Inhibitory effects of bisphosphonate (YM175) on bone resorption induced by a metastatic bone tumor

A method for the synthesis of unsymmetric bisphosphoric analogs of α-amino acids

Herein, we describe the first universal strategy for the synthesis of unsymmetric phosphonyl-phosphinyl and phosphonyl-phosphinoyl analogs of N-protected 1-aminobisphosphonates. The proposed user-friendly procedure, based on a one-pot reaction of the α-ethoxy derivatives of phosphorus analogs of protein and non-protein α-amino acids with triphenylphosphonium tetrafluoroborate and an appropriate phosphorus nucleophile (diethyl phenylphosphonite or methyl diphenylphosphinite), provides good to very good yields of 53-91% under mild catalyst-free conditions (temperature: rt to 40 °C, time: 1 to 6 hours). The progress of the transformation, running through the corresponding phosphonium salt as a reactive intermediate, was monitored by ³¹P NMR spectroscopy, which is a convenient tool for the identification of the transient species formed here. In this paper, we present the full characteristics of the spectroscopic properties of all 13 synthesized models of structurally diverse N-protected unsymmetric bisphosphoric analogs of α-amino acids. Therefore, these results contribute to increasing the practical applicability of our recently reported synthesis protocol of symmetric models of α-aminobisphosphonates derivatives and thus justify its universality.

One-Pot and Catalyst-Free Transformation of N-Protected 1-Amino-1-Ethoxyalkylphosphonates into Bisphosphonic Analogs of Protein and Non-Protein α-Amino Acids

Herein, we describe the development of one-pot transformation of α-ethoxy derivatives of phosphorus analogs of protein and non-protein α-amino acids into biologically important N-protected 1-aminobisphosphonates. The proposed strategy, based on the three-component reaction of 1-(N-acylamino)-1-ethoxyphosphonates with triphenylphosphonium tetrafluoroborate and triethyl phosphite, facilitates good to excellent yields under mild reaction conditions. The course of the reaction was monitored by ³¹P NMR spectroscopy, allowing the identification of probable intermediate species, thus making it possible to propose a reaction mechanism. In most cases, there is no need to use a catalyst to provide transformation efficiency, which increases its attractiveness both in economic and ecological terms. Furthermore, we demonstrate that the one-pot procedure can be successfully applied for the synthesis of structurally diverse N-protected bisphosphonic analogs of α-amino acids. As shown, the indirect formation of the corresponding phosphonium salt as a reactive intermediate during the conversion of 1-(N-acylamino)-1-ethoxyphosphonate into a 1-aminobisphosphonate derivative is a crucial component of the developed methodology.

Symptom Palliation in Patients with Bone Metastases Treated with Radiotherapy

Context: Skeleton is the most common organ affected by metastases. Bone pain is the most common symptom of metastatic bone disease. The treatment of bone metastasis is primarily palliative requiring multidisciplinary therapies; radiotherapy (RT), however, remains the cornerstone of the treatment. Aims: The aim of this study is to measure the effectiveness of RT in terms of symptomatic relief in pain and insomnia, improvement in stability/movement, and decrease in the requirement of analgesics by patients using the Hundred Paisa Pain Scale. Subjects and Methods: The RT records of 226 patients with bone metastasis treated at the department of Radiotherapy, SMS Medical College, Jaipur; from July 2015 to December 2016 over cobalt-60 teletherapy unit were analyzed. The RT dose fractionation ranged from 30 Gy in 10 daily fractions, 20 Gy in 5 daily fractions, 12.5 Gy in 2 weekly fractions, and 8 Gy in single fraction. Results: The median age of the cohort was 54 (range, 29–84) years. The most common site of primary tumor was lung (30.1%), followed by breast (12.4%) and prostate (11.9%). The most common bone involved was vertebrae (71.2%), followed by pelvis (14.6%); among vertebrae, thoracic vertebrae were most commonly involved (63.9%), followed by lumbar vertebrae (57.8%). The maximum relief in pain was seen with 6.25 Gy/fraction schedule, whereas the maximum improvement in stability/movement was noted with 3 Gy/fraction schedule. The 8 Gy single-fraction schedule was associated with maximum relief in insomnia and decrease in analgesic requirement. Conclusion: The current institutional protocol of weekly hypofractionated palliative RT of 6.25 Gy per fraction up to a maximum of four fractions given on Saturday has shown results comparable with other schedules with well tolerance and achievement of acceptable symptom palliation. This weekly schedule is practically convenient to both the patients who mostly came from far-flung areas and the institute as it spares the already overburdened machine to carry on conventional RT from Monday to Friday.

Low bone mineral density is not related to failure in femoral neck fracture patients treated with internal fixation

BACKGROUND AND PURPOSE

Internal fixation (IF) in femoral neck fractures has high reoperation rates and some predictors of failure are known, such as age, quality of reduction, and implant positioning. Finding new predictors of failure is an ongoing process, and in this study we evaluated the importance of low bone mineral density (BMD).

PATIENTS AND METHODS

140 consecutive patients (105 females, median age 80) treated with IF had a dual-energy X-ray absorptiometry (DXA) scan of the hip performed median 80 days after treatment. The patients' radiographs were evaluated for fracture displacement, implant positioning, and quality of reduction. From a questionnaire completed during admission, 2 variables for comorbidity and walking disability were chosen. Primary outcome was low hip BMD (amount of mineral matter per square centimeter of hip bone) compared to hip failure (resection, arthroplasty, or new hip fracture). A stratified Cox regression model on fracture displacement was applied and adjusted for age, sex, quality of reduction, implant positioning, comorbidity, and walking disability.

RESULTS

49 patients had a T-score below -2.5 (standard deviation from the young normal reference mean) and 70 patients had a failure. The failure rate after 2 years was 22% (95% CI: 12-39) for the undisplaced fractures and 66% (CI: 56-76) for the displaced fractures. Cox regression showed no association between low hip BMD and failure. For the covariates, only implant positioning showed an association with failure.

INTERPRETATION

We found no statistically significant association between low hip BMD and fixation failure in femoral neck fracture patients treated with IF.

Denosumab and bisphosphonates: different mechanisms of action and effects

To treat systemic bone loss as in osteoporosis and/or focal osteolysis as in rheumatoid arthritis or periodontal disease, most approaches target the osteoclasts, the cells that resorb bone. Bisphosphonates are currently the most widely used antiresorptive therapies. They act by binding the mineral component of bone and interfere with the action of osteoclasts. The nitrogen-containing bisphosphonates, such as alendronate, act as inhibitors of farnesyl-pyrophosphate synthase, which leads to inhibition of the prenylation of many intracellular signaling proteins. The discovery of RANKL and the essential role of RANK signaling in osteoclast differentiation, activity and survival have led to the development of denosumab, a fully human monoclonal antibody. Denosumab acts by binding to and inhibiting RANKL, leading to the loss of osteoclasts from bone surfaces. In phase 3 clinical studies, denosumab was shown to significantly reduce vertebral, nonvertebral and hip fractures compared with placebo and increase areal BMD compared with alendronate. In this review, we suggest that the key pharmacological differences between denosumab and the bisphosphonates reside in the distribution of the drugs within bone and their effects on precursors and mature osteoclasts. This may explain differences in the degree and rapidity of reduction of bone resorption, their potential differential effects on trabecular and cortical bone, and the reversibility of their actions.

A c-fms tyrosine kinase inhibitor, Ki20227, suppresses osteoclast differentiation and osteolytic bone destruction in a bone metastasis model

In bone metastatic lesions, osteoclasts play a key role in the development of osteolysis. Previous studies have shown that macrophage colony-stimulating factor (M-CSF) is important for the differentiation of osteoclasts. In this study, we investigated whether an inhibitor of M-CSF receptor (c-Fms) suppresses osteoclast-dependent osteolysis in bone metastatic lesions. We developed small molecule inhibitors against ligand-dependent phosphorylation of c-Fms and examined the effects of these compounds on osteolytic bone destruction in a bone metastasis model. We discovered a novel quinoline-urea derivative, Ki20227 (N-{4-[(6,7-dimethoxy-4-quinolyl)oxy]-2-methoxyphenyl}-N'-[1-(1,3-thiazole-2-yl)ethyl]urea), which is a c-Fms tyrosine kinase inhibitor. The IC(50)s of Ki20227 to inhibit c-Fms, vascular endothelial growth factor receptor-2 (KDR), stem cell factor receptor (c-Kit), and platelet-derived growth factor receptor beta were found to be 2, 12, 451, and 217 nmol/L, respectively. Ki20227 did not inhibit other kinases tested, such as fms-like tyrosine kinase-3, epidermal growth factor receptor, or c-Src (c-src proto-oncogene product). Ki20227 was also found to inhibit the M-CSF-dependent growth of M-NFS-60 cells but not the M-CSF-independent growth of A375 human melanoma cells in vitro. Furthermore, in an osteoclast-like cell formation assay using mouse bone marrow cells, Ki20227 inhibited the development of tartrate-resistant acid phosphatase-positive osteoclast-like cells in a dose-dependent manner. In in vivo studies, oral administration of Ki20227 suppressed osteoclast-like cell accumulation and bone resorption induced by metastatic tumor cells in nude rats following intracardiac injection of A375 cells. Moreover, Ki20227 decreased the number of tartrate-resistant acid phosphatase-positive osteoclast-like cells on bone surfaces in ovariectomized (ovx) rats. These findings suggest that Ki20227 inhibits osteolytic bone destruction through the suppression of M-CSF-induced osteoclast accumulation in vivo. Therefore, Ki20227 may be a useful therapeutic agent for osteolytic disease associated with bone metastasis and other bone diseases.

Cancer pain and its impact on diagnosis, survival and quality of life

Cancer pain significantly affects the diagnosis, quality of life and survival of patients with cancer. During the past decade, preclinical and clinical data has begun to provide insight into the mechanisms that drive and mask cancer pain and the mechanisms by which anti-neoplastic agents induce peripheral neuropathy. Developing a mechanism-based understanding and mechanism-based therapies to treat cancer-associated pain and sensory neuropathy, and incorporating these into mainstream cancer research and therapy, will be crucial to improving the quality of life and survival of patients with cancer.

Thrombin Inhibitor, Argatroban, Prevents Tumor Cell Migration and Bone Metastasis

It is well known that malignant cells show procoagulant activity, which is associated with their metastatic potential. Thrombin, the key enzyme of the blood coagulation system, is generated around tumor cells, promoting the migration and metastasis of tumor cells. In this study, we evaluated the effect of argatroban, a specific thrombin inhibitor, on the migration and metastasis of B16BL6 melanoma cells. In vitro argatroban dose-dependently inhibited cell migration, the maximum inhibition being observed in the presence of 10 microM argatroban (p < 0.0001). In order to investigate the antimetastatic effect of the thrombin inhibitor, we used an animal model that we have reported previously. C57BL6 mice which had received a bone (femur or tibia) transplanted into the dorsal subcutis were injected with B16 melanoma cells into the left heart ventricle. Intraperitoneal injection of argatroban (9 mg/kg/day for 4 weeks) significantly reduced the number of limbs with metastatic lesions as compared to a placebo (p < 0.05). These results suggest that argatroban was associated with reduced melanoma metastases by inhibiting cell migration. Our results showed that argatroban is effective for treatment of bone metastasis.

Direct effects of bisphosphonates on breast cancer cells

In addition to inhibiting bone resorption, bisphosphonates have also been shown to exhibit antitumour effects. In vitro, bisphosphonates inhibit proliferation and induce apoptosis in cultured human breast cancer cells. In addition, bisphosphonate treatment interferes with breast cancer cell adhesion to bone matrix, and inhibits cell migration and invasion. The combination of bisphosphonates with other anticancer drugs such as the taxoids markedly enhances these effects. These newly recognized direct actions of bisphosphonates on breast cancer cells indicate that these agents may have a greater role to play in treatment of patients suffering from cancers with a propensity to metastasize to bone.

Bisphosphonate acts on osteoclasts independent of ruffled borders in osteosclerotic (oc/oc) mice

We examined the effects of a third generation bisphosphonate [YM-175; disodium dihydrogen (cycloheptylamino)-methylene-1,1-bisphosphonate] on osteoclasts in osteosclerotic (oc/oc) mice to elucidate the cellular mechanism for incorporation of the bisphosphonate. Osteoclasts of oc/oc mice were in direct contact with bone matrix but devoid of ruffled borders. Tartrate-resistant acid phosphatase (TRAPase) showed spotty localization intercellularly, whereas vacuolar H(+)-ATPase (V-ATPase) immunoreactivity was observed homogeneously in the cytoplasm. Upon injection of bisphosphonate, most osteoclasts lost cell polarity and were detached from bone surfaces. The detached osteoclasts underwent apoptosis as characterized by condensation of chromatin, absence of Golgi apparatus, and formation of many vesicles in the cytoplasm. Both TRAPase and V-ATPase were evenly distributed in the cytoplasm. The pyknotic nuclei of osteoclasts revealed DNA fragments as evidenced by the terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end-labeling (TUNEL) method. The results indicate that osteoclasts lacking ruffled borders in oc/oc mice incorporated the bisphosphonate from a site different from ruffled borders and that bisphosphonate may directly affect osteoclasts without mediating its deposition to the bone matrix.

The evaluation of a rat model for the analysis of densitometric and biomechanical properties of tumor-induced osteolysis

Pathologic fractures from a reduction in bone mass and strength are a debilitating complication affecting the quality of life of individuals with metastatic lesions. There are a number of existing animal models for studying the effects of bone metastases experimentally, but these models are unsuitable for measuring structural changes in metastatic bone. Our goal was to present an in vivo model for directly investigating the densitometric and structural consequences of tumor-induced osteolysis in long bones. One femur from female Sprague Dawley rats was implanted with Walker Carcinosarcoma 256 malignant breast cancer cells or with a Sham implant. After 28 days, the animals were killed, and both femora of each animal evaluated using histomorphometry, densitometry, and mechanical testing. Compared to Sham-operated controls, we found an 11% decrease in bone mineral content, a 9% decrease in bone mineral density using dual energy X-ray absorptiometry, and a 16% decrease in bone density using peripheral quantitative computed tomography in the group with tumor cell implants. In addition, failure torque was decreased by 35% compared to the contralateral controls and by 41% compared to the Sham-operated controls. Torsional stiffness in the tumor cell-implanted femora was decreased by 35% compared to contralateral controls and by 39% compared to Sham-operated controls. Bone density was only weakly to moderately associated with bone strength in our model. By creating reproducible localized tumor-induced osteolytic lesions in a long bone, this model provides the most direct evaluation of the structural consequences of bone metastases. In the future, this model may provide a method for determining the effects of new therapeutic approaches on the preservation of bone mass and bone strength in the presence of metastatic bone disease.

Melanoma cells stimulate osteoclastogenesis, c-Src expression and osteoblast cytokines

Malignant melanomas metastasise to the bone and enhance osteoclast bone resorption. We demonstrated that a 48-h-B16 melanoma cell conditioned media (B16CM) induced osteoclastogenesis in mouse bone marrow cultures, without the requirement of B16 cell-bone marrow cell co-culture. B16 cells transcriptionally expressed detectable levels of TGFbeta1, IL-6, M-CSF, GM-CSF and TNFalpha mRNAs, albeit to a lower extent compared with levels in osteoblasts, and failed to express PTHrP, OPGL, OPG and IL-1beta. Interestingly, B16CM greatly upregulated IL-1beta, IL-6 and GM-CSF, and modestly enhanced TNFalpha and OPGL mRNA expression in osteoblasts, suggesting a potential indirect stimulation of osteoclastogenesis via the osteogenic lineage. B16CM barely upregulated c-Fos, but strongly and time-dependently enhanced c-Src expression in the total bone marrow cultures during osteoclast differentiation. Moreover, c-Src expression was enhanced in differentiated and purified osteoclast preparations to higher levels than in stromal cells. In conclusion, melanoma induces osteoclast generation with a paracrine mechanism independent of cell-cell contact, specifically upregulating c-Src in osteoclasts and cytokine expression in osteoblasts.

Concentration of bisphosphonate (incadronate) in callus area and its effects on fracture healing in rats

The aim of the present study was to investigate effects of incadronate on early stages of fracture healing and to detect its concentration in callus area (Ca.Ar). Rats were injected three times per week with either two doses of incadronate (10 microg/kg and 100 microg/kg) or vehicle for 2 weeks. Femora were then fractured and fixed and animals were divided into pretreatment (P-10 and P-100) and continuous treatment (C-10 and C-100) groups. Incadronate treatment was stopped in P-10 and P-100 groups but continued in C-10 and C-100 groups. Animals were killed at 2 weeks and 4 weeks after fracture. Results showed significantly large callus, compared with the control, only in C-100 group at 4 weeks but not at 2 weeks. Both linear labeled surface (LS) and eroded surface (ES) decreased significantly in C-10 and C-100 groups at 2 weeks and 4 weeks. Osteoclast number (N.Oc) decreased significantly in C-10 and C-100 groups at 2 weeks but increased slightly at 4 weeks. However, there was no significant difference in the above parameters in P-10 and P-100 groups at 4 weeks. Apoptotic osteoclasts were observed only in the C-100 group at 4 weeks. A time-course decrease in incadronate concentration was detected in P-10 and P-100 groups whereas an increase was observed in C-10 and C-100 groups. These findings suggest that larger callus under incadronate treatment may result from the inhibition of bone resorption, histological characteristics of callus may be correlated with incadronate concentration, and metabolism of incadronate in bone may be related to the rate of bone turnover.

Association between histomorphometry and biochemical markers of bone turnover in a longitudinal rat model of parathyroid hormone-related peptide (PTHrP)-mediated tumor osteolysis

Advanced tumor osteopathy is characterized by abnormal bone turnover. Using a rat model of parathyroid hormone-related peptide (PTHrP)-mediated tumor osteolysis, the aim of the present study was to define the sequential changes in, and the association between, biochemical and histomorphometric indices of bone metabolism during the early stages of developing tumor osteopathy. Eight-month-old Wistar rats (n = 48) were subcutaneously inoculated with either 2 x 10(6) cells of the Walker carcinosarcoma 256, or saline on day 0, and treated with either saline or the bisphosphonate ibandronate until killing on day 8. Serum calcium (sCa), alkaline phosphatase (sTAP), and osteocalcin (sOC) and urinary calcium (uCa), deoxypyridinoline (uDPD), and pyridinoline (uPYD) were measured daily. In a second semilongitudinal experiment (n = 70), the number of osteoclasts and osteoblasts (N.Oc, N.Ob), trabecular bone volume (BV/TV), and osteoid volume (O.Ar) were assessed by histomorphometry. In untreated tumor-bearing animals, osteoclast numbers increased by 74% on day 3 (5.4 +/- 2.4 vs. 3.1 +/- 1.5/mm(2), p < 0.05), and trabecular bone volume fell by 24% on day 4 (12.5 +/- 2.0 vs. 15.8 +/- 1.2%, p < 0.05). Both time course and magnitude of these changes were closely reflected by an increase in uDPD (0.46 +/- 0.14 vs. 0. 31 +/- 0.15 nmol/12 h, p < 0.05) and uPYD on day 4 (1.44 +/- 0.25 vs. 1.03 +/- 0.3 nmol/12 h, p < 0.05), sCa (3.8 +/- 0.52 vs. 3.0 +/- 0. 13 mmol/L, p < 0.01), and uCa (0.13 +/- 0.08 vs. 0.03 +/- 0.01 mmol/12 h, p < 0.001) on day 6, and sTAP (254 +/- 127 vs. 120 +/- 40 U/L, p < 0.001) on day 7 (mean +/- SD), whereas sOC remained unchanged until day 8. When combining the results of the two experiments, a high correlation was found between the number of osteoclasts and the urinary excretion of PYD (r = 0.91) and DPD (r = 0.89). Treatment with ibandronate delayed hypercalcemia, abolished hypercalciuria, and accelerated bone resorption. We conclude that osteoclast activation is an early event in PTHrP-mediated osteolysis, which is closely reflected by the renal excretion of pyridinium cross-links of type I collagen. Therefore, specific biochemical markers of collagen breakdown may be useful as early indicators of developing tumor osteopathy.

Effects of bisphosphonate on experimental jaw metastasis model in nude mice

The mechanism of osteolysis associated with metastatic cancer of the jaws is essentially osteoclast-mediated. Therefore, it is likely that potent osteoclastic bone resorption inhibitors such as bisphosphonates would be efficacious for the treatment of jaw metastasis. We examined the effects of a third generation bisphosphonate, YM175, in a nude mice jaw metastasis model with intracardiac injection of a human breast cancer cell line, MDA-MB-231. The metastatic lesions in untreated mice were radiographically observed at the body and angle of the mandible. Histology of the mandible of untreated mice revealed that most of the bone marrow cavities had been occupied by the metastatic tumor with active osteoclasts along the trabecular bone. The experimental group showed that YM175 markedly reduced the size of tumor and the number of osteoclasts. These results suggest that YM175 may suppress metastasis formation and tumor growth in jaw through inhibition of osteoclastic bone resorption.

Effect of bisphosphonate (incadronate) on fracture healing of long bones in rats

This study was designed to test whether bisphosphonates disturb the process of fracture healing. Female Sprague-Dawley rats were injected with either two doses of bisphosphonate (incadronate) (10 microg/kg and 100 microg/kg) or vehicle three times a week for 2 weeks. Right femora were then fractured and fixed with intramedullary wires. Incadronate treatment was stopped in pretreatment groups (P-10 and P-100 groups), while the treatment was continued in continuous treatment groups (C-10 and C-100 groups). Animals were sacrificed at 6 and 16 weeks after surgery. Soft X-ray of all fractured femora was taken. After mechanical testing, fractured femora were stained in Villanueva bone stain and embedded in methyl methacrylate. Cross-sections near fracture line were analyzed by microradiography and histomorphometry. Radiographic study showed that bony callus was present in all the fractures and incadronate treatment led to a larger callus, especially in C-100 group at both 6 and 16 weeks. Histologic study showed that the process of fracture healing in pretreatment groups was delayed at 6 weeks, but reached control level thereafter and showed same characteristics as in control at 16 weeks. Woven bony callus could still be seen in continuous treatment groups at 16 weeks. Mechanical study indicated that the ultimate load of C-100 group was slightly higher than the other treatment groups and control. The results suggest that pretreatment with incadronate did not affect fracture healing at 16 weeks after fracture. However, continuous incadronate treatment could lead to larger callus, but it delayed remodeling process during fracture healing, especially with high-dose treatment.

Drug disposition of incadronate, a new bisphosphonate, in rats with bone metastases

1. Drug disposition of incadronate in the nude rat with bone metastases induced by A375 human melanoma cells was studied after intravenous administration. 2. The pharmacokinetics of incadronate (plasma concentration, urinary excretion and bone uptake) in rat with bone metastases was not markedly different from that in the control rat. This compound, however, was selectively taken up in the bone region around metastatic tumour nests. 3. Drug concentrations in the bone region around tumour nests were 3-10 micrograms/g, these levels being higher than the IC50 (0.35 microgram/ml) for the inhibitory effect of this drug on osteoclasts in vitro. 4. In contrast, concentrations in the tumour nest itself was < 0.7 microgram/g, being markedly lower than the IC50 (35 micrograms/ml) for the inhibitory effect on the proliferation of tumour cells in vitro. 5. These results strongly suggest that pharmacological action of incadronate in mouse with bone metastases (inhibitory effect on the growth of metastatic tumour in bone) is caused not by the direct action on the tumour cells but by the distribution of the drug in the perifocal bone region followed by inhibition of the activity of osteoclasts, resulting in inhibition of the osteolytic process, which is necessary for the progress of metastatic tumour.

Effects of bisphosphonate (pamidronate) on bone resorption resulting from metastasis of a squamous cell carcinoma: report of an autopsy case and evaluation of bone resorbing activity in an experimental animal model

PURPOSE

This study evaluated the ability of bisphosphonate to prevent bone resorption induced by metastatic tumor cells.

MATERIALS AND METHODS

Autopsy specimens of a bone metastasis from a woman with a primary squamous cell carcinoma of the tongue who developed multiple osteolytic lesions and hypercalcemia and was treated with pamidronate were studied histologically, histochemically, and ultrastructurally. In an animal experiment, cultured tumor cells (1 x 10(5)) obtained from a metastatic submandibular lymph node in the same patient were injected in the left ventricle of nude mice, and a resulting metastatic bone lesion was studied histologically and histochemically.

RESULTS

In the autopsy specimens, despite the presence of many resorption lacunae on bone surface, only a few small tartrate-resistant acid phosphatase (TRAPase)-positive cells were observed, and most of them were stained weakly and detached from the bone surface. In the animal experiment, 1 of 10 animals (10%) formed osteolytic bone metastasis, and many TRAPase-positive cells were observed histochemically.

CONCLUSIONS

Biphosphonate inhibits bone resorption induced by tumor, possibly by decreasing the number of osteoclasts and inhibiting their function.