REVIEW article

Front. Pharmacol., 23 November 2017

Sec. Gastrointestinal and Hepatic Pharmacology

Volume 8 - 2017 | https://doi.org/10.3389/fphar.2017.00855

Drugs and Targets in Fibrosis

  • 1. Department of Gastroenterology, School of Life Sciences and Technology, Shanghai East Hospital, Tongji University, Shanghai, China

  • 2. Department of Pediatrics, Digestive Diseases and Nutrition Center, State University of New York at Buffalo, Buffalo, NY, United States

  • 3. Genome, Environment and Microbiome Community of Excellence, State University of New York at Buffalo, Buffalo, NY, United States

  • 4. Center for Drug Discovery, SINO High Goal Chemical Technology Co., Ltd., Shanghai, China

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Abstract

Fibrosis contributes to the development of many diseases and many target molecules are involved in fibrosis. Currently, the majority of fibrosis treatment strategies are limited to specific diseases or organs. However, accumulating evidence demonstrates great similarities among fibroproliferative diseases, and more and more drugs are proved to be effective anti-fibrotic therapies across different diseases and organs. Here we comprehensively review the current knowledge on the pathological mechanisms of fibrosis, and divide factors mediating fibrosis progression into extracellular and intracellular groups. Furthermore, we systematically summarize both single and multiple component drugs that target fibrosis. Future directions of fibrosis drug discovery are also proposed.

Introduction

Fibrosis, characterized by excess accumulation of extracellular matrix (ECM), is a common pathological process in many chronic diseases or injuries. Many irritations trigger the pro-fibrotic responses, including persistent infections, radiation, chemical agents, genetic disorders, and autoimmune diseases. The development of fibrosis is accompanied by the loss of a fraction of resident cells and their replacement by ECM, which would finally lead to tissue remodeling and organ failure. Fibrosis contributes to high morbidity and mortality in many diseases such as dilated cardiomyopathy and idiopathic pulmonary fibrosis (IPF) (Gulati et al., 2013; Hutchinson et al., 2015), and inevitably causes a prominent global clinical burden (Raimundo et al., 2016). For example, a study of medicare population aged 65 years and older showed that the incidence of IPF was around 93.7 cases per 100,000 person-years while the cumulative prevalence increased steadily to 494.5 cases per 100,000 person-years across 2001 to 2011 in US (Raghu et al., 2014). Besides, the mortality of non-alcoholic fatty liver disease (NAFLD) patients with a high probability of fibrosis was 69% higher than those without fibrosis (Kim et al., 2013).

As a long-lasting pathological phenomenon, fibrosis occurs in various tissues and organs (Figure 1), more often in heart, lung, kidney, liver, skin (Rockey et al., 2015), and less frequently in other tissues and organs such as pancreas, intestine, eye (Wynn, 2008), nerve system (Kawano et al., 2012), mediastinum (Parish and Rosenow, 2002), retroperitoneum (Caiafa et al., 2013), joint and tendon (arthrofibrosis).

Figure 1

Figure 1

Fibrosis and related diseases in various tissues and organs. Fibrosis is a pathological process that could occur in many tissues and organs and is associated with multiple diseases. Commonly reported fibrosis and associated diseases are listed.

Fibrosis contributes to the development of many diseases. First, many studies have demonstrated that the core mechanisms in fibrosis across various tissues and organs are similar. Wang and colleagues found that the interaction between transforming growth factor-β(TGF-β) and connective tissue growth factor signaling is required in kidney, liver, and lung fibrosis (Wang Q. et al., 2011). Makarev and colleagues identified a number of common pathways between lung and liver fibrogenesis, such as TGF-β, interleukin-6(IL-6), and integrin-linked kinase signaling (Makarev et al., 2016). Moreover, Wenzke and colleagues detected 90 genes, as well as several networks associated with connective tissue disorders, that play important roles in multi-organ fibrosis including lung, heart, liver, and kidney (Wenzke et al., 2012). On the basis of common pathogenesis across fibroproliferative diseases, some new drugs were proved effective in the treatment of fibrosis across different tissues and organs. For example, Pirfenidone has entered into the phase II clinical trial for treating the systemic sclerosis(SSc) (Khanna et al., 2016) and the phase III for IPF (King et al., 2014), respectively. Interferon drug Actimmune has been evaluated in patients with IPF (Skaria et al., 2015), liver (Muir et al., 2006), and cystic fibrosis (Moss et al., 2005).

Second, in different tissues and organs, multiple fibrotic diseases are related to each other. They are usually triggered by the same irritation and occur simultaneously. For example, heart and kidney together develop fibrosis (cardiorenal fibrosis) owing to the imbalance of natriuretic peptide system pathway and renin angiotensin aldosterone system/TGF-β1 pathway in aging (Sangaralingham et al., 2016). Chronic or acute renal failure may induce nephrogenic systemic fibrosis developed from thickening skin (Reiter et al., 2012) to impaired internal organs. In addition, cystic fibrosis, caused by gene mutation, could widely affect multiple organs, such as lung, kidney, and pancreas. Moreover, fibrosis is frequently a common pathological process in NAFLD and inflammatory bowel disease. Replacement of heart tissues by fibrotic protein could alter the ventricle size and shape, leading to hypertrophic cardiomyopathy (Khan and Sheppard, 2006). Cancers such as hepatocellular carcinoma share a series of risk factors with liver fibrosis (De Minicis et al., 2012).

Here we review the current knowledge on the pathological mechanisms of fibrosis and systematically summarize drugs targeting fibrosis in different fibroproliferative diseases. Future directions for fibrosis drug discovery are also proposed.

Pathogenesis of fibrosis

Fibrosis is considered as pathological outcomes of normal wound healing (Figure 2). When injuries occur and epithelial and/or endothelial cells are damaged, pro-inflammatory cytokines are released by the coagulation cascade for immune cell recruitment, mainly neutrophils and macrophages. These recruited immune cells function as the scavenger to remove tissue debris and dead cells, resulting in acute inflammation. Meanwhile, immune cells themselves release factors like chemokines and cytokines to amplify inflammatory reactions. Next, the released factors, such as TGF-β (Thannickal et al., 2003), platelet derived growth factor (PDGF) (Tang et al., 1996), interleukin-13 and interleukin-4 (Hashimoto et al., 2001), induce the limited activation and proliferation of myofibroblasts. Besides resident fibroblasts, myofibroblasts are derived from multiple cells (Hinz et al., 2007), including fibrocytes, epithelial cells via epithelial-mesenchymal transition (EMT), endothelial cells via endothelial-mesenchymal transition, pericytes, and smooth muscle cells related to blood vessels. In liver and pancreas, precursor cells like hepatic stellate cells (HSC) (Moreira, 2007) and pancreatic stellate cells (Apte et al., 2012) could also acquire myofibroblastic phenotype. Activated myofibroblasts migrate to injury sites, and their abilities to generate cell traction force enable them to stimulate wound closure (Li and Wang, 2011). Then, the balance of ECM synthesis and degradation could be achieved by myofibroblasts, resulting in ECM homeostasis. Finally, immune cells undergo apoptosis and epithelial/endothelial cells proliferate to regenerate injury sites, leading to wound healing.

Figure 2

Figure 2

In normal wound healing condition, there is a series of ordered process: injury, immune cell recruitment and acute inflammation, myfibroblasts limited activation, and proliferation and ECM homeostasis, leading to wound closure after injury. While in pro-fibrotic condition, pathological process including chronic inflammation, myfibroblasts persistent activation, and proliferation and ECM deposition leading to fibrosis. Fibrosis itself could result in a secondary assault. Extracellular and intracellular factors interact with each other. Their abnormalities contribute to the fibrosis progression and in return are affected by pathological changes. Green lines and blocks represent normal wound healing while red lines and blocks represent fibrosis progression.

In contrast to normal wound healing process, the abnormalities of multiple factors could cause fibrosis (Biernacka et al., 2011) (Figure 2). Under some persistent stimuli, the overexpression of factors like pro-inflammatory cytokines or growth factors would overactivate (Kim et al., 2008) and interact with multiple kinases or nuclear receptors. The deficiencies of some factors would also contribute to fibrosis progression (Allen and Spiteri, 2002). Then, the abnormal signaling sustains to switch normal wound healing process to pro-fibrotic process, acting on the recruitment of excess immune cells, the induction of the myofibroblasts activation and proliferation and the promotion of ECM production. Pro-fibrotic process also promotes the activation of these factors conversely, thereby amplifying inflammatory responses and causing chronic inflammation. Finally, the sustained myofibroblasts activation would generate masses of ECM and tilt the balance in favor of synthesizing ECM to produce fibrosis. Furthermore, the pro-fibrotic process itself could contribute to secondary injury to the wound and cause a chronic vicious circle of pathological responses.

Below we divide factors modulating fibrosis progression into extracellular and intracellular groups, and discuss how they influence fibrosis progression.

Extracellular factors mediating the progression of fibrosis

The majority of the fibrosis-related extracellular factors are receptor-binding ligands, such as growth factors and cytokines. These factors target adjacent and distant cells in autocrine, paracrine, or endocrine signaling pathways. Then they bind to specific receptors on cell membrane and trigger the intracellular signaling, leading to pro-fibrotic cellular responses. Other extracellular factors, mainly enzymes such as matrix metalloproteinases (MMPs) could degrade ECM to prevent its excessive accumulation.

Growth factors contain a huge family of proteins that stimulate cell growth and proliferation. They are secreted by fibroblasts, immune cells, and epithelial/endothelial cells, and are able to orchestrate cellular responses. While epithelium/endothelium are damaged, cells in these tissues massively upregulate the production of growth factors to promote the proliferation of immune cells and fibroblasts. Among growth factors, TGF-β is the “master” modulator in fibrogensis (Meng et al., 2016), as it could provoke fibrosis through SMAD-dependent pathway (Lan, 2011) and SMAD-independent pathway related to a number of other pro-fibrotic reactions (Zhang, 2009). TGF-β signaling cascade results in differentiation of effector cells via inducing the expression of myofibroblasts hallmark α-hallmar muscle actin(α-SMA) (Sebe et al., 2008). In addition, TGF-β signaling leads to the transcription of collagen I and III genes (Fine and Goldstein, 1987; Chen et al., 1999) contributing to ECM accumulation. Interacting with TGF-β, many other growth factors have distinct roles in pro-fibrotic process. For example, PDGF induces HSC proliferation and type I collagen expression via downstream focal adhesion kinase/phosphoinositide 3-kinase/protein kinase B signaling (Reif et al., 2003). On the contrary, some growth factors have anti-fibrotic property, such as hepatocyte growth factor (HGF), the overexpression of which alleviates fibrosis in cardiomyopathic hamster through activation of MMP-1 and urokinase-type plasminogen activator (Taniyama et al., 2002). Excessive cytokines are usually secreted by immune cells, such as macrophages, neutrophils, and T cells in inflammation phase of wound healing. Compared with growth factors, cytokines tend to act as cell signaling transmitters to augment immunological responses and then lead to inflammation. One major type of cytokines is chemokines, which guide the recruitment of immune cells and fibroblasts to injury sites. Different immune cells are recruited by different chemokines. Neutrophils could be recruited by chemokine (C-X-C motif) ligand 1 and chemokine (C-X-C motif) ligand 8 by binding glycosaminoglycans with receptors in slightly different ways (Sawant et al., 2016). Chemokine (C-C motif) ligand 5 has been a major factor to induce the migration of HSC in liver fibrosis (Seki et al., 2009). Another type of cytokines is T cell cytokines, which are mainly secreted by activated T lymphocytes. They include interleukins, interferons and tumor necrosis factors (TNF), mediating adaptive immune responses and inflammation that might promote fibrosis. For example, IL-6 has been reported to shift the tissue repair to a chronic inflammatory state by signal transducer and activator of transcription 3(STAT3) signaling pathway in peritoneal fibrosis (Fielding et al., 2014). In contrast, some cytokines have anti-fibrotic effects. It has been reported that interferon-γ down-regulated the Adenosine A2A receptor signaling to prevent the production of type I collagen in HSC (Block and Cronstein, 2010). Moreover, some T cell cytokines, such as TNF-α, exhibit two-sided effects, pro-fibrotic or anti-fibrotic effect depending on the alternative status of macrophages and micro-environment (Redente et al., 2014).

MMPs are the extracellular endopeptidases degrading ECM including collagens, proteoglycans, laminins, and fibronectin. Tissue inhibitor of metalloproteinases (TIMPs) work as the inhibitors of MMPs. The balance of MMPs and TIMPs modulates the process throughout fibrosis development, including the formation of multiple cell injuries, the activation of latent cytokines and myofibroblasts and mainly, the maintenance of the homeostasis of ECM (Giannandrea and Parks, 2014). Some MMPs have pro-fibrotic functions whereas some have anti-fibrotic according to cell types and phases. The dysregulation of MMP-19 has been proved to cause the degradation of normal liver ECM and initiate liver injury (Jirouskova et al., 2012). Conversely, MMP-2 has been reported to cleave type I collagen and attenuate collagen deposition by HSC, inhibiting liver fibrosis (Radbill et al., 2011). As to TIMPs, they could inhibit or activate fibrosis via MMPs. For example, TIMP-3 inhibits MMPs to induce inflammation (Gill et al., 2010) in lung injury, and TIMP-1 has been found to play a dual role in liver fibrosis (Wang H. et al., 2011).

Other extracellular factors include a wide range of proteins and peptides. They mainly guide the differentiation of myofibroblasts, and are closely related to each other and growth factors. For example, the hedgehog (Hh) signaling pathway mediates EMT during the fetal development, and responds to injury through the repression of epithelial marker epithelial-cadherin by Snail and Twist. Overactivation of Hh signaling pathway contributes to biliary fibrosis and related liver fibrosis (Omenetti et al., 2008). In fibrotic kidney, the upregulated Wnt signaling has been reported to result in abundant of β-catenin. The signaling regulates genes such as Twist, LEF1 to induce EMT, thus to aggravate disease (He et al., 2009).

Intracellular factors mediating the progression of fibrosis

Intracellular factors, mainly multiple kinases, propagate the signaling received by cells through phosphorylation and other pathways. A common consequence of the signaling is that, transcription activators or inhibitors translocate into nucleus to regulate fibrosis-related gene expression and cell responses. In certain inflammatory pathways, intracellular factors also modulate the expression of extracellular factors, such as growth factors and cytokines, and secrete them out of cells to amplify inflammatory responses. Besides, epigenetic factors are emerging as a new way to affect fibrosis-related gene expression.

Intracellular factors include a number of kinases. In inflammation phase, many upstream factors, such as TGF-β, TNF-α, and epidermal growth factors initiate mitogen-activated protein kinase (MAPK) pathway. An element of MAPK pathway, mitogen-activated protein kinase-activated protein kinase-2 mediates myofibroblasts differentiation and regulates the gene expression of several matrix proteins such as col1a2, col3a1, and lox (Vittal et al., 2013). Another important intracellular signaling, mechanistic target of rapamycin (mTOR) pathway is activated by Wnt and TNF-α. Then, mTOR pathway activates ribosomal protein S6 kinase β-1 and modulates protein p21 or p27, which regulates the cell cycle of many cells including fibroblasts. In addition, the inhibition of mTOR pathway reduces collagen deposition and cardiac fibrosis (Chen et al., 2012). Besides serving as amplifiers of signal transduction, some intracellular enzymes such as cathepsin K, which belongs to lysosomal cysteine proteases, have been proved to be able to degrade ECM in lysosome after phagocytosis (Fukumori et al., 2003; Buhling et al., 2004).

Nuclear receptors are receptors located in cytoplasm and nucleus that could receive signals from intracellular ligands and bind to DNA to regulate gene expression. For example, peroxisome proliferator activated receptor γ(PPAR-γ), may directly regulate type I collagen gene (Yang et al., 2006) and block TGF-β signaling (Ghosh et al., 2009). Another nuclear receptor, farnesoid-X receptor (FXR), exhibits anti-fibrotic effect via the reduction of proliferating cholangiocytes and subsequent reduction of TGF-β (Liu et al., 2003). The activation of FXR also decreases a series of pro-fibrotic factors including TIMP-1, collagens, α-SMA, and MMP-2 (Zhang et al., 2009).

Nowadays, epigenetics including microRNAs, DNA methylation and lncRNAs, are found involved in machinery of pro-fibrotic process mainly through regulating fibrosis-related gene expression. Some microRNAs are found to negatively regulate translation of ECM components. Among them, miR-21 induces extracellular-signal regulated kinase/MAPK activity via the inhibition of Spry1 to protect cardiac fibroblasts survival (Thum et al., 2008). It has been reported that the levels of DNA methylation at specific CpG sites of pro-fibrotic genes (PPARα, PPARδ, TGFβ1, Collagen1A1, and PDGFα) differ among different fibrosis stages in NAFLD (Zeybel et al., 2015).

There are factors that affect fibrosis process both extra- and intracellularly, including reactive oxygen species (ROS), galectin-3 and lysyl oxidase homolog 2 (LOXL2). ROS can be generated through tissue injuries, cell damages and NADPH oxidase activities. Extracellular ROS targets latency-associated peptides and then activates TGF-β signaling while intracellular oxidative stress induces p53-dependent apoptosis in lung fibrosis via the caspases-9/3 activation in mitochondria (Cheresh et al., 2013). As to galectin-3, extracellular galectin-3 induces T cell apoptosis and plays a dual function inside and outside cells (Li et al., 2014). Another factor LOXL2 is generally considered as extracellular enzyme that promotes collagen production and crosslink with collagen fibers in response to mechanical stress (Yang et al., 2016). While on the other hand, intracellular LOXL2 has been reported to induce EMT in carcinoma progression (Peinado et al., 2005).

Many studies proved that different fibroproliferative diseases share common underlying mechanisms (Wenzke et al., 2012). The existence of common mechanisms facilitates the complete interpretation of fibrosis pathogenesis and enhances our understanding of fibrosis-related diseases. On this basis, it is necessary to reconsider targets involved in these mechanisms and evaluate their potential roles in fibrosis treatment across tissues and organs.

Drugs and targets in fibrosis

Motivated by huge clinical burdens, continuous intense researches on drug targeting fibrosis have been conducted, many of which have led to clinical trials. Due to the strong associations between inflammation and fibrosis, more efforts have been devoted to anti-inflammation drugs in the past few years (Dinwiddie, 2005). Nowadays, new targets and drugs for fibrosis are constantly emerging with the progress in understanding fibrosis pathology. Here we summarize them in Tables 14, including single (Tables 13) and multi component (Table 4) drugs with their verified and potential targets in fibrosis.

Table 1

TargetDrugClinical trialbReference
GroupTarget or mechanism typeTarget or mechanismOrgansaDrug NameMechanismClassDiseasePhaseReference/Trial identifierc
Growth factorsExtracellular TGF-β signalingTGF-βdLiver, Kidney, Lung, Heart, Pancreas, Skin, GutSHP-627 (FT011)InhibitorSmall moleculeCardiac fibrosisPreclinicalZhang et al., 2012
Hydronidone (F351)InhibitorSmall moleculeLiver fibrosis2(unknown)NCT02499562
PXS-25InhibitorSmall moleculeIPFdPreclinicalMaldonado et al., 2009; Wong et al., 2011
Disitertide (P-144)InhibitorSmall moleculeSkin fibrosis2(completed)NCT00574613
Fresolimumab (GC-1008)InhibitorMonoclonal antibodyIPF; SScd1(completed); 1(completed)NCT00125385; NCT01284322
LY2382770InhibitorMonoclonal antibodyDiabetic kidney disease2(terminated)NCT01113801
Integrin αvβ6STX-100InhibitorMonoclonal antibodyIPF2(completed)NCT01371305
CWHM-12InhibitorSmall moleculeLiver fibrosis; Lung fibrosisPreclinicalHenderson et al., 2013
ALK5dSB-431542AntagonistSmall moleculePulmonary fibrosisPreclinicalKoh et al., 2015
BMP-7dTHR-184AgonistSmall moleculeRenal fibrosis2(completed)NCT01830920
CTGFdCTGFPF-06473871InhibitorSmall moleculeHypertrophic scar2(completed)NCT01730339
RXI-109InhibitorSmall moleculeHypertrophic scar2(completed)NCT02030275
FG-3019InhibitorMonoclonal antibodyIPF2(active, not recruiting)NCT01890265
PDGFd/VEGFdPDGFRdImatinibAntagonistSmall moleculeNephrogenic systemic fibrosis; SSc; IPFApproved| 2(completed); 2(completed); 3(completed)NCT00677092; NCT00613171; NCT00131274
BOT-191AntagonistSmall moleculeLiver fibrosisPreclinicalvan Dijk et al., 2015
Nilotinib (AMN-107)AntagonistSmall moleculeSScApproved| 2(completed)NCT01166139
DasatinibAntagonistSmall moleculeScleroderma pulmonary fibrosisApproved| 2(completed)NCT00764309
VEGFRd/PDGFRNintedanib (BIBF-1120)AntagonistSmall moleculeScleroderma; IPFApproved| 3(recruiting); 3(completed)NCT02597933; NCT01335464
Sorafenib (BAY 43-9006)AntagonistSmall moleculeExtensive keloidsApproved| 2(terminated)NCT01425216
TNFdTNFThalidomideInhibitorSmall moleculeIPFApproved| 2(completed)NCT00162760
PomalidomideInhibitorSmall moleculeIPFApproved| 2(withdrawn)NCT01135199
EtanerceptInhibitorRecombinant proteinIPFApproved| 2(completed)NCT00063869
BelimumabInhibitorMonoclonal antibodySScApproved| 2(completed)NCT01670565
HGFdHGFLiver, Kidney, Lung, Heart, SkinRefanalin (BB-3)StimulantSmall moleculeLiver fibrosis; IPFPreclinicalFallowfield, 2011
CytokinesInterleukinIL-13dLiver, Kidney, Lung, Heart, Pancreas, Skin, GutDectrekumab (QAX-576)InhibitorMonoclonal antibodyIPF; IPF secondary to SSc2(terminated); 2(terminated)NCT01266135; NCT00581997
TralokinumabInhibitorMonoclonal antibodyIPF2(terminated)NCT01629667
IL-1R1Liver, Kidney, Lung, Heart, Skin, GutAnakinraAntagonistRecombinant proteinCystic fibrosisApproved| PreclinicalIannitti et al., 2016
IL-1βRRilonaceptAntagonistRecombinant proteinSScApproved| 2(active, not recruiting)NCT01538719
IL-13/IL-4SAR156597InhibitorMonoclonal antibodySSc; IPF2(recruiting); 2(completed)NCT02921971; NCT01529853
CC chemokineCCL2dLiver, Kidney, Lung, Heart, Pancreas, Skin, GutCarlumab (CNTO-888)InhibitorMonoclonal antibodyIPF2(completed)NCT00786201
BindaritInhibitorSmall moleculeMyocardial fibrosis; Renal fibrosisPreclinicalLin et al., 2009; Zhu et al., 2009
CCR5dLiver, Kidney, LungMaravirocAntagonistSmall moleculeLiver fibrosisApproved| PreclinicalGonzalez et al., 2014
CCR2Liver, Kidney, Lung, Heart, Pancreas, Skin, GutRS-504393AntagonistSmall moleculeRenal fibrosisPreclinicalKitagawa et al., 2004
InterferonIFN-γRdActimmuneStimulantInterferonIPF; Liver fibrosis; Cystic fibrosisApproved| 3(completed); 2(completed); 2(completed)NCT00047658; NCT00043303; NCT00043316
IFN-αLiver, Kidney, LungInterferon alpha oral lozengeStimulantInterferonPulmonary fibrosis2(completed)NCT01442779
MMPd/TIMPdMMP/TIMPMMP-2/MMP-9/TIMP-1Liver, Kidney, Lung, Heart, Pancreas, Skin, GutBatimastat(BB-49)InhibitorSmall moleculeIPFPreclinicalCorbel et al., 2001
MMP/TIMPMarimastatInhibitorSmall moleculeLiver fibrosisApproved| Preclinicalde Meijer et al., 2010
Other proteins and peptidesEndothelinET-1 receptordLiver, Kidney, Lung, Heart, Skin, GutMacitentanAntagonistSmall moleculeIPFApproved| 2(completed)NCT00903331
BosentanAntagonistSmall moleculeIPF; SSc;Approved| 3(completed); 3(completed); 4(completed)NCT00070590; NCT00319696; NCT01395732
AmbrisentanAntagonistSmall moleculeIPF; SScApproved| 3(terminated); 4(unknown)NCT00879229; NCT01051960
Sparsentan (RE-021)AntagonistSmall moleculeFocal segmental glomerulosclerosis2(active, not recruiting)NCT01613118
AtrasentanAntagonistSmall moleculeRenal fibrosisPreclinicalSamad et al., 2015
Angiotensin IIAT1 receptordLiver, Kidney, Lung, Heart, Pancreas, Skin, GutLosartanAntagonistSmall moleculeLiver fibrosis; Cystic fibrosisApproved| 4(completed); 2(not yet recruiting)NCT00298714; NCT03206788
GPCRdLPARdLiver, Kidney, Lung, SkinBMS-986020AntagonistSmall moleculeSSc; IPF2(withdrawn); 2(completed)NCT02588625; NCT01766817
SAR-100842AntagonistSmall moleculeSSc2(completed)NCT01651143
PAR1dLiver, Kidney, Lung, Heart, Pancreas, SkinPAR1 antagonismAntagonistSmall moleculeLiver fibrosisPreclinicalFiorucci et al., 2004
CB1 receptordLiverCurcumin*AntagonistSmall moleculeLiver fibrosis; Renal fibrosis; IPFPreclinicalSmith et al., 2010; Zhang et al., 2013; Sun et al., 2017
Silymarin*AntagonistSmall moleculeLiver fibrosisPreclinicalTsai et al., 2008; Zhang et al., 2013
CB2 receptordβ-caryophyllene*AgonistSmall moleculeLiver fibrosisPreclinicalCalleja et al., 2013; Mahmoud et al., 2014
Prostacyclin receptorLiver, Kidney, Lung, Heart, PancreasBeraprostAgonistSmall moleculeRenal fibrosis; Cardiac fibrosisPreclinicalChen et al., 2014
IloprostAgonistSmall moleculeSScApproved| 2(completed)NCT00109681
TreprostinilAgonistSmall moleculeIPF; SScApproved| 2(terminated); 2(completed)NCT00703339; NCT00775463
VIP receptorLungAviptadilAgonistPeptide hormoneCystic fibrosisPreclinicalMathioudakis et al., 2013
Leukocyte elastaseLeukocyte elastaseSivelestatInhibitorSmall moleculeIPFPreclinicalTakemasa et al., 2012
TAFIdTAFILiver, Kidney, LungUK-396082InhibitorSmall moleculeRenal fibrosisPreclinicalAtkinson et al., 2015
RelaxinRelaxin receptorLiver, Kidney, Lung, Heart, SkinSerelaxinStimulantPeptide hormoneCardiac fibrosis; Renal fibrosisPreclinicalSamuel et al., 2014; Huuskes et al., 2015
SAPdSAP (mimic)PRM-151StimulantRecombinant proteinIPF2(active, not recruiting)NCT02550873
Integrin αIntegrin α5LiverDioscin*InhibitorSmall moleculeLiver fibrosisPreclinicalLiu et al., 2015; Zhang et al., 2015a,b; Gu et al., 2016; Xu et al., 2017; Yin et al., 2017
TGMdTGM2Kidney, LungNTU281InhibitorSmall moleculeRenal fibrosisPreclinicalJohnson et al., 2007

Single-component drugs targeting extracellular factors.

*

Drug belongs to monomer extracted from natural products.

a

Organs that had study report of corresponding targets in fibrosis treatment.

b

Clinical trial resource are from http://Clinicaltrials.gov.

c

Trial Identifier is the clinical trail identifier of corresponding drug

d

TGF-β, transforming growth factor-β; IPF, idiopathic pulmonary fibrosis; SSc, systematic sclerosis; ALK5, TGF-β receptor 1; BMP-7, bone morphogenetic protein 7; CTGF, connective tissue growth factor; PDGF, platelet-derived growth factor; PDGFR, platelet-derived growth factor receptor; VEGF, vascular endothelial growth factor; VEGFR, vascular endothelial growth factor receptor; TNF, tumor necrosis factor; HGF, hepatocyte growth factor; IL-13, interleukin-13; CCL2, chemokine (C-C motif) ligand 2; CCR5, C-C chemokine receptor type 5; IFN-γR, interferon-γ receptor; MMP, matrix metalloproteinase; TIMP, tissue inhibitor of metalloproteinase; ET-1 receptor, endothelin-1 receptor; AT1 receptor, angiotensin II receptor type 1; GPCR, G protein-coupled receptor; LPAR, lysophosphatidic acid receptor; PAR1, protease-activated receptor 1; CB1 receptor, cannabinoid receptor type 1; TAFI, thrombin activatable fibrinolysis inhibitor; SAP, serum amyloid P; VIP, vasoactive intestinal peptide; TGM2, transglutaminase.

Single-component drugs targeting extracellular factors mediating fibrosis

Nowadays, most approved and investigational drugs are single-component drugs, which only contain one organic component and have distinct targets. As we described previously, fibrosis progression results from a combination of the abnormalities of extracellular and intracellular factors. Drugs targeting extracellular factors are prevalent, about 60% of known targets are receptors located on cell membrane mainly because the extracellular targets are accessible and serve as upstream signals (Overington et al., 2006), and so are the targets of fibrosis-related drugs. The binding of receptors and ligands triggers the downstream signaling, thus the blockade of receptors or ligands is considered to be an effective choice to alleviate fibrosis (Table 1).

The majority of anti-fibrosis drugs targeting extracellular factors are inhibitors of ligands such as growth factors, cytokines and MMPs. Most inhibitors could directly bind to the active sites of targets. The majority of approved inhibitor drugs in Table 1 target TNF, which are widely used in fibrosis-related diseases and could suppress the action of TNF through multiple mechanisms. These drugs include small molecules Thalidomide and Pomalidomide (Weingartner et al., 2012), recombinant protein Etanercept and monoclonal antibodies Belimumab. Thalidomide and Etanercept have completed the phase II trial in IPF (Raghu et al., 2008; Horton et al., 2012) while Belimumab has completed the phase II trial in SSc. Besides, some inhibitor drugs targeting growth factors are still under investigation. For example, Disitertide, a synthetic peptide derived from TGF-β type III receptor, inhibits the binding of TGF-β and its receptor and exhibit anti-fibrotic function (Ezquerro et al., 2003). Drugs that inhibit interleukins are always monoclonal antibodies. Tralokinumab, a human IgG4 monoclonal antibody, shows pro-apoptotic effects via IL-induced apoptotic factors in IPF (Murray et al., 2014). Many natural products act as inhibitor drugs like Dioscin, which is a monomer extracted from Dioscoreae Rhizoma and could ameliorate liver fibrosis (Liu et al., 2015; Zhang et al., 2015a,b; Gu et al., 2016; Xu et al., 2017; Yin et al., 2017). In addition, some preclinical drugs inhibit MMPs, like Marimastat, which simultaneously down-regulates MMPs gene expression and MMPs activities. However, Marimastat reduces inflammation and liver injuries while increases fibrosis in mice model. This may result from the indiscriminative inhibition of MMPs, some of which function to degrade ECM (de Meijer et al., 2010).

Compared with inhibitor drugs, antagonists achieve the same inhibition effect by targeting cell membrane receptors to dampen downstream signaling. These small molecules bind to receptors without effectively activating them. The receptors of PDGF, vascular endothelial growth factor, endothelin (ET), and angiotensin all have approved antagonist drugs. An antagonist for tyrosine kinase receptors of PDGF, Imatinib, has showed protective effect by reducing differentiation of resting fibroblasts in SSc mice model (Akhmetshina et al., 2009). However, it did not show efficacy in phase II clinical trial in IPF (Daniels et al., 2010) and the high-dose of Imatinib may lead to severe adverse events (Khanna et al., 2011). Macitentan, a dual antagonist of ETA and ETB receptor, is beneficial for lung fibrosis. Similarly, another drug Losartan targeting angiotensin II receptor has been evaluated in IPF patients (Couluris et al., 2012). Some preclinical antagonist drugs including Maraviroc (Gonzalez et al., 2014), Atrasentan (Ritter et al., 2014), and PAR1 antagonists (Fiorucci et al., 2004) were under investigation for fibrosis treatment.

On the contrary, many drugs exert their therapeutic effects by activating their targets. Many anti-fibrotic receptors can be targets of these exogenous agonists that augment the downstream biological responses to suppress fibrosis. An approved agonist drug in this category is Iloprost, which can reverse right ventricle fibrosis by re-establishing collagen balance (Gomez-Arroyo et al., 2015). Another agonist of vasoactive intestinal peptide, Treprostinil, reduces inflammation and collagen deposition (Manitsopoulos et al., 2015). Other anti-fibrotic agonists for cell membrane receptors include Aviptadil, INT-767 (Baghdasaryan et al., 2011) and Beraprost (Kaneshige et al., 2007).

Moreover, a few drugs are synthetic proteins that bind receptors to serve as stimulants and perform the same functions as native proteins. An approved drug, synthetic interferon-γ, Actimmune, has completed phase II or phase III study in multiple fibrosis including IPF (Skaria et al., 2015), liver fibrosis (Muir et al., 2006), and cystic fibrosis (Moss et al., 2005). Another stimulant Refanalin, a HGF mimetic, is a potential drug for liver fibrosis (Fallowfield, 2011; Pellicoro et al., 2014).

Single-component drugs targeting intracellular factors mediating fibrosis

Compared with extracellular factors, intracellular targets are less popular owing to their inaccessibility. Drugs targeting intracellular factors are less varied because most of them are small molecules. Small molecules could readily translocate into cytoplasm while large molecules such as monoclonal antibodies face more challenges to cross the plasma membrane (Imai and Takaoka, 2006). Nevertheless, more and more studies concerned intracellular factors as targets in recent years, and numerous candidate targets are identified in cytoplasm, nucleus, and mitochondrion. Many approaches, including increasing membrane permeation, combination with supercharged proteins and activating transport through receptors, were implemented to deliver drugs across cell membrane (Mitragotri et al., 2014).

Fibrosis drugs targeting intracellular factors are summarized and classified into four categories: enzymes, nuclear receptors, other proteins, and epigenetics (Table 2). Many drugs acting through intracellular factors are also inhibitors. These drugs inhibit a wide range of kinases located in cytoplasm, and consequently suppress the translocation of transcription factors that drive the expression of pro-fibrotic genes. Rapamycin and Sirolimus are approved drugs that inhibit mTOR. Rapamycin prevents the activation of macrophages and myofibroblasts and the subsequent release of TGF-β in chronic kidney disease (CKD) (Chen et al., 2012). Sirolimus shows anti-inflammatory and anti-fibrotic effects in IPF (Tulek et al., 2011). Besides kinases, there are many other intracellular proteins that serve as potential targets for fibrosis management. Pirfenidone, one of the IPF drugs, has completed phase III trial in IPF patients with alleviated disease progression and acceptable side effects (King et al., 2014). The potential mechanism of Pirfenidone is inhibiting the nuclear accumulation of intracellular proteins SMAD2/3 to regulate TGF-β signaling (Choi et al., 2012). Other approved inhibitor drugs include Ruxolitinib for bone marrow fibrosis (Wilkins et al., 2013), Paquinimod for SSc (Stenstrom et al., 2016), and Pentoxifylline (Okunieff et al., 2004) combined with vitamin E (Jacobson et al., 2013).

Table 2

TargetDrugClinical trialbReference
GroupTarget or mechanism typeTarget or mechanismOrgansaDrug NameMechanismClassDiseasePhaseReference/Trial identifierc
EnzymesmTORdmTORC1/2dLiver, Kidney, Lung, Heart, Skin, GutRapamycin (Sirolimus)*InhibitorSmall moleculeRenal interstitial fibrosisApproved| 3(completed)NCT01079143
Palomid-529 (RES-529)InhibitorSmall moleculeMacular degeneration1(completed)NCT01033721
JAK-STATdJAK1/JAK2dRuxolitinibInhibitorSmall moleculeMyelofibrosisApproved| 3(completed)NCT00952289
BaricitinibInhibitorSmall moleculeRenal interstitial fibrosisPreclinicalBreyer and Susztak, 2016
PI3K-AktdAktLiver, Kidney, Lung, Heart, SkinOmipalisib (GSK2126458)InhibitorSmall moleculeIPFd1(completed)NCT01725139
FAK1dLiver, Kidney, Lung, Heart, Pancreas, SkinPF-562271InhibitorSmall moleculePulmonary fibrosis; Cardiac fibrosis; Liver fibrosisPreclinicalLagares et al., 2012; Fan et al., 2015; Zhao et al., 2017
MAPKdJNKdTanzisertib (CC-930)InhibitorSmall moleculeIPF2(terminated)NCT01203943
MAPKLiver, Kidney, Lung, Heart, Pancreas, Skin, GutMMI-0100InhibitorSmall moleculeIPF; Cardiac fibrosisPreclinicalXu et al., 2014
NF-κBdIKKdIMD-1041InhibitorSmall moleculeCardiac fibrosisPreclinicalTanaka et al., 2012
Bardoxolone methyl (CDDO-Me)InhibitorSmall moleculePulmonary hypertension2(recruiting)NCT02036970
NF-κBAntisense NF-κBInhibitorAntisense oligonucleotideIntestinal fibrosisPreclinicalLawrance et al., 2003
Baicalein*InhibitorSmall moleculeRenal fibrosis; IPFPreclinicalGao et al., 2013; Wang et al., 2015
SulfasalazineInhibitorSmall moleculeLiver fibrosis; Pancreatic fibrosisApproved| PreclinicalChavez et al., 2012; Wang et al., 2016
cAMP-PKAdROCKdY-27632InhibitorSmall moleculeRenal fibrosis; Liver fibrosisPreclinicalTada et al., 2001
Non-kinase enzyme26S proteaseLiver, Kidney, Lung, HeartBortezomibInhibitorSmall moleculeSSc pulmonary fibrosisApproved| 2(recruiting)NCT02370693
CaspaseLiver, Kidney, Lung, Heart, SkinEmricasanInhibitorSmall moleculeLiver fibrosisPreclinicalBarreyro et al., 2015
VX-166InhibitorSmall moleculeLiver fibrosisPreclinicalWitek et al., 2009
Z-VAD-fmkInhibitorSmall moleculePulmonary fibrosisPreclinicalKuwano et al., 2001
PDEdKidney, HeartCTP-499InhibitorSmall moleculeDiabetic nephropathy1(completed)NCT01328821
Cathepsin BLiver, Lung, Heart, PancreasVBY-376InhibitorSmall moleculeLiver fibrosisPreclinicalAlkhouri et al., 2011
CA-074MeInhibitorSmall moleculePancreatic fibrosis; Cardiac fibrosis; Pulmonary fibrosisPreclinicalLerch and Halangk, 2006; Liu et al., 2013; Zhang et al., 2015
S100A9Liver, Lung, Heart, SkinPaquinimodInhibitorSmall moleculeSScd2(completed)NCT01487551
Procollagen-proline dioxygenaseLiver, LungHOE-077InhibitorSmall moleculeLiver fibrosisPreclinicalMatsumura et al., 1997
Nuclear receptorsPPARdPPAR-γLiver, Kidney, Lung, Heart, Pancreas, Skin, GutRosiglitazoneAgonistSmall moleculeLiver fibrosis;Approved| 2(completed)NCT00492700
Elafibranor (GFT-505)AgonistSmall moleculeLiver fibrosis3(recruiting)NCT02704403
SaroglitazarAgonistSmall moleculeLiver fibrosis2(recruiting)NCT03061721
PioglitazoneAgonistSmall moleculeCystic fibrosis; Liver fibrosisApproved| 1(completed); 1(completed)NCT00719381; NCT01454336
Docosahexaenoic acid*AgonistSmall moleculeLiver fibrosis; Pulmonary fibrosisPreclinicalDepner et al., 2013; Zhao et al., 2014
FXRdFXRLiver, Kidney, Lung, GutINT-767AgonistSmall moleculeLiver fibrosisPreclinicalBaghdasaryan et al., 2011
PX-102AgonistSmall moleculeLiver fibrosisPreclinicalAli et al., 2015
Obeticholic acid* (INT-747)AgonistSmall moleculeLiver fibrosisApproved| 3(recruiting)NCT02548351
Turofexorate isopropyl (WAY-362450)AgonistSmall moleculeLiver fibrosisPreclinicalZhang et al., 2009
GW4064AgonistSmall moleculeLiver fibrosisPreclinicalLiu et al., 2003
GRdGRLiver, Lung, Heart, SkinTriamcinoloneAgonistSmall moleculeKeloid scarringApproved| 1(terminated)NCT01978301
ERdERβLiverGenistein*AgonistSmall moleculePulmonary fibrosis; Liver fibrosisPreclinicalSalas et al., 2008; Nadadur et al., 2012
Other proteinsIntracellular TGF-βd signalingSMAD2/3Liver, Kidney, Lung, Heart, Pancreas, Skin, GutPirfenidoneInhibitorSmall moleculeIPF; SScApproved| 3(completed); 2(completed)NCT00287729; NCT01933334
SMAD3/4PentoxifyllineInhibitorSmall moleculeSkin fibrosisApproved| 2(completed)NCT00001437
SMAD3SIS-3InhibitorSmall moleculeRenal fibrosisPreclinicalMeng et al., 2015
Glycyrrhizin*InhibitorSmall moleculeLiver fibrosis3(terminated)NCT00686881
EpigeneticsmiRNAmiR-21Anti-miR-21InhibitorOligonucleotideIPF; Renal fibrosisPreclinicalLiu et al., 2010; Chau et al., 2012
methylationTransmethylationLiver, Kidney, Lung, Heart, Skin, GutAdemetionine (SAM)InhibitorSmall moleculeLiver fibrosisApproved| UnknownNCT02231333
BMPER (gene)LungDNA methylationInhibitorMethylationIPFPreclinicalHuan et al., 2015

Single-component drugs targeting intracellular factors.

*

Drug belongs to monomer extracted from natural products.

a

Organs that had study report of corresponding targets in fibrosis treatment.

b

Clinical trial resource are from http://Clinicaltrials.gov.

c

Trial Identifier is the clinical trail identifier of corresponding drug.

d

mTOR, mechanistic target of rapamycin; mTORC1, mechanistic target of rapamycin complex 1; JAK-STAT, janus kinase/signal transducers and activators of transcription; PI3K-Akt, phosphoinositide 3-kinase/protein kinase B; IPF, idiopathic pulmonary fibrosis; FAK1, focal adhesion kinase 1; MAPK, mitogen-activated protein kinase; JNK, c-Jun N-terminal kinases; NF-κB, nuclear factor kappa-light-chain-enhancer of activated B cells; IKK, I-kappa B kinase; cAMP-PKA, cyclic AMP- protein kinase A signaling; ROCK, rho-associated protein kinase; PDE, phosphodiesterase; SSc, systematic sclerosis; PPAR, peroxisome proliferator-activated receptor; FXR, farnesoid X receptor; GR, glucocorticoid receptor; ER, estrogen receptor; TGF-β, transforming growth factor-β.

In addition, there are also some nuclear receptors located in cytoplasm and nucleus, which could be activated by small molecule agonists, such as PPAR. Rosiglitazone, a PPAR-γ agonist, has anti-fibrotic effect as a consequence of activating MMP-1 and elevating HGF expression in patients with systemic sclerosis-related interstitial lung disease (Bogatkevich et al., 2012). Other approved PPAR targeting drugs like Elafibranor and Pioglitazone, have entered phase II and phase I studies, respectively. Obeticholic acid is an approved drug entering phase III study that decreases inflammation and fibrosis in NASH patients via activating FXR signaling (Verbeke et al., 2016).

Epigenetics are very different types of fibrosis therapies. The most studied epigenetics-based therapy for fibrosis is microRNA. MicroRNA could be neutralized by specific anti-miRNA oligonucleotides delivered into cells. Among them, anti-miR-21 has been reported to inhibit miR-21 activity and ameliorate fibrosis progression through PPAR signaling in CKD (Chau et al., 2012). Another strategy is the intervention of DNA methylation for proteins such as BMP endothelial cell precursor-derived regulator (BMPER), which acts as the regulator of fibroblasts activation. Altering methylation on BMPER gene has been reported to decrease BMPER level and thus to inhibit fibroblasts activity (Huan et al., 2015). Besides, some drugs targeting both extracellular and intracellular factors are also incorporated (Table 3). A majority of them are antioxidants, including an approved drug N-acetylcysteine (Zhang et al., 2014).

Table 3

TargetDrugClinical trialbReference
Target or mechanism typeTarget or mechanismOrgansaDrug NameMechanismClassDiseasePhaseReference/Trial identifierc
LOXdLOXL2dLiver, Kidney, Lung, Heart, Skin, Gutβ-aminopropionitrile (BAPN)InhibitorSmall moleculeCardiac fibrosisPreclinicalMartinez-Martinez et al., 2016
Simtuzumab (GS-6624)InhibitorMonoclonal antibodyLiver fibrosis; IPFd2(completed); 2(terminated)NCT01452308; NCT01769196
ROSdNOX1d/NOX4Liver, Kidney, Lung, Heart, Pancreas, SkinGM-CT-01InhibitorPolymerLiver fibrosisPreclinicalTraber and Zomer, 2013
GR-MD-02InhibitorPolymerLiver fibrosis2(completed)NCT02421094
GCS-100InhibitorPolymerRenal fibrosis2(completed)NCT01843790
ROSGKT137831InhibitorSmall moleculeLiver fibrosisPreclinicalAoyama et al., 2012
N-acetylcysteine*InhibitorSmall moleculeIPFApproved| PreclinicalDemedts et al., 2005; Zhang et al., 2014
MitoquinoneInhibitorSmall moleculeLiver fibrosisPreclinicalVilaseca et al., 2017
Salvianolic acid B*InhibitorSmall moleculeLiver fibrosis; Renal fibrosis; IPFPreclinicalLiu et al., 2002, 2016; Pan et al., 2011
Resveratrol*InhibitorSmall moleculeLiver fibrosis3(completed)NCT02030977
Vitamin (mimic)Liver, Kidney, Lung, Heart, Pancreas, Skin, GutPyridoxamineInhibitorSmall moleculeRenal fibrosis2(completed)NCT00320060
α-tocopherolInhibitorSmall moleculeIPFApproved| PreclinicalDeger et al., 2007
Collagen (mimic)Liver, Kidney, Lung, SkinIW001InhibitorCollagenIPF1(completed)NCT01199887

Single-component drugs targeting both extra- and intracellular factors.

*

Drug belongs to monomer extracted from natural products.

a

Organs that had study report of corresponding targets in fibrosis treatment.

b

Clinical trial resource are from http://Clinicaltrials.gov.

c

Trial Identifier is the clinical trail identifier of corresponding drug.

d

LOX, lysyl oxidase; LOXL2, lysyl oxidase homolog 2; IPF, idiopathic pulmonary fibrosis; ROS, reactive oxygen species; NOX1, NADPH oxidase 1.

Multi-component drugs used for fibrosis

Differed from single-component drugs that target a single protein or other simple targets, multi-component drugs contain more than one active ingredient. Traditional Chinese medicines (TCM) therapies, usually appeared as herbal formula, have been studied for thousands of years as multi-component drugs (Wang et al., 2012). Nowadays, single compound acting on multiple targets and multiple compounds acting on multiple targets are popular strategies in drug development (Hopkins, 2008). Fibrosis includes numerous complicated pathological pathways. Multi-component drugs, aiming at different targets, have the advantage in modulating these pathways simultaneously and producing synergistic effects. Moreover, multi-component drugs are expected to provide great resources for discovering new effective drug molecules. Many studies have revealed the pharmacology of multi-component drugs in the fibrosis treatment (Feng et al., 2009; Yang et al., 2009; Li and Kan, 2017) (Table 4). For example, Fuzhenghuayu capsule (FZHY), a well-known multi-component drug for treating liver fibrosis, inhibits liver fibrosis and improves liver function in patients via inhibition of nuclear factor kappa-B kinase subunit β/nuclear factor κF and TGF-β signaling (Liu et al., 2005). Another emerging multi-component drug, Qishenyiqi (QSYQ), is under phase II clinical trial for ischemic heart failure. QSYQ attenuates cardiac fibrosis via IL-6/STAT3 and TNF-α/nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) signalings and anti-apoptosis activities (Wang et al., 2017). Multi-component drugs act on different physiological reactions associated with fibrosis, such as inflammation and angiogenesis, leading to a systematic improvement of disease. Qushi Huayu Decoction (QHD) is a multitargeting drug that alleviates fibrosis by reducing ROS via the induction of glutathione and modulating lipid metabolism and gut barrier function (Feng et al., 2017).

Table 4

DrugClinical trialaReference
Drug NameMechanismDiseasePhaseReference/Trial identifierb
Fuzhenghuayu capsule (FZHY)TGF-βc/MMP-2cLiver fibrosis2(completed); 4(recruiting)NCT00854087; NCT02241616
Qishenyiqi (QSYQ)TNFc/TGF-β/β-CateninIschemic heart failure2(recruiting)NCT02875639
Qushi Huayu Decoction (QHD)ROScLiver fibrosisPreclinicalFeng et al., 2017
Herbal compound 861 (Cpd 861)TGF-β/MMP-1/TIMP-1cLiver fibrosisPreclinicalHou et al., 2016
Xiao-Chai-Hu Tang (XCHT)IL-6c/TNF-α/Bax proteinLiver cancer2(completed)NCT00040898; Zhou et al., 2012
Dahuangzhechong pill (DHZCP)α-SMAc/TNF-α/IL-13/p38 MAPKc/ERKcLiver fibrosisPreclinicalCai et al., 2010
Han-dan-gan-leROS/collagenLiver fibrosisPreclinicalLi et al., 1998
Qianggan-Rongxian DecoctionLiver fibrosisPreclinicalLi et al., 2008
Yi-gan-kang granuletype I collagen/TIMP-1Liver fibrosisPreclinicalYao et al., 2005
Ginkgo biloba extractTGF-βLiver fibrosisPreclinicalDing et al., 2005
Rosa laevigata Michx (RLTS)ROS/CYP2Elc/TGF-β/SMAD/FAKc-PI3Kc-Aktc-p70S6Kc/MAPKLiver fibrosisPreclinicalDong et al., 2015
Liuweiwuling (LWWL) tabletsTGF-β/SMAD/ NF-κBcLiver fibrosisPreclinicalLiu et al., 2017
Xuefuzhuyu (XFZY) decoctionHIF-Yc/DDAHc/ADMAc/VEGFcLiver fibrosisPreclinicalZhou et al., 2014
Diwu Yanggan (DWYG)TGF-β/BMP-7cLiver fibrosisPreclinicalShen et al., 2014
Ocimum gratissimum extracts (OGEs)ROS/α-SMALiver fibrosisPreclinicalChiu et al., 2014
Yin-Chiao-San (YCS)ROS/TNF-αIPFcPreclinicalYen et al., 2007
Renshen pingfei decoctionTGF-β/SMAD3IPFPreclinicalChen et al., 2016
Hu-qi-yinTGF-βIPFPreclinicalZhou et al., 2007
Decoction for Strengthening Qi and Replenishing Lung (DSQRL)IPFPreclinicalZhang et al., 2008
Modified Kushen Gancao Formula (mKG)TGF-β/IL-6/IL-17AIPFPreclinicalGao et al., 2016
Sho-seiryu-to (TJ-19)ROSIPFPreclinicalYang et al., 2010
Hochu-ekki-to (TJ-41)IL-5/IL-4/IFN-γIPFPreclinicalTajima et al., 2007
Shenlong DecoctionMMsP/TIMPsIPFPreclinicalLu et al., 2010
YupingfengHMGB1c/TGF-βIPFPreclinicalCui et al., 2015
Danggui–Buxue–Tang (DBTG)TNF-α/TGF-βIPFPreclinicalLv et al., 2012

Multi-component drugs.

a

Clinical trial resource are from http://Clinicaltrials.gov.

b

Trial Identifier is the clinical trail identifier of corresponding drug.

c

TGF-β, transforming growth factor-β; MMP-2, matrix metalloproteinase 2; TNF, tumor necrosis factor; ROS, reactive oxygen species; TIMP, tissue inhibitor of metalloproteinase; IL-6, interleukin-6; α-SMA, α-smooth muscle actin; MAPK, mitogen-activated protein kinase; ERK, extracellular signal-regulated kinase; PDGF-BB, platelet-derived growth factor-BB; IPF, idiopathic pulmonary fibrosis; HMGB1, high mobility group box 1; CYP2E1, cytochrome P450 2E1; FAK, focal adhesion kinase; PI3K, phosphatidylinositol-3-kinase; Akt, amino kinase terminal; p70S6K, 70-kDa ribosomal S6 Kinase; NF-κB, nuclear factor kappa-light-chain-enhancer of activated B cells; HIF-α, hypoxia inducible factors; DDAH, dimethylarginine dimethylaminohydrolase; ADMA, asymmetric dimethylarginine; VEGF, vascular endothelial grow factor; BMP-7, bone morphogenetic protein 7.

With multiple targets being discovered, it becomes apparent that more common targets will be shared across many fibrotic diseases with common mechanisms, though some proteins will not express in special conditions. Meanwhile, there will be more chance for drug repositioning, which indicate common drugs will be shared across different targets andfibroproliferative diseases.

Perspective

Fibrosis is a common pathological process in many diseases, causing a great clinical burden in recent years. The development of state-of-the-art technologies facilitate discovery of fibrosis therapies. Multi-omics analysis provides a more convenient and systematic way for researching on disease mechanisms (Fernandes and Husi, 2017). The seamless combination of traditional transcriptomics approaches with emerging technologies, including proteomics (Ordureau et al., 2014), metabolomics (Shah et al., 2012), and metagenomics (Jiao et al., 2017), will offer unprecedented opportunities to precisely elucidating and dissecting fibrosis mechanisms. Nowadays, the application of cryo-electron microscopy (cryo-EM) in macromolecular structure determination make it easier to identify drug targets (Zheng et al., 2015). Compared with traditional X-ray crystallography, cryo-EM has advantage in determining the structure of more complex and flexible receptors (Huang et al., 2016; Zhang et al., 2017). Finally, with the advent of the era of big data, artificial intelligence technology, especially deep learning, provides more accurate algorithms for drug repositioning (LeCun et al., 2015; Alaimo et al., 2016). The continuous development and application of the above technologies and methods will make it possible to identify and discover more common mechanisms, targets and drugs in fibrosis.

Statements

Author contributions

RZ and LZ conceived and designed the project. Each author has contributed significantly to the submitted work. XL drafted the manuscript. LZ, BW, MY, and RZ revised the manuscript. All authors read and approved the final manuscript.

Acknowledgments

This work was supported by National Natural Science Foundation of China 31200986 (to RZ), 41530105 (to RZ), Natural Science Foundation, the Shanghai Committee of Science and Technology 16ZR1449800 (to RZ), a departmental start-up fund (to LZ), the Peter and Tommy Fund, Inc., Buffalo, NY (to LZ), and Funds from the University at Buffalo Community of Excellence in Genome, Environment and Microbiome (GEM) (to LZ). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The reviewer XT and handling Editor declared their shared affiliation.

    Abbreviations

  • ECM

    extracellular matrix

  • IPF

    idiopathic pulmonary fibrosis

  • NAFLD

    non-alcoholic fatty liver disease

  • TGF-β

    transforming growth factor-β

  • IL-6

    interleukin-6

  • SSc

    systemic sclerosis

  • PDGF

    platelet derived growth factor

  • EMT

    epithelial-mesenchymal transition

  • HSC

    hepatic stellate cell

  • MMPs

    matrix metalloproteinases

  • α-SMA

    α-smooth muscle actin

  • HGF

    hepatocyte growth factor

  • TNF

    tumor necrosis factor

  • STAT3

    signal transducer and activator of transcription 3

  • TIMPs

    tissue inhibitor of metalloproteinases

  • Hh signaling

    hedgehog signaling

  • mTOR

    mechanistic target of rapamycin

  • MAPK

    mitogen-activated protein kinase

  • PPAR-γ

    peroxisome proliferator activated receptor γ

  • FXR

    farnesoid-X receptor

  • LOXL2

    lysyl oxidase homolog 2

  • ROS

    reactive oxygen species

  • CKD

    chronic kidney disease

  • ET

    endothelin

  • BMPER

    BMP endothelial cell precursor-derived regulator

  • TCM

    traditional Chinese medicines

  • FZHY

    Fuzhenghuayu capsule

  • NFκB

    nuclear factor kappa-light-chain-enhancer of activated B cells

  • QSYQ

    Qishenyiqi

  • QHD

    Qushi Huayu Decoction.

  • cryo-EM

    cryo-electron microscopy.

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Summary

Keywords

fibrosis, drug, target, pathological mechanism, pharmacology

Citation

Li X, Zhu L, Wang B, Yuan M and Zhu R (2017) Drugs and Targets in Fibrosis. Front. Pharmacol. 8:855. doi: 10.3389/fphar.2017.00855

Received

28 August 2017

Accepted

08 November 2017

Published

23 November 2017

Volume

8 - 2017

Edited by

Jinyong Peng, Dalian Medical University, China

Reviewed by

Xufeng Tao', Dalian Medical University, China; Ramin Massoumi, Lund University, Sweden

Updates

Copyright

*Correspondence: Lixin Zhu

This article was submitted to Gastrointestinal and Hepatic Pharmacology, a section of the journal Frontiers in Pharmacology

Disclaimer

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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