Discovery of a Long-Acting Parathyroid Hormone 1-34 Analogue to Treat Hypoparathyroidism.

Hypoparathyroidism (HP) is a rare disease with clinical manifestations of hypocalcemia and hyperphosphatemia, resulting from deficient or absent parathyroid hormone (PTH) secretion. Conventional treatment for patients with HP involves extensive calcium and vitamin D supplementation. In 2015, PTH1-84 was approved by the United States Food and Drug Administration as an adjunct for HP patients who cannot be well-controlled on conventional treatment. However, PTH1-84 therapy requires a daily injection, leading to poor patient compliance. The purpose of this study was to develop a long-acting PTH1-34 analogue by increasing its affinity to albumin. Three PTH1-34 variants were generated by substituting two of the three lysine (Lys) residues with arginine, reserving a single Lys as the modification site in each sequence. A series of side chains, containing fatty acid, deoxycholic acid, or biotin groups, were synthesized to modify these PTH1-34 variants by using a solid-liquid phase synthesis approach. In vitro bioactivity and albumin affinity tests were used to screen these new PTH1-34 analogues. Finally, Lys27-AAPC was selected from 69 synthesized analogues as a candidate therapeutic compound because it retained potency and exhibited a high albumin-binding capacity. In pharmacodynamic experiments, Lys27-AAPC demonstrated enhanced and prolonged efficacy in serum calcium elevating relative to PTH1-84. Moreover, a lyophilized powder for injection containing Lys27-AAPC was developed for further testing and represented a potential long-acting HP treatment.

A computational study of the dual effect of intermittent and continuous administration of parathyroid hormone on bone remodeling.

Bone remodeling is a process known to be governed by constant interactions between osteoblast and osteoclast through complex pathway networks mediated by signaling factors. Experimental studies show that intermittent and continuous administration of PTH/PTHrP led to opposite outcomes in terms of bone mass. To investigate this dual effect of PTH/PTHrP, we develop a computational model based on a simplified signaling pathway network which includes relevant molecular effectors and cells. Multiple ordinary differential equations linking all considered components in the signaling pathway network through reaction kinetics are solved with dose values and patterns of injection from experiments as input. Modeling results show good agreement with experimental observations in that continuous injection of PTH/PTHrP generates catabolic effect on bone mass while intermittent injection yields anabolic effect. The signaling factors governing the interaction between osteoblast and osteoclast indeed play a key role in the dual effect of PTH/PTHrP. Furthermore, there appears to be an optimal interval for intermittent injection of PTH/PTHrP for yielding the most bone regeneration, and a synergistic outcome could be achieved by combining intermittent injection of PTH/PTHrP with application of a treatment (to mimic the filling of bone defects with polymeric scaffolds). This modeling work sheds valuable insights into the influence of temporal control of PTH/PTHrP on bone mass and presents a possible path toward bridging bioengineering approaches with clinical treatment strategies. STATEMENT OF SIGNIFICANCE: A computational model considering simplified signaling pathways containing crucial components of PTH, PTHrP, osteoblast precursor, osteoblast, osteoclast precursor, osteoclast, RANKL and IL-6 family cytokoines has been developed to study the dual effect of PTH/PTHrP on bone metabolism. The model takes the dose values and patterns of injection from experiments as input and yields predictions that convincingly match experimental measurements. This work highlights the importance of providing an optimal hormone treatment strategy for maintaining healthy bone metabolism. Moreover, the integrative approach of relying on experimental observations to find reasonable values for relevant modeling parameters has been proven to be powerful in advancing our understanding of biological interactions among cells and signaling factors.

A comparative study of dissolving hyaluronic acid microneedles with trehalose and poly(vinyl pyrrolidone) for efficient peptide drug delivery.

We studied the role of the additives trehalose and poly(vinyl pyrrolidone) in the physical and pharmacokinetic properties of peptide drug incorporated hyaluronic acid microneedles. Poly(vinyl pyrrolidone) increases the mechanical strength of microneedles and ameliorates drug bioavailability in vivo, suggesting that poly(vinyl pyrrolidone) can be a promising additive in the fabrication of peptide drug-encapsulated fully dissolving microneedles.

Prolonged Pharmacokinetic and Pharmacodynamic Actions of a Pegylated Parathyroid Hormone (1-34) Peptide Fragment.

Polyethylene glycol (PEG) addition can prolong the pharmacokinetic and pharmacodynamic actions of a bioactive peptide in vivo, in part by impeding rates of glomerular filtration. For parathyroid hormone (PTH) peptides, pegylation could help in exploring the actions of the hormone in the kidney; e.g., in dissecting the relative roles that filtered versus blood-borne PTH play in regulating phosphate transport. It could also lead to potential alternate forms of treatment for hypoparathyroidism. We thus synthesized the fluorescent pegylated PTH derivative [Lys13 (tetramethylrhodamine {TMR}), Cys35 (PEG-20,000 Da)]PTH(1-35) (PEG-PTHTMR ) and its non-pegylated counterpart [Lys13 (TMR), Cys35 ]PTH(1-35) (PTHTMR ) and assessed their properties in cells and in mice. In PTHR1-expressing HEK-293 cells, PEG-PTHTMR and PTHTMR exhibited similar potencies for inducing cAMP signaling, whereas when injected into mice, the pegylated analog persisted much longer in the circulation (>24 hours versus ∼ 1 hour) and induced markedly more prolonged calcemic and phosphaturic responses than did the non-pegylated control. Fluorescence microscopy analysis of kidney sections obtained from the injected mice revealed much less PEG-PTHTMR than PTHTMR on the luminal brush-border surfaces of renal proximal tubule cells (PTCs), on which PTH regulates phosphate transporter function, whereas immunostained phosphorylated PKA substrate, a marker of cAMP signaling, was increased to similar extents for the two ligands and for each, was localized to the basolateral portion of the PTCs. Pegylation of a bioactive PTH peptide thus led to prolonged pharmacokinetic/pharmacodynamic properties in vivo, as well as to new in vivo data that support a prominent role for PTH action at basolateral surfaces of renal proximal tubule cells. © 2016 American Society for Bone and Mineral Research.

Kinetics of parathyroid hormone after parathyroidectomy in chronic hemodialysis patients.

Secondary hyperparathyroidism is a common complication in chronic renal failure. The treatment in some cases requires parathyroidectomy. The kinetics of the parathyroid hormone (PTH) levels after surgery helps to evaluate the efficacy of parathyroidectomy. Prospective analysis was made of the kinetics of intact PTH (iPTH) after parathyroidectomy in 10 chronic hemodialysis (HD) patients who had secondary hyperparathyroidism. We determined the levels of iPTH before surgery and its evolution after parathyroidectomy at regular intervals: Day 0, D7, D15, D30 and D90. The mean age of our patients was 40 ± 13 years, with a sex ratio of 1. The mean duration on HD was 122 ± 63 months. The duration of secondary hyperparathyroidism varied from one year to 12 years. All patients had received medical treatment for hyperparathyroidism. The indications for parathyroidectomy included resistance to medical treatment in seven cases, development of brown tumors in two cases and soft tissue calcifications in one case. All patients had radiographic evidence of hyperparathyroidism. The parathyroidectomy was sub-total in all patients, 6/8 in four cases and 7/8 in six cases. The mean iPTH level was 2341 ± 1946 pg/mL before surgery. A sharp drop in this level was noticed on D0, with a median of 92 pg/mL and, thereafter, the levels were 79 pg/mL on D7, 25 pg/mL on D15 and 36 pg/mL after 1 month. At 3 months post-surgery, the mean iPTH level was 302 pg/mL. Histological examination of the resected gland showed parathyroid hyperplasia in all patients. In our series, the efficacy of sub-total parathyroidectomy was satisfactory with rapid normalization of PTH, which is consistent with the literature data. Sub-total parathyroidectomy still has a place in the treatment of secondary hyperparathyroidism in chronic renal failure. Its indications should be limited to cases resistant to medical treatment and, in particular, in cases with occurrence of complications.

Pharmacokinetics and pharmacodynamics of subcutaneous recombinant parathyroid hormone (1-84) in patients with hypoparathyroidism: an open-label, single-dose, phase I study.

BACKGROUND: Impaired mineral homeostasis affecting calcium, phosphate, and magnesium is a result of parathyroid hormone (PTH) deficiency in hypoparathyroidism. The current standard of treatment with active vitamin D and oral calcium does not control levels of these major minerals. Recombinant full-length human PTH 1-84 (rhPTH[1-84]) is being developed for the treatment of hypoparathyroidism. OBJECTIVE: The goal of this study was to investigate the pharmacokinetics and pharmacodynamics of a single subcutaneous injection of rhPTH(1-84) in patients with hypoparathyroidism. METHODS: This was an open-label, dose-escalating study of single subcutaneous administration of 50 µg and then 100 µg of rhPTH(1-84). Enrolled patients (age range, 25-85 years) had ≥12 months of diagnosed hypoparathyroidism defined according to biochemical evidence of hypocalcemia with concomitant low-serum intact PTH and were taking doses ≥1000 mg/d of oral calcium and ≥0.25 µg/d of active vitamin D (oral calcitriol). The patient's prescribed dose of calcitriol was taken the day preceding but not on the day of or during the 24 hours after rhPTH(1-84) administration. Each patient received a single 50-µg rhPTH(1-84) dose, had at least a 7-day washout interval, and then received a single 100-µg rhPTH(1-84) dose. The following parameters were assessed: plasma PTH; serum and urine total calcium, magnesium, phosphate, and creatinine; and urine cyclic adenosine monophosphate. RESULTS: After administration of rhPTH(1-84) 50 µg (n = 6) and 100 µg (n = 7), the approximate t½ was 2.5 to 3 hours. Plasma PTH levels increased rapidly, then declined gradually back to predose levels at ~12 hours. The median AUC was similar with calcitriol and rhPTH(1-84) for serum 1,25-dihydroxyvitamin D (calcitriol, 123-227 pg · h/mL; rhPTH[1-84], 101-276 pg · h/mL), calcium (calcitriol, 3.3-3.7 mg · h/dL; rhPTH[1-84], 3.3-7.6 mg · h/dL), and magnesium (calcitriol, 0.7-0.9 mg · h/dL; rhPTH[1-84], 1.3-2.8 mg · h/dL). In contrast, the median AUC for phosphate was strongly negative with rhPTH(1-84) (calcitriol, -1.0 to 0.8 mg · h/dL; rhPTH[1-84], -21.3 to -26.5 mg · h/dL). Compared with calcitriol, rhPTH(1-84) 50 µg reduced 24-hour calcium excretion and calcium-to-creatinine ratios by 12% and 23%, respectively, and rhPTH(1-84) 100 µg reduced them by 26% and 27%. There was little overall impact on urine magnesium levels. Compared with calcitriol, rhPTH(1-84) 50 µg increased urinary phosphate excretion and phosphate-to-creatinine ratios by 53% and 54%, respectively, and rhPTH(1-84) 100 µg increased them by 45% and 42%. Urine cyclic adenosine monophosphate-to-creatinine ratio increased with rhPTH(1-84) by 2.3-fold (50 µg) and 4.4-fold (100 µg) compared with calcitriol. CONCLUSIONS: PTH replacement therapy with rhPTH(1-84) regulated mineral homeostasis of calcium, magnesium, phosphate, and vitamin D metabolism toward normal in these study patients with hypoparathyroidism.

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

The pharmacokinetics of a hybrid peptide consisting of the N-terminal biologically active region of human parathyroid hormone (PTH) linked to a collagen-binding domain (CBD) were evaluated in female Sprague-Dawley rats. The peptide, PTH-CBD, consists of the first 33 amino acids of PTH linked as an extension of the amino acid chain to the CBD peptide derived from ColH collagenase of Clostridium histolyticum. Serum concentrations arising from single dose administration by the subcutaneous and intravenous routes were compared with those measured following route-specific mole equivalent doses of PTH(1-34). Population-based modeling demonstrated similar systemic absorption kinetics and bioavailability for both peptides. Exposure to PTH-CBD was sixfold higher because of a systemic clearance of approximately 20% relative to PTH(1-34); however, these kinetics were consistent with more than 95% of a dose being eliminated from serum within 24 h. Results obtained support continued investigation of PTH-CBD as a bone-targeted anabolic agent for the treatment of postmenopausal osteoporosis.

[Medical therapy of osteoporosis in patients with mildly to moderate decreased renal function]. / Medicinsk behandling af osteoporose hos patienter med moderat til svaert nedsat nyrefunktion.

Both chronic kidney disease and osteoporosis are frequent conditions in the general population. Most drugs for treating osteoporosis seem safe in terms of affecting renal function for patients with mildly to moderate decreased renal function. There are very few data on the efficacy (reduction in fracture risk) or safety in patients with severely decreased renal function (glomerular filtration rate < 30 ml/min) or on dialysis.

Synthesis, characterization and preliminary in vitro evaluation of PTH 1-34 loaded chitosan nanoparticles for osteoporosis.

Human Parathyroid hormone 1-34 (PTH1-34) loaded chitosan nanoparticles (PTH 1-34 chitosan nanoparticles) via simple ionic gelation technique were prepared which can improve the bioavailability and half-life of the peptide. Chitosan nanoparticles and PTH 1-34 chitosan nanoparticles were synthesised and characterized by DLS, SEM, AFM, FT-IR and TG/DTA. Chitosan nanoparticles (40-60 nm) and PTH 1-34 chitosan nanoparticles (60-80 nm) with zeta potential of +60 and +40 mV respectively were subjected to haemolysis assay and tested for agglomeration in blood. MTT and LDH was performed assay using Saos-2, UMR 106, L929, NIH3T3. The in vitro peptide release profile at pH 7.5 for 144 h was quantified using PTH 1-34 ELISA Kit. Effect of released PTH 1-34 on Saos-2 was determined with ALP and BCA assay. These preliminary results pave way for the prospective use of such a carrier for the delivery of PTH 1-34 by multiple routes for the benefit of patients undergoing treatment for osteoporosis.

Formulations for intermittent release of parathyroid hormone (1-34) and local enhancement of osteoblast activities.

The objective of these studies was to develop simple, implantable devices that intermittently release PTH(1-34) and thus could be used for locally stimulating bone formation. The formulations were based on the association polymer system of cellulose acetate phthalate and Pluronic F-127. Release profiles for intermittent devices showed five discrete peaks, whereas sustained devices exhibited zero-order kinetics. Osteoblastic activity was greater for cells intermittently treated with PTH(1-34) compared to sustained exposure. These controlled release devices delivering PTH(1-34) in an intermittent manner may be useful for affecting osteoblast activities in a localized area.

The use of N-terminal immobilization of PTH(1-34) on PLGA to enhance bioactivity.

The objective of this work was to control the orientation of bioactive molecules immobilized on a biodegradable substrate to improve their accessibility for binding to cell surface receptors and, therefore, to increase bioactivity. The osteotropic peptide, parathyroid hormone (1-34) (PTH(1-34)), was used to demonstrate the approach. To this end, the intrinsic N-terminal serine residue was oxidized to create an aldehyde group that specifically bound to hydrazide-derivatized poly(lactide-co-glycolide) under neutral conditions to form a hydrazone bond. Use of dihydrazide spacers significantly increased the amount of peptide immobilized compared to simple adsorption or direct, random attachment. In probing accessibility of immobilized PTH(1-34), attachment using longer dihydrazide spacers enhanced binding of an antibody against an epitope in the N-terminal region of the peptide. The longest spacer also increased binding of a C-terminal antibody. Furthermore, substrates with peptide tethered via spacers stimulated intracellular synthesis of cAMP, with activity increasing with dihydrazide length. PTH(1-34) immobilized using the longest spacer was significantly more effective than both random binding and adsorption. Site-directed binding of bioactive peptides to surfaces presents biomolecules for binding with cells so as to enhance interaction with receptors, and therefore the approach may be useful for obtaining preferred localized tissue responses.

Infrequent delivery of a long-acting PTH-Fc fusion protein has potent anabolic effects on cortical and cancellous bone.

UNLABELLED: Skeletal anabolism with PTH is achieved through daily injections that result in brief exposure to the peptide. We hypothesized that similar anabolic effects could be achieved with less frequent but more sustained exposures to PTH. A PTH-Fc fusion protein with a longer half-life than PTH(1-34) increased cortical and cancellous BMD and bone strength with once- or twice-weekly injections. INTRODUCTION: The anabolic effects of PTH are currently achieved with, and thought to require, daily injections that result in brief exposure to the peptide. We hypothesized that less frequent but more sustained exposures to PTH could also be anabolic for bone, provided that serum levels of PTH were not constant. MATERIALS AND METHODS: PTH(1-34) was fused to the Fc fragment of human IgG1 to increase the half-life of PTH. Skeletal anabolism was examined in mice and rats treated once or twice per week with this PTH-Fc fusion protein. RESULTS: PTH-Fc and PTH(1-34) had similar effects on PTH/PTHrP receptor activation, internalization, and signaling in vitro. However, PTH-Fc had a 33-fold longer mean residence time in the circulation of rats compared with that of PTH(1-34). Subcutaneous injection of PTH-Fc once or twice per week resulted in significant increases in bone volume, density, and strength in osteopenic ovariectomized mice and rats. These anabolic effects occurred in association with hypercalcemia and were significantly greater than those achievable with high concentrations of daily PTH(1-34). PTH-Fc also significantly improved cortical bone volume and density under conditions where daily PTH(1-34) did not. Antiresorptive co-therapy with estrogen further enhanced the ability of PTH-Fc to increase bone mass and strength in ovariectomized rats. CONCLUSIONS: These results challenge the notion that brief daily exposure to PTH is essential for its anabolic effects on cortical and cancellous bone. PTH-derived molecules with a sustained circulating half-life may represent a powerful and previously undefined anabolic regimen for cortical and cancellous bone.

Influence of fillers in powder formulations containing N-acetyl-L-cysteine on nasal peptide absorption.

We examined the influence of filler species on the nasal absorbability of peptide drugs via a newly developed powdery formulation system containing N-acetyl-l-cysteine (NAC) as an absorption enhancer. Using salmon calcitonin (SCT) as the principal model drug, we tested the effects of various formulations with different powder materials as fillers on the nasal absorption of SCT in rats. An intranasal administration experiment revealed that the use of less wettable powders provided better nasal absorbability, and the highest absolute bioavailability (30.0% +/- 8.6%) was obtained when ethylcellulose was used as a filler. All these results were readily explicable in terms of our hypothetical enhancing mechanism. Furthermore, human parathyroid hormone and insulin were applied to this ethylcellulose formulation system, giving nasal bioavailabilities of 28.2% +/- 6.5% and 23.4% +/- 10.6%, respectively, thus suggesting that this formulation system is widely applicable to peptide drugs.

Defining a noncarcinogenic dose of recombinant human parathyroid hormone 1-84 in a 2-year study in Fischer 344 rats.

The carcinogenic potential of human parathyroid hormone 1-84 (PTH) was assessed by daily subcutaneous injection (0, 10, 50, 150 microg/kg/day) for 2 years in Fischer 344 rats. Histopathological analyses were conducted on the standard set of soft tissues, tissues with macroscopic abnormalities, selected bones, and bones with abnormalities identified radiographically. All PTH doses caused widespread osteosclerosis and significant, dose-dependent increases in femoral and vertebral bone mineral content and density. In the mid-and high-dose groups, proliferative changes in bone increased with dose. Osteosarcoma was the most common change, followed by focal osteoblast hyperplasia, osteoblastoma, osteoma and skeletal fibrosarcoma. The incidence of bone neoplasms was comparable in control and low-dose groups providing a noncarcinogenic dose for PTH of 10 microg/kg/day at a systemic exposure to PTH that is 4.6-fold higher than for a 100 microg dose in humans. The ability of PTH to interact with and balance the effects of both the PTH-1 receptor and the putative C-terminal PTH receptor, may lead to the lower carcinogenic potential observed with PTH than reported previously for teriparatide.

Therapeutic utility of a novel tight junction modulating peptide for enhancing intranasal drug delivery.

Previously, a novel tight junction modulating (TJM) peptide was described affording a transient, reversible lowering of transepithelial electrical resistance (TER) in an in vitro model of nasal epithelial tissue. In the current report, this peptide has been further evaluated for utility as an excipient in transepithelial drug formulations. Chemical stability was optimal at neutral to acidic pH when stored at or below room temperature, conditions relevant to therapeutic formulations. The TJM peptide was tested in the in vitro tissue model for potential to enhance permeation of a low-molecular-weight (LMW) drug, namely the acetylcholinesterase inhibitor galantamine, as well as three peptides, salmon calcitonin, parathyroid hormone 1-34 (PTH(1-34)), and peptide YY 3-36 (PYY(3-36)). In all cases, the TJM peptide afforded a dramatic improvement in drug permeation across epithelial tissue. In addition, a formulation containing PYY(3-36) and TJM peptide was dosed intranasally in rabbits, resulting in a dramatic increase in bioavailability. The TJM peptide was as or more effective in enhancing PYY(3-36) permeation in vivo at a 1000-fold lower molar concentration compared to using LMW enhancers. Based on these in vitro and in vivo data, the novel TJM peptide represents a promising advancement in intranasal formulation development.

Effects of endogenous estrogen on renal calcium and phosphate handling in elderly women.

High postmenopausal endogenous estrogen concentrations are an important determinant of preservation of bone mass and reduced fracture in elderly women. Calcium supplementation can also reduce bone loss in these patients, suggesting an interaction between estrogen deficiency and calcium balance. Potential mechanisms of estrogen on calcium transport include direct effects on the bone, the kidney, and the bowel. Previous studies have demonstrated effects of estrogen on renal phosphate handling. We have used a cross-sectional, population-based analysis of biochemical data obtained from ambulant elderly women to determine the association of endogenous estradiol with urine calcium and phosphorus excretion. The subjects were 293 postmenopausal women >70 yr old. Factors associated with renal calcium and phosphate excretion were measured, including the filtered calcium and phosphate load, parathyroid hormone (PTH), estradiol, and sex hormone-binding globulin (SHBG). The free estradiol concentration (FE) was calculated from a previously described formula. A high plasma estradiol concentration (r(2) = 0.023, P = 0.01) and a high FE (r(2) = 0.045, P = 0.001) were associated with reduced renal calcium excretion. The estradiol and FE effect on renal calcium excretion remained significant after adjusting for calcium filtered at the glomerulus and serum PTH. A high FE was associated with a reduced renal phosphate threshold in univariate analysis (r(2) = 0.023, P = 0.010). The effect remained significant after adjustment for serum PTH. The size of the effect of the FE was of the same order of magnitude as the effect of PTH on reducing renal calcium excretion and increasing renal phosphate excretion. These data support in vitro and animal data demonstrating an effect of estradiol on renal calcium and phosphate handling and indicate that, in elderly postmenopausal women, the effect is of a similar magnitude to the well-recognized effects of PTH on these physiologically regulated parameters.

The release profiles and bioactivity of parathyroid hormone from poly(lactic-co-glycolic acid) microspheres.

Poly(lactic-co-glycolic acid) (PLGA) microspheres containing bovine serum albumin (BSA) or human parathyroid hormone (PTH)(1-34) were prepared using a double emulsion method with high encapsulation efficiency and controlled particle sizes. The microspheres were characterized with regard to their surface morphology, size, protein loading, degradation and release kinetics, and in vitro and in vivo assessments of biological activity of released PTH. PLGA5050 microspheres degraded rapidly after a 3-week lag time and were degraded completely within 4 months. In vitro BSA release kinetics from PLGA5050 microspheres were characterized by a burst effect followed by a slow release phase within 1-7 weeks and a second burst release at 8 weeks, which was consistent with the degradation study. The PTH incorporated PLGA5050 microspheres released detectable PTH in the initial 24h, and the released PTH was biologically active as evidenced by the stimulated release of cAMP from ROS 17/2.8 osteosarcoma cells as well as increased serum calcium levels when injected subcutaneously into mice. Both in vitro and in vivo assays demonstrated that the bioactivity of PTH was maintained largely during the fabrication of PLGA microspheres and upon release. These studies illustrate the feasibility of achieving local delivery of PTH to induce a biologically active response in bone by a microsphere encapsulation technique.

Parathyroid hormone after adenectomy for primary hyperparathyroidism. A study of peptide hormone elimination kinetics in humans.

The study of the elimination kinetics of peptide hormones in humans is limited, because determining hormone levels in different compartments is difficult. We calculated the elimination kinetics of intact PTH (1-84) after adenoma removal in primary hyperparathyroidism, based on a 2-compartment model. In 12 patients, blood samples were drawn in short intervals preoperatively, during surgery, and up to 4 days postoperatively. Plasma levels of PTH (1-84), calcium (Ca), and inorganic phosphate were determined. PTH (1-84) levels remained constant before surgery and during adenoma preparation; 2.5 min after clamping of the adenoma's blood supply, PTH (1-84) decreased (34.9 +/- 4.8 vs. 23.3 +/- 2.9 pmol/L, mean +/- SEM, P < 0.001) and then reached a minimum of 0.96 +/- 0.06 pmol/L at 5 h. The elimination half-lives for PTH (1-84) were 3.43 +/- 0.1 min and 81.7 +/- 12.7 min. Ionized Ca started to decrease 30 min after adenoma removal (1.58 +/- 0.04 vs. 1.56 +/- 0.04 pmol/L, P < 0.001). This decrease was paralleled by a decrease in total Ca. Inorganic phosphate increased 24 h after adenoma removal. In conclusion, PTH (1-84) elimination after adenectomy is characterized by a rapid initial decrease and a subsequent prolonged period with a lower elimination rate. This elimination pattern may also apply to other human peptide hormones.

Distribution and pharmacokinetics of a potent peptide antagonist of parathyroid hormone and parathyroid hormone-related protein in the rat.

Humoral hypercalcemia of malignancy results from the production by cancer cells of parathyroid hormone related protein that activates receptors in bone. Peptide antagonists that block parathyroid hormone receptors in vivo would be instrumental in the clinical treatment of humoral hypercalcemia of malignancy. We report the in vivo whole body distribution and blood plasma pharmacokinetics of the parathyroid hormone receptor antagonist [Nle8,18,D-Trp12,monoiodinated Tyr34]bPTH(7-34)amide to determine parameters that are likely to affect its administration regimen. A single intravenously injected dose of [Nle8,18,D-Trp12,monoiodinated Tyr34]bPTH(7-34)amide was rapidly cleared from blood plasma. The plasma concentration reaches a maximum at 10 min (Cmax = 1.93 +/- 0.27% of total injected CPM/ml), and the intact PTH derivative was detectable in plasma by HPLC analysis at this time. In vivo binding to plasma proteins was noncovalent. The peptide was rapidly cleared from blood by the liver, and more slowly by the kidney. Radiolabel was detected in excreted feces at 8 hr, but the preferred route of excretion was renal as judged by significant counts in excreted urine. Absorption of labeled peptide by skin and bone was sustained. Strong and sustained absorption also occurred in the vas deferens, seminal vesicle and hypothalamus. Given the rapid clearance of antagonist, multiple or sustained dosing schemes might be necessary to achieve the desired pharmacological effect. The high counts in liver at early time points after i.v. injection suggest that other routes of administration that do not bypass the hepatic first-pass effect would result in very low blood levels of drug.