The effects of zoledronic acid in the bone and vasculature support of hematopoietic stem cell niches

Hematopoietic stem cells (HSC) are maintained in a tightly regulated bone microenvironment constituted by a rich milieu of cells. Bone cells such as osteoblasts are associated with niche maintenance as regulators of the endosteal microenvironment. Bone remodeling also plays a role in HSC mobilization although it is poorly defined. The effects of zoledronic acid (ZA), a potent bisphosphonate that inhibits bone resorption, were investigated on bone marrow cell populations focusing on HSCs, and the endosteal and vascular niches in bone. ZA treatment significantly increased bone volume and HSCs in both young and adult mice (4 week and 4 month old, respectively). ZA increased vessel numbers with no overall change in vascular volume in bones of young and had no effect on vasculature in adult mice. Since both young and adult mice had increased HSCs and bone mass with differing vasculature responses, this suggests that ZA indirectly supports HSCs via the osteoblastic niche and not the vascular niche. Additionally, gene expression in Lin- cells demonstrated increased expression of self-renewal-related genes Bmi1 and Ink4a suggesting a role of ZA in the modulation of cell commitment and differentiation toward a long-term self-renewing cell. Genes that support the osteoblastic niche, BMP2 and BMP6 were also augmented in ZA treated mice. In conclusion, ZA-induced HSC expansion occurs independent of the vascular niche via indirect modulation of the osteoblastic niche.

Signaling between transforming growth factor β (TGF-β) and transcription factor SNAI2 represses expression of microRNA miR-203 to promote epithelial-mesenchymal transition and tumor metastasis

TGF-β promotes tumor invasion and metastasis by inducing an epithelial-mesenchymal transition (EMT). Understanding the molecular and epigenetic mechanisms by which TGF-β induces EMT may facilitate the development of new therapeutic strategies for metastasis. Here, we report that TGF-β induced SNAI2 to promote EMT by repressing miR-203. Although miR-203 targeted SNAI2, SNAI2 induced by TGF-β could directly bind to the miR-203 promoter to inhibit its transcription. SNAI2 and miR-203 formed a double negative feedback loop to inhibit each other's expression, thereby controlling EMT. Moreover, we found that miR-203 was significantly down-regulated in highly metastatic breast cancer cells. The restoration of miR-203 in highly metastatic breast cancer cells inhibited tumor cell invasion in vitro and lung metastatic colonization in vivo by repressing SNAI2. Taken together, our results suggest that the SNAI2 and miR-203 regulatory loop plays important roles in EMT and tumor metastasis.

The multifaceted actions of PTHrP in skeletal metastasis

PTHrP, identified during the elucidation of mediators of malignancy-induced hypercalcemia, plays numerous roles in normal physiology as well as pathological conditions. Recent data support direct functions of PTHrP in metastasis, particularly from tumors with strong bone tropism. Bone provides a unique metastatic environment because of mineralization and the diverse cell populations in the bone marrow. PTHrP is a key regulator of tumor-bone interactions and regulates cells in the bone microenvironment through proliferative and prosurvival activities that prime the 'seed' and the 'soil' of the metastatic lesion. This review highlights recent findings regarding the role of PTHrP in skeletal metastasis, including direct actions in tumor cells, as well as alterations in the bone microenvironment and future perspectives involving the potential roles of PTHrP in the premetastatic niche, and tumor dormancy.

Impact of proteoglycan-4 and parathyroid hormone on articular cartilage

Proteoglycan-4 (Prg4) protects synovial joints from arthropathic changes by mechanisms that are incompletely understood. Parathyroid hormone (PTH), known for its anabolic actions in bone, increases Prg4 expression and has been reported to inhibit articular cartilage degeneration in arthropathic joints. To investigate the effect of Prg4 and PTH on articular cartilage, 16-week-old Prg4 mutant and wild-type mice were treated with intermittent PTH (1-34) or vehicle control daily for six weeks. Analyses included histology of the knee joint, micro-CT of the distal femur, and serum biochemical analysis of type II collagen fragments (CTX-II). Compared to wild-type littermates, Prg4 mutant mice had an acellular layer of material lining the surfaces of the articular cartilage and menisci, increased articular cartilage degradation, increased serum CTX-II concentrations, decreased articular chondrocyte apoptosis, increased synovium SDF-1 expression, and irregularly contoured subchondral bone. PTH-treated Prg4 mutant mice developed a secondary deposit overlaying the acellular layer of material lining the joint surfaces, but PTH-treatment did not alter signs of articular cartilage degeneration in Prg4 mutant mice. The increased joint SDF-1 levels and irregular subchondral bone found in Prg4 mutant mice introduce novel candidate mechanisms by which Prg4 protects articular cartilage.

The soluble interleukin-6 receptor is a mediator of hematopoietic and skeletal actions of parathyroid hormone

Both PTH and IL-6 signaling play pivotal roles in hematopoiesis and skeletal biology, but their interdependence is unclear. The purpose of this study was to evaluate the effect of IL-6 and soluble IL-6 receptor (sIL-6R) on hematopoietic and skeletal actions of PTH. In the bone microenvironment, PTH stimulated sIL-6R protein levels in primary osteoblast cultures in vitro and bone marrow in vivo in both IL-6(+/+) and IL-6(-/-) mice. PTH-mediated hematopoietic cell expansion was attenuated in IL-6(-/-) compared with IL-6(+/+) bone marrow, whereas sIL-6R treatment amplified PTH actions in IL-6(-/-) earlier than IL-6(+/+) marrow cultures. Blocking sIL-6R signaling with sgp130 (soluble glycoprotein 130 receptor) inhibited PTH-dependent hematopoietic cell expansion in IL-6(-/-) marrow. In the skeletal system, although intermittent PTH administration to IL-6(+/+) and IL-6(-/-) mice resulted in similar anabolic actions, blocking sIL-6R significantly attenuated PTH anabolic actions. sIL-6R showed no direct effects on osteoblast proliferation or differentiation in vitro; however, it up-regulated myeloid cell expansion and production of the mesenchymal stem cell recruiting agent, TGF-β1 in the bone marrow microenvironment. Collectively, sIL-6R demonstrated orphan function and mediated PTH anabolic actions in bone in association with support of myeloid lineage cells in the hematopoietic system.

Prostate cancer and parasitism of the bone hematopoietic stem cell niche

A subpopulation of men that appear cured of prostate cancer (PCa) develop bone metastases many years after prostatectomy. This observation indicates that PCa cells were present outside of the prostate at the time of prostatectomy and remained dormant. Several lines of evidence indicate that there are disseminated tumor cells (DTCs) in the bone marrow at the time of prostatectomy. DTCs parasitize the bone microenvironment, where they derive support and impact the microenvironment itself. These DTCs appear to be a heterogeneous population of PCa cells; however, some of them appear to have some aspects of a cancer stem cell (CSC) phenotype as they can develop into clinically detectable metastases. The concept of CSC is controversial; however, several markers of CSC have been identified for PCa, which may represent cells of either basal or luminal origin. These DTCs have now been shown to compete for the hematopoietic stem cell niche in bone, where they may be placed in a dormant state. Interaction with a variety of host factors, including cytokine and cells, may impact the metastatic development and progression, including the dormant state. For example, myeloid cells have been shown to impact both the premetastatic niche and established tumors. Understanding the concepts of how PCa successfully parasitizes the bone microenvironment is paramount toward identifying therapeutic candidates to prevent or diminish PCa bone metastases.

Prevalence of prostate cancer metastases after intravenous inoculation provides clues into the molecular basis of dormancy in the bone marrow microenvironment

Bone is the preferred metastasis site of advanced prostate cancer (PCa). Using an in vivo murine model of human PCa cell metastasis to bone, we noted that the majority of animals that develop skeletal metastasis have either spinal lesions or lesions in the bones of the hindlimb. Much less frequently, lesions develop in the bones of the forelimb. We therefore speculated whether the environment of the forelimb bones is not permissive for the growth of PCa. Consequently, data on tumor prevalence were normalized to account for the number of PCa cells arriving after intravascular injection, marrow cellularity, and number of hematopoietic stem cell niches. None of these factors were able to account for the observed differences in tumor prevalence. An analysis of differential gene and protein levels identified that growth arrest specific-6 (GAS6) levels were significantly greater in the forelimb versus hindlimb bone marrow. When murine RM1 cells were implanted into subcutaneous spaces in immune competent animals, tumor growth in the GAS6(-/-) animals was greater than in GAS6(+/+) wild-type animals. In an osseous environment, the human PC3 cell line grew significantly better in vertebral body transplants (vossicles) derived from GAS6(-/-) animals than in vossicles derived from GAS6(+/+) animals. Together, these data suggest that the differences in tumor prevalence after intravascular inoculation are a useful model to study the molecular basis of tumor dormancy. Importantly, these data suggest that therapeutic manipulation of GAS6 levels may prove useful as a therapy for metastatic disease.

Cyclophosphamide creates a receptive microenvironment for prostate cancer skeletal metastasis

A number of cancers predominantly metastasize to bone, due to its complex microenvironment and multiple types of constitutive cells. Prostate cancer especially has been shown to localize preferentially to bones with higher marrow cellularity. Using an experimental prostate cancer metastasis model, we investigated the effects of cyclophosphamide, a bone marrow-suppressive chemotherapeutic drug, on the development and growth of metastatic tumors in bone. Priming the murine host with cyclophosphamide before intracardiac tumor cell inoculation was found to significantly promote tumor localization and subsequent growth in bone. Shortly after cyclophosphamide treatment, there was an abrupt expansion of myeloid lineage cells in the bone marrow and the peripheral blood, associated with increases in cytokines with myelogenic potential such as C-C chemokine ligand (CCL)2, interleukin (IL)-6, and VEGF-A. More importantly, neutralizing host-derived murine CCL2, but not IL-6, in the premetastatic murine host significantly reduced the prometastatic effects of cyclophosphamide. Together, our findings suggest that bone marrow perturbation by cytotoxic chemotherapy can contribute to bone metastasis via a transient increase in bone marrow myeloid cells and myelogenic cytokines. These changes can be reversed by inhibition of CCL2.

The basic helix loop helix transcription factor Twist1 is a novel regulator of ATF4 in osteoblasts

Parathyroid hormone (PTH) is an essential regulator of endochondral bone formation and an important anabolic agent for the reversal of bone loss. PTH mediates its functions in part by regulating binding of the bone-related activating transcription factor 4 (ATF4) to the osteoblast-specific gene, osteocalcin. The basic helix-loop-helix (bHLH) factors Twist1 and Twist2 also regulate osteocalcin transcription in part through the interaction of the C-terminal "box" domain in these factors and Runx2. In this study, we discovered a novel function of PTH: its ability to dramatically decrease Twist1 transcription. Since ATF4 is a major regulator of the PTH response in osteoblasts, we assessed the mutual regulation between these factors and determined that Twist proteins and ATF4 physically interact in a manner that affects ATF4 DNA binding function. We mapped the interaction domain of Twist proteins to the C-terminal "box" domain and of ATF4, to the N-terminus. Furthermore, we demonstrate that Twist1 overexpression in osteoblasts attenuates ATF4 binding to the osteocalcin promoter in response to PTH. This study thus identifies Twist proteins as novel inhibitory binding partners of ATF4 and explores the functional significance of this interaction.

Nuclear localization of parathyroid hormone-related peptide confers resistance to anoikis in prostate cancer cells

Prostate cancer remains a leading cause of cancer-related death in men, largely attributable to distant metastases, most frequently to bones. Despite intensive investigations, molecular mechanisms underlying metastasis are not completely understood. Among prostate cancer-derived factors, parathyroid hormone-related peptide (PTHrP), first discovered as an etiologic factor for malignancy-induced hypercalcemia, regulates many cellular functions critical to tumor growth, angiogenesis, and metastasis. In this study, the role of PTHrP in tumor cell survival from detachment-induced apoptosis (i.e. anoikis) was investigated. Reduction of PTHLH (encoding PTHrP) gene expression in human prostate cancer cells (PC-3) increased the percentage of apoptotic cells when cultured in suspension. Conversely, overexpression of PTHrP protected prostate cancer cells (Ace-1 and LNCaP, both typically expressing low or undetectable basal PTHrP) from anoikis. Overexpression of nuclear localization signal (NLS)-defective PTHrP failed to protect cells from anoikis, suggesting that PTHrP-dependent protection from anoikis is an intracrine event. A PCR-based apoptosis-related gene array showed that detachment increased expression of the TNF gene (encoding the proapoptotic protein tumor necrosis factor-α) fourfold greater in PTHrP-knockdown PC-3 cells than in control PC-3 cells. In parallel, TNF gene expression was significantly reduced in PTHrP-overexpressing LNCaP cells, but not in NLS-defective PTHrP overexpressing LNCaP cells, when compared with control LNCaP cells. Subsequently, in a prostate cancer skeletal metastasis mouse model, PTHrP-knockdown PC-3 cells resulted in significantly fewer metastatic lesions compared to control PC-3 cells, suggesting that PTHrP mediated antianoikis events in the bloodstream. In conclusion, nuclear localization of PTHrP confers prostate cancer cell resistance to anoikis, potentially contributing to prostate cancer metastasis.

Twenty-five years of PTHrP progress: from cancer hormone to multifunctional cytokine

Twenty-five years ago a "new" protein was identified from cancers that caused hypercalcemia. It was credited for its ability to mimic parathyroid hormone (PTH), and hence was termed parathyroid hormone-related protein (PTHrP). Today it is recognized for its widespread distribution, its endocrine, paracrine, and intracrine modes of action driving numerous physiologic and pathologic conditions, and its central role in organogenesis. The multiple biological activities within a complex molecule with paracrine modulation of adjacent target cells present boundless possibilities. The protein structure of PTHrP has been traced, dissected, and deleted comprehensively and conditionally, yet numerous questions lurk in its past that will carry into the future. Issues of the variable segments of the protein, including the enigmatic nuclear localization sequence, are only recently being clarified. Aspects of PTHrP production and action in the menacing condition of cancer are emerging as dichotomies that may represent intended temporal actions of PTHrP. Relative to PTH, the hormone regulating calcium homeostasis, PTHrP "controls the show" locally at the PTH/PTHrP receptor throughout the body. Great strides have been made in our understanding of PTHrP actions, yet years of exciting investigation and discovery are imminent. © 2012 American Society for Bone and Mineral Research.

Systemic Teriparatide Administration Promotes Osseous Regeneration of an Intrabony Defect: A Case Report

INTRODUCTION

Teriparatide comprises the first 34 amino acids of parathyroid hormone and is a systemic anabolic agent that is Food and Drug Administration approved for the treatment of osteoporosis but not for periodontitis. To our knowledge, this is the first clinical case report to document the treatment of a patient with severe periodontitis using an open-flap debridement procedure in conjunction with teriparatide.

CASE PRESENTATION

A 45-year-old female patient was diagnosed with severe chronic periodontitis, including the presence of an intrabony defect on tooth #6. She received open-flap debridement surgery in conjunction with daily systemic administration of 20 μg teriparatide, oral vitamin D, and calcium supplements for 6 weeks. Radiographic, clinical, gingival crevicular fluid (pyridinoline cross-linked carboxy-terminal propeptide of type I procollagen, procollagen type 1 N-propeptide, and osteocalcin), and serum parameters (parathyroid hormone, bone alkaline phosphatase, calcium, and 25-hydroxyvitamin D) were assessed. Treatment outcomes were evaluated over 4 years, with successful radiographic and clinical results throughout the follow-up period.

CONCLUSION

Teriparatide administration in conjunction with traditional open-flap debridement surgery offers potential for the treatment of severe intrabony defects resulting from chronic periodontitis.

Amelioration of type I diabetes-induced osteoporosis by parathyroid hormone is associated with improved osteoblast survival

Type 1 diabetic osteoporosis results from impaired osteoblast activity and death. Therefore, anti-resorptive treatments may not effectively treat bone loss in this patient population. Intermittent parathyroid hormone (PTH) treatment stimulates bone remodeling and increases bone density in healthy subjects. However, PTH effects may be limited in patients with diseases that interfere with its signaling. Here, we examined the ability of 8 and 40 µg/kg intermittent PTH to counteract diabetic bone loss. PTH treatment reduced fat pad mass and blood glucose levels in non-diabetic PTH-treated mice, consistent with PTH-affecting glucose homeostasis. However, PTH treatment did not significantly affect general body parameters, including the blood glucose levels, of type 1 diabetic mice. We found that the high dose of PTH significantly increased tibial trabecular bone density parameters in control and diabetic mice, and the lower dose elevated trabecular bone parameters in diabetic mice. The increased bone density was due to increased mineral apposition and osteoblast surface, all of which are defective in type 1 diabetes. PTH treatment suppressed osteoblast apoptosis in diabetic bone, which could further contribute to the bone-enhancing effects. In addition, PTH treatment (40 µg/kg) reversed preexisting bone loss from diabetes. We conclude that intermittent PTH may increase type 1 diabetic trabecular bone volume through its anabolic effects on osteoblasts.

Pre-clinical mouse models of human prostate cancer and their utility in drug discovery

In vivo animal experiments are essential to current prostate cancer research, and are particularly critical to studying interactions between tumor cells and their microenvironment. Numerous pre-clinical animal models of prostate cancer are currently available, including transgenic mouse models and human prostate cancer xenograft mouse models. In contrast to transgenic mouse models producing more heterogeneous cohorts of tumors, xenograft mouse models provide more controlled approaches. This unit describes the detailed procedures necessary to establish several distinct pre-clinical mouse models of human prostate cancer, including an orthotopic prostate xenograft model, an orthotopic bone metastasis model, an experimental metastasis model of intra-cardiac injection, and a vossicle model of tumor-bone interaction.

Proteoglycan 4: a dynamic regulator of skeletogenesis and parathyroid hormone skeletal anabolism

Proteoglycan 4 (Prg4), known for its lubricating and protective actions in joints, is a strong candidate regulator of skeletal homeostasis and parathyroid hormone (PTH) anabolism. Prg4 is a PTH-responsive gene in bone and liver. Prg4 null mutant mice were used to investigate the impact of proteoglycan 4 on skeletal development, remodeling, and PTH anabolic actions. Young Prg4 mutant and wild-type mice were administered intermittent PTH(1-34) or vehicle daily from 4 to 21 days. Young Prg4 mutant mice had decreased growth plate hypertrophic zones, trabecular bone, and serum bone formation markers versus wild-type mice, but responded with a similar anabolic response to PTH. Adult Prg4 mutant and wild-type mice were administered intermittent PTH(1-34) or vehicle daily from 16 to 22 weeks. Adult Prg4 mutant mice had decreased trabecular and cortical bone, and blunted PTH-mediated increases in bone mass. Joint range of motion and animal mobility were lower in adult Prg4 mutant versus wild-type mice. Adult Prg4 mutant mice had decreased marrow and liver fibroblast growth factor 2 (FGF-2) mRNA and reduced serum FGF-2, which were normalized by PTH. A single dose of PTH decreased the PTH/PTHrP receptor (PPR), and increased Prg4 and FGF-2 to a similar extent in liver and bone. Proteoglycan 4 supports endochondral bone formation and the attainment of peak trabecular bone mass, and appears to support skeletal homeostasis indirectly by protecting joint function. Bone- and liver-derived FGF-2 likely regulate proteoglycan 4 actions supporting trabeculae formation. Blunted PTH anabolic responses in adult Prg4 mutant mice are associated with altered biomechanical impact secondary to joint failure.

An irradiation-altered bone marrow microenvironment impacts anabolic actions of PTH

PTH stimulates bone formation and increases hematopoietic stem cells through mechanisms as yet uncertain. The purpose of this study was to identify mechanisms by which PTH links actions on cells of hematopoietic origin with osteoblast-mediated bone formation. C57B6 mice (10 d) were nonlethally irradiated and then administered PTH for 5-20 d. Irradiation reduced bone marrow cellularity with retention of cells lining trabeculae. PTH anabolic activity was greater in irradiated vs. nonirradiated mice, which could not be accounted for by altered osteoblasts directly or osteoclasts but instead via an altered bone marrow microenvironment. Irradiation increased fibroblast growth factor 2, TGFβ, and IL-6 mRNA levels in the bone marrow in vivo. Irradiation decreased B220 cell numbers, whereas the percent of Lin(-)Sca-1(+)c-kit(+) (LSK), CD11b(+), CD68(+), CD41(+), Lin(-)CD29(+)Sca-1(+) cells, and proliferating CD45(-)Nestin(+) cells was increased. Megakaryocyte numbers were reduced with irradiation and located more closely to trabecular surfaces with irradiation and PTH. Bone marrow TGFβ was increased in irradiated PTH-treated mice, and inhibition of TGFβ blocked the PTH augmentation of bone in irradiated mice. In conclusion, irradiation created a permissive environment for anabolic actions of PTH that was TGFβ dependent but osteoclast independent and suggests that a nonosteoclast source of TGFβ drives mesenchymal stem cell recruitment to support PTH anabolic actions.

Roles of bone marrow cells in skeletal metastases: no longer bystanders

Bone serves one of the most congenial metastatic microenvironments for multiple types of solid tumors, but its role in this process remains under-explored. Among many cell populations constituting the bone and bone marrow microenvironment, osteoblasts (originated from mesenchymal stem cells) and osteoclasts (originated from hematopoietic stem cells) have been the main research focus for pro-tumorigenic roles. Recently, increasing evidence further elucidates that hematopoietic lineage cells as well as stromal cells in the bone marrow mediate distinct but critical functions in tumor growth, metastasis, angiogenesis and apoptosis in the bone microenvironment. This review article summarizes the key evidence describing differential roles of bone marrow cells, including hematopoietic stem cells (HSCs), megakaryocytes, macrophages and myeloid-derived suppressor cells in the development of metastatic bone lesions. HSCs promote tumor growth by switching on angiogenesis, but at the same time compete with metastatic tumor cells for occupancy of osteoblastic niche. Megakaryocytes negatively regulate the extravasating tumor cells by inducing apoptosis and suppressing proliferation. Macrophages and myeloid cells have pro-tumorigenic roles in general, suggesting a similar effect in the bone marrow. Hematopoietic and stromal cell populations in the bone marrow, previously considered as simple by-standers in the context of tumor metastasis, have distinct and active roles in promoting or suppressing tumor growth and metastasis in bone. Further investigation on the extended roles of bone marrow cells will help formulate better approaches to treatment through improved understanding of the metastatic bone microenvironment.

Development of a brain metastatic canine prostate cancer cell line

BACKGROUND

Prostate cancer in men has a high mortality and morbidity due to metastatic disease. The pathobiology of prostate cancer metastasis is not well understood and cell lines and animal models that recapitulate the complex nature of the disease are needed. Therefore, the goal of the study was to establish and characterize a new prostate cancer line derived from a dog with spontaneous prostate cancer.

METHODS

A new cell line (Leo) was derived from a dog with spontaneous prostate cancer. Immunohistochemistry and PCR were used to characterize the primary prostate cancer and xenografts in nude mice. Subcutaneous tumor growth and metastases in nude mice were evaluated by bioluminescent imaging, radiography and histopathology. In vitro chemosensitivity of Leo cells to therapeutic agents was measured.

RESULTS

Leo cells expressed the secretory epithelial cytokeratins (CK)8, 18, and ductal cell marker, CK7. The cell line grew in vitro (over 75 passages) and was tumorigenic in the subcutis of nude mice. Following intracardiac injection, Leo cells metastasized to the brain, spinal cord, bone, and adrenal gland. The incidence of metastases was greatest to the central nervous system (80%) with a lower incidence to bone (20%) and the adrenal glands (16%). In vitro chemosensitivity assays demonstrated that Leo cells were sensitive to Velcade and an HDAC-42 inhibitor with IC(50) concentrations of 1.9 nm and 0.95 µm, respectively.

CONCLUSION

The new prostate cancer cell line (Leo) will be a valuable model to investigate the mechanisms of the brain and bone metastases.

Osteoclasts and odontoclasts: signaling pathways to development and disease

Osteoclasts are cells essential for physiologic remodeling of bone and also play important physiologic and pathologic roles in the dentofacial complex. Osteoclasts and odontoclasts are necessary for tooth eruption yet result in dental compromise when associated with permanent tooth internal or external resorption. The determinants that separate their physiologic and pathologic roles are not well delineated. Clinical cases of primary eruption failure and root resorption are challenging to treat. Mineralized tissue resorbing cells undergo a fairly well characterized series of differentiation stages driven by transcriptional mediators. Signal transduction via cytokines and integrin-mediated events comprise the detailed pathways operative in osteo/odontoclastic cells and may provide insights to their targeted regulation. A better understanding of the unique aspects of osteoclastogenesis and osteo/odontoclast function will facilitate effective development of new therapeutic approaches. This review presents the clinical challenges and delves into the cellular and biochemical aspects of the unique cells responsible for resorption of mineralized tissues of the craniofacial complex.

Drugs which inhibit osteoclast function suppress tumor growth through calcium reduction in bone

Prostate carcinoma frequently metastasizes to bone where the microenvironment facilitates its growth. Inhibition of bone resorption is effective in reducing tumor burden and bone destruction in prostate cancer. However, whether drugs that inhibit osteoclast function inhibit tumor growth independent of inhibition of bone resorption is unclear. Calcium is released during bone resorption and the calcium sensing receptor is an important regulator of cancer cell proliferation. The goal of this investigation was to elucidate the role of calcium released during bone resorption and to determine the impact of drugs which suppress bone resorption on tumor growth in bone. To compare tumor growth in a skeletal versus non-skeletal site, equal numbers of canine prostate cancer cells expressing luciferase (ACE-1(luc)) were inoculated into a simple collagen matrix, neonatal mouse vertebrae (vossicles), human de-proteinized bone, or a mineralized collagen matrix. Implants were placed subcutaneously into athymic mice. Luciferase activity was used to track tumor growth weekly, and at one month tumors were dissected for histologic analysis. Luciferase activity and tumor size were greater in vossicles, de-proteinized bone and mineralized collagen matrix versus non-mineralized collagen implants. The human osteoblastic prostate carcinoma cell line C4-2b also grew better in a mineral rich environment with a greater proliferation of C4-2b cells reflected by Ki-67 staining. Zoledronic acid (ZA), a bisphosphonate, and recombinant OPG-Fc, a RANKL inhibitor, were administered to mice bearing vertebral implants (vossicles) containing ACE-1 osteoblastic prostate cancer cells. Vossicles or collagen matrices were seeded with ACE-1(luc) cells subcutaneously in athymic mice (2 vossicles, 2 collagen implants/mouse). Mice received ZA (5 μg/mouse, twice/week), (OPG-Fc at 10mg/kg, 3 times/week) or vehicle, and luciferase activity was measured weekly. Histologic analysis of the tumors, vossicles and endogenous bones and serum biochemistry were performed. Antiresorptive administration was associated with decreased serum TRAP5b, reduced osteoclast numbers, and increased tibia and vossicle bone areas. ZA significantly decreased bone marrow calcium concentrations without affecting serum calcium. ZA and OPG-Fc significantly inhibited tumor growth in bone but not in collagen implants. In conclusion, the inhibitory effects of ZA or OPG-Fc on prostate tumor growth in bone are mediated via blocking bone resorption and calcium release from bone.

Cancer to bone: a fatal attraction

When cancer metastasizes to bone, considerable pain and deregulated bone remodelling occurs, greatly diminishing the possibility of cure. Metastasizing tumour cells mobilize and sculpt the bone microenvironment to enhance tumour growth and to promote bone invasion. Understanding the crucial components of the bone microenvironment that influence tumour localization, along with the tumour-derived factors that modulate cellular and protein matrix components of bone to favour tumour expansion and invasion, is central to the pathophysiology of bone metastases. Basic findings of tumour-bone interactions have uncovered numerous therapeutic opportunities that focus on the bone microenvironment to prevent and treat bone metastases.

The impact of vitamin D status on periodontal surgery outcomes

Vitamin D regulates calcium and immune function. While vitamin D deficiency has been associated with periodontitis, little information exists regarding its effect on wound healing and periodontal surgery outcomes. This longitudinal clinical trial assessed outcomes of periodontal surgery and teriparatide administration in vitamin-D-sufficient and -insufficient individuals. Forty individuals with severe chronic periodontitis received periodontal surgery, daily calcium and vitamin D supplements, and self-administered teriparatide or placebo for 6 wks to correspond with osseous healing time. Serum 25(OH)D was evaluated at baseline, 6 wks, and 6 mos post-surgery. Clinical and radiographic outcomes were evaluated over 1 yr. Placebo patients with baseline vitamin D deficiency [serum 25(OH)D, 16-19 ng/mL] had significantly less clinical attachment loss (CAL) gain (-0.43 mm vs. 0.92 mm, p < 0.01) and probing depth (PPD) reduction (0.43 mm vs. 1.83 mm, p < 0.01) than vitamin-D-sufficient individuals. Vitamin D levels had no significant impact on CAL and PPD improvements in teriparatide patients at 1 yr, but infrabony defect resolution was greater in teriparatide-treated vitamin-D-sufficient vs. -deficient individuals (2.05 mm vs. 0.87 mm, p = 0.03). Vitamin D deficiency at the time of periodontal surgery negatively affects treatment outcomes for up to 1 yr. Analysis of these data suggests that vitamin D status may be critical for post-surgical healing. (ClinicalTrials.gov number, CT00277706).

Dickkopf-1 (DKK-1) stimulated prostate cancer growth and metastasis and inhibited bone formation in osteoblastic bone metastases

BACKGROUND

Osteoblastic bone metastasis is the predominant phenotype observed in prostate cancer patients and is associated with high patient mortality and morbidity. However, the mechanisms determining the development of this phenotype are not well understood. Prostate cancer cells secrete several osteogenic factors including Wnt proteins, which are not only osteoinductive but also oncogenic. Therefore, the purpose of the study was to investigate the contribution of the Wnt signaling pathway in prostate cancer growth, incidence of bone metastases, and osteoblastic phenotype of bone metastases. The strategy involved overexpressing the Wnt antagonist, DKK-1, in the mixed osteoblastic and osteolytic Ace-1 prostate cancer cells.

METHODS

Ace-1 prostate cancer cells stably expressing human DKK-1 or empty vector were established and transduced with lentiviral yellow fluorescent protein (YFP)-luciferase (Luc). The Ace-1/vector(YFP-LUC) and Ace-1/DKK-1(YFP-LUC) cells were injected subcutaneously, intratibially, or in the left cardiac ventricle in athymic mice.

RESULTS

Unexpectedly, DKK-1 significantly increased Ace-1 subcutaneous tumor mass and the incidence of bone metastases after intracardiac injection of Ace-1 cells. DKK-1 increased Ace-1 tumor growth associated with increased phospho46 c-Jun amino-terminal kinase by the Wnt noncanonical pathway. As expected, DKK-1 decreased the Ace-1 osteoblastic phenotype of bone metastases, as confirmed by radiographic, histopathologic, and microcomputed tomographic analysis. DKK-1 decreased osteoblastic activity via the Wnt canonical pathway evidenced by an inhibition of T-cell factor activity in murine osteoblast precursor ST2 cells.

CONCLUSION

The present study showed that DKK-1 is a potent inhibitor of bone growth in prostate cancer-induced osteoblastic metastases.

Inhibitory effects of megakaryocytic cells in prostate cancer skeletal metastasis

Prostate cancer cells commonly spread through the circulation, but few successfully generate metastatic foci in bone. Osteoclastic cellular activity has been proposed as an initiating event for skeletal metastasis. Megakaryocytes (MKs) inhibit osteoclastogenesis, which could have an impact on tumor establishment in bone. Given the location of mature MKs at vascular sinusoids, they may be the first cells to physically encounter cancer cells as they enter the bone marrow. Identification of the interaction between MKs and prostate cancer cells was the focus of this study. K562 (human MK precursors) and primary MKs derived from mouse bone marrow hematopoietic precursor cells potently suppressed prostate carcinoma PC-3 cells in coculture. The inhibitory effects were specific to prostate carcinoma cells and were enhanced by direct cell-cell contact. Flow cytometry for propidium iodide (PI) and annexin V supported a proapoptotic role for K562 cells in limiting PC-3 cells. Gene expression analysis revealed reduced mRNA levels for cyclin D1, whereas mRNA levels of apoptosis-associated specklike protein containing a CARD (ASC) and death-associated protein kinase 1 (DAPK1) were increased in PC-3 cells after coculture with K562 cells. Recombinant thrombopoietin (TPO) was used to expand MKs in the marrow and resulted in decreased skeletal lesion development after intracardiac tumor inoculation. These novel findings suggest a potent inhibitory role of MKs in prostate carcinoma cell growth in vitro and in vivo. This new finding, of an interaction of metastatic tumors and hematopoietic cells during tumor colonization in bone, ultimately will lead to improved therapeutic interventions for prostate cancer patients.

Teriparatide and osseous regeneration in the oral cavity

BACKGROUND

Intermittent administration of teriparatide, a drug composed of the first 34 amino acids of parathyroid hormone, has anabolic effects on bone. Although teriparatide has been evaluated for the treatment of osteoporosis and for the healing of fractures, clinical trials evaluating it for the treatment of osseous conditions of the oral cavity in humans are lacking.

METHODS

A total of 40 patients with severe, chronic periodontitis underwent periodontal surgery and received daily injections of teriparatide (20 μg) or placebo, along with oral calcium (1000 mg) and vitamin D (800 IU) supplementation, for 6 weeks. The patients were followed for 1 year. The primary outcome was a radiographic linear measurement of alveolar bone level. Secondary outcomes included clinical variables, bone turnover markers in serum and oral fluid, systemic bone mineral density, and quality of life.

RESULTS

Radiographic linear resolution of osseous defects was significantly greater after teriparatide therapy than after placebo beginning at 6 months, with a mean linear gain in bone at 1 year of 29% as compared with 3% (P<0.001). Clinical improvement was greater in patients taking teriparatide than in those taking placebo, with a reduction in periodontal probing depth of 33% versus 20% (2.42 mm vs. 1.32 mm) and a gain in clinical attachment level of 22% versus 7% (1.58 mm vs. 0.42 mm) in target lesions at 1 year (P = 0.02 for both comparisons). No serious adverse events were reported; however, the number of patients in the study was small. No significant differences were noted with respect to the other variables that were assessed.

CONCLUSIONS

Teriparatide, as compared with placebo, was associated with improved clinical outcomes, greater resolution of alveolar bone defects, and accelerated osseous wound healing in the oral cavity. Teriparatide may offer therapeutic potential for localized bone defects in the jaw. (Funded by the National Institutes of Health and others; ClinicalTrials.gov number, NCT00277706 .).

Effect of zoledronate on oral wound healing in rats

PURPOSE

Osteonecrosis of the jaw (ONJ) is a growing concern in patients who receive bisphosphonates that target osteoclasts. As osteoclasts play multifunctional roles in the bone marrow, their suppression likely affects bone homeostasis and alters wound healing of the jaw. The objective was to delineate the impact of osteoclast suppression in the bone marrow and wound healing of the jaw.

EXPERIMENTAL DESIGN

Zoledronate was administered to senile rats for 14 weeks. A portion of the gingiva was removed to denude the palatal bone. Gene expression in the bone marrow was assessed and histologic sections were analyzed to determine the wound healing status.

RESULTS

Angiogenesis-related genes, CD31 and VEGF-A, were not altered by zoledronate. VEGF-C, which plays a role in lymphangiogenesis, was suppressed. There was a decrease in gene expression of Tcirg1 and MMP-13. Bone denudation caused extensive osteocyte death indicative of bone necrosis. In zoledronate-treated rats, the necrotic bone was retained in the wound while, in controls, osteoclastic resorption of the necrotic bone was prominent. Even though large necrotic bone areas existed in zoledronate-treated rats, overlaying soft tissue healed clinically. Immunohistochemical staining showed rich vascularity in the overlaying soft tissue.

CONCLUSIONS

Zoledronate therapy impacts bone marrow by suppressing genes associated with lymphangiogenesis and tissue remodeling, such as VEGF-C and MMP-13. Zoledronate was associated with impaired osseous wound healing but had no effect on angiogenic markers in the bone marrow or soft tissue wound healing. Zoledronate selectively blunts healing in bone but does not affect soft tissue healing in the oral cavity.

c-Maf and you won't see fat

Osteoporosis is a common, age-related bone disease that results from an imbalance between the processes of bone formation and bone resorption, resulting in reduced bone mass and increased risk of fracture. Mesenchymal stem cells have the capacity to differentiate into osteoblastic and adipogenic lineages; recent research suggests that the switch between these two fates may be key to the decreased bone density that occurs with aging. In this issue, Nishikawa et al. demonstrate that the basic leucine-zipper transcription factor Maf (also known as c-Maf) is central to osteoblast lineage commitment. In addition, they find that increased oxidative stress - as occurs with aging - decreases Maf expression. This work advances understanding of the transcriptional regulation of cell fate decisions and may help direct the development of new therapies to fight age-related bone loss.

Abstract 5039: Novel insight into mechanisms of parathyroid hormone-related protein (PTHrP) action in prostate cancer growth and skeletal metastasis: Altered anoikis and angiogenesis

PTHrP was first discovered as an etiologic factor in malignancy-induced hypercalcemia, and was later shown to regulate many important functions in tumor progression, particularly in prostate and breast cancer skeletal metastasis. However, the underlying mechanisms are understudied and controversial. In this study, the roles of PTHrP in prostate cancer growth and skeletal metastasis were examined in vitro and in vivo, focusing on anoikis and angiogenesis.

PC-3 (expressing high endogenous PTHrP) and ACE-1 (expressing low endogenous PTHrP) prostate carcinoma cells were used in these studies. Luciferase-labeled human prostate cancer cells (PC-3L) were transduced with PTHrP-directed shRNA lentiviral vectors or empty vector (EV), and stable clones (PC-3L-shPTHrP and PC-3L-EV, respectively) were subsequently isolated and expanded. ACE-1 cells were stably transfected with a PTHrP overexpression vector. For the in vitro anoikis assay, cells were seeded in agarose-covered plates to prevent attachment and harvested 12 hours later for flow cytometric analysis of Annexin V+ apoptotic cells. For in vivo experiments, PC-3L-shPTHrP or PC-3L-EV cells were transplanted into male athymic mice via subcutaneous (to examine tumor growth and angiogenesis) or intra-cardiac (to examine metastasis) routes. Tumor growth and/or metastasis were monitored by weekly bioluminescence imaging. Subcutaneous tumor tissues were harvested for determination of angiogenesis (via mean vessel density quantification) and recruitment of hematopoietic stem/progenitor cells to the tumor (via enumeration of Lin−CD150+ cells).

Reduction of PTHrP expression in PC-3L cells resulted in a significant increase in detachment-induced apoptosis (i.e. anoikis) in vitro that was rescued when PTHrP was overexpressed. In addition, intra-cardiac injection of PC-3L-shPTHrP clones resulted in significantly fewer tumor cells (as quantified by bioluminescence) localized in the mandibular and hind limb skeletal regions at an early time point (day-5) compared to the empty vector control, suggesting an anoikis-mediated event in the bloodstream. PC-3L-shPTHrP cells were also found to produce smaller subcutaneous tumors in vivo compared to PC-3L-EV control tumors, while the in vitro proliferation rate was not affected. Interestingly, PTHrP-knockdown tumor tissues resulted in a significant reduction in CD31+ mean vessel density, and significantly fewer Lin−CD150+ stem cells in the tumor tissues compared with control tumors.

In conclusion, these findings suggest that tumor-derived PTHrP contributes to prostate cancer skeletal metastasis by conferring resistance to anoikis. Additionally, PTHrP promotes tumor growth in vivo at least partially by increasing angiogenesis and recruitment of hematopoietic stem/progenitor cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5039.

The midregion, nuclear localization sequence, and C terminus of PTHrP regulate skeletal development, hematopoiesis, and survival in mice

The functions of parathyroid hormone-related protein (PTHrP) on morphogenesis, cell proliferation, apoptosis, and calcium homeostasis have been attributed to its N terminus. Evidence suggests that many of these effects are not mediated by the N terminus but by the midregion, a nuclear localization sequence (NLS), and C terminus of the protein. A knock-in mouse lacking the midregion, NLS, and C terminus of PTHrP (Pthrp(Delta/Delta)) was developed. Pthrp(Delta/Delta) mice had craniofacial dysplasia, chondrodysplasia, and kyphosis, with most mice dying by d 5 of age. In bone, there were fewer chondrocytes and osteoblasts per area, bone mass was decreased, and the marrow was less cellular, with erythroid hypoplasia. Cellular proliferation was impaired, and apoptosis was increased. Runx2, Ocn, Sox9, Crtl1, beta-catenin, Runx1, ephrin B2, cyclin D1, and Gata1 were underexpressed while P16/Ink4a, P21, GSK-3beta, Il-6, Ffg3, and Ihh were overexpressed. Mammary gland development was aberrant, and energy metabolism was deregulated. These results establish that the midregion, NLS, and C terminus of PTHrP are crucial for the commitment of osteogenic and hematopoietic precursors to their lineages, and for survival, and many of the effects of PTHrP on development are not mediated by its N terminus. The down-regulation of Runx1, Runx2, and Sox9 indicates that PTHrP is a modulator of transcriptional activation during stem cell commitment.

Case report of implant placement in a patient with Paget's disease on bisphosphonate therapy

Paget's disease is the second most common bone disease following osteoporosis. Paget's disease is characterized by abnormal resorption and deposition of bone. The most widely used agents to treat Paget's disease are bisphosphonates. Bisphosphonates have been given much attention due to reports of osteonecrosis associated with their use. This case report demonstrates the placement of implants in a patient with Paget's disease on a six-month-course of bisphosphonate therapy. The patient had post-operative complications and a secondary placement but no signs of bisphosphonate-associated osteonecrosis of the jaw (ONJ). Although complications may exist, the placement of implants in a patient with Paget's disease taking bisphosphonates can have a positive outcome.

JunB as a potential mediator of PTHrP actions: new gene targets Ephrin B1 and VCAM-1

Parathyroid hormone-related protein (PTHrP) is an integral mediator of physiologic and pathologic processes and has demonstrated actions in the periodontium. PTHrP functions via AP-1, and specifically through JunB. This study identified JunB-dependent downstream mediators of PTHrP using OCCM cementoblastic transfectants with JunB over- or reduced expression. Over-expressing cells showed an increase in proliferation, while the opposite was seen in siRNA transfected cells. Microarray analysis of over-expressing cells revealed more than 1000 regulated genes. Three genes were investigated in more detail. The PTH/PTHrP receptor (PTHR1) and ephrin B1 (EfnB1) were down-regulated, and vascular cell adhesion molecule-1 (VCAM-1) was up-regulated with JunB over-expression. JunB siRNA transfectants had increased PTHR1, but reduced ephrin B1 and unaltered VCAM-1 in vitro. To validate these targets, parental OCCM cells and primary osteoblasts were treated with PTHrP, resulting in reduced PTHR1 and ephrin B1, and increased VCAM-1. Cell transfectants were implanted subcutaneously in vivo, and microarray analysis and RT-PCR performed. Over-expression of JunB down-regulated PTHR1 and ephrin B1, and increased VCAM-1. JunB siRNA transfectant implants had increased PTHR1 and ephrin B1, but no altered VCAM-1. These data highlight new gene targets for PTHrP and indicate JunB is a critical mediator of PTHrP actions.

A destructive cascade mediated by CCL2 facilitates prostate cancer growth in bone

Monocyte chemoattractant protein 1 (CCL2) is a recently identified prominent regulator of prostate cancer growth and metastasis. The purpose of this study was to investigate the mechanistic role of CCL2 in prostate cancer growth in bone. The present study found that CCL2 was up-regulated in osteoblasts (3-fold by PC-3 and 2-fold by VCaP conditioned medium) and endothelial cells (2-fold by PC-3 and VCaP conditioned medium). Parathyroid hormone-related protein (PTHrP) treatment of osteoblastic cells up-regulated CCL2 and was blocked by a PTHrP antagonist, suggesting that prostate cancer-derived PTHrP plays an important role in elevation of osteoblast-derived CCL2. CCL2 indirectly increased blood vessel formation in endothelial cells through vascular endothelial growth factor-A, which was up-regulated 2-fold with administration of CCL2 in prostate cancer cells. In vivo, anti-CCL2 treatment suppressed tumor growth in bone. The decreased tumor burden was associated with decreased bone resorption (serum TRAP5b levels were decreased by 50-60% in anti-CCL2-treated animals from VCaP or PC-3 cell osseous lesions) and microvessel density was decreased by 70% in anti-CCL2-treated animals with bone lesions from VCaP cells. These data suggest that a destructive cascade is driven by tumor cell-derived, PTHrP-mediated induction of CCL2, which facilitates tumor growth via enhanced osteoclastic and endothelial cell activity in bone marrow. Taken together, CCL2 mediates the interaction between tumor-derived factors and host-derived chemokines acting in cooperation to promote skeletal metastasis.

Tumor expressed PTHrP facilitates prostate cancer-induced osteoblastic lesions

Expression of parathyroid hormone-related protein (PTHrP) correlates with prostate cancer skeletal progression; however, the impact of prostate cancer-derived PTHrP on the microenvironment and osteoblastic lesions in skeletal metastasis has not been completely elucidated. In this study, PTHrP overexpressing prostate cancer clones were stably established by transfection of full length rat PTHrP cDNA. Expression and secretion of PTHrP were verified by western blotting and IRMA assay. PTHrP overexpressing prostate cancer cells had higher growth rates in vitro, and generated larger tumors when inoculated subcutaneously into athymic mice. The impact of tumor-derived PTHrP on bone was investigated using a vossicle co-implant model. Histology revealed increased bone mass adjacent to PTHrP overexpressing tumor foci, with increased osteoblastogenesis, osteoclastogenesis and angiogenesis. In vitro analysis demonstrated pro-osteoclastic and pro-osteoblastic effects of PTHrP. PTHrP enhanced proliferation of bone marrow stromal cells and early osteoblast differentiation. PTHrP exerted a pro-angiogenic effect indirectly, as it increased angiogenesis but only in the presence of bone marrow stromal cells. These data suggest PTHrP plays a role in tumorigenesis in prostate cancer, and that PTHrP is a key mediator for communication and interactions between prostate cancer and the bone microenvironment. Prostate cancer-derived PTHrP is actively involved in osteoblastic skeletal progression.

Osteonecrosis of the jaw: an update and review of recommendations

Bisphosphonates have had a very positive impact as therapeutic agents for cancer and osteoporosis, but have also been associated with osteonecrosis of the jaw (ONJ) which has emerged as an idiosyncratic oral complication. Bisphosphonate-associated ONJ has generated wide attention despite its considerably rare occurrence. Many speculations exist as to why bisphosphonates may increase the incidence of ONJ. The American Society for Bone and Mineral Research established a task force on bisphosphonate-associated ONJ and recently released a summary report of their findings. A case definition delineated a confirmed case of ONJ as 'an area of exposed bone in the maxillofacial region that did not heal within 8 weeks after identification by a health care provider, in a patient who was receiving or had been exposed to a bisphosphonate and had not had radiation therapy to the craniofacial region'. Treatment recommendations have been developed by the American Dental Association, the American Association of Oral and Maxillofacial Surgeons and the American Society for Bone and Mineral Research. Considering the scientific evidence, little is known about the true incidence and pathophysiology, and many questions persist. New epidemiologic studies are surfacing and attempts to ameliorate the condition may shed light on the likely complex etiology. The bones of the oral cavity provide a unique environment relative to blood flow, oral microbiota, bone structure and function. Although little is known of the mechanisms and course of ONJ, even less is known about the spectrum of issues of altered healing that could fall short of defined ONJ.

Hematopoietic stem cells regulate mesenchymal stromal cell induction into osteoblasts thereby participating in the formation of the stem cell niche

Crosstalk between hematopoietic stem cells (HSCs) and the cells comprising the niche is critical for maintaining stem cell activities. Yet little evidence supports the concept that HSCs regulate development of the niche. Here, the ability of HSCs to directly regulate endosteal development was examined. Marrow was isolated 48 hours after "stressing" mice with a single acute bleed or from control nonstressed animals. "Stressed" and "nonstressed" HSCs were cocultured with bone marrow stromal cells to map mesenchymal fate. The data suggest that HSCs are able to guide mesenchymal differentiation toward the osteoblastic lineage under basal conditions. HSCs isolated from animals subjected to an acute stress were significantly better at inducing osteoblastic differentiation in vitro and in vivo than those from control animals. Importantly, HSC-derived bone morphogenic protein 2 (BMP-2) and BMP-6 were responsible for these activities. Furthermore, significant differences in the ability of HSCs to generate a BMP response following stress were noted in aged and in osteoporotic animals. Together these data suggest a coupling between HSC functions and bone turnover as in aging and in osteoporosis. For the first time, these results demonstrate that HSCs do not rest passively in their niche. Instead, they directly participate in bone formation and niche activities. Disclosure of potential conflicts of interest is found at the end of this article.

Parathyroid hormone mediates bone growth through the regulation of osteoblast proliferation and differentiation

PTH (1-34) is the only FDA-approved anabolic agent for osteoporosis treatment in the U.S., but its mechanisms are not completely understood. This study investigated PTH effects on osteogenic cells at various stages of differentiation and proliferation using an engineered bone growth model in vivo. Ossicles were generated from bone marrow stromal cells (BMSCs) implanted in immunocompromised mice. Three weeks of PTH (40 microg/kg/day) or vehicle treatment initiated 1 day, 1, 2, or 3 weeks after BMSC implantation resulted in an anabolic response in PTH-treated implants (via histomorphometry and muCT) in all treatment groups. A novel in vivo tracking strategy with luciferase tagged BMSCs and weekly bioluminescent imaging of ossicles revealed increased donor cell proliferation in PTH-treated ossicles. The greatest increase occurred during the first week, and the activity remained elevated in PTH-treated implants over time. Zoledronic acid (ZA) was combined with PTH to delineate interactive mechanisms of these bone active agents. Combining ZA with PTH treatment reduced the PTH-mediated increase in luciferase BMSC activity, serum osteocalcin, and serum tartrate resistant acid phosphotase-5b (TRAP-5b) but ZA did not reduce the PTH-induced increase in total bone. Since zoledronic acid reduced PTH-induced proliferation without reducing bone volume, these data suggest that combining PTH and bisphosphonate therapy warrants further investigation in the treatment of bone disorders.

Ossicle and vossicle implant model systems

Bone regeneration and repair is a goal of many skeletal therapies and numerous agents positively or negatively impact these processes. New therapeutic agents and effective model systems are continually sought to identify agents and characterize their mechanisms of action are in constant demand. In addition, investigations of tumor cell-bone interaction in the skeletal metastatic microenvironment require well-defined and readily orchestrated models. This chapter describes a novel ectopic ossicle model and a vossicle modification that can be used to provide focused and rapid feedback of bone growth and bone-cellular interactions. The ossicle model is a bone marrow stromal cell (BMSC)-based model and the vossicle model is a neonatal vertebral bone transplant model. These models offer opportunities to mix and compare mesenchymal (donor derived) and hematopoietic elements (host derived). Multiple implants can be placed in one mouse to facilitate various outcome analyses, such as histomorphometry, micro-CT, gene expression studies, and cell tracking using markers such as luciferase, in response to pharma cological or genetic manipulation. Implants can also be combined with other cell types, such as cancer cells to evaluate the bone-tumor microenvironment.

Pulsatile release of parathyroid hormone from an implantable delivery system

Intermittent (pulsatile) administration of parathyroid hormone (PTH) is known to improve bone micro-architecture, mineral density and strength. Therefore, daily injection of PTH has been clinically used for the treatment of osteoporosis. However, this regimen of administration is not convenient and is not a favorable choice of patients. In this study, an implantable delivery system has been developed to achieve pulsatile release of PTH. A well-defined cylindrical device was first fabricated with a biodegradable polymer, poly(l-lactic acid) (PLLA), using a reverse solid-free form fabrication technique. Three-component polyanhydrides composed of sebacic acid, 1,3-bis(p-carboxyphenoxy) propane and poly(ethylene glycol) were synthesized and used as isolation layers. The polyanhydride isolation layers and PTH-loaded alginate layers were then stacked alternately within the delivery device. The gap between the stacked PTH-releasing core and the device frame was filled with PLLA to seal. Multi-pulse PTH release was achieved using the implantable device. The lag time between two adjacent pulses were modulated by the composition and the film thickness of the polyanhydride. The released PTH was demonstrated to be biologically active using an in vitro assay. Timed sequential release of multiple drugs has also been demonstrated. The implantable device holds promise for both systemic and local therapies.

Bisphosphonate-associated osteonecrosis of the jaw: report of a task force of the American Society for Bone and Mineral Research

ONJ has been increasingly suspected to be a potential complication of bisphosphonate therapy in recent years. Thus, the ASBMR leadership appointed a multidisciplinary task force to address key questions related to case definition, epidemiology, risk factors, diagnostic imaging, clinical management, and future areas for research related to the disorder. This report summarizes the findings and recommendations of the task force.

INTRODUCTION

The increasing recognition that use of bisphosphonates may be associated with osteonecrosis of the jaw (ONJ) led the leadership of the American Society for Bone and Mineral Research (ASBMR) to appoint a task force to address a number of key questions related to this disorder.

MATERIALS AND METHODS

A multidisciplinary expert group reviewed all pertinent published data on bisphosphonate-associated ONJ. Food and Drug Administration drug adverse event reports were also reviewed.

RESULTS AND CONCLUSIONS

A case definition was developed so that subsequent studies could report on the same condition. The task force defined ONJ as the presence of exposed bone in the maxillofacial region that did not heal within 8 wk after identification by a health care provider. Based on review of both published and unpublished data, the risk of ONJ associated with oral bisphosphonate therapy for osteoporosis seems to be low, estimated between 1 in 10,000 and <1 in 100,000 patient-treatment years. However, the task force recognized that information on incidence of ONJ is rapidly evolving and that the true incidence may be higher. The risk of ONJ in patients with cancer treated with high doses of intravenous bisphosphonates is clearly higher, in the range of 1-10 per 100 patients (depending on duration of therapy). In the future, improved diagnostic imaging modalities, such as optical coherence tomography or MRI combined with contrast agents and the manipulation of image planes, may identify patients at preclinical or early stages of the disease. Management is largely supportive. A research agenda aimed at filling the considerable gaps in knowledge regarding this disorder was also outlined.

Cyclin D1 as a target for the proliferative effects of PTH and PTHrP in early osteoblastic cells

PTHrP induced a proliferative cyclin D1 activation in low-density osteoblastic cells. The process was PKA and MAPK dependent and involved both AP-1 and CRE sites. In ectopic ossicles generated from implanted bone marrow stromal cells, PTH upregulated cyclin D1 after acute or intermittent anabolic treatment. These data suggest a positive role of PTH and PTHrP in the cell cycle of early osteoblasts.

INTRODUCTION

The mechanisms underlying the actions of PTH and its related protein (PTHrP) in osteoblast proliferation, differentiation, and bone remodeling remain unclear. The action of PTH or PTHrP on the cell cycle during osteoblast proliferation was studied.

MATERIALS AND METHODS

Mouse calvarial MC3T3-E1 clone 4 cells were synchronized by serum starvation and induced with 100 nM PTHrP for 2-24 h under defined low serum conditions. Western blot, real-time PCR, EMSAs, and promoter/luciferase assays were performed to evaluate cyclin D1 expression. Pharmacological inhibitors were used to determine the relevant signaling pathways. Ectopic ossicles generated from implanted bone marrow stromal cells were treated with acute (a single 8- or 12-h injection) or intermittent anabolic PTH treatment for 7 days, and RNA and histologic analysis were performed.

RESULTS

PTHrP upregulated cyclin D1 and CDK1 and decreased p27 expression. Cyclin D1 promoter/luciferase assays showed that the PTHrP regulation involved both activator protein-1 (AP-1) and cyclic AMP response element binding protein (CRE) sites. AP-1 and CRE double mutants completely abolished the PTHrP effect of cyclin D1 transcription. Upregulation of cyclin D1 was found to be protein kinase A (PKA) and mitogen-activated protein kinase (MAPK) dependent in proliferating MC3T3-E1 cells. In vivo expression of cyclin D1 in ectopic ossicles was upregulated after a single 12-h PTH injection or intermittent anabolic PTH treatment for 7 days in early developing ossicles.

CONCLUSIONS

These data indicate that PTH and PTHrP induce cyclin D1 expression in early osteoblastic cells and their action is developmental stage specific.

Synthesis and Erosion Properties of PEG-Containing Polyanhydrides

To tailor the erosion rate of polyanhydrides while retaining their surface erosion characteristics, new three-component polyanhydrides of sebacic acid, 1,3-bis(p-carboxyphenoxy)propane and poly(ethylene glycol) were synthesized. The hydrophilicity of the polymer increased and its mechanical strength decreased with increasing PEG content. Correspondingly, the erosion rate increases with increasing PEG content, whereas it decreases with increasing specimen thickness. This indicates that the incorporation of poly(ethylene glycol) into traditional two-component polyanhydrides retains their surface erosion properties while making the erosion rate tunable. The new polyanhydrides hold potential for drug delivery applications.

Effect of long-term oral bisphosphonates on implant wound healing: literature review and a case report

BACKGROUND

Bisphosphonates suppress osteoclast activity, and their intravenous use has been reported in hundreds of cases to be associated with osteonecrosis in the jaw. Little is known of the risks associated with long-term use of oral bisphosphonates despite their use for >10 years by an oral mode of delivery for the treatment of osteopenia, osteoporosis, and Paget's disease of bone. The purpose of this report is to review the literature associated with bisphosphonate use that could impact bone healing and to report a case of bone necrosis in a patient on long-term oral bisphosphonates.

METHODS

A Medline search was carried out to find relevant articles from both medical and dental literature between 1960 and 2006. A patient, who had been taking an oral bisphosphonate for >10 years, developed unexplained clinical signs of bone necrosis after routine dental implant placement. This case was followed, documented, and the treatment of the osteonecrosis described.

RESULTS

A summary of how bisphosphonates may play a role in wound healing is presented. The compromised healing noted in a patient, who was under long-term oral bisphosphonate use, was successfully treated with systemic antibiotics, local microbial mouthrinse, and aggressive defect management (detoxification and mixture of bone graft and tetracycline).

CONCLUSIONS

This case suggests that patients under long-term oral bisphosphonate use should be treated with caution. Well-controlled, prospective clinical trials on the effect of oral bisphosphonates on bone are warranted to determine which patients may be at risk for such complications.

Skeletal metastasis: Established and emerging roles of parathyroid hormone related protein (PTHrP)

Parathyroid hormone related protein (PTHrP) is a well characterized tumor derived product that also has integral functions in normal development and homeostasis. PTHrP is produced by virtually all tumor types that metastasize to bone and numerous studies have demonstrated a correlation between PTHrP expression and skeletal localization of tumors. PTHrP has prominent effects in bone via its interaction with the PTH-1 receptor on osteoblastic cells. Through indirect means, PTHrP supports osteoclastogenesis by upregulating the receptor activator of NFkappaB ligand (RANKL) in osteoblasts. PTHrP also regulates osteoblast proliferation and differentiation in manners that are temporal and dose dependent. Bone turnover has been implicated in the localization of tumors to bone and PTHrP increases bone turnover. Bone turnover results in the release of growth factors such as TGFbeta and minerals such as calcium, both of which impact tumor cell growth and contribute to continued PTHrP production. PTHrP also has anabolic properties and could be in part responsible for osteoblastic type reactions in prostate cancer. Finally, emerging roles of PTH and PTHrP in the support of hematopoietic stem cell development in the bone marrow microenvironment suggest that an interaction between hematopoietic cells and tumor cells warrants further investigation.

Extracellular calcium as a candidate mediator of prostate cancer skeletal metastasis

Prostate cancer almost exclusively metastasizes to skeletal sites, indicating that the bone provides a favorable microenvironment for its localization and progression. A natural yet understudied factor in bone that could facilitate tumor localization is elevated extracellular calcium ([Ca2+]o). The present study found that elevated [Ca2+]o (2.5 mmol/L) enhanced proliferation of skeletal metastatic prostate cell lines (PC-3 and C4-2B), but not the nonskeletal metastatic, epithelial-derived prostate cell line LNCaP. The proliferative effect of elevated [Ca2+]o was associated with higher expression of the calcium-sensing receptor (CaSR), a heterotrimeric G-protein-coupled receptor that is the predominant cell-surface sensor for [Ca2+]o. Knockdown of the CaSR via RNA interference reduced cell proliferation in vitro and metastatic progression in vivo. CaSR signaling in PC-3 cells was evaluated by measuring the elevated [Ca2+]o-dependent inhibition of cyclic AMP accumulation, induced by either prostaglandin E2 or forskolin. Elevated [Ca2+]o stabilized expression of cyclin D1, a protein required for cell cycle transition. Furthermore, elevated [Ca2+]o triggered activation of the Akt signaling pathway and enhanced PC-3 cell attachment. Both pertussis toxin (a G-protein inhibitor) and LY294002 (an inhibitor of Akt signaling) reduced cell attachment. These data suggest that elevated [Ca2+]o following increased bone remodeling could facilitate metastatic localization of prostate cancer via the CaSR and the Akt signaling pathway. Taken together, [Ca2+]o is a candidate mediator of prostate cancer bone metastasis.

The impact of primary hyperparathyroidism on the oral cavity

CONTEXT

Primary hyperparathyroidism (HPT) is a systemic disease causing bone loss. Periodontal disease is a local inflammatory disease characterized by alveolar bone loss. The older literature records that HPT is associated with loss of radicular lamina dura and brown tumors of the bone, but contemporary studies are lacking.

OBJECTIVE

The objective of the study was to determine the effects of HPT on oral bony structures and periodontal disease in a contemporary population.

DESIGN

This was a cross-sectional, case-controlled study.

SETTING

The study was conducted at the clinics of endocrine surgery and hospital dentistry.

PATIENTS AND OTHER PARTICIPANTS

Fifty-nine patients, 39 with HPT and 20 thyroid controls, were included in the study.

MAIN OUTCOME MEASURES

Periodontal clinical measures and dental radiographic analyses were used in this study.

RESULTS

HPT patients were more likely to have tori and reductions in radicular lamina dura on dental radiographs. Widening of the periodontal ligament space surrounding teeth correlated with serum PTH levels. Panoramic radiographs demonstrated reduced cortical bone thickness at the angle of the mandible in HPT patients but no evidence of brown tumors or other overt pathologies.

CONCLUSIONS

Changes in the oral cavity observed in patients with HPT suggested both decreased cortical density and increased likelihood of oral tori. The contemporary oral manifestations of primary HPT are different from those previously reported, and health care providers should be aware of newer, more subtle findings that may be present when treating patients with HPT.

Accuracy and consistency of radiographic interpretation among clinical instructors in conjunction with a training program

There are inaccuracies and inconsistencies of radiographic interpretation among clinical instructors. The purpose of this investigation was to determine if a training program could improve the accuracy and consistency of instructors' ratings of bone loss. A total of thirty-five clinical instructors consisting of periodontal faculty (periodontists and general dentists), dental hygiene faculty, and periodontal graduate students viewed projected digitized radiographic images and quantified bone loss for twenty-five teeth into four descriptive categories. Ratings of bone loss were made immediately before (pretest) and after (post-test 1) initiation of the training program and then again three months later (post-test 2). Ratings were compared to the correct choice categories as determined by direct measurement using the Schei ruler. Overall agreement with the correct choice improved over time (from 64.5 percent to 85.2 percent) with the greatest change from pretest (64.5 percent) to post-test 1 (76.5 percent). Mean and absolute differences improved in three of the four categories, but worsened in one from pretest to post-test 1. This category returned to its original high value at post-test 2. The greatest improvement in consistency among instructors' ratings was seen in one of the four categories, which was "none" (no bone loss). Extension of the training program may further enhance the accuracy and consistency of instructors' radiographic interpretation.