Pyridinium-1-yl bisphosphonates are potent inhibitors of farnesyl diphosphate synthase and bone resorption

We report the design, synthesis and testing of a series of novel bisphosphonates, pyridinium-1-yl-hydroxy-bisphosphonates, based on the results of comparative molecular similarity indices analysis and pharmacophore modeling studies of farnesyl diphosphate synthase (FPPS) inhibition, human Vgamma2Vdelta2 T cell activation and bone resorption inhibition. The most potent molecules have high activity against an expressed FPPS from Leishmania major, in Dictyostelium discoideum growth inhibition, in gammadelta T cell activation and in an in vitro bone resorption assay. As such, they represent useful new leads for the discovery of new bone resorption, antiinfective and anticancer drugs.     

A quantitative structure-activity relationship and pharmacophore modeling investigation of aryl-X and heterocyclic bisphosphonates as bone resorption agents

We have used quantitative structure-activity relationship (QSAR) techniques, together with pharmacophore modeling, to investigate the relationships between the structures of a wide variety of geminal bisphosphonates and their activity in inhibiting osteoclastic bone resorption. For aryl-X (X = alkyl, oxyalkyl, and sulfanylalkyl) derivatives of pamidronate and one alendronate, a molecular field analysis (MFA) yielded an R(2) value of 0.900 and an F-test of 54 for a training set of 29 compounds. Using reduced training sets, the activities of 20 such compounds were predicted with an average error of 2.1 over a 4000x range in activity. Such good results were only obtained when using the X-ray crystallographic structure of farnesyl pyrophosphate (FPP) bound to the target enzyme, farnesyl pyrophosphate synthase (FPP synthase), to guide the initial molecular alignment. For a series of heterocyclic bisphosphonates, use of the MFA method yielded an R(2) of 0.873 and an F-test of 36 for a training set of 26 compounds. Using a reduced training set, the activities of 20 compounds were predicted with an average error of 2.5 over a 2000x range in activity. With the heterocyclic compounds, test calculations indicated the importance of correct choice of protonation of the heterocyclic rings. For example, thiazoles, pyrazoles, and triazoles have low ( approximately 2-3) pK(a) values and the derived bisphosphonates are inactive in bone resorption since they cannot readily be side chain protonated and are thus poor carbocation reactive intermediate analogues. On the other hand, aminothiazoles, imidazoles, pyridyl, and aminopyridyl species typically have pK(a) values in the range approximately 5-9 and, in the absence of unfavorable steric interactions, the corresponding bisphosphonates are generally good inhibitors. However, aminoimidazole bisphosphonates are generally less active, since their pK(a)s ( approximately 11) are so high, due to guanidinium-like resonance, that they cannot readily be deprotonated, which we propose results in poor cellular uptake. The results of pharmacophore modeling using the Catalyst program revealed the importance of two negative ionizable and one positive charge feature for both aryl-X and heterocyclic pharmacophores, together with the presence of a distal hydrophobic feature in the aryl bisphosphonate and a more proximal aromatic feature in the heterocyclic bisphosphonate pharmacophores. When taken together, these results show that it is now possible to predict the activity, within a factor of about 2.3, of a wide range of aryl-X and heterocyclic bisphosphonates. The results emphasize the importance of utilizing crystallographic structural information to guide the initial alignment of extended bisphosphonates, and in the case of heterocyclic bisphosphonates, the importance of side chain protonation state. These simple ideas may facilitate the design of other, novel bisphosphonates, of use in bone resorption therapy, and as antiparasitic and immunotherapeutic agents.     

Genistein prevents bone resorption diseases by inhibiting bone resorption and stimulating bone formation

Genistein, a soybean-derived isoflavone, has been shown to suppress osteoclastic bone resorption. To clarify the mechanisms underlying this action, we investigated the effects of genistein on the differentiation, cytoskeleton and function in mice osteoclasts in vitro and bone metabolism in ovariectomized rats. Study design: Primary OCs were isolated from 3 week-old mice and induced by 1,25(OH)(2)D(3). Then OCs were exposed to genistein at various concentration of 0 M, 10(-9) M, 10(-8) M, 10(-7) M, 10(-6) M, and 10(-5) M. The number of TRAP+ cells were counted as well as the surface area of bone resorption on bone slice. F-actin change was observed by Confocal. In vivo, forty 12 week-old female SD rats were randomly assigned to four groups: (1) sham operated (Sham); (2) (OVX); (3) ovariectomized and treated with estradiol (OVX-E); (4) ovariectomized and received genistein (OVX-G). After 12 weeks, BMD, body weight, serum level of alkaline phosphatase (ALP), acid phosphatase (ACP), osteocalcin (OC), IL-1beta, TNFalpha, IL-6 and calcitonin (CT) were evaluated. Femur were sectioned. In addition, the serum estradiol, the weight of uteri and histological behavior were also examined to indicate the side effect of genistein to the uteri. Results: In vitro, the number of TRAP+ cells decreased depending on the concentration of genistein as well as the area of bone resorption. F-actin became disorder under Confocal. In vivo, after treated with genistein, BMD and the serum level of ALP, ACP, osteocalcin increased significantly, while the serum level of IL-1beta and TNFalpha decreased. Especially, the increase of ALP and osteocalcin of OVX-G was higher than that of OVX-E. Histologically, the pachy-trabecula were observed as well as the more mineral deposition lines. Additionally, the uterus weight index and the serum estradiol in OVX-G rats were lower significantly than those of OVX-E. The epithelia of uteri gland in OVX-G appeared cubic while those of OVX-E became squamous. Conclusions: Genistein can prevent bone resorption diseases by the promotion of bone formation and the prevention of bone resorption with slight side effect.     

Stimulative effects of cadmium on bone resorption in neonatal parietal bone resorption.

Effects of cadmium on bone resorption were investigated using neonatal mouse parietal bone culture system. Cadmium at 0.5 microM and above stimulated hydroxyproline release as well as 45Ca release. As cadmium-stimulated bone resorption was inhibited by calcitonin, bone resorption induced by cadmium is osteoclast-mediated bone resorption. CI-1, collagenase inhibitor, depressed cadmium-stimulated bone resorption in a dose-dependent manner. Osteoblasts are also involved in cadmium-induced bone resorption. Indomethacin-inhibited cadmium-stimulated bone resorption and cadmium-treated bones released prostaglandin E2 to a greater extent than untreated bones. Cadmium-stimulated bone resorption was shown to be dependent on the production of prostaglandin E2. 3-Isobutyl-1-methylxanthine potentiated cadmium-stimulated bone resorption and verapamil depressed it. It is possible that an increase in levels of cAMP and calcium ion in bone cells is involved in cadmium-induced bone resorption. From these results, cadmium was found to stimulate osteoclast-mediated bone resorption which is dependent on prostaglandin E2. Second messengers in cadmium-induced bone resorption may be cAMP and calcium ion.     

Synthesis and anti-proliferative in-vitro activity of two natural dihydrostilbenes and their analogues

A total synthetic route for two natural dihydrostilbenes with significant cytotoxicity toward human cancer cell lines, (3-(2-(7-methoxybenzo[d][1,3]dioxol-5-yl)ethyl)phenol 1a and 6-(3-hydroxyphenethyl)benzo[d][1,3]dioxol-4-ol 1b), which were isolated from Bulbophyllum odoratissimum Lindl, was developed via Wittig-Horner reaction. The natural products 1a and 1b were obtained in 28% and 20% overall yield, respectively. Additionally, nine analogues, 1c-1k, of the two natural dihydrostilbenes were synthesized and evaluated for their anti-proliferative activity against human SGC-7901, KB and HT-1080 cell lines by MTT assay. The activities of 1c and 1d were in the same range as those of the natural products 1a and 1b.     

The cellular mechanism of action of bisphosphonates

Present understanding of the cellular mechanism of action of bisphosphonates as in vitro and in vivo inhibitors of bone resorption is reviewed. This mechanism appears to involve the osteoclast at more than one stage of its maturation process, and way well be receptor-mediated, although the molecular mechanism itself is thus far unknown.     

Effect of cathepsin K inhibitors on bone resorption

On the basis of the pyrrolopyrimidine core structure that was previously discovered, cathepsin K inhibitors having a spiro amine at the P3 have been explored to enhance the target, bone marrow, tissue distribution. Several spiro structures were identified with improved distribution toward bone marrow. The representative inhibitor 7 of this series revealed in vivo reduction in C-terminal telopeptide of type I collagen in rats and monkeys.     

New bisphosphonates in the treatment of bone diseases

Bisphosphonates are pyrophosphate analogues, in which the oxygen in P-O-P has been replaced by a carbon, resulting in a P-C-P structure. They are characterised by a strong anti-osteoclastic activity and for this pharmacological property they are now considered the treatment of choice for Paget's disease of the bone, malignant hypercalcaemia and bone metastases. Etidronate, clodronate and pamidronate have been registered in several countries for these indications. Etidronate and alendronate are also extensively used for the prevention and treatment of postmenopausal and senile osteoporosis. In this article, we review the most recent findings on the newest bisphosphonates, which will become available in the near future. The aminobisphosphonate risedronate is undergoing a huge programme of clinical development for the treatment of osteoporosis. In a study of the prevention of early postmenopausal bone loss, oral risedronate 5 mg fully prevented the bone loss observed in the placebo group. Similar effects have been observed with an intermittent dosage regimen of oral risedronate 30 mg/day for 2 out of 12 weeks, which corresponds to 5 mg/day in terms of cumulative dose. With lower doses [5 mg on alternate fortnights (2 weeks)] the prevention of bone loss was half that observed with continuous 5 mg/day therapy, indicating that this might not yet be the maximum effective dose. The use of intermittent intravenous bisphosphonates for osteoporosis therapy has been pioneered by studies with clodronate, pamidronate and alendronate. This treatment regimen has been chosen for an extensive clinical development programme for ibandronate. In a phase 2 study, this new bisphosphonate was administered as an intravenous bolus (0.25, 0.5, 1 or 2 mg) every 3 months for a year, with increases in spinal bone mass of 5.2%. Tiludronate, alendronate and risedronate have been recently introduced for the treatment of Paget's disease of bone. Daily doses of tiludronate 400 mg, alendronate 40 mg and risedronate 30 mg for 3 to 6 months have been shown to be superior to etidronate 400 mg/day. The intravenous administration of ibandronate, zoledronate and alendronate (40 mg, 10 mg and 5 mg, respectively) have achieved the normalisation of serum alkaline phosphatase in more than 70% of the patients and these treatments may provide an alternative for patients intolerant oral bisphosphonates. Intravenous ibandronate has been also developed for the treatment of hypercalcaemia of malignancy. The effective doses ranged from 2 to 4 mg. Zoledronate appears to be the most powerful bisphosphonate under investigation, and the effective doses used in cancer hypercalcaemia are as low as 1 to 2 mg. The new generation of bisphosphonates are likely to increase clinical options in terms of administration regimens, but their real advantage over those already available in terms of clinical efficacy remains uncertain.     

Effects of methylprednisolone on bone formation and resorption in rats

Excessive glucocorticoids induce osteoporosis. However, there is some controversy regarding the mechanism of action, and even the endpoint result. The present study was carried out to obtain further insight into the action of glucocorticoids on bone formation and resorption in rats. Growing rats were injected subcutaneously with methylprednisolone (mPSL) at doses of 0, 2.5, 5, 10 or 20 mg/kg per day for 4 weeks. Bone mineral density (BMD), enchondral and periosteal bone formation, collagen synthetic activities of osteoblasts, numbers of osteoblasts and osteoclasts, and serum markers to assess bone turnover were determined. Administration of mPSL dose-dependently increased the BMD in the tibial metaphysis, while it dose-dependently decreased the BMD in the diaphysis. Both enchondral and periosteal bone formation were decreased in a dose-dependent fashion. The incorporation and secretion of (3)H-proline by osteoblasts were both decreased in trabecular and cortical bones. The number of osteoclasts, together with the number of osteoblasts, in the tibial metaphysis was drastically decreased. Serum alkaline phosphatase and osteocalcin were decreased at higher doses. These results support the recent notion that glucocorticoids inhibit both bone formation and resorption. In addition, BMD as an endpoint result might differ from site to site in bone due to a different balance between bone formation and resorption.     

Stimulant action of pethidine on the pregnant rat uterus in-vitro

Pethidine's stimulant action on the 22-day pregnant rat isolated uterus does not involve receptors sensitive to methysergide and is unlikely to involve the synthesis and release of endogenous prostaglandins. The sensitivity of pethidine-induced contractions to verapamil suggests that mobilization of extracellular calcium is necessary for pethidine's action.     

Zinc-induced hypocalcemia and bone resorption in rats

The changes of calcium levels in serum and in the femur were examined in rats administered oral doses of zinc sulfate (0.1, 1.0, and 10 mg Zn/100 g body weight) for 3 days. All doses of zinc caused significant decreases in calcium levels in serum and in the femoral diaphysis and epiphysis. The decrease in these femoral calcium levels was seen 1 day after administration of zinc (10 mg/100 g). Furthermore, time course studies of the effect of zinc administration showed that, at 1 hr after zinc administration, calcium levels in serum and in femoral epiphysis but not in diaphysis were significantly decreased. In thyroparathyroidectomized rats, however, no significant decrease of the epiphyseal calcium was observed by administration of zinc (10 mg Zn/100 g), but the serum calcium level was significantly lowered. Zinc administration to intact rats caused a significant increase in acid phosphatase activity in the femoral epiphysis but not in the diaphysis. This increase was clearly prevented by thyroparathyroidectomy. Accumulations of zinc in the femoral epiphysis and diaphysis after zinc administration was not significantly altered by thyroparathyroidectomy. These results suggest that zinc-induced hypocalcemia may cause bone resorption which is primarily mediated by the action of the parathyroid hormone and it is related to calcium homeostasis in rats.     

The effect of toremifene on bone and uterine histology and on bone resorption in ovariectomised rats

The effect of the selective oestrogen receptor modulator, toremifene, to inhibit ovariectomy-induced bone loss was studied in rats. The oral doses were 0.3, 3.0 or 30 mg/kg/day for 2 months. 17beta-oestradiol (5 microg/kg/day, subcutaneously) was used as positive control. One group was also treated with a combination of 17beta-oestradiol (5 microg/kg) and toremifene (3.0 mg/kg). Biochemical markers were urinary hydroxyproline and calcium (adjusted with urinary creatinine levels) and the serum level of pyridinoline cross-linked carboxy terminal telopeptide, a bone specific collagen breakdown product. The femoral and sternal trabecular bone thickness served as histological parameters. Ovarectomy increased the levels of hydroxyproline and pyrodinoline and decreased the trabecular bone thickness compared to the sham-operated control group. This was inhibited by both test compounds but 17beta-oestradiol was more efficient. Toremifene did not reverse the ovariectomy-induced reduction of urinary calcium but inhibited the 17beta-oestradiol-related increase. When administered together with oestradiol, toremifene did not reverse the positive effect of 17beta-oestradiol on bone, however toremifene reversed the oestradiol-related uterothrophic effects. These findings indicate that the antagonistic features of toremifene dominate in the rat uterus the agonistic properties do in the bone.     

Synthesis and pharmacological action of some N-alkyl morpholines and their salts

The preparation is described of some 2-hydroxy-2- and 4-alkylmorpholines by ring closure of the corresponding phenacyl hydroxyalkylamines. The influence of structure upon the ring closure reaction is examined and the weak pharmacological action of the title compounds on leptazol convulsions, the autonomic nervous system and in the mouse hot-plate test is discussed in relation to the reversed esters of pethidine.     

New insights into the molecular mechanisms of action of bisphosphonates

Bisphosphonates are currently the most important and effective class of anti-resorptive drugs available, but the exact molecular mechanisms by which they inhibit osteoclast-mediated bone resorption have only recently been identified. Due to the targeting of bisphosphonates to bone mineral and the ability of osteoclasts to release bone-bound bisphosphonate, a direct effect on mature osteoclasts appears to be the most important route of action. As a result of recent discoveries concerning their molecular mechanism of action, bisphosphonates can be grouped into two classes. The simple bisphosphonates that closely resemble PPi (such as clodronate, etidronate and tiludronate) can be metabolically incorporated into non-hydrolysable analogues of ATP that accumulate intracellularly in osteoclasts, resulting in induction of osteoclast apoptosis. By contrast, the more potent, nitrogen-containing bisphosphonates (such as pamidronate, alendronate, risedronate, ibandronate and zoledronate) appear to act as analogues of isoprenoid diphosphate lipids, thereby inhibiting FPP synthase, an enzyme in the mevalonate pathway. Inhibition of this enzyme in osteoclasts prevents the biosynthesis of isoprenoid lipids (FPP and GGPP) that are essential for the post-translational farnesylation and geranylgeranylation of small GTPase signalling proteins. Loss of bone-resorptive activity and osteoclast apoptosis is due primarily to loss of geranylgeranylated small GTPases. Identification of FPP synthase as the target of nitrogen-containing bisphosphonates has also helped explain the molecular basis for the adverse effects of these agents in the GI tract and on the immune system.     

Recent advances in understanding the mechanism of action of bisphosphonates

Bisphosphonates (BPs) are widely used in the treatment of diseases associated with excessive osteoclast-mediated bone resorption, such as osteoporosis. Although several years ago the molecular target of the potent nitrogen-containing BPs (N-BPs) was identified as farnesyl diphosphate synthase, an enzyme in the mevalonate pathway, recent data have shed new light on the precise mechanism of inhibition and demonstrated that the acute-phase reaction, an adverse effect of N-BPs, is also caused by inhibition of this enzyme. In addition, the identification of BP analogues that inhibit different enzymes in the mevalonate pathway could lead to the development of novel inhibitors of bone resorption with potential applications in the treatment of bone disease.