Targeted Therapy for Lung CancerRajesh Kukunoor, MD, Jigar Shah, MD,

and Tarek Mekhail, MD, MSc, FRCSI, FRCSEd

AddressTaussig Cancer Center, The Cleveland Clinic Foundation, R35, 9500 Euclid Avenue, Cleveland, OH 44195, USA.E-mail: Mekhait@ccf.orgCurrent Oncology Reports 2003, 5:326–333Current Science Inc. ISSN 1523-3790Copyright © 2003 by Current Science Inc.

IntroductionThe observation that mustard gases, used in World War Iand II, caused lymphopenia and splenic involutions, andthe findings by Osborn and Huennekens, in 1958, thataminopterin specifically inhibited dihydrofolate reductase,an enzyme essential for DNA and RNA synthesis, inspiredthe search for drugs that target key pathways in cell devel-opment. Our understanding of the biology and function ofthe subcellular components of cancer cells has helpeddefine several new targets for cancer therapy. Since the1970s, the biology and pathogenesis of cancer have begunto be elucidated. Investigators have identified many of themolecular mechanisms that lead to the development andspread of malignancies. The two common features in thepathogenesis of all cancers are loss of regulation of growthand the ability to locally invade tissues and to metastasize.

The molecular differences between normal cells andtumor cells are thus central to our understanding of howcancer starts and to devising optimal strategies to eliminateit. A common misconception is that cancer cells replicatefaster than normal cells. Rather, the growth of malignanttumors appears to result from two factors: 1) lack of appro-priate control responses to the signals that normally inter-rupt the cell cycle; and 2) failure of cellular deathprogramming and the response to appropriate stimuli orstresses (apoptosis).

The transformation from a normal cell to a tumor cellis now considered to be dependent on mutations in gene

products that are important for integrating extracellularand intracellular signals to the cell cycle and cell deathmachinery and on those gene products involved in directlycontrolling cell-cycle progression. Loss of either type offunction leads to loss of regulatory cell growth signals. Thediscovery of oncogenes in the 1970s and their overexpres-sion or increased activity in tumor cells led to the sugges-tion that the abnormality in tumor cells was the presenceof too much signal that pushed the cell through the cellcycle. The discovery of tumor-suppressive genes in the1980s added to this model by suggesting that the growthabnormality of tumor cells resulted from a combination oftoo few cell-cycle brakes (tumor suppressors), and toomany cell-cycle accelerators (oncogenes).

An extracellular signal often triggers a robust array ofintracellular signaling pathways that simultaneouslycommunicate a multitude of signals. This process isknown as signal transduction. Cell signaling is thus criti-cal to the life cycle and biologic function of all cells and iscritically important in governing such processes as prolif-eration and differentiation.

A better understanding of these genetic pathways hasled to the development of a multitude of new therapeuticagents and the promise of a targeted, nontoxic, effectiveanticancer drug. A great deal of excitement has been raisedby the development and success of the fairly specific inhib-itor of the cAbl kinase, imatinib mesylate (Gleevec; Novar-tis, East Hanover, NJ) for the treatment of chronicmyelogenous leukemia.

An estimated 169,400 new cases of lung cancer werediagnosed in the year 2002, accounting for approximately154,900 deaths [1]. This level of mortality is more thanthat attributed to all other cancers combined. The overallcure rate of lung cancer is a dismal 15%, primarily becauseof a delayed stage at diagnosis and inability of conven-tional chemotherapy to cure systemic disease [2]. Lungcancer is therefore a legitimate target for investigation ofnovel therapeutic agents. This article briefly discusses thestatus of some of these targeted agents in the treatment oflung cancer.

Protein Tyrosine KinasesProtein tyrosine kinases (PTKs) are the largest family ofoncogenes that encode for glycoproteins that function asgrowth factor receptors. Receptor tyrosine kinases containan extracellular ligand-binding domain that confers ligand

Lung cancer remains the leading cause of death in men and women in the United States. This status is attributed to late diagnosis and lack of effective chemotherapy for metastatic lung cancer. Understanding of the mechanism by which mutated genes confer a neoplastic phenotype on cells has resulted in the development of many potential targeted cancer therapies. This article briefly discusses the work being done with some of these targeted agents in the treat-ment of lung cancer.

Targeted Therapy for Lung Cancer • Kukunoor et al. 327

specificity, a transmembrane hydrophobic domain thatanchors the receptor to the membrane, and an intracellulardomain with phosphorylation sites [3••]. Ligand bindinginitially induces receptor dimerization, which is followedby phosphorylation of binding sites. This in turn activatessuch downstream signal transduction pathways as phos-pholipase C (PLC) and ras. Epidermal growth factor recep-tors (EGFR) and vascular endothelial growth factorreceptors (VEGFR) are among the more commonly studiedsubgroups of PTKs.

Epidermal growth factor receptorsThe erb family of oncogenes (erb 1–4) encodes a familyof growth factor receptors including EGFR/erb B1 anderb B2 (HER2). Several ligands, including EGF andtransforming growth factor (TGF)-α, bind EGFR, lead-ing to dimerization and induction of downstream sig-naling. EGFR expression is increased in non–small-celllung cancer (NSCLC), whereas it is seldom overex-pressed in small-cell lung cancer (SCLC). However, datacorrelating EGFR expression with prognosis are con-flicting [4,5]. EGFR blockade can be accomplished byreceptor antibodies as well as small molecule tyrosinekinase inhibitors.

Anti-EGFR antibodiesCetuximab (C225, Erbitux; Bristol-Myers Squibb, Princeton,NJ) is a chimeric monoclonal antibody that has demonstratedenhancement of platinum- and taxane-induced cytotoxicity inresistant tumor xenograft models. Its safety profile and a stan-dard dosing regimen of 400 mg/m2 loading dose at week 1,followed by 250 mg/m2/wk, have been established in a phaseI trial [6]. Cetuximab has been tested in combination with twostandard chemotherapy doublets (carboplatin–paclitaxel andcarboplatin–gemcitabine) in chemotherapy-naïve patientswith metastatic NSCLC in a phase II trial; these studies haveclosed, and the results are awaited.

ABX-EGF (Abgenix; Amgen, Fremont, CA and Seattle, WA)is a fully humanized monoclonal antibody that binds EGFRwith high affinity. It has been shown to cause tumor regressionin multiple tumor types in a mouse xenograft model, with nodemonstrable activity against EGFR-negative tumors [7]. Find-ings from a recent phase I study demonstrated its safety at adose of 0.75 mg/kg with a loading dose of 1.0 mg/kg [8]. Aphase II trial of ABX-EGR combined with standard chemother-apy versus chemotherapy alone is in progress.

Small molecule receptor tyrosine kinase inhibitorsSmall molecule receptor tyrosine kinase inhibitors (TKIs)are the most extensively studied group among the tar-geted therapies. They are administered orally and are gen-erally tolerated well. Common toxicities with TKIsinclude a reversible acneiform rash and diarrhea. It hasbeen suggested that the rash may be a surrogate for drugactivity because increased expression of EGFR is noted inthe basal layer of the epidermis.

ZD1839 (Iressa; AstraZeneca, Wilmington, DE) is a selec-tive inhibitor of the EGFR (HER1) RTK. Three phase I trialshave confirmed its safety and demonstrated some efficacy in asubset of patients with lung cancer [9–11]. These findingsprompted two phase II trials that compared 250 mg/d to 500mg/d of ZD1839 in refractory NSCLC: Iressa Dose Evaluationin Advanced Lung Cancer (IDEAL)-1 and -2.

IDEAL-1 evaluated the objective response rates andsafety of these two dose schedules of ZD1839 in 210patients with locally advanced or metastatic NSCLC whohad been refractory to one or two (at least one plati-num-based therapy) chemotherapy regimens [12•]. Nodifference in response rates (18.1% vs 19%), progres-sion-free survival (2.7 vs 2.8 months), and overall sur-vival (7.6 vs 8.1 months) was noted between the twoarms. Toxicities were lower in the 250-mg arm, butresponse rates were similar whether ZD1839 was used inthe second- or third-line setting.

The IDEAL-2 trial evaluated the tumor response rates,disease-related symptoms, response, and safety of dailyoral ZD1839 in the same two doses (250 mg vs 500 mg/d)in patients with locally advanced or metastatic NSCLCwho had failed two or more prior chemotherapy regimenscontaining platinum and docetaxel [13•]. Response rateswere 11.8% and 8.8%, and median survival was 6.0 and6.1 months for the 250-mg/d and 500-mg/d arms, respec-tively; grade 3 and 4 toxicities were noted in 6.4% of thepatients in the 250-mg arm and 17.5% of the patients inthe 500-mg arm. These results led to the approval of Iressaby the US Food and Drug Administration (FDA) for treat-ment of refractory metastatic NSCLC that has progressedafter platinum-based and docetaxel chemotherapy.

The INTACT 1 and INTACT 2 trials comparedZD1839 in combination with either paclitaxel and car-boplatin or gemcitabine and cisplatin versus standardchemotherapy alone in the initial treatment of meta-static lung cancer. These results are not yet published,but preliminary reports released by the manufacturerconfirm that ZD1839 failed to show any survival advan-tage in combination with standard chemotherapy in thefirst-line therapy of metastatic NSCLC.

OSI-774 (Tarceva; developed by OSI Pharmaceuticals,Melville, NY) is another selective inhibitor of EGFR-PTKautophosphorylation. Perez-Soler et al. [14] evaluated thesafety and efficacy of 150 mg/d of oral OSI-774 in 56patients with advanced platinum-resistant NSCLC andEGFR overexpression (≥ 10% of tumor cells). An overallresponse rate of 11%, stable disease rate of 26%, andmedian survival of 32 weeks were noted.

Two large phase III trials with OSI-774 in NSCLC havecompleted accrual. The first evaluates OSI-774 as monother-apy in the second- or third-line treatment of locally advancedor metastatic lung cancer. The second study evaluates thecombination of OSI-774 and standard chemotherapy versuscombination chemotherapy in chemotherapy-naïve patientswith advanced NSCLC. The results of these trials are eagerly

328 Lung Cancer

awaited and are likely to have a great impact on the develop-ment of this class of drugs.

Anti-HER2 antibodiesThe HER2/neu (erbB-2) receptors are expressed in multipleNSCLC cell lines. These receptors are associated withshorter survival and may be a marker for intrinsic multi-drug resistance in NSCLC cell lines [15]. Trastuzumab(Herceptin; Genentech, South San Francisco, CA) is arecombinant DNA-derived humanized monoclonal anti-body based on human IgG. It binds HER2 receptors,which, when activated, alter several downstream signals,especially the MAP kinase pathways, causing cell-cyclearrest in the G0 to G1 phase [16,17].

In vitro clonogenic assays demonstrated synergybetween trastuzumab and several chemotherapy agents[18]. Three published phase II trials of trastuzumab incombination with standard chemotherapy in the treatmentof NSCLC demonstrated response rates ranging from 18%to 50%. These results were not different from what isexpected with chemotherapy alone. Thus, trastuzumabmay not have a role in the treatment of NSCLC.

MVF-HER2 (628-647) is a peptide vaccine developedin a mouse model that elicited high titers of antibodiesthat are cross-reactive with the HER2 receptors. These anti-bodies have shown encouraging preclinical results withtransgression of HER2/neu–overexpressing mammarytumors in 83% of transgenic mice [19]. A National CancerInstitute (NCI) phase I trial is now accruing patients.

c-Kit/stem cell factor receptorPublished data suggest that Kit (CD117) and its ligandstem cell factor (SCF) are expressed in 50% to 70% ofSCLC cell lines. Imatinib mesylate is a small moleculeinhibitor of the Kit TK that also demonstrates in vitroinhibitor activity against the cAbl TK and PDGF RTK[20,21]. This coexpression constitutes a functional auto-crine loop, implying that Kit TK could be a valuable targetfor treatment of SCLC.

In in vitro studies, Krystal et al. [22] demonstrated thatimatinib inhibited SCF-mediated Kit activation with an IC50of 0.1 µmol. However, imatinib failed to enhance carbo-platin- or etoposide-induced cytotoxicity in vitro. In a phaseII trial, Johnson et al. [23] evaluated the objective responserate to a 600-mg dose of imatinib administered daily to 19SCLC patients who were chemotherapy naïve or in sensitiverelapse. No objective responses were noted. One patient hadprolonged stabilization of disease. Overall survival at 6months was 68%. Only four patients in this study hadtumors that were positive for Kit (CD117).

Protein Kinase C PathwayThe protein kinase C (PKC) pathway is comprised of agroup of serine–threonine protein kinases that facilitate

signal transduction for ras and other oncogenes in criticalprocesses such as cell growth, proliferation, differentiation,and cell death [24]. The enzymes consist of a regulatoryand a catalytic domain. The catalytic domains of the differ-ent PKCs share homology with the cyclin-dependentkinase (CDK) enzymes. Therefore, several nonspecifickinase inhibitors act on both PKC and CDKs. Inhibition ofPKCs is known to induce differentiation and enhance cyto-toxicity of chemotherapy.

Staurosporine, and its congeners UCN-01 and PKC 412,inhibit the catalytic domain of PKC25. Phase I results withthis agent for lung cancer have not been encouraging[26,27]. Another agent in clinical trials, bryostatin, wasoriginally isolated from the marine organism, Bugula ner-itina. It inhibits the regulatory domain of PKC, and myal-gia is its dose-limiting toxicity [28,29]. Phase II trials ofcombination chemotherapy in NSCLC are ongoing.

Antisense oligonucleotide therapyInhibition of gene and protein expression by targeting ofspecific RNA sequences with complementary oligonucle-otides to reduce mRNA translation forms the basis for anti-sense therapy. ISIS 3521, a selective inhibitor of PKC-αexpression, is a 20-mer antisense phosphorothioate oligo-nucleotide to PKC-α mRNA that effectively reduces thePKC-α expression involved in several critical cell pathways[3••]. A phase II trial by Yuen et al. [30] reported a 42%overall response rate with a median survival of 19 monthsand an actuarial 1-year survival rate of 75% with thecombination of ISIS 3521 and a standard chemotherapydoublet of carboplatin and paclitaxel. Another phase IIstudy demonstrated the safety and modest efficacy of ISIS3521 in combination with cisplatin and gemcitabine inadvanced NSCLC [31]. However, initial results of a phaseIII trial of ISIS 3521 in combination with carboplatin andpaclitaxel failed to show a survival advantage (ISIS 3521, 10months vs chemotherapy, 9.7 months).

Farnesyl Transferase InhibitorsFarnesylation involves addition of a 15-carbon moiety tothe carboxyl terminus of cationic proteins catalyzed by theenzyme farnesyl transferase (FT). G-proteins such as Rasand Rho, among several others, are the substrates for FT32.

The Ras protein triggers several critical cell pathways,including PI3 kinase and Raf/Mek/Erk kinase, and there-fore plays a major role in cell proliferation and transforma-tion. Ras mutations are reported in approximately 30% to40% of patients with NSCLC. FT inhibitors were developedbecause farnesylation of Ras is central to several down-stream pathways. Adjei et al. [33] reported preliminaryphase II data with single-agent R11577, an FT inhibitor, inuntreated advanced NSCLC. They reported no objectiveresponses, but 14% of the study patients had stable diseasefor greater than 6 months.

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RetinoidsRetinoids are vitamin A derivatives that are required formaintenance of normal cell growth, differentiation, andloss within epithelial tissues. Suppression of carcinogene-sis by retinoids has been shown in several animal models.Retinoid action is mediated through at least two classes ofnuclear receptors: the retinoic acid receptor (RAR) and theretinoid X receptor (RXR) [34]. In the leukemic HL-60 cellline, Nagy et al. [35] demonstrated that activation of RARsinduces differentiation, whereas activation of RXRs inducesapoptosis. Retinoids have been studied extensively in thechemoprevention of lung cancer with varying results [36].

Fenretinide is a potent inducer of apoptosis in SCLCcell lines. Its action is mediated through the generation ofreactive oxygen species. Preclinical studies indicate that ithas good activity against SCLC and possible synergy withstandard chemotherapeutic agents, including cisplatin,etoposide, and paclitaxel [37]. Fenretinide is in phase IItesting in patients with relapsed SCLC.

Bexarotene is a novel oral retinoid that selectively tar-gets the RXR. Unlike other retinoids, it has a favorable tox-icity profile. Khuri et al. [38] reported results of a multi-institutional phase I/II trial of oral bexarotene in combina-tion with cisplatin and vinorelbine in advanced NSCLC.The observed response rate was 25%, with a median sur-vival of 14 months. Two additional phase III trials are eval-uating bexarotene in chemotherapy-naïve patients withadvanced NSCLC with carboplatin–paclitaxel and cispla-tin–vinorelbine doublets compared with the same combi-nation without bexarotene.

Cell Survival PathwaysCyclin-dependent kinasesCyclins and cyclin-dependent kinases are a group of regu-latory proteins that catalyze the hyperphosphorylation ofthe retinoblastoma gene product, RB, and many othercomponents of the cell-cycle machinery [39]. Stimulationof cdk results in release of transcription factor E2F-1,which transitions the cell from G1 to S phase, a processthat is inhibited by the cdk inhibitors, thereby inducingcell-cycle arrest.

Flavopiridol is a synthetic flavone that inhibits severalcyclin-dependent kinases (1, 2, 4, and 7), decreases cyclinD1 and bcl-2 expression, and induces cell-cycle arrest andapoptosis [40,41]. Synergy of flavopiridol with docetaxelwas demonstrated in a murine adenocarcinoma model[42]. In a phase I study of a combination of flavopiridolwith paclitaxel and carboplatin in advanced NSCLC, themaximum tolerated dose was 85 mg/m2, and the responserate was 36% (complete responses [CR] + partial responses[PR]) [43]. Flavopiridol is being evaluated in the phase II/III setting in combination with docetaxel compared withdocetaxel alone.

Cyclic GMP (cGMP), is a second messenger that acti-vates protein kinase G, which in turn is involved in regula-

tion of apoptosis through complex pathways. cGMP can berendered inactive by a family of enzymes called phospho-diesterases (PDEs). PDE inhibition by exisulind, a deriva-tive of sulindac, raises cGMP levels, facilitating apoptosisthrough increased levels of protein kinase G [44].

Exisulind induces apoptosis through bcl-2- and p53-independent mechanisms, as supported by studies of pre-clinical synergy with several chemotherapeutic agents [45].Phase I studies found a dosage of 250 mg/d of exisulind tobe tolerated well in combination with docetaxel and carbo-platin. A modest response rate of 45% and a stable diseaserate of 40% were noted [46]. A phase III randomized, dou-ble-blind, placebo-controlled, multicenter study compar-ing exisulind and docetaxel with docetaxel plus placebo inthe second-line setting after failure of a platinum-basedregimen is underway.

Cyclooxygenase-2Cyclooxygenase-2 (COX-2) is an inducible enzyme thatcatalyzes the synthesis of several prostaglandins. PGE2, adownstream product of COX-2, can promote tumorgrowth and invasion through stimulation of VEGF, upregu-lation of bcl-2 and various metalloproteinases, and inhibi-tion of immune surveillance. COX-2 expression isincreased in lung cancer, especially in adenocarcinoma,whereas its expression is negligible in SCLC and squamouscell cancer. COX-2 inhibition is therefore an attractive tar-get in the treatment of NSCLC.

Celecoxib, a COX-2 inhibitor, has shown preclinicalsynergy with several agents [47]. A recent study reportedincreased resectability and clinical and pathologicresponse rates in patients with early-stage NSCLC treatedwith celecoxib, 400 mg twice a day, in combination withcarboplatin and paclitaxel in the neoadjuvant setting [48].

Csiki et al. [49] reported preliminary results of a phaseII study evaluating the combination of celecoxib and doce-taxel in treatment of recurrent NSCLC. Fifteen patientswith no response to prior chemotherapy were treated andshowed a 15.4% response rate and a 23.1% stable diseaserate. Accrual continues, and final results are awaited.

p53The p53 gene is a tumor suppressor gene that is activatedby diverse cellular mechanisms including DNA damageand hypoxia. The p53 protein serves as a transcription fac-tor, regulating downstream genes involved in cell-cyclearrest, DNA repair, and programmed cell death. Geneticalterations of the p53 system confer genomic instability,impaired apoptosis, and diminished cell-cycle restraint.This portends a poor prognosis in a variety of cancers,including NSCLC [50]. In preclinical models of NSCLC,intratumoral injection with adenoviral mediated wild-typep53 caused apoptosis and rendered cells more radio- andchemosensitive [51,52]. Several problems have been notedwith systemic administration of p53, including high immu-nogenicity of viral rectors, cross-reacting antibodies, and

330 Lung Cancer

possible inactivation of wild-type p53 in normal host cells.In one of the earliest published reports, Roth et al. [53]described good responses in three of nine patients withNSCLC to intratumoral injection of retrovirus-mediatedp53. All three responders had endobronchial disease. Insubsequent phase I trials, intratumoral administration ofadenovirus-mediated p53 was tolerated well, with minimalside effects, and the majority of patients achieved stabledisease [54,55]. Encouraging results were reported in aphase II study of a combination of adenovirus-mediatedp53 and radiotherapy in patients with localized NSCLCwho were not candidates for surgery or chemoradiotherapy[56]. Pathologic negative biopsies were noted in 62% ofthe patients, CRs in 39%, and PRs in 15%, and the overallrate of 1-year survival was 65%. However, in a multicenterphase II study of p53 plus standard chemotherapy inadvanced NSCLC, Schuler et al. [57] reported no addedbenefit of SCH58500 (adenovirus wild-type p53) to thealready established response to first-line chemotherapy inadvanced NSCLC. Median survival was 10.5 months with a44% rate of 1-year survival.

Bcl-2The Bcl-2 family of proteins harbors pro- and antiapo-ptotic members. The proapoptotic survival members of theBcl-2 family are bcl-2 and bcl-xl. Bcl-2 is upregulated inseveral solid tumors and augments resistance to chemo-therapy- and radiation-induced apoptotic cell death.

G3139 (Genasense; Genentech, South San Francisco,CA) is an antisense oligonucleotide that inhibits bcl-2 syn-ergy with several chemotherapeutic agents, as noted in pre-clinical studies. In a completed pilot study of G3139 withpaclitaxel in 12 patients with refractory SCLC, no objectiveresponses were observed, but two patients achieved pro-longed stable disease [58].

AngiogenesisNeovascularization is a prerequisite for progression oftumors and their metastasis. A variety of proangiogenicand antiangiogenic factors, including VEGF, bFGF, andmatrix metalloproteinases, regulate this process. Inhibitionof angiogenesis is an innovative therapeutic approach thatcould represent a powerful adjunct to traditional therapyfor malignant tumors.

Vascular endothelial growth factorVEGF, a 45-kDa glycoprotein, is the most abundant andpotent isoform of the VEGF family. It binds with highaffinity to two tyrosine kinase receptors, VEGFR-1 (flt-1)[59] and VEGFR-2 (flk-1/KDR) [60].

VEGF and its receptors are upregulated in response tohypoxia with resultant increased tumor vascularity[61•,62]. Mutant p53 upregulates VEGF promoter activity[63], and interleukin (IL)-1β increases VEGF expression[64]. VEGF may also play a role in increased vascular per-

meability, allowing tumor dissemination, plasma proteinleakage, and fibril deposition into the extracellular matrix.

RhuMAb-VEGF is a recombinant humanized mono-clonal antibody to VEGF. A phase II study compared stan-dard chemotherapy with a regimen of chemotherapy pluslow-dose RhuMAb-VEGF and a second regimen of che-motherapy plus high-dose RhuMAb-VEGF [65•]. In theirfinal analysis, the investigators reported endpoint data ina subset of patients with nonsquamous histology becausefatal hemoptysis was noted in four patients with squa-mous cell cancer. The overall response rates for the threecohorts were 31.3%, 21.9%, and 40%; time to progressionwas 6 months, 3.9 months, and 7 months; and mediansurvival was 14.9 months, 11.6 months, and 17.7months, respectively. A large phase III Eastern Coopera-tive Oncology Group/Cancer and Leukemia Group B trialcomparing standard chemotherapy with a regimen ofcombination chemotherapy plus RhuMAb-VEGF isunderway. RhuMAb-VEGF in combination with carbo-platin and paclitaxel is also being tested in the neoadju-vant setting as part of an ongoing phase II trial. A phase Itrial of combination targeted therapies (RhuMAb-VEGFplus OSI-774) is accruing patients.

Squalamine lactate (MSSI-1256F) is an angiostatic ste-roid that was originally isolated from the liver of the dog-fish shark (Squalus acanthicus). It has a unique mechanismof action in that it selectively inhibits the brush borderNa+/H+ exchanger isoform NHE3 [66]. This causes lumi-nal narrowing because of change in shape of endothelialcells leading to microvascular occlusion [67]. Squalaminelactate has shown preclinical synergy exclusively with plati-num compounds [68]. Schiller et al. [69] demonstratedobjective response rates of 27% and a median survival of10 months in chemotherapy-naïve patients with advancedNSCLC treated with a combination of squalamine and car-boplatin–paclitaxel.

Extracellular MatrixMatrix metalloproteinases (MMP) are part of a proteolyticcascade capable of degrading and remodeling the extracel-lular matrix (ECM). Subsequent migration of endothelialcells and tumor cells to the ECM facilitates angiogenesisand metastasis respectively. Inhibition of the MMPs there-fore cripples several pathways that foster tumor growth andsustenance in the ECM. Marimastat and prinomastat aretwo MMP inhibitors that have undergone clinical testing.Final results of a prospective, randomized, double-blind,placebo-controlled study of marimastat after response tofirst-line chemotherapy in patients with SCLC not onlyfailed to show a survival advantage for the marimastat armbut also showed an adverse impact on quality of life [70].In addition, prinomastat had no impact on survival in aphase III trial comparing combination chemotherapy withcarboplatin–paclitaxel plus prinomastat at three differentdosages [71]. Although efforts thus far have been disap-

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pointing, it may be premature to conclude that MMPs areineffective in the treatment of lung cancer because differentMMPs inhibit different molecules in the ECM.

Neovastat (AE-941; Aeterna, Orlando, FL) is a natu-rally occurring multifunctional antiangiogenic agent orig-inally isolated from shark cartilage. It inhibits MMP-2,MMP-9, and MMP-12. It also inhibits VEGF binding toendothelium, VEGF-dependent tyrosine phosphoryla-tion, and VEGF-induced vascular permeability and hassignificant antitumor activity [72]. Phase II data inpatients with refractory NSCLC showed a median survivalof 6.15 months [73]. A phase III trial comparing combi-nation chemotherapy and radiation with or without AE-941 in patients with newly diagnosed locally advancedNSCLC is underway.

Tumor VaccinesSeveral immunogenic antigens are overexpressed in SCLC,including the gangliosides GM2, GD2, GD3, and FUC-GM1. Novel strategies using GD3 as a target have beentested in patients with SCLC.

Mitumomab (BEC2; ImClone Systems, New York, NY)is an anti-idiotypic monoclonal antibody that mimics theGD3 antigen, thereby stimulating a strong immuneresponse to SCLC cells expressing GD3. BEC2 must beadministered with a nonspecific immune stimulant suchas the bacille Calmette-Guérin (BCG) vaccine to be fullyactive. Results of a phase I trial showed a median disease-free survival duration of 11 months for extensive-stage dis-ease and greater than 47 months for limited-stage disease[74]. A phase III study of optimally treated limited-stageSCLC with chemoradiotherapy followed by randomizationto either observation or BEC2/BCG vaccine is ongoing.

Autologous tumor vaccinesA novel approach in tumor immunology is derived fromgranulocyte-macrophage colony-stimulating factor (GM-CSF) is one of the most potent stimulants of the antitumorresponse [75]. Irradiated autologous tumor cells are trans-fected with a GM-CSF gene in such a way that they secretethe cytokine into the tumor milieu. The cell suspension isthen administered intradermally or subcutaneously in thepatient. A few patients undergoing this therapy have expe-rienced prolonged disease-free survival [76]. In a recentphase I study, two patients who were rendered disease freeby surgery were given an autologous tumor vaccine andcontinued to be free of disease at 43 and 42 monthsrespectively. Five patients had stable disease for durationsof 33, 19, 12, 10, and 3 months, respectively [77•].

ConclusionsTargeted therapy with novel agents has been a very activeand fashionable area of basic and translational research in

the past few years. However, the preclinical efficacy ofmany of these agents has not yet been transferred to theclinical arena. Development of new targeted agents for thetreatment of lung cancer has been challenging. Betterunderstanding of the disease, careful patient selection, andproper clinical trial design are needed before we can sortout a myriad of potential targets in our search for a few thatmay have an impact on a deadly disease, lung cancer.

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A novel GM-CSF–secreting tumor vaccine study in NSCLC.