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`
`SIR
`
`MINI REVIEW
`
`Cyrokine & Growth Factor Reviews Vol. 7. No. 2, pp.
`
`l33——l4l, 1996
`
`PII: S1359-6101(96)00016-0
`
`Copyright if; 1996 Elsevier Science Ltd. All rights reserved
`Printed in Great Britain.
`
`l359—6l0l/96 $32.00-l—0.00
`
`The Epidermal Growth Factor Receptor and its Ligands as Therapeutic
`Targets in Human Tumors
`
`Valerie Rusch,*T¢ John Mendelsohn§1l and Ethan Dmitrovskyill
`
`The epidermal growth factor receptor (EGFR) is detected on many non—haematopoietic tissues and
`is frequently overexpressed in human tumors. With its ligand, TGF-at, it forms a well—defined
`autocrine growth loop. Several clinical approaches, using EGFR as a therapeutic target, are being
`investigated, particularly monoclonal antibodies combined with chemotherapy, and pharmacological
`inhibition of downstream components of the EGFR signaling pathway. Copyright «rt 1996 Elsevier Science rm.
`
`Key words: EGFR ° Ligands ° Therapeutic targets - Human tumors.
`
`Growth factors and their receptors are known to play an
`important role in normal cell proliferation and in neo-
`plastic growth, but their signaling mechanisms are not
`yet fully elucidated. The epidermal growth factor receptor
`(EGFR) and its ligand, transforming growth factor alpha
`(TGF—oc), form one of the best defined autocrine growth
`loops in human tumors. Methods of interrupting this
`stimulatory loop by specific antagonists exist. The use of
`EGFR or its ligands as targets for the treatment of human
`malignancies is now being explored. Thus understanding
`the structure, function and potential clinical implications
`of regulating the EGFR loop is a paradigm for the study
`of other growth factors and their receptors in cancer
`diagnosis and treatment. The role of the EGFR and its
`ligands as therapeutic targets in human tumors is the
`focus of this review.
`
`STRUCTURE AND FUNCTION OF THE EGFR
`
`The EGFR is a 53-amino acid, 170-kDa trans-
`membrane peptide present on many non-haematopoietic
`human tissues. It is composed of three major domains:
`
`§Laboratories of Receptor Biology, and iMolecular Medicine,
`1lDepartment of Medicine, Memorial Sloan-Kettering Cancer
`Center, New York, 10021, USA.
`* To whom correspondence should be addressed at: Memorial
`Sloan-Kettering Cancer Center, 1275 York Avenue, New York,
`NY 10021, U.S.A. Tel: 212-639-5873; Fax:2l2—639-2807;
`e-mail: ruschv@,mskcc.org
`
`an extracellular domain connected via a transmembrane
`
`lipophilic segment to an intracellular protein tyrosine
`kinase domain. The extracellular domain binds receptor
`specific ligands and activates the cytoplasmic domain,
`which then initiates a cascade of biological signals from
`the cytoplasm to the nucleus, ultimately resulting in mito-
`genesis [1, 2].
`Five ligands for the EGFR have been identified: the
`epidermal growth factor (EGF), TGF-oz,
`the vaccinia
`virus growth factor (VGF), amphiregulin and cripto.
`Although there is little overall sequence conservation
`(approximately 22%), these EGF—like molecules bind the
`EGFR with similar afiinities. The most widely expressed
`ligand for the EGFR in human tissues is TGF~oc. The
`active form of TGF—:x, a 50 amino acid peptide, is pro-
`duced by proteolytic cleavage of the extracellular com-
`ponent of its precursor form, pro—TGF-ac, which includes
`a transmembrane domain.
`
`Following ligand binding, the EGFR undergoes dimer-
`ization [3]. Since a single ligand molecule binds to a
`single EGFR molecule, this is thought to occur through
`a conformational change in the receptor [4-6]. Dimer-
`ization activates the intrinsic protein tyrosine kinase via
`intermolecular autophosphorylation (Figure 1). The
`tyrosine autophosphorylated regions function as high
`affinity binding sites for cytoplasmic target proteins
`involved in the transmission of biological signals to the
`nucleus [7, 8]. Protein binding is mediated by conserved
`regions of approximately 100 amino acids termed SRC
`homology 2 (SH2) domains. SH3 domains, another con-
`served region of 50 amino acids whose function is poorly
`understood, are often associated with SH2 domains.
`
`133
`
`APOTEX EX. 1017-001
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`

`
`134
`
`V. Rusch et al.
`
`INACTIVE
`MONOMERS
`
`ACTIVE
`
`rnaus AUTO-
`PHOSPHORVLATION
`
`“
`
`DIMERS
`
`T Y R 05 I N E DE -
`PHOSPMORYLATION
`
`
`
`Although further investigation is required to define the
`mechanisms through which EGF R activation leads to
`mitogenesis, its effects on cell proliferation [15] are estab-
`lished. Introduction of either the TGF-at or EGF genes
`into cells expressing EGFRS can lead to cell
`trans-
`formation and enhanced proliferation [l6~l9]. TGF-oz
`over—expression is only weakly transforming in cultured
`cells that have a modest number of EGFRS on the cell
`
`surface. Conversely, EGFR overexpression at high levels
`only leads to transformation when cells are also exposed
`to high levels of EGF and TFG-oz. Thus,
`the estab-
`lishment of an autocrine loop responsible for trans-
`formation seems
`to
`require
`two distinct
`events,
`overexpression of EGFR and one of its ligands [20].
`Disruption of this growth stimulatory loop leads to Gl
`cell cycle arrest, and under some unusual circumstances,
`apoptosis [21]. This has been shown in several in vitro
`studies which also provide information about the poten-
`tial mediators of this G1 arrest. Apoptosis may result
`from interactions between the EGFR pathway and other
`growth regulatory loops. For instance, in a human col-
`orectal carcinoma cell line DiFi, which expresses high
`levels of EGFR, monoclonal antibodies to EGF R induce
`G1 cell cycle arrest and apoptosis. The addition of high
`concentrations of insulin or of insulin-like growth factor
`(IGF-1) delays apoptosis, but does not reverse G1 cell
`cycle arrest [22]. In these cells, blockade of the EGF
`receptor by monoclonal antibody results in elevation of
`the p27K"" inhibitor, accompanied by decreased cyclin-
`dependent kinase activity and decreased Rb phos-
`phorylation [22, 23]. Thus, the EGFR pathway plays an
`important role in cell transformation and proliferation
`and may also regulate aspects of apoptosis. For these
`reasons, it is of interest to examine expression of EGFR
`and its ligands in normal and neoplastic cells. A431
`human squamous carcinoma cells, which express high
`numbers of EGFR, are paradoxically growth-inhibited
`by the addition of nanomolar concentrations of EGF,
`which induces p2lC“"/WAR‘ expression, and reduces
`CDK2 activity. The induction of p2lC“°"“""F”‘ expression
`in these cells is inhibited by specific EGFR tyrosine kinase
`inhibitors, including anti-EGF receptor monoclonal anti-
`body 225 and tyrphostin AGl478, suggesting that its
`induction is a direct result of tyrosine kinase activation
`[24].
`
`EXPRESSION OF EGFR AND ITS LIGANDS IN
`HUMAN TISSUES AND TUMORS
`
`The EGFR is expressed in most normal human epi-
`thelial tissues and overexpressed in many human epi-
`thelial malignancies, including lung, breast, oesophageal,
`head and neck, and bladder cancers. Operexpression of
`EGFR ligands, particularly TGF-oz,
`is also frequently
`seen. EGFR mutations are rare, DNA amplification of
`the EGFR loci
`is more common, and EGFR over-
`expression often results from overexpression of its
`mRNA. In some tumors, EGFR overexpression is viewed
`
`APOTEX EX. 1017-002
`
`
`
`SUBST RATE
`PHOSPHOIIYLATION
`
`Figure 1. Ligand binding induces receptor dimerization, which
`leads to activation of the intrinsic protein tyrosine kinase
`activity and receptor autophosphorylation. Tyrosine auto-
`phosphorylation on multiple sites creates specific binding sites
`for target proteins, which bind to the activated receptor with
`their SH2 domains. (Schlessinger and Ullrich, Neuron 1992, 9,
`384, with permission.)
`
`Although not yet completely identified, target proteins
`are divided into two main groups: type-I proteins, which
`contain distinct enzymatic activities, and type-II proteins,
`which serve as regulatory subunits of downstream sig-
`naling proteins (Figure 2). Type-I proteins include phos-
`pholipase C-y (PCL-32) and the GTP-ase activating
`protein (GAP) of ras. Type-ll proteins include GRB-2
`which may also control ras signaling by stimulating a
`GDP-~GTP exchange factor or by inhibiting ras GTP-ase
`activity [1, 2]. The proteins further downstream in the
`cytoplasm which transmit signals to the nucleus are being
`defined. An important component of signaling appears
`to be the STAT proteins, so-called because they are recog-
`nized for their dual function in signal transduction in the
`cytoplasm and activation of transcription in the nucleus.
`The STAT proteins are known to be activated through
`the Jak kinases, a group of receptor-linked protein tyro-
`sine kinases. EGF causes activation of the STAT—l and -
`
`3 proteins in cultured hepatoma cells in the mouse liver,
`but whether the same mechanism is present in human
`tumors and whether other EGFR ligands function in a
`similar manner are not yet known [9—14].
`
`

`
`EGFR and its Ligands in Human Tumors
`
`135
`
`
`
`Ptd|ns—3K
`PLCV
`0
`O
`l
`fig
`DAG
`‘P3 Ptdlns(3)P
`
`l
`l Ca2+
`
`Figure 2. Direct phosphorylation (black dots on symbols) of substrates phospholipase C—y (PLCyi), phosphatidylinositol 3-kinase
`(ptdlns-3K), and ras GTPase—activating protein (GAP) to secondary events. including enzymatic activation and metabolite
`formation, activation of enzymatic functions by association, and serine/threonine phosphorylation (white dot on symbol) of
`substrates. Phosphorylation of raf is an indirect event, thought to be mediated via phosphokinase C. DAG = diaclyglycerol;
`1P3 = inositol l.4,5—triphosphate; Ptdlns(3)P = phosphatidylinositol 3-phosphate. (Modified from Ullrich and Schlessinger. Cell
`1990, 61, 208, with permission.)
`
`as an indicator of a poor clinical outcome, but this is not
`a universal
`finding [25—28]. Although EGFR over-
`expression is often present in epithelial carcinomas, its
`role in tumor initiation, growth and progression needs to
`be better defined. Non-small cell lung cancer (NSCLC)
`is one malignancy in which this has been extensively
`studied. and it serves as a paradigm for studies in other
`cancers.
`
`EGF R overexpression is found in lung cancer cell lines
`and primary tumors. Protein and binding assays show
`that NSCLC cell lines express higher levels of EGFR
`than do small cell lung cancer (SCLC) cell lines, and that
`this occurs in all histological subtypes of NSCLC [29,
`30]. Derynck at al. examined a large number of human
`tumors and tumor cell lines, including lung cancers, for
`the presence of TGF—oc and EGF R mRNA. By Northern
`analysis, TG F—a mRNA was strongly expressed in a squa-
`mous cell and a large cell carcinoma, but not in two
`adenocarcinomas of the lung or in normal lung tissue.
`Expression of EGFR mRNA was found in lung tumors
`of all histologies and in a normal lung specimen [31]. A
`larger study of lung cancers, derived from 68 patients,
`revealed ”5I—EGF binding in all NSCLC histologies, but
`especially in the squamous cell carcinomas. By Southern
`analysis, gene amplification was noted in two out of six
`samples of squamous cell carcinomas. In contrast to pre
`vious reports on breast and bladder cancers, there was
`no correlation between EGFR level and histological fea-
`tures of dilferentiation of tumor stage [32].
`Additional
`studies confirmed the frequent over-
`expression of EGFR in NSCLC, especially in squamous
`cell carcinomas, as assessed by binding assay and im-
`munohistochemistry [3342] Some of these studies cor-
`related EGFR overexpression with clinical outcome.
`Reported results vary widely with poorer survival being
`found in some reports [35, 37———39] and improved survival
`
`in others [36, 43]. These discrepant findings are probably
`explained by the small numbers of patients studied. the
`different techniques used to assess EGFR expression (e. g.
`paralfin embedded vs. frozen tissue, different monoclonal
`antibodies or binding assay) and the frequent lack of
`control specimens from normal lung tissue. One study
`examined EGFR overexpression by Northern analysis
`and immunohistochemistry on paired samples of primary
`tumor and benign lung obtained from 57 carefully staged
`patients and found no significant correlation with his-
`tology tumor stage or overall survival. This study also
`examined mRNA overexpression for
`three EGFR
`ligands, EGF, TGF-or and amphiregulin. EGF was not
`expressed in either primary tumors or benign lung tissue.
`whereas TGF-ac expression was increased in 61% of
`tumor vs. normal tissues, and amphiregulin expression
`was decreased in 63% of tumors [44]. Taken as a whole,
`these studies suggest that overexpression of EGFR and
`its ligand TGF-or is a frequent event, occurring in at least
`half of all NSCLC but does not clearly correlate with
`clinical or pathological indicators of aggressive tumor
`behavior.
`
`The presence of EGFR and TGF—:x overexpression in
`premalignant lesions of the lung, e. g. bronchial dysplasia,
`was only examined in a single study. in 62 preneoplastic
`bronchial lesions retrospectively identified in 34 patients
`who had resection of a NSCLC, overexpression of
`EGFR, TGF—oc and p53 was assessed by immuno-
`histochemistry [45]. Thirty (48%) of the bronchial lesions
`showed overexpression of EGF R, and this occurred as
`frequently in areas of metaplasia and atypia as it did in
`dysplasia and carcinoma in sizu. This study confirmed
`findings of the previous report
`[44]
`in which immu-
`nohistochemical staining for EGFR was consistently seen
`in the basal layer of the bronchial epithelium, but not in
`the pulmonary parenchyma. ln bronchial neoplasia. all
`
`APOTEX EX. 1017-003
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`

`
`136
`
`V. Rusch et al.
`
`‘layers of the epithelium stain for EGFR (Figure 3). In
`contrast, staining for TGF-oz is consistently seen in nerves
`and submucosal salivary glands, but is variably present
`in both normal and premalignant bronchial epithelium.
`Although TGF-ac was strongly expressed in 16 out of
`34 primary tumors, overexpression of TGF-oz did not
`consistently accompany malignant transformation of the
`bronchial epithelium.
`These findings suggest that EGFR overexpression may
`be a more important step in tumor initiation than pro-
`gression of NSCLC. Overexpression of TGF-ac, although
`common in established NSCLC, is a much less frequent
`event in early bronchial neoplasia. On the other hand,
`autocrine expression of EGF or of cripto does not appear
`to play an important growth-regulating role in overt
`NSCLC ([44] and V. Rusch, Memorial Sloan-Kettering
`Cancer Center). The potential clinical implications of
`decreased amphiregulin expression in NSCLC vs. normal
`lung tissues are not yet known.
`
`EGFR: A POTENTIAL TARGET FOR CANCER
`THERAPY
`
`The frequent overexpression of EGF R in NSCLC and
`other human tumors and its apparent role in tumori-
`genesis make it a target for cancer treatment. Four poten-
`tial strategies using EGFR as a therapeutic target are
`now under study: (1) monoclonal antibodies alone, (2)
`immunotoxins, (3) monoclonal antibodies in conjunction
`with standard chemotherapy and (4) pharmacological
`agents inhibiting downstream components of the EGFR
`pathway, e. g. tyrosine kinase inhibitors.
`Several rodent monoclonal antibodies to the EGFR
`
`have been tested in vitro and in xenograft tumor models
`[46]. Dean et al. tested a panel of rat monoclonal anti-
`bodies to EGFR against three head and neck carcinoma
`cell lines, and A549, a squamous cell carcinoma of the
`lung, and found partial growth inhibition. These mono-
`clonal antibodies also caused regression of EGFR over-
`expressing tumors in athymic nude mice [47]. Aboud-
`Pirak et al. tested iodine—l25-labeled monoclonal anti-
`
`body 108.4 against subcutaneous xenografts in nude mice
`of a human oral epidermoid carcinoma cell with high
`levels of EGF R expression, and found that it inhibited
`tumor growth, and prolonged the survival of animals.
`Experimental lung metastases generated by intravenous
`injection of these cells also were growth-inhibited by this
`antibody. The simultaneous administration of cisplatin
`enhanced the growth suppressive effects of the antibody
`in the subcutaneous xenograft tumor model [48].
`The most extensively studied murine monoclonal anti-
`bodies against EGFR are 528 IgG2a and 225 IgGl [49,
`50]. These differ in their isotypes but bind to EGFR with
`similar affinities, down-regulate tyrosine protein kinase
`activity to a comparable degree, and block activation of
`the receptor. In vitro cytoxicity studies against A431 cells
`reveal that 528 IgG2a, but not 225 IgGl, induces partial
`complement-mediated cytoxocity.
`In
`thymic mice,
`
`tumors generated by subcutaneous injection of A431 cells
`with activated macrophages, showed enhancement of
`antitumour effects with suboptimal doses of 528 IgG2a,
`suggesting that immune mechanisms may contribute to
`the anti-tumor effect of this antibody. In contrast, the
`225 IgGl is thought to act primarily by altering EGFR
`function [51].
`j
`,
`Anti—EGFR murine monoclonal antibodies have been
`
`safely administered in high doses in human clinical trials.
`In a Phase I trial, Perez-Soler et al. treated 15 patients
`(13 with NSCLC, two with head and neck cancer) with
`escalating doses of an anti-EGFR monoclonal antibody,
`RG 83852, which activates the receptor kinase and down-
`regulates the receptor. No clinical toxicities were seen
`at doses that resulted in high tumor EGFR saturation, ac-
`companied by an antibody-medicated 3-4-fold upregu-
`lation of tyrosine kinase activity 24 h post therapy [52].
`In another Phase I trial, Divgi et al. studied the effect of
`indium-labeled (‘”In)225 IgGl antibody in 20 patients.
`At doses ranging from 1
`to 300 mg, no toxicity was
`observed, and tumors were imaged by single photon-
`emission-computed tomography (SPECT) in all patients
`who received doses of 20 mg or more [53]. All patients
`produced anti-murine antibodies (known as a HAMA
`response), underscoring a limitation to this therapeutic
`strategy in human clinical trials. A chimerized form of
`this anti-EGFR monoclonal antibody currently being
`tested in Phase I—Il trials, could allow repeated antibody
`administration since it has not been found to elicit a
`
`HAMA response (J. Mendelsohn, Memorial Sloan-Kett-
`ering Cancer Center). Another important limitation of
`clinical treatment only using anti-EGFR monoclonal
`antibodies, is that, in most cases, these appear to suppress
`the growth of cultured tumor cells without inducing cyto-
`toxicity. Therefore, combined treatment with other can-
`cer therapies is likely required to achieve a clinically
`meaningful response.
`Anti—EGFR monoclonal antibodies have been linked
`
`to plant or bacterial toxins to breast cell-specific immuno-
`toxins. Vollmar et al.
`tested two chimeric molecules,
`
`Ab 225 and EGF, both conjugated to ricin. Both caused
`growth inhibition of HeLa cells which have a high EGFR
`number, but not of 3T3-NR6 cells which are EGFR
`deficient [54]. Using gelonin, a 605-ribosome-inactivating
`hemotoxin, conjugated to the murine monoclonal anti-
`body B4G7, Ozawa et al. showed cytoxicity of four
`EGFR-rich squamous cell carcinoma cell lines but not of
`two EGFR-deficient cell lines [55]. Kirk et al. developed
`a novel chimeric recombinant cytotoxin composed of two
`independent domains, TGF-oz and a 40 kDa segment
`of the Pseudomonas exotoxin protein, designated PE-
`40. When tested against several human breast and lung
`cancer cell lines, toxicity was found to be directly related
`to the EGFR expression levels of each cell line tested [56].
`Although anti-EGFR immunotoxins are effective in in
`vitro models,
`there is no clinical experience with this
`therapeutic approach. The potential toxicities of immuno-
`toxins against normal human tissues could limit the
`therapeutic efficacy in the clinical setting.
`
`APOTEX EX. 1017-004
`
`

`
`EGFR and its Ligands in Human Tumors
`
`l37
`
`Figure 3. Positive immunohistochemical staining for EGFR in an invasive carcinoma (a). The normal respiratory epithelium
`generally shows positivity in the basal layer (b), while the superficial cell layers are negative. In areas of dysplasia, positivity is
`often seen in more superficial layers as well (0), while areas of CIS show full thickness staining (d).
`
`APOTEX EX. 1017-005
`
`

`
`MAb 523
`HHHHH
`DOXQ
`
`MN? 523
`llllllllll
`DOXO
`
`control
`
`V. Rusch et al.
`
`(B)
`
`A
`1")
`
`E
`3
`G.)
`3;:
`(I)
`
`E
`2
`
`MAb 528
`
`138
`
`(A)
`
`14
`
`12
`
`r‘\1O
`('3
`
`E
`3
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`40
`
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`
`10
`
`20
`
`4o
`
`50
`
`0
`
`10
`
`20
`30
`d3YS
`days
`Figure 4. Antitumour activity of MAb 528 in combination with doxorubicin (DOXO) on well-established A431 squamous cell
`carcinoma xenografts in athymic mice. Treatment was started when tumors reached a mean size of 0.4 cm‘ on day ll in Fig. 4A,
`or day 9 in Fig. 4B. Each treatment group consisted of at least five animals. A total of 10 mice were treated in the combination
`group in the experiment plotted in Fig. 4A. and eight animals in Fig. 4B. Results are given in mean tumor sizeiSE. Error bars
`are not present when fewer than three animals remained alive in a certain treatment group. Doxorubicin (100 pg/20 g body weight)
`was given intraperitoneally on days 1 and 2 of the treatment (day 11 and 12 or day 9 and 10 after tumor cell inoculation). MAb
`528 (1 mg) was given intraperitoneally on day l of the treatment and twice a week thereafter for a total of 10 doses. (A) Treatment
`with either doxorubicin alone or MAb alone partially inhibited tumor growth. Doxorubicin in combination with MAb 528
`completely eradicated all tumors in the animals surviving on day 30 (N = 8). (B) Doxorubicin in combination with non-specific
`mouse IgG did not result in a greater antitumor effect than doxorubicin alone, while doxorubicin in combination with MAb 528
`resulted in the disappearance of all tumors in the animals surviving on day 30 (N = 6). Arrows show the days on which the
`treatment was administered. (Baselga et al., J Nat Cancer Inst 1993, 85, 1330, with permission.)
`
`Recently, the strategy of eliciting tumor cytoxicity by
`combined administration of anti-EGFR antibodies and
`
`chemotherapy has been explored. Baselga et al. used
`monoclonal antibodies 528 IgG2a and 225 IgGl indi-
`vidually in combination with doxorubicin to effectively
`treat xenograft tumors from human A431 squamous cell
`carcinoma and human MDA-468 breast adenocarcinoma
`cell
`lines. These monoclonal antibodies enhanced the
`
`antitumor effects of doxorubicin producing at least addi-
`tive growth suppression. These results were further con-
`firmed by the treatment of wel1—established xenografts in
`athymic mice [57]. Combination treatment of mice bear-
`ing A431 xenografts resulted in tumor eradication in at
`least 40% of the mice, compared to only temporary
`growth inhibition when either antibody or doxorubicin
`was administered alone (Figures 4 and 5). Similar
`enhancement of antitumor activity against xenografts
`was observed when 225 IgAl therapy was combined with
`cisplatinum treatment of human tumor xenografts [58].
`As a result of these promising pre-clinical findings, clini-
`cal trials testing the use of standard chemotherapeutic
`
`agents (e.g. doxorubicin, cisplatin) in conjunction with
`humanized anti-EGFR antibodies, are now in progress
`in patients with metastatic cancer.
`Another therapeutic strategy currently under study is
`to block downstream steps involved in EGFR pathway
`signaling [59—62]. Tyrosine knase inhibitors antogonize
`the critical step in this pathway. Osherov tested two
`groups of tyrosine kinase inhibitors (tyrphostins), one
`specific for the EGFR,
`the other for the neu/erb-B2
`kinases, and found that these could block EGF-induced
`mitogenic signaling in NIH3T3 cells [63]. More recently,
`Fry er al. tested a small molecule called PD 143035 which
`preferentially inhibits the EGF R tyrosine kinase. In a
`human squamous cell carcinoma cell line and in Swiss
`3T3 fibroblasts, PD 153035 selectively blocked EGF-
`mediated events, including early gene expression (c-jun),
`cell transformation and mitogenesis [64]. Conceivably,
`identification of other
`important downstream com-
`ponents of the EGFR pathway could allow the devel-
`opment of additional inhibitors. Clinical application of
`such compounds may not be realistic until issues of effec-
`
`APOTEX EX. 1017-006
`
`

`
`MAW25
`HHH
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`
`control
`
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`
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`
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`
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`
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`
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`
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`
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`
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`
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`
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`
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`
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`
`EGFR and its Ligands in Human Tumors
`
`139
`
`(B) 1'2
`
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`
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`
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`
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`
`DOXO+MAb528
`
`1o
`
`20
`
`so
`
`40
`
`so
`
`days
`Figure 5. (A) Antitumour activity of MAb 225 in combination with doxorubicin (DOXO) on well-established A431 squamous
`cell carcinoma xenografts. Treatment was started when tumors reached a mean size of 0.3 cm‘. A total of 10 mice were treated in
`the combination group. Results are given in mean tumors size:SE. Doxorubicin (100 ,ug/20 g body weight) was given intra-
`peritoneally on days 1 and 2. MAb 225 (1 mg) was given intraperitoneally on day 1 and twice a week thereafter for a total of 10
`doses. Treatment with either doxorubicin alone of MAb alone resulted in a transient inhibition of tumor growth. Doxorubincin.
`in combination with MAb 225, had a pronounced antitumor activity. Arrows show the days on which the treatment was
`administered. (B) Antitumor activity of MAb 528 in combination with doxorubicin (DOXO) on well-established MDA-468 breast
`adenocarcinoma xenografts. The treatment was started when the tumor reached a mean size of 0.2 cm’. A total of nine mice were
`treated in the combination group. Results are given in mean tumor size 1 SE. Doxorubicin (100 pg/20 g body weight) was given
`intraperiteoneally on days 1 and 2. MAb 528 (2 mg) was given intraperiotoneally on day 1 and twice a week thereafter for a total
`of 10 doses. Treatment with either doxorubicin alone or MAb alone resulted in transient inhibition of tumor growth. Arrows
`show the days on which the treatment was administered. (Beselga er al., J Nat Cancer Inst 1993. 85, 1331. with permission.)
`
`tive drug dose and delivery and selectively are addressed.
`Phase I clinical
`trials using these compounds will be
`needed.
`
`The EGF R and its ligands serve as a paradigm for the
`study of receptor-mediated signaling and how growth
`factors affect cellular transformation and proliferation.
`Translating our knowledge about this pathway to the
`treatment of human tumors is becoming a clinical reality,
`particularly employing combined use of cytotoxic chemo-
`therapy and anti—EGFR monoclonal antibodies. Con-
`tinued investigation of the mechanisms through which
`growth factors and their receptors transmit signals to the
`cell nucleus is needed to better understand how these
`
`pathways can be manipulated for the benefit of cancer
`patients.
`
`Acknowledgement: The authors wish to acknowledge Melody
`Owens for her expert assistance in the preparation of this manu-
`script.
`
`REFERENCES
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