Nitrogen-containing bisphosphonates inhibit isopentenyl pyrophosphate isomerase/farnesyl pyrophosphate synthase activity with relative potencies corresponding to their antiresorptive potencies in vitro and in vivo

The farnesyl transferase inhibitor R115777 (Zarnestra) synergistically enhances growth inhibition and apoptosis induced on epidermoid cancer cells by Zoledronic acid (Zometa) and Pamidronate

Pamidronate (PAM) and zoledronic acid (ZOL) are aminobisphosphonates (BPs) able to affect the isoprenylation of intracellular small G proteins. We have investigated the antitumor activity of BPs and R115777 farnesyl transferase inhibitor (FTI) against epidermoid cancer cells. In human epidermoid head and neck KB and lung H1355 cancer cells, 48 h exposure to PAM and ZOL induced growth inhibition (IC(50) 25 and 10 microM, respectively) and apoptosis and abolished the proliferative and antiapoptotic stimuli induced by epidermal growth factor (EGF). In these experimental conditions, ZOL induced apoptosis through the activation of caspase 3 and a clear fragmentation of PARP was also demonstrated. A strong decrease of basal ras activity and an antagonism on its stimulation by EGF was recorded in the tumor cells exposed to BPs. These effects were paralleled by impaired activation of the survival enzymes extracellular signal regulated kinase 1 and 2 (Erk-1/2) and Akt that were not restored by EGF. Conversely, farnesol induced a recovery of ras activity and antagonized the proapoptotic effects induced by BPs. The combined treatment with BPs and R115777 resulted in a strong synergism both in growth inhibition and apoptosis in KB and H1355 cells. The synergistic activity between the drugs allowed BPs to produce tumor cell growth inhibition and apoptosis at in vivo achievable concentrations (0.1 micromolar for both drugs). Moreover, the combination was highly effective in the inhibition of ras, Erk and Akt activity, while farnesol again antagonized these effects. In conclusion, the combination of BPs and FTI leads to enhanced antitumor activity at clinically achievable drug concentrations that resides in the inhibition of farnesylation-dependent survival pathways and warrants further studies for clinical translation.

Nitrogen-containing bisphosphonates inhibit cell cycle progression in human melanoma cells

Cutaneous melanoma is one of the highly malignant human tumours, due to its tendency to generate early metastases and its resistance to classical chemotherapy. We recently demonstrated that pamidronate, a nitrogen-containing bisphosphonate, has an antiproliferative and proapoptotic effect on different melanoma cell lines. In the present study, we compared the in vitro effects of three different bisphosphonates on human melanoma cell lines and we demonstrated that the two nitrogen-containing bisphosphonates pamidronate and zoledronate inhibited the proliferation of melanoma cells and induced apoptosis in a dose- and time-dependent manner. Moreover, cell cycle progression was altered, the two compounds causing accumulation of the cells in the S phase of the cycle. In contrast, the nonaminobisphosphonate clodronate had no effect on melanoma cells. These findings suggest a direct antitumoural effect of bisphosphonates on melanoma cells in vitro and further support the hypothesis of different intracellular mechanisms of action for nitrogen-containing and nonaminobisphosphonates. Our data indicate that nitrogen-containing bisphosphonates may be a useful novel therapeutic class for treatment and/or prevention of melanoma metastases.

Selective in vitro effects of the farnesyl pyrophosphate synthase inhibitor risedronate on Trypanosoma cruzi

We present the results of the first detailed study of the molecular and cellular basis of the antiproliferative effects of the bisphosphonate risedronate (Ris) on Trypanosoma cruzi, the causative agent of Chagas' disease. Ris and related compounds, which block poly-isoprenoid biosynthesis at the level of farnesyl pyrophosphate synthase, are currently used for the treatment of bone resorption disorders, but also display selective activity against trypanosomatid and apicomplexan parasites. Ris induced a dose-dependent effect on growth of the extracellular epimastigote form of T. cruzi; complete growth arrest and cell lysis ensued at 150 microM. Growth inhibition was associated with depletion of the parasite's endogenous sterols, but complete growth arrest and loss of cell viability took place before full depletion of these compounds, suggesting that disappearance of other essential poly-isoprenoids is involved in its anti-parasitic action. Ris had a variety of effects on cellular ultrastructure, including mitochondrial swelling, disorganisation of other organelles, such as reservosomes and the kinetoplast, together with the appearance of autophagic vesicles and progressive vacuolization of the cytoplasm. Ris had selective antiproliferative effects against the clinically relevant amastigote form of T. cruzi, and at 100 microM, was able to prevent completely the development of T. cruzi infection of murine muscle heart or Vero cells, and to cure cultures which were already infected. Ris induced drastic ultrastructural alterations in the intracellular parasites and blocked amastigote to trypomastigote differentiation, with no biochemical or ultrastructural effects on the host cells, which fully recovered their normal structure and activity after treatment. Ris is, therefore, a promising lead compound for the development of new drugs against T. cruzi.

Heteromeric geranyl diphosphate synthase from mint: construction of a functional fusion protein and inhibition by bisphosphonate substrate analogs

Geranyl diphosphate synthase catalyzes the condensation of dimethylallyl diphosphate (C(5)) with isopentenyl diphosphate (C(5)) to produce geranyl diphosphate (C(10)), the essential precursor of monoterpenes. The enzyme from peppermint and spearmint (Menthaxpiperita and Mentha spicata, respectively) functions as a heterodimer or heterotetramer consisting of a 40kDa subunit and 33kDa subunit. The DNAs encoding each subunit were joined with different sized linkers and in both possible orders, and expressed in Escherichia coli to yield the corresponding fused protein. The properties of the recombinant fused version, in which the small subunit was followed by the large subunit with a 10 amino acid linker, resembled those of the native heteromeric enzyme in kinetics, product chain-length specificity, and architecture, and this form thus provided a suitable single gene transcript for biotechnological purposes. Bisphosphonate substrate analogs of the type that inhibit farnesyl diphosphate synthase (C(15)) and geranylgeranyl diphosphate synthase (C(20)) also inhibited the fused geranyl diphosphate synthase, apparently by interacting at both the allylic and homoallylic co-substrate binding sites. The results of inhibition studies, along with the previously established role of the small subunit and related mutagenesis experiments, suggest that geranyl diphosphate synthase employs a different mechanism for chain-length determination than do other short-chain prenyltransferases.

Structural basis for bisphosphonate-mediated inhibition of isoprenoid biosynthesis

Farnesyl pyrophosphate synthetase (FPPS) synthesizes farnesyl pyrophosphate through successive condensations of isopentyl pyrophosphate with dimethylallyl pyrophosphate and geranyl pyrophosphate. Nitrogen-containing bisphosphonate drugs used to treat osteoclast-mediated bone resorption and tumor-induced hypercalcemia are potent inhibitors of the enzyme. Here we present crystal structures of substrate and bisphosphonate complexes of FPPS. The structures reveal how enzyme conformational changes organize conserved active site residues to exploit metal-induced ionization and substrate positioning for catalysis. The structures further demonstrate how nitrogen-containing bisphosphonates mimic a carbocation intermediate to inhibit the enzyme. Together, these FPPS complexes provide a structural template for the design of novel inhibitors that may prove useful for the treatment of osteoporosis and other clinical indications including 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.

Zoledronate sensitizes endothelial cells to tumor necrosis factor-induced programmed cell death: evidence for the suppression of sustained activation of focal adhesion kinase and protein kinase B/Akt

Bisphosphonates are potent inhibitors of osteoclast function widely used to treat conditions of excessive bone resorption, including tumor bone metastases. Recent evidence indicates that bisphosphonates have direct cytotoxic activity on tumor cells and suppress angiogenesis, but the associated molecular events have not been fully characterized. In this study we investigated the effects of zoledronate, a nitrogen-containing bisphosphonate, and clodronate, a non-nitrogen-containing bisphosphonate, on human umbilical vein endothelial cell (HUVEC) adhesion, migration, and survival, three events essential for angiogenesis. Zoledronate inhibited HUVEC adhesion mediated by integrin alphaVbeta3, but not alpha5beta1, blocked migration and disrupted established focal adhesions and actin stress fibers without modifying cell surface integrin expression level or affinity. Zoledronate treatment slightly decreased HUVEC viability and strongly enhanced tumor necrosis factor (TNF)-induced cell death. HUVEC treated with zoledronate and TNF died without evidence of enhanced annexin-V binding, chromatin condensation, or nuclear fragmentation and caspase dependence. Zoledronate inhibited sustained phosphorylation of focal adhesion kinase (FAK) and in combination with TNF, with and without interferon (IFN) gamma, of protein kinase B (PKB/Akt). Constitutive active PKB/Akt protected HUVEC from death induced by zoledronate and TNF/IFNgamma. Phosphorylation of c-Src and activation of NF-kappaB were not affected by zoledronate. Clodronate had no effect on HUVEC adhesion, migration, and survival nor did it enhanced TNF cytotoxicity. Taken together these data demonstrate that zoledronate sensitizes endothelial cells to TNF-induced, caspase-independent programmed cell death and point to the FAK-PKB/Akt pathway as a novel zoledronate target. These results have potential implications to the clinical use of zoledronate as an anti-angiogenic or anti-cancer agent.

The mevalonate synthesis pathway as a therapeutic target in cancer

Farnesyl transferase inhibitors have emerged as bona fide anticancer agents whereas the development of geranylgeranyl transferase inhibitors has been mitigated by overt systemic toxicities. Evidence suggests that the therapeutic value of farnesyl transferase inhibitors is an indirect result of perturbations in the function of geranylgeranylated Rho proteins. To address this question, we used inhibitors of the mevalonate synthesis pathway to decrease cellular levels of farnesly and geranylgeranly isoprenoids and supplemented our culture systems with exogenous isoprenoids accordingly. Using a murine lung alveolar carcinoma cell line (Line 1), we report a dose-dependent inhibition of tumor cell proliferation, adhesion and invasiveness, in response to alendronate (3-30 micromol/L) and mevastatin (1-10 micromol/L). Supplementation of cultures with geranylgeranyl pyrophosphates (100 micromol/L) was observed to rescue drug-induced phenotypic changes whereas farnesyl pyrophosphate (100 micromol/L) had a minimal effect. Our observations highlight the mevalonate synthesis pathway as a target for anticancer therapies and suggest a greater role for geranylgeranylated proteins in cellular processes germane to cancer.

Intracellular membrane trafficking in bone resorbing osteoclasts

There is ample evidence now that the two major events in bone resorption, namely dissolution of hydroxyapatite and degradation of the organic matrix, are performed by osteoclasts. The resorption cycle involves several specific cellular activities, where intracellular vesicular trafficking plays a crucial role. Although details of these processes started to open up only recently, it is clear that vesicular trafficking is needed in several specific steps of osteoclast functioning. Several plasma membrane domains are formed during the polarization of the resorbing cells. Multinucleated osteoclasts create a tight sealing to the extracellular matrix as a first indicator of their resorption activity. Initial steps of the sealing zone formation are alpha(v)beta(3)-integrin mediated, but the final molecular interaction(s) between the plasma membrane and mineralized bone matrix is still unknown. A large number of acidic intracellular vesicles then fuse with the bone-facing plasma membrane to form a ruffled border membrane, which is the actual resorbing organelle. The formation of a ruffled border is regulated by a small GTP-binding protein, rab7, which indicates the late endosomal character of the ruffled border membrane. Details of specific membrane transport processes in the osteoclasts, e.g., the formation of the sealing zone and transcytosis of bone degradation products from the resorption lacuna to the functional secretory domain remain to be clarified. It is tempting to speculate that specific features of vesicular trafficking may offer several potential new targets for drug therapy of bone diseases.

Farnesyl pyrophosphate synthase is an essential enzyme in Trypanosoma brucei. In vitro RNA interference and in vivo inhibition studies

We report the cloning and sequencing of a gene encoding the farnesyl pyrophosphate synthase (FPPS) of Trypanosoma brucei. The protein (TbFPPS) is an attractive target for drug development because the growth of T. brucei has been shown to be inhibited by analogs of its substrates, the nitrogen containing bisphosphonates currently in use in bone resorption therapy. The protein predicted from the nucleotide sequence of the gene has 367 amino acids and a molecular mass of 42 kDa. Several sequence motifs found in other FPPSs are present in TbFPPS, including an 11-mer peptide insertion present also in the Trypanosoma cruzi FPPS. Heterologous expression of TbFPPS in Escherichia coli produced a functional enzyme that was inhibited by several nitrogen-containing bisphosphonates, such as pamidronate and risedronate. Risedronate was active in vivo against T. brucei infection in mice (giving a 60% survival rate), but pamidronate was not effective. The essential nature of TbFPPS was studied using RNA interference (RNAi) to inhibit the expression of the gene. Expression of TbFPPS double-stranded RNA in procyclic trypomastigotes caused specific degradation of mRNA. After 4 days of RNAi, the parasite growth rate declined and the cells subsequently died. Similar results were obtained with bloodstream form trypomastigotes, except that the RNAi system in this case was leaky and mRNA levels and parasites recovered with time. Molecular modeling and structure-activity investigations of enzyme and in vitro growth inhibition data resulted in similar pharmacophores, further validating TbFPPS as the target for bisphosphonates. These results establish that FPPS is essential for parasite viability and validate this enzyme as a target for drug development.

Bisphosphonates

Bisphosphonates now occupy a prominent position among therapeutic options for the prevention and treatment of various forms of osteoporosis. Their clinical profile of bone-specific efficacy, rapid response, protection from both spine and hip fractures in patients with osteoporosis, and excellent tolerability is all that can be expected of an anti-remodeling drug. Even in the era of anabolic agents, bisphosphonates will continue to be important treatment options. It is not possible to compare or contrast the clinical effectiveness of the various bisphosphonates on the basis of existing data. Despite marked differences in the in vitro potency of drugs, the clinical responses to each of the bisphosphonates discussed above are similar. New bisphosphonates may not be more effective but will provide different tolerability profiles and different routes of administration, thereby increasing the number of patients in whom bisphosphonates can be used. Having these effective agents challenges clinicians to identify the most appropriate patients for bisphosphonate use and to develop strategies to improve acceptance of and adherence to these useful agents.

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.

Nephrotic proteinuria associated with high-dose pamidronate in multiple myeloma

Five patients receiving increased dose or frequency of pamidronate beyond the recommended dose (90 mg/monthly) exhibited nephrotic proteinuria (range 3.96-24 g/24 h). On dose reduction or discontinuation, three of these patients showed decreased proteinuria to normal levels (< 1 g/24 h), and proteinuria decreased to 4.5 g/24 h from a peak of 24 g/24 h in one patient. One patient on haemodialysis (hence not evaluable) had proteinuria of 2 g/24 h and elevated creatinine levels. One other patient continued to show elevated creatinine levels (272.8 micro mol/l). Renal biopsies obtained in two patients revealed focal segmental glomerulosclerosis.

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.

Directions of drug discovery in osteoporosis

Osteoporosis is a condition of increasing importance and prevalence in all parts of the world and particularly in Asia. Recent advances have led to the introduction of effective drugs that decrease bone resorption and stabilize bone mass. However, these drugs have been identified by serendipity rather than rational drug design and are not ideal because of limited bioavailability, mode of administration, or other unwanted effects. There is still a place for even more suitable and effective resorption inhibitors than those currently available. The more compelling need in this field is an acceptable drug that is anabolic for bone, that safely and acceptably increases bone mass and improves the disturbances in bone microarchitecture that characterize established and advanced osteoporosis. Possible approaches to identifying more effective resorption inhibitors and new anabolic agents are discussed.

Synergism of aminobisphosphonates and farnesyl transferase inhibitors on tumor metastasis

Aminobisphosphonates have shown significant antitumor activity in vitro and in vivo with selective pharmacodistribution to bone, and an established role in the treatment of malignant bone disease. Given that the mode of action of aminobisphosphonates involves decreasing the prenylation of the Rho family of proteins, through decreasing the availability of prenyl groups (farnesyl and geranylgeranyl isoprenoids), the authors sought the inhibition of Rho protein prenylation at two points, by using an aminobiphosphonate (alendronate) in conjunction with a prenyl transferase inhibitor (R115777, a specific farnesyl transferase inhibitor with limited effects in geranylgeranyl transferase). The authors show synergistic inhibition of the prenylation dependent membrane association and migratory function of Rho proteins, translating into a suppressive effect on in vitro tumor cell invasiveness and in vivo metastasis. The findings support the use of aminobisphosphonates in conjunction with farnesyl transferase inhibitors in the prevention of metastatic progression and suggest that metastatic progression is a valid end point in assessing the antitumor activity of farnesyl transferase inhibitors.

The effect of alendronate (Fosamax) and implant surface on bone integration and remodeling in a canine model

Patients at high risk for osteoporosis and its associated morbidity, including postmenopausal women, are being pharmacologically managed to stabilize and improve bone mass. Alendronate sodium (Fosamax) is a commonly used antiresorptive agent effective in osteopenic women for reducing bone resorption, increasing bone density, and decreasing fracture incidence. With the increased incidence of alendronate-treated women who are undergoing hip replacement or fracture repair by prosthesis placement, data are needed to predict how alendronate affects host bone integration with uncemented surfaces. The aim of this study was to determine the effect of alendronate on new bone formation and attachment to implant surfaces in a normal and simulated estrogen-deficient, calcium-deficient canine model, using an implantable bone growth chamber. Alendronate did not affect host bone integration to surfaces commonly used in uncemented total joint arthroplasty, but there were significant differences dependent solely on the type of surface.

Effect of statins on bone mineral density and bone histomorphometry in rodents

Statins have been postulated to affect bone metabolism. We investigated the effects of different doses of simvastatin (1, 5, 10, and 20 mg. kg(-1). d(-1)), atorvastatin (2.5 mg. kg(-1). d(-1)), and pravastatin (10 mg. kg(-1). d(-1)) administered orally for 12 weeks to intact female Sprague-Dawley rats and the effect of 20 mg. kg(-1). d(-1) simvastatin in sham-operated and ovariectomized rats on femoral bone mineral density (BMD) and quantitative bone histomorphometry (QBH) and compared them with controls. BMD was decreased by 1 mg. kg(-1). d(-1) simvastatin (P=0.042), atorvastatin (P=0.0002), and pravastatin (P=0.002). The effect on QBH parameters differed with different doses of simvastatin (ANOVA, P=0.00012). QBH parameters of both bone formation and resorption were equivalently and markedly increased by 20 mg. kg(-1). d(-1) simvastatin in 2 separate groups of intact rats and were reflected by a relatively unchanged BMD. At lower doses, 1 mg. kg(-1). d(-1) simvastatin decreased bone formation while increasing bone resorption, as reflected by a marked decrease in BMD. Ovariectomized animals receiving 20 mg. kg(-1). d(-1) simvastatin showed no change in BMD relative to the untreated, ovariectomized controls; their increase in bone formation was smaller than in sham-operated rats receiving simvastatin, and there was no change in bone resorption. Dose-response curves of simvastatin for bone formation and resorption differed. These studies indicate that (1) statins decrease BMD in rodents, (2) high-dose simvastatin increases bone formation and resorption, (3) low-dose simvastatin decreases bone formation and increases bone resorption, (4) the effects of simvastatin on QBH differ at different dosages, (5) the effects of simvastatin seen in intact rats are not observed in ovariectomized rats, and (6) simvastatin is unable to prevent bone loss caused by ovariectomy.

Pamidronate improves the quality of life and induces clinical remission of bone metastases in patients with thyroid cancer

Skeletal metastases from thyroid cancer are poorly responsive to medical or radioiodine treatment. Bone destruction in skeletal metastases results from osteoclast-induced bone resorption. Therefore, a new approach in the therapy of bone metastases consists in using aminobisphosphonates, such as pamidronate, which are potent inhibitors of osteoclastic activity. In the present study, 10 thyroid cancer patients with painful osteolytic bone metastases were administered pamidronate (90 mg, as a 2 hour intravenous infusion) monthly for 12 consecutive cycles. Bone pain, quality of life, performance status, analgesic consumption and disease staging were evaluated before and during the trial. The patients who had been administered pamidronate showed a significant decrease in bone pain (P = 0.0052). Performance status improved nearly significantly (P = 0.051), while the quality of life showed a remarkable amelioration. However, no significant decrease in analgesic consumption was recorded. Partial radiographic response of bone lesions was observed in 2/10 patients. The side effects of pamidronate were mild and transient. In conclusion, monthly infusion of pamidronate is a well-tolerated treatment that induces significant relief from bone pain and improves the quality of life of thyroid cancer patients with symptomatic and osteolytic bone metastases.

Incadronate and etidronate accelerate phosphate-primed mineralization of MC4 cells via ERK1/2-Cbfa1 signaling pathway in a Ras-independent manner: further involvement of mevalonate-pathway blockade for incadronate

Two types of bisphosphonates (BPs), incadronate (INC) and etidronate (ETI) accelerated phosphate (Pi)-primed mineralization of MC4 cells in a subnanomolar dose range. Intracellular signaling pathways involved were examined. 1) The effect of INC but not ETI was partially suppressed by two mevalonate (MVA) pathway metabolites, farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP). 2) The BP-like accelerating effect was produced by statins and also by Toxin B, a Rho GTPases-specific inhibitor. 3) INC induced Cbfa1-nuclear localization within hours; and in an in vivo experiment using ovariectomized mice, its 3 weeks dosing exhibited the same effect in tibial extracts. 4) BPs promoted luciferase expression in murine p1.3-osteocalcin gene 2-luc and p6-osteoblast specific element 2-luc transfected cells, just as MVA, FPP and GGPP did independently and additively to INC. 5) BPs activated extracellular signal-regulated kinase (ERK1/2) in a Ras-independent manner within 5 min, and Pi was found to sensitize MC4 cells to BPs. MVA and its metabolites also activated ERKs but in a Ras-dependent manner and additively to INC. Ras dependency was determined using N17Ras-transfected cells. A MEK (MAP kinase-ERK kinase)-specific inhibitor PD98059 alone partly and with FPP completely blocked INC-induced mineralization. The results suggest that BPs act on Pi-sensitized MC4 cells to accelerate mineralization via nonRas-MEK-ERK1/2-Cbfa1 transactivation pathway and INC additionally acts by inhibiting the MVA pathway.

Catabolic and anabolic signals in bone: therapeutic implications

Bone remodelling accounts for the continuous renewal of the adult skeleton, and its disturbances constitute the pathophysiological basis of most skeletal disorders. Recently identified bone signalling pathways explain the action of known therapeutic agents and provide targets for new developments in the management of bone diseases.

The palliative management of skeletal metastases in prostate cancer: use of bone-seeking radionuclides and bisphosphonates

In prostate cancer, the development of skeletal metastases is associated with a significant increase in morbidity, mainly because of severe bone pain, which eventually becomes refractory to conventional analgesia. Androgen ablation is the treatment of choice, but the majority of patients relapse within 2 to 3 years from initiation of treatment. After failure of hormone therapy, external-beam irradiation therapy is effective in the palliation of pain, but radionuclides represent an attractive and cost-effective alternative. Strontium 89 is currently the most commonly used radionuclide in the palliative management of prostate cancer metastatic to the skeleton. The rationale for the use of bisphosphonates in metastatic prostate cancer is not immediately obvious, given the predominantly osteoblastic nature of the metastatic process. The clinical use of these agents rests on a number of basic and clinical observations that provide ample evidence that, in prostate cancer, the metastatic process is associated with increased bone resorption. Evidence regarding the beneficial effects of bisphosphonates in reducing morbidity from metastatic prostate cancer is reasonably solid, although the choice of optimal bisphosphonate, mode of administration, dose, and duration of treatment must be determined in large, controlled studies before their widespread clinical use can be advocated. Available therapeutic modalities that use either radionuclides or bisphosphonates can effectively and safely be used in the palliative management of metastatic prostate cancer. Neither radionuclides nor bisphosphonates have been shown to prolong survival, but the potential of both agents to beneficially alter the metastatic process in prostate cancer is intriguing.

Effects of alendronate on osteopenic postmenopausal Chinese women

To evaluate the effects of alendronate on postmenopausal Chinese women with osteopenia, we treated 46 subjects daily with either 10 mg alendronate (N = 24) or placebo plus 500 mg calcium supplement (N = 22), and measured their bone mineral density (BMD) at the lumbar spine and hip, and urinary bone resorption markers before, during, and after the 1 year treatment period. The bone markers included N-telopeptide of type I collagen (NTx) and deoxypyridinoline (Dpd); both were corrected by the concentration of creatinine in the same sample (NTx/Cr and Dpd/Cr). Both NTx/Cr and Dpd/Cr decreased significantly by 44% and 28%, respectively (p < 0.05 for both), in 1 month in the active treatment group but did not change in the placebo group. BMD at the spine, femoral neck, trochanter, and Ward's triangle increased significantly by 6 months and showed a further increase through month 12 at the spine in the alendronate-treated group. Relative to the placebo group, BMD changes at various sites in the alendronate-treated group were higher at 12 months by 6%-11%. Thus, our data suggest that 10 mg alendronate daily resulted in significant increases in spine and hip BMD, and decreases of urinary resorption markers in the osteopenic postmenopausal Chinese women studied. The amplitude of responses was higher than in previous reports in the USA and Europe.

Inhibitors of prenylation of Ras and other G-proteins and their application as therapeutics

Anchoring of small G-proteins to cellular membranes via a covalently bound lipophylic prenyl group is essential for the functioning of these proteins. For example, the farnesylation of Ras by the action of the enzyme protein:farnesyl transferase (PFT) is pivotal for its signalling function in cell growth and differentiation. The development of inhibitors of PFT was triggered by the role of mutated Ras in certain types of cancer and by the observation that non-farnesylated Ras is inactive. Besides the screening of existing compounds for PFT inhibition, rational drug design has also led to new inhibitors. Our research is in the field of atherosclerosis and concerns the development of inhibitors of the growth of vascular smooth muscle cells. The latter process gives rise to reocclusion of the coronary artery (restenosis) after balloon angioplasty. We and others have developed several analogues of the two substrates of PFT, i.e. farnesyl pyrophosphate (FPP) and the so-called CAAX peptide consensus sequence, which were tested in vitro for the inhibition of PFT and of other enzymes involved in protein prenylation, such as protein:geranylgeranyl transferase-1 (PGGT-1). The FPP analogue TR006, a strong inhibitor of PFT (IC(50) of 67 nM), blocked the proliferation of cultured human smooth muscle cells and inhibited platelet-derived growth factor- and basic fibroblast growth factor-induced DNA synthesis. Similar but more highly charged compounds failed in this respect, probably because of an impaired uptake in the cells. Less charged derivatives were designed to circumvent this problem. The effect on the GF-induced activation of intermediates in signal transduction pathways was investigated in order to gain insight into the mechanism of action within the cells. TR006 decreased the bFGF activation of extracellular signal-regulated kinase 1 (ERK1), suggesting its involvement in inhibiting Ras activity. Although other analogues inhibited DNA synthesis, they affected neither ERK1 activation nor p38/stress-activated protein kinase 2 or Jun N-terminal kinase 1 activation. Since some of these compounds were also shown to be inhibitors of in vitro PGGT-1 activity, the geranylgeranylation of other G-proteins may be decreased by these compounds. Rho seems to be a good candidate as a target for inhibitors of PGGT-1. This uncertainty as to the mechanism of action within non-transformed as well as transformed cells applies to all prenylation inhibitors, but is not holding back their further development as drugs. Their current and possible future application as therapeutics in cancer, restenosis, angiogenesis, and osteoporosis is briefly discussed.

Involvement of interleukin-1 in the inflammatory actions of aminobisphosphonates in mice

Aminobisphosphonates (aminoBPs) are potent inhibitors of bone resorption. However, they cause undesirable inflammatory reactions, including fever, in humans. Intraperitoneal injection of aminoBPs into mice also induces inflammatory reactions, including a prolonged elevation of the activity of the histamine-forming enzyme, histidine decarboxylase (HDC). Because interleukin-1 (IL-1) is a typical pyrogen and a strong inducer of HDC, we examined whether aminoBPs induce inflammatory reactions in mice deficient in genes for both IL-1alpha and IL-1beta (IL-1-KO mice). In control mice, aminoBPs induced an elevation of HDC activity and other inflammatory reactions (enlargement of the spleen, atrophy of the thymus, exudate in the thorax and increase in granulocytic cells in the peritoneal cavity). These responses were all weak or undetectable in IL-1-KO mice. We have previously shown that lipopolysaccharides (LPSs) from Escherichia coli and Prevotella intermedia (a prevalent gram-negative bacterium both in periodontitis and endodontal infections) are capable of inducing HDC activity in various tissues in mice. In control mice treated with an aminoBP, the LPS-induced elevations of serum IL-1 (alpha and beta) and tissue HDC activity were both markedly augmented. However, such an augmentation of HDC activity was small or undetectable in IL-1-KO mice. These results, taken together with our previous findings (i) suggest that IL-1 is involved in the aminoBP-induced inflammatory reactions and (ii) lead us to think that under some conditions, inflammatory reactions induced by gram-negative bacteria might be augmented in patients treated with an aminoBP. In this study, we also obtained a result suggesting that IL-1-deficiency might be compensated by a second, unidentified, mechanism serving to induce HDC in response to LPS when IL-1 is lacking.

Semi-automatic liquid chromatographic analysis of olpadronate in urine and serum using derivatization with (9-fluorenylmethyl)chloroformate

The semi-automatic bioanalytical assays for olpadronate [(3-dimethylamino-1-hydroxypropylidene)bisphosphonate] involves a protein precipitation with trichloroacetic acid and a double co-precipitation with calcium phosphate for serum samples and a triple calcium co-precipitation for urine samples. These manual procedures are followed by an automated solid-phase extraction on a cation-exchange phase. The procedure is continued either directly, at high olpadronate levels in urine, or after off-line evaporation under nitrogen and reconstitution in water on the same robotic workstation. The continued automatic procedure comprehends derivatization with (9-fluorenylmethyl)chloroformate, ion-pair liquid-liquid extraction and ion-pair HPLC with fluorescence detection at 274/307 nm. The intra- and inter-day precisions for urine and serum samples are typically in the 5-8% range for different olpadronate concentrations [levels near the lower limit of quantification (LLQ) excluded]. The LLQ is 5 ng/ml olpadronate for a 2.5-ml urine sample and 10 ng/ml for a 1-ml serum sample, respectively.

Alendronate is a specific, nanomolar inhibitor of farnesyl diphosphate synthase

Alendronate, a nitrogen-containing bisphosphonate, is a potent inhibitor of bone resorption used for the treatment and prevention of osteoporosis. Recent findings suggest that alendronate and other N-containing bisphosphonates inhibit the isoprenoid biosynthesis pathway and interfere with protein prenylation, as a result of reduced geranylgeranyl diphosphate levels. This study identified farnesyl disphosphate synthase as the mevalonate pathway enzyme inhibited by bisphosphonates. HPLC analysis of products from a liver cytosolic extract narrowed the potential targets for alendronate inhibition (IC(50) = 1700 nM) to isopentenyl diphosphate isomerase and farnesyl diphosphate synthase. Recombinant human farnesyl diphosphate synthase was inhibited by alendronate with an IC(50) of 460 nM (following 15 min preincubation). Alendronate did not inhibit isopentenyl diphosphate isomerase or GGPP synthase, partially purified from liver cytosol. Recombinant farnesyl diphosphate synthase was also inhibited by pamidronate (IC(50) = 500 nM) and risedronate (IC(50) = 3.9 nM), negligibly by etidronate (IC50 = 80 microM), and not at all by clodronate. In osteoclasts, alendronate inhibited the incorporation of [(3)H]mevalonolactone into proteins of 18-25 kDa and into nonsaponifiable lipids, including sterols. These findings (i) identify farnesyl diphosphate synthase as the selective target of alendronate in the mevalonate pathway, (ii) show that this enzyme is inhibited by other N-containing bisphosphonates, such as risendronate, but not by clodronate, supporting a different mechanism of action for different bisphosphonates, and (iii) document in purified osteoclasts alendronate inhibition of prenylation and sterol biosynthesis.

Mechanism of aminobisphosphonate action: characterization of alendronate inhibition of the isoprenoid pathway

Alendronate (ALN), an aminobisphosphonate compound used for the treatment of osteoporosis and other disorders of bone resorption, has been suggested to act by inhibition of the formation of GGPP. In the present study we used an S(10) homogenate fraction of rat liver to show that ALN causes a dose-dependent inhibition of [(3)H]MVA incorporation into sterols and a concomitant increase in incorporation of radiolabel into IPP and DMAPP. We further show that ALN is a potent inhibitor of cytosolic trans-prenyltransferase (FPP synthase). The inhibition is competitive with respect to allylic pyrophosphate substrates, but not IPP, suggesting that ALN acts as an allylic pyrophosphate analog and binds to the free enzyme. The K(i) is in the 0.5 microM range.

Bisphosphonates act directly on the osteoclast to induce caspase cleavage of mst1 kinase during apoptosis. A link between inhibition of the mevalonate pathway and regulation of an apoptosis-promoting kinase

Bisphosphonates (BPs) include potent inhibitors of bone resorption used to treat osteoporosis and other bone diseases. BPs directly or indirectly induce apoptosis in osteoclasts, the bone resorbing cells, and this may play a role in inhibition of bone resorption. Little is known about downstream mediators of apoptosis in osteoclasts, which are difficult to culture. Using purified osteoclasts, we examined the effects of alendronate, risedronate, pamidronate, etidronate, and clodronate on apoptosis and signaling kinases. All BPs induce caspase-dependent formation of pyknotic nuclei and cleavage of Mammalian Sterile 20-like (Mst) kinase 1 to form the active 34-kDa species associated with apoptosis. Withdrawal of serum and of macrophage colony stimulating factor, necessary for survival of purified osteoclasts, or treatment with staurosporine also induce apoptosis and caspase cleavage of Mst1. Consistent with their inhibition of the mevalonate pathway, apoptosis and cleavage of Mst1 kinase induced by alendronate, risedronate, and lovastatin, but not clodronate, are blocked by geranylgeraniol, a precursor of geranylgeranyl diphosphate. Together these findings suggest that BPs act directly on the osteoclast to induce apoptosis and that caspase cleavage of Mst1 kinase is part of the apoptotic pathway. For alendronate and risedronate, these events seem to be downstream of inhibition of geranylgeranylation.

Farnesyl pyrophosphate synthase is the molecular target of nitrogen-containing bisphosphonates

Bisphosphonates (Bps), inhibitors of osteoclastic bone resorption, are used in the treatment of skeletal disorders. Recent evidence indicated that farnesyl pyrophosphate (FPP) synthase and/or isopentenyl pyrophosphate (IPP) isomerase is the intracellular target(s) of bisphosphonate action. To examine which enzyme is specifically affected, we determined the effect of different Bps on incorporation of [(14)C]mevalonate (MVA), [(14)C]IPP, and [(14)C]dimethylallyl pyrophosphate (DMAPP) into polyisoprenyl pyrophosphates in a homogenate of bovine brain. HPLC analysis revealed that the three intermediates were incorporated into FPP and geranylgeranyl pyrophosphate (GGPP). In contrast to clodronate, the nitrogen-containing Bps (NBps), alendronate, risedronate, olpadronate, and ibandronate, completely blocked FPP and GGPP formation and induced in incubations with [(14)C]MVA a 3- to 5-fold increase in incorporation of label into IPP and/or DMAPP. Using a method that could distinguish DMAPP from IPP on basis of their difference in stability in acid, we found that none of the NBps affected the conversion of [(14)C]IPP into DMAPP, catalyzed by IPP isomerase, excluding this enzyme as target of NBp action. On the basis of these and our previous findings, we conclude that none of the enzymes up- or downstream of FPP synthase are affected by NBps, and FPP synthase is, therefore, the exclusive molecular target of NBp action.

Nitrogen-containing bisphosphonates as carbocation transition state analogs for isoprenoid biosynthesis

Nitrogen-containing bisphosphonates are potent bone antiresorptive agents as well as having herbicidal and antiparasitic activity, and are thought to act by inhibiting enzymes of the mevalonate pathway. Using molecular modeling and ab initio quantum chemical calculations, we show that bisphosphonates can act as aza-isoprenoid transition state analogs, thereby inhibiting isoprenoid biosynthesis. The two phosphonate groups of the 1,1-bisphosphonates readily dock into the diphosphate-Mg(2+) binding site in farnesyl diphosphate synthase, while the charged ammonium (or pyridinium or imidazolium) groups act as carbocation transition state analogs, whose binding is stabilized by a cluster of oxygen atoms in the active site cleft, and an overall negative electrostatic potential in this region. Enhanced activity is shown to correlate with increasing van der Waals stabilization due to N-alkylation, or the presence of a charged, planar (sp(2)-hybridized) aromatic residue in the carbocation binding site. These results are of general interest since they suggest a rational approach to bisphosphonate drug design.

The pharmacology of bisphosphonates and new insights into their mechanisms of action

Bisphosphonates are chemically stable analogs of inorganic pyrophosphate, which are resistant to breakdown by enzymatic hydrolysis. The biological effects of bisphosphonates on calcium metabolism were originally ascribed to their physico-chemical effects on hydroxyapatite crystals. Although such effects may contribute to their overall action, their effects on cells are probably of greater importance, particularly for the more potent compounds. Remarkable progress has been made in increasing the potency of bisphosphonates as inhibitors of bone resorption, and the most potent compounds in current use are characterized by the presence of a nitrogen atom at critical positions in the side chain which, together with the bisphosphonate moiety itself, seems to be essential for maximal activity. As a class the bisphosphonates offer a very effective means of treating Paget's disease.