Soluble Decoy Receptor Research Articles

Picking and choosing

Designing drugs against the fibroblast growth factor (FGF) pathway is complicated by the fact that there are several FGF family members with different biological activities. Blocking the hormonal FGFs causes toxicities; so, Harding et al. developed a soluble decoy receptor, FP-1039, that binds only the mitogenic FGFs. FP-1039 blocked FGF- and vascular endothelial growth factor (VEGF)-induced angiogenesis in vivo, and inhibited tumour growth in several xenograft mouse models with minimal toxicity. Xenografts of cancer cells with FGF pathway alterations were particularly sensitive to FP-1039.

Abstract 540: Role of EphB4-EphrinB2 as novel target in Her2 positive breast cancer.

Abstract Background: Her2 amplification drives tumor growth in 20% of breast cancers. Her2 targeted therapies have improved survival, but eventual failure occurs and additional targeted therapies to overcome resistance are needed. EphB4 and EphrinB2 receptor kinase -ligand pair is induced in Her2 positive tumors and is a novel target. Methods: Her2 positive tumor cell lines and Her2 transgenic mouse lines were studied for expression of EphB4-EphrinB2. The role of EphB4-EphrinB2 was examined by knock down with shRNA. In vivo tumor xenograft studies with Her2 positive cell lines resistant or sensitive to Her2 targeted therapy, and Her2 transgenic mouse were treated with soluble decoy receptor (soluble EphB4-Albumin fusion protein). Tumor response and activation status of Her2 were examined. Results: EphB4 and EphrinB2 are induced in Her2 positive tumor cell lines with further induction in trastuzumab (Herceptin) resistant tumor lines. Knock down of EphB4 with shRNA reduced the cell viability by nearly 80% compared to control shRNA. In vivo studies with sEphB4-Albumin also reduced the tumor growth by 70-80% accompanied by the reduction in pHer2 and pEGFR. No effect was seen on pHer3. Combination with lapatinib and sEphB4-Albumin was additive. sEphB4-Albumin inhibited tumor growth in Her2 resistant tumor cell lines by 56%. Conclusion: EphB4 and EphrinB2 are induced by Herceptin sensitive and resistant Her2 positive tumors. EphB4 provides survival advantage to Her2 positive trastuzumab sensitive and resistant tumors. sEphB4-Albumin inhibits tumor growth as single agent in both trastuzumab sensitive and resistant tumors. sEphB4-Albumin is currently in the clinical development and thus worthy of investigation in Her2 positive cancers. Citation Format: A. Duarte, J. Quaresma, A. Trindade, P. Tripathy, X. Liu, V. Krasnoperov, R. Liu, P.S. Gill. Role of EphB4-EphrinB2 as novel target in Her2 positive breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 540. doi:10.1158/1538-7445.AM2013-540

ST2 as a Cardiovascular Risk Biomarker: From the Bench to the Bedside

ST2 is a member of the interleukin (IL)-1 receptor family discovered in a classical translational science fashion, and exists in two forms, a trans-membrane receptor (ST2L) as well as a soluble decoy receptor (sST2). The ligand of ST2 is IL-33, which is involved in reducing fibrosis and hypertrophy in mechanically strained tissues. In in vitro and in vivo models, ST2L transduces the effects of IL-33, while excess sST2 or abnormalities in ST2 signaling leads to cardiac hypertrophy, fibrosis, and ventricular dysfunction. Clinically, in patients with symptomatic heart failure (HF), elevated concentrations of sST2 are strongly associated with severity of the diagnosis, and powerfully predict increased risk of complications, independent of other established or emerging biomarkers. sST2 testing has also been shown to predict onset of symptomatic HF in patients with acute myocardial infarction, while in community-based subjects, sST2 values independently predict future HF, cardiovascular disease events, and mortality.

Stress responses and pre-eclampsia

Biological stress may affect individual cells, tissues or whole organisms, arising from disturbed homoeostasis of any cause. Stress is rarely localised. Because biological systems are closely integrated, it spreads to involve other systems. Stress responses are highly integrated and work to restore homoeostasis. Different response pathways overlap and interlink. If the responses fail or decompensate, distress ensues, of which the end-stage is death. Pre-eclampsia results from a series of biological stresses, possibly from conception, which become established by abnormal placentation and affect the mother, her foetus and her placenta. The stresses involve dialogue between mother and placenta. Even a normal placenta imposes substantial stress on maternal systems. When placental growth and perfusion is abnormal (poor placentation) then the placenta, particularly its outer trophoblast layer, becomes stressed - loosely denoted hypoxic damage or oxidative stress. Signals from the placenta spread the stress to the mother, who develops signs of pre-eclampsia. Cellular stress sensors initiate stress responses. Different stresses may trigger similar responses in specific cell types. The first cell response is reduced protein synthesis. However some synthetic pathways are spared or activated to produce stress signals. In relation to pre-eclampsia and the placenta, an excessive release of sFlt-1 a soluble decoy receptor for vascular endothelial growth factor (VEGF) is a trophoblast related stress signal. SFlt1 perturbs the angiogenic balance in the maternal circulation and is considered to cause many of the specific features of the maternal syndrome in pre-eclampsia. Three key points will be emphasised. First, multiple stressors, not simply hypoxia, stimulate the release of sFlt-1 from trophoblast. Second, sFlt-1 is only one of the group of stress signals delivered by trophoblast to the mother. Third, sFlt-1 is not the only trophoblast derived factor to perturb the maternal circulation in pre-eclampsia.

Intravitreal Aflibercept for Neovascular Age-Related Macular Degeneration

Neovascular age-related macular degeneration (AMD) is the leading cause of legal blindness in patients over the age of 50 in the western world. Intravitreally administered anti-VEGF drugs have been developed to halt neovascular growth in AMD. Randomized trials have demonstrated the excellent safety profile and significant benefit of anti-VEGF therapy in maintaining vision. Aflibercept (Eylea(®); Regeneron, NY, USA) is a soluble decoy receptor against VEGF that offers greater potency and binding affinity than other anti-VEGF drugs. Having received US FDA approval for neovascular AMD in November 2011, aflibercept given every 8 weeks after a loading dose was 'clinically equivalent' and statistically noninferior to the current FDA-approved therapy ranibizumab (Lucentis(®); Genentech, CA, USA), given every 4 weeks. This article discusses the clinical background of AMD, development of aflibercept, results of the clinical trials and the future role of aflibercept in ocular neovascular diseases.

Association of serum osteoprotegerin with vascular calcification in patients with type 2 diabetes

BackgroundOsteoprotegerin is a member of the tumor necrosis factor-related family and inhibits RANK stimulation of osteoclast formation as a soluble decoy receptor. The goal of this study was to determine the relationship of serum osteoprotegerin with vascular calcification in patients with type 2 diabetes.MethodsThe subjects were 124 patients with type 2 diabetes mellitus, including 88 males and 36 females with a mean (± SD) age of 65.6 ± 8.2 years old. Serum levels of osteoprotegerin, osteocalcin, fibroblast growth factor 23 (FGF23), 25-hydroxyvitamin D3 and adiponectin were measured by ELISA. Vascular calcification in the cervical artery was examined by ultrasound sonography. The subjects were divided into 4 quartiles depending on serum osteoprotegerin levels.ResultsVascular calcification was significantly higher in the 4th quartile and significantly lower in the 1st quartile of serum osteoprotegerin levels, compared to other quartiles. There were no differences in serum osteoprotegerin and vascular calcification among patients with different stages of diabetic nephropathy, but serum FGF23 levels were elevated in those with stage 4 diabetic nephropathy. Simple regression analysis showed that serum osteoprotegerin levels had significant positive correlations with age, systolic blood pressure and serum adiponectin levels, and significant negative correlations with BMI and serum 25-hydroxyvitamin D3.ConclusionsThese findings suggest that elevated serum osteoprotegerin may be involved in vascular calcification independently of progression of diabetic nephropathy in patients with type 2 diabetes.

Soluble RAGE Plasma Levels in Patients with Coronary Artery Disease and Peripheral Artery Disease

The objective of the present study was define in a relatively large patient population with coronary artery disease (CAD) whether the concomitant presence of peripheral artery disease (PAD), which is known to convey additional cardiovascular risk, was associated with different circulating levels of sRAGE with respect to CAD alone and control subjects. Clinical and laboratory parameters including the ankle brachial index (ABI) and sRAGE (enzyme-linked immunosorbent assay kit) were investigated in 544 patients with angiographically documented CAD and 328 control subjects. 213/554 CAD patients (39%) showed an ABI <0.9 associated with typical symptoms (group CAD + PAD), whereas 331 patients were free from PAD. The concentration of plasma sRAGE was significantly lower (P < 0.0001) in CAD population, with and without PAD, than in control subjects. Among CAD patients, those with PAD showed lower levels of sRAGE. The distribution of the three groups (CAD, CAD + PAD, and controls) according to sRAGE tertiles showed that lower levels were more frequent in patients with CAD and CAD + PAD, whereas higher levels were more frequently found in controls. CAD patients presenting with PAD have lower sRAGE levels than CAD patients without peripheral atherosclerosis showing that stable atherosclerotic lesions in different vascular districts are inversely related to soluble decoy receptor sRAGE.

Disordered IL-33/ST2 Activation in Decidualizing Stromal Cells Prolongs Uterine Receptivity in Women with Recurrent Pregnancy Loss

Decidualization renders the endometrium transiently receptive to an implanting blastocyst although the underlying mechanisms remain incompletely understood. Here we show that human endometrial stromal cells (HESCs) rapidly release IL-33, a key regulator of innate immune responses, upon decidualization. In parallel, differentiating HESCs upregulate the IL-33 transmembrane receptor ST2L and other pro-inflammatory mediators before mounting a profound anti-inflammatory response that includes downregulation of ST2L and increased expression of the soluble decoy receptor sST2. We demonstrate that HESCs secrete factors permissive of embryo implantation in mice only during the pro-inflammatory phase of the decidual process. IL-33 knockdown in undifferentiated HESCs was sufficient to abrogate this pro-inflammatory decidual response. Further, sequential activation of the IL-33/ST2L/sST2 axis was disordered in decidualizing HESCs from women with recurrent pregnancy loss. Signals from these cultures prolonged the implantation window but also caused subsequent pregnancy failure in mice. Thus, Il-33/ST2 activation in HESCS drives an autoinflammatory response that controls the temporal expression of receptivity genes. Failure to constrain this response predisposes to miscarriage by allowing out-of-phase implantation in an unsupportive uterine environment.

Roles of Wnt signals in bone resorption during physiological and pathological states

Osteoclasts, multinucleated giant cells, are responsible for bone resorption in physiological and pathological conditions such as osteoporosis and rheumatoid arthritis. Osteoclasts develop from the monocyte/macrophage lineage under the strict control of bone-forming osteoblasts. Osteoblast-lineage cells express two cytokines essential for osteoclast differentiation, colony-stimulating factor-1, and receptor activator of nuclear factor κB ligand (RANKL) and also express osteoprotegerin, a soluble decoy receptor for RANKL. The signaling molecule Wnt has been shown to be important for the differentiation of osteoblasts through β-catenin-dependent canonical and β-catenin-independent noncanonical pathways. Recent studies have established that Wnt-mediated signals are also crucial for bone resorption in both physiological and pathological conditions. In this review, we introduce recent advances in roles of Wnt signaling in bone formation and bone resorption.

Aflibercept for Intravitreal Injection

Aflibercept is a recombinant human fusion protein that acts as a soluble decoy receptor for vascular endothelial growth factor (VEGF) family members VEGF-A, VEGF-B and placental growth factor, thereby preventing these ligands from binding to, and activating, their cognate receptors. The efficacy of intravitreal aflibercept in the treatment of wet (neovascular) age-related macular degeneration has been compared with that of intravitreal ranibizumab, the current gold standard for this indication, in two pivotal phase III studies of virtually identical design (VIEW 1 and 2). In both trials, the recommended regimen of aflibercept [2 mg every second month (after three initial monthly doses)] was shown to be noninferior to the recommended regimen of ranibizumab (0.5 mg every month) in terms of the primary endpoint of the proportion of patients who maintained their vision after 1 year of treatment; similar results were seen when monthly dosing with aflibercept (0.5 or 2 mg) was compared with ranibizumab. Over a period of 96 weeks in the VIEW studies, patients receiving the recommended regimen of aflibercept during the first year followed by modified quarterly treatment during the second year had a similar visual acuity gain to those receiving the recommended regimen of ranibizumab during first year followed by modified quarterly treatment during the second year, but on average required five fewer injections. Aflibercept was generally well tolerated in the VIEW studies; the ocular and non-ocular adverse event profile of the drug was similar to that of ranibizumab.

Treating inflammation by blocking interleukin-1 in a broad spectrum of diseases.

Interleukin-1 (IL-1) is a highly active pro-inflammatory cytokine that lowers pain thresholds and damages tissues. Monotherapy blocking IL-1 activity in autoinflammatory syndromes results in a rapid and sustained reduction in disease severity, including reversal of inflammation-mediated loss of sight, hearing and organ function. This approach can therefore be effective in treating common conditions such as post-infarction heart failure, and trials targeting a broad spectrum of new indications are underway. So far, three IL-1-targeted agents have been approved: the IL-1 receptor antagonist anakinra, the soluble decoy receptor rilonacept and the neutralizing monoclonal anti-IL-1β antibody canakinumab. In addition, a monoclonal antibody directed against the IL-1 receptor and a neutralizing anti-IL-1α antibody are in clinical trials.

AAV2-mediated gene transfer of VEGF-Trap with potent suppression of primary breast tumor growth and spontaneous pulmonary metastases by long-term expression

Vascular endothelial growth factor (VEGF) is an important signaling protein and a predominant mediator of angiogenesis in tumor growth and metastasis. Therefore, antagonism of the VEGF pathway results in inhibition of abnormal angiogenesis, then suppression of tumor growth and metastasis. VEGF-Trap, a high-affinity soluble decoy receptor, is currently in phase II clinical trails, and has demonstrated more efficacy in different types of solid tumors by intravenous injection every two weeks. In our study, we used recombinant AAV2 as a delivery vehicle to achieve long-lasting expression of VEGF Trap protein in a mouse model for the first time. We report that AAV2-VEGF-Trap can be safely administered and sustained expression invivo via a single intravenously administration, simultaneously suppressing primary tumor growth and preventing the pulmonary metastases of 4T1 tumors. Decreased microvessel density and increased tumor cell apoptosis were observed in the treatment group. AAV2-VEGF-Trap can obviously decrease not only the concentration of VEGF in sera, but also the concentration of other angiogenic factors, such as aFGF, bFGF, angiopoietin-1 and others. These studies suggest that AAV-mediated long-term expression of VEGF-Trap is a useful and safe tool to block tumor progression and inhibit spontaneous pulmonary metastases.

Specific elevation of DcR3 in sera of sepsis patients and its potential role as a clinically important biomarker of sepsis

Because of its potentially important role in the pathogenesis of sepsis, the expression of soluble decoy receptor 3 (DcR3) was investigated in sera of sepsis patients. The serum levels of DcR3 and its tumor necrosis factor–like ligand TL1A and homologous decoy receptor OPG were quantified by ELISA. The values of DcR3 to diagnose sepsis were analyzed by receiver-operating characteristic (ROC) curves. The results showed that DcR3 was significantly elevated in sepsis compared to systemic inflammatory response syndrome (SIRS), a condition similar to sepsis but resulting from noninfectious insults. DcR3 showed superior area under the ROC curve (AUC, 0.958) compared to poor AUCs of TL1A and OPG. At a cut-off of 3.24 ng/mL, DcR3 predicted sepsis from SIRS with 96% sensitivity and 82.6% specificity. DcR3 also predicted sepsis from cancer and inflammatory bowel disease with equally excellent values. Therefore, DcR3 serum level has the potential to serve as a reliable biomarker of sepsis.

Skeletal and extraskeletal actions of denosumab

Osteoclasts and osteoblasts define skeletal mass, structure and strength through their respective actions in resorbing and forming bone. This remodeling process is orchestrated by the actions of hormones and growth factors, which regulate a cytokine system comprising the receptor activator of nuclear factor κB ligand (RANKL), its receptor RANK and the soluble decoy receptor osteoprotegerin (OPG). Bone resorption depends on RANKL, which determines osteoclast formation, activity and survival. Importantly, cells of the osteoblastic lineage mainly provide RANKL and therefore, are central in the regulation of osteoclast functions. Catabolic effects of RANKL are inhibited by OPG, a TNF receptor family member that binds RANKL, thereby preventing the activation of its receptor RANK, which is expressed by osteoclast precursors. Because this cytokine network is pivotal for the regulation of bone mass in health and diseases, including osteoporosis, rheumatoid arthritis and malignant bone conditions, it has been successfully used for the generation of a targeted therapy to block osteoclast actions. The clinical approval of denosumab, a fully monoclonal antibody against RANKL, provides a novel option to treat bone diseases with a potent, targeted and reversible inhibitor of bone resorption. Although RANKL is also expressed by endothelial cells, T lymphocytes, synovial fibroblasts and various tumor cells, no meaningful clinical extraskeletal effects have been reported after administration of denosumab. This article summarizes the molecular and cellular basis of the RANKL/RANK/OPG system and presents preclinical and clinical studies on the skeletal actions of denosumab.

Soluble Vascular Endothelial Growth Factor Decoy Receptor FP3 Exerts Potent Antiangiogenic Effects

The binding of vascular endothelial growth factor (VEGF) to its receptors stimulates tumor growth; therefore, modulation of VEGF would be a viable approach for antiangiogenic therapy. We constructed a series of soluble decoy receptors containing different VEGF receptor 1 (FLT1) and VEGF receptor 2 (KDR) extracellular domains fused with the Fc region of human immunoglobulin (Ig) and evaluated their antiangiogenic effects and antitumor effects. Results of in vitro binding and cell proliferation assays revealed that decoy receptor FP3 had the highest affinity to VEGF-A and -B. Compared with bevacizumab, FP3 more effectively inhibited human umbilical vein endothelial cell (HUVEC) migration and vessel sprouting from rat aortic rings. FP3 significantly reduced phosphorylation of AKT and ERK1/2, critical proteins in the VEGF-mediated survival pathway in endothelial cells. Moreover, FP3 inhibited tumor growth in human hepatocellular carcinoma (HepG2), breast cancer (MCF-7), and colorectal cancer (LoVo) tumor models, and reduced microvessel density in tumor tissues. The FP3-mediated inhibition of tumor growth was significantly higher than that of bevacizumab at the same dose. FP3 also demonstrated synergistic antitumor effects when combined with 5-fluorouracil (5-FU). Taken together, FP3 shows a high affinity for VEGF and produced antiangiogenic effects, suggesting its potential for treating angiogenesis-related diseases such as cancer.

Human milk oligosaccharides: Every baby needs a sugar mama

Human milk oligosaccharides (HMOs) are a family of structurally diverse unconjugated glycans that are highly abundant in and unique to human milk. Originally, HMOs were discovered as a prebiotic "bifidus factor" that serves as a metabolic substrate for desired bacteria and shapes an intestinal microbiota composition with health benefits for the breast-fed neonate. Today, HMOs are known to be more than just "food for bugs". An accumulating body of evidence suggests that HMOs are antiadhesive antimicrobials that serve as soluble decoy receptors, prevent pathogen attachment to infant mucosal surfaces and lower the risk for viral, bacterial and protozoan parasite infections. In addition, HMOs may modulate epithelial and immune cell responses, reduce excessive mucosal leukocyte infiltration and activation, lower the risk for necrotizing enterocolitis and provide the infant with sialic acid as a potentially essential nutrient for brain development and cognition. Most data, however, stem from in vitro, ex vivo or animal studies and occasionally from association studies in mother-infant cohorts. Powered, randomized and controlled intervention studies will be needed to confirm relevance for human neonates. The first part of this review introduces the pioneers in HMO research, outlines HMO structural diversity and describes what is known about HMO biosynthesis in the mother's mammary gland and their metabolism in the breast-fed infant. The second part highlights the postulated beneficial effects of HMO for the breast-fed neonate, compares HMOs with oligosaccharides in the milk of other mammals and in infant formula and summarizes the current roadblocks and future opportunities for HMO research.

Abstract 1819: A MUC1-C oncoprotein soluble decoy receptor effectively suppresses the growth of human breast cancer cells

Abstract The Mucin 1 (MUC1) transmembrane glycoprotein is aberrantly overexpressed by most human breast carcinomas and contributes to the malignant phenotype. MUC1 is expressed as two subunits (MUC1-N and MUC1-C) that form a stable heterodimer at the cell surface. MUC1-N is shed to contribute to a protective physical barrier, leaving the oncogenic MUC1-C subunit at the cell surface as a putative receptor for signaling the presence of stress to the interior of the cell. As shown for the VEGF receptor TRAP, aflibercept, a potential approach for blocking MUC1-C function is to generate a soluble decoy receptor by fusing the MUC1-C extracellular domain to an Ig constant (Fc) region. The present studies demonstrate that in vitro treatment of human ZR-75-1 breast carcinoma cells with the MUC1-C soluble decoy receptor is associated with a dose-dependent induction of cell death. Similar findings were obtained with human MCF-7 breast cancer cells. To explore the potential of the MUC1-C soluble decoy receptor as an anti-cancer agent, we evaluated its ability to block the growth of breast cancer cells in subcutaneous tumor xenograft models growing in nude mice. Administration of the MUC1-C soluble decoy receptor to nude mice bearing established ZR-75-1 breast tumor xenografts was associated with a dose-dependent loss of tumorigenicity and prolonged tumor regressions after completing therapy. Taken together, these findings demonstrate that targeting the MUC1-C oncoprotein with a soluble decoy receptor is effective in inducing death of human breast cancer cells in vitro and in tumor models. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1819. doi:1538-7445.AM2012-1819

Abstract 306: TWEAK functions as chemotactic factor for glioma cells via Lyn activation

Abstract The long-term survival of patients with glioblastoma multiforme is compromised by the tumor's proclivity for local invasion into the surrounding normal brain. These invasive cells escape surgery and display resistance to chemotherapeutic- and radiation-induced apoptosis. We have previously shown that tumor necrosis factor-like weak inducer of apoptosis (TWEAK), a member of the tumor necrosis factor superfamily, can stimulate glioma cell invasion and survival via binding to the fibroblast growth factor-inducible 14 (Fn14) receptor and subsequent activation of the Rac1/NF-kappaB pathway. In addition, we have reported previously that Fn14 is expressed at high levels in migrating glioma cells in vitro and invading glioma cells in vivo. Here we demonstrate that TWEAK can act as a chemotactic factor for glioma cells, a potential process to drive cell invasion into the surrounding brain tissue. Specifically, we detected a chemotactic migration of glioma cells to the concentration gradient of TWEAK using the Modified Boyden chamber assay. Because TWEAK has been shown to be expressed in normal astrocytes, microglia, and endothelial cells, we neutralized TWEAK using a recombinant soluble murine Fn14-Fc decoy receptor and examined the effect on glioma cell invasion in the ex vivo rat brain slice model. Incubation of the brain slice with the Fn14-Fc decoy receptor reduced glioma cell invasion as compared to control IgG treated brain slice. Since Src family kinases (SFK) have been implicated in chemotaxis, we next determined whether TWEAK:Fn14 engagement activated these cytoplasmic tyrosine kinases. Our data shows that TWEAK stimulation of glioma cells results in a rapid phosphorylation of Src as detected by Western blot analysis using a pan-Src phosphorylation antibody. To determine which SFK member is phosphorylated by TWEAK, we applied the multiplex Luminex assay and identified Lyn as a candidate SFK. Immunoprecipitation of Lyn from TWEAK-treated cells verified that Lyn is phosphorylated as determined by phosphotyrosine immunoblot analysis. Immunodepletion of Lyn by siRNA oligonucleotides suppressed the chemoattractive effect of TWEAK on glioma cells. We hypothesize that TWEAK secretion by cells present in the glioma microenvironment induce invasion of glioma cells into the brain parenchyma. Understanding the function and signaling of the TWEAK-Fn14 ligand-receptor system may lead to development of novel therapies to therapeutically target invasive glioma cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 306. doi:1538-7445.AM2012-306

Delayed Toxicity Associated with Soluble Anthrax Toxin Receptor Decoy-Ig Fusion Protein Treatment

Soluble receptor decoy inhibitors, including receptor-immunogloubulin (Ig) fusion proteins, have shown promise as candidate anthrax toxin therapeutics. These agents act by binding to the receptor-interaction site on the protective antigen (PA) toxin subunit, thereby blocking toxin binding to cell surface receptors. Here we have made the surprising observation that co-administration of receptor decoy-Ig fusion proteins significantly delayed, but did not protect, rats challenged with anthrax lethal toxin. The delayed toxicity was associated with the in vivo assembly of a long-lived complex comprised of anthrax lethal toxin and the receptor decoy-Ig inhibitor. Intoxication in this system presumably results from the slow dissociation of the toxin complex from the inhibitor following their prolonged circulation. We conclude that while receptor decoy-Ig proteins represent promising candidates for the early treatment of B. anthracis infection, they may not be suitable for therapeutic use at later stages when fatal levels of toxin have already accumulated in the bloodstream.

Osteoclastic bone resorption directly activates osteoblast function

Osteoclasts, the multinucleated cells that resorb bone, originate from cell cycle-arrested quiescent osteoclast precursors [1]. Mesenchymal osteoblastic cells are involved in osteoclast differentiation. Osteoclast precursors express RANK (a receptor of RANKL), recognize RANKL expressed by osteoblasts through cell-cell interaction and differentiate into osteoclasts in the presence of M-CSF. OPG, produced mainly by osteoblasts, is a soluble decoy receptor for RANKL. Deficiency of OPG in mice induces osteoporosis caused enhanced bone resorption. Elevated osteoblastic activity was suppressed by bisphosphonate administration in OPG-deficient mice. These results suggest that bone formation is accurately coupled with bone resorption. Collagen sponge disks containing BMP-2 were implanted into the dorsal muscle pouches in OPG-deficient mice. TRAP-positive osteoclasts and ALP-positive osteoblasts were observed in BMP-2-disks preceding the onset of calcification for one week. OPG and soluble RANK inhibited BMP-2-induced osteoclast formation but not the appearance of ALP-positive cells in OPG-deficient mice. We then examined how osteoblasts are involved in osteoclastogenesis other than RANKL expression, using RANKL-deficient mice. RANKL-deficient mice showed severe osteopetrosis due to loss of osteoclasts. Injection of RANKL into RANKL-deficient mice induced many osteoclasts in bone but not soft tissues [2]. These results suggest that osteoblasts determine the place of osteoclastogenesis from haemopoietic stem cells in bone. We next explored roles of osteoclasts in ectopic bone formation induced by BMP using op/op and c-fos-deficient osteopetrotic mice. The ectopic bones formed in op/op mice showed extremely rough surfaces, whereas those in wild-type mice showed smooth ones. Bone mineral density of BMP-induced ectopic bone in op/op mice was about 2-times higher than that in wild-type mice. TRAP-positive osteoclasts exhibit in outer of the ectopic bone in the wild-type mice. In op/op mice, although osteoclasts strongly exhibit in inside of the BMP-induced ectopic bone, TRAP-positive osteoclasts did not exhibit in outer of the BMP-induced ectopic bone. Furthermore, the accentuation of the BMP-induced ectopic bone formation did not exist in osteopetrotic c-Fos-deficient mice. In c-Fos-deficient mice, which are completely osteoclasts deficiency, the accentuation of the BMP-induced ectopic bone formation did not exist. Furthermore, there is no RANK-positive osteoclast progenitors in bone derived from c-Fos-deficient mice. These results suggest that RANK-positive osteoclast progenitors are positively regulate the signal of bone formation. In summary, osteoclastic bone resorption directly activates osteoblast function and osteoclasts are involved in normal bone morphogenesis.