O SlideShare utiliza cookies para otimizar a funcionalidade e o desempenho do site, assim como para apresentar publicidade mais relevante aos nossos usuários. Se você continuar a navegar o site, você aceita o uso de cookies. Leia nosso Contrato do Usuário e nossa Política de Privacidade.
O SlideShare utiliza cookies para otimizar a funcionalidade e o desempenho do site, assim como para apresentar publicidade mais relevante aos nossos usuários. Se você continuar a utilizar o site, você aceita o uso de cookies. Leia nossa Política de Privacidade e nosso Contrato do Usuário para obter mais detalhes.
Fibrose Pulmonar Idiopática: Uma Doença com similaridades e suas conexões com a biologia do câncer
Eur Respir J 2010; 35: 496–504DOI: 10.1183/09031936.00077309CopyrightßERS Journals Ltd 2010PERSPECTIVEIdiopathic pulmonary fibrosis: a diseasewith similarities and links to cancer biologyC. Vancheri*, M. Failla*, N. Crimi* and G. Raghu#ABSTRACT: Several clinical trials have recently targeted specific pathways implicated in the AFFILIATIONSpathogenesis of idiopathic pulmonary fibrosis (IPF). However, IPF remains plagued by a median *Dept of Internal Medicine and Specialistic Medicine, Section ofsurvival of 3 yrs and emphasises the need for further research with new insights and Respiratory Diseases, University ofperspectives. The prevailing pathogenic hypotheses assume that either an inflammatory Catania, Catania, Italy. #process or an independent epithelial/fibroblastic disorder may propagate the disease process. Dept of Medicine; Division ofBased on knowledge developed with considerable scientific evidence, we provide our Pulmonary and Critical Care Medicine, University of Washingtonperspectives with an alternative point of view that IPF be considered as a neoproliferative Medical Center, Seattle, WA, USA.disorder of the lung. Genetic alterations, response to growth and inhibitory signals, resistance toapoptosis, myofibroblast origin and behaviour, altered cellular communications, and intracellular CORRESPONDENCE C. Vancherisignalling pathways are all fundamental pathogenic hallmarks of both IPF and cancer. The Dept of Internal Medicine andconcept of IPF as a lethal malignant disorder of the lung might extend beyond the pathogenic link Specialistic Medicine,between these two diseases and disclose new pathogenic mechanisms leading to novel Section of Respiratory Diseasestherapeutic options, adopted from cancer biology. Moreover, this vision might dawn the University of Cataniaawareness of the public, political and scientific community of this devastating disease from an Via S. Sofia 78 95123angle different from the current perception and provoke new ideas and studies to get a better 187. 95125understanding to control the otherwise relentless progressive disease. Catania Italy E-mail: firstname.lastname@example.orgKEYWORDS: Cancer research, cell proliferation control mechanisms, epigenetics, lung fibroblasts,lung fibrosis, myofibroblasts Received: May 12 2009 Accepted after revision: espite the increased knowledge through deposited extracellular matrix within the alveolarD Aug 19 2009 basic and clinical research over the last walls results in distorted pulmonary architecture, decade, idiopathic pulmonary fibrosis vascular remodelling, decreased oxygenation,(IPF) remains one of the most elusive lung respiratory failure and death . Histologically,disorders associated with a fatal outcome. Recent subepithelial fibrotic foci of fibroblasts are theclinical trials have targeted specific pathways characteristic pathologic abnormality; they prolif-implicated in the pathogenesis of IPF and these erate and invade gas exchange units and, alonghave included c-interferon, endothelin receptor with the deposited extracellular matrix, are spa-antagonists, antioxidants, etanercept, pirfenidone tially connected and may be akin to an organisedand tyrosine kinase inhibitors [1–6]. However, an neoplastic proliferation of the pulmonary parench-effective treatment regimen to improve survival yma (fig. 1) . However, based on apparent lackhas yet to be determined. Thus, the disease is of monoclonality within the fibroblast foci, it isunfortunately characterised by a dismal median assumed that these areas of fibrosis represent asurvival of ,3 yrs , which emphasises the reactive process rather than implicating the poten-continued need for further research to gain newer tials of a neoplastic-cancer-like nature of IPF .insights and perspectives. Prevailing concepts of However, a lack of monoclonality should notthe pathogenesis of IPF have considered fibrosis preclude cancer conditions and has been reportedas: 1) a relentless fibrotic process reactive to a in haematologic malignancies, as well as in breast,presumed inflammatory process; 2) an aberrant head, neck and pancreas cancers [10–12]. Further-fibroproliferative response to a recurrent injury to more, the apparent incapacity to metastasise is notthe epithelium; and/or 3) epithelial–mesenchymal a sufficient argument to exclude the potentials of a European Respiratory Journalinteractions/transformation. Regardless, the incre- neoproliferative behaviour of mesenchymal cells in Print ISSN 0903-1936ased number of fibroblast-like cells and the IPF; other neoplastic disorders can cause local Online ISSN 1399-3003496 VOLUME 35 NUMBER 3 EUROPEAN RESPIRATORY JOURNAL
C. VANCHERI ET AL. PERSPECTIVEtissue infiltration without metastasis such as desmoid tumours hypothesis if the mutation of p53 and other TSGs are the cause orwhich are mesenchymal tumours characterised histologically the consequence of lung fibrosis. Certainly TSGs are implicatedby fibroblast proliferation and marked production of collagen in other cellular homeostasis disturbances that resemble fibrosis;. In this perspective, we provide an alternative point of for example, p53 mutations have been detected in keloid scar, aview on the pathogenic mechanisms leading to IPF and an paradigm of abnormal wound healing . Furthermore,argument for IPF to be considered as a neoproliferative association with Epstein–Barr virus infection  or frequentdisorder of the lung. Our hypothesis is based on the evidence point mutations of the p53 gene have been detected inthat the fundamental hallmarks of cancer, such as genetic pulmonary fibrosis, suggesting that disruption of p53 functionalterations, uncontrolled proliferation and tissue invasion are, on cell cycle arrest and DNA repair might pathologicallyin fact, the essence of the pathobiological characteristics and interfere with cellular homeostasis in the lung in this conditionhallmark features of IPF. Acknowledging that the survival rate . Other TSGs acting on cell cycle and apoptosis, such as FHIT,of IPF is worse than several cancers and that the similarities of which certainly plays a crucial role in lung carcinogenesis, arethe demographics of IPF compared with lung cancer are mutated in IPF as well. FHIT gene mutations and FHIT proteinevident (figs 2, 3 and 4), we wish to link the concept of the reduction have been demonstrated in IPF lungs especially in theaberrant fibroblast proliferation to cancer biology and alert the peripheral honeycomb areas . Microsatellite instability (MI)interests of basic and clinic scientists to provoke further and loss of heterozygosity (LOH) are usually correlated with aresearch from an oncologist’s view. It is our hope that such high rate of mutation and with DNA repair. MI and LOH,an awareness will lead to the design of new clinical trials to targeting MYCL1, FHIT, SPARC, p16Ink4 and TP53, have beendetermine safety and efficacy of agent(s) with antiproliferative demonstrated in ,50% of IPF patients , suggesting that IPF,characteristics by choosing specific biomarkers of tissue independently of lung cancer, exhibits an high mutationalresponse as primary endpoints, besides those traditionally frequency which may well affect other genes leading toused to assess overall clinical and physiological outcomes in deregulated control of cell cycle and apoptosis. More recently,patients with IPF. other mutations so far exclusively related to carcinogenesis, such as telomere shortening and telomerase expression, have beenGENETIC ALTERATIONS described in both familial and sporadic IPF [23–25].Cytogenetic alterations are considered the very first eventsleading to cancer. Activated carcinogens, such as those found Recent evidence also suggests that epigenetic alterations mayin tobacco smoke, might interact with genes, such as p53, k-ras have a role in IPF. So far these post-translational modificationsand fragile histidine triad (FHIT) leading to genetic or in DNA, such as histone acetylation or methylation, have beenepigenetic alterations which deregulate proliferative control described in cancer. In some cancers the methylation of theat the molecular level. The p53 gene is a tumour suppressor Thy-1 gene promoter region leads to gene silencing, which isgene (TSG) involved in apoptosis, DNA repair, and cell associated with a more invasive behaviour of the disease.proliferation and differentiation, which is altered in most cases Thy-1 is a glycoprotein normally expressed by fibroblastsof cancer and its mutation in lungs from patients with IPF has involved in the modulation of cell-to-cell and cell-matrixbeen demonstrated, possibly explaining the higher incidence of interaction. The loss of Thy-1 is also linked to the transforma-lung cancer in pulmonary fibrosis . It remains central to our tion of fibroblasts into myofibroblasts as observed in the myofibroblasts forming fibroblast foci which are, largely, a) c) Thy-1 negative . SANDERS et al.  have recently demon- strated that in lung tissue from IPF patients there is a reduced Thy-1 expression due to a hypermethylation of the Thy-1 promoter region. They also showed that methylation of the Thy-1 gene reduces the in vitro expression of this gene in human lung fibroblasts and, most importantly, that the pharmacological inhibition of methylation can restore the expression of Thy-1, suggesting a novel pathogenic mechanism of lung fibrosis and possibly a new therapeutic approach for b) this disease . Another evident cause of DNA damage likely related to epigenetics alterations is oxidative stress. Reactive oxygen species (ROS) overproduction may influence several cellular processes fundamental in cancer development, such as cell proliferation and senescence likely through genetic but also via epigenetic mechanisms. A number of studies suggest that oxidative stress may cause alterations in DNA methylation patterns and specific histone modifications leading to anFIGURE 1. Section of idiopathic pulmonary fibrosis/usual interstitial pneumo- aberrant gene expression and possibly triggering the multi-nia tissue at low (a) and high (b) power, showing fibroblast foci (arrow). c) Three- stage process of carcinogenesis. In hepatocellular, breast, renaldimensional reconstruction of fibroblast foci forming a ‘‘fibroblast reticulum’’. and prostate cancers, it has been demonstrated that hyper-Pleural surface (yellow), blood vessels (red) and fibroblast reticulum (green) areshown. Reproduced from  with permission from the publisher. methylation silences the promoter region of genes related to the expression of major antioxidant enzymes . cEUROPEAN RESPIRATORY JOURNAL VOLUME 35 NUMBER 3 497
PERSPECTIVE C. VANCHERI ET AL. 100 60 80 Death rate per 100000 5-yr survival rate % 40 60 40 20 20 0 0 Pancreas Pancreas Bladder Breast Lung Skin Bladder Breast Lung Skin Colon Kidney Lymphoma Prostate Thyroid Colon Kidney Lymphoma Prostate Thyroid Leukaemia Uterus Leukaemia Uterus IPF IPFFIGURE 2. Comparison of the 5-yr survival rate for idiopathic pulmonary FIGURE 3. Comparison of the death rate per 100,000 population for idiopathicfibrosis (IPF) and different forms of cancer . Statistics for cancer are from the US pulmonary fibrosis (IPF) and different forms of cancer . Statistics for cancer areNational Cancer Institute . from the US National Cancer Institute .Indeed, oxidant/antioxidant balance is also implicated in the inflamed fibrotic lungs is evident. Indeed, fibroblast culturespathogenesis of IPF. Oxidative stress induces apoptosis of isolated from areas of densely fibrotic and endstage honey-epithelial cells, activates several intracellular signalling path- comb lung behave similar to senescent cells . Otherways and upregulates the synthesis of profibrotic cytokines investigators have demonstrated a clonal expansion of fibro-ultimately leading to tissue injury and fibrosis. In bronchial blast cultures from IPF lung . Thus, the potentials for thealveolar lavage fluid and in plasma from patients with IPF, an transformation to more overt characteristics of neoplasticexcessive oxidant production and diminished glutathione processes have been documented over two decades ago.production has been shown . N-acetylcysteine (NAC), aprecursor of glutathione synthesis has been used as an oral In normal conditions, the homeostatic control of cell prolifera-medication to augment levels of glutathione in patients with tion and survival is finely tuned by multiple mechanisms ofIPF and improve pulmonary functions in patients with IPF  feedback. Self-sufficiency in growth signals, insensitivity toand recently demonstrated better preservation of pulmonary growth inhibitory signals, evasion of apoptosis and alteredfunction tests if used as an adjunct medication with standard cell-to-cell communication are instead crucial features oftherapy with prednisone and azathioprine . The biological cancer cells . Myofibroblasts in IPF may present functionalplausibility of NAC and glutathione in the treatment of IPF features similar to cancer cells; they are a significant source ofbased on the importance of balancing the oxidant/antioxidant several cytokines including the fibrogenic transforming growthvia glutathione has been recently emphasised . Although factor (TGF)-b which, in an autocrine way, may furtherthe role of antioxidants is of some importance in the prevention stimulate myofibroblasts. Moreover, they produce less of theof cancer, therapeutic interventions with antioxidants have anti-fibrotic prostaglandin (PG)E2 and have an impaired abilitybeen so far disappointing. The effect of oxidative stress on to up-regulate PGE2 synthesis in response to TGF-b with thecancer cells is not exclusively related to DNA damage but also consequent loss of the anti-proliferative response to TGF-brelates to the fine modification of cellular signalling pathways normally mediated by PGE2 . In addition, in bleomycin-crucial for cancer biology. Based on that, new promising induced fibrosis the lack of response of fibroblasts to theevidence emerging from preclinical studies has demonstrated inhibitory activity of PGE2 is attributable to the diminishedshifts in the course of cancer signalling by antioxidants. Hence, ability of these cells to express the E prostanoid receptor 2the role of antioxidants in oncology may be of potential signal undertaking important inhibitory actions of PGE2 on fibro-transduction modifiers to be used in combination with other blasts such as collagen expression and TGF-b-induced transi-signal transduction inhibitors . tion of fibroblasts into myofibroblasts . Enhanced collagen synthesis has been induced by TGF-b in fibroblasts isolatedUNCONTROLLED, ABERRANT CELLULAR from fibrotic lungs from patients with IPF . The lack ofPROLIFERATION growth inhibition and delayed apoptosis showed by fibroticDifferential proliferative potentials of lung fibroblasts in cell cells might be also related to a modified response to tumourcycle analyses of fibroblasts isolated from different areas of the necrosis factor (TNF)-a due to a reduced expression of the TNFfibrotic lung from patients with IPF have demonstrated receptor 1, known to mediate growth inhibition and deathinherent proliferative potentials in serum-free conditions. events . In fact, there is evidence that myofibroblasts in IPFEven though the inherent increased proliferative characteris- are resistant to apoptosis . TGF-b protects these cells fromtics were observed in diploid cells in serum-free conditions, the apoptosis and this effect is, at least in part, due to the activationpotentials of the mutations in these fibroblasts isolated from of the phosphoinositide 3-kinase (PI3K)/ phosphatase and498 VOLUME 35 NUMBER 3 EUROPEAN RESPIRATORY JOURNAL
C. VANCHERI ET AL. PERSPECTIVE 45 fibroblasts have in fact reduced GJIC and diminished CX43 expression. Lung cancer cell lines from mouse and human lung 40 carcinoma have low or absent levels of CX43 and the deletion 35 of the CX43 gene results in higher susceptibility to lung 30 adenoma formation in mice after urethane administration. On Diagnosis % the contrary, the transfection of human lung carcinoma cell 25 lines with CX43 cDNA induces a reduced growth rate in these 20 cells [47, 48]. 15 ORIGIN OF MYOFIBROBLASTS 10 The origin of myofibroblasts in pulmonary fibrosis is con- troversial. Although a number of studies suggest that the 5 differentiation of myofibroblasts mainly starts from resident 0 lung fibroblasts and is induced by profibrotic cytokines such as 18–34 35–44 45–54 55–64 65–74 75+ TGF-b, recent evidence supports the role of EMT . This Age yrs phenomenon is triggered by an abnormal stimulus which induces cells to acquire a more suited phenotype to withstandFIGURE 4. Number of people diagnosed with idiopathic pulmonary fibrosis the original stimulus itself. It has been shown that alveolar(&) distributed by age and compared with lung cancer (&). Idiopathic pulmonary epithelial cells exposed to TGF-b gradually lose epithelialfibrosis diagnosis is based on a narrow case definition . markers, such as cytokeratin, while they acquire specific mesenchymal markers including a-SMA, vimentin and type Itensin homologue (PTEN)-AKT pathway . TIAN et al.  collagen . In pulmonary fibrosis, epithelial cells surround-have shown that the transfection of fibroblasts with active PI3K ing fibroblast foci express both epithelial and mesenchymalincreases the phosphorylation of AKT protecting these cells markers, suggesting that EMT is undergoing in those areas offrom apoptosis whereas PTEN overexpression inhibits TGF-b lung tissue . These and other similar observations supportinduced myofibroblast differentiation. It is interesting to note an active role for EMT in contributing to lung fibrogenesis.that the activation of the PI3K/PTEN-AKT signalling pathway Indeed, EMT is a form of metaplasia, even though it may notis a fundamental event for many cancers where the over- be considered as a ‘‘cancerogenetic’’ event, it is a crucialexpression of phosphorylated AKT is linked to a poor feature of many cancers and is involved in early steps ofprognosis . carcinogenesis and cancer cell invasion . Another impor- tant source of lung myofibroblasts are extrapulmonaryALTERED CELL–CELL COMMUNICATIONS progenitor cells named fibrocytes. These are bone marrow-Cell communication through gap junctions is fundamental in derived cells that co-express markers of haematopoietic cellscell proliferation, tissue repair and cancer growth. Gap and fibroblasts, such as cluster of differentiation (CD)45, Col Ijunctions are membrane channels formed by aggregates of and CXC chemokine receptor (CXCR)4. Blocking CXCL12, theproteins named connexins which directly connect the cyto- ligand of CXCR4, PHILIPS et al.  have shown a markedplasm of neighbouring cells allowing the metabolic and reduction of fibrocyte recruitment into the lung and aelectrical coupling of cells. Connexin 43 (CX43) is by far the significant attenuation of lung fibrosis in bleomycin-treatedmost represented on fibroblasts and several studies have mice. In addition, MEHRAD et al.  have shown a highershown its involvement in wound healing. MORI et al.  have number of fibrocytes and an increased plasmatic level ofdemonstrated in an in vitro model of fibroblast wound-healing CXCL12 in patients with pulmonary fibrosis compared withthat the reduction of CX43 leads to increased expression of healthy individuals suggesting a potential role of these cells inTGF-b, collagen production, myofibroblast differentiation and promoting fibrosis. However, the fibrogenic role played byhence to a faster healing process. Furthermore, in fibroblasts bone marrow-derived fibrocytes is counteracted by evidencefrom keloid and hypertrophic scar tissue, compared with showing a protective role for these cells. It has been shown thatnormal skin, CX43 levels are significantly lower. We have also myelosuppression enhances susceptibility to bleomycinshown that in primary lung fibroblasts from IPF patients there damage whereas transfer of bone marrow-derived mesenchy-is a reduced expression of CX43 which functionally translates mal stem cells, which is followed by the presence of fibrocytesinto a reduced gap junction intercellular communication in the lung, protects lungs from bleomycin-induced injury,(GJIC), an event linked with loss of contact inhibition restraints likely via the repair of alveolar epithelial damage . Recentand as such with uncontrolled proliferation . reports have demonstrated that some of the myofibroblasts forming the tumour stroma are also derived from bone-CX43 protein expression is regulated by many events involved marrow stem cells . Of note, CD34+ a-SMA- cells are oftenin the pathogenesis of IPF and cancer, such as oxidative stress present in benign tumours whereas CD34- a-SMA+ fibroblastsand TGF-b production, which may directly reduce CX43 are frequent in more aggressive cancers implying an acquisitionexpression via the activation of the protein kinase C and for these cells of myofibroblast-like features that could facilitatePI3K/AKT pathways respectively. Oxidative stress may also tumour progression and, at the same time, the loss of theirincrease TGF-b expression thus indirectly promoting antigen-presenting capacity with the subsequent reduction of theepithelial–mesenchymal transition (EMT) which in turn has local immune response . In spite of these data, the exact rolebeen shown to reduce the expression of CX43 in embryoniccarcinoma cells . Neoplastic cells, like keloids and fibrotic played by fibrocytes in cancer and IPF needs to be further investigated, it is not completely clear yet whether fibrocytes in cEUROPEAN RESPIRATORY JOURNAL VOLUME 35 NUMBER 3 499
PERSPECTIVE C. VANCHERI ET AL.cancer are rather devoted to define progression whereas in IPF In this way, myofibroblasts infiltrate lung tissue formingare recruited in an attempt to repair lung injury. In both cases, the aggregates of cells named fibroblast foci. These clusters of cellslocal microenvironment could play a fundamental role in are mainly found within areas of active pulmonary fibrosis andchanging the genuine mission of these cells. Regardless of their their presence in the lung parenchyma is considered by someorigin, myofibroblasts have been increasingly acknowledged to authors clinically relevant since their number and extensionbe one of the key cells contributing to local tissue invasion and may correlate with disease progression and survival [58, 59]. Aprogression in fibrosis and neoplasm in the pathogenesis of both three-dimensional reconstruction of the IPF lung showed thatIPF and cancer (fig. 5). fibroblast foci are connected among them forming a reticulum throughout the lung. Interestingly, this structure was com-TISSUE INVASION pared to a sort of neoplasm infiltrating the lung parenchymaMyofibroblasts are activated cells and add to the heightened (fig. 1) . Indeed, in primary, as well as in metastatic cancers,collagen expression the capacity to produce several cytokines the presence of myofibroblasts in close contact with cancerincluding the profibrotic TGF-b. In normal wound healing, cells, at the invasive front of the tumour, is a typical feature.once the active phase of repair is ended, myofibroblasts Similarly to what occurs during wound healing these cells mayprogressively disappear via apoptosis. In contrast, in lung be recruited from bone marrow derived stem cells or infibrosis where an aberrant tissue repair takes place, they alternative they may derive from the transition of epithelialpersist and nourish the fibrotic process contributing to the cells into mesenchymal cells. However, the major source ofexcessive deposition of extracellular matrix that characterises ‘‘cancer myofibroblasts’’ is still considered the recruitment ofthis disease. Although there are some evidence showing that resident fibroblasts from the surrounding connective tissue. Inmyofibroblasts produce elevated levels of inhibitors of the same way as lung fibrosis, TGF-b, mainly produced bymetalloproteinases creating a sort of non-degradative environ- cancer-derived epithelial cells is responsible for the emergencement which may be responsible for extracellular matrix of myofibroblasts in the context of the stroma reaction thataccumulation it has also been shown that myofibroblasts are usually accompanies cancer. Myofibroblasts in turn produceable to produce large amounts of gelatinases A and B which additional TGF-b, other inflammatory mediators and metallo-are capable of destroying the alveolar basement membrane proteinases determining a sort of vicious cycle that, in the end,facilitating the penetration of these cells into the alveoli . may facilitate cancer invasiveness. A number of studies have Fibrotic infiltrative front Myofibroblast roles Cancer invasive front Trophic factors secretion Structural support Invasion Differentiation Circulating fibrocytes Epithelial–mesenchymal transition Myofibroblast originsFIGURE 5. The myofibroblast march in idiopathic pulmonary fibrosis and cancer.500 VOLUME 35 NUMBER 3 EUROPEAN RESPIRATORY JOURNAL
C. VANCHERI ET AL. PERSPECTIVEshown that the amount of TGF-b expressed by different cancer progression . Furthermore, there is recent evidence that, incells, including lung-cancer cells, is related to disease progres- addition to the so-called canonical way of activation of thesion. In colorectal, breast and hepatocellular carcinomas, Wnt/b-catenin pathway, there is a cross-talk between themyofibroblasts produce large amount of matrix metalloprotei- fibrogenic cytokine TGF-b and this signalling pathway. Wenases that breaking up the basement membrane of the neigh- have recently demonstrated that TGF-b, via the phosphoryla-bouring tissues may foster cancer progression. Moreover, in tion of extracellular signal-regulated kinases (ERK)1/2, maysmall-cell lung cancer, increased levels of metalloproteinases activate the Wnt pathway inhibiting GSK-3b activity, thusare considered as a negative prognostic factor of survival . promoting the cytosolic accumulation and subsequent nuclearNeoplastic invasion is also driven by a number of molecules translocation of b-catenin . The pro-fibrotic activity ofable to promote tumour cell migration. Laminin, for example, a TGF-b is also mediated by the release of endothelin (ET)-1component of the extracellular matrix, stimulates migration which is considered as a downstream mediator of some of itsand tumour progression. In lung adenocarcinomas, as well as pro-fibrotic activities including a-SMA and collagen I expres-in several other cancers, laminin-5-c2 chain is specifically sion . The antagonism of the two ET-1 receptors ETA andexpressed at the invasive front of the tumour and its ETB has in fact been used as a potential treatment for IPF. It isoverexpression is considered a marker of invasiveness often of note that ET-1 produced by stromal and also by cancer cellsassociated with poor prognosis . Matrilysin, a protease activates several signalling pathways such as AKT, mitogen-involved in tumour cell invasion, is coexpressed, in some activated protein kinase and protein kinase C which regulateforms of cancer with laminin suggesting that matrilysin cell proliferation, migration, invasion, angiogenesis and apop-produced by cancer cells cleaves lamin-5 from the extracellular tosis, hence supporting the numerous evidence showing thematrix, exposing its promigratory site, hence stimulating cell role played by ET-1 in promoting the progression of severalmotility and tumour invasion . Other molecules expressed different cancers such as prostatic, colorectal, breast, lung,by cancer cells and associated with invasiveness, poor bladder and brain cancer. ET-1 has been proposed as aprognosis and resistance to treatment are heat shock proteins negative prognostic marker in some cancers and the blockade(HSPs) and fascin. HSP27 prevents cell apoptosis interfering at of ET-1 receptors has been found to enhance the efficacy ofdifferent levels in the programmed cell death process. Fascin is anticancer therapy .instead an actin-bundling protein involved in cell-matrixadhesion and cell migration which is widely expressed in IMPLICATIONS FOR TREATMENT STRATEGIESmesenchymal tissues but virtually absent in normal epithelia. Over the last decade, several well-designed clinical trials haveIn many human carcinomas, including non-small cell lung investigated new modes of treatment in an attempt to abortcarcinoma, fascin is instead strongly up-regulated particularly specific events in the cascade of the inflammatory fibroticat the advancing edge of the cancer and its overexpression is events implicated in the pathogenesis of IPF [1–6]. The resultsalso related to poor patient prognosis [63, 64]. The expression have been unfortunately disappointing, as an effective treat-of extracellular matrix molecules such as laminin, fascin and ment regimen remains elusive. While several clinical trials areHSPs has also been investigated in IPF. Interestingly, CHILOSI et underway in pursuit of an efficacious regimen, the approachal.  have shown that the epithelium encircling fibroblast taken in these studies are similar to the ones that havefoci expresses large amounts of laminin, fascin and HSP27. unfortunately yielded negative results to date. Perhaps, weCells expressing these molecules were exclusively bronchiolar need to strategise the treatment protocols from an oncologist’sbasal cells layered between luminal epithelial cells on one side point of view and target proliferative and molecular propertiesand myofibroblasts on the other. This particular three layers of cell behaviour, similar to neoplastic cells, and design studiesarrangement of negative-positive-negative cells was effica- with different outcomes, such as biomarkers of mesenchymalciously compared to a sandwich and these areas of lung tissue cell proliferation and extracellular matrix synthesis/degrada-named by the same authors ‘‘sandwich fibroblast-foci’’ . tion rather than entirely focusing on outcome measurements,The expression of molecules so involved in cell migration and such as pulmonary function tests. Specific phenotype ofinvasion in bronchiolar basal cells which are adjacent to fibroblasts (e.g. myofibroblasts, fibrocytes) may need to bemyofibroblasts and, at the same time, facing the luminal targeted by gene therapy/transfer and/or modulate theepithelium is very reminiscent of what has already been fibrotic response by applying stem cell transplant biology.described in cancer where these molecules are expressed at the Indeed, the well-defined mutual relationship between cancerinvasive front of carcinomas. In addition there is evidence that and stromal cells suggests that targeting those mechanismsthe expression of laminin, fascin and matrilysin as well as which promote fibroblast activation and differentiation mayother molecules involved in cancer progression such as cyclin- prove to be a potential therapeutic approach not only forD1 is regulated by the Wnt/b-catenin signalling pathway. An cancer but also for lung fibrosis. i.e. targeting the fibroblast–aberrant activation of this signalling pathway has been myofibroblast transition with halofuginone synergises withobserved in several human cancers including lung cancer chemotherapy in achieving a significant anti-tumoural effect,and mesothelioma  and more recently in different avoiding the need of high-dose chemotherapy . TGF-bfibroproliferative disorders of the liver and kidney [67, 68]. receptor antagonists exert a blockade of TGF-b activities thatCHILOSI et al.  also demonstrated that an aberrant activation has shown to be of some clinical benefit in both cancer andof the Wnt/b-catenin pathway occurs in IPF. They observed an fibrosis . Several clinical trials have studied the effect of theintense immunoreactivity for b-catenin in IPF tissue, and a inhibition of some subsets of metalloproteinases produced bycontemporary expression of high levels of the two downstream myofibroblasts in a variety of cancers, including small-cell lunggenes of the Wnt/b-catenin pathway, cyclin-D1 and matrilysin,molecules fully involved in cancer invasiveness and fibrosis cancer. Although these studies fail to show a real benefit of this treatment on tumour progression, they do not exclude that the cEUROPEAN RESPIRATORY JOURNAL VOLUME 35 NUMBER 3 501
PERSPECTIVE C. VANCHERI ET AL.contemporary inhibition of more subsets of metalloproteinases Genetic alterations, similar responses to growth and inhibitorycould be more effective . In the bleomycin-induced model of signals, resistance to programmed cell death, altered cell-celllung fibrosis, through the blockage of CXCL12, the ligand of communications, myofibroblast origin and behaviour withCXCR4 was obtained a marked reduction of fibrocyte recruit- respect to the invasion of the surrounding tissues are all veryment into the lung and subsequently a significant attenuation of similar in cancer and IPF. Even intracellular signalling path-lung fibrosis . However, fibrocytes are not merely targets of ways crucial in the pathogenesis of cancer such as Wnt/b-new therapies but, more interestingly, might be the vehicle for catenin and the PI3K/AKT pathways are fully involved in IPF.new therapeutic approaches and, once again, the lesson comesfrom cancer biology. Bone marrow-derived mesenchymal stem In our opinion, implications of such a vision will extend wellcells (BMMSC) possess the physiological ability to home to beyond the pathogenic link between IPF and cancer. The needtumour-associated stroma. This innate quality of BMMSC has and increased support for cancer research is evident by thebeen recently used as a new approach for cancer therapy. well awareness of the unknown cause and fatal outcomeBMMSC can be used as vehicles for the selective delivery of nature of cancer. Considering that IPF is a fatal disorder ofdifferent kind of anticancer therapies including apoptosis- unknown aetiology with a very high mortality rate worse thaninducing proteins, immunomodulatory signals, cell-cycle reg- several cancers and that several treatment regimen that haveulators, antiangiogenic molecules, oncolytic viruses and other been tried have failed to improve the survival, it is time toanticancer agents. STUDENY et al.  have induced BMMSC to acknowledge that patients with IPF are worse than those withexpress interferon beta showing its efficacy against solid cancer. The concept of IPF as a distinct and unique ‘‘clinicallymelanomas in nude mice while DUAN et al.  using BMMSC malignant disorder of the lung’’ might highlight the continuedtrasfected with IL-12 have demonstrated the regression of Ewing need to further understand the pathobiology of the fibroticsarcoma. Strikingly, BMMSC also preferentially migrate to sites process by exploring new pathogenic mechanisms and ther-of inflammation, tissue damage and repair, suggesting that such apeutic options gleaned from cancer biology. Additionally, thistherapeutic strategy is possibly exploitable in lung fibrosis. vision might prove to be useful in helping raise public, politicalAlthough much work remains to be done before the therapeutic and scientific community awareness of this devastating diseaseuse of BMMSC can be fully realised, the concept of specifically that is currently underestimated by the general public, clinicaltargeting proliferative and/or molecular properties of fibroblasts and scientific community and worthy of more intensive researchand/or epithelial cells in lung fibrosis is worth pursuing [78, 79]. and sponsors.Finally, the potential of autologous stem cell transplants andallogeneic bone marrow are additional concepts that may be STATEMENT OF INTERESTworthwhile to embark new treatment strategies to ‘‘start all over None declared.again’’ with new progenitor cells, following such transplants. ACKNOWLEDGEMENTSCONCLUSION The authors wish to acknowledge the precious contribution of N.The pathobiology and mortality of IPF and cancer have several Abrahams for editing the manuscript.striking similarities. A number of analogies are common inboth of these fatal disorders dictated by proliferating cells in anaberrant manner (table 1). While some of the intrinsic cellular REFERENCESand molecular behaviour is obviously malignant or precancer- 1 Azuma A, Nukiwa T, Tsuboi E, et al. Double-blind, placebo-ous in both disorders, other circumstantial factors such as the controlled trial of pirfenidone in patients with idiopathicepi- and ecogenetic factors, cigarette smoking, viruses, and pulmonary fibrosis. Am J Respir Crit Care Med 2005; 171: 1040–1047.occupational and environmental factors contribute in the 2 Demedts M, Behr J, Buhl R, et al. High-dose acetylcysteine inpathogenesis of both fibrotic lung disorders and lung cancer. idiopathic pulmonary fibrosis. N Engl J Med 2005; 353: 2229–2242. 3 King TE Jr, Behr J, Brown KK, et al. BUILD-1: a randomized placebo-controlled trial of bosentan in idiopathic pulmonary fibrosis. Am J Respir Crit Care Med 2008; 177: 75–81. TABLE 1 Pathogenic similarities between idiopathic 4 King TE Jr, Albera C, Bradford WZ, et al. Effect of interferon c-1b pulmonary fibrosis and cancer on survival in patients with idiopathic pulmonary fibrosis (INSPIRE): a multicentre, randomised, placebo-controlled trial. Genetic alterations Tumour suppressor gene mutations Lancet 2009; 18, 374: 222–228. Telomere shortening 5 Raghu G, Brown KK, Bradford WZ, et al. A placebo-controlled trial Epigenetic alterations Hypermethylation of the Thy-1 promoter region of interferon c-1b in patients with idiopathic pulmonary fibrosis. Uncontrolled proliferation Self-sufficiency in growth signals N Engl J Med 2004; 350: 125–133. Insensitivity to growth inhibitory signals 6 Raghu G, Brown KK, Costabel U, et al. Treatment of idiopathic Evasion of apoptosis pulmonary fibrosis with etanercept: an exploratory, placebo- Altered cell-to-cell communications controlled trial. Am J Respir Crit Care Med 2008; 178: 948–955. Tissue invasion Myofibroblasts recruitment and differentiation 7 Daniil ZD, Gilchrist FC, Nicholson AG, et al. A histologic pattern Myofibroblast infiltrative ability of nonspecific interstitial pneumonia is associated with a better prognosis than usual interstitial pneumonia in patients with Expression invasive molecules cryptogenic fibrosing alveolitis. Am J Respir Crit Care Med 1999; Signal transduction Activation Wnt/b-catenin pathway 160: 899–905. pathways Activation phosphoinositide 3-kinase/ 8 Selman M, King TE, Pardo A. Idiopathic pulmonary fibrosis: phosphatase and tensin homologue-AKT pathway prevailing and evolving hypotheses about its pathogenesis and implications for therapy. Ann Intern Med 2001; 134: 136–151.502 VOLUME 35 NUMBER 3 EUROPEAN RESPIRATORY JOURNAL
C. VANCHERI ET AL. PERSPECTIVE 9 Cool CD, Groshong SD, Rai PR, et al. Fibroblast foci are not 32 Sharifi N. Commentary: Antioxidants for cancer: new tricks for an discrete sites of lung injury or repair: the fibroblast reticulum. Am J old dog? Oncologist 2009; 14: 213–215. Respir Crit Care Med 2006; 174: 654–658. 33 Raghu G, Chen YY, Rusch V, et al. Differential proliferation of10 Davidsson J, Paulsson K, Johansson B. Multicolor fluorescence in fibroblasts cultured from normal and fibrotic human lungs. Am situ hybridization characterization of cytogenetically polyclonal Rev Respir Dis 1988; 138: 703–708. hematologic malignancies. Cancer Genet Cytogenet 2005; 163: 180–183. 34 Jordana M, Schulman J, McSharry C, et al. Heterogeneous11 Parsons BL. Many different tumor types have polyclonal tumor proliferative characteristics of human adult lung fibroblast lines origin: evidence and implications. Mutat Res 2008; 659: 232–247. and clonally derived fibroblasts from control and fibrotic tissue.12 Lyons JG, Lobo E, Martorana AM, et al. Clonal diversity in Am Rev Respir Dis 1988; 137: 579–584. carcinomas: its implications for tumour progression and the 35 Hanahan D, Weinberg RA. The hallmarks of cancer. Cell 2000; 100: contribution made to it by epithelial-mesenchymal transitions. 57–70. Clin Exp Metastasis 2008; 25: 665–677. 36 McAnulty RJ, Hernandez-Rodriguez NA, Mutsaers SE, et al.13 Kotiligam D, Lazar AJ, Pollock RE, et al. Desmoid tumor: a disease Indomethacin suppresses the anti-proliferative effects of trans- opportune for molecular insights. Histol Histopathol 2008; 23: forming growth factor-b isoforms on fibroblast cell cultures. 117–126. Biochem J 1997; 321: 639–643.14 Olson AL, Swigris JJ, Lezotte DC, et al. Mortality from pulmonary 37 Moore BB, Ballinger MN, White ES, et al. Bleomycin-induced E fibrosis increased in the United States from 1992 to 2003. Am J prostanoid receptor changes alter fibroblast responses to prosta- Respir Crit Care Med 2007; 176: 277–284. glandin E2. J Immunol 2005; 174: 5644–5649.15 SEER cancer statistics review, http://seer.cancer.gov Date last 38 Raghu G, Masta S, Meyers D, et al. Collagen synthesis by normal updated: April 15, 2009. and fibrotic human lung fibroblasts and the effect of transforming16 Raghu G, Weycker D, Edelsberg J, et al. Incidence and prevalence growth factor-b. Am Rev Respir Dis 1989; 140: 95–100. of idiopathic pulmonary fibrosis. Am J Respir Crit Care Med 2006; 39 Vancheri C, Sortino MA, Tomaselli V, et al. Different expression of 174: 810–816. TNF-a receptors and prostaglandin E(2)Production in normal and17 Kuwano K, Kunitake R, Kawasaki M, et al. P21Waf1/Cip1/Sdi1 fibrotic lung fibroblasts: potential implications for the evolution of and p53 expression in association with DNA strand breaks in the inflammatory process. Am J Respir Cell Mol Biol 2000; 22: idiopathic pulmonary fibrosis. Am J Respir Crit Care Med 1996; 154: 628–634. 477–483. 40 Thannickal VJ, Horowitz JC. Evolving concepts of apoptosis in18 Saed GM, Ladin D, Olson J, et al. Analysis of p53 gene mutations in idiopathic pulmonary fibrosis. Proc Am Thorac Soc 2006; 3: 350–356. keloids using polymerase chain reaction-based single-strand 41 Horowitz JC, Lee DY, Waghray M, et al. Activation of the pro- conformational polymorphism and DNA sequencing. Arch survival phosphatidylinositol 3-kinase/AKT pathway by trans- Dermatol 1998; 134: 963–967. forming growth factor-b1 in mesenchymal cells is mediated by p3819 Lok SS, Stewart JP, Kelly BG, et al. Epstein-Barr virus and wild p53 MAPK-dependent induction of an autocrine growth factor. J Biol in idiopathic pulmonary fibrosis. Respir Med 2001; 95: 787–791. Chem 2004; 279: 1359–1367.20 Hojo S, Fujita J, Yamadori I, et al. Heterogeneous point mutations 42 Tian B, Lessan K, Kahm J, et al. b1 integrin regulates fibroblast of the p53 gene in pulmonary fibrosis. Eur Respir J 1998; 12: 1404– viability during collagen matrix contraction through a phospha- 1408. tidylinositol 3-kinase/Akt/protein kinase B signaling pathway.21 Uematsu K, Yoshimura A, Gemma A, et al. Aberrations in the J Biol Chem 2002; 277: 24667–24675. fragile histidine triad (FHIT) gene in idiopathic pulmonary 43 Tang JM, He QY, Guo RX, et al. Phosphorylated Akt over- fibrosis. Cancer Res 2001; 61: 8527–8533. expression and loss of PTEN expression in non-small cell lung22 Demopoulos K, Arvanitis DA, Vassilakis DA, et al. MYCL1, FHIT, cancer confers poor prognosis. Lung Cancer 2006; 51: 181–191. SPARC, p16(INK4) and TP53 genes associated to lung cancer in 44 Mori R, Power KT, Wang CM, et al. Acute downregulation of idiopathic pulmonary fibrosis. J Cell Mol Med 2002; 6: 215–622. connexin43 at wound sites leads to a reduced inflammatory23 Cronkhite JT, Xing C, Raghu G, et al. Telomere shortening in response, enhanced keratinocyte proliferation and wound fibro- familial and sporadic pulmonary fibrosis. Am J Respir Crit Care blast migration. J Cell Sci 2006; 119: 5193–5203. Med 2008; 178: 729–737. 45 Trovato-Salinaro A, Trovato-Salinaro E, Failla M, et al. Altered24 Liu T, Chung MJ, Ullenbruch M, et al. Telomerase activity is intercellular communication in lung fibroblast cultures from required for bleomycin-induced pulmonary fibrosis in mice. J Clin patients with idiopathic pulmonary fibrosis. Respir Res 2006; 7: 122. Invest 2007; 117: 3800–3809. 46 Johnson LN, Koval M. Cross-talk between pulmonary injury,25 Tsakiri KD, Cronkhite JT, Kuan PJ, et al. Adult-onset pulmonary oxidant stress, and gap junctional communication. Antioxid Redox fibrosis caused by mutations in telomerase. Proc Natl Acad Sci USA Signal 2009; 11: 355–367. 2007; 104: 7552–7557. 47 Cesen-Cummings K, Fernstrom MJ, Malkinson AM, et al. Frequent26 Sanders YY, Kumbla P, Hagood JS. Enhanced myofibroblastic reduction of gap junctional intercellular communication and differentiation and survival in Thy-1(-) lung fibroblasts. Am J connexin43 expression in human and mouse lung carcinoma cells. Respir Cell Mol Biol 2007; 36: 226–235. Carcinogenesis 1998; 19: 61–67.27 Sanders YY, Pardo A, Selman M, et al. Thy-1 promoter hyper- 48 Avanzo JL, Mesnil M, Hernandez-Blazquez FJ, et al. Increased methylation: a novel epigenetic pathogenic mechanism in pul- susceptibility to urethane-induced lung tumors in mice with monary fibrosis. Am J Respir Cell Mol Biol 2008; 39: 610–618. decreased expression of connexin43. Carcinogenesis 2004; 25: 1973–28 Franco R, Schoneveld O, Georgakilas AG, et al. Oxidative stress, 1982. DNA methylation and carcinogenesis. Cancer Lett 2008; 266: 6–11. 49 Willis BC, duBois RM, Borok Z. Epithelial origin of myofibroblasts29 Rahman I, MacNee W. Oxidative stress and regulation of during fibrosis in the lung. Proc Am Thorac Soc 2006; 3: 377–382. glutathione in lung inflammation. Eur Respir J 2000; 16: 534–554. 50 Kim KK, Kugler MC, Wolters PJ, et al. Alveolar epithelial cell30 Behr J, Maier K, Degenkolb B, et al. Antioxidative and clinical mesenchymal transition develops in vivo during pulmonary effects of high-dose N-acetylcysteine in fibrosing alveolitis. fibrosis and is regulated by the extracellular matrix. Proc Natl Adjunctive therapy to maintenance immunosuppression. Am J Acad Sci USA 2006; 103: 13180–13185. Respir Crit Care Med 1997; 156: 1897–1901. 51 De WO, Pauwels P, De CB, et al. Molecular and pathological31 Hunninghake GW. Antioxidant therapy for idiopathic pulmonary fibrosis. N Engl J Med 2005; 353: 2285–2287. signatures of epithelial-mesenchymal transitions at the cancer invasion front. Histochem Cell Biol 2008; 130: 481–494. cEUROPEAN RESPIRATORY JOURNAL VOLUME 35 NUMBER 3 503
PERSPECTIVE C. VANCHERI ET AL.52 Phillips RJ, Burdick MD, Hong K, et al. Circulating fibrocytes 67 Bowley E, O’Gorman DB, Gan BS. b-catenin signaling in traffic to the lungs in response to CXCL12 and mediate fibrosis. fibroproliferative disease. J Surg Res 2007; 138: 141–150. J Clin Invest 2004; 114: 438–446. 68 Surendran K, McCaul SP, Simon TC. A role for Wnt-4 in renal53 Mehrad B, Burdick MD, Zisman DA, et al. Circulating peripheral fibrosis. Am J Physiol Renal Physiol 2002; 282: F431–F441. blood fibrocytes in human fibrotic interstitial lung disease. Biochem 69 Chilosi M, Poletti V, Zamo A, et al. Aberrant Wnt/beta-catenin Biophys Res Commun 2007; 353: 104–108. pathway activation in idiopathic pulmonary fibrosis. Am J Pathol54 Rojas M, Xu J, Woods CR, et al. Bone marrow-derived mesench- 2003; 162: 1495–1502. ymal stem cells in repair of the injured lung. Am J Respir Cell Mol 70 Caraci F, Gili E, Calafiore M, et al. TGF-b1 targets the GSK-3b/b- Biol 2005; 33: 145–152. catenin pathway via ERK activation in the transition of human55 Direkze NC, Hodivala-Dilke K, Jeffery R, et al. Bone marrow lung fibroblasts into myofibroblasts. Pharmacol Res 2008; 57: contribution to tumor-associated myofibroblasts and fibroblasts. 274–282. Cancer Res 2004; 64: 8492–8495. 71 Shi-wen X, Kennedy L, Renzoni EA, et al. Endothelin is a56 Quan TE, Cowper SE, Bucala R. The role of circulating fibrocytes downstream mediator of profibrotic responses to transforming in fibrosis. Curr Rheumatol Rep 2006; 8: 145–150. growth factor b in human lung fibroblasts. Arthritis Rheum 2007;57 Phan SH. The myofibroblast in pulmonary fibrosis. Chest 2002; 56: 4189–4194. 122: 286S–289S. 72 Bagnato A, Spinella F, Rosano L. The endothelin axis in cancer: the58 Nicholson AG, Fulford LG, Colby TV, et al. The relationship promise and the challenges of molecularly targeted therapy. Can J between individual histologic features and disease progression in Physiol Pharmacol 2008; 86: 473–484. idiopathic pulmonary fibrosis. Am J Respir Crit Care Med 2002; 166: 73 Sheffer Y, Leon O, Pinthus JH, et al. Inhibition of fibroblast to 173–177. myofibroblast transition by halofuginone contributes to the59 Enomoto N, Suda T, Kato M, et al. Quantitative analysis of chemotherapy-mediated antitumoral effect. Mol Cancer Ther 2007; fibroblastic foci in usual interstitial pneumonia. Chest 2006; 130: 6: 570–577. 22–29. 74 Dumont N, Arteaga CL. Targeting the TGF b signaling network in60 Micke P, Ostman A. Tumour-stroma interaction: cancer-associated human neoplasia. Cancer Cell 2003; 3: 531–536. fibroblasts as novel targets in anti-cancer therapy? Lung Cancer 75 Shepherd FA, Giaccone G, Seymour L, et al. Prospective, 2004; 45: Suppl. 2, S163–S175. randomized, double-blind, placebo-controlled trial of marimastat61 Moriya Y, Niki T, Yamada T, et al. Increased expression of after response to first-line chemotherapy in patients with small- laminin-5 and its prognostic significance in lung adenocarcinomas cell lung cancer: a trial of the National Cancer Institute of Canada- of small size. An immunohistochemical analysis of 102 cases. Clinical Trials Group and the European Organization for Research Cancer 2001; 91: 1129–1141. and Treatment of Cancer. J Clin Oncol 2002; 20: 4434–4439.62 Masaki T, Sugiyama M, Matsuoka H, et al. Coexpression of 76 Studeny M, Marini FC, Dembinski JL, et al. Mesenchymal stem matrilysin and laminin-5 c2 chain may contribute to tumor cell cells: potential precursors for tumor stroma and targeted-delivery migration in colorectal carcinomas. Dig Dis Sci 2003; 48: 1262–1267. vehicles for anticancer agents. J Natl Cancer Inst 2004; 96: 1593–63 Garrido C, Schmitt E, Cande C, et al. HSP27 and HSP70: potentially 1603. oncogenic apoptosis inhibitors. Cell Cycle 2003; 2: 579–584. 77 Duan X, Guan H, Cao Y, et al. Murine bone marrow-derived64 Pelosi G, Pastorino U, Pasini F, et al. Independent prognostic value mesenchymal stem cells as vehicles for interleukin-12 gene of fascin immunoreactivity in stage I nonsmall cell lung cancer. Br delivery into Ewing sarcoma tumors. Cancer 2009; 115: 13–22. J Cancer 2003; 88: 537–547. 78 Hall B, Dembinski J, Sasser AK, et al. Mesenchymal stem cells in65 Chilosi M, Zamo A, Doglioni C, et al. Migratory marker expression cancer: tumor-associated fibroblasts and cell-based delivery in fibroblast foci of idiopathic pulmonary fibrosis. Respir Res 2006; vehicles. Int J Hematol 2007; 86: 8–16. 7: 95. 79 Corsten MF, Shah K. Therapeutic stem-cells for cancer treatment:66 Mazieres J, He B, You L, et al. Wnt signaling in lung cancer. Cancer hopes and hurdles in tactical warfare. Lancet Oncol 2008; 9: Lett 2005; 222: 1–10. 376–384.504 VOLUME 35 NUMBER 3 EUROPEAN RESPIRATORY JOURNAL