SMG1, a nonsense-mediated mRNA decay (NMD) regulator, as a candidate therapeutic target in multiple myeloma

Early data suggested that CC-115, a clinical molecule, already known to inhibit the mammalian target of rapamycin kinase (TORK) and DNA-dependent protein kinase (DNA-PK) may have additional targets beyond TORK and DNA-PK. Therefore, we aimed to identify such target(s) and investigate a potential therapeutic applicability. Functional profiling of 141 cancer cell lines revealed inhibition of kinase suppressor of morphogenesis in genitalia 1 (SMG1), a key regulator of the RNA degradation mechanism nonsense-mediated mRNA decay (NMD), as an additional target of CC-115. CC-115 treatment showed a dose-dependent increase of SMG1-mediated NMD transcripts. A subset of cell lines, including multiple myeloma (MM) cell lines sensitive to the endoplasmic reticulum stress-inducing compound thapsigargin, were highly susceptible to SMG1 inhibition. CC-115 caused the induction of UPR transcripts and cell death by mitochondrial apoptosis, requiring the presence of BAX/BAK and caspase activity. Superior antitumor activity of CC-115 over TORK inhibitors in primary human MM cells and three xenograft mouse models appeared to be via inhibition of SMG1. Our data support further development of SMG1 inhibitors as possible therapeutics in MM.

Clinical activity of CC-90011, an oral, potent, and reversible LSD1 inhibitor, in advanced malignancies

Background

CC‐90011 is an oral, potent, selective, reversible inhibitor of lysine‐specific demethylase 1 (LSD1) that was well tolerated, with encouraging activity in patients who had advanced solid tumors or relapsed/refractory marginal zone lymphoma. The authors present long‐term safety and efficacy and novel pharmacodynamic and pharmacokinetic data from the first‐in‐human study of CC‐90011.

Methods

CC‐90011‐ST‐001 (ClincalTrials.gov identifier NCT02875223; Eudract number 2015–005243‐13) is a phase 1, multicenter study in which patients received CC‐90011 once per week in 28‐day cycles. The objectives were to determine the safety, maximum tolerated dose, and/or recommended phase 2 dose (primary) and to evaluate preliminary efficacy and pharmacokinetics (secondary).

Results

Sixty‐nine patients were enrolled, including 50 in the dose‐escalation arm and 19 in the dose‐expansion arm. Thrombocytopenia was the most common treatment‐related adverse event and was successfully managed with dose modifications. Clinical activity with prolonged, durable responses were observed, particularly in patients who had neuroendocrine neoplasms. In the dose‐escalation arm, one patient with relapsed/refractory marginal zone lymphoma achieved a complete response (ongoing in cycle 58). In the dose‐expansion arm, three patients with neuroendocrine neoplasms had stable disease after nine or more cycles, including one patient who was in cycle 46 of ongoing treatment. CC‐90011 decreased levels of secreted neuroendocrine peptides chromogranin A, progastrin‐releasing peptide, and RNA expression of the blood pharmacodynamic marker monocyte‐to‐macrophage differentiation–associated.

Conclusions

The safety profile of CC‐90011 suggested that its reversible mechanism of action may provide an advantage over other irreversible LSD1 inhibitors. The favorable tolerability profile, clinical activity, durable responses, and once‐per‐week dosing support further exploration of CC‐90011 as monotherapy and in combination with other treatments for patients with advanced solid tumors and other malignancies.

This first‐in‐human study evaluated CC‐90011, a highly potent, selective, and reversible oral lysine‐specific demethylase 1 inhibitor, in patients with advanced solid tumors and relapsed/refractory lymphoma. The tolerability, clinical activity, and once‐weekly dosing support further exploration of CC‐90011 in patients with advanced malignancies.

Phase I study of CC-90010, a reversible, oral BET inhibitor in patients with advanced solid tumors and relapsed/refractory non-Hodgkin's lymphoma

BACKGROUND

Bromodomain and extra-terminal (BET) proteins are epigenetic readers that regulate expression of genes involved in oncogenesis. CC-90010 is a novel, oral, reversible, small-molecule BET inhibitor.

PATIENTS AND METHODS

CC-90010-ST-001 (NCT03220347; 2015-004371-79) is a phase I dose-escalation and expansion study of CC-90010 in patients with advanced or unresectable solid tumors and relapsed/refractory (R/R) non-Hodgkin's lymphoma (NHL). We report results from the dose escalation phase, which explored 11 dose levels and four dosing schedules, two weekly (2 days on/5 days off; 3 days on/4 days off), one biweekly (3 days on/11 days off), and one monthly (4 days on/24 days off). The primary objectives were to determine the safety, maximum tolerated dose (MTD) and/or recommended phase II dose (RP2D) and schedule. Secondary objectives were to evaluate signals of early antitumor activity, pharmacokinetics, and pharmacodynamics.

RESULTS

This study enrolled 69 patients, 67 with solid tumors and two with diffuse large B-cell lymphoma (DLBCL). The median age was 57 years (range, 21-80) and the median number of prior regimens was four (range, 1-9). Treatment-related adverse events (TRAEs) were mostly mild and manageable; grade 3/4 TRAEs reported in more than two patients were thrombocytopenia (13%), anemia, and fatigue (4% each). Six patients had dose-limiting toxicities. MTDs were 15 mg (2 days on/5 days off), 30 mg (3 days on/11 days off), and 45 mg (4 days on/24 days off). The RP2D and schedule selected for expansion was 45 mg (4 days on/24 days off). As of 8 October 2019, one patient with grade 2 astrocytoma achieved a complete response, one patient with endometrial carcinoma had a partial response, and six patients had prolonged stable disease ≥11 months.

CONCLUSIONS

CC-90010 is well tolerated, with single-agent activity in patients with heavily pretreated, advanced solid tumors.

First-In-Human Phase I Study Of A Dual mTOR Kinase And DNA-PK Inhibitor (CC-115) In Advanced Malignancy

Purpose

This first-in-human Phase I study investigated the safety, pharmacokinetics (PK), pharmacodynamic profile, and preliminary efficacy of CC-115, a dual inhibitor of mammalian target of rapamycin (mTOR) kinase and DNA-dependent protein kinase.

Patients and Methods

Patients with advanced solid or hematologic malignancies were enrolled in dose-finding and cohort expansion phases. In dose-finding, once-daily or twice-daily (BID) ascending oral doses of CC-115 (range: 0.5-40 mg/day) in 28-day continuous cycles identified the maximum-tolerated dose for cohort expansion in 5 specified tumor types. Twelve additional patients with mixed solid tumors participated in a bioavailability substudy.

Results

Forty-four patients were enrolled in the dose-finding cohort. Dose-limiting toxicity included thrombocytopenia, stomatitis, hyperglycemia, asthenia/fatigue, and increased transaminases. CC-115 10 mg BID was selected for cohort expansion (n=74) in which fatigue, nausea, and decreased appetite were the most frequent toxicities. Dose-proportional PK was found. CC-115 distributed to glioblastoma tissue (mean tumor/plasma concentration ratio: 0.713). Total exposure of CC-115 was similar under fasting and fed conditions. A patient with endometrial carcinoma remained in complete remission >4 years. Partial response (PR; n=2) and stable disease (SD; n=4) were reported in the bioavailability substudy; SD was reached in 53%, 22%, 21%, and 64% of patients with head and neck squamous cell carcinoma, Ewing sarcoma, glioblastoma multiforme, and castration-resistant prostate cancer, respectively. Chronic lymphocytic leukemia/small lymphocytic lymphoma showed 38% PR and 25% SD.

Conclusion

CC-115 was well-tolerated, with toxicities consistent with mTOR inhibitors. Together with biomarker inhibition and preliminary efficacy, oral CC-115 10 mg BID is a promising novel anticancer treatment.

Clinical trial registration

NCT01353625.

A phase 2 study of an oral mTORC1/mTORC2 kinase inhibitor (CC-223) for non-pancreatic neuroendocrine tumors with or without carcinoid symptoms

Second-generation mammalian target of rapamycin (mTOR) inhibitors such as CC-223 may have theoretical advantages over first-generation drugs by inhibiting TOR kinase in mTOR complex 1 (mTORC1) and 2 (mTORC2), potentially improving clinical efficacy for well-differentiated neuroendocrine tumors (NET).Enrolled patients had metastatic, well-differentiated NET of non-pancreatic gastrointestinal or unknown origin, with/without carcinoid symptoms, had failed ≥1 systemic chemotherapy, and were taking a somatostatin analog (SSA). Oral once-daily CC-223 was administered in 28-day cycles starting at 45 mg (n = 24), with a subsequent cohort starting at 30 mg (n = 23). Objectives were to evaluate tolerability, preliminary efficacy, and pharmacokinetic and biomarker profiles of CC-223. Forty-seven patients completed the study, with mean treatment duration of 378 days and mean dose of 26 mg; 26% of patients remained on the starting dose. Most frequent grade ≥3 toxicities were diarrhea (38%), fatigue (21%), and stomatitis (11%). By investigator, 3 of 41 evaluable patients (7%) showed partial response (PR) and 34 (83%) had stable disease (SD) for a disease control rate (DCR) of 90% (95% confidence interval [CI] 76.9–97.3%). Duration of PR was 125–401 days; median SD duration was 297 days (min–max, 50–1519 days). Median progression-free survival was 19.5 months (95% CI 10.4–28.5 months). Carcinoid symptoms of flushing, diarrhea, or both improved in 50%, 41%, and 39% of affected patients, respectively. For the first time, this study describes that a second-generation mTOR pathway inhibitor can result in highly durable tumor regression and control of NET carcinoid symptoms. The manageable safety profile, high DCR, and durable response, coupled with reduction in carcinoid symptoms refractory to SSA, make CC-223 a promising agent for further development.

Pleiotropic Impact of DNA-PK in Cancer and Implications for Therapeutic Strategies

PURPOSE

DNA-dependent protein kinase catalytic subunit (DNA-PK) is a pleiotropic kinase involved in DNA repair and transcriptional regulation. DNA-PK is deregulated in selected cancer types and is strongly associated with poor outcome. The underlying mechanisms by which DNA-PK promotes aggressive tumor phenotypes are not well understood. Here, unbiased molecular investigation in clinically relevant tumor models reveals novel functions of DNA-PK in cancer.Experimental Design: DNA-PK function was modulated using both genetic and pharmacologic methods in a series of in vitro models, in vivo xenografts, and patient-derived explants (PDE), and the impact on the downstream signaling and cellular cancer phenotypes was discerned. Data obtained were used to develop novel strategies for combinatorial targeting of DNA-PK and hormone signaling pathways.

RESULTS

Key findings reveal that (i) DNA-PK regulates tumor cell proliferation; (ii) pharmacologic targeting of DNA-PK suppresses tumor growth both in vitro, in vivo, and ex vivo; (iii) DNA-PK transcriptionally regulates the known DNA-PK-mediated functions as well as novel cancer-related pathways that promote tumor growth; (iv) dual targeting of DNA-PK/TOR kinase (TORK) transcriptionally upregulates androgen signaling, which can be mitigated using the androgen receptor (AR) antagonist enzalutamide; (v) cotargeting AR and DNA-PK/TORK leads to the expansion of antitumor effects, uncovering the modulation of novel, highly relevant protumorigenic cancer pathways; and (viii) cotargeting DNA-PK/TORK and AR has cooperative growth inhibitory effects in vitro and in vivo.

CONCLUSIONS

These findings uncovered novel DNA-PK transcriptional regulatory functions and led to the development of a combinatorial therapeutic strategy for patients with advanced prostate cancer, currently being tested in the clinical setting.

DNA-Dependent Protein Kinase Drives Prostate Cancer Progression through Transcriptional Regulation of the Wnt Signaling Pathway

PURPOSE

Protein kinases are known to play a prominent role in oncogenic progression across multiple cancer subtypes, yet their role in prostate cancer progression remains underexplored. The purpose of this study was to identify kinases that drive prostate cancer progression.Experimental Design: To discover kinases that drive prostate cancer progression, we investigated the association between gene expression of all known kinases and long-term clinical outcomes in tumor samples from 545 patients with high-risk disease. We evaluated the impact of genetic and pharmacologic inhibition of the most significant kinase associated with metastatic progression in vitro and in vivo.

RESULTS

DNA-dependent protein kinase (DNAPK) was identified as the most significant kinase associated with metastatic progression in high-risk prostate cancer. Inhibition of DNAPK suppressed the growth of both AR-dependent and AR-independent prostate cancer cells. Gene set enrichment analysis nominated Wnt as the top pathway associated with DNAPK. We found that DNAPK interacts with the Wnt transcription factor LEF1 and is critical for LEF1-mediated transcription.

CONCLUSIONS

Our data show that DNAPK drives prostate cancer progression through transcriptional regulation of Wnt signaling and is an attractive therapeutic target in aggressive prostate cancer.

A technology platform to assess multiple cancer agents simultaneously within a patient's tumor

A fundamental problem in cancer drug development is that antitumor efficacy in preclinical cancer models does not translate faithfully to patient outcomes. Much of early cancer drug discovery is performed under in vitro conditions in cell-based models that poorly represent actual malignancies. To address this inconsistency, we have developed a technology platform called CIVO, which enables simultaneous assessment of up to eight drugs or drug combinations within a single solid tumor in vivo. The platform is currently designed for use in animal models of cancer and patients with superficial tumors but can be modified for investigation of deeper-seated malignancies. In xenograft lymphoma models, CIVO microinjection of well-characterized anticancer agents (vincristine, doxorubicin, mafosfamide, and prednisolone) induced spatially defined cellular changes around sites of drug exposure, specific to the known mechanisms of action of each drug. The observed localized responses predicted responses to systemically delivered drugs in animals. In pair-matched lymphoma models, CIVO correctly demonstrated tumor resistance to doxorubicin and vincristine and an unexpected enhanced sensitivity to mafosfamide in multidrug-resistant lymphomas compared with chemotherapy-naïve lymphomas. A CIVO-enabled in vivo screen of 97 approved oncology agents revealed a novel mTOR (mammalian target of rapamycin) pathway inhibitor that exhibits significantly increased tumor-killing activity in the drug-resistant setting compared with chemotherapy-naïve tumors. Finally, feasibility studies to assess the use of CIVO in human and canine patients demonstrated that microinjection of drugs is toxicity-sparing while inducing robust, easily tracked, drug-specific responses in autochthonous tumors, setting the stage for further application of this technology in clinical trials.

Blocking neuropilin-2 function inhibits tumor cell metastasis

Metastasis, which commonly uses lymphatics, accounts for much of the mortality associated with cancer. The vascular endothelial growth factor (VEGF)-C coreceptor, neuropilin-2 (Nrp2), modulates but is not necessary for developmental lymphangiogenesis, and its significance for metastasis is unknown. An antibody to Nrp2 that blocks VEGFC binding disrupts VEGFC-induced lymphatic endothelial cell migration, but not proliferation, in part independently of VEGF receptor activation. It does not affect established lymphatics in normal adult mice but reduces tumoral lymphangiogenesis and, importantly, functional lymphatics associated with tumors. It also reduces metastasis to sentinel lymph nodes and distant organs, apparently by delaying the departure of tumor cells from the primary tumor. Our results demonstrate that Nrp2, which was originally identified as an axon-guidance receptor, is an attractive target for modulating metastasis.

TGF-beta regulates the mechanical properties and composition of bone matrix

The characteristic toughness and strength of bone result from the nature of bone matrix, the mineralized extracellular matrix produced by osteoblasts. The mechanical properties and composition of bone matrix, along with bone mass and architecture, are critical determinants of a bone's ability to resist fracture. Several regulators of bone mass and architecture have been identified, but factors that regulate the mechanical properties and composition of bone matrix are largely unknown. We used a combination of high-resolution approaches, including atomic-force microscopy, x-ray tomography, and Raman microspectroscopy, to assess the properties of bone matrix independently of bone mass and architecture. Properties were evaluated in genetically modified mice with differing levels of TGF-beta signaling. Bone matrix properties correlated with the level of TGF-beta signaling. Smad3+/- mice had increased bone mass and matrix properties, suggesting that the osteopenic Smad3-/- phenotype may be, in part, secondary to systemic effects of Smad3 deletion. Thus, a reduction in TGF-beta signaling, through its effector Smad3, enhanced the mechanical properties and mineral concentration of the bone matrix, as well as the bone mass, enabling the bone to better resist fracture. Our results provide evidence that bone matrix properties are controlled by growth factor signaling.

Loss of the serine/threonine kinase fused results in postnatal growth defects and lethality due to progressive hydrocephalus

The Drosophila Fused (Fu) kinase is an integral component of the Hedgehog (Hh) pathway that helps promote Hh-dependent gene transcription. Vertebrate homologues of Fu function in the Hh pathway in vitro, suggesting that Fu is evolutionarily conserved. We have generated fused (stk36) knockout mice to address the in vivo function of the mouse Fu (mFu) homologue. fused knockouts develop normally, being born in Mendelian ratios, but fail to thrive within 2 weeks, displaying profound growth retardation with communicating hydrocephalus and early mortality. The fused gene is expressed highly in ependymal cells and the choroid plexus, tissues involved in the production and circulation of cerebral spinal fluid (CSF), suggesting that loss of mFu disrupts CSF homeostasis. Similarly, fused is highly expressed in the nasal epithelium, where fused knockouts display bilateral suppurative rhinitis. No obvious defects were observed in the development of organs where Hh signaling is required (limbs, face, bones, etc.). Specification of neuronal cell fates by Hh in the neural tube was normal in fused knockouts, and induction of Hh target genes in numerous tissues is not affected by the loss of mFu. Furthermore, stimulation of fused knockout cerebellar granule cells to proliferate with Sonic Hh revealed no defect in Hh signal transmission. These results show that the mFu homologue is not required for Hh signaling during embryonic development but is required for proper postnatal development, possibly by regulating the CSF homeostasis or ciliary function.

Angiogenesis is required for successful bone induction during distraction osteogenesis

The role of angiogenesis during mechanically induced bone formation is incompletely understood. The relationship between the mechanical environment, angiogenesis, and bone formation was determined in a rat distraction osteogenesis model. Disruption of either the mechanical environment or endothelial cell proliferation blocked angiogenesis and bone formation. This study further defines the role of the mechanical environment and angiogenesis during distraction osteogenesis.

INTRODUCTION

Whereas successful fracture repair requires a coordinated and complex transcriptional program that integrates mechanotransductive signaling, angiogenesis, and osteogenesis, the interdependence of these processes is not fully understood. In this study, we use a system of bony regeneration known as mandibular distraction osteogenesis (DO) in which a controlled mechanical stimulus promotes bone induction after an osteotomy and gradual separation of the osteotomy edges to examine the relationship between the mechanical environment, angiogenesis, and osteogenesis.

MATERIALS AND METHODS

Adult Sprague-Dawley rats were treated with gradual distraction, gradual distraction plus the angiogenic inhibitor TNP-470, or acute distraction (a model of failed bony regeneration). Animals were killed at the end of distraction (day 13) or at the end of consolidation (day 41) and examined with muCT, histology, and immunohistochemistry for angiogenesis and bone formation (n = 4 per time-point per group). An additional group of animals (n = 6 per time-point per group) was processed for microarray analysis at days 5, 9, 13, 21, and 41.

RESULTS AND CONCLUSIONS

Either TNP-470 administration or disruption of the mechanical environment prevented normal osteogenesis and resulted in a fibrous nonunion. Subsequent analysis of the regenerate showed an absence of angiogenesis by gross histology and immunohistochemical localization of platelet endothelial cell adhesion molecule in the groups that failed to heal. Microarray analysis revealed distinct patterns of expression of genes associated with osteogenesis, angiogenesis, and hypoxia in each of the three groups. Our findings confirm the interdependence of the mechanical environment, angiogenesis, and osteogenesis during DO, and suggest that induction of proangiogenic genes and the proper mechanical environment are both necessary to support new vasculature for bone induction in DO.

WISP-1 is an osteoblastic regulator expressed during skeletal development and fracture repair

Wnt-1-induced secreted protein 1 (WISP-1) is a member of the CCN (connective tissue growth factor, Cyr61, NOV) family of growth factors. Experimental evidence suggests that CCN family members are involved in skeletogenesis and bone healing. To investigate the role of WISP-1 in osteogenic processes, we characterized its tissue and cellular expression and evaluated its activity in osteoblastic and chondrocytic cell culture models. During embryonic development, WISP-1 expression was restricted to osteoblasts and to osteoblastic progenitor cells of the perichondral mesenchyme. In vitro, we showed that WISP-1 expression in differentiating osteoblasts promotes BMP-2-induced osteoblastic differentiation. Using in situ and cell binding analysis, we demonstrated WISP-1 interaction with perichondral mesenchyme and undifferentiated chondrocytes. We evaluated the effect of WISP-1 on chondrocytes by generating stably transfected mouse chondrocytic cell lines. In these cells, WISP-1 increased proliferation and saturation density but repressed chondrocytic differentiation. Because of the similarity between skeletogenesis and bone healing, we also analyzed WISP-1 spatiotemporal expression in a fracture repair model. We found that WISP-1 expression recapitulates the pattern observed during skeletal development. Our data demonstrate that WISP-1 is an osteogenic potentiating factor promoting mesenchymal cell proliferation and osteoblastic differentiation while repressing chondrocytic differentiation. Therefore, we propose that WISP-1 plays an important regulatory role during bone development and fracture repair.

Creation and characterization of a mouse model of mandibular distraction osteogenesis

While the histological and ultrastructural changes associated with distraction osteogenesis have been extensively characterized using various animal models, the molecular mechanisms governing this technique remain poorly understood. In the current study, for the first time, we describe a mouse mandibular distraction osteogenesis model. Development of this model will allow assessment of factors involved in normal vs. abnormal healing (especially in non-unions) of craniofacial skeletal elements. Complete osteotomies were created on the right hemimandibles of 51 adult male CD-1 mice and customized distraction devices attached. Thirty-three animals underwent gradual distraction (5 days latency, distraction at 0.2 mm BID x 8 days, 28 days consolidation), while the remaining 18 mice underwent acute lengthening (immediate distraction to 3.2 mm) at the time of surgery. Mandibles were harvested at time points corresponding to the latent (POD 5), distraction (POD 9, 13), and consolidation (POD 28, 41) periods and processed for histological or quantitative real-time RT-PCR analysis. Specimens from each group were processed for microCT analysis. Histological and radiological data demonstrated that all mandibles undergoing gradual distraction achieved complete bony union by the end of consolidation, while those undergoing acute lengthening formed a fibrous non-union. Quantitative real-time RT-PCR demonstrated upregulation of mRNA for VEGF, FGF-2, collagen I, and osteopontin during gradual distraction but not during acute lengthening. These data validate our novel mouse mandibular distraction model and demonstrate its utility in elucidating the molecular mechanisms regulating bone formation during distraction osteogenesis as compared to those that are expressed during the formation of fibrous non-unions.

Angiogenesis and bone repair

The intimate connection, both physical and biochemical, between blood vessels and bone cells has long been recognized. Genetic, biochemical, and pharmacological studies have identified and characterized factors involved in the conversation between endothelial cells (EC) and osteoblasts (OB) during both bone formation and repair. The long-awaited FDA approval of two growth factors, BMP-2 and OP-1, with angiogenic and osteogenic activity confirms the importance of these two processes in human skeletal healing. In this review, the role of osteogenic factors in the adaptive response and interactive function of OB and EC during the multi-step process of bone repair will be discussed.

A slow release formulation of insulin as a treatment for osteoarthritis

OBJECTIVE

To examine the potential of insulin, in a sustained delivery system, as a treatment for arthritis.

DESIGN

The effect of insulin on matrix synthesis, matrix breakdown, and nitric oxide production in primary cartilage explants was examined. The activity of insulin on diseased cartilage from Dunkin Hartley guinea pigs, diabetic mice, and osteoarthritic patients was measured. The specificity of insulin stimulation was compared to that of IGF-I using osteoblasts and fibroblasts. Finally, the stability of insulin in a biologically relevant system was tested, and a slow-release formulation of insulin was developed and characterized.

RESULTS

In articular cartilage explants, insulin stimulated proteoglycan (PG) synthesis, inhibited PG release and nitric oxide production, and overcame the detrimental effects of interleukin 1 (IL-1). The mechanism whereby insulin decreased matrix breakdown was through inhibition of aggrecanase activity. Insulin was active on cartilage at concentrations at which insulin does not cross-react with insulin-like growth factor I (IGF-I) receptors nor stimulate proliferation of other cells types. The response of cartilage to insulin did not diminish with age or disease. Insulin stimulated matrix synthesis in osteoarthritic cartilage and local treatment with insulin overcame endogenous suppression of matrix synthesis in diabetic cartilage. Poly-lactic-coglycolic acid (PLGA) was found to be an effective carrier for delivery of insulin, and PLGA-Insulin was active on articular cartilage in vitro and in vivo.

CONCLUSIONS

As the incidence of arthritis increases with the aging population, an effective therapy to induce repair of cartilage is needed. Based on its biological activities, insulin appears to be an attractive protein therapeutic candidate. Maximum insulin effectiveness may require a sustained delivery system.

Stanniocalcin 1 alters muscle and bone structure and function in transgenic mice

Fish stanniocalcin (STC) inhibits uptake of calcium and stimulates phosphate reabsorption. To determine the role of the highly homologous mammalian protein, STC-1, we created and characterized transgenic mice that express STC-1 under control of a muscle-specific promoter. STC-1 transgenic mice were smaller than wild-type littermates and had normal growth plate cartilage morphology but increased cartilage matrix synthesis. In STC-1 mice, the rate of bone formation, but not bone mineralization, was decreased. Increased cortical bone thickness and changes in trabeculae number, density, and thickness in STC-1 mice indicated a concomitant suppression of osteoclast activity, which was supported by microcomputed tomography analyses and histochemistry. Skeletal muscles were disproportionately small and showed altered function and response to injury in STC-1 mice. Electron microscopy indicated that muscle mitochondria were dramatically enlarged in STC-1 mice. These changes in STC-1 mice could not be explained by deficits in blood vessel formation, as vascularity in organs and skeletal tissues was increased as was induction of vascularity in response to femoral artery ligation. Our results indicate that STC-1 can affect calcium homeostasis, bone and muscle mass and structure, and angiogenesis through effects on osteoblasts, osteoclasts, myoblasts/myocytes, and endothelial cells.

Interleukin 17 induced nitric oxide suppresses matrix synthesis and protects cartilage from matrix breakdown

OBJECTIVE

To investigate the role of nitric oxide (NO) in basal and cytokine induced cartilage matrix breakdown and synthesis across different species and in chondrocytes cultured as isolated cells or as tissue explants.

METHODS

Articular cartilage from bovine, porcine, or human joints was cultured as explants in serum-free media. Explants or monolayer cultures of primary chondrocytes were treated with cytokines in the absence or presence of inhibitors [antibodies to leukemia inhibitory factor (anti-LIF) or tumor necrosis factor-alpha, dexamethasone, or inhibitors of aggrecanase or NO synthase]. NO production and matrix breakdown and synthesis were measured.

RESULTS

At low concentrations, a novel interleukin 17 (IL-17) family member induced matrix breakdown without altering NO production. Treatment of articular cartilage explants with dexamethasone or anti-LIF blocked NO production by IL-17, but not by IL-1alpha. Inhibition of NO production in cytokine treated cartilage explants enhanced matrix breakdown and partially overcame suppression of matrix synthesis. In isolated chondrocytes, inhibition of NO production decreased expression of gelatinase and increased expression of stromelysin.

CONCLUSION

Endogenous NO serves a dual function in cartilage: to protect the tissue from matrix breakdown and to mediate suppression of proteoglycan synthesis by cytokines. Despite the similarities in biological function between IL-I and IL-17, their downstream signaling pathways are distinct and appear to be affected by extracellular matrix degradation.

Vascular endothelial growth factor stimulates bone repair by promoting angiogenesis and bone turnover

Several growth factors are expressed in distinct temporal and spatial patterns during fracture repair. Of these, vascular endothelial growth factor, VEGF, is of particular interest because of its ability to induce neovascularization (angiogenesis). To determine whether VEGF is required for bone repair, we inhibited VEGF activity during secondary bone healing via a cartilage intermediate (endochondral ossification) and during direct bone repair (intramembranous ossification) in a novel mouse model. Treatment of mice with a soluble, neutralizing VEGF receptor decreased angiogenesis, bone formation, and callus mineralization in femoral fractures. Inhibition of VEGF also dramatically inhibited healing of a tibial cortical bone defect, consistent with our discovery of a direct autocrine role for VEGF in osteoblast differentiation. In separate experiments, exogenous VEGF enhanced blood vessel formation, ossification, and new bone (callus) maturation in mouse femur fractures, and promoted bony bridging of a rabbit radius segmental gap defect. Our results at specific time points during the course of healing underscore the role of VEGF in endochondral vs. intramembranous ossification, as well as skeletal development vs. bone repair. The responses to exogenous VEGF observed in two distinct model systems and species indicate that a slow-release formulation of VEGF, applied locally at the site of bone damage, may prove to be an effective therapy to promote human bone repair.

Pathways by which interleukin 17 induces articular cartilage breakdown in vitro and in vivo

Overexpression of interleukin (IL-)17 has recently been shown to be associated with a number of pathological conditions. Because IL-17 is found at high levels in the synovial fluid surrounding cartilage in patients with inflammatory arthritis, the present study determined the direct effect of IL-17 on articular cartilage. As shown herein, IL-17 was a direct and potent inducer of matrix breakdown and an inhibitor of matrix synthesis in articular cartilage explants. These effects were mediated in part by leukemia inhibitory factor (LIF), but did not depend on interleukin-1 activity. The mechanism whereby IL-17 induced matrix breakdown in cartilage tissue appeared to be due to stimulation of activity of aggrecanase(s), not matrix metalloproteinase(s). However, IL-17 upregulated expression of matrix metalloproteinase(s) in chondrocytes cultured in monolayer. In vivo, IL-17 induced a phenotype similar to inflammatory arthritis when injected into the intra-articular space of mouse knee joints. Furthermore, a related protein, IL-17E, was found to have catabolic activity on human articular cartilage. This study characterizes the mechanism whereby IL-17 acts directly on cartilage matrix turnover. Such findings have important implications for the treatment of degenerative joint diseases such as arthritis.

IL-17s adopt a cystine knot fold: structure and activity of a novel cytokine, IL-17F, and implications for receptor binding

The proinflammatory cytokine interleukin 17 (IL-17) is the founding member of a family of secreted proteins that elicit potent cellular responses. We report a novel human IL-17 homolog, IL-17F, and show that it is expressed by activated T cells, can stimulate production of other cytokines such as IL-6, IL-8 and granulocyte colony-stimulating factor, and can regulate cartilage matrix turnover. Unexpectedly, the crystal structure of IL-17F reveals that IL-17 family members adopt a monomer fold typical of cystine knot growth factors, despite lacking the disulfide responsible for defining the canonical "knot" structure. IL-17F dimerizes in a parallel manner like neurotrophins, and features an unusually large cavity on its surface. Remarkably, this cavity is located in precisely the same position where nerve growth factor binds its high affinity receptor, TrkA, suggesting further parallels between IL-17s and neurotrophins with respect to receptor recognition.

Functional inactivation of the IGF-I receptor delays differentiation of skeletal muscle cells

Skeletal myoblasts are inherently programmed to leave the cell cycle and begin the differentiation process following removal of exogenous growth factors. Serum withdrawal results in a marked induction of IGF production which is essential for skeletal muscle differentiation in vitro. However, the potential role of the tyrosine kinase IGF-I receptor (thought to be the principal mediator of both IGF-I and II signaling in skeletal muscle) in the decision of myoblasts to begin differentiation following serum withdrawal is unknown. To explore the role of the IGF-I receptor in this decision by skeletal myoblasts, we functionally inactivated endogenous IGF-I receptors in mouse C2C12 cells using a dominant negative, kinase-inactive IGF-I receptor in which the ATP-binding site lysine (K) at residue 1003 has been mutated to alanine (A). Cell lines with the greatest degree of mutant IGF-I receptor expression (A/K cells) demonstrated functional inactivation of endogenous IGF-I receptors as determined by their impaired ability to phosphorylate the principal substrate of the IGF-I receptor, IRS-1, in response to treatment with IGF-I. In addition, the proliferative response of myoblasts to IGF-I was completely abolished in A/K cells. Following withdrawal of exogenous growth factors, A/K cells demonstrated a marked delay in the induction of the gene expression of myogenin, a skeletal muscle-specific transcription factor essential for differentiation, and a subsequent delay in the induction of muscle creatine kinase activity. Delayed differentiation in A/K cells was associated with prolonged phosphorylation of the cell cycle regulatory retinoblastoma (Rb) protein; it is the un- (or hypo-) phosphorylated form of Rb which is known to promote differentiation in skeletal myoblasts. Thus, the IGF-I receptor regulates the timing of myoblast differentiation induced by serum withdrawal. The delayed differentiation of skeletal myoblasts with functionally inactive IGF-I receptors may result, at least in part, from delayed induction of myogenin gene expression and prolonged phosphorylation of the Rb protein.

Osteoblastic responses to TGF-beta during bone remodeling

Bone remodeling depends on the spatial and temporal coupling of bone formation by osteoblasts and bone resorption by osteoclasts; however, the molecular basis of these inductive interactions is unknown. We have previously shown that osteoblastic overexpression of TGF-beta2 in transgenic mice deregulates bone remodeling and leads to an age-dependent loss of bone mass that resembles high-turnover osteoporosis in humans. This phenotype implicates TGF-beta2 as a physiological regulator of bone remodeling and raises the question of how this single secreted factor regulates the functions of osteoblasts and osteoclasts and coordinates their opposing activities in vivo. To gain insight into the physiological role of TGF-beta in bone remodeling, we have now characterized the responses of osteoblasts to TGF-beta in these transgenic mice. We took advantage of the ability of alendronate to specifically inhibit bone resorption, the lack of osteoclast activity in c-fos-/- mice, and a new transgenic mouse line that expresses a dominant-negative form of the type II TGF-beta receptor in osteoblasts. Our results show that TGF-beta directly increases the steady-state rate of osteoblastic differentiation from osteoprogenitor cell to terminally differentiated osteocyte and thereby increases the final density of osteocytes embedded within bone matrix. Mice overexpressing TGF-beta2 also have increased rates of bone matrix formation; however, this activity does not result from a direct effect of TGF-beta on osteoblasts, but is more likely a homeostatic response to the increase in bone resorption caused by TGF-beta. Lastly, we find that osteoclastic activity contributes to the TGF-beta-induced increase in osteoblast differentiation at sites of bone resorption. These results suggest that TGF-beta is a physiological regulator of osteoblast differentiation and acts as a central component of the coupling of bone formation to resorption during bone remodeling.

Expression of a truncated, kinase-defective TGF-beta type II receptor in mouse skeletal tissue promotes terminal chondrocyte differentiation and osteoarthritis

Members of the TGF-beta superfamily are important regulators of skeletal development. TGF-betas signal through heteromeric type I and type II receptor serine/threonine kinases. When over-expressed, a cytoplasmically truncated type II receptor can compete with the endogenous receptors for complex formation, thereby acting as a dominant-negative mutant (DNIIR). To determine the role of TGF-betas in the development and maintenance of the skeleton, we have generated transgenic mice (MT-DNIIR-4 and -27) that express the DNIIR in skeletal tissue. DNIIR mRNA expression was localized to the periosteum/perichondrium, syno-vium, and articular cartilage. Lower levels of DNIIR mRNA were detected in growth plate cartilage. Transgenic mice frequently showed bifurcation of the xiphoid process and sternum. They also developed progressive skeletal degeneration, resulting by 4 to 8 mo of age in kyphoscoliosis and stiff and torqued joints. The histology of affected joints strongly resembled human osteo-arthritis. The articular surface was replaced by bone or hypertrophic cartilage as judged by the expression of type X collagen, a marker of hypertrophic cartilage normally absent from articular cartilage. The synovium was hyperplastic, and cartilaginous metaplasia was observed in the joint space. We then tested the hypothesis that TGF-beta is required for normal differentiation of cartilage in vivo. By 4 and 8 wk of age, the level of type X collagen was increased in growth plate cartilage of transgenic mice relative to wild-type controls. Less proteoglycan staining was detected in the growth plate and articular cartilage matrix of transgenic mice. Mice that express DNIIR in skeletal tissue also demonstrated increased Indian hedgehog (IHH) expression. IHH is a secreted protein that is expressed in chondrocytes that are committed to becoming hypertrophic. It is thought to be involved in a feedback loop that signals through the periosteum/ perichondrium to inhibit cartilage differentiation. The data suggest that TGF-beta may be critical for multifaceted maintenance of synovial joints. Loss of responsiveness to TGF-beta promotes chondrocyte terminal differentiation and results in development of degenerative joint disease resembling osteoarthritis in humans.

Induction of myogenesis in mesenchymal cells by MyoD depends on their degree of differentiation

Expression of a transfected MyoD gene induces myogenic differentiation of most cell types. In this study, we evaluated the ability of an exogenous MyoD gene to induce myogenic conversion in two pairs of matched cell lines with different degrees of differentiation within either the osteoblastic or chondrocytic lineage. We show that osteoblasts and chondrocytes are resistant to the myogenic effects of MyoD alone. However, in their less-differentiated cell line counterparts, MyoD induces expression of muscle-cell-specific markers. Less-differentiated osteoblasts can be made resistant to MyoD-induced myogenic conversion by induction of adipogenic differentiation using dexamethasone. Finally, a dominant positive form of MyoD, one which is tethered to a partner, E47, activates muscle-specific gene expression in osteoblasts. Our results suggest that the response of a cell to MyoD depends on its lineage and its degree of differentiation. Furthermore, commitment of cells to the osteoblastic or chondrocytic lineage may involve inhibition of alternative pathways, such as those leading to myoblastic differentiation. Finally, osteoblasts may express a protein(s) which interferes with the activity of MyoD by inhibiting its association with E proteins. This interference can be overcome by expression of the MyoD-E47 hybrid, suggesting that osteoblasts are otherwise competent to undergo myogenic conversion.

Transforming growth factor-beta (TGF-beta)-induced down-regulation of cyclin A expression requires a functional TGF-beta receptor complex. Characterization of chimeric and truncated type I and type II receptors

Transforming growth factor-beta (TGF-beta) inhibits the proliferation of epithelial cells by altering the expression or function of various components of the cell cycle machinery. Expression of one of these components, cyclin A, is inhibited by TGF-beta treatment. We have identified a 760-base pair fragment of the human cyclin A gene promoter that is sufficient to confer TGF-beta responsiveness. Using this promoter fragment, we have developed a cyclin A-based luciferase reporter assay that quantitates the growth inhibitory effect of TGF-beta in transient transfection assays. This assay was used to determine which domains of the type I (RI) and type II (RII) receptors were required for the antiproliferative effect of TGF-beta. In parallel, the functionality of chimeric receptors, between RI and RII (RI-RII or RII-RI), was tested for TGF-beta effect on gene expression using a reporter assay based on the plasminogen activator inhibitor type 1 (PAI-1) promoter. We found that TGF-beta-induced inhibition of cyclin A expression was absent in RI or RII-deficient Mv1Lu cells and that this response was restored by expression of wild-type type I or type II receptors in these cells. Furthermore, expression of a single chimeric receptor, either RI-RII or RII-RI, did not confer cyclin A regulation by TGF-beta. However, expression of two reciprocal chimeras (RI-RII and RII-RI) resulted in growth inhibition, similarly to wild-type receptors. In addition, chimeric receptors as well as mutant receptors with a deleted cytoplasmic domain and kinase-negative receptors inhibited TGF-beta responsiveness in the cyclin A reporter assay in a dominant negative fashion. Finally, in both receptor types, the juxtamembrane domain preceding the kinase domain was essential for receptor function but the cytoplasmic tail was dispensable. Our results suggest that a functional TGF-beta receptor complex is required for TGF-beta-dependent down-regulation of cyclin A gene expression and illustrate the identical receptor requirements for TGF-beta-induced growth inhibition and gene expression.

Vgr-1/BMP-6 induces osteoblastic differentiation of pluripotential mesenchymal cells

The transforming growth factor-beta (TGF-beta) superfamily is a group of secreted growth factors that appears to play a central role in mesenchymal differentiation, including cartilage and bone formation. The present study examines the role of one member of this family, vgr-1, also called bone morphogenetic protein-6, in mesenchymal cell differentiation. This factor may be considered as a prototype for the largest subgroup of related factors within the TGF-beta superfamily, the function of which has as yet been poorly defined. vgr-1 has been localized previously to hypertrophic cartilage and has been shown to induce endochondral bone formation in vivo. To further characterize the role of vgr-1 in bone and cartilage differentiation, we stably transfected the pluripotent mesenchymal cell line ROB-C26 with a vector to overexpress vgr-1. Overexpression of this factor did not affect cell shape or morphology, but it enhanced osteoblastic differentiation in vitro and altered cellular responsiveness to retinoic acid. Furthermore, the extracellular matrix produced by these vgr-1-overexpressing cells induced ectopic bone formation in vivo and osteoblastic differentiation in vitro, similar to the matrix produced by C26 cells treated with retinoic acid. The osteoinductive effect of the matrix from vgr-1-overexpressing cells was blocked using a neutralizing vgr-1 antibody but not with a neutralizing TGF-beta 1 antibody, indicating that vgr-1 alone was required for this osteogenic effect. In contrast, the osteoinductive effect of matrix from retinoic acid-treated cells was blocked with both vgr-1 and TGF-beta 1 antibodies, suggesting that TGF-beta 1 may act prior to vgr-1 during osteoblastic differentiation. We further demonstrated that osteoinduction by vgr-1 was dependent on presentation of vgr-1 within the matrix, because the osteoinductive effect of matrix from vgr-1-overexpressing cells could not be mimicked with the addition of soluble vgr-1 to parental C26 cells. Finally, overexpression of MyoD within the C26 cells overexpressing vgr-1 converted the cells to myoblasts, indicating that vgr-1 had induced early osteoblastic.

Inhibition of myogenic differentiation in myoblasts expressing a truncated type II TGF-beta receptor

Transforming growth factor-beta (TGF-beta) is thought to play a role in mesenchymal cell development and, specifically, in muscle differentiation, yet its precise role in the latter process remains unclear. TGF-beta has been shown to both inhibit and induce myoblast maturation in vitro, depending on the culture conditions. Whether the type I or type II TGF-beta receptor mediates the various TGF-beta effects on myogenesis is not known. In the present study, C2C12 myoblasts were transfected with an expression vector for a truncated type II TGF-beta receptor, which has been shown to act as a dominant negative inhibitor of type II receptor signaling. In contrast to the parental cells, the transfected clones did not efficiently form myotubes or induce expression of MyoD, myogenin and several other differentiation markers following incubation in low serum media. However, some muscle differentiation markers continued to be expressed in the transfected cells suggesting that at least two pathways are involved in muscle cell differentiation. These cells could still growth arrest in low serum media, showing that decreased proliferation can be dissociated from differentiation. Unlike several oncogenes known to block myogenic differentiation, expression of the truncated TGF-beta receptor did not result in myoblast transformation. Injection of the parental or the transfected C2C12 cells into the limb muscle of nude mice revealed quantitative and qualitative differences in their behavior, and suggested that myoblasts expressing the truncated TGF-beta receptor cannot fuse in vivo. Finally, retrovirus-mediated expression of MyoD in the transfected cells restored their ability to form myotubes in vitro, indicating that inhibition of myoblast differentiation by the truncated TGF-beta receptor may depend on decreased MyoD expression. We propose that TGF-beta signaling through the type II receptor is required for several distinct aspects of myogenic differentiation and that TGF-beta acts as a competence factor in this multistep process.