Histomorphometric analysis of osteoclastic bone resorption in metastatic bone disease from various primary malignomas

Osteoclast Fusion: Physiological Regulation of Multinucleation through Heterogeneity-Potential Implications for Drug Sensitivity

Classically, osteoclast fusion consists of four basic steps: (1) attraction/migration, (2) recognition, (3) cell-cell adhesion, and (4) membrane fusion. In theory, this sounds like a straightforward simple linear process. However, it is not. Osteoclast fusion has to take place in a well-coordinated manner-something that is not simple. In vivo, the complex regulation of osteoclast formation takes place within the bone marrow-in time and space. The present review will focus on considering osteoclast fusion in the context of physiology and pathology. Special attention is given to: (1) regulation of osteoclast fusion in vivo, (2) heterogeneity of osteoclast fusion partners, (3) regulation of multi-nucleation, (4) implications for physiology and pathology, and (5) implications for drug sensitivity and side effects. The review will emphasize that more attention should be given to the human in vivo reality when interpreting the impact of in vitro and animal studies. This should be done in order to improve our understanding of human physiology and pathology, as well as to improve anti-resorptive treatment and reduce side effects.

Zoledronic Acid Is Not Equally Potent on Osteoclasts Generated From Different Individuals

Zoledronic acid is a bisphosphonate commonly used to treat bone diseases such as osteoporosis and cancer‐induced bone disease. Patients exhibit a variable sensitivity to zoledronic acid; the underlying explanation for this remains unclear. The objective of this study was to obtain more knowledge in this regard. We hypothesized that osteoclasts generated from different individuals would show a variable sensitivity to zoledronic acid in vitro. Osteoclasts were generated using monocytes from 46 healthy female blood donors (40 to 66 years). Matured osteoclasts were reseeded onto bone slices precoated with different concentrations of zoledronic acid. IC50 values were determined based on total eroded bone surface after 3 days of resorption. The IC50 for inhibition of osteoclastic bone resorption varied from 0.06 to 12.57μM zoledronic acid; thus, a more than 200‐fold difference in sensitivity to zoledronic acid among osteoclasts from different individuals was observed. Multiple linear regression analyses showed that the determined IC50 correlated with smoking status, and the average number of nuclei per osteoclast in vitro. Further analyses showed that: (i) increasing protein levels of mature cathepsin K in osteoclast cultures rendered the osteoclasts less sensitive to zoledronic acid; (ii) surprisingly, neither the gene nor the protein expression of farnesyl diphosphate synthase was found to correlate with the IC50; and (iii) trench‐forming osteoclasts were found to be more sensitive to zoledronic acid than pit‐forming osteoclasts within the same cell culture. Thus, we conclude that there indeed is a high degree of variation in the potency of zoledronic acid on osteoclasts when generated from different individuals. We propose that our findings can explain some of the varying clinical efficacy of zoledronic acid therapy observed in patients, and may therefore be of clinical importance, which should be investigated in a clinical trial combining in vitro and in vivo investigations. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Comparison between CEA, TPA, CA 15/3 and Hydroxyproline, Alkaline Phosphatase, Whole Body Retention of 99mTc MDP in the follow-up of Bone Metastases in Breast Cancer

The development of bone metastases in cancer can be monitored easily using three markers: 24 h urinary hydroxyproline excretion (HOP) (an index of osteoclastic activity), serum alkaline phosphatase (Alk.Ph.) (an index of osteoblastic activity) and 24 h whole body retention of 99mTc-methylene diphosphonate (WBR%) (an index of bone turnover). To evaluate the effectiveness of this group of bone tumor markers in breast cancer we compared it with the following group of three markers which are commonly used in the monitoring of breast cancer and in the follow-up of advanced disease with or without bone metastases: carcinoembryonic antigen (CEA), tissue polypeptide antigen (TPA) and breast carcinoma antigen (CA 15/3).

In 48 patients with bone metastases CEA, TPA and CA 15/3 were shown to be sensitive (79%, 85%, 90% respectively), while HOP, Alk.Ph. and WBR%, which are commonly accepted as reliable markers of bone activity, showed a lower sensitivity (67%, 46%, 75% respectively).

These results may be explained by the lack of osteoclastic or osteoblastic (or both) activity at the time of diagnosis. This explanation is supported by the fact that the bone markers HOP, Alk.Ph. and WBR% were found to be more sensitive than the others in the subsequent follow-up study.

We conclude that in our study, CEA, TPA and CA 15/3 are at first more sensitive than Alk. Ph., HOP and WBR% but during the follow-up Alk.Ph., HOP and WBR% are possibly both more specific and more sensitive

The role of the BMP signaling antagonist noggin in the development of prostate cancer osteolytic bone metastasis

Members of the BMP and Wnt protein families play a relevant role in physiologic and pathologic bone turnover. Extracellular antagonists are crucial for the modulation of their activity. Lack of expression of the BMP antagonist noggin by osteoinductive, carcinoma-derived cell lines is a determinant of the osteoblast response induced by their bone metastases. In contrast, osteolytic, carcinoma-derived cell lines express noggin constitutively. We hypothesized that cancer cell-derived noggin may contribute to the pathogenesis of osteolytic bone metastasis of solid cancers by repressing bone formation. Intra-osseous xenografts of PC-3 prostate cancer cells induced osteolytic lesions characterized not only by enhanced osteoclast-mediated bone resorption, but also by decreased osteoblast-mediated bone formation. Therefore, in this model, uncoupling of the bone remodeling process contributes to osteolysis. Bone formation was preserved in the osteolytic lesions induced by noggin-silenced PC-3 cells, suggesting that cancer cell-derived noggin interferes with physiologic bone coupling. Furthermore, intra-osseous tumor growth of noggin-silenced PC-3 cells was limited, most probably as a result of the persisting osteoblast activity. This investigation provides new evidence for a model of osteolytic bone metastasis where constitutive secretion of noggin by cancer cells mediates inhibition of bone formation, thereby preventing repair of osteolytic lesions generated by an excess of osteoclast-mediated bone resorption. Therefore, noggin suppression may be a novel strategy for the treatment of osteolytic bone metastases.

Morphological, histomorphometric, and microstructural alterations in human bone metastasis from breast carcinoma

Bone is one of the most common sites of breast cancer metastasis. Metastases are often associated with bone destruction and are a major cause of morbidity. We examined structural bone changes induced by metastatic tumor in bone biopsies from 33 patients with metastatic breast carcinoma (20 from patients with pathological femoral fracture and 13 with no fracture) and 20 normal controls. In all metastatic biopsies bone remodeling was shown to be tumor volume-dependent. Bone resorption and bone formation were biphasic with both increasing at earlier stages of metastatic bone disease and decreasing later on. A comparison of patients with fracture and no fracture did not reveal statistically significant differences in the extent of bone destruction or trabecular thinning. Bone histomorphometry showed limited ability to explain the higher bone volume loss in fracture patients (decreases of 42% and 25%, respectively, in fracture and nonfracture patients compared with controls). However, changes in bone quality, including increased disconnectivity and decreased connectivity, as evaluated by node-strut analysis, suggested that there were more structural changes in the fracture compared with the nonfracture group. The nonfracture group included six patients with no radiological evidence of bone metastasis (occult metastasis). They showed a higher tumor volume and a twofold lower eroded surface compared with the rest of the group. The decrease in bone volume (14% lower than controls) was below the limit of X-ray detection. Because we observed no increase in osteoclast-related parameters and no correlation between osteoclast surface and eroded surface, we believe that, in occult metastasis, osteoclastic bone resorption is not an important factor in overall bone resorption. Quantitatively, the eroded surface in direct contact with tumor cells was threefold higher than the osteoclast surface in occult metastasis, whereas the rest of the metastatic group (27 of 33) showed predominantly osteoclast-mediated eroded surface. Node-strut analysis on occult metastasis revealed a significant increase in disconnectivity without a concomitant significant decrease in bone volume and trabecular thinning. We conclude that, in occult metastasis, bone resorption may be more osteoclast-independent and other mechanisms involving the tumor cells may be more prevalent.

Immunolocalization of matrix metalloproteinases and their inhibitors in clinical specimens of bone metastasis from breast carcinoma

Matrix metalloproteinases (MMPs) are essential in several stages of the metastatic process, and in normal bone development and remodeling. We explored whether the interaction between tumor cells and bone leads to changes in MMP and tissue inhibitor of MMP (TIMP) expression thus affecting osteolysis in metastatic bone disease. Using immunohistochemistry we have investigated the MMP/TIMP expression in tumor cells, fibroblasts, osteoblasts and osteoclasts. Thirty one specimens of bone metastasis from breast carcinoma were stained for MMP-1, -2, -9, MT1-MMP and TIMP-1, and -2 and compared with staining in normal breast tissue, primary breast carcinoma and normal bone. Specimens came from patients in three clinical scenarios: from open biopsies without or with pathological fracture, or bone marrow biopsies containing tumor from patients with pancytopenia but without clinical evidence of osteolysis. By bone histomorphometry the latter group showed a heavy tumor load not different from the open biopsy groups but displayed little active bone resorption and low numbers of osteoclasts. Cell type-specific MMP/TIMP expression was observed and the staining patterns were comparable between the three groups of patients. Though no major differences in the MMP/TIMP staining of tumor cells and fibroblasts were observed between bone metastasis and primary tumor, we showed that tumor cells do express MMPs capable of degrading bone matrix collagen. The number and activity of osteoclasts and osteoblasts was increased dramatically in bone metastases, their MMP/TIMP profiles, however, were not different from normal bone, suggesting that the mechanism of bone degradation by osteoclasts is not different from normal bone remodelling.

Review of cellular mechanisms of tumor osteolysis

The cellular and biochemical mechanisms that direct the destruction of bone at sites of tumor osteolysis are unknown. To better understand the mechanisms through which tumors direct bone resorption, research has focused on developing in vivo and in vitro experimental models that are useful for studying this process. In vivo experimental systems have been developed that permit study of tumor osteolysis from human and murine tumors, and that permit the study of tumors that arise from (sarcoma) or can metastasize (breast cancer) to bone. Recent research has focused on three questions: (1) Are osteoclasts or tumor cells responsible for bone resorption during tumor osteolysis? (2) What are the cellular mechanisms that are responsible for bone resorption during tumor osteolysis, and (3) what are the tumor cell products that regulate the cellular mechanisms that are responsible for tumor osteolysis? It has been determined that osteoclasts are responsible for bone resorption at sites of tumor osteolysis by enhancing the binding of osteoclast to bone, by inducing osteoclastic bone resorption, and by stimulating osteoclast formation. Attempts to identify tumor cell products that regulate these cellular mechanisms are in progress, and findings suggest that production of macrophage colony stimulating factor may be required for tumor osteolysis to occur with some tumors.

Osteoclasts are required for bone tumors to grow and destroy bone

It has been hypothesized that bone resorption during tumor osteolysis is performed by osteoclasts. Data supporting this hypothesis have been provided from analysis of human biopsy specimens obtained from sites of tumor osteolysis, as well as from experimentation with in vivo animal models. Experiments in this report take this concept one step further by testing the hypothesis that osteoclasts are required for bone tumors to grow and destroy bone. To test this hypothesis, the influence of an osteolytic sarcoma tumor, NCTC clone 2472 (2472), on bone was studied in animals that are osteoclast deficient (microphthalmic, strain B6C3Fe-a/a-Mitf(mi)) but whose osteoclast deficiency can be reversed following bone marrow transplantation. Femora of these mice and unaffected wild-type siblings were injected with 10(5) 2472 cells, and after 14 days the femora were analyzed by radiographic and histomorphometric analysis. Macroscopic tumor, tumor-induced osteolysis, and increased osteoclast number were noted in femora of normal mice but not in femora of osteoclast-deficient mice (p < 0.001). Bone marrow transplantation converted osteoclast-deficient mice to mice with femora that contained osteoclasts in 4 weeks. Femora of these mice were then injected with 10(5) 2472 tumor cells; after 14 days, in contrast to the findings in the original osteoclast-deficient mice, macroscopic tumor was present, tumor-induced osteolysis was noted on roentgenograms, and osteoclast number was increased when tumor-bearing limbs were compared with sham-injected limbs (p < 0.001). These data prove the hypothesis that osteoclasts are required for 2472 tumor-induced osteolysis, and they introduce the exciting possibility that osteoclasts are also required for tumors to grow in bone.

Histomorphometric analysis of osteoclastic resorption in bone directly invaded by gingival squamous cell carcinoma

Whole frontal sections of the mandibular bone from 18 patients with gingival squamous cell carcinoma showing direct bone invasion were prepared for histometrical analysis by a non-decalcified grinding method. The osteoclast cytoplasmic area in tumor sites was larger and its relative frequency distribution was broader than that of osteoclasts in non-tumor sites. The index of bone resorption was significantly increased, while that of bone formation was decreased, in the tumor sites compared to the non-tumor sites (P < 0.01). In the tumor sites, the indices of bone resorption and formation in the group showing greatest chemotherapy and radiation therapy effects (CRE) were significantly different from those in the group with low CRE (P < 0.01). A history of irradiation therapy was associated with significantly decreased bone resorption (P < 0.05).

Localized, tumor-associated osteolysis involves the recruitment and activation of osteoclasts

The cellular and biochemical mechanisms that direct destruction of bone at the site of tumor osteolysis are unknown. In order to understand this process better, a murine model designed for the study of tumor osteolysis was developed and the influence of osteolytic and nonosteolytic tumors on bone was investigated. Tumors developed following femoral intramedullary injection of sarcoma (2472) and melanoma (G3.26) cell lines; however, only tumors from the 2472 cell line caused osteolysis. It was determined that 2472 tumor-induced osteolysis commenced 6 days after the femora had been inoculated with 2472 cells. There were more osteoclasts per millimeter of bone surface in 2472 tumor-bearing limbs (16.7 +/- 5.0) than in sham-injected limbs (3.8 +/- 0.9) (p < 0.015). In addition, an increase in the osteoclast size (area) was detected in 2472 tumor-bearing limbs: 412 +/- 65 micron2 compared with 187 +/- 17 micron2 (p < 0.01). In vitro bone resorption experiments indicated that 2472 tumor cells had a limited ability to destroy bone in comparison with macrophages and osteoclasts. Taken in total, these findings define a model that is useful for the study of tumor osteolysis, and the data from analyses of the model demonstrate that the cellular mechanisms responsible for 2472 tumor-induced osteolysis include both an increase in the number of osteoclasts and activation of mature osteoclasts.

Histomorphometric evidence for osteoclast-mediated bone resorption in metastatic breast cancer

We studied bone biopsies from 65 normocalcaemic women with breast cancer and predominantly osteolytic bone metastases in order to examine the pathophysiology of bone destruction in metastatic bone disease. Quantitative histomorphometric measurements were made at sites of tumour involvement, at sites adjacent to tumour tissue and at sites distant from tumour tissue. There were no significant differences in bone volume or in indices of bone resorption or formation between biopsies taken from sites distant from tumour and the controls. Bone resorption, as judged by eroded surface, increased progressively from bone distant from tumour to tumour-laden bone. The number of osteoclasts was significantly increased in bone immediately adjacent to tumour and within metastases. There was no decrease in the ratio of osteoclast to eroded surface in breast cancer compared to controls suggesting that increased resorption in breast cancer was mainly osteoclast mediated and locally activated by the tumour. Two thirds of the biopsies taken from tumour involved regions showed osteosclerosis with woven bone formation. The volume of the pre-existing lamellar trabecular bone was lower than normal in 75% of these biopsies, suggesting that bone resorption must have been increased before the onset of woven bone formation. Since all patients were receiving hormonal treatment or chemotherapy, it is likely that osteosclerosis at sites of previous resorption mainly resulted from the basic cancer treatment as a sign of response to treatment. Osteoclastic bone resorption was, however, not completely inhibited by the active cancer treatment.

Comparative effects of clodronate and calcitonin on bone in metastatic breast cancer: a histomorphometric study

We studied the effects of long-term treatment with clodronate, calcitonin or placebo on bone in 36 normocalcaemic women with osteolytic metastases due to breast cancer. Clodronate (1.6 g daily given to 12 patients) induced a significant decrease in osteoclast surface and osteoclast number, and a significant fall in serum calcium and urinary excretion of calcium and hydroxyproline, an effect not noted after treatment with calcitonin (100 U in 12 patients) or in 12 placebo-treated patients. Treatment with clodronate did not abnormally suppress bone turnover nor impair mineralisation, as measured by bone formation and mineral apposition rates.

Mechanisms involved in the metastasis of cancer to bone

The metastasis of cancer to bone is a frequent outcome of common malignancies and is often associated with significant morbidity due to osteolysis. Bone metastasis is also selective in that a disproportionately small number of malignancies account for the majority of tumors which spread to bone. While the mechanisms of bone destruction have been studied, those responsible for the site-specific nature of bone metastasis are poorly understood. As a metastatic target, bone is unique in that it is continuously being remodelled under the influence of local and systemic growth factors, many of which are embedded in the bone matrix. This review summarizes evidence for the hypothesis that the formation of metastatic tumors in bone is the consequence of a unique microenvironment where metastatic cells can alter the metabolism of bone, thereby regulating the release of soluble bone-derived growth factors as a consequence of bone resorption. These, in turn, can modulate the malignant phenotypic properties of receptive cells. Transforming growth factor-beta is one factor which can promote the growth and motility of Walker 256 cells, a rat cell line with a propensity to metastasize spontaneously to bone.