Structure-activity relationships of various bisphosphonates

Bisphosphonates as Radiopharmaceuticals: Spotlight on the Development and Clinical Use of DOTAZOL in Diagnostics and Palliative Radionuclide Therapy

Bisphosphonates are therapeutic agents that have been used for almost five decades in the treatment of various bone diseases, such as osteoporosis, Paget disease and prevention of osseous complications in cancer patients. In nuclear medicine, simple bisphosphonates such as 99mTc-radiolabelled oxidronate and medronate remain first-line bone scintigraphic imaging agents for both oncology and non-oncology indications. In line with the growing interest in theranostic molecules, bifunctional bisphosphonates bearing a chelating moiety capable of complexing a variety of radiometals were designed. Among them, DOTA-conjugated zoledronate (DOTAZOL) emerged as an ideal derivative for both PET imaging (when radiolabeled with 68Ga) and management of bone metastases from various types of cancer (when radiolabeled with 177Lu). In this context, this report provides an overview of the main medicinal chemistry aspects concerning bisphosphonates, discussing their roles in molecular oncology imaging and targeted radionuclide therapy with a particular focus on bifunctional bisphosphonates. Particular attention is also paid to the development of DOTAZOL, with emphasis on the radiochemistry and quality control aspects of its preparation, before outlining the preclinical and clinical data obtained so far with this radiopharmaceutical candidate.

Bisphosphonates Targeting Ion Channels and Musculoskeletal Effects

Bisphosphonates (BPs) are the most used bone-specific anti-resorptive agents, often chosen as first-line therapy in several bone diseases characterized by an imbalance between osteoblast-mediated bone production and osteoclast-mediated bone resorption. BPs target the farnesyl pyrophosphate synthase (FPPS) in osteoclasts, reducing bone resorption. Lately, there has been an increasing interest in BPs direct pro-survival/pro-mineralizing properties in osteoblasts and their pain-relieving effects. Even so, molecular targets involved in these effects appear now largely elusive. Ion channels are emerging players in bone homeostasis. Nevertheless, the effects of BPs on these proteins have been poorly described. Here we reviewed the actions of BPs on ion channels in musculoskeletal cells. In particular, the TRPV1 channel is essential for osteoblastogenesis. Since it is involved in bone pain sensation, TRPV1 is a possible alternative target of BPs. Ion channels are emerging targets and anti-target for bisphosphonates. Zoledronic acid can be the first selective musculoskeletal and vascular KATP channel blocker targeting with high affinity the inward rectifier channels Kir6.1-SUR2B and Kir6.2-SUR2A. The action of this drug against the overactive mutants of KCNJ9-ABCC9 genes observed in the Cantu’ Syndrome (CS) may improve the appropriate prescription in those CS patients affected by musculoskeletal disorders such as bone fracture and bone frailty.

Bisphosphonates-much more than only drugs for bone diseases

α,α-Bisphosphonates (BPs) are well established in the treatment of bone diseases such as osteoporosis and Paget's disease. Their successful application originates from their high affinity to hydroxyapatite. While the initially appreciated features of BPs are already beneficial to many patients, recent developments have further expanded their pleiotropic applications. This review describes the background of the interactions of BPs with bone cells that form the basis of the classical treatment. A better understanding of the mechanism behind their interactions allows for the parallel application of BPs against bone cancer and metastases followed by palliative pain relief. Targeted therapy with bone-seeking BPs coupled with a diagnostic agent in one particle resulted in theranostics which is also described here. For example, in such a system, BP moieties are bound to contrast agents used in magnetic resonance imaging or radionuclides used in positron emission tomography. In addition, another example of the pleiotropic function of BPs which involves targeting the imaging agents to bone tissues accompanied by pain reduction is presented in this work.

Synthesis and Immunomodulatory Activity of Fluorine-Containing Bisphosphonates

Immune checkpoint blockade using anti-PD-1/PD-L1 or anti-CTLA-4 monoclonal antibodies (mAbs) has revolutionized cancer treatment. However, many types of cancer do not respond and for those that do, only a minority of patients achieve durable remissions. Therefore, oncoimmunologists are working to develop adoptive cell therapies for non-hematopoietic tumors by harnessing immune effector cells such as αβ T cells and γδ T cells. In contrast to conventional αβ T cells that recognize peptides in the context of MHC class I or II molecules, γδ T cells expressing Vγ2Vδ2 T cell receptors (also termed Vγ9Vδ2) are stimulated by isoprenoid metabolites (phosphoantigens) such as isopentenyl diphosphate in a butyrophilin-3A1-dependent manner. Vγ2Vδ2 T cells kill almost all types of tumor cells that have been treated with bisphosphonates. In this study, we synthesized a series of fluorine-containing bisphosphonates based on current drugs and found that they stimulated Vγ2Vδ2 T cell killing of tumor cells. A fluorine-containing prodrug analogue of zoledronate where phosphonate moieties were masked with pivaloyloxymethyl groups markedly enhanced Vγ2Vδ2 T-cell-mediated cytotoxicity, and also promoted the expansion of peripheral blood Vγ2Vδ2 T cells. These results demonstrate that a prodrug of a fluorine-containing zoledronate analogue can sensitize tumor cells for killing as well as expand Vγ2Vδ2 T cells for adoptive cell therapy.

Role of Pamidronate Disodium in the Treatment of Metastatic Bone Disease

Aims and Background

Bone metastases are a common feature of advanced neoplastic disease and are considered to be among the most frequent causes of pain and complications in oncologic patients. The main objective of the treatment of such patients is to control their symptoms and improve their quality of life. Pamidronate disodium is a second-generation bisphosphonate capable of inhibiting bone resorption (particularly osteoclast activity) without affecting bone reminerali-zation. After a brief introduction concerning the pathophysiology of bone metastases and neoplastic bone pain, we herein present data on the clinical pharmacology and toxicity of bisphosphonates in general, and pamidronate in particular. We conclude by reviewing the literature on the use of pamidronate in phase II and III trials involving patients with metastatic bone disease.

Methods

The paper is based on a review of articles published between 1984 and 1997 selected from the Cancerline and Medline databases.

Results

In the considered phase II and III studies involving patients with bone metastases (breast cancer and multiple myeloma in particular), pamidronate proved to be efficacious in reducing the incidence of pain and skeletal complications, decreasing the excretion of metabolic markers of bone resorption and improving the quality of life. Intravenous infusions of 60-90 mg over a period of 2 hr every 3-4 weeks did not cause any significant toxic effects and was easily managed.

Conclusions

Pamidronate is a bisphosphonate that is efficacious in the treatment of symptomatic bone metastases and can be considered an important therapeutic option in association with systemic treatments, radiotherapy and normal supportive care, especially in patients with breast cancer and multiple myeloma. Further randomized studies are necessary to confirm the positive preliminary results in other neoplasms, analyze the cost/benefit ratio of the treatment, and verify the possibility that, in addition to being used for palliative purposes, pamidronate may also prevent or delay the appearance of bone metastases.

The Pharmacological Profile of a Novel Highly Potent Bisphosphonate, OX14 (1-Fluoro-2-(Imidazo-[1,2-α]Pyridin-3-yl)-Ethyl-Bisphosphonate)

Bisphosphonates are widely used in the treatment of clinical disorders characterized by increased bone resorption, including osteoporosis, Paget's disease, and the skeletal complications of malignancy. The antiresorptive potency of the nitrogen-containing bisphosphonates on bone in vivo is now recognized to depend upon two key properties, namely mineral binding affinity and inhibitory activity on farnesyl pyrophosphate synthase (FPPS), and these properties vary independently of each other in individual bisphosphonates. The better understanding of structure activity relationships among the bisphosphonates has enabled us to design a series of novel bisphosphonates with a range of mineral binding properties and antiresorptive potencies. Among these is a highly potent bisphosphonate, 1-fluoro-2-(imidazo-[1,2 alpha]pyridin-3-yl)-ethyl-bisphosphonate, also known as OX14, which is a strong inhibitor of FPPS, but has lower binding affinity for bone mineral than most of the commonly studied bisphosphonates. The aim of this work was to characterize OX14 pharmacologically in relation to several of the bisphosphonates currently used clinically. When OX14 was compared to zoledronate (ZOL), risedronate (RIS), and minodronate (MIN), it was as potent at inhibiting FPPS in vitro but had significantly lower binding affinity to hydroxyapatite (HAP) columns than ALN, ZOL, RIS, and MIN. When injected i.v. into growing Sprague Dawley rats, OX14 was excreted into the urine to a greater extent than the other bisphosphonates, indicating reduced short-term skeletal uptake and retention. In studies in both Sprague Dawley rats and C57BL/6J mice, OX14 inhibited bone resorption, with an antiresorptive potency equivalent to or greater than the comparator bisphosphonates. In the JJN3-NSG murine model of myeloma-induced bone disease, OX14 significantly prevented the formation of osteolytic lesions (p < 0.05). In summary, OX14 is a new, highly potent bisphosphonate with lower bone binding affinity than other clinically relevant bisphosphonates. This renders OX14 an interesting potential candidate for further development for its potential skeletal and nonskeletal benefits. © 2017 American Society for Bone and Mineral Research.

M4IDP, a zoledronic acid derivative, induces G1 arrest, apoptosis and autophagy in HCT116 colon carcinoma cells via blocking PI3K/Akt/mTOR pathway

AIMS

The aim of this work was to examine the antitumor effects and mechanisms of M₄IDP, a zoledronic acid derivative, on human colorectal cancer (CRC) HCT116 cells.

MAIN METHODS

The effects of M₄IDP on proliferation, cell cycle and ROS production were determined by CCK-8 and flow cytometry assays. Annexin-V-FITC/PI, Hoechst 33258, MDC staining assays and Ad-mCherry-GFP-LC3B fluorescence assay were performed to investigate apoptosis and autophagy. The effects of M₄IDP on the induction of ER stress as well as the expression of cell cycle, apoptosis and autophagy-related proteins were analyzed by western blot assay.

KEY FINDINGS

M₄IDP exhibited strong and sustained inhibitory effect on the growth of HCT116 cells. G1 arrest caused by M₄IDP might be attributed to the enhancement of p27 and reduction of cyclin D1 expression. Proper-time treatment of M₄IDP activated autophagy and promoted autophagic flux, while long-time treatment might inhibit the autophagic degradation and undermine the autophagy. M₄IDP-induced apoptosis and autophagy were related to the ROS production and subsequent ER stress. M₄IDP treatment increased the expression of PTEN, inhibited the phosphorylation of PDK1, Akt, mTOR, p70S6K, and increased the phosphorylation of GSK-3β and Bad, suggesting that the inhibition of PI3K/Akt/mTOR pathway might be involved in the antitumor activities of M₄IDP.

SIGNIFICANCE

Our study indicates the antitumor properties of M₄IDP and its potential clinical use in CRC therapy by blocking PI3K/Akt/mTOR pathway. This study also provides a better understanding of the antitumor effects and the underlying mechanisms of bisphosphonates in the field of CRC therapy.

Pathophysiology of Osteonecrosis of the Jaws

Osteonecrosis of the jaw (ONJ) is a multifactorial disease in patients with primary or metastatic bone malignancy or osteoporosis undergoing systemic antiresorptive therapy, where pathophysiology has not yet been fully determined. The staging of ONJ is based on severity of symptoms and extent of clinical and radiographic findings. Treatment strategies range from conservative local wound care to aggressive resective surgery of all necrotic bone. The first ONJ cases were reported in 2003 and 2004, and although significant progress has been made in our understanding of the disease, much more work needs to be done to completely explain its pathophysiology.

Surgical treatment of bisphosphonate-associated osteonecrosis: Prognostic score and long-term results

Over a century after the first synthesis of bisphosphonates (1897) and a decade (2003) since the initial report on bisphosphonate-related osteonecrosis of the jaw (ONJ), this osteopathy remains a serious clinical challenge. A single center longitudinal study (2005-2014) was carried out to prospectively characterize inpatients with manifest ONJ and to evaluate their outcomes. The data recorded were: medical history, bisphosphonate treatment, localization, imaging, treatment, histomorphological features, and complications. A prognostic score (modified UCONN-Score) was adopted to predict outcomes. Eighty patients were included (mean age 69.4 years; 40 male, 40 female). Breast cancer (n = 25), multiple myeloma (n = 16), and prostate cancer (n = 15) were the three most common malignancies; and cardiovascular disease (n = 31), diabetes mellitus (16), and renal disorders (6) were the most important comorbidities. The severity of ONJ was stage I in three patients, stage II in 37, and stage III in 40, being predominantly localized in the posterior mandible and needing gradual resection. The average duration of bisphosphonate treatment was 38.3 months. The typical histological aspects of ONJ were predominantly osteonecrosis, bone marrow fibrosis, and bacterial colonization (Actinomyces) with suppurative inflammation. Within the resected jawbone a primary malignancy was diagnosed in two cases. The overall success rate was 83.6% (follow-up 23.5 months), with a UCONN-Score ≥15 predicting unfavorable treatment results (OR = 5.2). The past decade has enhanced experience with ONJ treatment and knowledge about its pathogenesis, which seems to be a multistep process. This study demonstrates the importance of bone and multilayer soft tissue management, preferably as an early intervention. The UCONN-Score might help to assess individual prognosis in ONJ surgery and the potential benefit of an antiresorptive drug holiday. To our knowledge it is the first use of a prognostic score in ONJ surgery.

Development and dissolution studies of bisphosphonate (clodronate)-containing hydroxyapatite-polylactic acid biocomposites for slow drug delivery

An increase in clinical demand on the controlled release of bisphosphonates (BPs) due to complications associated with systemic administration, has been the current driving force on the development of BP drug-release systems. Bisphosphonates have the ability to bind to divalent metal ions, such as Ca²⁺ , in bone mineral and prevent bone resorption by influencing the apoptosis of osteoclasts. Localized delivery using biodegradable materials, such as polylactic acid (PLA) and hydroxyapatite (HAp), which are ideal in this approach, have been used in this study to investigate the dissolution of clodronate (non-nitrogen-containing bisphosphonate) in a new release system. The effects of coral structure-derived HAp and the release kinetics of the composites were evaluated. The release kinetics of clodronate from PLA-BP and PLA-HAp-BP systems seemed to follow the power law model described by Korsmeyer-Peppas. Drug release was quantified by ³¹ P-NMR with detection and quantification limits of 9.2 and 30.7 mM, respectively. The results suggest that these biocomposite systems could be tuned to release clodronate for both relatively short and prolonged period of time. In addition to drug delivery, the degradation of HAp supplies both Ca²⁺ and phosphate ions that can help in bone mineralization. Copyright © 2015 John Wiley & Sons, Ltd.

Structural requirements for bisphosphonate binding on hydroxyapatite: NMR study of bisphosphonate partial esters

Eighteen different bisphosphonates, including four clinically used bisphosphonate acids and their phosphoesters, were studied to evaluate how the bisphosphonate structure affects binding to bone. Bisphosphonates with weak bone affinity, such as clodronate, could not bind to hydroxyapatite after the addition of one ester group. Medronate retained its ability to bind after the addition of one ester group, and hydroxy-bisphosphonates could bind even after the addition of two ester groups. Thus, several bisphosphonate esters are clearly bone binding compounds. The following conclusions about bisphosphonate binding emerge: (1) a hydroxyl group in the geminal carbon takes part in the binding process and increases the bisphosphonate's ability to bind to bone; (2) the bisphosphonate's ability to bind decreases when the amount of ester groups increases; and (3) the location of the ester groups affects the bisphosphonate's binding ability.

Basic research and clinical applications of bisphosphonates in bone disease: what have we learned over the last 40 years?

It is now 40 years since bisphosphonates (BPs) were first used in the clinic. So, it is timely to provide a brief review of what we have learned about these agents in bone disease. BPs are bone-specific and have been classified into two major groups on the basis of their distinct molecular modes of action: amino-BPs and non-amino-BPs. The amino-BPs are more potent and they inhibit farnesyl pyrophosphate synthase (FPPS), a key enzyme of the mavalonate/cholesterol biosynthetic pathway, while the non-amino-BPs inhibit osteoclast activity, by incorporation into non-hydrolyzable analogs of ATP. Both amino-BPs and non-amino-BPs can protect osteoblasts and osteocytes against apoptosis. The BPs are widely used in the clinic to treat various diseases characterized by excessive bone resorption, including osteoporosis, myeloma, bone metastasis, Legg-Perthes disease, malignant hyperparathyroidism, and other conditions featuring bone fragility. This review provides insights into some of the adverse effects of BPs, such as gastric irritation, osteonecrosis of the jaw, atypical femoral fractures, esophageal cancer, atrial fibrillation, and ocular inflammation. In conclusion, this review covers the biochemical and molecular mechanisms of action of BPs in bone, particularly the discovery that BPs have direct anti-apoptotic effects on osteoblasts and osteocytes, and the current situation of BP use in the clinic.

Zoledronic acid exerts its antitumor effect in multiple myeloma interfering with the bone marrow microenvironment

Multiple myeloma (MM) is a B-cell malignancy characterized by an excess of monotypic plasma cells which localize almost exclusively in the bone marrow provoking bone destruction via the activation of the osteoclasts. The bone marrow microenvironment, mainly through stromal cells, is strictly involved in the evolution of the disease supporting MM cell growth and survival [1]. MM plasma cells reside in the bone marrow by binding to adhesion molecule of extracellular matrix (ECM) and stromal cells. The activation of some signaling pathways within the stromal cells increases the production of several cytokines which in turn favors the myeloma cell proliferation and survival [2-6], and enhance the drug resistance by anti-apoptotic mechanisms [1,7-9]. Novel therapeutic agents target not only the myeloma cells but also the interaction between MM cells and the bone marrow microenvironment [8]. Bisphosphonates (Bps) interfere as well with bone microenvironment inhibiting the survival of stromal cells and hampering the contact between plasma and stromal cells. In this review we will revise preclinical evidences, and the potential mechanisms of the antitumor activity of zoledronic acid.

Gammadelta T cells: innately adaptive immune cells?

T cells employ a cell surface heterodimeric molecule, the T cell receptor (TCR), to recognize specific antigens (Ags) presented by major histocompatibility complex (MHC) molecules and carry out adaptive immune responses. Most T cells possess a TCR with an α and a β chain. However, a TCR constituted by a γ and a δ chain has been described, defining a novel subset of T cells. γδ TCRs specific for a wide variety of ligands, including bacterial phosphoantigens, nonclassical MHC-I molecules and unprocessed proteins, have been found, greatly expanding the horizons of T cell immune recognition. This review aims to provide background in γδ T cell history and function in mouse and man, as well as to provide a critical view of some of the latest developments on this still enigmatic class of immune cells.

Effects of etidronate on calcification of scales and ribs in the goldfish, Carassius auratus

Effects of etidronate on the calcification of scales and ribs were investigated in goldfish. Daily intraperitoneal injections of etidronate at doses of 1 and 10 mgP/kg body weight for 2 weeks inhibited calcification of ontogenic scales and ribs without affecting the accretion of organic matrices. Removal of some scales induced their regeneration within the two-week period. Their newly formed organic matrix was fully uncalcified in fish treated with 10 mgP/kg, whereas in those treated with 1 mgP/kg, the regenerating scales were only partially calcified. Daily administration of etidronate 10 mgP/kg resulted in an increase of body weight. These results suggested that the inhibitory effect of etidronate on the calcification of osseous tissues in mammals can be expected also on comparable tissues in fishes. An appropriate dose of etidronate that inhibits hard tissue calcification but not affects the body growth in fish seemed to exist between 1 and 10 mgP/kg.

Effects of alendronate on human osteoblast-like MG63 cells and matrix metalloproteinases

OBJECTIVE

The objective of this study was to examine the effects of alendronate on the expression and activity of matrix metalloproteinases (MMPs) and the expression of the tissue inhibitors of MMPs (TIMPs) from human osteoblast-like MG63 cells.

MATERIALS AND METHODS

MG63 cells were exposed to various concentrations of alendronate. Cell proliferation and cytotoxicity were evaluated by water-soluble tetrazolium-1 and lactate dehydrogenase, respectively. MG63-mediated collagen degradation was assessed utilising Type I collagen assays. Conditioned media and membrane extracts were collected for Western blot analyses of select MMPs and TIMPs. Gelatin zymography gels were incubated with alendronate to assess its effects on MMP-2 activity.

RESULTS

Alendronate affected MG63 proliferation and cytotoxicity at concentrations equal to/or greater than 10(-5) M (all p < 0.05). There were no significant differences in the collagen degrading ability of treated cells at non-toxic levels vs. untreated cells. Alendronate had no effects on the expression of MMP-2 or MT1-MMP (membrane type-1 MMP) in the conditioned media or membrane extracts, and of MMP-1 or TIMP-2 in the conditioned media. TIMP-2 in the membrane extracts was not detectable. MMP-2 activity in the zymograms was inhibited by 10(-3) and 10(-2) M alendronate.

CONCLUSION

Alendronate at 10(-5) M or higher was toxic to the cells. Alendronate at 10(-8) to 10(-6) M did not alter the expression of MMP-1, MMP-2, MT1-MMP or TIMP-2, as well as did not alter collagen degradation. Alendronate inhibited MMP-2 activity at 10(-3) and 10(-2) M in the zymograms. In conclusion, non-toxic levels of alendronate (10(-8) to 10(-6) M) did not alter MMP expression in MG63 cells or inhibit MMP-2 activity.

Marked improvement of calcinosis in adult dermatomyositis with etidronate therapy

We report a 26-year-old woman with severe calcinosis associated with dermatomyositis. Although calcinosis of the skin or muscles is unusual in adults with dermatomyositis, this patient developed subcutaneous calcinosis with tenderness on the arms, axillary areas, shoulder areas, chest, abdomen, pelvis, and limbs. The calcinosis steadily increased and spread until joint motions were severely limited. Radiographic examination showed extensive soft-tissue calcification with a reticular pattern and severe osteoporosis. The patient was treated with oral etidronate (800 mg/day for 3 months every 6 months) to prevent calcification of the lesions. Three months later, the patient showed a dramatic improvement in symptoms with softening of the calcinosis, reduced pain, and marked increase in joint mobility. Radiographic examination showed marked decreases in the size of the calcified lesions compared to pre-treatment findings, and this effect persisted with a constant progressive efficacy for 3 years. The 3-year course of etidronate therapy also resulted in marked improvement of the severe osteoporosis and the patient was able to return to work and enjoy a normal life. We propose etidronate as a beneficial and effective therapy for calcinosis with osteoporosis.

Bisphosphonates: the first 40 years

The first full publications on the biological effects of the diphosphonates, later renamed bisphosphonates, appeared in 1969, so it is timely after 40years to review the history of their development and their impact on clinical medicine. This special issue of BONE contains a series of review articles covering the basic science and clinical aspects of these drugs, written by some of many scientists who have participated in the advances made in this field. The discovery and development of the bisphosphonates (BPs) as a major class of drugs for the treatment of bone diseases has been a fascinating story, and is a paradigm of a successful journey from 'bench to bedside'. Bisphosphonates are chemically stable analogues of inorganic pyrophosphate (PPi), and it was studies on the role of PPi as the body's natural 'water softener' in the control of soft tissue and skeletal mineralisation that led to the need to find inhibitors of calcification that would resist hydrolysis by alkaline phosphatase. The observation that PPi and BPs could not only retard the growth but also the dissolution of hydroxyapatite crystals prompted studies on their ability to inhibit bone resorption. Although PPi was unable to do this, BPs turned out to be remarkably effective inhibitors of bone resorption, both in vitro and in vivo experimental systems, and eventually in humans. As ever more potent BPs were synthesised and studied, it became apparent that physico-chemical effects were insufficient to explain their biological effects, and that cellular actions must be involved. Despite many attempts, it was not until the 1990s that their biochemical actions were elucidated. It is now clear that bisphosphonates inhibit bone resorption by being selectively taken up and adsorbed to mineral surfaces in bone, where they interfere with the action of the bone-resorbing osteoclasts. Bisphosphonates are internalised by osteoclasts and interfere with specific biochemical processes. Bisphosphonates can be classified into at least two groups with different molecular modes of action. The simpler non-nitrogen containing bisphosphonates (such as etidronate and clodronate) can be metabolically incorporated into non-hydrolysable analogues of ATP, which interfere with ATP-dependent intracellular pathways. The more potent, nitrogen-containing bisphosphonates (including pamidronate, alendronate, risedronate, ibandronate and zoledronate) are not metabolised in this way but inhibit key enzymes of the mevalonate/cholesterol biosynthetic pathway. The major enzyme target for bisphosphonates is farnesyl pyrophosphate synthase (FPPS), and the crystal structure elucidated for this enzyme reveals how BPs bind to and inhibit at the active site via their critical N atoms. Inhibition of FPPS prevents the biosynthesis of isoprenoid compounds (notably farnesol and geranylgeraniol) that are required for the post-translational prenylation of small GTP-binding proteins (which are also GTPases) such as rab, rho and rac, which are essential for intracellular signalling events within osteoclasts. The accumulation of the upstream metabolite, isopentenyl pyrophosphate (IPP), as a result of inhibition of FPPS may be responsible for immunomodulatory effects on gamma delta (γδ) T cells, and can also lead to production of another ATP metabolite called ApppI, which has intracellular actions. Effects on other cellular targets, such as osteocytes, may also be important. Over the years many hundreds of BPs have been made, and more than a dozen have been studied in man. As reviewed elsewhere in this issue, bisphosphonates are established as the treatments of choice for various diseases of excessive bone resorption, including Paget's disease of bone, the skeletal complications of malignancy, and osteoporosis. Several of the leading BPs have achieved 'block-buster' status with annual sales in excess of a billion dollars. As a class, BPs share properties in common. However, as with other classes of drugs, there are obvious chemical, biochemical, and pharmacological differences among the various BPs. Each BP has a unique profile in terms of mineral binding and cellular effects that may help to explain potential clinical differences among the BPs. Even though many of the well-established BPs have come or are coming to the end of their patent life, their use as cheaper generic drugs is likely to continue for many years to come. Furthermore in many areas, e.g. in cancer therapy, the way they are used is not yet optimised. New 'designer' BPs continue to be made, and there are several interesting potential applications in other areas of medicine, with unmet medical needs still to be fulfilled. The adventure that began in Davos more than 40 years ago is not yet over.

Synthesis and characterization of surface-modified PBLG nanoparticles for bone targeting: in vitro and in vivo evaluations

In this study, poly(γ-benzyl-l-glutamate) (PBLG) polypeptide derivatives were synthesized by ring-opening polymerization of amino acid N-carboxyanhydride using selected amine-terminated initiators. Alendronate, a targeting moiety that has a strong affinity for bone, was conjugated to PBLG. Monomethoxy polyethylene glycol (PEG) was used for a hydrophilic layer on the surface of the nanoparticles (NPs) to avoid reticuloendothelial system uptake. NPs were prepared by nanoprecipitation technique not only for PBLG or PBLG-PEG but also for composite polymers with different ratios. Fluorescein isothiocyanate would be attached to the NPs as a labeling agent. The size and morphology of NPs were evaluated by dynamic laser light scattering and transmission electron microscopy, and were found to be in a useful range (less than 80 nm) for bone-targeted drug delivery. In addition, the PEGylation of NPs was supported by isothermal titration calorimetry analysis. The bone-targeting potential of NPs was evaluated in vitro by calcium binding and hydroxyapatite affinity assays, and in vivo by fluorescent imaging experiments on rats. The targeted NPs showed bright fluorescent labeling in femur tissue. These results demonstrated the possibility of optimized NPs prepared with new PBLG derivatives to accumulate in bone successfully.

Orally active, antimetastatic, nontoxic diphenyl ether-derived carbamoylphosphonate matrix metalloproteinase inhibitors

Seven 4-phenoxybenzenesulfonamidopolymethylene carbamoylphosphonates (CPOs) bearing two to eight methylene units in the polymethylene chain were synthesized and evaluated as matrix metalloproteinase (MMP) inhibitors. The five lowest homologues [(CH₂)₂-₆] are selective MMP-2 inhibitors, whereas the two with the longest linkers [(CH₂)₇,₈] lack inhibitory activity. The most potent homologues are those with (CH₂)₅,₆; these two were evaluated for antimetastatic activity in a murine melanoma model and showed good potency both by oral and intraperitoneal administration without any toxic--including musculoskeletal--side effects. In contrast to the previously reported cis-ACCP, which was shown to inhibit MMP-2 for ∼30 min, the new compounds inhibit MMP activity for the duration of measurement, lasting several hours. Pharmacokinetic evaluation revealed, on the one hand, low oral bioavailability; on the other hand, a relatively large calculated volume of distribution, consistent with the observed reversible absorption of CPO 5 to hydroxyapatite, as a model for bone.

Pamidronate and zoledronate effects in the increment of bone mineral density and histomorphometry in rats

PURPOSE

To compare increment of bone mineral density (BMD) with pamidronate, zoledronate and the isolated effect of proteinous diet in undernourished oophorectomized and non-oophorectomized female rats, besides validating BMD's indexes.

METHODS

60 young female Lewis rats were divided into five experimental groups and a control group, oophorectomized and non-oophorectomized. The administration of drugs were submitted to proteinous and aproteinous diets. The variables analyzed were weight, bone densitometry, histomorphometry and biochemical evolution.

RESULTS

In weight evaluation, the first interval showed a statistically meaningful increase in oophorectomized sample. In densitometry evaluation, the first interval showed statistically meaningful decrease in four medicated groups and third showed a statistically meaningful increase in 2 non-oophorectomized groups. In laboratory evaluation, there were an increase of total proteins and globulin, decrease of alkaline phosphatase, phosphorus and calcium (except for the oophorectomized) in four medicated groups and increase of phosphorus and calcium in 2 not medicated groups. In histomorphometric evaluation, the oophorectomized groups had smaller increment of BMD.

CONCLUSIONS

The pamidronate and zoledronate have shown effectives in the increment of BMD. The proteinous diet itself possesses therapeutic effect in BMD though not significant compared with medicated animals. The results of histomorphometry allow validating BMD's indexes in this experimental model.

Effect of alendronate on pseudomembrane cytokine expression in patients with aseptic osteolysis

To determine whether alendronate alters the pseudomembrane inflammatory cytokine profile in patients with established aseptic osteolysis. A prospective, double-blind, randomized, controlled trial was conducted. Ten individuals listed for revision surgery for aseptic failure of a primary cemented arthroplasty were randomly assigned placebo/alendronate 70 mg once weekly for 8 weeks before revision surgery. Formalin-preserved pseudomembrane samples were paraffin-sectioned for immunohistochemical analysis to assess inflammatory cytokine protein expression. Polymerase chain reaction was carried out to assess expression of relevant mRNA. No significant difference was detected in the inflammatory cytokine protein or mRNA expression between groups. Alendronate 70 mg administered for an 8-week period before surgery did not alter the pseudomembrane inflammatory cytokine profile in patients with established aseptic osteolysis. Any potential biological effects may occur due to downstream effects on osteoclast and osteoblast function.

Triclosan-loaded tooth-binding micelles for prevention and treatment of dental biofilm

PURPOSE

To develop tooth-binding micelle formulations of triclosan for the prevention and treatment of dental caries.

METHODS

Alendronate (ALN) was conjugated to the chain termini of different Pluronic copolymers to confer tooth-binding ability to the micelles. Using 3 different formulation methods, Pluronics and ALN-modified Pluronics were used to prepare triclosan-loaded tooth-binding micelles. The formulation parameters were optimized for triclosan solubility, particle size, hydroxyapatite (HA) binding capability and in vitro drug release profile. The optimized formulation was tested on an in vitro biofilm model.

RESULTS

Direct dissolution was selected as the best formulation method. Triclosan-loaded tooth-binding micelles were able to inhibit initial biofilm growth of Streptococcus mutans UA159 by 6-log CFU/HA disc compared to the untreated control. These tooth-binding micelles were also able to reduce the viability of preformed biofilm by 4-log CFU/HA disc compared to the untreated control.

CONCLUSIONS

Triclosan-loaded tooth-binding micelle formulations have been successfully developed and optimized in this study. These micelle formulations demonstrated promising anti-cariogenic bacteria capabilities and may find applications in the prevention and treatment of dental caries.

Switching breast cancer patients with progressive bone metastases to third-generation bisphosphonates: measuring impact using the Functional Assessment of Cancer Therapy-Bone Pain

Because bone metastases cause significant pain, we developed a questionnaire to evaluate its nature, severity, and impact. This 16-item questionnaire is the Functional Assessment of Cancer Therapy-Bone Pain (FACT-BP). We also developed a 13/18-item questionnaire, the Functional Assessment of Chronic Illness Therapy-Treatment Satisfaction-Bone Treatment Convenience and Satisfaction Questionnaire (FACIT-TS-BTCSQ), to evaluate patients' expectations and acceptance of bone-specific therapies. We evaluated the performance of these scales in two clinical trials. In both trials, we enrolled patients with metastatic breast cancer, who had progressive bone metastases despite first-line therapy with pamidronate or clodronate. We administered intravenous zoledronic acid to 31 patients in one trial and oral ibandronate to 30 patients in the other. Patients completed the FACT-BP questionnaire and FACIT-TS-BTCSQ at baseline, then at Weeks 4, 8, and 12. The FACT-BP scale showed good internal consistency reliability [Cronbach's alpha (alpha)=0.93-0.96]. There was evidence of construct validity, and known-group validity was supported by score shifts in the anticipated direction (Cohen's d effect size=0.36). The FACT-BP score reflected clinical change as evidenced by differences in performance status. This cross-sectional anchor-based criterion suggested reasonable clinically important differences (effect size=0.36). The FACIT-TS-BTCSQ showed good internal consistency reliability for treatment expectation (alpha=0.87) and treatment experience (alpha's=0.89-0.92). The FACT-BP scale is meaningful and appears appropriate for broader use. The assessment of satisfaction (FACIT-TS-BTCSQ) raised questions that will require further research.

Zoledronic acid inhibits both the osteolytic and osteoblastic components of osteosarcoma lesions in a mouse model

PURPOSE

To evaluate the efficacy of zoledronic acid (ZOL) against osteosarcoma (OS) growth, progression, and metastatic spread using an animal model of human OS that closely resembles the human disease.

EXPERIMENTAL DESIGN

Human K-HOS or KRIB OS cells, tagged or untagged with a luciferase reporter construct, were transplanted directly into the tibial cavity of nude mice. ZOL was given as weekly, or a single dose of 100 microg/kg body weight, equivalent to the 4 mg i.v. dose used clinically. Tumor growth at the primary site and as pulmonary metastases was monitored by bioluminescence imaging and histology, and OS-induced bone destruction was measured using high-resolution micro-computed tomography.

RESULTS

Mice transplanted with OS cells exhibited aberrant bone remodeling in the area of cancer cell transplantation, with areas of osteolysis mixed with extensive new bone formation extending from the cortex. ZOL administration prevented osteolysis and significantly reduced the amount of OS-induced bone formation. However, ZOL had no effect on tumor burden at the primary site. Importantly, ZOL failed to reduce lung metastasis and in some cases was associated with larger and more numerous metastatic lesions.

CONCLUSIONS

Our data show that clinically relevant doses of ZOL, while protecting the bone from OS-induced bone destruction, do not inhibit primary tumor growth. Moreover, lung metastases were not reduced and may even have been promoted by this treatment, indicating that caution is required when the clinical application of the bisphosphonate class of antiresorptives is considered in OS.

The effect of a bisphosphonate on bone volume and eggshell structure in the hen

Bisphosphonates, used in the prevention and treatment of osteoporosis, in man, can prevent bone loss in experimental models of osteoporosis in mammals. In egg-laying hens there is a high incidence of bone fractures which are due to osteoporosis. Alendronate, a bisphosphonate, was given to three groups of hens in mid-lay. Different doses of alendronate were given to each group and group 4 was a control. The birds were killed after 2 weeks of treatment. The hens receiving the highest dosage of alendronate (1 mg/kg every 2nd day) ceased laying and had reduced serum calcium concentrations. Lower dosages of alendronate (0.1 and 0.01 mg/kg every 2nd day) resulted in normal egg production and serum calcium concentrations. Egg shells with ultra-structural features indicative of reduced shell quality were produced by hens on the two higher dosages, but the egg shells from the controls and from the hens on the lowest dosage were considered normal. When alendronate was administered to hens in mid-lay there was no effect on trabecular bone volumes, but there was a reduction in mean medullary bone volume in some groups. In a second experiment, pullets were treated with alendronate (0.01 mg/kg twice a week) before the onset of lay. The pullets were killed after laying their first egg. In the pullets treated with alendronate, this protocol resulted in a significantly greater volume of trabecular (structural) bone at the onset of lay.

Bisphosphonates: how do they work?

Bisphosphonates (BPs) are taken up preferentially by the skeleton and decrease osteoclast-mediated bone resorption. The capacity of the skeleton to retain BPs is large, and there is no indication for saturation of binding sites with the doses used in osteoporosis. The anti-resorptive action of BPs includes their selective binding to calcium crystals and their subsequent release and uptake by the osteoclasts. There are differences in the affinities of PBs for bone as well as in their anti-resorptive potencies, and the whole molecule is responsible for their inhibitory effect on bone resorption. At the tissue level, they decrease the rate of bone resorption and turnover, increase bone mineral density, and maintain or improve structural and material properties of bone and thereby reduce the risk of fractures. Current studies address questions related primarily to the pharmacological properties of these compounds that are essential for their optimal clinical use, such as for example long-term safety and efficacy.

The role of bisphosphonates in the management of patients that have cancer

Bisphosphonates are pharmacologic agents widely used in people for managing pathologic bone resorptive conditions. Based on their physicochemical properties, bisphosphonates concentrate within areas of active bone remodeling and induce osteoclast apoptosis. Appropriate use of bisphosphonates for treating companion animals requires a thorough understanding of how bisphosphonates exert their biologic effects. This review article highlights general properties of bisphosphonates, including their pharmacology, mechanisms of action, adverse side effects, anticancer mechanisms, surrogate markers for assessing response, and potential clinical utility for treating dogs and cats diagnosed with malignant skeletal tumors.

Repeated intermittent low-dose therapy with zoledronic acid induces an early, sustained, and long-lasting decrease of peripheral vascular endothelial growth factor levels in cancer patients

PURPOSE

On the basis of stimulating data on animals reporting that weekly regimens of zoledronic acid (ZA) were effective in reducing skeletal tumor burden, we designed a study on humans to investigate the potential antiangiogenic role of a weekly low-dose therapy with ZA in patients with malignancies.

EXPERIMENTAL DESIGN

Twenty-six consecutive patients with advanced solid cancer and bone metastases received 1 mg of ZA every week for four times (days 1, 7, 14, and 21) followed by 4 mg of ZA with a standard 28-day schedule repeated thrice (days 28, 56, and 84). Patients were prospectively evaluated for circulating levels of vascular endothelial growth factor (VEGF) just before the beginning of drug infusion (0) and again at 7, 14, 21, 28, 56, and 84 days after the first ZA infusion.

RESULTS

The median VEGF basal value showed an early statistically significant (P = 0.038) decrease 7 days after the first 1-mg infusion of ZA. This effect on VEGF-circulating levels persisted also after the following 1-mg infusions at 14 (P = 0.002), 21 (P = 0.001), and 28 days (P = 0.008). Interestingly, the decrease of VEGF-circulating levels persisted also at each programmed time point during the second phase of the study (ZA 4 mg every 4 weeks). No significant differences were recorded in platelet levels, WBC count, or hemoglobin concentration before and after each ZA infusion.

CONCLUSIONS

In the present study, we report that a repeated low-dose therapy with ZA is able to induce an early significant and long-lasting decrease of VEGF levels in cancer patients.

Inorganic polyphosphate: a possible stimulant of bone formation

Inorganic polyphosphates [Poly(P)] are often distributed in osteoblasts. We undertook the present study to verify the hypothesis that Poly(P) stimulates osteoblasts and facilitates bone formation. The osteoblast-like cell line MC 3T3-E1 was cultured with Poly(P), and gene expression and potential mineralization were evaluated by reverse-transcription polymerase chain-reaction. Alkaline phosphatase activity, von Kossa staining, and resorption pit formation analyses were also determined. The potential role of Poly(P) in bone formation was assessed in a rat alveolar bone regeneration model. Poly(P) induced osteopontin, osteocalcin, collagen 1alpha, and osteoprotegerin expression and increased alkaline phosphatase activity in MC 3T3-E1 cells. Dentin slice pit formation decreased with mouse osteoblast and bone marrow macrophage co-cultivation in the presence of Poly(P). Promotion of alveolar bone regeneration was observed locally in Poly(P)-treated rats. These findings suggest that Poly(P) plays a role in osteoblastic differentiation, activation, and bone mineralization. Thus, local poly(P) delivery may have a therapeutic benefit in periodontal disease.

Effects of neridronic acid on osteoclasts derived by physiological dual-cell cultures

Increased osteoclastic activity is observed in many osteopathic disorders - including postmenopausal osteoporosis, Paget's disease, primary bone tumours, lytic bone metastases, multiple myeloma and rheumatoid arthritis - that involve increased bone resorption and a loss of bone mass. Bisphosphonates are highly effective inhibitors of bone resorption that selectively affect the osteoclasts. The aim of this study was to obtain more information about the mechanism of action of bisphosphonates such as neridronic acid using a dual-cell culture model. As a model of osteoclastogenesis we used a murine monocyte/macrophage cell line RAW 264.7 type CRL 2278 co-cultured with murine osteoblasts. The monocyte-osteoblast system allows physiological experimentation of bone anti-resorption drugs, simulating bone turnover in pathologies such as osteoporosis. The direct actions of neridronic acid on cell proliferation and functionality in the co-culture model were examined using tartrate-resistant acid phosphatase (TRAP) assay, immunohistochemical localization of actin, and transmission and scanning electron microscopy (SEM). Results showed that the percentage of TRAP-positive cells, an early marker of osteoclastic differentiation, was significantly higher in control cultures than in co-cultures treated with variable concentrations of neridronic acid. Neridronic acid induced dramatic morphological changes, characterized by the loss of the ruffled border. The actin ring associated with the plasma membrane of the cells treated with neridronic acid was shown to break down. The tissue-specific targeting of neridronic acid to bone mineral suggests that it may inhibit bone resorption by direct effects on osteoclasts or other bone cells in the immediate microenvironment of the osteoclasts. From our study, we conclude that structural alterations induced by neridronic acid in our co-culture system lead to decreased osteoclast function. This may encourage the use of neridronic acid to reduce bone resorption in the therapy of demineralizing metabolic bone disorders.

Immunomodulating role of bisphosphonates on human gamma delta T cells: an intriguing and promising aspect of their antitumour activity

Vgamma9Vdelta2 T cells have the ability to produce inflammatory cytokines involved in protective immunity against intracellular pathogens and tumours and to display strong cytolytic as well as bactericidal activities. This suggests a direct involvement of Vgamma9Vdelta2 T lymphocytes in immune control of cancer and infections. These observations have recently aided development of novel immunotherapeutic approaches aimed at Vgamma9Vdelta2 T cell activation. Nitrogen-containing bisphosphonates (N-BPs) play a crucial role in Vgamma9Vdelta2 T lymphocyte activation and in the acquisition of effector functions. The preliminary results of these innovative strategies are encouraging. Moreover, compelling evidence in the literature supports the hypothesis that the antitumour effect of bisphosphonates is exerted through direct as well as indirect mechanisms. An additional and not yet well explored mechanism by which N-BPs may display antineoplastic effect is related to their immunomodulatory properties. It is fascinating that N-BPs influence the immune system in various but interrelated ways, being able to enhance the innate and to promote the adaptive immune responses. For all these reasons, Vgamma9Vdelta2 T lymphocytes represent a particularly interesting target for immunotherapeutic protocols based on N-BP administration. All these unexpected effects of N-BPs on the immune system have opened new and intriguing possibilities of therapeutic use for these drugs.

Effect of long-term oral bisphosphonates on implant wound healing: literature review and a case report

BACKGROUND

Bisphosphonates suppress osteoclast activity, and their intravenous use has been reported in hundreds of cases to be associated with osteonecrosis in the jaw. Little is known of the risks associated with long-term use of oral bisphosphonates despite their use for >10 years by an oral mode of delivery for the treatment of osteopenia, osteoporosis, and Paget's disease of bone. The purpose of this report is to review the literature associated with bisphosphonate use that could impact bone healing and to report a case of bone necrosis in a patient on long-term oral bisphosphonates.

METHODS

A Medline search was carried out to find relevant articles from both medical and dental literature between 1960 and 2006. A patient, who had been taking an oral bisphosphonate for >10 years, developed unexplained clinical signs of bone necrosis after routine dental implant placement. This case was followed, documented, and the treatment of the osteonecrosis described.

RESULTS

A summary of how bisphosphonates may play a role in wound healing is presented. The compromised healing noted in a patient, who was under long-term oral bisphosphonate use, was successfully treated with systemic antibiotics, local microbial mouthrinse, and aggressive defect management (detoxification and mixture of bone graft and tetracycline).

CONCLUSIONS

This case suggests that patients under long-term oral bisphosphonate use should be treated with caution. Well-controlled, prospective clinical trials on the effect of oral bisphosphonates on bone are warranted to determine which patients may be at risk for such complications.

Zoledronic acid in the management of metastatic bone disease

Bisphosphonate therapy has become a standard of therapy for patients with malignant bone disease. Moreover, in vivo preclinical and preliminary clinical data suggest that bisphosphonates may prevent cancer treatment-induced bone loss and the onset of malignant bone disease in patients with early-stage cancer. This comprehensive review critically reports the several preclinical evidences of action of bisphosphonates on osteoclasts, lymphocytes and tumour cells. In addition, all the clinical trials evaluating the effects of principal bisphosphonates on skeletal disease progression in patients with breast cancer, prostate cancer, non-small cell lung cancer and other cancers have been reported. Of the available bisphosphonates, intravenous zoledronic acid has demonstrated the broadest clinical activity and is actually approved for the treatment of bone metastases from any solid tumour in many countries. Renal safety is an important consideration for oncologists who are treating patients with bisphosphonates. This issue and the other topics relating to the safety of bisphosphonates are discussed in this review.

Bisphosphonates: mode of action and pharmacology

The profound effects of the bisphosphonates on calcium metabolism were discovered over 30 years ago, and they are now well established as the major drugs used for the treatment of bone diseases associated with excessive resorption. Their principal uses are for Paget disease of bone, myeloma, bone metastases, and osteoporosis in adults, but there has been increasing and successful application in pediatric bone diseases, notably osteogenesis imperfecta. Bisphosphonates are structural analogues of inorganic pyrophosphate but are resistant to enzymatic and chemical breakdown. Bisphosphonates inhibit bone resorption by selective adsorption to mineral surfaces and subsequent internalization by bone-resorbing osteoclasts where they interfere with various biochemical processes. The simpler, non-nitrogen-containing bisphosphonates (eg, clodronate and etidronate) can be metabolically incorporated into nonhydrolysable analogues of adenosine triphosphate (ATP) that may inhibit ATP-dependent intracellular enzymes. In contrast, the more potent, nitrogen-containing bisphosphonates (eg, pamidronate, alendronate, risedronate, ibandronate, and zoledronate) inhibit a key enzyme, farnesyl pyrophosphate synthase, in the mevalonate pathway, thereby preventing the biosynthesis of isoprenoid compounds that are essential for the posttranslational modification of small guanosine triphosphate (GTP)-binding proteins (which are also GTPases) such as Rab, Rho, and Rac. The inhibition of protein prenylation and the disruption of the function of these key regulatory proteins explains the loss of osteoclast activity. The recently elucidated crystal structure of farnesyl diphosphate reveals how bisphosphonates bind to and inhibit at the active site via their critical nitrogen atoms. Although bisphosphonates are now established as an important class of drugs for the treatment of many bone diseases, there is new knowledge about how they work and the subtle but potentially important differences that exist between individual bisphosphonates. Understanding these may help to explain differences in potency, onset and duration of action, and clinical effectiveness.