Full length parathyroid hormone,PTH(1-84), for the treatment of severe osteoporosis in postmenopausal women

ABSTRACT

Objective: To review and analyse the evidence supporting the use of full length parathyroid hormone, PTH(1-84), in the treatment of osteoporosis based on a search of several literature sources; articles selected for review were published between 1990 and 2008.

Background: PTH(1-84) is approved for the treatment of osteoporosis in postmenopausal women at high risk of fracture in Europe. It was well tolerated in clinical trials and demonstrated bone building properties and fracture prevention particularly for the lumbar spine in the treatment of postmenopausal women.

Results: The TOP clinical trial showed that PTH(1-84) treatment for 18 months resulted in a 61% reduction (p = 0.001) in new vertebral fracture incidence when compared with placebo and reduced the risk of a first vertebral fracture by 68% (p = 0.006) in women without a prevalent fracture at baseline. PTH(1-84) increased bone mineral density (BMD) at vertebral and non-vertebral sites the lumbar spine BMD increasing regardless of T-score, age, prior osteoporosis therapy or number of years post-menopause. The PaTH study showed that treatment with PTH(1-84) for 12 months increased BMD at the trabecular spine and hip. Lumbar spine BMD gains were largest with sequential administration of PTH(1-84) followed by alendronate but were smaller with concurrent administration involving anabolic and antiresorptive agents. Lumbar spine BMD increases were also seen in trials involving PTH with raloxifene and PTH in combination with hormone replacement therapy.

Conclusions: PTH(1-84) has demonstrated effective bone building qualities and extends the therapeutic options available to osteoporotic women. The use of PTH(1-84) followed by sequential administration of an antiresorptive has proved effective at increasing trabecular BMD and points towards new treatment regimens offering improvements in BMD and fracture prevention.     

Combination antiresorptive and osteoanabolic therapy for osteoporosis: We are not there yet

Abstract

Osteoanabolic therapy is theoretically and practically an appealing therapeutic option for men and postmenopausal women with osteoporosis because bone formation is directly stimulated, an action that is not shared by any antiresorptive agent. Parathyroid hormone (PTH), in the form of the full-length molecule (PTH[1-84]) and its fully active but truncated amino-terminal fragment teriparatide (PTH[1-34]), belong to this osteoanabolic class. Both formulations of PTH increase bone mineral density, increase biochemical markers of bone turnover, and reduce fracture incidence. They improve skeletal microstructure. While antiresorptive agents are considered by most to be first line for the treatment of osteoporosis, there are situations when anabolic therapy could be reasonably considered as first line. In most situations, however, treatment with PTH follows a course of antiresorptive therapy. Simultaneous combination therapy with PTH and an antiresorptive drug does not appear to provide any advantages over monotherapy. After the recommended 2-year period of PTH treatment, an antiresorptive should be used to maintain densitometric gains. The drugs are well tolerated. Early safety concerns about osteosarcoma in rats have not been borne out after almost 9 years experience with human subjects.     

Investigational anabolic therapies for osteoporosis

Importance of the field: Anabolic therapy, or stimulating the function of bone-forming osteoblasts, is the preferred pharmacological intervention for osteoporosis.

Areas covered in this review: We reviewed bone anabolic agents currently under active investigation. The bone anabolic potential of IGF-I and parathyroid hormone-related protein is discussed in the light of animal data and human studies. We also discuss the use of antagonists of the calcium-sensing receptor (calcilytics) as orally administered small molecules capable of transiently elevating serum parathyroid hormone (PTH). Further, we reviewed novel anabolic agents targeting members of the wingless tail (Wnt) signaling family that regulate bone formation including DKK-1, sclerostin, Thp1, and glycogen synthase kinase 3β. We have also followed up on the promise shown by β-blockers in modulating the activity of sympathetic nervous system, thus affecting bone anabolism. We give critical consideration to neutralizing the activity of activin A, a negative regulator of bone mass by soluble activin receptor IIA, as a strategy to promote bone formation.

What the reader will gain: Update on various strategies to promote osteoblast function currently under evaluation.

Take home message: In spite of favorable results in experimental models, none of these strategies has yet achieved the ultimate goal of providing an alternative to injectable PTH, the sole anabolic therapy in clinical use.     

Bone anabolic effects of PTH(1-34) and salmon calcitonin in ovariectomy- and ovariectomy-steroid-induced osteopenic rats: a histomorphometric and biomechanical study

Using an experimental model of type 1 osteoporosis under the chronic therapy with an anti-inflammatory steroid, the bone anabolic effect of PTH(1-34) was evaluated by histomorphometrical and biomechanical analysis. Wistar female rats (12-week-old) were ovariectomized and allowed to develop an osteopenic model in the presence or absence of methylprednisolone acetate (MPA: 0.1 mg/kg, s.c., 3-days-a-week basis from the 5th week after ovariectomy (OVX)). The osteopenia that developed for the first 12 weeks after OVX was almost completely normalized by subsequent PTH pulsing (20 microg/kg, s.c., 5-days-a-week) for 8 weeks starting at the 13th week; the following characteristics were observed: 1) proximal tibial metaphysis: recovered bone volume, rather increased trabecular thickness and osteoid volume, and normalized eroded surface; 2) 5th lumbar vertebra (L-5): partially recovered trabecular connectivity; 3) femur and 4th lumbar vertebra (L-4): recovered mechanical strength in maximum elastic load and maximum elastic energy. The anabolic effect of PTH(1-34) was not substantially modified by MPA. Salmon calcitonin (SCT: 10 U/kg per day, s.c., 5-days-a-week, for 8 weeks) was anabolic in limited parameters: decreased number of osteoclasts, recovered maximum elastic load in femur, and partially recovered maximum elastic load in L-4. The results suggest that PTH(1-34) pulsing is able to recover OVX-induced osteopenia in the structure and mechanical strength not only of the cancellous bone but also of the cortical bone, and the anabolic effect can be clinically expected even under steroid medication.     

Design and applications of parathyroid hormone analogues.

The endocrine parathyroid hormone (PTH) is the major regulator of serum calcium levels. In contrast, the autocrine/paracrine parathyroid hormone-related peptide (PTHrP) has been associated with organism development. Both are secreted as much larger molecules but have their major functions associated with their N-terminal 34 residues. They share a common receptor expressed in organs critical to PTH function - bone, kidney, and intestine. PTH and PTHrP receptor activation stimulates adenylyl cyclase (AC), phospholipase C (PLC), and phospholipase D (PLD) in target cells. It has been possible to separate the AC-stimulation from that of PLC. AC-stimulation requires at least the N-terminal 28 residues of PTH and PLC-stimulation requires a minimum of residues 29-32-NH2. Intermittent administration of PTH stimulates bone growth and requires AC-stimulation. The shortest linear sequence of hPTH with essentially full anabolic activity for bone growth-stimulation is hPTH(1-31)NH2. Two applications are postulated for PTH and PTHrP-based pharmaceuticals - treatment of bone loss due to osteoporosis and reversal of the hypercalcemic effect of malignancy. PTHrP analogues which strongly inhibit PTHrP AC-stimulation showed promise for the treatment of malignancy-associated hypercalcemia in animal trials but failed in human ones. However, both animal and human trials of hPTH have shown significant bone growth-stimulating effects. New deletion, substitution and cyclized analogues of PTH show great promise both for greater in vitro activity and possibly for improved delivery and greater specificity as agents for restoration of bone loss in osteoporosis.     

Vincristine-loaded hydroxyapatite nanoparticles as a potential delivery system for bone cancer therapy

Despite advances in the development of new therapeutic agents and diagnostic imaging techniques, the 5-year survival of osteosarcoma, the most common type of bone cancer, remains practically unaltered for the last three decades at around 60%. Nanoparticle-based carriers have emerged as new class of drug delivery systems that could potentially overcome conventional chemotherapy limitations, by promoting a better drug biodistribution profile by allowing a preferential accumulation of the drug in the desired tissue, while minimising non-targeted tissue toxicity, thus resulting in an improved overall therapeutic effectiveness. Hydroxyapatite nanoparticles (HANP) are known to be biocompatible and non-immunogenic and have shown to be preferentially accumulated in bone tissues being considered a promising carrier to bone tissues. Herein, we successfully synthesised mesoporous hydroxyapatite nanoparticles with mean size of 285.32?±?10.29?nm and superficial area of 103.5 m²/g, containing significant quantities of chemotherapeutic drug vincristine. A spectrophotometric method was developed and validated aiming to quantify the vincristine (VCR)-loaded in nanoparticles. Chorioallantoic membrane assay revealed relevant anti-angiogenic activity of system, leading to accentuated reduction in the number of blood vessels in fertilised eggs. Findings presented in this paper suggested that VCR-loaded HANP has a promising future as a nanocarrier for bone cancer treatment.     

Self-assembling protein nanocarrier for selective delivery of cytotoxic polypeptides to CXCR4+ head and neck squamous cell carcinoma tumors

Loco-regional recurrences and distant metastases represent the main cause of head and neck squamous cell carcinoma (HNSCC) mortality. The overexpression of chemokine receptor 4 (CXCR4) in HNSCC primary tumors associates with higher risk of developing loco-regional recurrences and distant metastases, thus making CXCR4 an ideal entry pathway for targeted drug delivery. In this context, our group has generated the self-assembling protein nanocarrier T22-GFP-H6, displaying multiple T22 peptidic ligands that specifically target CXCR4. This study aimed to validate T22-GFP-H6 as a suitable nanocarrier to selectively deliver cytotoxic agents to CXCR4⁺ tumors in a HNSCC model. Here we demonstrate that T22-GFP-H6 selectively internalizes in CXCR4⁺ HNSCC cells, achieving a high accumulation in CXCR4⁺ tumors in vivo, while showing negligible nanocarrier distribution in non-tumor bearing organs. Moreover, this T22-empowered nanocarrier can incorporate bacterial toxin domains to generate therapeutic nanotoxins that induce cell death in CXCR4-overexpressing tumors in the absence of histological alterations in normal organs. Altogether, these results show the potential use of this T22-empowered nanocarrier platform to incorporate polypeptidic domains of choice to selectively eliminate CXCR4⁺ cells in HNSCC. Remarkably, to our knowledge, this is the first study testing targeted protein-only nanoparticles in this cancer type, which may represent a novel treatment approach for HNSCC patients.     

Delivery of parathyroid hormone for the treatment of osteoporosis

Parathyroid hormone (PTH), along with its fragments and analogues, potently restores bone mass and biomechanical strength in animal models of osteoporosis, and reduces fractures by up to 65% in clinical trials in osteoporotic patients. Despite this demonstrated efficacy, patient acceptance and compliance with PTH is limited by the need for daily subcutaneous injections. The development of an equally efficacious, noninjectable form of PTH would significantly expand the present market. A challenge to the development of an alternative delivery system is the requirement for low-dose, daily, intermittent pulses of PTH to induce the anabolic actions on bone. In this review, recent basic and clinical efforts to deliver PTH by oral, buccal, sublingual, transdermal, nasal and pulmonary approaches will be addressed.     

Delivery of parathyroid hormone for the treatment of osteoporosis

Parathyroid hormone (PTH), along with its fragments and analogues, potently restores bone mass and biomechanical strength in animal models of osteoporosis, and reduces fractures by up to 65% in clinical trials in osteoporotic patients. Despite this demonstrated efficacy, patient acceptance and compliance with PTH is limited by the need for daily subcutaneous injections. The development of an equally efficacious, noninjectable form of PTH would significantly expand the present market. A challenge to the development of an alternative delivery system is the requirement for low-dose, daily, intermittent pulses of PTH to induce the anabolic actions on bone. In this review, recent basic and clinical efforts to deliver PTH by oral, buccal, sublingual, transdermal, nasal and pulmonary approaches will be addressed.     

Acid-Responsive Polymeric Nanocarriers for Topical Adapalene Delivery

Purpose

The acne skin is characteristic of a relatively lower pH microenvironment compared to the healthy skin. The aim of this work was to utilize such pH discrepancy as a site-specific trigger for on-demand topical adapalene delivery.

Methods

The anti-acne agent, adapalene, was encapsulated in acid-responsive polymer (Eudragit® EPO) nanocarriers via nanoprecipitation. The nanocarriers were characterized in terms of particle size, surface morphology, drug-carrier interaction, drug release and permeation.

Results

Adapalene experienced a rapid release at pH 4.0 in contrast to that at pH 5.0 and 6.0. The permeation study using silicone membrane revealed a significant higher drug flux from the nanocarrier (6.5?±?0.6 μg.cm^?2.h^?1) in comparison to that (3.9?±?0.4 μg.cm^?2.h^?1) in the control vehicle (Transcutol®). The in vitro pig skin tape stripping study showed that at 24 h post dose-application the nanocarrier delivered the same amount of drug to the stratum corneum as the positive control vehicle did.

Conclusions

The acid-responsive nanocarriers hold promise for efficient adapalene delivery and thus improved acne therapy. Figure

pH liable nanocarriers enhance the adapalene delivery to acne skin.     

Bone Regeneration Using Gene-Activated Matrices

Gene delivery to bone is a potential therapeutic strategy for directed, sustained, and regulated protein expression. Tissue engineering strategies for bone regeneration include delivery of proteins, genes (viral and non-viral-mediated delivery), and/or cells to the bone defect site. In addition, biomimetic scaffolds and scaffolds incorporating bone anabolic agents greatly enhance the bone repair process. Regional gene therapy has the potential of enhancing bone defect healing and bone regeneration by delivering osteogenic genes locally to the osseous lesions, thereby reducing systemic toxicity and the need for using supraphysiological dosages of therapeutic proteins. By implanting gene-activated matrices (GAMs), sustained gene expression and continuous osteogenic protein production in situ can be achieved in a way that stimulates osteogenesis and bone repair within osseous defects. Critical parameters substantially affecting the therapeutic efficacy of gene therapy include the choice of osteogenic transgene(s), selection of non-viral or viral vectors, the wound environment, and the selection of ex vivo and in vivo gene delivery strategies, such as GAMs. It is critical for gene therapy applications that clinically beneficial amounts of proteins are synthesized endogenously within and around the lesion in a sustained manner. It is therefore necessary that reliable and reproducible methods of gene delivery be developed and tested for their efficacy and safety before translating into clinical practice. Practical considerations such as the age, gender, and systemic health of patients and the nature of the disease process also need to be taken into account in order to personalize the treatments and progress towards developing a clinically applicable gene therapy for healing bone defects. This review discusses tissue engineering strategies to regenerate bone with specific focus on non-viral gene delivery systems.     

Synthesis and structural identification of fluorine‐18 labeled parathyroid hormone

Parathyroid hormone (PTH) is an 84 amino acid peptide hormone that plays a key role in bone and mineral metabolism. The biological actions of PTH are mediated via the N‐terminal PTH(1–34) fragment, serving as the PTH receptor‐binding sequence, and which is therefore used clinically to treat conditions of low bone mass such as osteoporosis. In this study, PTH(1–34) was conjugated with non‐radioactive (stable F isotope) N‐succinimidyl 4‐fluorobenzoate (SFB) leading to three isomeric mono‐fluorobenzoated (FBz) PTH followed by Liquid chromatography‐Tandem mass spectrometry (LC‐MS/MS) assisted structural identification. Corresponding [¹⁸F]SFB‐labeled PTH derivatives were prepared respectively and the Lys¹³ site‐specific labeled [¹⁸F]FBz PTH was isolated by HPLC with radiochemical purity >99% and specific activity of 2.78 GBq/µmol, suitable for future application with in vivo pharmacokinetic/pharmacodynamic studies of PTH, using preclinical Positron Emission Tomography Computed Tomography (PET/CT) imaging.     

Nanotechnology in cancer therapy

Abstract

Cancer is one of the major causes of mortality worldwide and advanced techniques for therapy are urgently needed. The development of novel nanomaterials and nanocarriers has allowed a major drive to improve drug delivery in cancer. The major aim of most nanocarrier applications has been to protect the drug from rapid degradation after systemic delivery and allowing it to reach tumor site at therapeutic concentrations, meanwhile avoiding drug delivery to normal sites as much as possible to reduce adverse effects. These nanocarriers are formulated to deliver drugs either by passive targeting, taking advantage of leaky tumor vasculature or by active targeting using ligands that increase tumoral uptake potentially resulting in enhanced antitumor efficacy, thus achieving a net improvement in therapeutic index. The rational design of nanoparticles plays a critical role since structural and physical characteristics, such as size, charge, shape, and surface characteristics determine the biodistribution, pharmacokinetics, internalization and safety of the drugs. In this review, we focus on several novel and improved strategies in nanocarrier design for cancer therapy.     

Transactivation of core binding factor alpha1 as a basic mechanism to trigger parathyroid hormone-induced osteogenesis

During 28-day culture of bone marrow- and calvaria-derived osteoblasts, the constant presence of parathyroid hormone (PTH)(1-34) retarded differentiation and nodule formation (NF) in a dose-dependent fashion (C-phase). In contrast, addition of PTH(1-34) in late stage cultures (from day 10 to 21) accelerated NF (A-phase). The stable production of such an A-phase allowed us to study the mechanism of bone anabolic action of PTH(1-34). Subcellular localization studies of core binding factor alpha1 (Cbfa1) and reporter assays provided the results indicating that in the A-phase, PTH(1-34) triggers its bone anabolic action via enhancement of Cbfa1 transactivation. RT-PCR and Northern blot analyses revealed that alkaline phosphatase, osteocalcin and bone sialoprotein expression decreased in the C-phase and increased in the A-phase; however, expression of other bone proteins (Cbfa1, PTH/PTH-related peptide-receptor, osteopontin, collagen I alpha1, collagen I alpha2, vitamin K-dependent gamma-glutamyl carboxylase) did not change in a phase transition-related manner. Ovariectomized osteopenic mice, treated with PTH(1-34) (4 and 40 microg/kg, s.c., every other day, 4 or 6 weeks), recovered lost bone, displayed elevated nuclear localization of Cbfal in tibiae without alteration of its cytosolic level and exhibited upregulation of expressions of the same set of proteins (alkaline phosphatase, osteocalcin and bone sialoprotein) in femora. These results obtained by a concerted study in vitro and in vivo suggest that PTH triggers its osteogenic action via promotion of the transactivation of Cbfa1.     

Molecular mechanisms of ligand recognition by parathyroid hormone 1 (PTH1) and PTH2 receptors

The mammalian parathyroid hormone (PTH) / PTH receptor family includes PTH1 and PTH2 receptors and three related ligands (PTH, PTH-related protein (PTHrP) an d tuberoinfundibular peptide of 39 residues (TIP39)). Here we comparatively and systematically review the pharmacological properties of PTH receptors and ligands, structure of the ligands, and molecular mechanisms of receptor-ligand interaction. The PTH1 receptor is activated by PTH and PTHrP but not by TIP39. The PTH2 receptor is activated by TIP39 but not by PTHrP. PTH strongly activates the human PTH2 receptor but is a weak partial agonist for rat and zebrafish PTH2 receptors. Receptor-G-protein interaction increases the receptor binding selectivity of PTHrP and TIP39. Despite different primary structures, the secondary structures of PTH, PTHrP and TIP39 are quite similar. Each ligand contains an N-terminal and a C-terminal alpha-helix in secondary structure-inducing conditions. Receptor-bound ligand structure is less well-characterized. The orientation of receptor-ligand interaction is highly similar for PTH and PTHrP binding to the PTH1 receptor and TIP39 interaction with the PTH2 receptor. Ligands bind according to a 'two-site' mechanism, in which the C-terminal portion of the ligand binds the extracellular N-terminal domain of the receptor (N-interaction), and the N-terminal ligand portion binds to the juxtamembrane receptor domain (J-interaction). The N-interaction provides most of the PTH1-receptor binding energy for PTH and PTHrP but provides less energy for PTH2 receptor-TIP39 interaction. The J-interaction stimulates G-protein activation. For the PTH-PTH1 receptor interaction, the efficacy-generating component of the J-interaction is independent of the N-domain of the receptor and C-terminal portion of the ligand. This finding suggests that it might be possible to design low molecular-weight PTH1 receptor agonists, which could be bone anabolic agents and used for the treatment of osteoporosis.     

Investigational parathyroid hormone receptor analogs for the treatment of osteoporosis

Introduction: Intermittent parathyroid hormone (PTH) administration, acting through multiple signaling pathways, exerts an osteoanabolic effect on the skeleton that surpasses the effect of other antiosteoporotic agents. However, its efficacy is limited by the coupling effect and relatively common adverse events. Thus, the development of more sophisticated PTH receptor analogs seems imperative.

Areas covered: In this review, the authors summarize the role of PTH signaling pathway in bone remodeling. The authors also summarize investigational analogs targeting this pathway, which may be potential treatments for osteoporosis.

Expert opinion: β-arrestins are multifunctional cytoplasmic molecules that are decisive for regulating intracellular PTH signaling. Recently, in preclinical studies, arrestin analogs have achieved the anabolic bone effect of PTH without an accompanying increase in bone resorption. However, it is not yet known whether these analogs have adverse effects and there are no clinical data for their efficacy to date. On the other hand, several molecules derived either from PTH and PTH-related protein (PTHrP) molecules have been developed. Alternative routes of PTH 1 – 34 delivery (oral, transdermal), the PTH analog ostabolin and the N-terminal PTHrP analogs PTHrP 1 – 36 and abaloparatide, have recently been or are currently being tested in clinical trials and are more likely to become available for use in the near future.     

Improvement of chemosensitivity and inhibition of migration via targeting tumor epithelial-to-mesenchymal transition cells by ADH-1-modified liposomes

How to overcome drug resistance and prevent tumor metastasis is key to the success of malignant tumor therapy. In this paper, ADH-1 peptide-modified liposomes (A-LP) have been successfully constructed for restoring chemosensitivity and suppressing cancer cell migration. With a particle size of about 90?nm, this functionalized nanocarrier was loaded with fluorescent probe or paclitaxel (PTX). Cellular uptake studies showed that A-LP facilitated the delivery of anticancer drug to tumor cells undergoing EMT. Interestingly, this nanocarrier enhanced chemosensitivity by assessing the cell activity using CCK-8 assay. Further, the results of Wound scratch assay and Transwell migration assay showed the inhibition effect of this nanocarrier on tumor cell migration. Moreover, this nanocarrier exhibited significant tumor-targeting ability and anti-tumor efficacy in vivo. Collectively, A-LP might be a novel targeted drug delivery system to enhance the efficacy of chemotherapy and prevent tumor metastasis.