EGFR: A molecular approach to cancer therapy

Targeting HER1/EGFR: A Molecular Approach to Cancer Therapy Carlos Arteaga The varying efficacy and toxicity of traditional cancer therapies has driven the development of novel targetbased agents. Members of the HER (Human Epidermal Receptor) family, in particular epidermal growth factor receptor (HER1/EGFR), are attractive therapeutic targets because they are overexpressed and/or dysregulated in many solid tumors. Activation of HER1/EGFR mediated through ligand binding triggers a network of signaling processes that promote tumor cell proliferation, migration, adhesion, and angiogenesis, and decrease apoptosis. Therefore, inhibiting HER1/EGFR activity could effectively block downstream signaling events and, consequently, tumorigenesis. Various approaches are being investigated to target members of the HER family, particularly HER1/EGFR and HER2. At the forefront are monoclonal antibodies and small molecules that inhibit the receptor tyrosine kinase activity. Monoclonal antibodies have been developed that act against HER1/EGFR and HER2. Monoclonal antibodies block ligand binding and prevent ligand-induced activation. Tyrosine kinase inhibitors block receptor phosphorylation, preventing downstream signal transduction. Several HER1/EGFR-targeted agents are advanced in clinical development and attention is focused on optimizing their clinical use. While this process may prove challenging, it promises to be beneficial. Semin Oncol 30 (suppl 7):3-14. © 2003 Elsevier Inc. All rights reserved.

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STIMATES based on recent studies indicate that over 3.2 million individuals in the United States were affected or diagnosed with cancer during the last 5 years.1 Global statistics from 2000 document 10 million new cases of cancer, 6 million cancer-related deaths, and 22 million people living with cancer.2 In the absence of improved treatment and prevention measures, these figures are projected to rise by 2020 to 15 million new cases and 10 million deaths.2 Traditional anticancer treatments such as chemotherapy and radiotherapy have advanced over the last 50 years. However, it is clear that these therapies are unlikely to cure or palliate many types of cancer. Chemotherapy and radiotherapy are limited by their lack of specificity.3 In addition, the side effects associated with these treatments often cause significant discomfort to cancer patients with an already poor prognosis. Therefore, there is a need to develop novel cancer-specific, nontoxic agents that, by targeting and inhibiting tumor cells, can increase patient survival and imSeminars in Oncology, Vol 30, No 3, Suppl 7 (June), 2003: pp 3-14

prove quality of life. There is also hope that these agents may stabilize tumors and convert aggressive cancers into chronic, indolent processes, similar to other controllable chronic inflammatory states or infections. Our improved understanding of the intracellular signaling processes responsible for transformation and tumor progression has enabled us to identify potential therapeutic targets. The HER (erbB) family of receptor tyrosine kinases (TKs) is one of these targets. HERs are transmembrane receptor TKs that play a pivotal role in normal cell growth, lineage determination, repair, and functional differentation.4 These receptors are overexpressed and/or dysregulated in several solid tumor types where they are associated with a more virulent phenotype.5-8 Ligand binding activates these receptors, causing receptor dimerization and autophosphorylation, triggering a signaling network that results in tumor cell proliferation,9 angiogenesis,10 motility, metastasis,11 and protection from apoptosis.12 Therefore, inhibiting members of the HER family may prevent tumor onset and progression. This article reviews the function of the HER family. It also introduces the various approaches being developed to disable this signaling network in tumors and some of the challenges these agents are now encountering. THE HER FAMILY

The HER family consists of four closely related transmembrane receptors: epidermal growth factor receptor (HER1/EGFR), HER2, HER3, and HER4. These receptors are structurally similar, although they have distinct characteristics that dictate their signaling specificity. Each receptor

From the Departments of Medicine and Cancer Biology, Breast Cancer Research Program, Vanderbilt-Ingram Comprehensive Cancer Center, Vanderbilt University School of Medicine, Nashville, TN. Address reprint requests to Carlos L. Arteaga, MD, Division of Oncology, Vanderbilt University School of Medicine, 2220 Pierce Avenue, 777 PRB, Nashville, TN 37232-6307. © 2003 Elsevier Inc. All rights reserved. 0093-7754/03/3003-0702$30.00/0 doi:10.1016/S0093-7754(03)00185-4 3

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has an extracellular ligand-binding domain, a transmembrane region, and an intracellular cytoplasmic domain.4 For example, the structure of HER1/EGFR is shown in Fig 1. The amino-terminal extracellular domain of HER1/EGFR has two cysteine-rich regions that form the ligand-binding domain. The transmembrane region is a single alpha-helix that anchors the receptor to the cell.4 The cytoplasmic domain contains a TK region and a carboxy-terminal tail that contains at least five tyrosine autophosphorylation sites. Importantly, the TK domains of HER2 and HER4 show approximately 80% homology to that of HER1/EGFR,7 whereas HER3 lacks intrinsic TK activity.13 In addition to these receptors, a mutant receptor, EGFRvIII, is commonly detected on many types of human tumors.14 EGFRvIII lacks residues 6–276 in the extracellular ligand-binding domain. This alteration results in ligand-independent, constitutive activation of the mutant receptor protein (Fig 1).15 Various ligands can bind to HER1/EGFR, HER3, and HER4 (Fig 2). These ligands have different specificities for each receptor,16 resulting in different cellular effects.17 Ligand binding induces HER1/EGFR homodimerization as well as heterodimerization with other HER receptors.6,18 Importantly, HER2 does not bind to any known ligand, but is the preferred heterodimerization partner for other HERs.19-22 HER3 homodimers are TK deficient and cannot initiate signal transduction.13,18 Epidermal growth factor receptor dimerization induces TK catalytic activity, which leads to autophosphorylation in several tyrosines within the receptor’s carboxyl-terminal tail. The resulting phosphotyrosines (Y992, Y1068, Y1086, Y1448, and Y1173) act as “docking” sites for a number of signal-transducing enzymes and adaptor proteins.4,23 Two major pathways are involved in HER signaling, the ras-raf-mitogen–activated protein kinase (MAPK)24 and the phosphatidylinositol 3-kinase (PI3K)/Akt pathways.25 The various post-receptor signaling cascades activated through ligand binding and dimer formation result in different cellular effects. For instance, the MAPK pathway is important mainly for cell proliferation26 and the PI3K pathway has a predominant role in cell survival27 (Fig 3). The mutant variant, EGFRvIII, also activates downstream signaling, but does not require ligand binding.14,15 It is clear that signaling by HER1/EGFR in tumor cells is

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highly modulated by the level of coexpressed HER receptors, as well as local receptor ligands. HER1/EGFR – A GOOD TARGET FOR ANTICANCER THERAPY

HER1/EGFR is perhaps the most widely studied member of the HER family, and extensive research provides compelling evidence for using HER1/ EGFR as a target for anticancer therapy. Abnormal receptor activation or dysregulation of the HER1/EGFR signal transduction pathways can result from a number of different mechanisms that are potentially relevant to the growth and/or development of human carcinomas. Overexpression of Receptors HER1/EGFR is frequently overexpressed in many types of cancer.5,28-32 In addition to HER1/ EGFR, many tumors, particularly in situ and invasive breast carcinomas, also overexpress HER2 (Table 1).5,33 Interestingly, several studies suggest that the level of HER1/EGFR expression correlates with poor disease prognosis and reduced survival.5,34 However, there is no consensus on the correlation between expression and prognosis for most tumors.35 This may be explained by the difficulties in quantifying HER1/EGFR expression and the inherent heterogeneity of human tumors. Overproduction of Growth Factors Another important mechanism of abnormal signaling by HER1/EGFR in tumor cells is the overproduction of HER1/EGFR ligands, such as transforming growth factor-␣ (TGF-␣) (Table 1). Overproduction of ligands can increase receptor activation in an autocrine manner, leading to enhanced transformation. The establishment of an autocrine ligand–receptor system causes independent growth of tumor cells and is believed to be a vital step in the development of hormone-resistant tumors, particularly of the breast and prostate.36,37 Ligand-Independent Receptor Activation As discussed, EGFRvIII is the most common HER1/EGFR mutant. EGFRvIII has a truncated extracellular domain, is constitutively activated, and is resistant to downregulation by endocytosis.15,38 EGFRvIII is overexpressed in some solid tumors, particularly in high-grade gliomas mainly as the result of gene amplification (Table 1).28,39 The presence of EGFRvIII is believed to confer a

TARGETING HER1/EGFR

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Fig 1. Structure of HER1/EGFR. (Reprinted from Int J Biochem Cell Biol, vol 31, A. Wells, EGF receptor, pp 637-643, 1999, with permission from Elsevier.4)

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Fig 2. The HERs – A dysfunctional family of receptors.13,92-96 EGF, epidermal growth factor; TGF, transforming growth factor; HB, heparin-binding; NRG, neuregulin.

more malignant tumor phenotype.38 Importantly, preclinical studies show that EGFRvIII can enhance tumor invasion in the absence of HER1/ EGFR ligands.40,41 Immunohistochemical studies show that EGFRvIII is present in other epithelial tumors such as breast, prostate, and non–small cell lung cancer (NSCLC) (Table 1)28; however, its clinical significance in these tumor types remains unproven. Cross-Talk With Heterologous Receptors The resulting signaling output from activated HER1/EGFR is highly dependent on the activating ligand, as well as the cellular levels of other coreceptors (HER family and other receptors).6 For example, overexpression of HER2 can potentiate HER1/EGFR signals.6 This is because, following ligand binding, HER1/EGFR homodimers are usually degraded; however, HER2 stabilizes HER1/ HER2 heterodimers and promotes their rapid recycling to the cell surface (Fig 3).42 The net effect of HER1/EGFR dimerizing with HER2 is increased signaling output to MAPK and the recruitment of other signal transduction intermediaries, such as the cytosolic TK Src. Therefore, although HER2 has no known binding ligand, it can still potenti-

ate signaling with its partners and enhance transformation and cancer progression.6,42 Furthermore, HER1/EGFR acts as a point of integration for signals arising from G-protein– coupled receptors and cytokine receptors. Consequently, HER1/EGFR can cross-talk with various heterologous receptors activated by neurotransmitters, lymphokines, and stress inducers.6 TARGETING THE HER FAMILY

Members of the HER family are established therapeutic targets for the development of novel anticancer agents. In view of this, several approaches are being used to block these receptors. The mechanism of action of HER1/EGFR inhibitors is shown in Fig 4 and Table 2 summarizes the compounds currently in clinical development. Extracellular Blockade This strategy uses antibodies to block the extracellular ligand-binding region of the receptor. Two anti-HER2 monoclonal antibodies (MAbs), trastuzumab (Herceptin; Genentech, Inc, South San Francisco, CA) and 2C4 (pertuzumab), with different epitopes, have been developed. Several

TARGETING HER1/EGFR

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Fig 3.

Key pathways involved in HER signaling.

anti-HER1/EGFR MAbs are also in clinical development. Trastuzumab is the first example of a successful HER-targeted agent and it proves the principle of

molecular targeted therapies in human cancer. It acts against HER2-overexpressing tumors, in part, by inducing receptor endocytosis.7 HER2 is amplified in approximately 25% to 30% of human breast

Table 1. Incidence of HER1/EGFR and HER2 Overexpression and/or Dysregulation in Selected Human Tumors5,28 –32

Tumor Type

HER1/EGFR Expression (%)

HER1/EGFR Mutation (%)

TGF-␣ Expression (%)

HER2 Expression (%)

Breast Colorectal Esophageal Glioblastoma HNSCC NSCLC Ovarian Pancreatic Prostate

14–91 25–77 35–88 40–60 95 40–80 35–70 30–50 41–100

78 NA NA 57 NA 16 73 NA NA

40–70 50–90 46–88 NA 88 85–100 55–100 95 NA

15–30 11–20 NA NA NA 0–35 0–32 19–45 14–86

Abbreviations: HER1/EGFR, epidermal growth factor receptor; TGF, transforming growth factor; HNSCC, head and neck squamous cell cancer; NSCLC, non–small cell lung cancer; NA, data not available.

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Fig 4. Approaches for targeting HER1/EGFR. Antibodies block ligand binding to the receptor inducing HER1/EGFR endocytosis, which may be followed by degradation by lysosomal enzymes. Tyrosine kinase inhibitors compete for binding with adenosine triphosphate in the receptor’s TK domain, blocking downstream signal transduction. (Source: Arteaga CL: The epidermal growth factor receptor: From mutant oncogene in nonhuman cancers to therapeutic target in human neoplasia. J Clin Oncol 19:32s-40s, 2001. Reprinted with permission of the American Society of Clinical Oncology.7)

cancers.8 Pivotal clinical trials have shown that trastuzumab provides significant clinical benefits as monotherapy,43,44 and improves survival when used in combination with chemotherapy com-

pared with chemotherapy alone in women with HER2-overexpressing metastatic breast tumors.45 Several ongoing studies are using trastuzumab in combination with chemotherapeutic and other

Table 2. Monoclonal Antibodies and Tyrosine Kinase Inhibitors in Clinical Development

Compound

Property

Specific Target

Highest Development Phase

Erlotinib Gefitinib EKB-569 GW-016 CI-1033 Trastuzumab 2C4 Cetuximab ABX-EGF h-R3

Reversible TKI Reversible TKI Irreversible TKI Reversible TKI Irreversible TKI Humanized IgG1 Humanized IgG1 Humanized IgG1 Fully human IgG2 Humanized IgG1

HER1/EGFR HER1/EGFR HER1/EGFR HER1/EGFR; HER2 HER1/EGFR; HER2; HER4 HER2 HER2 HER1/EGFR HER1/EGFR HER1/EGFR

III III I I II Launched I III II I

Abbreviations: TKI, tyrosine kinase inhibitor; HER1/EGFR: epidermal growth factor receptor; IgG, immunoglobulin G.

TARGETING HER1/EGFR

molecular therapies, including erlotinib HCl (Tarceva; Genentech, Inc, South San Francisco, CA).46 2C4 is a humanized anti-HER2 MAb that binds to a different HER2 epitope than trastuzumab.47 In contrast to trastuzumab, 2C4 inhibits the heterodimerization of HER2 with other HER family members. Studies indicate that this unique mechanism of action could result in efficacy against tumors with low HER2 expression that would not be targets for trastuzumab treatment.47 2C4 is currently in phase I clinical trials and is expected to enter phase II trials in 2003. Several antibodies directed against the extracellular ligand-binding domain of HER1/EGFR have been developed. Cetuximab (Erbitux; Imclone Systems, Inc, New York, NY) is a humanized antiHER1/EGFR MAb. Preclinical studies show that cetuximab binds to HER1/EGFR with an affinity (KD 0.1 nmol/L) comparable with that of the natural HER1/EGFR ligands, EGF and TGF-␣. The high-affinity binding of cetuximab to HER1/ EGFR prevents ligand binding and subsequent receptor activation. Several phase II clinical trials of cetuximab in combination with chemotherapy and/or radiotherapy have been completed in a range of indications, including NSCLC, head and neck squamous cell cancer (HNSCC), and colorectal cancer.48-53 Data from preclinical studies with cetuximab in combination with chemotherapy and/or radiotherapy are particularly encouraging and these combinations are a focus of its clinical development. Cetuximab is currently in phase III development for the treatment of HNSCC in combination with cisplatin, and colorectal cancer in combination with irinotecan. ABX-EGF, a fully humanized anti-HER1/EGFR MAb,54 has been investigated in a multiple-dose phase I trial in patients with various solid tumors and a multiple-dose phase II trial in patients with renal cell cancer.55 Trials with ABX-EGF are ongoing. h-R3 is another anti-HER1/EGFR MAb that has shown antitumor activity in preclinical studies.56 h-R3 is currently in clinical trials, and encouraging activity has been observed in combination with radiotherapy in patients with HNSCC.57,58 Intracellular Blockade Other HER-targeted agents act at an intracellular level. These compounds are low-molecular-

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weight TK inhibitors. HER1/EGFR-TK inhibitors compete with adenosine triphosphate for binding to the adenosine triphosphate site in the receptor’s kinase pocket.59 By inhibiting TK activity, these agents block both the receptor’s catalytic activity and autophosphorylation, preventing downstream signal transduction.60-63 Several of these small molecules are being investigated in clinical trials. Two agents currently in phase III development are erlotinib and gefitinib (Iressa; AstraZeneca, Wilmington, DE). Tyrosine kinase inhibitors have the theoretical advantage that, compared with agents that block activation at an extracellular level (ie, receptor MAbs), they can also block activating cytoplasmic signals. Interestingly, limited preclinical data suggest that erlotinib, but not gefitinib, can inhibit EGFRvIII.64,65 However, these preliminary data require confirmation. It is unclear whether this difference, if true, is caused by structural or potency differences between the agents or other, as yet unknown, cell-type– dependent factors. In addition, these agents are administered orally, a property that makes them suitable for chronic therapy.7 Erlotinib and gefitinib are both reversible, HER1/EGFR-specific inhibitors.66,67 However, recent studies show erlotinib also inhibits HER2 phosphorylation and downstream signal transduction in HER2/HER3 overexpressing cells.68 Similar data are available for gefitinib.69-71 Other reversible and irreversible covalent TK inhibitors in development inhibit two or more members of the HER family (Table 2). It is unclear at this stage whether these alternative approaches will provide any additional clinical benefit and/or a broader toxicity profile. Extensive preclinical studies with erlotinib and gefitinib show that both agents effectively inhibit tumor cell growth when used alone and in combination with various chemotherapeutic agents.72,73 These encouraging preclinical data provide a strong rationale for investigating both compounds in the clinical setting. Data from phase I/II monotherapy clinical trials with both erlotinib and gefitinib show that both agents are well tolerated and induce an antitumor effect.74-83 Furthermore, results from a phase II study of erlotinib monotherapy in patients with advanced NSCLC75,76 suggest the possibility of a survival benefit compared with historical data from chemotherapy reg-

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imens in a similar patient population.84,85 Findings from two phase II monotherapy trials with gefitinib in patients with advanced NSCLC also show evidence of response and quality-of-life benefits.82,83 Both erlotinib and gefitinib were generally well tolerated in these phase II studies. Recent data from two pivotal phase III clinical trials (INTACT I and II) of gefitinib in previously untreated, advanced NSCLC fail to show any survival benefit when added to standard, first-line platinum-based chemotherapy.86,87 The trials were large in size and patient characteristics were typical for advanced NSCLC. There was no difference in toxicity between the study groups, suggesting that inhibition of HER1/EGFR-TK does not enhance chemotherapy-induced side effects. In contrast to clinical studies, preclinical studies show that inhibition of HER1/EGFR TK in NSCLC modestly enhances chemotherapeutic activity.88,89 The most probable explanation for the “negative” outcomes of these studies is the lack of selection of patients in whom this drug– drug synergy may be beneficial. It is possible that patients who benefited from the combination were diluted within the total (unselected) study population; this would have masked any potential benefit from the experimental combinations. Until a predictive marker of response to therapy with HER1/EGFR inhibitors is identified, the interpretation of studies such as INTACT I and II is difficult. However, at this time, there is every reason to believe that HER1/ EGFR inhibitors will have a role in the treatment of patients with advanced NSCLC. This is supported by the results of the phase II monotherapy trials with gefitinib in patients with previously treated, advanced NSCLC, although neither trial was placebo controlled.82,83 A placebo-controlled phase III trial of erlotinib monotherapy for patients with advanced, refractory NSCLC (BR.21) is in progress and results are expected at the end of 2003. Two large phase III trials with erlotinib in combination with chemotherapy – TRIBUTE (erlotinib with carboplatin and paclitaxel) and TALENT (erlotinib with gemcitabine and cisplatin) – are in progress and are expected to be completed in late 2003. In these studies, erlotinib is being administered at its maximum tolerated dose (150 mg/day), resulting in high tissue exposure.74 In these pivotal trials, patients with an Eastern Cooperative Oncology performance status of 2 or stage IIIA disease are not

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eligible for inclusion. Therefore, the patient population is slightly different from that accrued in the INTACT trials. Patients were enrolled in this study regardless of their HER1/EGFR status, although it will be analyzed retrospectively. While erlotinib and gefitinib belong to the same class, they are distinct agents with potentially important pharmacologic differences. It is difficult to predict whether differences in agent pharmacology, dosing, patient characteristics, or regimen may result in different clinical benefit between these two drugs. Recent results highlight that preclinical studies of targeted agents, particularly in combination with other agents, may not be good predictors of clinical response. Therefore, to optimize the use of these agents, alternative approaches are being explored. One favored avenue of exploration is selecting responsive patients before therapy based on a predictive marker of response. A model for this approach is trastuzumab, where patients are selected for therapy based on the level of tumor HER2 overexpression. This approach was obvious for trastuzumab because preclinical studies consistently showed that HER2-overexpressing tumor cells, and not those with low HER2 levels, were sensitive to trastuzumab-induced growth inhibition. In contrast, preclinical and clinical studies have not found a strong correlation between HER1/EGFR level and response to HER1/EGFRtargeted therapies.69,70,76,77,79,90,91 This suggests that patient selection for trials with these agents should not be based solely on HER1/EGFR expression. Numerous studies are in progress to identify markers that may predict for response to HER1/ EGFR inhibitors. CONCLUSION

The identification of HER1/EGFR as an important receptor in the pathogenesis of human tumors has prompted considerable research, focusing in particular on the HER-family signaling network. Dysregulation of HER1/EGFR activity can occur as a result of several mechanisms, including receptor overexpression, ligand overproduction, the presence of constitutively active receptor mutants, and cross-talk with other amplified receptors and signaling systems, among others. Our increased understanding of the structure and function of these receptors has led to the development of various molecular targeted agents, such as MAbs

TARGETING HER1/EGFR

and small-molecule TK inhibitors. Preclinical and early clinical data from trials with erlotinib and other agents show that these inhibitors are well tolerated and could benefit patients with a variety of cancers. When data with other agents become available, their clinical application will become clearer and new questions and challenges will emerge. It is certain that further understanding of the HER-family signaling pathways and their interactions with other networks within tumor cells are necessary to optimize the clinical development of these targeted agents. Finally, a predictive marker that will help select patients for treatment with HER1/EGFR inhibitors is sorely needed to maximize the information derived from ongoing clinical studies. REFERENCES 1. Pisani P, Bray F, Parkin DM: Estimates of the worldwide prevalence of cancer for 25 sites in the adult population. Int J Cancer 97:72-81, 2002 2. Parkin DM: Global cancer statistics in the year 2000. Lancet Oncol 2:533-543, 2001 3. Rowinsky E: The pursuit of optimal outcomes in cancer therapy in a new age of rationally designed target-based anticancer agents. Drugs 60:1-14, 2000 (suppl 1) 4. Wells A: EGF receptor. Int J Biochem Cell Biol 31:637643, 1999 5. Salomon DS, Brandt R, Ciardiello F, et al: Epidermal growth factor-related peptides and their receptors in human malignancies. Crit Rev Oncol Hematol 19:183-232, 1995 6. Yarden Y, Sliwkowski MX: Untangling the ErbB signalling network. Nat Rev Mol Cell Biol 2:127-137, 2001 7. Arteaga CL: The epidermal growth factor receptor: From mutant oncogene in nonhuman cancers to therapeutic target in human neoplasia. J Clin Oncol 19:32S-40S, 2001 8. Slamon DJ, Clark GM, Wong SG, et al: Human breast cancer: Correlation of relapse and survival with amplification of the HER-2/neu oncogene. Science 235:177-182, 1987 9. Giordano A, Rustum YM, Wenner CE: Cell cycle: molecular targets for diagnosis and therapy: Tumor suppressor genes and cell cycle progression in cancer. J Cell Biochem 70:1-7, 1998 10. de Jong JS, van Diest PJ, van der Valk P, et al: Expression of growth factors, growth-inhibiting factors, and their receptors in invasive breast cancer. II: Correlations with proliferation and angiogenesis. J Pathol 184:53-57, 1998 11. Wells A: Tumor invasion: Role of growth factor-induced cell motility. Adv Cancer Res 78:31-101, 2000 12. Gibson S, Tu S, Oyer R, et al: Epidermal growth factor protects epithelial cells against Fas-induced apoptosis. Requirement for Akt activation. J Biol Chem 274:17612-17618, 1999 13. Guy PM, Platko JV, Cantley LC, et al: Insect cellexpressed p180erbB3 possesses an impaired tyrosine kinase activity. Proc Natl Acad Sci U S A 91:8132-8136, 1994 14. Moscatello DK, Holgado-Madruga M, Emlet DR, et al: Constitutive activation of phosphatidylinositol 3-kinase by a

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naturally occurring mutant epidermal growth factor receptor. J Biol Chem 273:200-206, 1998 15. Voldborg BR, Damstrup L, Spang-Thomsen M, et al: Epidermal growth factor receptor (EGFR) and EGFR mutations, function and possible role in clinical trials. Ann Oncol 8:1197-1206, 1997 16. Jones JT, Akita RW, Sliwkowski MX: Binding specificities and affinities of egf domains for ErbB receptors. FEBS Lett 447:227-231, 1999 17. Gullick WJ: The type 1 growth factor receptors and their ligands considered as a complex system. Endocr Relat Cancer 8:75-82, 2001 18. Pinkas-Kramarski R, Soussan L, Waterman H, et al: Diversification of Neu differentiation factor and epidermal growth factor signaling by combinatorial receptor interactions. EMBO J 15:2452-2467, 1996 19. Tzahar E, Pinkas-Kramarski R, Moyer JD, et al: Bivalence of EGF-like ligands drives the ErbB signaling network. EMBO J 16:4938-4950, 1997 20. Graus-Porta D, Beerli RR, Daly JM, et al: ErbB-2, the preferred heterodimerization partner of all ErbB receptors, is a mediator of lateral signaling. EMBO J 16:1647-1655, 1997 21. Klapper LN, Glathe S, Vaisman N, et al: The ErbB-2/ HER2 oncoprotein of human carcinomas may function solely as a shared coreceptor for multiple stroma-derived growth factors. Proc Natl Acad Sci U S A 96:4995-5000, 1999 22. Cho H, Mason K, Ramyar K, et al: Structure of the extracellular region of HER2 alone and in complex with the Herceptin Fab. Nature 421:756-760, 2003 23. Schlessinger J: Cell signaling by receptor tyrosine kinases. Cell 103:211-225, 2000 24. Blenis J: Signal transduction via the MAP kinases: Proceed at your own RSK. Proc Natl Acad Sci U S A 90:58895892, 1993 25. Burgering BM, Coffer PJ: Protein kinase B (c-Akt) in phosphatidylinositol-3-OH kinase signal transduction. Nature 376:599-602, 1995 26. Zhang W, Liu HT: MAPK signal pathways in the regulation of cell proliferation in mammalian cells. Cell Res 12: 9-18, 2002 27. Cantley LC: The phosphoinositide 3-kinase pathway. Science 296:1655-1657, 2002 28. Moscatello DK, Holgado-Madruga M, Godwin AK, et al: Frequent expression of a mutant epidermal growth factor receptor in multiple human tumors. Cancer Res 55:5536-5539, 1995 29. Garcia de Palazzo IE, Adams GP, Sundareshan P, et al: Expression of mutated epidermal growth factor receptor by non–small cell lung carcinomas. Cancer Res 53:3217-3220, 1993 30. Kumar VL, Majumder PK, Gujral S, et al: Comparative analysis of epidermal growth factor receptor mRNA levels in normal, benign hyperplastic and carcinomatous prostate. Cancer Lett 134:177-180, 1998 31. Nagane M, Lin H, Cavenee WK, et al: Aberrant receptor signaling in human malignant gliomas: Mechanisms and therapeutic implications. Cancer Lett 162:S17-S21, 2001 (suppl) 32. Di Lorenzo G, Tortora G, D’Armiento FP, et al: Expression of epidermal growth factor receptor correlates with disease

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relapse and progression to androgen-independence in human prostate cancer. Clin Cancer Res 8:3438-3444, 2002 33. Hynes NE, Stern DF: The biology of erbB-2/neu/HER-2 and its role in cancer. Biochim Biophys Acta 30:2-3, 1994 34. Nicholson RI, Gee JM, Harper ME: EGFR and cancer prognosis. Eur J Cancer 37:9-15, 2001 35. Arteaga CL: Epidermal growth factor receptor dependence in human tumorsmore than just expression? Oncologist 7:31-39, 2002 (suppl 4) 36. Normanno N, Kim N, Wen D, et al: Expression of messenger RNA for amphiregulin, heregulin, and cripto-1, three new members of the epidermal growth factor family, in human breast carcinomas. Breast Cancer Res Treat 35:293-297, 1995 37. De Miguel P, Royuela ??, Bethencourt R, et al: Immunohistochemical comparative analysis of transforming growth factor alpha, epidermal growth factor, and epidermal growth factor receptor in normal, hyperplastic and neoplastic human prostates. Cytokine 11:722-727, 1999 38. Pedersen MW, Meltorn M, Damstrup L, et al: The type III epidermal growth factor receptor mutation. Biological significance and potential target for anti-cancer therapy. Ann Oncol 12:745-760, 2001 39. Wong AJ, Ruppert JM, Bigner SH, et al: Structural alterations of the epidermal growth factor receptor gene in human gliomas. Proc Natl Acad Sci U S A 89:2965-2969, 1992 40. Lal A, Glazer CA, Martinson HM, et al: Mutant epidermal growth factor receptor up-regulates molecular effectors of tumor invasion. Cancer Res 62:3335-3339, 2002 41. Damstrup L, Wandahl Pedersen M, Bastholm L, et al: Epidermal growth factor receptor mutation type III transfected into a small cell lung cancer cell line is predominantly localized at the cell surface and enhances the malignant phenotype. Int J Cancer 97:7-14, 2002 42. Worthylake R, Opresko LK, Wiley HS: ErbB-2 amplification inhibits down-regulation and induces constitutive activation of both ErbB-2 and epidermal growth factor receptors. J Biol Chem 274:8865-8874, 1999 43. Cobleigh MA, Vogel CL, Tripathy D, et al: Multinational study of the efficacy and safety of humanized anti-HER2 monoclonal antibody in women who have HER2-overexpressing metastatic breast cancer that has progressed after chemotherapy for metastatic disease. J Clin Oncol 17:2639-2648, 1999 44. Vogel CL, Cobleigh MA, Tripathy D, et al: Efficacy and safety of trastuzumab as a single agent in first-line treatment of HER2-overexpressing metastatic breast cancer. J Clin Oncol 20:719-726, 2002 45. Slamon DJ, Leyland-Jones B, Shak S, et al: Use of chemotherapy plus a monoclonal antibody against HER2 for metastatic breast cancer that overexpresses HER2. N Engl J Med 344:783-792, 2001 46. Baselga J: Herceptin alone or in combination with chemotherapy in the treatment of HER2-positive metastatic breast cancer: pivotal trials. Oncology 61:14-21, 2001 (suppl 2) 47. Agus DB, Akita RW, Fox WD, et al: Targeting ligandactivated ErbB2 signaling inhibits breast and prostate tumor growth. Cancer Cell 2:127-137, 2002 48. Bonner JA, Raisch KP, Trummell HQ, et al: Enhanced apoptosis with combination C225/Radiation treatment serves

CARLOS ARTEAGA

as the impetus for clinical investigation in head and neck cancers. J Clin Oncol 18:47S-53S, 2000 49. Robert F, Ezekiel MP, Spencer SA, et al: Phase I study of anti-epidermal growth factor receptor antibody cetuximab in combination with radiation therapy in patients with advanced head and neck cancer. J Clin Oncol 19:3234-3243, 2001 50. Kies MS, Arquette M, Nabell L, et al: Final report of the efficacy and safety of the anti-epidermal growth factor antibody, cetuximab (IMC-C225), in combination with cisplatin in patients with recurrent squamous cell carcinoma of the head and neck (SCCHN) refractory to cisplatin containing chemotherapy. Proc Am Soc Clin Oncol 21:232a, 2002 (abstr 925) 51. Baselga J, Trigo JM, Bourhis J, et al: Cetuximab (C225) plus cisplatin/carboplatin is active in patients (pts) with recurrent/metastatic squamous cell carcinoma of the head and neck (SCCHN) progressing on a same dose and schedule platinumbased regimen. Proc Am Soc Clin Oncol 21:226a, 2002 (abstr 900) 52. Burtness BA, Li Y, Flood W, et al: Phase III trial comparing cisplatin (C) ⫹ placebo (P) to C ⫹ anti-epidermal growth factor antibody (EGF-R) C225 in patients (pts) with metastatic/recurrent head & neck cancer (HNC). Proc Am Soc Clin Oncol 21:226a, 2002 (abstr 901) 53. Saltz L, Rubin M, Hochster H, et al: Cetuximab (IMCC225) plus irinotecan (CPT-11) is active in CPT-11-refractory colorectal cancer (CRC) that expresses epidermal growth factor receptor (EGFR). Proc Am Soc Clin Oncol 21:2a, 2001 (abstr 7) 54. Yang X, Jia X, Corvalan JR, et al: Development of ABX-EGF, a fully human anti-EGF receptor monoclonal antibody, for cancer therapy. Crit Rev Oncol Hematol 38:17-23, 2001 55. Schwartz G, Dutcher J, Vogelzang N, et al: Phase 2 clinical trial evaluating the safety and effectiveness of ABXEGF in renal cell cancer (RCC). Proc Am Soc Clin Oncol 21:24a, 2002 (abstr 91) 56. Morales-Morales A, Duconge J, Caballero-Torres I, et al: Biodistribution of 99mTc-labeled anti-human epidermal growth factor receptor (EGF-R) humanized monoclonal antibody h-R3 in a xenograft model of human lung adenocarcinoma. Nucl Med Biol 26:275-279, 1999 57. Crombet T, Osorio M, Cruz T, et al: Use of the antiEGFR antibody h-R3 in combination with radiotherapy in the treatment of advanced head and neck cancer. Proc Am Soc Clin Oncol 21:14a, 2002 (abstr 53) 58. Winquist E, Nabid A, Sicheri D, et al: A phase I dose escalation study of a humanized monoclonal antibody to EGFR (hR3) in patients with locally advanced squamous cell cancer of the head and neck (SCCHN) treated with radiotherapy (RT). Proc Am Soc Clin Oncol 21:232a, 2002 (abstr 926) 59. Stamos J, Sliwkowski MX, Eigenbrot C: Structure of the epidermal growth factor receptor kinase domain alone and in complex with a 4-anilinoquinazoline inhibitor. J Biol Chem 277:46265-46272, 2002 60. Baselga J, Hammond L: HER-targeted tyrosine-kinase inhibitors. Oncology 63:6-16, 2002 61. Ciardiello F, Tortora G: Anti-epidermal growth factor receptor drugs in cancer therapy. Expert Opin Invest Drugs 11:755-768, 2002 62. Shawver LK, Slamon D, Ullrich A: Smart drugs: Ty-

TARGETING HER1/EGFR

rosine kinase inhibitors in cancer therapy. Cancer Cell 1:117123, 2002 63. Mendelsohn J: Targeting the epidermal growth factor receptor for cancer therapy. J Clin Oncol 20:1S-13S, 2002 64. Iwata KK, Provoncha K, Gibson N: Inhibition of mutant EGFRvIII transformed cells by tyrosine kinase inhibitor OSI774 (Tarceva). Proc Am Soc Clin Oncol 21:21a, 2002 (abstr 79) 65. Heimberger AB, Learn CA, Archer GE, et al: brain tumors in mice are susceptible to blockade of epidermal growth factor receptor (EGFR) with the oral, specific, EGFR-tyrosine kinase inhibitor ZD1839 (Iressa). Clin Cancer Res 8:34963502, 2002 66. Moyer JD, Barbacci EG, Iwata KK, et al: Induction of apoptosis and cell cycle arrest by CP-358,774, an inhibitor of epidermal growth factor receptor tyrosine kinase. Cancer Res 57:4838-4848, 1997 67. Baselga J, Averbuch SD: ZD1839 (“Iressa”) as an anticancer agent. Drugs 60:33-40, 2000 (suppl 1) 68. Akita RW, Dugger D, Lewis Phillips G, et al: Effects of the EGFR inhibitor Tarceva on activated ErbB2. Proc Am Assoc Cancer Res 43:1003, 2002 (abstr 4973) 69. Moulder SL, Yakes FM, Muthuswamy SK, et al: Epidermal growth factor receptor (HER1) tyrosine kinase inhibitor ZD1839 (Iressa) inhibits HER2/neu (erbB2)-overexpressing breast cancer cells in vitro and in vivo. Cancer Res 61:88878895, 2001 70. Moasser MM, Basso A, Averbuch SD, et al: The tyrosine kinase inhibitor ZD1839 (“Iressa”) inhibits HER2-driven signaling and suppresses the growth of HER2-overexpressing tumor cells. Cancer Res 61:7184-7188, 2001 71. Anderson N, Ahmad T, Chan K, et al: ZD1839 (Iressa), a novel epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, potently inhibits the growth of EGFR-positive cancer cell lines with or without erbB2 overexpression. Int J Cancer 94:774-782, 2001 72. Pollack VA, Savage DM, Baker DA, et al: Inhibition of epidermal growth factor receptor-associated tyrosine phosphorylation in human carcinomas with CP-358,774: Dynamics of receptor inhibition in situ and antitumor effects in athymic mice. J Pharmacol Exp Ther 291:739-748, 1999 73. Wakeling A, Guy S, Woodburn J, et al: ZD1838 (Iressa): an orally active inhibitor of epidermal growth factor signaling with potential for cancer therapy. Cancer Res 62:5749-5754, 2002 74. Hidalgo M, Siu LL, Nemunaitis J, et al: Phase I and pharmacologic study of OSI-774, an epidermal growth factor receptor tyrosine kinase inhibitor, in patients with advanced solid malignancies. J Clin Oncol 19:3267-3279, 2001 75. Pe´ rez-Soler R, Chachoua A, Huberman M, et al: A phase II trial of the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor OSI-774, following platinum-based chemotherapy, in patients (pts) with advanced-EGFR-expressing, non–small cell lung cancer (NSCLC). Proc Am Soc Clin Oncol 20:310a, 2001 (abstr 1235) 76. Pe´ rez-Soler R, Chachoua A, Huberman M. , et al: Determinants of tumor response and survival in patients with relapsing NSCLC treated with Tarceva (erlotinib HCl; OSI774). Final report of a phase II study. Presented at the American Society of Clinical Oncology Molecular Therapy Symposium, November 8-10, 2002, San Diego, CA

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77. Finkler N, Gordon A, Crozier M, et al: Phase 2 evaluation of OSI-774, a potent oral antagonist of the EGFR-TK in patients with advanced ovarian carcinoma. Proc Am Soc Clin Oncol 20:208a, 2001 (abstr 831) 78. Senzer NN, Soulieres D, Siu L, et al: Phase 2 evaluation of OSI-774, a potent oral antagonist of the EGFR-TK in patients with advanced squamous cell carcinoma of the head and neck. Proc Am Soc Clin Oncol 20:2a, 2001 (abstr 6) 79. Hidalgo M: Phase I studies/combination therapy with Tarceva (erlotinib HCl;OSI-774) in head and neck cancer. Presented at the First Annual Opinion Leader Consortium on Novel and Targeted Therapies for Head and Neck Cancer, San Juan, Puerto Rico, February 5-9, 2003 80. Ranson M, Hammond LA, Ferry D, et al: ZD1839, a selective oral epidermal growth factor receptor-tyrosine kinase inhibitor, is well tolerated and active in patients with solid, malignant tumors: results of a phase I trial. J Clin Oncol 20:2240-2250, 2002 81. Baselga J, Rischin D, Ranson M, et al: Phase I safety, pharmacokinetic, and pharmacodynamic trial of ZD1839, a selective oral epidermal growth factor receptor tyrosine kinase inhibitor, in patients with five selected solid tumor types. J Clin Oncol 20:4292-4302, 2002 82. Fukouka M, Yano S, Giaccone G, et al: Final results from a phase II trial of ZD1839 (‘Iressa’) for patients with advanced non–small cell lung cancer (IDEAL 1). Proc Am Soc Clin Oncol 21:298a, 2002 (abstr 1188) 83. Kris MG, Natale RB, Herbst RS, et al: A phase II trial of ZD1839 (‘Iressa’) in advanced non–small cell lung cancer (NSCLC) patients who had failed platinum- and docetaxelbased regimens (IDEAL 2). Proc Am Soc Clin Oncol 21:292a, 2002 (abstr 1166) 84. Gandara DR, Vokes E, Green M, et al: Activity of docetaxel in platinum-treated non–small-cell lung cancer: Results of a phase II multicenter trial. J Clin Oncol 18:131-135, 2000 85. Mattson K, Bosquee L, Dabouis G, et al: Phase II study of docetaxel in the treatment of patients with advanced non– small cell lung cancer in routine daily practice. Lung Cancer 29:205-216, 2000 86. Giaccone G: A phase III clinical trial of ZD1839 (‘Iressa’) in combination with gemcitabine and cisplatin in chemotherapy-naive patients with advanced non–small cell lung cancer (INTACT I). Ann Oncol 13:2, 2002 (suppl 5) (abstr 4) 87. Johnson D: ZD1839 (‘Iressa’) in combination with paclitaxel and carboplatin in chemotherapy-naive patients with advanced non–small-cell lung cancer (NSCLC): Results from a phase III clinical trial (INTACT II). Ann Oncol 13:127, 2002 (suppl 5) (abstr 468) 88. Sirotnak FM, Zakowski MF, Miller VA, et al: Efficacy of cytotoxic agents against human tumor xenografts is markedly enhanced by coadministration of ZD1839 (Iressa), an inhibitor of EGFR tyrosine kinase. Clin Cancer Res 6:4885-4892, 2000 89. Ciardiello F, Caputo R, Bianco R, et al: Antitumor effect and potentiation of cytotoxic drugs activity in human cancer cells by ZD-1839 (Iressa), an epidermal growth factor receptor-selective tyrosine kinase inhibitor. Clin Cancer Res 6:2053-2063, 2000 90. Christensen JG, Schreck RE, Chan E, et al: High levels of HER-2 expression alter the ability of epidermal growth factor

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receptor (EGFR) family tyrosine kinase inhibitors to inhibit EGFR phosphorylation in vivo. Clin Cancer Res 7:4230-4238, 2001 91. Saltz L, Rubin M, Hochster H: Acne-like rash predicts response in patients treated with cetuximab (IMC-C225) plus irinotecan (CPT-11) in CPT-11-refractory colorectal cancer (CRC) that expresses epidermal growth factor receptor (EGFR). Clin Cancer Res 7:3766, 2001 (suppl) (abstr 559) 92. Gregory H: Isolation and structure of urogastrone and its relationship to epidermal growth factor. Nature 257:325-327, 1975 93. De Larco JE, Reynolds R, Carlberg K, et al: Sarcoma growth factor from mouse sarcoma virus-transformed cells. Pu-

CARLOS ARTEAGA

rification by binding and elution from epidermal growth factor receptor-rich cells. J Biol Chem 255:3685-3690, 1980 94. Shoyab M, McDonald VL, Bradley JG, et al: Amphiregulin: A bifunctional growth-modulating glycoprotein produced by the phorbol 12-myristate 13-acetate-treated human breast adenocarcinoma cell line MCF-7. Proc Natl Acad Sci U S A 85:6528-6532, 1988 95. Shing Y, Christofori G, Hanahan D, et al: Betacellulin: A mitogen from pancreatic beta cell tumors. Science 259:16041607, 1993 96. Toyoda H, Komurasaki T, Uchida D, et al: Epiregulin. A novel epidermal growth factor with mitogenic activity for rat primary hepatocytes. J Biol Chem 270:7495-7500, 1995