Advances in treating metastatic bone cancer: summary statement for the First Cambridge Conference.

The First Cambridge Conference on Advances in Treating Metastatic Bone Cancer, a symposium held in Cambridge, Massachusetts, October 28 to 29, 2005, was convened to discuss recent advances and research related to the natural history of bone metastases and skeletal complications, bone cancer biology, treatment of myeloma and other solid tumors, and treatment-induced bone loss. The conference format combined brief presentations with extended periods of discussion. The conclusions reached during the 2-day meeting are summarized in this article and presented in more detail in the individual articles and accompanying discussion sessions that comprise the conference proceedings.

CRTAP is required for prolyl 3- hydroxylation and mutations cause recessive osteogenesis imperfecta.

Prolyl hydroxylation is a critical posttranslational modification that affects structure, function, and turnover of target proteins. Prolyl 3-hydroxylation occurs at only one position in the triple-helical domain of fibrillar collagen chains, and its biological significance is unknown. CRTAP shares homology with a family of putative prolyl 3-hydroxylases (P3Hs), but it does not contain their common dioxygenase domain.

Future anti-catabolic therapeutic targets in bone disease.

Understanding of the regulation of bone catabolism has advanced significantly over the past two decades with the identification of key enzymes that regulate osteoclast formation, activation, and survival following their knockout in mice or recognition of mutations in humans. This led to the discovery of specific inhibitors of some of these key enzymes as proof-of-concept lead compounds or potential clinical candidates for the prevention of osteoporosis and other diseases associated with increased bone resorption. Bisphosphonates have been the major therapeutic agents prescribed for the prevention of bone loss in a variety of pathologic conditions for over 30 years.

Autoimmunity and bone.

Focal erosions of cartilage and bone, which occur in the joints of patients with autoimmune inflammatory arthritis (i.e., rheumatoid arthritis (RA) and psoriatic arthritis [PsA]), represent the most debilitating and irreversible components of the disease.

Osteoclast precursors: cytokine-stimulated immunomodulators of inflammatory bone disease.

Purpose Of Review: Proinflammatory cytokines produced in inflamed joints promote the generation and release from the bone marrow of osteoclast precursors (OCPs). These OCPs are recruited to inflamed joints where, in response to proinflammatory cytokines, they differentiate into osteoclasts and behave as immunomodulatory cells. We review the regulation of OCP formation and differentiation, and propose that they are not only sources of bone-resorbing osteoclasts, but also of immune cells that influence the progression of inflammatory bone diseases.

Tumor necrosis factor-alpha increases circulating osteoclast precursor numbers by promoting their proliferation and differentiation in the bone marrow through up-regulation of c-Fms expression.

Osteoclasts are essential cells for bone erosion in inflammatory arthritis and are derived from cells in the myeloid lineage. Recently, we reported that tumor necrosis factor-alpha (TNFalpha) increases the blood osteoclast precursor (OCP) numbers in arthritic patients and animals, which are reduced by anti-TNF therapy, implying that circulating OCPs may have an important role in the pathogenesis of erosive arthritis. The aim of this study is to investigate the mechanism by which TNFalpha induces this increase in OCP frequency.

Tumor necrosis factor promotes Runx2 degradation through up-regulation of Smurf1 and Smurf2 in osteoblasts.

Tumor necrosis factor (TNF) plays an important role in the pathogenesis of inflammatory bone loss through stimulation of osteoclastic bone resorption and inhibition of osteoblastic bone formation. Compared with the well established role of TNF in osteoclastogenesis, mechanisms by which TNF inhibits osteoblast function have not been fully determined. Runx2 is an osteoblast-specific transcription factor whose steady-state protein levels are regulated by proteasomal degradation, mediated by the E3 ubiquitin ligases, Smurf1 and Smurf2.

Osteoprotegerin, the bone protector, is a surprising target for beta-catenin signaling.

Osteoblasts influence bone mass by the amount of bone they synthesize and by regulating osteoclasts, the cells that degrade bone. In the December issue of , Kieslinger et al. (2005) show that immature osteoblasts regulate expression of the osteoclast inhibitor, osteoprotegerin, through an early B cell factor and β-catenin signaling.

Osteoclast precursors, RANKL/RANK, and immunology.

Rapid progress has been made in recent years in our understanding of the mechanisms regulating the formation, activation, and survival of osteoclasts, which are derived from precursor cells in the myeloid lineage. In contrast, study of the regulation of osteoclast precursors (OCPs) has been relatively slow, in part because it has been hard to accurately identify them. However, following the discovery of cell-surface markers that facilitated purification of OCPs, recent studies have demonstrated that peripheral blood OCP numbers are increased in tumor necrosis factor (TNF)-mediated arthritis, both in animals and humans, and these numbers correlate with serum TNF levels.

TNF-alpha and pathologic bone resorption.

Chronic inflammatory bone diseases, such as rheumatoid arthritis, periodontal disease and aseptic periprosthetic osteolysis, are characterized by bone loss around affected joints and teeth caused by increased osteoclastic bone resorption. This resorption is mediated largely by the increased local production of pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNFa). These cytokines may induce resorption indirectly by affecting the production of the essential osteoclast differentiation factor, receptor activator of NF-kB ligand, and/or its soluble decoy receptor, osteoprotegerin, by osteoblast/stromal cells or directly by enhancing proliferation and/or activity of cells in the osteoclast lineage.

Tumor necrosis factor prevents alendronate-induced osteoclast apoptosis in vivo by stimulating Bcl-xL expression through Ets-2.

Objective: To investigate why bisphosphonates are less effective at preventing focal bone loss in rheumatoid arthritis (RA) patients than in those with generalized osteoporosis, and the mechanisms involved.

Methods: The response of osteoclasts to alendronate (ALN) in tumor necrosis factor-transgenic (TNF-Tg) mice that develop erosive arthritis and in wild-type littermates was studied. TNF-Tg and wild-type mice were given ALN, and the osteoclast numbers in the inflamed joints and in the long bones were compared.

Dysmorphic neuromuscular junctions associated with motor ability in cerebral palsy.

Cerebral palsy (CP) is the most prevalent neurologic disease in children and a leading cause of severe physical disability. Research and clinical experience indicate that children with CP have abnormal neuromuscular junctions (NMJs), and we present evidence that nonapposition of neuromuscular junction components is associated with the severity of motor system deficit in CP. Leg muscle biopsies collected from ambulatory (n = 21) or nonambulatory (n = 38) CP patients were stained in order to detect acetylcholine receptor (AChR) and acetylcholine esterase (AChE).

Roles for NF-kappaB and c-Fos in osteoclasts.

NF-kappaB and c-Fos are transcription factors that are activated in immune cells and in most other cell types following stimulation by a variety of factors, including cytokines, growth factors, and hormones. They regulate the expression of a large number of genes, and both are activated in osteoclast precursors after RANKL, IL-1, or TNF bind to their respective receptors. However, of these cytokines, only RANKL is required for the induction of osteoclast formation in vivo.

Lead exposure inhibits fracture healing and is associated with increased chondrogenesis, delay in cartilage mineralization, and a decrease in osteoprogenitor frequency.

Lead exposure continues to be a significant public health problem. In addition to acute toxicity, Pb has an extremely long half-life in bone. Individuals with past exposure develop increased blood Pb levels during periods of high bone turnover or resorption.

Remodeling of cortical bone allografts mediated by adherent rAAV-RANKL and VEGF gene therapy.

Structural allograft healing is limited because of a lack of vascularization and remodeling. To study this we developed a mouse model that recapitulates the clinical aspects of live autograft and processed allograft healing. Gene expression analyses showed that there is a substantial decrease in the genes encoding RANKL and VEGF during allograft healing.

Regulation of apoptosis in osteoclasts and osteoblastic cells.

In postnatal life, the skeleton undergoes continuous remodeling in which osteoclasts resorb aged or damaged bone, leaving space for osteoblasts to make new bone. The balance of proliferation, differentiation, and apoptosis of bone cells determines the size of osteoclast or osteoblast populations at any given time. Bone cells constantly receive signals from adjacent cells, hormones, and bone matrix that regulate their proliferation, activity, and survival.

Malignant autosomal recessive osteopetrosis caused by spontaneous mutation of murine Rank.

Unlabelled: We report the first case of lethal autosomal recessive osteopetrosis in mice caused by a spontaneous 8-bp deletion in exon 2 of the Rank gene. The phenotype, including a block in RANKL-dependent osteoclast differentiation and lymph node agenesis, copies that of Rank(-/-) mice, which have been produced by targeted recombination.

Introduction: Commitment of osteoclast progenitors to the osteoclast lineage requires RANKL/RANK-mediated intercellular signals.

4-thiophenoxy-N-(3,4,5-trialkoxyphenyl)pyrimidine-2-amines as potent and selective inhibitors of the T-cell tyrosine kinase p56lck.

We have developed a series of 4-thiophenoxy-N-(3,4,5-trialkoxyphenyl) pyrimidine-2-amines as potent and selective inhibitors of p56lck tyrosine kinase activity. In particular, the most potent inhibitor shows cellular activity in T-cell receptor (TCR) stimulated models of cytokine release, which suggests an immunomodulatory role for this class of inhibitor.

RANK signaling is not required for TNFalpha-mediated increase in CD11(hi) osteoclast precursors but is essential for mature osteoclast formation in TNFalpha-mediated inflammatory arthritis.

Unlabelled: To address the controversy of whether TNFalpha can compensate for RANKL in osteoclastogenesis in vivo, we used a TNFalpha-induced animal model of inflammatory arthritis and blocked RANKL/RANK signaling. TNFalpha increased osteoclast precursors available for RANK-dependent osteoclastogenesis. RANK signaling is not required for the TNFalpha-stimulated increase in CD11b(hi) osteoclast precursors but is essential for mature osteoclast formation.

Systemic tumor necrosis factor alpha mediates an increase in peripheral CD11bhigh osteoclast precursors in tumor necrosis factor alpha-transgenic mice.

Objective: To investigate the mechanisms whereby tumor necrosis factor alpha (TNFalpha) increases osteoclastogenesis in vivo.

Methods: TNFalpha-transgenic (TNF-Tg) and wild-type mice injected with TNFalpha were studied. In vitro osteoclastogenesis assays, monocyte colony-forming assays, and fluorescence-activated cell sorting were performed using splenocytes, peripheral blood mononuclear cells (PBMCs), and bone marrow cells to quantify and characterize osteoclast precursors (OCPs).

The preliminary impact of Maryland's medical director and attending physician regulations.

Objectives: To identify the impact of the regulations implemented in Maryland in 2001, related to nursing home attending physicians and medical directors, and nursing home quality assurance requirements, on Maryland nursing homes, administrators, and physicians.

Design: Two surveys were mailed to all nursing home administrators in Maryland, one for their completion and one to give to their medical directors to complete. These surveys were to be returned by mail to the authors.

NF-kappaB specifically activates BMP-2 gene expression in growth plate chondrocytes in vivo and in a chondrocyte cell line in vitro.

Bone morphogenetic protein-2 (BMP-2) regulates growth plate chondrogenesis during development and postnatal bone growth, but the control mechanisms of BMP-2 expression in growth plate chondrocytes are unknown. Here we have used both in vitro and in vivo approaches to demonstrate that transcription factor, NF-kappaB, regulates BMP-2 gene expression in chondrocytes. Two putative NF-kappaB response elements were found in the -2712/+165 region of the BMP-2 gene.

Regulation of bone remodeling and emerging breakthrough drugs for osteoporosis and osteolytic bone metastases.

Major advances have been made in the past 10 years in our understanding of the molecular basis of bone cell formation and bone remodeling. For example, the discovery of osteoprotegerin, the decoy receptor and inhibitor of receptor activator of NF-kappaB ligand (RANKL), and the RANKL/receptor activator of NF-kappaB (RANK) signaling pathway that is essential for osteoclastogenesis, has helped clarify the mechanisms regulating osteoclast formation, activation, and survival. PTH, like most other osteoclast stimulating factors, promotes RANKL production by osteoblast/stromal cells when they are exposed to it continuously, but when given intermittently it stimulates bone formation and reduces fracture risk in postmenopausal women.