Clodronate and liposome-encapsulated clodronate are metabolized to a toxic ATP analog, adenosine 5'-(beta, gamma-dichloromethylene) triphosphate, by mammalian cells in vitro

Pharmacological management of metastatic boney pain

Many malignancies metastasise to the skeleton. This often results in a relatively unique pain process, which dramatically affects a patient's quality of life. With one in three members of the population likely to develop cancer at some stage in their lives, the prevalence of bone metastases is high. Despite the large financial investment on therapies for these patients, treatment is still suboptimal. In this article, the various treatments available are reviewed. Opiates and bisphosphonates, the mainstays in current practise, are covered in detail, and evolving therapies that may shape future management are also discussed.

The bisphosphonate pamidronate on the surface of titanium stimulates bone formation around tibial implants in rats

Many materials with differing surfaces have been developed for clinical implant therapy in dentistry and orthopedics. We analyzed the quantity of new bone formed in vivo around calcium-immobilized titanium implants with surfaces modified using pamidronate (PAM), a nitrogen-containing bisphosphonate (N-BP), implants of pure titanium, and titanium implants immobilized with calcium ions. New bone formation was visualized using fluorescent labeling (calcein blue and alizarin complexone) with intravenous injection at 1 and 3 weeks after implantation. After 4 weeks, undecalcified sections were prepared, and new bone formation around the implants was examined by morphometry using confocal laser scanning microscopy images. After 1 week, more new bone formed around the PAM-immobilized implant than around the calcium-immobilized and pure titanium implants. This was also seen with the new bone formation after 3 weeks. After 4 weeks, significantly more new bones were formed around the BP-immobilized implant than around the calcium ion-implanted and pure titanium implants. The new N-BP-modified titanium surface stimulates new bone formation around the implant, which might contribute to the success of implant therapy.

Clinical Pharmacology of Potent New Bisphosphonates for Postmenopausal Osteoporosis

Bisphosphonates are potent inhibitors of bone resorption, used in most bone diseases associated with high bone resorption levels. Several bisphosphonates, developed to prevent and treat postmenopausal osteoporosis, increase bone mineral density and decrease biochemical markers of bone turnover, and more importantly, reduce fracture risk. Alendronate and risedronate have proven their efficacy to reduce vertebral and hip fracture risk among postmenopausal osteoporotic women, using daily regimens. Weekly intermittent schedules, however, are now most commonly prescribed, because they have shown pharmacologic equivalence to the daily regimen. Ibandronate has been the first bisphosphonate to demonstrate vertebral fracture risk reduction using an intermittent regimen. Studies using ibandronate as intravenous injections every 3 months are under way. Zoledronic acid may also be an attractive option for the treatment of postmenopausal osteoporosis if a large ongoing trial proves that a single annual injection of this compound allows osteoporotic fracture risk reduction.

Bisphosphonates: preclinical review

Bisphosphonates effectively inhibit osteoclast-mediated bone resorption and are integral in the treatment of benign and malignant bone diseases. The evolution of bisphosphonates over the past 30 years has led to the development of nitrogen-containing bisphosphonates (N-BPs), which have a mechanism of action different from that of the nonnitrogen-containing bisphosphonates. Studies conducted over the past decade have elucidated the mechanism of action and pharmacologic properties of the N-BPs. N-BPs exert their effects on osteoclasts and tumor cells by inhibiting a key enzyme in the mevalonate pathway, farnesyl diphosphate synthase, thus preventing protein prenylation and activation of intracellular signaling proteins such as Ras. Recent evidence suggests that N-BPs also induce production of a unique adenosine triphosphate analogue (Apppi) that can directly induce apoptosis. Our increased understanding of the pharmacologic effects of bisphosphonates is shedding light on the mechanisms by which they exert antitumor effects. As a result of their biochemical effects on protein prenylation, N-BPs induce caspase-dependent apoptosis, inhibit matrix metalloproteinase activity, and downregulate alpha(v)beta(3) and alpha(v)beta(5) integrins. In addition, zoledronic acid (Zometa; Novartis Pharmaceuticals Corp.; East Hanover, NJ and Basel, Switzerland) exerts synergistic antitumor activity when combined with other anticancer agents. Zoledronic acid also inhibits tumor cell adhesion to the extracellular matrix and invasion through Matrigel trade mark and has antiangiogenic activity. A growing body of evidence from animal models demonstrates that zoledronic acid and other bisphosphonates can reduce skeletal tumor burden and prevent metastasis to bone. Further studies are needed to fully elucidate these biochemical mechanisms and to determine if the antitumor potential of bisphosphonates translates to the clinical setting.

Steroid-free medium discloses oestrogenic effects of the bisphosphonate clodronate on breast cancer cells

Tamoxifen is the standard first-line endocrine therapy for breast cancer, but recent data indicate that it is likely to be replaced by the effective aromatase inhibitors (AIs), in both the metastatic and adjuvant settings. Aromatase inhibitors induce complete oestrogen deprivation that leads to clinically significant bone loss. Several ongoing or planned trials combine AIs with bisphosphonates, even more so that recent data reveal that clodronate may reduce the incidence of bone metastases and prolong survival in the adjuvant setting. Bisphosphonates can inhibit breast cancer cell growth in vitro, but they have never been studied in steroid-free medium (SFM), an in vitro environment that mimics the effects of AIs in vivo. Quite surprisingly, in SFM, clodronate stimulated MCF-7 cell growth in a time- and dose-dependent manner by up to two-fold (crystal violet staining assay), whereas it had no mitogenic activity in complete medium. The bisphosphonate similarly increased the proliferation of IBEP-2 cells, which also express a functional oestrogen receptor (ER), while it weakly inhibited the growth of the ER-negative MDA-MB-231 cells. Expectedly, 17beta-oestradiol stimulated the growth of MCF-7 and IBEP-2 cells cultured in SFM, and had no effect on MDA-MB-231 cells. Moreover, partial (4-OH-tamoxifen) and pure antioestrogens (fulvestrant, ICI 182,780), in combination with clodronate, completely suppressed the mitogenic effect of the bisphosphonate, suggesting that it was mediated by an activation of ER. In accordance with this view, clodronate induced ER downregulation, weakly increased progesterone receptor expression, and stimulated the transcription of an oestrogen-responsive reporter gene. In conclusion, we report a previously unknown stimulatory effect of clodronate on MCF-7 cells grown in SFM, in vitro conditions that are potentially relevant to the use of AIs for breast cancer. Moreover, our data suggest that ER is involved in these effects of clodronate on cancer cell growth.

From molds and macrophages to mevalonate: a decade of progress in understanding the molecular mode of action of bisphosphonates

Although bisphosphonates were first used as therapeutic agents to inhibit bone resorption in the early 1970s, their mode of action at the molecular level has only become fully clear within the last few years. One of the reasons for this lack of understanding was the difficulty in isolating large numbers of pure osteoclasts for biochemical studies. In the last decade, the identification of appropriate surrogate models that reflected the antiresorptive potencies of bisphosphonates, such as Dictyostelium slime molds and macrophages, helped overcome this problem and proved to be instrumental in elucidating the molecular pathways by which these compounds inhibit osteoclast-mediated bone resorption. This brief review summarizes our current understanding of these pathways.

Advances in the use of bisphosphonates in the prostate cancer setting

Prostate cancer incidence is rising, and represents a major public health issue. Bone is by far the most common site for metastases in this disease, accounting for considerable morbidity. Until recently, there have been few viable options for the treatment of patients with hormone-refractory metastatic disease. This review examines the pathophysiology underlying the development of bone metastases. It also summarises some of the clinical approaches for the management of this common condition, focusing on recent evidence supporting the use of zoledronic acid, a member of one of the most promising groups of pharmacological agents, the third-generation bisphosphonates.

In vitro toxicity of bisphosphonates on human neuroblastoma cell lines

Neuroblastoma is the commonest extracranial solid tumor of childhood and frequently metastasizes to the bone. Bisphosphonates are standard treatment of osteolytic lesions by bone metastasis. Since recent studies suggested direct antitumor effects of bisphosphonates, we screened the toxicity of different bisphosphonates on neuroblastoma cell lines. The nitrogen-containing bisphosphonate pamidronate was significantly more toxic on a panel of eight neuroblastoma cell lines than the non-nitrogen-containing bisphosphonates, clodronate and tiludronate. After 72 h, GI50 concentrations (inhibiting cell growth by 50% compared to untreated controls) for pamidronate ranged from 12.8 to >500 microM. CHLA-90 and SH-SY5Y were the most sensitive cell lines. In CHLA-90, zoledronate was the most cytotoxic bisphosphonate, followed by alendronate, pamidronate and ibandronate. In SH-SY5Y, alendronate was the most cytotoxic bisphosphonate, followed by ibandronate, pamidronate and zoledronate. The GI50 values after 72 h were 34.1 (SH-SY5Y) and 3.97 microM (CHLA-90) for zoledronate, and 22.4 (SH-SY5Y) and 9.55 microM (CHLA-90) for alendronate. Neuroblastoma cells treated with bisphosphonates showed signs of differentiation and finally underwent apoptosis. The observed GI50 concentrations suggest that local nitrogen-containing bisphosphonate concentrations at the bone interface can directly target neuroblastoma cell penetration into the bone matrix. In summary, these observations warrant the investigation of adjuvant bisphosphonate treatment in controlled clinical trials.

Bone microenvironment-related growth factors modulate differentially the anticancer actions of zoledronic acid and doxorubicin on PC-3 prostate cancer cells

OBJECTIVES

We analyzed the actions of zoledronic acid (10-250 microM) and doxorubicin (10-250 nM) on PC-3 prostate cancer cells using both continuous (48-96 hr) and pulsatile exposures (15 min/day for up to three consecutive days).

RESULTS

The proliferation of PC-3 cells was inhibited by either continuous or pulsatile exposures of zoledronic acid in a dose-dependent manner. In contrast, pulsatile exposures of doxorubicin failed to inhibit the growth of PC-3 cells. In addition, the inhibition of PC-3 cells by zoledronic acid was partially neutralized by exogenous administration of geranylgeranyl pyrophosphate (GGPP), however, not by farnesyl pyrophosphate (FPP). Furthermore, exogenous administration of transforming growth factor beta 1 (TGF-beta1), interleukin 6 (IL-6), basic fibroblast growth factor (bFGF), and more potently, insulin-like growth factor 1 (IGF-1) inhibited the doxorubicin-induced apoptosis of PC-3 cells. Under identical experimental conditions, these growth factors failed to alter the cytotoxicity of PC-3 cells induced by zoledronic acid.

CONCLUSIONS

These data suggest that (i) repetitive and pulsatile (15 min/day) exposure to zoledronic acid inhibited the growth of PC-3 cells, (ii) this anticancer action of zoledronic acid was partially mediated by the attenuation of GGPP production, and (iii) bone microenvironment-related growth factors do not alter the anticancer actions of zoledronic acid on PC-3 cells.

Cytostatic and Apoptotic Effects of Bisphosphonates on Prostate Cancer Cells

BACKGROUND

Bisphosphonates are potent inhibitors of bone resorption frequently used for breast cancer and myeloma-induced bone disease. Zoledronic acid has been recently shown to also reduce skeletal morbidity from prostate cancer.

METHODS

We have investigated the biological effects of bisphosphonates on PC-3 cell survival (MTT assay and DNA content). We compared four bisphosphonates at doses ranging from 10(-6) to 10(-4) M: clodronate, pamidronate, ibandronate and zoledronic acid. We analyzed cell cycle phases and assessed apoptotic effects of bisphosphonates by three different methods.

RESULTS

Clodronate exhibited only a slight inhibitory effect on cell growth. In contrast, aminobisphosphonates markedly decreased cell growth in a time- and dose-dependent manner exerting cytostatic and apoptotic effects. The largest effects were observed after six days of exposure to 10(-4) M bisphosphonates. Cytostatic effects were observed with all three aminobisphosphonates whereas apoptotic effects were especially evident after zoledronic acid incubation.

CONCLUSIONS

Aminobisphosphonates, especially zoledronic acid, markedly inhibited PC-3 cancer cell growth, through a variable combination of cytostatic and apoptotic effects. This activity could potentially contribute to the beneficial effects of bisphosphonates in prostate cancer patients with bone metastases.

The Emerging Role of Bisphosphonates in Prostate Cancer

Bisphosphonates are a class of therapeutic agents originally designed to treat loss of bone density. It has been shown that the primary mechanism of action is inhibition of osteoclastic activity. Accumulating data show that these drugs are useful in diseases with propensities toward osseous metastases. In particular, they are effective in diseases in which there is clear upregulation of osteoclastic or osteolytic activity such as breast cancer and multiple myeloma. Despite the fact that osseous metastases in prostate cancer manifest as osteosclerosis rather than osteolysis, studies now show that bisphosphonates are useful in the management of this disease. In particular, they have demonstrated an impact on osteoporosis associated with hormonal therapy, bone pain from metastases, and skeleton-related events from prostatic adenocarcinoma. This review briefly summarizes the available clinical data on the utilization of bisphosphonates in the disease of prostate cancer.

Differentiating the mechanisms of antiresorptive action of nitrogen containing bisphosphonates

Bisphosphonates (BPS) inhibit bone resorption and are divided into two classes according to their chemical structure and mechanism of action: nonnitrogen containing BPS such as etidronate and clodronate that are of low potency and inhibit osteoclast function via metabolism into toxic ATP-metabolites and nitrogen-containing BPS (NBPS), such as alendronate and risedronate that inhibit the enzyme of the mevalonate biosynthetic pathway farnesyl pyrophosphate synthase (FPPS), resulting in inhibition of the prenylation of small GTP-binding proteins in osteoclasts and disruption of their cytoskeleton. Previously, studies in various cell types suggested, however, that pamidronate functions by mechanism(s) additional or independent of the mevalonate pathway. To examine if such mechanism(s) are also involved in the action of NBPS on osteoclastic bone resorption, we examined the action of alkyl and heterocyclic NBPS with close structural homology on FPPS/isopentenyl pyrophosphate isomerase (IPPI) activity, on osteoclastic resorption, and on reversibility of this effect with GGOH. As expected, both pamidronate and alendronate suppressed bone resorption and FPPS/IPPI activity, the latter with greater potency than the first. Surprisingly, however, unlike alendronate, the antiresorptive effect of pamidronate was only partially reversible with GGOH, indicating the involvement of mechanism(s) of action additional to that of suppression of FPPS. Comparable results were obtained with the heterocyclic NBP NE-21650, a structural analog of risedronate. Thus, despite an effect on FPPS, the actions on bone resorption of some NBPS may involve mechanisms additional to suppression of FPPS. These findings may lead to identification of additional pathways that are important for bone resorption and may help to differentiate among members of the NBP class which are currently distinguished only according to their potency to inhibit bone resorption.

Mechanism of action of bisphosphonates

In recent years, substantial progress has been made in understanding the mechanism for bisphosphonate suppression of bone turnover. Bisphosphonates can now be distinguished based on their molecular and cellular mechanisms of action. Simple bisphosphonates such as clodronate and etidronate inhibit bone resorption through induction of osteoclast apoptosis. Clodronate, and perhaps etidronate, triggers apoptosis by generating a toxic analog of adenosine triphosphate, which then targets the mitochondria, the energy center within the cell. For nitrogen-containing bisphosphonates, the direct intracellular target is the enzyme farnesyl diphosphate synthase in the cholesterol biosynthetic pathway. Its inhibition suppresses a process called protein geranylgeranylation, which is essential for the basic cellular processes required for osteoclastic bone resorption. Although nitrogen-containing bisphosphonates can induce osteoclast apoptosis, this is not necessary for their inhibition of bone resorption.

Induction of cell death of human osteogenic sarcoma cells by zoledronic acid resembles anoikis

The aim of this study was to investigate the cytotoxic activity of the third-generation nitrogen-containing bisphosphonate zoledronic acid (ZOL) as a single agent, and in combination with clinically relevant anticancer drugs, in a panel of human osteogenic sarcoma cell lines (HOS, BTK-143, MG-63, SJSA-1, G-292, and SAOS2). We found that ZOL, when used alone, reduced cell number in a dose- and time-dependent manner, due either to cell cycle arrest in S-phase or to the induction of apoptosis. In the sensitive HOS, BTK-143, and G-292 cell lines, genomic DNA fragmentation and morphological changes characteristic of apoptosis were evident, and cells became nonadherent. Induction of apoptosis in osteosarcoma cells by ZOL was associated with caspase activation. However, coaddition of the broad-spectrum caspase inhibitors, z-VAD-fmk, Boc-D-fmk, or the caspase-3-specific inhibitor z-DEVD fmk, failed to protect these cells from ZOL-induced apoptosis. Our data support a ZOL-specific induction of cell apoptosis that involves cell detachment (anoikis), and in which caspase activation occurs secondarily to, and is redundant as a mediator of cell death. The addition of geranylgeraniol, an intermediate of the mevalonate pathway, suppressed the ZOL-induced apoptosis, suggesting that the cytotoxic effects of ZOL in osteosarcoma cells were mediated by the mevalonate pathway. While treatment of osteosarcoma cells with the chemotherapeutic agents doxorubicin or etoposide decreased cell viability, combination of these agents with ZOL did not significantly augment apoptosis in any of the cell lines tested. These observations suggest that ZOL has direct effects on the proliferation and survival of osteosarcoma cells in vitro, which has implications for future therapy of osteosarcoma.

Bisphosphonates antagonise bone growth factors' effects on human breast cancer cells survival

Bone tissue constitutes a fertile 'soil' for metastatic tumours, notably breast cancer. High concentrations of growth factors in bone matrix favour cancer cell proliferation and survival, and a vicious cycle settles between bone matrix, osteoclasts and cancer cells. Classically, bisphosphonates interrupt this vicious cycle by inhibiting osteoclast-mediated bone resorption. We and others recently reported that bisphosphonates can also induce human breast cancer cell death in vitro, which could contribute to their beneficial clinical effects. We hypothesised that bisphosphonates could inhibit the favourable effects of 'bone-derived' growth factors, and indeed found that bisphosphonates reduced or abolished the stimulatory effects of growth factors (IGFs, FGF-2) on MCF-7 and T47D cell proliferation and inhibited their protective effects on apoptotic cell death in vitro under serum-free conditions. This could happen through an interaction with growth factors' intracellular phosphorylation transduction pathways, such as ERK1/2-MAPK. In conclusion, we report that bisphosphonates antagonised the stimulatory effects of growth factors on human breast cancer cell survival and reduced their protective effects against apoptotic cell death. Bisphosphonates and growth factors thus appear to be concurrent compounds for tumour cell growth and survival in bone tissue. This could represent a new mechanism of action of bisphosphonates in their protective effects against breast cancer-induced osteolysis.

Inhibition of mevalonate pathway is involved in alendronate-induced cell growth inhibition, but not in cytokine secretion from macrophages in vitro

Bisphosphonates are antiresorptive drugs used for the treatment of metabolic bone diseases. They can be divided into two different pharmacological classes: nitrogen-containing and non-nitrogen-containing bisphosphonates. Non-nitrogen-containing bisphosphonates, like clodronate, are metabolised to a toxic ATP-analogue preventing osteoclast mediated bone resorption. Nitrogen-containing bisphosphonates, including alendronate, prevent osteoclast function by inhibiting the mevalonate pathway. Clodronate is known to have anti-inflammatory properties while alendronate induces cytokine secretion from lipopolysaccharide- (LPS) induced macrophages. This study investigates whether the cytotoxicity and cytokine production induced by alendronate and LPS could be counteracted by clodronate or products of mevalonate pathway: oxidized low density lipoprotein (ox-LDL), farnesol and geranylgeraniol. Treatment with alendronate increased LPS-induced secretion of IL-1beta, IL-6 and TNF-alpha from RAW 264 macrophages 2.4-, 1.4- and 1.8-fold, respectively. This treatment was cytotoxic for macrophages as indicated by lowered cell viability. Clodronate and ox-LDL both counteracted the cytokine secretion and cytotoxicity of alendronate. Farnesol and geranylgeraniol did neither reverse the cytokine secretion nor reduce the cytotoxicity of alendronate. Clodronate and ox-LDL were able to counteract the effects of alendronate on macrophages in vitro, probably by their known ability to inhibit DNA binding activity of transcription factors, nuclear factor-kappaB (NF-kappaB) and activating protein-1 (AP-1). These findings suggest that inhibition of mevalonate pathway is not the mechanism responsible for the proinflammatory response caused by alendronate, as it is in alendronate-induced apoptosis and prevention of osteoclast function.

Bisphosphonate treatment of osteoporosis

Bisphosphonates represent the agents of choice for most patients with osteoporosis. They are the best studied of all agents for the prevention of bone loss and reduction in fractures. They increase BMD, primarily at the lumbar spine, but also at the proximal femur. In patients who have established osteoporosis, bisphosphonates reduce the risk of vertebral fractures, and are the only agents in prospective trials to reduce the risk of hip fractures and other nonvertebral fractures. Bisphosphonates reduce the risk of fracture quickly. The risk of radiographic vertebral deformities is reduced after 1 year of treatment with risedronate [68]. The risk of clinical vertebral fractures is reduced after 1 year of treatment with alendronate [69] and just 6 months' treatment with risedronate [157]. The antifracture effect of risedronate has been shown to continue through 5 years of treatment [158]. Alendronate and risedronate are approved by the FDA for prevention of bone loss in recently menopausal women, for treatment of postmenopausal osteoporosis, and for prevention (risedronate) and treatment (alendronate and risedronate) of glucocorticoid-induced osteoporosis. Alendronate is also approved for treatment of osteoporosis in men. Other bisphosphonates (etidronate for oral use, pamidronate and zoledronate for intravenous infusion) are also available and can be used off label for patients who cannot tolerate approved agents. Although bisphosphonates combined with estrogen or raloxifene produce greater gains in bone mass compared with single-agent treatment, the use of two antiresorptive agents in combination cannot be recommended because the benefit on fracture risk has not been demonstrated and because of increased cost and side effects.

Cellular uptake and metabolism of clodronate and its derivatives in Caco-2 cells: a possible correlation with bisphosphonate-induced gastrointestinal side-effects

PURPOSE

To investigate possible reasons for the low frequency of GI side-effects of clodronate, even though clodronate is known to be metabolised into a cytotoxic nucleotide analogue (AppCCl(2)p) by many cell types. The effects of some lipophilic prodrugs of clodronate were also studied.

METHODS

The effects of clodronate and its lipophilic derivatives on the proliferation and viability of Caco-2 cells were examined using an MTT assay. The intracellular uptake of 14C-clodronate and the accumulation of a clodronate metabolite (AppCCl(2)p) in Caco-2 cells were evaluated using ion-pairing HPLC-ESI-MS.

RESULTS

Clodronate had little effect on growth of proliferating, or the viability of confluent, Caco-2 cells. The uptake of clodronate by Caco-2 cells was only about 0.04% of total clodronate. The potentially cytotoxic clodronate metabolite, AppCCl(2)p, was detected in Caco-2 cell extracts after 3 h of exposure. Dianhydride- and triPOM-clodronate were metabolised to AppCCl(2)p more efficiently and also affected the viability of Caco-2 cells more than clodronate.

CONCLUSIONS

Clodronate appears to be metabolised into a cytotoxic ATP-analogue (AppCCl(2)p) by any cell type capable of internalising the drug. However, the cytotoxicity depends on the degree of uptake of clodronate. Due to the very low initial uptake of clodronate by epithelial Caco-2 cells, they do not accumulate sufficient intracellular concentrations of AppCCl(2)p to affect cell function. This explains the low frequency of gastrointestinal side-effects caused by oral clodronate therapy.

The potential role of bisphosphonates in prostate cancer

Skeletal morbidity secondary to metastases and osteoporosis is common in patients with advanced prostate cancer. Despite the typically sclerotic nature of prostate cancer metastases, osteoclast mediated osteolysis may play a significant role. This review addresses the newly recognised antitumour effects of bisphosphonates in addition to their role in inhibiting osteoclast mediated bone resorption. Both preclinical and clinical evidence of a role for bisphosphonates in the treatment and prevention of bone metastases secondary to prostate cancer is assessed.

Antagonistic effects of different classes of bisphosphonates in osteoclasts and macrophages in vitro

Nitrogen-containing bisphosphonates, such as alendronate and ibandronate, inhibit bone resorption by preventing protein prenylation in osteoclasts, whereas non-nitrogen-containing bisphosphonates, such as clodronate, are metabolized to nonhydrolyzable analogs of ATP, resulting in osteoclast apoptosis. Because these two classes of bisphosphonates have different molecular mechanisms of action, we examined in vitro whether combined treatment with clodronate and alendronate would alter antiresorptive effectiveness. Although, in cultures of rabbit osteoclasts, the antiresorptive effect of 10 microM alendronate was increased by the addition of clodronate, the effect of higher concentrations of alendronate was not altered by addition of clodronate. Furthermore, the inhibition of protein prenylation in osteoclasts caused by higher alendronate concentrations was partially prevented by cotreatment with clodronate. As in osteoclasts, the inhibition of protein prenylation in J774 cells caused by alendronate or ibandronate treatment was dose-dependently prevented by cotreatment with clodronate. Furthermore, alendronate-induced J774 apoptosis was significantly inhibited in the presence of clodronate. The presence of clodronate also decreased the short-term cellular uptake of [14C]ibandronate. These observations suggest that combined treatment with clodronate could enhance the antiresorptive effect of a low concentration of nitrogen-containing bisphosphonate, but clodronate can also antagonize some of the molecular actions and effects of higher concentrations of nitrogen-containing bisphosphonates. The exact molecular basis for the antagonistic effects between bisphosphonates remain to be determined, but could involve competition for cellular uptake by a membrane-bound transport protein.

Bisphosphonate mechanism of action

The nitrogen-containing bisphosphonates (N-BPs), alendronate and risedronate, are the only pharmacologic agents shown to prevent spine and nonvertebral fractures associated with postmenopausal and glucocorticoid-induced osteoporosis. At the tissue level, this is achieved through osteoclast inhibition, which leads to reduced bone turnover, increased bone mass, and improved mineralization. The molecular targets of bisphosphonates (BPs) have recently been identified. This review will discuss the mechanism of action of BPs, focusing on alendronate and risedronate, which are the two agents most widely studied. They act on the cholesterol biosynthesis pathway enzyme, farnesyl diphosphate synthase. By inhibiting this enzyme in the osteoclast, they interfere with geranylgeranylation (attachment of the lipid to regulatory proteins), which causes osteoclast inactivation. This mechanism is responsible for N-BP suppression of osteoclastic bone resorption and reduction of bone turnover, which leads to fracture prevention.

Changes in serum HDL and LDL cholesterol in patients with Paget's bone disease treated with pamidronate

Amino bisphosphonates represent one of the most important advances in the management of Paget's and other metabolic bone diseases. Although their mechanism of action has not yet been completely clarified, they seem to inhibit the mevalonate pathway and so they could interfere with cholesterol synthesis. The present study aimed to evaluate cholesterol and lipoprotein serum levels in patients with Paget's bone disease treated with intravenous pamidronate. The study included 20 consecutive patients (mean age, 67.6 +/- 11.0 years) with Paget's bone disease for at least 1 year, who needed intravenous amino bisphosphonate treatment; 12 patients with inactive Paget's bone disease served as controls. The patients with active Paget's bone disease underwent three cycles (every 3 months) of treatment with 60 mg of intravenous pamidronate. Controls were given a saline infusion following the same administration schedule. In all subjects total alkaline phosphatase (total ALP), bone alkaline phosphatase (bone ALP), total cholesterol (TC), tryglycerides (TG), and high- and low-density lipoprotein cholesterol (HDL-C and LDL-C, respectively) were measured before infusions (pamidronate or saline) at baseline and at 3-month intervals up to 9 months. In the control group no significant changes were observed through the study period for any of the biochemical parameters. In the pamidronate-treated patients, both bone ALP and total ALP significantly fell at the end of the study. In patients with active treatment, at the end of the study period HDL-C significantly (P < 0.05) increased by 10.3%, whereas LDL-C significantly (P < 0.05) decreased by 5.5%. In these patients TC showed a negative trend without reaching statistical significance, whereas the HDL-C/LDL-C ratio rose 16.2% above the basal value and TC/HDL-C decreased by 12.5%. In conclusion, pamidronate given intravenously seems to be able to induce a prolonged shifting in circulating cholesterol from the LDL-C to the HDL-C from associated with a weak decrease in total cholesterol, thus producing a possible improvement in the atherosclerotic risk index.

Drugs in development: bisphosphonates and metalloproteinase inhibitors

The destruction of bone and cartilage is characteristic of the progression of musculoskeletal diseases. The present review discusses the developments made with two different classes of drugs, the bisphosphonates and matrix metalloproteinase inhibitors. Bisphosphonates have proven to be an effective and safe treatment for the prevention of bone loss, especially in osteoporotic disease, and may have a role in the treatment of arthritic diseases. The development of matrix metalloproteinase inhibitors and their role as potential therapies are also discussed, especially in the light of the disappointing human trials data so far published.

Future directions in the treatment and prevention of bone metastases

Preclinical studies are providing a growing body of evidence that bisphosphonates, particularly nitrogen-containing bisphosphonates, have antitumor activity. Bisphosphonates induce tumor cell apoptosis and reduce skeletal tumor burden in tumor xenograft models. Clinical studies with daily oral clodronate suggest that bisphosphonates can prevent bone metastases when used in the adjuvant setting, but the effect on overall survival is less certain. The more potent nitrogen-containing bisphosphonates, i.e., pamidronate and zoledronic acid, have demonstrated antitumor activity at approximately 10- to 100-fold lower concentrations than clodronate in vitro. A number of important unanswered questions must be addressed regarding the optimal use of bisphosphonates for prevention of bone metastases. For example, when should treatment begin, how long must treatment be continued, and what are the optimal dose and schedule to achieve clinically meaningful antitumor effects? Adjuvant studies of zoledronic acid in patients with breast and prostate cancer are under development, and the results are eagerly anticipated.

Mechanisms of bisphosphonate effects on osteoclasts, tumor cell growth, and metastasis

Bisphosphonates are potent inhibitors of osteoclast-mediated bone resorption that also exhibit antitumor activity. There is now extensive in vitro evidence that bisphosphonates inhibit proliferation and induce apoptosis of tumor cell lines. In addition, they appear to inhibit tumor cell adhesion and invasion of the extracellular matrix. These data are supported by a growing body of evidence from animal models demonstrating that bisphosphonates can reduce skeletal tumor burden. This may reflect direct antitumor effects or indirect effects via osteoclast inhibition and alteration of the bone microenvironment. Research has begun to shed light on the complex mechanisms by which bisphosphonates inhibit bone resorption and interfere with the formation and growth of bone lesions. Nitrogen-containing bisphosphonates inhibit protein prenylation and thereby short-circuit intracellular signaling via small guanine triphosphatases, such as Ras, which require membrane localization. As a result of these biochemical effects on the mevalonate pathway, bisphosphonates appear to modulate the expression of bcl-2 leading to caspase-dependent apoptosis, inhibit matrix metalloproteinases, downregulate alphavbeta3 and alphavbeta5 integrins, and increase expression of osteoprotegerin, thereby antagonizing osteoclastogenesis. Further preclinical studies are ongoing to fully elucidate these biochemical mechanisms, and well-designed clinical trials are necessary to investigate whether the antitumor potential of bisphosphonates can be realized in the clinical setting.

[Pharmacological and clinical properties of alendronate sodium hydrate]

Alendronate (alendronate sodium hydrate; Bonalon Tablet, 5 mg) is a nitrogen-containing bisphosphonate, which combines with the bone surface and reduces osteoclast-mediated bone resorption. It is a third-generation bisphosphonate compound, specifically distributed on the surface of bone resorption and taken into osteoclasts. Under the closed circumstances which is formed with osteoclast and the bone surface, alendronate becomes detached from the bone surface and taken into osteoclast since acid released from osteoclast leads to pH decrease (acidified). The uptaken alendronate blocks the pathway of mevalonic acid synthesis, which is cholesteric synthesis, inhibits the prenylation of GTP binding protein, and decreases the osteoclast's function by influencing the cytoskeleton. This restraint of alendronate in bone resorption against osteoclasts is reversible, showing no cytotoxicity at more than hundredfold concentration level at which action occurs. Alendronate is an agent for the treatment of osteoporosis that has established safety with regards to bone quality since it neither inhibits bone calcification nor influences fracture healing in chronic administration. The most serious morbidity in osteoporosis is developing fractures. The efficacy of alendronate on restraining fracture, as well as on increase in BMD, is evidenced in Japan. Recently, in addition to senile or postmenopausal osteoporosis, drug-induced osteoporosis, such as steroid-induced osteoporosis, has attracted attention. In this regard, alendronate has been found to be an effective agent for the treatment of osteoporosis overseas, being approved in over 90 countries and used by more than 4.5 million patients. This review will give an outline of alendronate, the preparation to have introduced a concept of Evidence Based Medicine earlier, from pharmacodynamic action to clinical efficacy.

Promotion of xenogeneic hematopoietic chimerism in rodents by mononuclear phagocyte depletion

The successful establishment of tolerance toward pig tissues in primates through hematopoietic progenitor cell engraftment is restricted by the rapid disappearance of these cells in the recipient following infusion. We developed and tested the hypothesis that phagocytes of the reticuloendothelial system are responsible for the rapid clearance of infused pig hematopoietic cells using a mouse model. Mice received non-myeloablative conditioning and, on various days, were injected with medronate-encapsulated liposomes (M-L) or control blank liposomes, followed by the intravenous infusion of miniature swine hematopoietic cells. M-L were well-tolerated in mice (n=100) at levels that deplete mononuclear phagocytes. Depletion of mononuclear phagocytes in normal Balb/c mice as well as in severe combined immune deficient mice increased the accumulation of pig hematopoietic cells in the bone marrow (BM) by 10-fold when measured 24 h after the infusion of the cells. Colony-forming unit analysis showed an increased accumulation of pig hematopoietic progenitors in the BM of mice that were infused with medronate-liposomes. We conclude that depletion of mononuclear phagocytes by M-L has the potential to lower the barrier to the establishment of mixed chimerism and tolerance induction in xenotransplantation.

Clodronate: mechanisms of action on bone remodelling and clinical use in osteometabolic disorders

Clodronate (CI2MBP) is a non-aminated bisphosphonate that inhibits bone resorption. Studies on the mechanisms of action of this molecule on bone metabolism have been limited and only recently has information on the molecular machinery that underlies its effects on the bone remodelling process become available. Pharmacological and clinical studies have demonstrated the effectiveness of clodronate in the treatment of postmenopausal osteoporosis and in all conditions of excessive bone resorption, such as Paget's disease, hypercalcaemia of malignancy and osteolytic metastases. Clodronate is the only bisphosphonate currently available on the market for both oral and parenteral administration. Treatment with clodronate via intramuscular administration of doses of 100 mg/week has shown significant effects on bone mineral density after 6 months in patients with postmenopausal osteoporosis and these effects are maintained 3 years after the start of the treatment. In a recent controlled clinical study, a significant increase in bone mineral density was observed, associated with a 46% reduction in the incidence of vertebral fractures. However, most relevant studies have been small, unblinded and short-term and have not systematically examined the effects of the dose and dosing intervals on bone mineral density and markers of bone turnover. Ongoing controlled clinical studies may offer answers regarding potential use of clodronate in osteoporosis and also about dosage of intermittent administration. This review summarises the accumulated knowledge in the mechanisms of action of clodronate on bone remodelling. Moreover, the clinical trials on the use of clodronate in metabolic bone diseases are described in-depth. We believe that this work will help to better focus on the need for more research on a compound which has potential applications in prevention and therapy of osteoporosis. However, studies that demonstrate an effect on the rate of fractures are needed before any recommendation can be made.

The bisphosphonate pamidronate induces apoptosis in human melanoma cells in vitro

Pamidronate belongs to the class of nitrogen-containing bisphosphonates that are potent inhibitors of bone resorption frequently used for the treatment of osteoporosis and cancer-induced osteolysis. The inhibition of osteoclasts' growth has been suggested as the main mechanism of the inhibitory effect of pamidronate on bone metastases. Recent findings indicated that bisphosphonates also have a direct apoptotic effect on other types of tumour cells. Nitrogen-containing bisphosphonates were shown to inhibit farnesyl diphosphate synthase, thus blocking the synthesis of higher isoprenoids. By this mechanism they inactivate monomeric G-proteins of the Ras and Rho families for which prenylation is a functional requirement. On the background of the known key role of G-proteins in tumorigenesis, we investigated a possible beneficial use of pamidronate in the treatment of malignant melanoma. Our results indicate that pamidronate inhibits the cell growth and induces apoptosis in human melanoma cells in vitro. Susceptibility to pamidronate did not correlate to CD95 ligand sensitivity or p53 mutational status. Furthermore it is interesting to note that overexpression of bcl-2 did not abolish pamidronate-induced apoptosis. These data suggests that pamidronate has a direct anti-tumour effect on malignant melanoma cells, independently of the Bax/Bcl-2 level.

Bisphosphonates and periodontics: potential applications for regulation of bone mass in the periodontium and other therapeutic/diagnostic uses

Bisphosphonates are widely utilized in the management of systemic metabolic bone disease due to their ability to inhibit bone resorption. Recently, new uses of this unique class of pharmacological agents have been suggested. Given their known affinity to bone and their ability to increase osteoblastic differentiation and inhibit osteoclast recruitment and activity, there exists a possible use for bisphosphonates in the diagnosis and management of periodontal diseases. These bone-specific properties could also provide an interesting management strategy to stimulate osteogenesis in conjunction with regenerative materials around osseous defects and may also result in the promotion of bone formation around endosseous implants. The objective of this article is to review the scientific evidence regarding the potential applications of bisphosphonate drugs in the therapeutic management of periodontal diseases. Moreover, the mechanism of action and the pharmacology of these drugs will be reviewed. Finally, the potential role of bisphosphonates regarding their potential to accelerate bone formation, in addition to their usual uses for inhibition of bone resorption, is discussed.

Dissociation of angiogenesis and osteoclastogenesis during endochondral bone formation in neonatal mice

Invasion of the mineralized matrix by endothelial cells and osteoclasts is a key event in endochondral bone formation. To examine the putative role of osteoclast activity in the angiogenic process, we used two in vivo models of suppressed bone resorption: mice treated with the bisphosphonate clodronate and in osteoclast-deficient, osteopetrotic mice. Angiogenesis was assessed in caudal vertebrae of these neonatal mice. This model enables us to study the interaction between osteoclasts and endothelial cells during endochondral bone formation. In control conditions, sinusoid-like structures were detected in the vicinity of tartrate resistance acid phosphatase positive (TRAcP+) osteoclasts. Treatment with clodronate completely abolished osteoclastic bone resorption, whereas angiogenesis remained unaffected. In line with these observations, in the osteopetrotic mouse mutants c-fos knockout mice and op/op mice, capillaries invaded the calcified cartilage in the absence of osteoclasts. In conclusion, our data strongly suggest that during endochondral bone formation, vascular invasion can occur in the absence of osteo(chondro)clastic resorption. In addition, bisphosphonates show no apparent effect on angiogenesis in this in vivo model. These findings may have important clinical implications in the management of skeletal disorders such as metastatic bone disease, in which both osteoclastic bone resorption and angiogenesis contribute to tumor growth. On the other hand, our results confirm that bisphosphonates can be used safely in the treatment of disorders that affect the growing skeleton, such as in juvenile osteoporosis.

Bisphosphonates influence the proliferation and the maturation of normal human osteoblasts

The key pharmacological action for the clinical use of bisphosphonates lies in the inhibition of osteoclast-mediated bone resorption. Osteoblasts could be other target cells for bisphosphonates. We studied the effects of bisphosphonates on the proliferation and the differentiation of normal human bone trabecular osteoblastic cells (hOB). We tested 4 different compounds: clodronate, pamidronate and 2 newer compounds: ibandronate, a nitrogen-containing bisphosphonate and zoledronate, which is a heterocyclic imidazole compound. Ibandronate and zoledronate stimulated hOB cell proliferation by up to 30% (p<0.05) after 72 h for concentrations ranging from 10(-8) M to 10(-5) M. Clodronate transiently enhanced hOB cell survival after only 24 h (+60%, p<0.001) whereas pamidronate had no effect. Longer time course studies, in presence of fetal calf serum, revealed that cell growth was finally reduced by all 4 bisphosphonates (40% after 7 days). Type I collagen synthesis was transiently increased by all 4 bisphosphonates after only 48 h incubation (+17% to +67%, p<0.05). Clodronate increased ALP activity by up to 1.7-fold after 4 days of culture (p<0.05) whereas ibandronate or zoledronate exhibited lesser stimulatory effects (+17 to +30%), and pamidronate had no significant effect. In conclusion, we found that different bisphosphonates, currently used or tested in various clinical conditions, transiently stimulated the growth of preosteoblastic cells and thereafter increased their differentiation according to sequential events (type I collagen synthesis first, then ALP activity to a lesser extent). Our data suggest that the beneficial effects of bisphosphonate treatment on bone mass and integrity could be partly mediated through a direct action on osteoblasts.

Strategies for management of prostate cancer-related bone pain

Prostate cancer is one of the most common malignancies and a leading cause of cancer-related death in men worldwide. In the majority of cases, prostate cancer metastases to the skeleton, in which case cancer-related bone pain becomes a major cause of morbidity. Androgen ablation is the treatment of choice for securing regression of skeletal metastases in the majority of cases. Intermittent androgen ablation is an attractive alternative, aimed at minimising adverse effects of hormone deprivation but also potentially delaying hormone-refractoriness. The development of hormone-refractoriness is heralded by a significant increase in morbidity largely because of escalating bone pain caused by the progression of the metastatic process. Skillful use of analgesics is initially successful but eventually fails to control symptoms. Localised metastases are best treated with local radiotherapy that is rapidly effective. Over the last few years, it has become clear that therapeutic modalities using bone-seeking radionuclides or bisphosphonates have been effective in the palliation of prostate cancer-related bone pain, although not affecting survival. The main limiting factor with the use of radionuclides is bone marrow suppression, also a feature of the very late stages of prostate cancer. Bisphosphonates do not carry this disadvantage. Results of large double-blind, placebo-controlled studies should be awaited, however, before advocating the widespread use of these agents in the management of patients with prostate cancer and skeletal metastases.

Further insight into mechanism of action of clodronate: inhibition of mitochondrial ADP/ATP translocase by a nonhydrolyzable, adenine-containing metabolite

Bisphosphonates are currently the most important class of antiresorptive drugs used for the treatment of diseases with excess bone resorption. Recent studies have shown that bisphosphonates can be divided into two groups with distinct molecular mechanisms of action depending on the nature of the R(2) side chain. Alendronate, like other nitrogen-containing bisphosphonates, inhibits bone resorption and causes apoptosis of osteoclasts and other cells in vitro by preventing post-translational modification of GTP-binding proteins with isoprenoid lipids. Clodronate, a bisphosphonate that lacks a nitrogen, does not inhibit protein isoprenylation but can be metabolized intracellularly to a beta-gamma-methylene (AppCp-type) analog of ATP, which is cytotoxic to macrophages in vitro. The detailed molecular basis for the cytotoxic effects of adenosine-5'-[beta,gamma-dichloromethylene]triphosphate (AppCCl(2)p) has not been determined yet. We addressed this question by studying the effects of alendronate, clodronate, and the clodronate metabolite AppCCl(2)p on isolated mitochondria, mitochondrial fractions, and mitochondrial membrane potential in isolated human osteoclasts. We found that AppCCl(2)p inhibits mitochondrial oxygen consumption by a mechanism that involves competitive inhibition of the ADP/ATP translocase. Alendronate or the native form of clodronate did not have any immediate effect on mitochondria. However, longer treatment with liposome-encapsulated clodronate caused collapse of the mitochondrial membrane potential, although prominent apoptosis was a late event. Hence, inhibition of the ADP/ATP translocase by the metabolite AppCCl(2)p is a likely route by which clodronate causes osteoclast apoptosis and inhibits bone resorption.

Transduction of cell survival signals by connexin-43 hemichannels

Bisphosphonates, drugs used widely in the treatment of bone diseases, prevent osteoblast and osteocyte apoptosis by a mechanism involving extracellular signal-regulated kinase (ERK) activation. We report herein that hexameric connexin (Cx)-43 hemichannels, but not gap junctions, are the essential transducers of the ERK-activating/anti-apoptotic effects of bisphosphonates. Transfection of Cx-43, but not other Cxs, into Cx-43 naive cells confers de novo responsiveness to the drugs. The signal-transducing property of Cx-43 requires the pore forming as well as the C-terminal domains of the protein, the activation of both Src and ERK kinases, and the SH2 and SH3 domains of Src. This evidence adds Cx-43 to the list of transmembrane proteins capable of transducing survival signals in response to extracellular cues and raises the possibility that it may serve in this capacity for endogenously produced molecules or even other drugs.

Elimination of porcine hemopoietic cells by macrophages in mice

The difficulty in achieving donor hemopoietic engraftment across highly disparate xenogeneic species barriers poses a major obstacle to exploring xenograft tolerance induction by mixed chimerism. In this study, we observed that macrophages mediate strong rejection of porcine hemopoietic cells in mice. Depletion of macrophages with medronate-encapsulated liposomes (M-liposomes) markedly improved porcine chimerism, and early chimerism in particular, in sublethally irradiated immunodeficient and lethally irradiated immunocompetent mice. Although porcine chimerism in the peripheral blood and spleen of M-liposome-treated mice rapidly declined after macrophages had recovered and became indistinguishable from controls by wk 5 post-transplant, the levels of chimerism in the marrow of these mice remained higher than those in control recipients at 8 wks after transplant. These results suggest that macrophages that developed in the presence of porcine chimerism were not adapted to the porcine donor and that marrow-resident macrophages did not phagocytose porcine cells. Moreover, M-liposome treatment had no effect on the survival of porcine PBMC injected into the recipient peritoneal cavity, but was essential for the migration and relocation of these cells into other tissues/organs, such as spleen, bone marrow, and peripheral blood. Together, our results suggest that murine reticuloendothelial macrophages, but not those in the bone marrow and peritoneal cavity, play a significant role in the clearance of porcine hemopoietic cells in vivo. Because injection of M-liposomes i.v. mainly depletes splenic macrophages and liver Kupffer cells, the spleen and/or liver are likely the primary sites of porcine cell clearance in vivo.

Development of bisphosphonates

Bisphosphonates are synthetic compounds characterized by a P[bond]C[bond]P group, and are thus analogs of inorganic pyrophosphate. They are used in medicine mainly to inhibit bone resorption in diseases like osteoporosis, Paget's disease and tumor bone disease. They have been used for over a century in industry, and only in 1968 was it shown that bisphosphonates have biological effects. These effects consist mainly of an inhibition of bone resorption and, when given in large amounts, an inhibition of ectopic and normal calcification. While the latter effect is the consequence of a physical-chemical inhibition of calcium phosphate crystal formation, the former is due to a cellular effect involving both apoptosis of the osteoclasts and a destruction of the osteoclastic cytoskeleton, inducing a decrease in osteoclast activity. The biochemical basis of these effects for the nitrogen-containing compounds is an inhibition of the mevalonate pathway caused by the inhibition of farnesylpyrophosphate synthase, which leads to a decrease of the formation of isoprenoid lipids such as farnesylpyrophosphate and geranylgeranylpyrophosphate. The other bisphosphonates are incorporated into the phosphate chain of ATP-containing compounds so that they become non-hydrolyzable. The new P[bond]C[bond]P-containing ATP analogs inhibit cell function and may lead to apoptosis and death of osteoclasts.