common pathogenic mechanisms and pathways in the development of copd and lung cancer

1. Global burden of lung cancer

and COPD

2. Epidemiological evidence for

coexisting lung cancer and

COPD

3. Pathological features of

coexisting lung cancer and

COPD

4. Gene-environment interaction

in the aetiology of lung cancer

and COPD

5. Potential shared biological

mechanisms in lung cancer and

COPD

6. Potential shared genomic and

epigenomic susceptibility to

lung cancer and COPD

7. Expert opinion: implications

for developing therapeutic

targets

Review

Common pathogenic mechanismsand pathways in the developmentof COPD and lung cancerIan A Yang†, Vandana Relan, Casey M Wright, Morgan R Davidson,Krishna B Sriram, Santiyagu M Savarimuthu Francis, Belinda E Clarke,Edwina E Duhig, Rayleen V Bowman & Kwun M Fong†The Prince Charles Hospital, Department of Thoracic Medicine, Thoracic Research Laboratory,

Brisbane, Australia

Introduction: Lung cancer and COPD commonly coexist in smokers, and the

presence of COPD increases the risk of developing lung cancer. In addition

to smoking cessation and preventing smoking initiation, understanding the

shared mechanisms of these smoking-related lung diseases is critical, in order

to develop new methods of prevention, diagnosis and treatment of lung

cancer and COPD.

Areas covered: This review discusses the common mechanisms for susceptibil-

ity to lung cancer and COPD, which in addition to cigarette smoke, may

involve inflammation, epithelial--mesenchymal transition, abnormal repair,

oxidative stress, and cell proliferation. Furthermore, we discuss the underlying

genomic and epigenomic changes (single nucleotide polymorphisms (SNPs),

copy number variation, promoter hypermethylation and microRNAs) that

are likely to alter biological pathways, leading to susceptibility to lung cancer

and COPD (e.g., altered nicotine receptor biology).

Expert opinion: Strategies to study genomics, epigenomics and gene-

environment interaction will yield greater insight into the shared

pathogenesis of lung cancer and COPD, leading to new diagnostic and

therapeutic modalities.

Keywords: chronic obstructive, genomics, lung neoplasms, pathogenesis, pulmonary disease

Expert Opin. Ther. Targets (2011) 15(4):439-456

1. Global burden of lung cancer and COPD

Lung cancer and chronic obstructive pulmonary disease (COPD) commonly coexistin smokers, and the presence of COPD increases the risk of developing lung cancer.Lung cancer consists of small cell carcinoma and non-small cell carcinomas encom-passing squamous cell carcinoma, adenocarcinoma and large cell carcinoma. COPDis defined as a preventable and treatable pulmonary disease characterised by airflowlimitation that is not fully reversible, associated with an abnormal inflammatoryresponse to noxious particles or gases, with significant extrapulmonary effects [1].The World Health Organization (WHO)estimates that lung cancer is the mostcommon cause of cancer death world-wide, with over 1.3 million deaths eachyear. Furthermore, WHO estimates that 3 million people die of COPD eachyear, and that COPD will become the third leading cause of death worldwide by2030. In addition to smoking cessation and preventing smoking initiation, under-standing shared mechanisms of these smoking-related lung diseases is critical fordeveloping new methods of prevention, diagnosis and treatment of lung cancerand COPD [2]. Lung cancer is a frequent cause of death in patients with mild tomoderate COPD, and its relative frequency reduces in more severe COPD whererespiratory failure becomes more important as a cause of death [3].

10.1517/14728222.2011.555400 © 2011 Informa UK, Ltd. ISSN 1472-8222 439All rights reserved: reproduction in whole or in part not permitted

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2. Epidemiological evidence for coexistinglung cancer and COPD

Cross-sectional studies report that a prevalence of COPD(Global initiative for Chronic Obstructive Lund Disease(GOLD) stage I or higher) in approximately 46 -- 60% ofpatients with lung cancer [4,5]. COPD and airflow obstructionincrease the risk of developing lung cancer. Epidemiologicalstudies of cohorts of smokers have shown increased relativerisks of between twofold and sixfold for incident lung cancer,in smokers with airflow obstruction [4,6-9], when smokingintensity is controlled for. In a study of 3371 patients withperipheral arterial disease who underwent vascular surgery,increased severity of COPD was associated with excessiverisk of mortality from lung cancer [10]. Emphysema observedon chest CT is also an independent factor, in addition tothe presence airflow obstruction. Emphysema increased therisk of lung cancer threefold in the Pittsburgh Lung ScreeningStudy, when adjusted for GOLD COPD severity stage [11]. Ina prospective cohort of 1166 former and current smokers in alow dose CT screening program, the presence of emphysemaon CT was associated with an increased risk (RR 2.5) of lungcancer, when clinical confounders airway obstruction, age, sexand smoking history, were controlled for [12]. A study of140 patients with surgically resected NSCLC suggested thatCOPD increased the risk of the squamous cell carcinoma sub-type, in particular [13]. These data show that both COPDand emphysema are risk factors for lung cancer, even whensmoking history is adjusted for.

3. Pathological features of coexisting lungcancer and COPD

Lung cancer is often accompanied by a variety of pathologicalchanges within the adjacent lung (Figure 1). While secondaryinflammatory changes are common distal to the tumour,changes due to COPD are frequently seen more diffusely inthe lung. Pathologically, COPD can affect the large airways(chronic bronchitis), small airways (bronchiolitis) and alveoli(emphysema).The frequency of histological changes due to COPD in

resected lung cancer specimens has been studied by a numberof authors [14,15]. Kawabata et al. [14] found that the incidenceand severity of centrilobular emphysema, respiratory bronchi-olitis and ‘airway enlargement with fibrosis’ progressivelyincreased from non-smokers through mild and moderate tosevere smokers. Katzenstein et al. [15] found microscopicevidence of emphysema in all cases of resected lungcancer, respiratory bronchiolitis in 90% of smokers and‘smoking-related interstitial fibrosis’ in 65%.Changes affect the smaller airways that are less than 2 mm

in diameter. These changes have been reported to be indepen-dent of the cough and sputum production that characterisechronic bronchitis [16]. As COPD severity increases, the smallairway walls are thickened by increases in the epithelium,

connective tissue between the epithelium and muscle layer,muscle layer and adventitia and this is thought to be due torepair or remodelling. This is also accompanied by a variabledegree of mucous exudate and inflammation. These changescan ultimately lead to obliteration of terminal bronchioles.Some authors have reported that the bronchiolar tissuedecreased with progression of the COPD and that it mayprecede development of emphysema [17].

Respiratory bronchiolitis is an inflammatory and fibroticlesion of membranous bronchioles that is caused by tobaccosmoking [18]. It is frequently seen in association with chronicbronchitis and emphysema and is considered part of a spectrumwith desquamative interstitial pneumonitis (DIP) [19]. It ischaracterised by aggregation of tobacco macrophages withinand around respiratory bronchioles. There is subtle interstitialwidening by fibrosis and mild inflammation. When this isthe only finding in a patient with interstitial lung disease,it has been termed respiratory bronchiolitis-interstitial lungdisease (RB-ILD).

Emphysema is characterised by abnormal enlargement ofair spaces due to destruction and loss of parenchyma distalto the terminal bronchiole [20]. Grossly it is more severe inthe upper lobes and the apices of the lobes. Microscopically,within the distended air spaces there are free floating alveolarwalls that once were connected (Figure 2). Other findingsinclude small-airways disease and there may be a compo-nent of pulmonary hypertension secondary to hypoxia [20].Traditionally the absence of fibrosis has been used to diffe-rentiate emphysema from forms of interstitial fibrosis. How-ever, it is increasingly recognized that there is a degree offibrosis in association with emphysema [21]. It has beendemonstrated to subtly involve centrilobular emphysema butis also seen in the walls of bullae, in the lung away fromemphysema and in association with RB-ILD. Emphysemawith co-existing interstitial lung disease, particularly usualinterstitial pneumonia, is also well documented.

4. Gene-environment interaction in theaetiology of lung cancer and COPD

Smoking is the principal cause of lung cancer, and clearly,smoking avoidance and cessation are essential public healthmeasures; yet less than 20% of smokers develop lung cancer,suggesting the role of genetic predisposition. There is increas-ing evidence for inherited genetic susceptibility to lung can-cer [22], in addition to somatic genetic aberrations in thetumour itself. Similarly, cigarette smoking is the primarycause of COPD, accounting for the majority of the risk ofdevelopment of COPD. Only 15 -- 20% of smokers developCOPD, again indicating the role of gene--environment inter-action. Even in never smokers, the combination of emphy-sema and chronic bronchitis increased the risk of lungcancer 2.4-fold, in a large prospective study of 448,600 adultsin the USA [23]. Other potential common environmentalrisk factors include exposure to air pollution [24], and

Common pathogenic mechanisms and pathways in the development of COPD and lung cancer

440 Expert Opin. Ther. Targets (2011) 15(4)

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environmental or occupational toxins that are irritantsand carcinogens.

An example of gene--environment interaction in lungcancer and COPD is alpha-1 antitrypsin (AAT) deficiency.AAT deficiency, through the homozygous ZZ state, is awell-known, relatively infrequent genetic risk factor for pre-mature emphysema in smokers. The heterozygous MZ statehas been associated with a reduction of 3 to 4% in forcedexpiration volume in 1 sec:forced expiratory vital capacityFEV1:FVC ratio, in case-control and family studies [25].A case-control study of 1856 patients lung cancer and1585 healthy controls found an increased risk of developinglung cancer (OR 1.7, adjusted for smoking history and

COPD) in AAT deficiency state carriers, mainly S or Zvariants [26]. The population attributable risk for lung cancerwith the AAT deficiency polymorphisms was estimated at12%. The example of AAT deficiency shows the importanceof considering gene--environment interactions in combinedsusceptibility to lung cancer and COPD.

5. Potential shared biological mechanisms inlung cancer and COPD

A number of mechanisms have been proposed in thecommon pathogenesis of lung cancer and COPD, as reviewedin [27-30]. Shared pathogenetic mechanisms have been postu-lated for lung cancer and COPD, in addition to or inde-pendent of smoking exposure. These common mechanismsinclude inflammation, epithelial--mesenchymal transition(EMT), oxidative stress, altered DNA repair and cellularproliferation [2,27-29]. Genetic and epigenetic mechanisms arelikely to underpin these changes, as reviewed recently [30-32].

In this section, we summarise evidence for specific bio-logical mechanisms that are candidates for shared susceptibil-ity to lung cancer and COPD. These candidate pathways havebeen identified using in vivo and ex vivo approaches, mainlyprotein expression in model systems and biospecimens frompatients. We focus on inflammation and EMT, and surveyother pathways.

5.1 InflammationSmoking and inhalation of carcinogens lead to changesin airway inflammation and immune defences, resulting inabnormal processes potentially leading to tumour initiationand progression, and development of COPD, as reviewed indetail recently [29,33,34]. Inflammation in chronic airways dis-ease may contribute to alterations in bronchial epitheliumand lung microenvironment, which may then lead to onco-genesis. Macrophages, neutrophils and lymphocytes areinflammatory cells which are implicated in disease progressionin COPD, and are also known to build a tumour-promotingmicro-environment.

Immune dysfunction, abnormal activation of NF-kB, andaltered adhesion signalling pathways are pathways involvedin both COPD and lung cancer. Moreover, genes down-stream of the NF-kB pathway are involved in progressionand metastasis of lung cancer [29]. NF-kB is an importanttranscription factor involved in inflammation. In bronchialbiopsies of airway mucosa in patients with COPD, proteinexpression of the p65 subunit of NF-kB was increased com-pared with expression in non-smokers, and correlated withairflow obstruction [35]. Neutrophil elastase is an abundantproteolytic enzyme present in neutrophils and found in excessin the lungs of COPD patients. In a mouse lung adenocarci-noma model, mice with Kras mutations and knockout ofneutrophil elastase had better survival from lung cancer thanmice with neutrophil elastase [36]. Exposure of a mouse modelwith oncogenic Kras mutations to non-typeable Haemophilus

CarcinomaEmphysema

Figure 1. Coexisting lung cancer and COPD -- macroscopic

pathology. Resected right upper lobe from a 74 year

old female with emphysema and pleomorphic lung

adenocarcinoma.

Carcinoma

Emphysema

Figure 2. Coexisting lung cancer and COPD -- histology. An

example of non-small cell carcinoma (left), with adjacent

emphysematous pulmonary parenchyma characterised by

‘floating’ alveolar septa (right).

Yang, Relan, Wright et al.

Expert Opin. Ther. Targets (2011) 15(4) 441

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influenzae caused airway inflammation and increased lungtumour burden [37]. Neutrophil elastase was found to entercells and degrade insulin receptor substrate-1, leading toenhanced interaction between PI3K and platelet-derivedgrowth factor receptor (PDGFR), thereby increasing tumourcell proliferation. Signal transducer and activator of transcrip-tion 3 (STAT3) is another pro-inflammatory transcriptionfactor, which responds to cytokines such as IL-6 and also pro-motes cell cycle progression. Gene expression of STAT3was increased in COPD lung tissue, compared with normallung tissue, and further increased in lung cancer tissue [38],suggesting that STAT3 could be a marker of progressionfrom COPD to lung cancer. Overall, these findingsprovide a direct link between inflammation, COPD andtumour growth.Recent reports have also implicated dysregulated chemo-

kine expression in the development and metastasis of cancers.Mechanisms include post-transcriptional modifications ofchemokines. An example is the class of proteins, heteroge-neous nuclear ribonucleo-proteins (hnRNPs), which regulatemRNA processing and transport [34]. HnRNPs affect thestability of mRNAs of chemokines and pro-inflammatorymediators, which can lead to dysregulated inflammatoryresponse, resulting in chronic inflammation and inductionof pathways promoting the development of lung cancer [34].

5.2 Epithelial--mesenchymal transitionEpithelial--mesenchymal transition (EMT) represents a pro-cess in which cells with epithelial phenotype transform intocells with mesenchymal phenotype [39]. EMT has beenproposed as a mechanism of tumour growth and invasion incancer, through the development of cancer stem cells [40].EMT has also recently been identified in COPD. In a studyof airway mucosal biopsies, markers of EMT (S100A4,vimentin and MMP-9) were found on cells in the basalbronchial epithelial layer and in the respiratory basementmembrane, which was fragmented. These markers appear toindicate mesenchymal transition of cells, and possible activemigration of cells through the basement membrane [41]. InNSCLC, COX-2 has been found to be upregulated, andthis mediator also plays an important role in EMT [28]. Integ-rins mediate attachment between a cell and other cells orsurrounding extracellular matrix. As reviewed in [29], theexpression of integrins increases in bronchial epithelial cellsduring inflammation. Furthermore, integrin avb6 regulatesTGF-b and MMP-12, which are involved in EMT [29]. OtherEMT markers such as Wnt and Notch may also mediate theshared pathogenesis of COPD and lung cancer.

5.3 Other mechanismsA number of other mechanisms have been proposed asshared pathways for the development of lung cancer andCOPD. These mechanisms include oxidative stress (e.g., cyto-chrome P450 enzymes), altered DNA repair, abnormalwound repair (EGFR), angiogenesis (VEGF, HIF) and

cellular proliferation/anti-apoptosis, all of which can occurin both the neoplastic process of lung cancer, and the lunginjury occurring in COPD [2,27-29]. Alveolar cell apoptosis isprominent in emphysema. However, there is proliferationand influx of inflammatory cells, with impaired abilityof macrophages to phagocytose apoptotic cells (impairedefferocytosis), a state which can be ameliorated with azithro-mycin [42]. These pathways are likely to interact with inflam-mation and EMT, as a result of cross-talk between areasof injury and repair, and between different structures in theairway wall and underlying lung parenchyma.

6. Potential shared genomic andepigenomic susceptibility to lung cancerand COPD

Whilst specific candidate pathways for shared susceptibility tolung cancer and COPD have been identified (as discussed inthe previous section), genomic and epigenomic changes mayunderpin alterations in these and other pathways. In this sec-tion, we explore genomic and epigenomic strategies that maydiscover important pathways for shared susceptibility to lungcancer and COPD. The strength of using genomic methods isthat it is a bias-free approach to identifying potential mecha-nisms in lung cancer and COPD. Variability in gene and pro-tein expression in the lung is partly driven by variation inepigenetic regulation, single nucleotide polymorphisms,copy number variation and microRNA expression.

6.1 Epigenetic regulationEpigenetic modifications, including DNA methylationand histone modifications, underlie a myriad of humandiseases [31], including lung cancer and COPD [43-48]. DNAmethylation is a heritable, yet reversible epigenetic modifica-tion unaffected by DNA sequence alterations, involving addi-tion of a methyl group (-CH3) to cytosine (contained withincytosine-guanine (CpG) dinucleotides) at the fifth carbon ofthe pyrimidine ring [49]. These modifications are catalysedby a group of enzymes, DNA methyltransferases (DNMTs),which are responsible for establishing promoter and firstexon methylation patterns. DNA methyltransferases areinvolved in maintenance of partial methylated DNA duringreplication (DNMT1) and de novo methylation of CpG dinu-cleotides in unmethylated DNA (DNMT3A, DNMT3B)(Figure 3). CpG methylation is involved in several processesincluding genomic imprinting, X chromosome inactivation,tissue-specific silencing of gene expression, chromosome sta-bilisation and chromatin condensation [50]. Environmentalfactors such as diet, air pollution, infection and smoking canall affect DNA methylation patterns.

A scan of lung cancer genomes has found that a total of4.8% of CpG island promoters may be aberrantly methylatedin at least one tumour, indicating greater than 1400 possibleCpG loci targets in lung cancer [51]. Genes consistentlyfound to be methylated in NSCLC include retinoic acid



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receptor beta-2 (RARB), tissue inhibitor of metalloproteinase 3(TIMP-3). cyclin-dependent kinase 4 inhibitor A (p16INK4a),O6-methylguanine-DNA-methyltransferase (MGMT), death-associated protein kinase (DAPK), E-cadherin (ECAD),p14ARF, glutathione S-transferase P1 (GSTP1) and Ras associ-ation domain family protein 1 (RASSF1A). For example,investigation of the methylation status of RARB, TIMP3,p16INK4a, MGMT, DAPK, ECAD, p14ARF and GSTP1 byZochbauer-Muller and co-workers in 107 resected primary

NSCLC and 104 matching normal tissues by methylation-specific PCR, found that methylation of at least one of thesegenes occurred in 82% of NSCLC cases [52].

Furthermore, epigenetic silencing of pathway antagonistsoccurs more frequently than activating mutations of signallingmolecules that tend to characterise other cancer types. Anexample is signalling by the wingless-type mouse mammarytumour virus integration site family (Wnt). In coloncancer, Wnt signalling is associated with mutations in APC

A: DNA methylation

Hypermethylation

Hypomethylation

B: Histone/chromatin modification

Histone acetylation

HAT

HAT

HDAC

HDAC

Histone deacetylationHeterochromatin

Euchromatin Transcription

Histone tails

Transcription factor

Protein Gene silencing

Gene expression

Gene expression

Gene silencing

HDAC

Figure 3. Epigenomic principles. Genomic DNA is methylated by one of two mechanisms. (A) Maintenance methylation

involves DNA methyltransferase 1 (DNMT1) binding methyl groups (CH3) to partially methylated DNA during replication

while (B) de novo methylation involves DNMT3a and DNMT3b adding methyl groups to CpG dinucleotides within

unmethylated DNA. In cancer, de novo methylation may be responsible for methylation of tumour suppressor promoter

regions, encouraging tumour growth. DNA hypermethylation (increased CH3 tags) involves CpG islands in gene promoters

and often leads to reduced gene expression (red) and gene silencing. DNA hypomethylation (reduced CH3 tags) involves

repeated DNA sequences such as long interspersed nuclear elements or retrotransposons resulting in transcriptional

activation (green lines) and disruption of adjacent gene expression. Alternatively, histone modification alters chromatin

structure by changing the configuration of nucleosomes, the basic unit of chromatin. Histone acetylation involving

increased histone acetyltransferase (HAT) and decreased histone deacetyltransferase (HDAC) activity results in an open

chromatin structure (euchromatin), allowing increased gene expression (green), whereas histone deacetylation (decreased

HAT and increased HDAC) removes acetyl groups resulting in a condensed chromatin form (heterochromatin) facilitating

gene silencing (red).Reproduced with permission from [31].



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or b-catenin. In lung cancer, Wnt is silenced by hypermethy-lation of pathway antagonists such as secreted frizzled protein(SFRP1) [53,54], other secreted frizzled proteins [54], dickkopfproteins [54,55] and Wnt inhibitory factor-1 (WIF-1) [54-56].There is increasing recognition that epigenetic modificationsplay a role in normal regulation of miRNA expression andtheir deregulation in cancer. Weber et al. have proposed thatmethylation of miRNAs may be significantly higher thanthat of protein-coding genes [57]. Two recent studies havedemonstrated both hypermethylation and hypomethylationof miRNAs during lung carcinogenesis. Silencing ofmiR-124 resulted in activation of cyclin D kinase 6 (CDK6)and phosphorylation of retinoblastoma (Rb) [58], whilsthypomethylation (activation) of let-7a-3 correspondedwith increased let-7a-3 expression and enhanced tumourphenotypes and oncogenic function [59].Epigenetic modifications are implicated in COPD. His-

tone deacetylase (HDAC) activity, especially HDAC2, wasdecreased in the surgically resected lung tissue of patientswith COPD, and activity reduced with increasing severityof COPD [60]. As HDAC2 is involved in steroid-inducedreduction of inflammation, downstream of the transcriptionfactor, NF-kB, this epigenetic regulation is clinically and bio-logically important in airways disease [61]. Investigations bySood and colleagues correlating wood smoke exposure,COPD risk and gene promoter methylation of a panel ofeight lung cancer-related genes, showed that p16 methylationin sputum was associated with a significantly lower predictedFEV1 in subjects with prior wood smoke exposure [62]. Inaddition, higher odds of airflow obstruction and lower FEV1

percentage predicted were observed in the presence of aber-rantly methylated GATA-binding protein 4 (GATA4) [62].Interestingly, a study comparing lung cancer patients withand without COPD has also demonstrated significantlyincreased levels of methylation of IL-12Rb2 and Wif-1 inpatients with COPD, with the authors suggesting thatmethylation of these two genes may occur in the damagedbronchial epithelium in COPD and could affect the patho-genesis of COPD-related lung cancer. This evidence providessupport for common epigenetic mechanisms in COPDand NSCLC.

6.2 Single nucleotide polymorphismsShared genetic susceptibility to these smoking-related lungdiseases could occur through the effects of single nucleotidepolymorphisms (SNPs) that alter molecular function in bio-logical pathways involved in lung cancer and COPD. Geneticassociation studies have predominantly focused on SNPs inxenobiotic metabolising enzymes, DNA repair genes, cellcycle genes, oncogenes, tumour suppressor genes and relatedpathways [22,63]. For example, we have shown an increasedrisk of NSCLC with the Ile462Val polymorphism in the cyto-chrome P4501A1 (CYP1A1) gene [64-66], which is associatedwith altered xenobiotic metabolising activity. We havealso previously demonstrated that frequency of COPD

exacerbations is associated with SNPs in the mannose-bindinglectin gene, a host defence and inflammatory mediator [67].

6.2.1 Genome-wide association studies: nicotine

receptor polymorphisms implicatedIn addition to association studies of selected candidate genes,genome-wide association studies (GWAS) have now beenpublished for lung cancer, COPD and smoking behaviour(Tables 1 and 2). These large-scale studies recruited smokers,with and without lung cancer or COPD. The most frequentassociation for lung cancer was observed with SNPs inchromosomal region 15q25 containing the genes for theneuronal nicotinic acetylcholine receptor (nAChR) subunits(cholinergic receptor, nicotinic, alpha 3 and 5: CHRNA3and CHRNA5). This region has also been associated withsmoking behaviour for example number of cigarettes per day.

An issue with the association of the nicotine receptor SNPswith lung cancer is potential confounding by COPD [68],since COPD itself has been associated with nicotine receptorSNPs [69,70], although this has not been fully replicated [71].

This large body of evidence suggests that nicotine receptorSNPs are associated directly with lung cancer and COPD.Furthermore, as smoking behaviour is associated with nico-tine receptor SNPs, many of the genome-wide associationstudies and subsequent validation studies have controlled forsmoking intensity and the association with nicotine receptorSNPs has remained positive. Therefore it is highly plausiblethat variation in the biology of the nicotine receptor pathway,due to the presence of SNPs, is contributing directly to lungcancer susceptibility, in addition to or independent of smok-ing intensity. The presence of COPD in smokers furtherincreases the risk of developing lung cancer.

6.2.2 Nicotine receptor pathway biologyThe biological effects of nicotine in the lung have beendirectly implicated in the susceptibility to lung cancer [72].However, little is known about the mechanisms of action ofnicotine in the lung that may lead to lung disease. Moreover,there are few studies of the functional consequences ofnicotine receptor polymorphisms in the lung.

Neuronal nAChRs are activated by acetylcholine or nico-tine, and consist of five subunits (pentamers) in combinationsof a and b subunits (a1 to a10, b1 to b4). In the lungs,nAChRs are expressed in neurones, and also non-neuronalcells, including large airway human bronchial epithelial cells(HBECs), SAECs and lung cancer cells [73-79]. The a5 subunitwas markedly upregulated in lung adenocarcinoma, whereasthe a3 subunit was downregulated [80]. The D398N(rs16969968) SNP of CHRNA5 was associated with alteredmRNA expression of CHRNA5 in normal lung tissue [80]

and altered agonist response in HEK293T (human embryonickidney) cells [81]. These data indicate that nAChRs areexpressed in the normal lung and in lung cancer, and maypotentially be involved in biological effects leading to chroniclung disease.



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Several in vitro studies have characterised the effects ofnicotine exposure to bronchial epithelium. Acute exposure ofHBECs to nicotine results in nAChR overexpression, particu-larlya1,a5 anda7 [73,79] in human adult lung; this upregulationof nAChRs also occurs in the developing lung [82]. With chronicexposure, there is some desensitisation of the a5 subunit [73].Nicotine, when applied toHBECs or small airway epithelial cells(SAECs), activates the PI3K/Akt pathway through activation ofnAChRs, leading to anti-apoptotic and growth-independenteffects, characteristic of tumor properties [76]. Nicotine also indu-ces HIF-1a and promotes angiogenesis and tumor cell migra-tion [83]. Repeated exposure of HBECs to nicotine can lead to aneuronal-like phenotype, EGFR phosphorylation (involved incell proliferation, implicated in cancer development) andNF-kB translocation to the nucleus (involved in inflamma-tion, implicated in COPD development) [84]. a3, a5 andb2 nAChR subunits are involved inwound repair and cellmigra-tion of HBECs [85]. These characteristics of nicotine biology inbronchial epithelial cells provide evidence of functional effects

of nicotine in the lung, implicating nicotine directly in mecha-nisms that lead to lung cancer and COPD, not just through nic-otine addiction, smoking behaviour and the inhalation ofcarcinogens in cigarettes.

6.3 Copy number variationGene copy number variation (CNV) has been implicated inthe pathogenesis of solid organ cancers. Chromosomal aberra-tions can be identified by a wide variety of instruments, fromthe conventional chromosomal band karyotyping (low resolu-tion) to the state-of-the-art million plus SNP array platforms(high resolution). Advances in microarray technology her-alded the introduction of array comparative genomic hybrid-ization (aCGH) which has superior resolution compared withCGH (30 kb versus 5 -- 10 Mb). Oligonucleotide aCGHmicroarray platforms consist of 25 -- 85-mer oligonucleotideprobes and are categorised into either SNP or non-SNP oligo-nucleotide aCGH. The accuracy of aCGH experiment resultsdepends on the DNA quality of the specimens used

Table 1. Genome-wide association studies of lung cancer.

Study Lung cancer Controls Array (SNPs) Regions and genes associated

with lung cancer

Spinola 2007 [116] 335 smokers 338 smokers Affymetrix (116,204) 10p KLF6Amos 2008 [117] 1154 smokers 1137 smokers Illumina (317,498) 15q CHRNA3Hung 2008 [118] 1989 smokers 2625 smokers Illumina (317,139) 15q CHRNA3, CHRNA5Thorgeirsson 2008 [119] 1024 smokers 32,244 controls Illumina (306,207) 15q CHRNA3McKay 2008 [120] 3259 smokers 4159 smokers Illumina (315,194) 5p TERT, CLPTM1L, 15q CHRNA3Wang 2008 [121] 1952 smokers 1438 smokers Illumina (511,919) 5p CLPTM1L, 6p BAT3-MSH5,

15q CHRNA3Broderick 2009 [122] Meta-analysis Meta-analysis Meta-analysis 5p TERT, CLPTM1L, 6p BAT3-MSH5,

TNXB, 15q CHRNA3Landi 2009 [123] 5739 smokers 5848 smokers Illumina (515,922) 5p TERT, CLPTM1L, 15q CHRNA3

Subject numbers represent the initial discovery phase; larger subject numbers were genotyped in the validation phase.

BAT3: HLA-B associated transcript 3; CHRNA: Cholinergic receptor, nicotinic alpha; CLPTM1L: Cleft lip and palate transmembrane protein 1-like protein;

KLF6: Kruppel-like factor 6; MSH5: MutS protein homolog 5; TERT: Telomerase reverse transcriptase; TNXB: Tenascin XB.

Table 2. Genome-wide association studies of COPD and smoking behaviour.

Study [Ref.] COPD Controls Array Regions and genes associated

COPDPillai 2009 [69] 823 COPD 810 smokers Illumina (561,466) 4q HHIP, 15q CHRNA3, CHRNA5Cho 2010 [71] 2940 COPD 1380 smokers Various (> 500,000) 4q FAM13A

Smoking behaviourLiu 2010 [124] 41,150 from 20 cohorts Various (> 500,000) 15q CHRNA3, CHRNA5TAG 2010 [125] 74,053 from 16 cohorts Various (> 500,000) 9q EGLN2, 9q DBH, 11p BDNF,

15q CHRNA3Thorgeirsson2010 [126]

31,266 and 46,481subjects from cohorts

Various (> 500,000) 8p CHRNB3, 15q CHRNA3,CHRNA5, 19q CYP2A6

Subject numbers represent the initial discovery phase; larger subject numbers were genotyped in the validation phase.

BDNF: Brain-derived neurotrophic factor; CHRNA: Cholinergic receptor, nicotinic alpha; CHRNB: Cholinergic receptor, nicotinic beta; CYP2A6: Cytochrome P450, family 2,

subfamily A, polypeptide 6; DBH: Dopamine beta-hydroxylase; EGLN2: Egg-laying defective nine homolog 2;FAM13A: Family with sequence similarity 13, member A;

HHIP: Hedgehog interacting protein.



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for analysis. Most aCGH experiments are performed onformalin-fixed--paraffin embedded (FFPE) samples becausethey are commonly available in lung cancer tissue banks andhave accompanying clinical follow-up data. However due tothe nature and duration of storage, the DNA in FFPE speci-mens is often degraded and of sub-optimal quality [86].Another important limitation is contamination of cancer cellswith normal cells [87]. Histological analysis and preferablytumour microdissection of tissue specimens improves tumourcontent to an acceptable quality. Finally, that there is signifi-cant CNV (12%) among individuals from different ethnicgroups. This variation includes amplifications and deletionsand thus determines gene expression. Such variation addsfurther complexity when interpreting the results of aCGHstudies, making CNV an important confounding factor [88].NSCLC is typically characterized by several DNA copy

number aberrations [89]. Table 3 provides a summary of theexperimental design, array platforms and salient findings fromselected CGH and aCGH studies in NSCLC. Some DNAcopy number aberrations in NSCLC have been associatedwith a more aggressive phenotype. Chromosomal aberrationsin NSCLC that are associated with a metastatic phenotypeinclude deletions in 3p, 4p, 6q, 8p, 10q and 21q and amplifi-cations in 1q, 9q and 14q [90,91]. Boelens et al. [92] demonstratedthat in squamous cell carcinomas, certain copy number aberra-tions (7q, 8p, 10q, 12p and 4p) are associated with lymph nodemetastasis while others (8q22-24) are associated with distantmetastasis within 3 years of surgery. Broet et al. [93] foundthat amplification in 7q31--33 is associated with a high riskof relapse after surgery in stage I adenocarcinoma and largecell cancer. Gallegos Ruiz et al. integrated aCGH with geneexpression data and found that deletion in 14q32.3 andreduced expression ofHSP90 (located in the region of deletion)was associated with improved survival in a cohort of 32 NSCLCpatients [94].There has been one genomic study of CNV in COPD

(Table 3). DNA from blood samples of 32 patients withemphysema was analysed using aCGH. Areas of copy numbergain and loss were detected, and a number of candidate genesidentified. Although preliminary, this study indicates thepotential for copy number aberration to contribute to thepathogenesis of emphysema. Another study found that highercopy numbers of the gene coding for b-defensin 2 were morefrequent in patients with COPD than controls [95].

6.4 Altered gene and microRNA expressionAlterations in gene (mRNA) and microRNA (miRNA)expression occur in both COPD and lung cancer. Commonchanges could lead to shared susceptibility to these lung con-ditions. Comparison of global gene expression profiles is anefficient way to explore the common genetic mechanismsbetween COPD and lung cancer on resected lung tumourand emphysematous or non-malignant lung tissue, usinghigh-density microarrays [96]. To date, numerous lung cancerand COPD profiles in primary lung tissues and lung cell types

have been reported and banked in publicly available miningdatabases such as Gene Expression Omnibus (GEO)and Oncomine.

A number of molecular mechanisms have been described byanalysis of gene expression patterns, that are common to bothCOPD and lung cancer. Injury due to cigarette smoke causesinflammation, generation of reactive oxygen species and oxida-tive stress in the airway epithelium and lung of both COPDand lung cancer patients. Genes and gene ontologies enrichedin inflammatory markers have been identified in profiles oflung cancer [97] and COPD [98-100]. Genes involved in inflam-mation (Fc-gamma receptor IIIA (FCGR3A), IL8, CXCL2,CD55, CD164, prostaglandin D2 synthase (PTGDS), C1R,NOTCH2, human cervical cancer related (HCCR), prostaglan-din endoperoxide synthase (PTGS1)) [97,100] and oxidativestress (duax oxidase 1 (DUOX1), COX5B, BTB and CNHhomology 2 (BACH2), DUOX2, glucose-6-phosphate dehy-drogenase (G6PD), glutathione peroxidase 2 (GPX2)) [97,101]

were identified in lung cancer and COPD patients usingmicroarrays. We have recently reported on seven genes involvedin emphysema severity in COPD patients (Figure 4, shows aheatmap of differentially expressed genes). These genes werealso enriched in ontologies associated with lung cancer suchas cell cycle regulation (cyclin-dependent kinase 2A(CDNK2A)), glutathione metabolism/oxidative stress (glutathi-one S-transferase mu 3 (GSTM3)) and angiogenesis (SER-PINF1) [102]. Similarly lung cancer profiles portray evidenceof COPD-related mechanisms i.e., cell growth and movement,cell communication and cell signalling [103].

COPD-related gene signatures co-exist within lung cancerprofiles. A recent microarray study on SCC lung tumour sam-ples has identified 374 genes differentially expressed betweenthose with and without COPD [104]. An unsupervised clusteranalysis and principal component analysis of the 374 differen-tially expressed genes revealed grouping of the SCC samplesaccording to their COPD status. These genes were signifi-cantly related to mitochondrial localisation and located onchromosome 5q. Gene ontologies associated with DNArepair, growth rate, NADH-dehydrogenase activity, electrontransporter activity, glutathione metabolism and energymetabolism were significantly overrepresented.

The landmark study by Spira and colleagues on profilingof airway epithelial cells identified gene expression profilesunique to COPD classified by FEV1 [100,105]. The expressionof these genes was not altered in lung cancer patients.Most COPD expression studies have used histologicallynormal lung tissue resected from patients with lung can-cer [99,100,106,107]. Although this is a limitation, no consistentdifferences between tumour types within cases, within con-trols, or independent of lung function were found [106]. Infact, successful biomarkers that can predict independentCOPD datasets have been developed from lung tissues frompatients with co-existing lung tumour [102]. The differencesand similarities in the major biological and molecular eventsin COPD and lung cancer have been described recently [105].



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Table

3.Genomic

studiesofco

pynumbervariationin

lungcancerandCOPD.

Study[Ref.]

Samples

Arrayandapproach

Resu

lts

Lungcancer

Massion2002[127]

21SCCand16AC

aCGH

using348BAC

clonesofknowncancergenes

Identifieddifferentialcopynumberchangesbetw

een

SCCandAC.Gain

in3q22--26andloss

of3p

exclusive

toSCC

Jiang2004

[128]

14NSCLC

(6SCC,8AC)

cDNA

with8000clones

IdentifiedCNA

thatdistinguishbetw

eenAC

andSCC

GallegosRuiz

2008

[94]

32stageIandIINSCLC

IntegrationofaCGH

withgeneexpression.aCGH

with30,000olignucleotidemicroarrays;gene

expression:Agilentoligonucleotidemicroarrays

IdentifiedHSP90,agenein

anovelregionofdeletion

andreducedgeneexpression

Tonon2005[129]

42NSCLC

and34NSCLC

celllines

IntegrationstudyofaCGH

(cDNA

of~14,160

BAC

clones)andgeneexpressionoligonucleotide

microarray(Agilent22,500probes)

Integrationstudyshowedthat3qregionhadbest

correlationbetw

eenCN

andgeneexpression

Shibata

2005[130]

55AC

aCGH

using800BAC

clones

IdentifiedCNA

betw

eensubtypesofAC

Kim

2005

[131]

29SCCand21AC

aCGH

using2987BACclones

CNAassociatedwithpooroutcomeidentifiedon

multivariate

analysis:

6p21,7p,9qand9p

Garnis2006[132]

28NSCLC

celllines

(18AC,9SCC,1LC

C)

aCGH

using32,000BAC

clones

Differencesin

CN

betw

eenAC

andSCC

identified

AC:deletionsof2q,6,8p,9q,13q,15q,16,

amplifications:

3q22,12,14,17p

SCC:deletionsof17p,amplifications:

2q,3q23-26,13q

Li2006[133]

6AC

celllines

IntegrationstudyofaCGH,geneexpresssionand

protein

levels

IdentifiedgeneswithincreasedCN,geneexpression

andprotein

levels

Choi2006

[134]

14SCC

aCGH

using1440BACclones

Most

commonCN

gain

in3qandlossesin

14q32.33

Highlevelamplificationsin

1p,2q,3q,4q,6q,7p,8q,

9p,10q,12q,14qand19p

Choi2006

[135]

15AC

aCGH

using1440BACclones

Gain

of16pandlossesof14qwere

themost

common

HighlevelDNA

amplificationsoccuredin

1p,5p,7p,

9p,11p,11q,12q,14q,16p,17q,19q,20p,21qand22q

Dehan2007

[136]

23NSCLC

(7AC,15SCC,

1AdSq),3metastasesto

lungand10norm

allung

IntegrationofaCGH

withgeneexpression.aCGH:

AgilentcD

NAwith11,367clonesandgene

expression:Affym

etrix

Hu95Awith12,625probes

IdentifiedgeneswithconcordantCNAandgeneexpression

Lo2007

[137]

12SCC

IntegrationstudyofaCGH,geneexpressionand

protein

levels

Custom

aCGH

platform

andAgilentHu95A

IdentifiedregionswithconcordantCN

withgeneexpression:

gainsin

3q23-q29,5p15.1-q11.1,18and20,lossesin

3p26.3-p12.3,9p24.3-q34.3,17and19

Broet2009

[93]

85stageIB

NSCLC

IntegrationstudyofaCGH

withgeneexpression.

aCGH:BAC

with32,000clones.Geneexpression:

Hu133Plus2

with61,000probes

IdentifiedCN

associatedwithrelapse

freesurvival.Developed

prognostic

signature

basedonresultsofintegration

Boelens2009

[92]

34SCC(24without

metastases,8withmetastases)

aCGH

using6500BACclones

CNAin

SCC

withLN

metastasesidentified

SCCwithLN

metastasis:

gain

7q36,8p12,10q22,12p12,

loss

at4p14andhomozygousdeletionof4q

COPD

Choi2009

[138]

32patients

withemphysema

(bloodsamples)

aCGH

using4030BACclones

DNAgainsat1p,5p,11p,12p,15q,17p,18q,21q,22q

DNAlossesat7q,22q

Subject

numbers

representtheinitialdiscovery

phase;largersubject

numbers

were

genotypedin

thevalidationphase.

AC:Adenocarcinoma;aCGH:Arraycomparative

genomic

hybridization;AdSq:Adenosquamouscarcinoma;BAC:Bacterialartificialchromosome;CN:Copynumber;CNA:Copynumberaberrations;

LCC:Largecell

carcinoma;LN

:Lymphnode;SCC:Squamouscellcarcinoma.



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C6orf4 CTF1 KRT9 SIPA1 DOCK2 NP_060673 ANXA13 PIGR Q8IVG4 CAMK2B SART2 NP_974487 LAD1 TMEM15AK5NP_789843 DPP3 FBXO38 CYP21A2 TBX3 S100A14

SLC6A16

SDC4 NP_060398 GSTM3 SAMSN1 ANKRD46 NEDD4 ICT1 AP19_HUMAN PEX13 TTK

MYO10 COL6A3 ZNHIT6 IL3RA ELAP CDH8 NRN1 CDKN2A HSD11B1 PAIRBPLA2G2A SERPINF1 SRP54 GFRA1 RAB11FIP2

-2.2 2

Log-ratios

Moderate Mild

Figure 4. Heatmap of genes differentially expressed between mild and moderate emphysema. Supervised two-

dimensional hierarchical clustering of lung tissue from COPD patients with mild versus moderate emphysema based on gas

transfer measurements. Average linkage uncentered correlation of emphysema samples was performed using microarray

expression data for 51 genes represented in external datasets chosen for quantitative reverse transcriptase (qRT)-PCR

validation on the training set. Each column represents a sample and each row represents a gene. Mild emphysema samples are

indicated by the blue bar and moderate emphysema samples are indicated by the orange bar. Heatmap indicates level of

gene expression: red represents high expression and green low expression, in moderate compared with mild

emphysema severity.Reproduced with permission from [102].



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Although the initial stages of disease development after envi-ronmental insult are similar in these diseases, the later stageof the disease is different. Mechanisms in lung cancer includeuncontrolled cell proliferation, angiogenesis, lack of cellularapoptosis and invasion; conversely, mechanisms in COPDinclude apoptosis, matrix degradation, inflammation andanti-angiogenesis [105]. For instance, CDKN2A, a tumour sup-pressor gene, is downregulated in lung cancer but upregulatedin COPD, causing cellular senescence [102]. The lack ofcommonality in end-stage disease mechanisms betweenCOPD and lung cancer in smokers remains unclear.

Altered miRNA expression has been implicated in lungcancer and smoking effects in the lung. miRNAs contributean important mechanism of epigenetic regulation. miRNAsare non-coding, single-stranded RNA species of appro-ximately 22 nucleotides in length. miRNAs mediate genesilencing through mRNA degradation (partial complementar-ity to mRNA in the RNA-induced silencing complex) ortranslational repression (inhibition of translational machin-ery). The importance of miRNA signatures is emerging instudies of lung cancer versus non-tumour lung tissue [108],and lung cancer recurrence.

We have recently performed a study of miRNAs dysregu-lated due to CNV in lung cancer [109]. A total of 474 humanmiRNA genes were physically mapped to regions of chromo-somal loss or gain identified from a high-resolution genome-wide aCGH study of 132 primary NSCLCs (a training setof 60 squamous cell carcinomas and 72 adenocarcinomas).miRNAs were selected as candidates if their immediatelyflanking probes or host gene were deleted or amplified in atleast 25% of primary tumours. 97 miRNAs mapped toregions of CNV. Analysis of three independent publishedlung cancer aCGH datasets confirmed that 22 of thesemiRNA loci showed directionally concordant CNV. ThemiR-218 sequence, encoded on 4p15.31 and 5q35.1 withintwo host genes (SLIT2 and SLIT3), in a region of copy num-ber loss, was selected for follow-up as it is reported as beingunderexpressed in lung cancer. We confirmed decreasedexpression of mature miR-218 and its host genes by qRT-PCR in 39 NSCLCs relative to normal lung tissue. Ourresults demonstrate that putative lung cancer-associatedmiRNAs can be identified from genome-wide aCGH datasetsand that miR-218 is a strong candidate tumour suppressingmiRNA potentially involved in lung cancer [109]. Interestingly,miR-218 has also been shown to be differentially expressedin human bronchial epithelium in response to cigarettesmoking [110].

7. Expert opinion: implications fordeveloping therapeutic targets

Understanding and targeting common pathogenic mecha-nisms for lung cancer and COPD would have potentialdiagnostic and therapeutic implications, for patients with theselung diseases and for people at-risk. Whilst cigarette smoking

is the primary and direct cause of most cases of COPD andlung cancer, there are possible shared mechanisms of develop-ment of these smoking-related lung diseases. Epidemiologicalevidence shows that COPD and emphysema are independentrisk factors for the development of lung cancer, even whencumulative smoking history is controlled for. The challengenow is to develop the work in this field, to be able to find path-ways that could be targeted to prevent the development andprogression of lung cancer and COPD. This would be in addi-tion to smoking prevention and smoking cessation efforts,and other environmental preventive strategies to reduce envi-ronmental agents that lead to these conditions, for example,air pollutants, toxins and carcinogens.

Despite research to date, the understanding of mechanismsinvolved in COPD development is only moderately advanced,compared with lung cancer. A global ‘omic’ picture includinggenome, transcriptome, epigenome, miRNAome, SNPingand proteome analysisis required to pin down the exactmechanisms driving COPD development [96]. Comparingthe ‘omic’ profiles of COPD and lung cancer would provideinsights into the similarities and differences the pathogenesisand progression of these diseases.

Inflammation is an example of a putative shared pathwaythat might have therapeutic implications. If, for example,inflammation is shown to be an important shared mechanismin the development of lung cancer and COPD, then furtherclinical trials of anti-inflammatory agents could be proposed.Interestingly, a US Veterans cohort study of 10,474 COPDpatients in primary care clinics found that use of inhaled cor-ticosteroids (ICS), particularly higher doses, was associatedwith reduced risk of lung cancer [111]. COPD patients usinginhaled steroids with total daily dose > 1200 µg had a reducedhazard ratio (HR) of 0.39 (95% CI 0.16 -- 0.96) for lung can-cer, when adjusted for other risk factors and followed-up forover 3 years. Similarly, in a case-control study from the UKGeneral Practice Research Database, 127 patients with lungcancer were compared with 1470 controls without lung can-cer (all subjects were former smokers) [112]. ICS/long-actingbeta2-agonist (LABA) use was associated with a reducedincidence of lung cancer (HR 0.50, 95% CI 0.27 -- 0.90),compared to short-acting bronchodilator use. There was adose--response relationship, with higher number of filledprescriptions associated with lower risk. In contrast, in rando-mised controlled trials, cancer mortality (including lungcancer) did not appear to be reduced with salmeterol/fluticasone or fluticasone in the Towards a Revolution inCOPD Health (TORCH) study of 6112 patients [113]. Fur-thermore inhaled steroids have not been shown to be effectivein reducing pre-malignant lesions such as metaplasia anddysplasia in the bronchial epithelium [114,115]. This lack ofeffect could possibly due to the effect of steroid resistance insmokers and patients with coexisting COPD, from reducedhistone deacetylase activity.

Other putative pathways and mechanisms described in thisreview could equally have therapeutic potential (Figure 5



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and Table 4). Although the processes of COPD (destructionand increased apoptosis) and lung cancer (cell proliferationand evasion of apoptosis) seem opposed, there are mecha-nisms present in COPD that may predispose to lung cancer.These common mechanisms may involve chronic inflamma-tion, abnormal repair, matrix degradation, EMT and alterednicotine receptor biology. Furthermore the underlying basisof these alterations may be due to genetic (SNP andCNV)and epigenetic (DNA methylation and histone modification;miRNAs). Hence we propose that genomic and epigenomicapproaches will discover important mechanisms and pathwaysassociated with both COPD and lung cancer. Genomic and

epigenomic strategies would lay the foundations for furthertargeted functional studies.

Once validated, identification of relevant shared biologicalpathways would lead to the application of novel preventiveand therapeutic strategies, for example, anti-oxidants, inhibi-tors of the EMT process, interventions for functional effectsof SNPs and CNVs (depending on the target molecule),epigenomics (demethylating agents, histone deacetylaseinhibitors) and miRNAs (transfection of pre-miRs andanti-miRs to increase or decrease miRNA expression).

Strategies to study genomics and epigenomics, in additionto gene-environment interaction, will yield greater insight

COPDOxidative stress

Infection

Epithelial–mesenchymal transition (EMT)

Putative mechanismEnvironmental toxins

(Cigarette smoke, air pollutants, carcinogens)

Matrix degradation

e.g., - TGFβ -Wnt, Notch

-MMPs

-NF-κB-STAT3-IL-6-Neutrophil elastase

Evade immunesurveillance

↑ Angiogenesis

↓ Angiogenesis

ProteinRNADNA

SNPs Methylation Copy number miRNA

Underlying susceptibility:

Ineffective repair

Limitlessreplication

-EGFR-HIF-VEGF-nAChR

Inflammation

Wound repairCell proliferation

Angiogenesis

Lung cancerSelf-sustaining

growthTissue invasion and

metastasis

Figure 5. Potential shared mechanisms to be tested in the development of lung cancer and COPD. Whilst the basic

hallmarks of COPD and lung cancer appear divergent, several mechanisms have been proposed, that may be shared

processes between these two lung diseases, and could therefore contribute jointly to their pathogenesis. Furthermore there

are processes occurring in COPD (EMT, matrix degradation, inflammation, abnormal wound repair -- with their associated

key mediators) that could promote processes that lead to lung malignancy and metastasis. Underlying this variation

between at-risk individuals is likely to be genomic and epigenomic changes (alterations in DNA sequence or copy number;

promoter hypermethylation and other epigenetic changes; alterations in microRNAs (miRNAs)), that interact with

environmental exposure to ultimately determine susceptibility and progression of lung cancer and COPD. Understanding

and integrating these risk pathways would help to develop novel diagnostic and therapeutic tools for these lung diseases.aAChR: Nicotinic acetylcholine receptor; COPD: Chronic obstructive pulmonary disease; EMT: Epithelial--mesenchymal transition; HIF: Hypoxia-inducible factor;

STAT3: Signal transducer and activator of transcription 3.



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into the shared pathogenesis of lung cancer and COPD.The major challenge now is to define the effects of genomicand epigenomic variation, together with environmentalexposures, on the host, at the molecular, cellular, tissue andpatient level. For example, nicotine pathway biology mayunderpin the common susceptibility to lung cancer andCOPD in smokers. However the functional changes of nico-tine receptor SNPs have not been studied in detail in relationto nicotine receptor biology in the lung, and there is littleinformation about how this could relate directly to lung dis-ease (over and above nicotine addiction). Clearly, furtherwork is needed to explore genome/epigenome--environmentinteraction, not just for cigarette smoke but also air pollutantsand other inhaled toxins. These data would then need to benetworked with global profiling data from proteomic andphenomic studies.

Positive results from initial studies would form the foun-dations for ex vivo interventional studies of siRNA againstsmall airway targets related to the involved pathways, andin vivo animal models of prevention and treatment in thepresence of at risk factors and pathways. These studies wouldthen set the scene for clinical trials of biomarkers, preventiveagents and novel treatment modalities, to prevent and treatCOPD and lung cancer. Our vision is that understandingindividual genomic/epigenomic susceptibility to COPD

and lung cancer will lead to personalised approaches fordiagnosing, preventing and treating these devastatinglung diseases.

Acknowledgements

We thank the patients and staff of The Prince CharlesHospital, for their involvement in our research program.

Declaration of interest

All authors declare no conflict of interest. Funding sources:National Health and Medical research Council (NHMRC)project grants, NHMRC Practitioner Fellowship (KF),NHMRC Career Development Award (IY), NHMRC Bio-medical Scholarship (SS, CW), Cancer Council QueenslandPhD Scholarship (MD), Cancer Council Queensland SeniorResearch Fellowship (KF), Cancer Council Queensland proj-ect grants, Queensland Smart State project grants, Office ofHealth and Medical Research (OHMR) project grants, ThePrince Charles Hospital Foundation, Australian Lung Foun-dation/Boehringer Ingelheim COPD Research Fellowship(IY), NHMRC Postgraduate Medical Scholarship (KS),UQ PhD Scholarship (KS), UQ Early Career ResearcherFellowship (VR).

Table 4. Key points and recommendations for studying shared pathogenesis of COPD and lung cancer.

Lung cancer and COPD share common aetiology (smoking and other environmental agents)The presence of COPD increases the risk of developing lung cancer, even when smoking history is controlled for. Specific mechanismsimplicated in COPD may also increase the risk of developing lung cancer, in addition to tobacco smoke exposurePotential shared biological mechanisms in lung cancer and COPD include

InflammationEpithelial--mesenchymal transitionOxidative stressMatrix degradationCell proliferation and anti-apoptosisAbnormal wound repairAngiogenesis and other pathways

Potential underlying susceptibility to lung cancer and COPD may arise from a number of genomic and epigenomic aberrations,interacting with environment exposures:

Single nucleotide polymorphisms (SNPs) in genomic DNA, for example nicotine receptor polymorphismsCopy number variation in genomic and somatic DNAEpigenetic alterations, for example, promoter hypermethylation in genes, in genomic and somatic DNAAltered expression of mRNAs and microRNAs in lung and lung tumour tissue

Exploring biological mechanisms, underlying susceptibility and genome/epigenome--environment interaction will increaseunderstanding of the pathogenesis of these lung diseases, in order to develop more effective prevention and treatment strategies



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AffiliationIan A Yang†1,2, Vandana Relan1,2,

Casey M Wright1,2, Morgan R Davidson1,2,

Krishna B Sriram1,2,

Santiyagu M Savarimuthu Francis1,2,

Belinda E Clarke3, Edwina E Duhig3,

Rayleen V Bowman1,2 & Kwun M Fong1,2

†Author for correspondence1The Prince Charles Hospital,

Department of Thoracic Medicine,

Thoracic Research Laboratory,

Brisbane, Australia

E-mail: [email protected] University of Queensland,

UQ Thoracic Research Centre,

School of Medicine,

Brisbane, Australia3The Prince Charles Hospital,

Department of Anatomical Pathology,

Brisbane, Australia



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common pathogenic mechanisms and pathways in the development of copd and lung cancer

Documents

larger subject

prince charles

subject numbers

yield greater

squamous cell

single nucleotide

represents

squamous cell