Dickkopf-1 as a potential therapeutic target in Paget's disease of bone

Correlation between magnetic resonance imaging (MRI) findings and the new bone formation factor Dkk-1 in patients with spondyloarthritis

In recent years, MRI has been regarded as a major diagnostic tool for spondyloarthritis (SpA), and anti-TNF therapy has been widely confirmed as an effective treatment strategy. This study was designed to investigate the correlation between the secreted protein dickkopf-1 (Dkk-1) and abnormal findings on magnetic resonance imaging (MRI) through a prospective study of 30 cases of SpA. Thirty patients with active SpA were included, all treated with recombinant human tumor necrosis factor (TNF) receptor-antibody fusion protein (YiSaiPu) injection at 50 mg/week for 6 months. All patients were also examined for their clinical, serological, and imaging manifestations of the condition before and after treatment. In patients receiving TNF inhibitor treatment, the erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and clinical activity indices BASDAI, BASFI, BASMI, ASDAS-CRP were significantly decreased (p < 0.01). Serum Dkk-1 concentration was also significantly decreased (p < 0.05), as were the scores of bone marrow edema of the sacroiliac joints and the spine (p < 0.05). The score of sacroiliac joint backfill was significantly increased (p < 0.05), and the baseline and changes in the serum Dkk-1 concentration were significantly correlated with the baseline and changes in spinal bone marrow edema levels. Inhibition of the level of serum Dkk-1 by TNF inhibitors may be the molecular basis for inhibiting the formation of new bone in SpA patients. In addition, spinal marrow edema may have significance for predicting new bone formation.

A monoclonal antibody against the Wnt signaling inhibitor dickkopf-1 inhibits osteosarcoma metastasis in a preclinical model

The outcome of patients with metastatic osteosarcoma has not improved since the introduction of chemotherapy in the 1970s. Development of therapies targeting the metastatic cascade is a tremendous unmet medical need. The Wnt signaling pathway has been the focus of intense investigation in osteosarcoma because of its role in normal bone development. Although the role of Wnt signaling in the pathogenesis of osteosarcoma is controversial, there are several reports of dickkopf-1 (DKK-1), a Wnt signaling antagonist, possibly playing a pro-tumorigenic role. In this work we investigated the effect of anti-DKK-1 antibodies on the growth and metastasis of patient-derived osteosarcoma xenografts. We were able to detect human DKK-1 in the blood of tumor-bearing mice and found a correlation between DKK-1 level and tumor proliferation. Treatment with the anti-DKK-1 antibody, BHQ880, slowed the growth of orthotopically implanted patient-derived osteosarcoma xenografts and inhibited metastasis. This effect was correlated with increased nuclear beta-catenin staining and increased expression of the bone differentiation marker osteopontin. These findings suggest that Wnt signaling is anti-tumorigenic in osteosarcoma, and support the targeting of DKK-1 as an anti-metastatic strategy for patients with osteosarcoma.

Dectin-1 signaling inhibits osteoclastogenesis via IL-33-induced inhibition of NFATc1

Abnormal osteoclast activation contributes to osteolytic bone diseases (OBDs). It was reported that curdlan, an agonist of dectin-1, inhibits osteoclastogenesis. However, the underlying mechanisms are not fully elucidated. In this study, we found that curdlan potently inhibited RANKL-induced osteoclast differentiation and the resultant bone resorption. Curdlan inhibited the expression of nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1), the key transcriptional factor for osteoclastogenesis. Notably, dectin-1 activation increased the expression of MafB, an inhibitor of NFATc1, and IL-33 in osteoclast precursors. Mechanistic studies revealed that IL-33 enhanced the expression of MafB in osteoclast precursors and inhibited osteoclast precursors to differentiate into mature osteoclasts. Furthermore, blocking ST2, the IL-33 receptor, partially abrogated curdlan-induced inhibition of NFATc1 expression and osteoclast differentiation. Thus, our study has provided new insights into the mechanisms of dectin-1-induced inhibition of osteoclastogenesis and may provide new targets for the therapy of OBDs.

Genetic association study of Dickkopf-1 and sclerostin genes with paget disease of bone

Increased expression of DKK1 gene was reported in pagetic osteoblasts and stromal cells, and increased serum levels of DKK1 and SOST proteins were reported in patients with Paget disease of bone (PDB). This study aimed at identifying rare genetic variants of the DKK1 and SOST genes and at testing for genetic association with PDB in the French-Canadian population. Exons, promoters, and exon-intron junctions of these genes were sequenced in patients with PDB and healthy controls. An association study of Tag SNPs of both genes was also performed in 239 pagetic patients and 297 healthy individuals. Three rare variants were identified in this study, all located in the DKK1 gene: one variant in the second exon leading to alteration in a highly conserved amino acid (p.R120L), one in the 5'-untranslated region (-50 C/A), and one in a splice site of intron 1 (IVS1 184 T/C), although none of these rare variants were associated with PDB. A genetic association of a Tag SNP of the DKK1 gene was found: the G allele of rs1569198 was significantly decreased in patients in comparison to controls (42 vs. 49 %, uncorrected P = 0.03, OR = 0.77, 95 % CI 0.61-0.98). In conclusion, this study identified three rare genetic variants in DKK1 in the French-Canadian population. In addition, a weak genetic association of a common variant of DKK1, rs1569198, which is located on a predicted new acceptor site for splicing of this gene, was observed in PDB, whereas no rare variant or genetic association was found in the SOST gene.

Wnt signaling pathway in rheumatoid arthritis, with special emphasis on the different roles in synovial inflammation and bone remodeling

Rheumatoid arthritis (RA) is a chronic symmetrical autoimmune disease of unknown etiology that affects primarily the diarthrodial joints. Characteristic features of RA pathogenesis are synovial inflammation and proliferation accompanied by cartilage erosion and bone loss. Fibroblast-like synoviocytes (FLS) display an important role in the pathogenesis of RA. Several lines of evidence show that the Wnt signaling pathway significantly participates in the RA pathogenesis. The Wnt proteins are glycoproteins that bind to the Fz receptors on the cell surface, which leads to several important biological functions, such as cell differentiation, embryonic development, limb development and joint formation. Accumulated evidence has suggested that this signaling pathway plays a key role in the FLS activation, bone resorption and joint destruction during RA development. Greater knowledge of the role of the Wnt signaling pathway in RA could improve understanding of the RA pathogenesis and the differences in RA clinical presentation and prognosis. In this review, new advances of the Wnt signaling pathway in RA pathogenesis are discussed, with special emphasis on its different roles in synovial inflammation and bone remodeling. Further studies are needed to reveal the important role of the members of the Wnt signaling pathway in the RA pathogenesis and treatment.

Pathogenesis of Paget disease of bone

Paget disease of bone (PDB) is a common disease characterized by focal areas of increased and disorganized bone turnover. Some patients are asymptomatic, whereas others develop complications such as pain, osteoarthritis, fracture, deformity, deafness, and nerve compression syndromes. PDB is primarily caused by dysregulation of osteoclast differentiation and function, and there is increasing evidence that this is due, in part, to genetic factors. One of the most important predisposing genes is SQSTM1, which harbors mutations that cause osteoclast activation in 5-20 % of PDB patients. Seven additional susceptibility loci for PDB have been identified by genomewide association studies on chromosomes 1p13, 7q33, 8q22, 10p13, 14q32, 15q24, and 18q21. Although the causal variants remain to be discovered, three of these loci contain CSF1, TNFRSF11A, and TM7SF4, genes that are known to play a critical role in osteoclast differentiation and function. Environmental factors are also important in the pathogenesis of PDB, as reflected by the fact that in many countries the disease has become less common and less severe over recent years. The most widely studied environmental trigger is paramyxovirus infection, but attempts to detect viral transcripts in tissues from patients with PDB have yielded mixed results. Although our understanding of the pathophysiology of PDB has advanced tremendously over the past 10 years, many questions remain unanswered, such as the mechanisms responsible for the focal nature of the disease and the recent changes in prevalence and severity.

Human Dickkopf-1 (huDKK1) protein: characterization of glycosylation and determination of disulfide linkages in the two cysteine-rich domains

Human Dickkopf-1 (huDKK1), an inhibitor of the canonical Wnt-signaling pathway that has been implicated in bone metabolism and other diseases, was expressed in engineered Chinese hamster ovary cells and purified. HuDKK1 is biologically active in a TCF/lef-luciferase reporter gene assay and is able to bind LRP6 coreceptor. In SDS-PAGE, huDKK1 exhibits molecular weights of 27-28 K and 30 K at ∼ 1:9 ratio. By MALDI-MS analysis, the observed molecular weights of 27.4K and 29.5K indicate that the low molecular weight form may contain O-linked glycans while the high molecular weight form contains both N- and O-linked glycans. LC-MS/MS peptide mapping indicates that ∼ 92% of huDKK1 is glycosylated at Asn²²⁵ with three N-linked glycans composed of two biantennary forms with 1 and 2 sialic acid (23% and 60%, respectively), and one triantennary structure with 2 sialic acids (9%). HuDKK1 contains two O-linked glycans, GalNAc (sialic acid)-Gal-sialic acid (65%) and GalNAc-Gal[sialic acid] (30%), attached at Ser³⁰ as confirmed by β-elimination and targeted LC-MS/MS. The 10 intramolecular disulfide bonds at the N- and C-terminal cysteine-rich domains were elucidated by analyses including multiple proteolytic digestions, isolation and characterization of disulfide-containing peptides, and secondary digestion and characterization of selected disulfide-containing peptides. The five disulfide bonds within the huDKK1 N-terminal domain are unique to the DKK family proteins; there are no exact matches in disulfide positioning when compared to other known disulfide clusters. The five disulfide bonds assigned in the C-terminal domain show the expected homology with those found in colipase and other reported disulfide clusters.

Physiological inhibitors of Wnt signaling

Wnt signaling is crucial for cell proliferation and differentiation. It represents a complex network with mechanisms of self-regulation through positive and negative feedback. Recent increasing interest in this signaling pathway has led to the discovery of many new proteins that down-regulate Wnt activity. Here, we provide a short description of the most important and best-studied inhibitors, group them according to the target molecule within the Wnt cascade, and discuss their clinical potential. Although most of the inhibitors discussed here may also interact with proteins from other signaling pathways, we focus only on their ability to modulate Wnt signaling.

A rate-limiting role for Dickkopf-1 in bone formation and the remediation of bone loss in mouse and primate models of postmenopausal osteoporosis by an experimental therapeutic antibody

Genetic studies have linked both osteoporotic and high bone mass phenotypes to low-density lipoprotein receptor-related proteins (LRP4, LRP5, and LRP6). LRPs are receptors for inhibitory Dickkopf-1 (DKK1) protein, and treatment modalities that modulate LRP/DKK1 binding therefore may act as stimulators of bone mass accrual. Here, we report that RH2-18, a fully human monoclonal anti-DKK1 antibody elicits systemic pharmacologic bone efficacy and new bone formation at endosteal bone surfaces in vivo in a mouse model of estrogen-deficiency-induced osteopenia. This was paralleled by partial-to-complete resolution of osteopenia (bone mineral density) at all of the skeletal sites investigated in femur and lumbar-vertebral bodies and the restoration of trabecular bone microarchitecture. More importantly, testing of RH2-18 in adult, osteopenic rhesus macaques demonstrated a rate-limiting role of DKK1 at multiple skeletal sites and responsiveness to treatment. In conclusion, this study provides pharmacologic evidence for the modulation of DKK1 bioactivity in the adult osteopenic skeleton as a viable approach to resolve osteopenia in animal models. Thus, data described here suggest that targeting DKK1 through means such as a fully human anti-DKK1-antibody provides a potential bone-anabolic treatment for postmenopausal osteoporosis.

Emerging strategies and therapies for treatment of Paget's disease of bone

Paget's disease of bone (PDB) is a progressive monostotic or polyostotic metabolic bone disease characterized by focal abnormal bone remodeling, with increased bone resorption and excessive, disorganized, new bone formation. PDB rarely occurs before middle age, and it is the second most frequent metabolic bone disorder after osteoporosis, affecting up to 3% of adults over 55 years of age. One of the most striking and intriguing clinical features is the focal nature of the disorder, in that once the disease is established within a bone, there is only local spread within that bone and no systemic dissemination. Despite many years of intense research, the etiology of PDB has still to be conclusively determined. Based on a detailed review of genetic and viral factors incriminated in PDB, we propose a unifying hypothesis from which we can suggest emerging strategies and therapies. PDB results in weakened bone strength and abnormal bone architecture, leading to pain, deformity or, depending on the bone involved, fracture in the affected bone. The diagnostic assessment includes serum total alkaline phosphatase, total body bone scintigraphy, skull and enlarged view pelvis x-rays, and if needed, additional x-rays. The ideal therapeutic option would eliminate bone pain, normalize serum total alkaline phosphatase with prolonged remission, heal radiographic osteolytic lesions, restore normal lamellar bone, and prevent recurrence and complications. With the development of increasingly potent bisphosphonates, culminating in the introduction of a single intravenous infusion of zoledronic acid 5 mg, these goals of treatment are close to being achieved, together with long-term remission in almost all patients. Based on the recent pathophysiological findings, emerging strategies and therapies are reviewed: ie, pulse treatment with zoledronic acid; denosumab, a fully human monoclonal antibody directed against RANK ligand; tocilizumab, an interleukin-6 receptor inhibitor; odanacatib, a cathepsin K inhibitor; and proteasome and Dickkopf-1 inhibitors.

Wnt1 neuroprotection translates into improved neurological function during oxidant stress and cerebral ischemia through AKT1 and mitochondrial apoptotic pathways

Although essential for the development of the nervous system, Wnt1 also has been associated with neurodegenerative disease and cognitive loss during periods of oxidative stress. Here we show that endogenous expression of Wnt1 is suppressed during oxidative stress in both in vitro and in vivo experimental models. Loss of endogenous Wnt1 signaling directly correlates with neuronal demise and increased functional deficit, illustrating that endogenous neuronal Wnt1 offers a vital level of intrinsic cellular protection against oxidative stress. Furthermore, transient overexpression of Wnt1 or application of exogenous Wnt1 recombinant protein is necessary to preserve neurological function and rescue neurons from apoptotic membrane phosphatidylserine externalization and genomic DNA degradation, since blockade of Wnt1 signaling with a Wnt1 antibody or dickkopf related protein 1 abrogates neuronal protection by Wnt1. Wnt1 ultimately relies upon the activation of Akt1, the modulation of mitochondrial membrane permeability, and the release of cytochrome c to control the apoptotic cascade, since inhibition of Wnt1 signaling, the phosphatidylinositol 3-kinase pathway, or Akt1 activity abrogates the ability of Wnt1 to block these apoptotic components. Our work identifies Wnt1 and its downstream signaling as cellular targets with high clinical potential for novel treatment strategies for multiple disorders precipitated by oxidative stress.

Generation and selection of novel fully human monoclonal antibodies that neutralize Dickkopf-1 (DKK1) inhibitory function in vitro and increase bone mass in vivo

Wnt/LRP5 signaling is a central regulatory component of bone formative and resorptive activities, and the pathway inhibitor DKK1 is a suppressor of bone formation and bone mass accrual in mice. In addition, augmented DKK1 levels are associated with high bone turnover in diverse low bone mass states in rodent models and disease etiologies in human. However, examination of the precise role of DKK1 in the normal skeleton and in higher species requires the development of refined DKK1-specific pharmacological tools. Here, we report the strategy resulting in isolation of a panel of fully human anti-DKK1 antibodies applicable to studies interrogating the roles of mouse, rhesus, and human DKK1. Selected anti-DKK1 antibodies bind primate and human DKK-1 with picomolar affinities yet do not appreciably bind to DKK2 or DKK4. Epitopes mapped within the DKK1 C-terminal domain necessary for interaction with LRP5/6 and consequently effectively neutralized DKK1 function in vitro. When introduced into naïve normal growing female mice, IgGs significantly improved trabecular bone volume and structure and increased both trabecular and cortical bone mineral densities in a dose-related fashion. Furthermore, fully human DKK1-IgG displayed favorable pharmacokinetic parameters in non-human primates. In summary, we demonstrate here a rate-limiting function of physiologic DKK1 levels in the regulation of bone mass in intact female mice, amendable to specific pharmacologic neutralization by newly identified DKK1-IgGs. Importantly the fully human IgGs display a profile of attributes that recommends their testing in higher species and their use in evaluating DKK1 function in relevant disease models.