that ELISA was overestimating PTH 1-34 late concentrations in both volunteers. Qualitative mass spectrometry was performed and led to the discovery of PTH 1-33, a fragment of PTH 1-34 with unknown function. This study emphasized the importance of switching from immunoassays to mass spectrometry when measuring bioactive peptides prompt to proteolysis into fragments that may exhibit altered bioactivity and duration of action.