REVIEW

Review Article: Is Wnt Signaling an Attractive Targetfor the Treatment of Osteoarthritis?

Rik J. Lories . Silvia Monteagudo

Received: February 11, 2020 / Published online: April 10, 2020� The Author(s) 2020

ABSTRACT

Osteoarthritis is the most common chronicjoint disease affecting millions of peopleworldwide and a leading cause of pain and dis-ability. Increasing incidence of obesity andaging of the population are two factors thatsuggest that the impact of osteoarthritis willfurther increase at the society level. Currently,there are no drugs available that can manageboth structural damage to the joint or theassociated pain. Increasing evidence supportsthe view that the Wnt signaling pathway playsan important role in this disease. The currentconcept, based on genetic and functional stud-ies, indicates that tight regulation of Wnt sig-naling in cartilage is essential to keep the jointhealthy. In this review, we discuss how thisconcept has evolved, provide insights into theregulation of Wnt signaling, in particular byWnt modulators such as frizzled-related proteinand DOT1-like histone lysine

methyltransferase, and summarize preclinicalevidence and molecular mechanisms of loreci-vivint, the first Wnt antagonist in clinicaldevelopment for osteoarthritis.

Keywords: Cartilage; Joint disease;Osteoarthritis; Rheumatology; Wnt

Key Summary Points

The Wnt signaling pathway plays animportant role in osteoarthritis.

Targeting of the Wnt signaling pathway ispossible at different levels of thepathway’s activation cascade.

The first Wnt inhibitor for treatment ofosteoarthritis, lorecivivint, is enteringphase III clinical trials.

INTRODUCTION

Osteoarthritis is the most common chronicjoint disease, affecting over 250 million peopleworldwide [1]. Over 80% of these patientsreport limitations with joint movement andover 25% are not capable of normally

Digital Features To view digital features for this articlego to https://doi.org/10.6084/m9.figshare.12038913.

R. J. Lories � S. MonteagudoDepartment of Development and Regeneration,Skeletal Biology and Engineering Research Center,KU Leuven, Leuven, Belgium

R. J. Lories (&)Division of Rheumatology, University HospitalsLeuven, KU Leuven, Leuven, Belgiume-mail: rik.lories@kuleuven.be

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https://doi.org/10.1007/s40744-020-00205-8

performing activities of daily life. Therefore,osteoarthritis is rightfully considered a seriousdisease with a very high socio-economic impactand a high burden on individuals. As aging andobesity feature prominently among risk factorsfor the development of disease and its progres-sion, the impact of osteoarthritis on society islikely to further increase in the near future.

Currently, there is no cure for the diseaseand there are only limited treatment options.Standard approaches include physiotherapyand exercise programs combined with painkil-lers and anti-inflammatory drugs [2]. Localtreatments of disease flares by intra-articularsteroid or hyaluronic acid injections are part ofcommon practice. Of note, strong painkillershave been associated with severe side effects,including increased mortality and rapidly pro-gressive osteoarthritis in some patients [3, 4].Currently, there are no so-called structure ordisease-modifying treatments available and inhuge groups of patients, in particular those withlarge joint involvement, prosthesis, or othertypes of joint surgeries may become the onlyviable solution. Prosthesis surgeries are a formof joint replacement rather than joint restora-tion approaches and the life-time of theimplants may become too limited for theincreased life expectancy of many patients, thusleading to re-do surgery, which is often chal-lenging in particular in the very elderly.

The onset and course of osteoarthritis are noteasily explained in a simple model. In fact,osteoarthritis is best considered as the outcomeof different disease processes, representing arange of interactions between contributingmechanisms and factors depending on thecharacteristics of the individual patient. Riskfactors include, among others, obesity, meta-bolic disorders, injury, altered anatomy andbiomechanics of the joint, and inflammation[2]. With many different mechanisms con-tributing to the initiation as well as to the pro-gression of disease, it is not surprising that thedevelopment of specific targeted therapies is amajor challenge in the long process from benchto bedside, and that the clinical development ofsuch strategies will need to focus on well-de-fined subpopulations in order to establishquality data on an eventual effect of the

intervention. One molecular pathway of inter-est in this context is Wnt signaling [5]. In thisreview, we discuss how Wnt signaling wasidentified as a potential target for the treatmentof osteoarthritis and we present the underlyingmechanism of a Wnt signaling inhibitor that iscurrently progressing through clinical trials forthe treatment of patients with kneeosteoarthritis. This article is based on previouslyconducted studies and does not contain anynew studies with human participants or animalsperformed by any of the authors. Earlier workfrom the authors was approved by the EthicalCommittee for Clinical Research UniversityHospitals Leuven and the Ethical Committee forAnimal Research KU Leuven.

WNT SIGNALING: A CONSERVEDBIOLOGICAL SYSTEMWITH POTENTIAL FOR GREATDIVERSITY

Wnts are a family of at least 19 different secre-ted proteins in humans that affect a large arrayof biological processes. Originally defined asmorphogens in organisms such as Drosophilamelanogaster (fruit fly) and Xenopus laevis (trop-ical frog) or discovered as potential oncogenesin malignancies (for extensive review see [5–7]),our knowledge on their biological effects andimpact has steadily grown over the years, albeitthat many questions remain. The effects ofindividual Wnts have been difficult to study,not in the least because Wnts are poorly solubleand their isolation, specific identification aswell as their production as recombinant mole-cules are highly challenging. A major reason forthese research obstacles is found in the post-translational processing of the molecules in thecell before secretion. The Wnt ligands are linkedwith a lipid sidechain by an enzyme calledporcupine before their secretion [7–9]. This lipidside chain strongly reduces the solubility of theWnt ligand and its potential signaling range.We currently assume that Wnts have mostlyautocrine and paracrine, rather than endocrineeffects. Nevertheless, the affinity of Wnts forextracellular matrix or cell surface molecules

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like heparin-sulfated proteoglycans [10], andtheir binding to other secreted molecules suchas those belonging to the secreted frizzled rela-ted protein (SFRP) family that can serve asmolecular shuttles [11, 12], are factors thatimpact the signaling range of Wnts. Hence,following a biological principle from develop-ment, Wnts are molecules that typically buildconcentration gradients with an impact onadjacent cell behavior. As a consequence, tar-geting the Wnt signaling pathway for treatmentof diseases may need to overcome a majorchallenge in targeting the cells and tissueswhere active signaling is contributing topathology.

WNT SIGNALING PLAYS A KEY ROLEIN OSTEOARTHRITIS

Early suggestions that Wnt signaling may play arole in cartilage biology and joint disease camefrom the progressive insights into how Wntsignaling plays a role in skeletal development[13]. The current view on these processes holdsthat low activity of the cascade in skeletal pro-genitor cells contributes to the process of cellcondensation and commitment towards chon-drogenic differentiation in bone develop-ment[6], whereas in later stages activation ofWnt signaling is essential in the progressivedifferentiation from proliferating chondrocytestowards hypertrophic cells thereby stimulatingbone formation [13, 14]. In addition, Wnts havean anabolic impact on bone progenitor cellsdirectly [13]. Together, these observationsdemonstrate how modulation of pathway acti-vation controls the differentiation status ofskeletal cells and how fine-tuning of Wntactivity is essential for normal development, assuggested by skeletal malformations associatedwith mutations in key pathway genes [15, 16].

A potential role for Wnt signaling inosteoarthritis emerged based on a series of dif-ferent discoveries. First, in their search forgenetic factors potentially associated withosteoarthritis, investigators found evidence thatpolymorphisms in the SFRP3 gene, whichencodes Frizzled-related protein (FRZB), wereassociated with hip osteoarthritis [17]. FRZB was

earlier identified as a secreted antagonist of theWnt signaling cascade, as it is able to bind Wntproteins and prevent Wnt–Wnt receptor inter-actions [11]. Interestingly, FRZB was first iden-tified from a chondrogenic extract of articularcartilage and is expressed in the developingjoint [18]. Functional analyses suggested thatthe identified osteoarthritis-associated variantsin the SFRP3 gene affected the Wnt antagoniz-ing properties of FRZB [17]. Interestingly, otherinvestigators documented that expression levelsof SFRP3 were rapidly downregulated uponin vitro cartilage injury [19, 20]. Our researchgroup had developed Sfrp3 knockout mice tostudy the role of this molecule in skeletaldevelopment. However, primary analyses of thisnovel mouse strain did not demonstrate anyobvious skeletal abnormalities. Nevertheless,when studying these animals postnatally, wedemonstrated that the Sfrp3 knockout miceshowed more severe osteoarthritis in differentinduced models, and that FRZB appeared tointeract directly with cartilage matrix destruc-tive enzymes such as matrix metalloproteinase-3 [21]. In addition, absence of FRZB alsoincreased cortical bone thickness and anabolicresponses upon in vivo loading in the longbones [21]. The data from this mouse modelwere thereby the first evidence that increasedactivation of Wnt signaling in the joint cancontribute to the development of osteoarthritis,probably by multiple mechanisms.

FRZB and related SFRPs are soluble modula-tors of Wnt signaling. As they bind Wnt ligandsdirectly, they antagonize interaction of thegrowth factors with cell-surface receptors. Keyreceptors for the Wnt cascade are those of theFrizzled family, molecules found in the cellmembrane with an extra-cellular domain thatcan bind Wnts, and an intracellular tail thatinteracts with cytoplasmic proteins. The Wnt-Frizzled interaction attracts co-receptorslipoprotein-related protein 5 or 6 (LRP5/6) andtriggers a downstream intracellular signalingcascade. A key molecule in the subsequentintracellular events is beta-catenin [5, 7] (Fig. 1).Beta-catenin is a multi-functional protein that isnot only involved in the Wnt cascade but alsoin cell adhesion. In the absence of cell-surfaceinduced Wnt signaling activation, beta-catenin

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is caught in a multi-protein complex and tar-geted for phosphorylation, ubiquitination anddegradation by the proteasome. However, uponWnt ligand-receptor complex interaction, thedestruction complex is inactivated, allowingbeta-catenin to accumulate within the cyto-plasm and subsequently translocate towards thenucleus. Beta-catenin is not a transcriptionfactor but does associate with transcriptionfactors from the TCF/LEF family and binds inthis way indirectly to its target genes, therebyinducing a specific transcriptional programwithin the cells [5, 7]. The beta-catenin-depen-dent Wnt pathway is also called the canonicalWnt pathway. Alternative cascades are less wellstudied but include intracellular calciumrelease, changes in cell polarity, and activationof stress kinases.

A key role for beta-catenin in the mainte-nance of cartilage and joint health was subse-quently confirmed by two studies withopposing strategies. First, cartilage-specificinactivation of beta-catenin was demonstratedto lead to articular cartilage destruction mainlyby chondrocyte cell death [22], whereas over-expression of a constitutively active form ofbeta-catenin also resulted in osteoarthritis

characterized by increased cartilage cell hyper-trophy [23]. Together, these studies providedclear evidence that canonical Wnt signalingmust be tightly regulated within the joint inorder to maintain homeostasis and preventjoint disease such as osteoarthritis [24].

FINE-TUNING OF WNT SIGNALINGIS ESSENTIAL FOR JOINT HEALTH

Since these original discoveries, a large body ofevidence has been assembled that supports theview that controlling Wnt signaling is essentialto maintain joint homeostasis and prevent dis-ease. Strong activation of the canonical Wntsignaling pathway alters the molecular charac-teristics of the healthy articular chondrocyte,stimulates their further differentiation towardshypertrophic cells associated with the produc-tion of a calcified and therefore biomechani-cally inferior extracellular matrix. In contrast,in the superficial layer of the articular cartilage,Wnt16 production stimulates the synthesis andsecretion of lubricin, a lubricant molecule thatcontributes to minimize friction between the

Fig. 1 Simplified overview of canonical Wnt signalingpathway activation. Wnt ligands interact with Frizzledreceptors and LRP5/6 co-receptors, which leads to theinactivation of the multi-protein beta-catenin destruction

complex. This allows beta-catenin to accumulate withinthe cytoplasm and to translocate to the nucleus. Here,beta-catenin associates with transcription factors of theTCF/LEF family that bind to Wnt target gene promotors

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opposing cartilage surface in the moving joint[25].

Osteoarthritis is a not a simple cartilage dis-ease but a disorder that affects and involves allstructures of the joint organ [26, 27] (Fig. 2).The primacy of cartilage versus subchondralbone changes in the pathogenesis has beenextensively debated. The currently prevailingview suggests that different disease endotypesexist in which the initial changes may differ butultimately lead to the complex process thatleads to joint destruction and the associatedclinical problems. Activation of canonical Wntsignaling appears to contribute towardsincreased subchondral bone remodeling andtowards osteophyte formation, two pathologi-cal processes in the bone that are also associatedwith osteoarthritis development [24, 28].Moreover, activation of Wnt signaling in thesynovium contributes to inflammation anddirectly as well as indirectly towards progressivejoint destruction [29].

Taking into account these myriad effects thatactivation of Wnt signaling can have on differ-ent cells and distinct tissues, and the intrinsicimpact of such signals on a cell’s differentiationstatus, it should come as no surprise that Wnt

signaling is tightly regulated at every level ofthe cascade. As highlighted above, the SFRPs area family of secreted molecules that can bind andantagonize individual Wnt molecules. Otherantagonists also exist, including sclerostin, amolecule typically produced by the bone-mechanosensing osteocytes, and that serves tomaintain a tight regulation of the skeletal bonemass [16]. The dickkopf family (DKKs) arebinding to the Wnt co-receptors LRP5 and 6,providing a non-ligand related mechanism tocontrol the amplitude and extent of canonicalpathway Wnt signaling activation [30]. Theextent to which different individual Wnts trig-ger both types of cascades has not been wellunderstood, but there is solid evidence ofreciprocal interactions between canonical andnon-canonical pathway activation [30].

Within the cell cytoplasm, the multi-proteindestruction complex also contributes to finetuning of signaling. Different phosphorylationsites on distinct members of the complexmediate their molecular function or turnover,thus providing specific targets to modulate thisprocess. Small molecules inhibiting the activityof the destruction complex have been used ininvestigational settings to induce ligand-

Fig. 2 Osteoarthritis is the disease of the whole joint organ. Different tissues and structures in the joint are affected by thepathological processes. Wnt signaling appears to have a role in driving disease in many of these tissues

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independent signaling pathway activation. Thebiology of the destruction complex remains aninteresting field of study as there may be tissue-specific factors involved which would allow forthe development of targeted therapies, forexample for osteoarthritis.

The complexity of the signaling pathwayand its involvement in a wide range of biologi-cal processes appears to be a daunting perspec-tive for the development of therapies that havean impact on a disease such as osteoarthritis. Inaddition, therapies for an aging-associated dis-ease that is slowly progressing may require sus-tained administration of drugs over a long time-period in a population of patients that willlikely also show an increase in co-morbiditiesover time. Hence, safety of treatments is animportant consideration [31]. We propose thatthere are at least two ways to overcome thesechallenges, either by searching for tissue-speci-fic mechanisms of action or by developinghighly tissue-specific targeting approaches fordrug delivery.

Currently, multiple approaches can be con-sidered (Fig. 3). Inhibition of porcupine will

shut down Wnt secretion [32]. Antibodies ormolecular mimics could be used to interferewith ligand–receptor interactions [33]. Suchstrategies may also be developed towards co-agonists such as the R-spondin family [34],molecules that amplify canonical signalingpathway activation [35]. Drugs can stabilize thedestruction complex thereby stimulating beta-catenin breakdown [36]. Finally, intranucleareffects on gene transcription may confer thetissue specificity desired.

DOT1-LIKE HISTONE LYSINEMETHYLTRANSFERASE (DOT1L) ISA HISTONE METHYLTRANSFERASETHAT MODULATES WNTSIGNALING IN CARTILAGE

We identified a key role for epigenetic enzymeDOT1L in the regulation of Wnt signaling incartilage [37–39]. As for SFRP3, the first evidencefor an eventual role of DOT1L in osteoarthritiscame from genetic studies [39]. A genome-wideassociation study in a population cohort

Fig. 3 Potential therapeutic targets associated with acti-vation of the Wnt signaling pathway. Inhibition ofporcupine will stop Wnt ligand secretion. Wnt receptors,Wnt co-receptors, and accessory signals such as R-spondinLGR4/5 interactions can be inhibited. The destruction

complex can be stabilized to increased beta-catenindegradation. Transcription complex formation can bedisturbed by chemicals

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identified polymorphisms in the DOT1L gene tobe associated with cartilage thickness in the hip.This variable was considered a proxy for thedevelopment of osteoarthritis, and subse-quently the genetic association was also con-firmed in an osteoarthritis patient versuscontrol cohort. DOT1L is an enzyme thatmethylates lysine 79 on histone 3 (H3K79),resulting in a histone modification. Amonghistone methyltransferases, DOT1L is the majorH3K79 methyl transferase [40, 41]. Histonemodifications are one of the key epigeneticmechanisms to control gene expression. Withinthe cell nucleus, the DNA molecules are tightlywrapped around the histones for compactionand gene regulation. Modification of the his-tone protein tails by methylation or acetylationis a highly specific mechanism to affect theextent by which a particular stretch of DNA iswrapped around the histone and thereby to theavailability of the DNA and genes for tran-scription factor binding and eventualtranscription.

We subsequently demonstrated that DOT1Lis a key factor in maintaining cartilage home-ostasis and confers protection against thedevelopment of osteoarthritis [38]. Indeed,intra-articular injection of a small molecule thatinhibits DOT1L activity reduced H3K79methylation and triggered the development ofosteoarthritis. Molecular analysis of humanarticular chondrocytes treated with DOT1Linhibitor also demonstrated gene expressionsimilar to those seen in patients withosteoarthritis and with an enrichment formolecules of the Wnt signaling cascade. Furthermolecular analyses demonstrated that DOT1L isparticularly important when Wnt signaling isactivated, whereby it acts as a brake to limit theactivation of the pathway. Effectively, Blockadeof Wnt signaling by intra-articular injection of aWnt inhibitor could rescue the effect of DOT1Linactivity in the mouse model. DOT1L is foundin multi-protein complexes including beta-catenin, suggesting that it associated with thekey mediator of Wnt signaling upon pathwayactivation. Within the nucleus, it also interactswith SIRT1, another epigenetic modulator ofgene transcription. The different analyses per-formed allowed us to propose a model in which

DOT1L activity is able to maintain cartilagehomeostasis by restricting the activation of Wntsignaling, thus establishing an endogenouscontrol mechanism [38]. We also found thatlevels of H3K79 methylation are reduced inpatients with osteoarthritis, suggesting that thedisease is associated with reduced DOT1Lactivity. A parallel approach in aging andtrauma-triggered osteoarthritis mouse geneticmodels clearly confirmed that loss of DOT1Lactivity contributes to osteoarthritis [37].Interestingly, at least some of these effectsappeared to be cartilage-specific as the Wntactivation control mechanism documented inchondrocytes appeared to be largely absent inbone cells [38].

LORECIVIVINT IS A SMALLMOLECULE WNT PATHWAYINHIBITOR

The important role of Wnt signaling in a num-ber of diseases, including osteoarthritis andosteoporosis, has sparked interest from phar-maceutical and biotechnology companies totarget the pathway for the treatment of thesedisorders. In a drug library screening, differentWnt modulators were identified of which lore-civivint (SM04690) was selected for studies onosteoarthritis [42]. Of note, the -vivint suffixdefinition has been attributed to the novel classof Wnt pathway inhibitors. Preclinical devel-opment highlighted the potential of loreciviv-int to be used in osteoarthritis. In vitroexperiments demonstrated that the addition oflorecivivint to differentiation cultures of humanmesenchymal progenitor cells towards cartilageincreased chondrogenesis, as demonstrated byincreased extracellular matrix accumulation,including proteoglycans and collagens [42].Further cartilage protection could be conferredby the inhibitory effects of lorecivivint on theexpression of tissue destructive enzymes fromthe matrix metalloproteinase family [42]. Ofnote, the compound also demonstrated anti-inflammatory effects by reducing the expressionof cytokines such as interleukin-1b, tumornecrosis factor and interleukin-6 in synovialfibroblasts and in peripheral blood

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mononuclear cells [43], two groups of cells thatcan play a role in the inflammatory reactionthat is often seen in patients with osteoarthritis.

These promising results prompted the use oflorecivivint in in vivo models of osteoarthritis[42]. Remarkable, intra-articular injectionresulted in sustained high levels of the moleculeover several months, mostly in cartilage and toa far lesser extent in bone. Systemic levels of thedrug were extremely low. Intra-articular injec-tion also provided clear protection againstosteoarthritis development in rats both in asurgical instability model [42] and in modelcharacterized by inflammation and pain [43],thus paving the way for human trials.

Further in vitro work identified a uniquemechanism of action for lorecivivint [43](Fig. 4). The compound works as a kinase inhi-bitor and was demonstrated to mainly affect theactivity of CDC-like kinase enzymes (CLKs) [43],in particular CLK2, in nanomolar concentra-tions, and dual-specificity tyrosine phosphory-lation-regulated kinase enzymes (DYRK) [43], inparticular DYRK1A, again in nanomolar con-centrations. These molecules had not yet beenclearly associated with Wnt signaling, thereby

requiring further investigations. CLK2 plays animportant role in the steps from DNA tran-scription towards protein translation. RNA thatis the result of gene transcription requires fur-ther processing by splicing, for example toremove introns. Splicing is regulated by phos-phorylation of pre-mRNA binding proteins suchas the serine/arginine-rich splicing factors(SRSF) by CLKs. Inhibition of CLK2 affects thisprocess and results in abnormal transcripts thatmay have dominant negative effects on thesignaling cascade. Experimental data suggestthat the effects on Wnt signaling transcriptionfactors reduce the levels of Wnt target genes andsimultaneously increase the levels of markersassociated with the healthy chondrocyte profilesuch as aggrecan, collagen type 2, and DOT1L[43]. Moreover, negative modulation of CLK2activity also appears to inhibit NF-kB signaling,a strong pro-inflammatory cascade.

Kinase inhibitors rarely have total specificity,and this also applies to lorecivivint. Interest-ingly, in addition to inhibition of CLK2, effectson DYRK1A offers an interesting perspective onthe mechanism of action. DYRK1A is associatedwith anti-inflammatory effects as it affects the

Fig. 4 Proposed dual mechanism of action of lorecivivint.Inhibition of CLK2 results in dysregulation of transcrip-tion and mRNA slicing leading to decreased expression ofWnt target genes and of inflammatory cytokines. Inhibi-tion of DYRK1 reduces SIRT1 and FOXO1 phosphory-lation, thereby inhibiting Wnt pathway activation and

proinflammatory cascade while also having direct chon-droprotective effects. Arrows indicate positive effects, closedlines (red) inhibitory effects

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JAK/STAT signaling pathway [43]. Moreover,DYRK1A also affects activity of transcriptionfactor FOXO1 and of epigenetic modulatorSIRT1 [43]. Inhibition of SIRT1 in a context ofWnt hyper-activation may contribute to carti-lage homeostasis [38]. Positive regulation ofFOXO1 stimulates cartilage homeostasis andlubricin production [44].

These preclinical data have been used tosupport the use of lorecivivint for the treatmentof knee osteoarthritis in human clinical trials.Based on a phase 1 study with an excellentsafety profile [45], phase II trials have recentlybeen finished suggesting effectiveness on bothsigns and symptoms as well as structural dam-age in patients with knee osteoarthritis, in par-ticular those without widespread pain [46, 47].As a caveat, data are currently only available inmeeting abstract format. In the first phase IItrial, 455 patients with knee osteoarthritis wereincluded and three different dosages (0.03, 0.07,and 0.23 mg) by single intra-articular injectionwere compared to placebo for up to 52 weeks,with the primary endpoint a change frombaseline in the target knee in the WesternOntario and McMaster UniversitiesOsteoarthritis Index (WOMAC) pain sub-scorecompared to placebo [47]. This primary end-point was not met, but at all time-points clini-cally meaningful change from baseline in thisparameter was seen. At 52 weeks, the 0.07 mggroup showed significant improvement in theWOMAC pain and function score compared toplacebo within a pre-specified group of unilat-eral knee osteoarthritis patients, an effect thatwas more pronounced in a pre-specified groupof unilateral knee osteoarthritis patients with-out widespread pain. Hence, this first phase IItrial suggested a target population and apotential optimal dosage. Of note, at 52 weeks,the 0.07 mg unilateral symptomatic and0.07 mg unilateral symptomatic without wide-spread pain demonstrated a significant increasefrom baseline in medial joint space width,reflecting cartilage thickness, compared toplacebo.

A phase IIb study over 24 weeks was then setup to refine outcome measures, target popula-tion and dosage, while further evaluating safety[46]. Single intra-articular injection over a wider

dosage range (0.03, 0.07, 0.15, and 0.23 mg) wascompared to placebo or sham-injection in 695patients with clinically dominant unilateralknee osteoarthritis (high pain score in targetknee, low pain score in contra-lateral knee). Thestudy showed statistically significant differencesbetween the 0.07 and 0.23 mg dosages for painevaluated by Numeric Rating Scale (NRS), forWOMAC pain and physical function, as well asfor patient global assessment. In both phase IItrials, there were no apparent safety issues. Thedata convinced the company to continue itsclinical development program and currentlyphase III trials are ongoing.

CONCLUSIONS

The Wnt signaling pathway is an importantbiological cascade in joint homeostasis and injoint diseases such as osteoarthritis. Wnt sig-naling is tightly regulated at all levels of thecascade thereby providing many opportunitiesfor drug development. However, optimalstrategies may require cell-specific and cell-di-rected targeting. DOT1L is an epigenetic mod-ulator of the Wnt cascade that acts as a brakemechanism on signaling pathway activationthereby preventing cartilage damage. Loreci-vivint is a Wnt inhibitor with a novel mecha-nism of action that is currently progressing inclinical trials and may have a double mecha-nism: differential splicing of target genes andanti-inflammatory effects. Extrapolation sug-gests that the former mechanism contributes tomaintenance of the cartilage and joint struc-ture, whereas the latter has symptomatic effects.

ACKNOWLEDGEMENTS

Funding. No funding or sponsorship wasreceived for this study or publication of thisarticle.

Authorship. All named authors meet theInternational Committee of Medical JournalEditors (ICMJE) criteria for authorship for thisarticle, take responsibility for the integrity of

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the work as a whole, and have given theirapproval for this version to be published.

Disclosures. Leuven Research and Develop-ment, the technology transfer office of KULeuven has received consultancy and speaker’sfees, and research grants on behalf of RikLories from AbbVie, Boehringer-Ingelheim,Celgene, Eli-Lilly, Galapagos, Janssen, MSD,Novartis, Pfizer, Samumed, and UCB. Academicresearch in the Lories & Monteagudo laboratoryis supported by FWO Vlaanderen (FlandersResearch Foundation), KU Leuven, the Excel-lence of Science initiative of the FederalGovernment, the EU H2020 and IMI2 program,Foreum and the VIB-Grand ChallengesProgram.

Compliance with Ethics Guidelines. Thisarticle is based on previously conducted studiesand does not contain any new studies withhuman participants or animals performed byany of the authors. Earlier work from theauthors was approved by the Ethical Committeefor Clinical Research University Hospitals Leu-ven and the Ethical Committee for AnimalResearch KU Leuven.

Data Availability. Data sharing is notapplicable to this article as no datasets weregenerated or analyzed during the current study.

Open Access. This article is licensed under aCreative Commons Attribution-NonCommer-cial 4.0 International License, which permitsany non-commercial use, sharing, adaptation,distribution and reproduction in any mediumor format, as long as you give appropriate creditto the original author(s) and the source, providea link to the Creative Commons licence, andindicate if changes were made. The images orother third party material in this article areincluded in the article’s Creative Commonslicence, unless indicated otherwise in a creditline to the material. If material is not includedin the article’s Creative Commons licence andyour intended use is not permitted by statutoryregulation or exceeds the permitted use, youwill need to obtain permission directly from thecopyright holder. To view a copy of this licence,

visit http://creativecommons.org/licenses/by-nc/4.0/.

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