Vecchi e nuovi “targets”, vecchi e nuovi farmaci Fortunato Ciardiello Division of Medical Oncology, Department of Clinical and Experimental Medicine, Second University of Naples, Italy 1 1

The EGFR (erbB) Family and Ligands TGFa Amphiregulin b-cellulin HB-EGF Epiregulin NRG2 NRG3 Heregulins b-cellulin Heregulins Cysteine-rich domains 100 44 82 33 36 59 24 48 79 28 The EGFR family consists of four members, HER1/erbB-1 through HER4/erbB-4. They all share the same structure – an extracellular domain that interacts with specific ligands, a short transmembrane domain and a tyrosine kinase domain within the cell, which is the activator of downstream signaling. Each receptor has some homology with the others but they vary in terms of ligand binding and tyrosine kinase activity. Tyrosine kinase domain C-terminus HER1 EGFR ErbB-1 HER2/neu ErbB-2 HER3 ErbB-3 HER4 ErbB-4

Ligand-induced Receptor Dimerization TGFa TGFa HER2/ neu HER3 HER4 EGFR Cell Membrane EGFR EGFR EGFR tyrosine kinase After ligand binding to each receptor, a complex process, the start of intracellular signaling, is activated. The first part of this process is formation of dimers of the receptor. Heterodimers form when two different receptors interact with each other and homodimers form when two of the same receptors dimerize. Receptor dimerization is essential for activation of tyrosine kinase activity and for downstream signaling, which leads to signal-dependent modulation of gene activation. tyrosine kinase HER2/neu nucleus

Receptor Dimerization is Essential for Intracellular Signaling Individual receptor pairings can consist of two molecules of the same type (homodimers), or two molecules of different types (heterodimers). All possible homo- and heterodimeric receptor complexes between members of the EGFR family have been identified in living cells. Formation of heterodimers can significantly affect the duration (different internalization rate) and the type (activation of different pathways) of signaling.

The EGFR/erbB Signaling Network Src Cbl PLCg PI3K Shp2 GAP Akt Bad S6K PKC Sos Grb2 Nck Ras-GTP Ras-GDP MAPK MEK RAF JNK JNKK PAK Abl Rac Vav Shc Grb7 Crk Jak Cytokines NRG3 (4) NRG2 (4) NRG1 (3,4) Amphi- regulin (1) HB-EGF (1,4) b-cellulin (1) Epiregulin (1,4) EGF (1) TGFa (1) LPA, thrombin ET, etc. NRG4 (4) Elk Jun Fos Myc Sp1 Egr1 Stat Apoptosis Migration Growth Adhesion Differentiation 1 3 2 4 Input layer Signal- processing layer Output layer Ligands Receptor dimers Adaptors and enzymes Cascades Transcription factors A complex signaling network can be triggered upon ligand binding to each receptor. There is great complexity due to the formation of different dimers and the activity of different signaling pathways in the cell. The final output through activation of nuclear events is an effect, direct or indirect, on important cellular functions that are very relevant for cancer formation, such as apoptosis, migration, growth, cell adhesion and differentiation. Yarden Y and Sliwkowski M. Nat Rev Mol Cell Biol 2001; 2: 127–37.

HER2/neu: Role in Breast Cancer HER2/neu plays an important role in the development and progression of human breast cancer. HER2/neu is overexpressed in 25-30% of human breast cancers. Protein overepression is generally due to gene amplification. HER2/neu overexpression is generally associated with poor prognosis and with resistance to hormone therapy.

TGFa: Role in Breast Cancer Mitogen for mammary epithelial cells. Estrogen-inducible in estrogen-dependent breast cancer. Expression increases from atypical hyperplasia to carcinoma in situ, to invasive carcinoma. Overexpression in 50-70% primary breast cancer.

EGFR: Role in Breast Cancer Expressed in 35-60% primary breast cancers. Overexpression correlates with multidrug resistance. Inverse correlation with ER and PgR. Overexpression correlates with resistance to hormonotherapy. Overexpression is generally associated with poor prognosis.

Co-expression of EGFR and ErbB-2 Co-expression of EGFR and ErbB-2 has been observed in 10-30% primary human breast carcinomas. Overexpression of both ErbB-2 and EGFR is associated with a poorer prognosis than overexpression of either receptor alone in breast cancer patients. A recent study has demonstrated an adverse prognostic independent role of P-ErbB-2 and EGFR coexpression in a subset of radically resected early breast cancers (Di Giovanna et al., JCO, 23: 1152-1160, 2005).

Open clinical issues for the therapeutic use of EGFR-targeted drugs Appropriate selection of potentially responding patients to EGFR-targeted agents: EGFR expression is necessary. Is EGFR expression sufficient? “Gain of function” somatic EGFR gene mutations. Expression of ligands and receptors of the erbB family. Downstream signaling molecules activation (MAPK, AKT). Timing and schedule for the combination of cytotoxic treatments and EGFR-targeted agents. Combination with other signal transduction inhibitors and molecular targeted therapies. Control of cancer cell resistance to EGFR-targeted agents.

No effect on tumor growth EGFR inhibitors in pretreated NSCLC patients: possible interpretration of clinical results PR Non-Responders SD 10 - 15% 20 - 30% 55 - 70% Apoptosis No effect on tumor growth Growth arrest EGFR-dependent Growth Non-EGFR-dependent Growth

Intermediate clinical TGFa TGFa TGFa Major clinical benefit: PR Intermediate clinical benefit: SD No clinical benefit: PD EGFR mutations or Wild-type EGFR +  HER2/HER3 +  EGFR ligands + loss of Cbl Smokers with wild-type EGFR (males? squamous?) EGFR mutations/ gene amplification Modified from an original concept of Carlos Arteaga

Possible mechanisms of resistance to EGFR inhibitors Target loss in cancer cells. Loss/inactivation of downstream signaling molecules. Activation of downstream signaling pathways through EGFR-independent mechanisms: Other cell membrane growth factor receptors (IGF-I R); PTEN-PI3K-AKT pathway; Raf-ras-MEK-ERK pathway; Pro-angiogenic growth factors (VEGF) production; Bcl-2/Bcl-xL pathway. Molecular changes in cancer cells which affect EGFR inhibitor uptake.

Resistance to gefitinib in EGFR-overexpressing MDA-468 breast cancer cells with mutant PTEN and constitutive Akt activation Bianco R, et al. Oncogene 2003;22:2812–2822.

Reconstution of PTEN function restores sensitivity to EGFR inhibitors in EGFR-overexpressing MDA-468 breast cancer cells Bianco R, et al. Oncogene 2003;22:2812–2822.

Strategies to overcome resistance to EGFR inhibitors Combination with other tumor cell-directed signal transduction inhibitors: Bcl-2/Bcl-xL PKA-I COX-2 MDM-2 MAPK AKT Combination with anti-angiogenic treatment modalities: VEGF signaling inhibitors (VEGF antisense oligos; VEGF neutralizing antibodies; VEGFR blocking antibodies; VEGFR small molecule inhibitors); Other angiogenesis inhibitors (endostatin).

Rational basis for combination of EGFR and VEGF inhibitors Activation of EGFR by EGF or TGFα can up-regulate the production of VEGF in cancer cells. EGFR inhibition reduces VEGF production. Resistance to EGFR inhibitors is associated with VEGF overexpression.

ZD6474: a VEGFR and EGFR inhibitor ZD6474 is a quinazoline, an orally bioavailable small molecule, that inhibits the tyrosine kinase domain of the VEGF Receptor 2 (KDR/FLK-1). ZD6474 is a potent angiogenesis inhibitor. ZD6474 is in phase II clinical development. ZD6474 also inhibits the EGFR tyrosine kinase. HN N O Cl F Gefitinib ZD6474 Wedge SR, et al. Cancer Res 2002;62:4645–4655. Ciardiello F, et al. Clin Cancer Res 2003;9:1546–1556.

Proposed antitumor activity of ZD6474 TGF ZD6474 EGFR ras raf Endothelial cell Cancer cell KDR MEK VEGF MAPK Block of endothelial cell proliferation Cyclin D1 Block of cancer cell proliferation

Development of resistant GEO colon cancer xenografts following chronic treatment with Cetuximab or Gefitinib, but not with ZD6474 Ciardiello F. et al. Clin Cancer Res 2004; 10: 784-793.

in GEO cells resistant to Cetuximab or to Gefitinib EGFR expression in GEO cells resistant to Cetuximab or to Gefitinib Effect of Gefitinib on EGFR phosphorylation in GEO cells resistant to Cetuximab or to Gefitinib Ciardiello F. et al. Clin Cancer Res 2004; 10: 784-793.

Characteristics of EGFR-targeted drugs resistant GEO cells Ciardiello F. et al. Clin Cancer Res 2004; 10: 784-793.

Acquired and constitutive resistance to EGFR inhibitors: Differential sensitivity to EGFR inhibitors Cell line PTEN status EGFR levels Gefitinib C225 ZD6474 MDA-468 mutated high low very low GEO normal moderate GEO-Gef-R GEO-Cet-R PC3 deleted PC3-Gef-R

PC3 PC3-Gef-R Acquired and constitutive resistance to EGFR inhibitors: Role of optimal pAKT inhibition PC3 PC3-Gef-R Cetuximab Gefitinib ZD6474 Gefitinib ZD6474 Ctr Ctr pAKT AKT pMAPK MAPK

ZD6474: Summary of preclinical data ZD6474 is an orally available, small molecule tyrosine kinase inhibitor that blocks both the VEGFR-2 (FLK-1/KDR) and the EGFR. ZD6474 in addition to inhibiting endothelial cell proliferation by blocking VEGF-induced signaling could inhibit cancer cell growth by blocking EGFR autocrine signaling. ZD6474 produces a dose-dependent inhibition of tumour growth in a range of human xenograft models. Long-term treatment of GEO xenografts with selective EGFR inhibitors results in the development of EGFR inhibitor-resistant cancer cells. Growth of EGFR inhibitor-resistant tumors can be inhibited by ZD6474. Inhibition of VEGF signaling by ZD6474 is a potential anti-cancer strategy in tumors that become resistant to EGFR inhibitors. ZD6474 inhibits AKT activation and cell proliferation in a panel of human cancer cell lines with intrinsic or acquired resistance to gefitinib or cetuximab.

Increase in activated EGFR/HER2 dimers in tamoxifen-resistant breast cancer cells Knowlden et al., Endocrinology 2003

Increase in activated EGFR/HER2 dimers in tamoxifen-resistant breast cancer cells Knowlden et al., Endocrinology 2003

ER-HER2 cross talk in ER/HER2 positive breast cancer Chou et al., JNCI 2004

ER-HER2 cross talk in ER/HER2 positive breast cancer Chou et al., JNCI 2004

resistance to tamoxifen HER2 overexpression Increased active EGFR/HER2 dimers with MAPK activation phosphorylation and activation of CoA-AIB1  levels of activated CoA-AIB1 increase estrogen agonist activity of complex “Tamoxifen-ER” resistance to tamoxifen

restored sensitivity to tamoxifen HER2 overexpression Increased active EGFR/HER2 dimers with MAPK activation phosphorylation and activation of CoA-AIB1  levels of activated CoA-AIB1 increase estrogen agonist activity of complex “Tamoxifen-ER” restored sensitivity to tamoxifen EGFR and/or HER2 inhibitors

ER-HER2 cross talk in ER/HER2 positive breast cancer: Summary EGFR-HER2 and ER pathways are linked in breast cancer cells overexpressing HER2 with cross-phoshorylation of both ER and EGFR and HER2, activation of AKT, MAPK and AIB1 by estrogen treatment. Elevated active EGFR-HER2 heterodimers are formed after continous exposure and development of tamoxifen resistance in breast cancer cells. Breast cancer cells overexpressing HER2 are growth stimulated by tamoxifen which behaves as an estrogen agonist in this situation. Treatment of breast cancer cells overexpressing HER2 with the EGFR selective small molecule tyrosine kinase inhibitor Gefitinib and/or with the anti-HER2 monoclonal antibody Trastuzumab could block ER/EGFR-HER2 cross-talk, eliminate tamoxifen’s agonistic effects and restore its antitumor activity.

Acquired resistance mechanisms to gefitinib in breast cancer and features of the phenotype: Mediated by the compensatory upregulation / activation of other growth factor receptor pathways to maintain cell growth i.e. IGF-1R signalling

Generation of MCF-7 breast cancer cells resistant to gefitinib: TAM-R TAM/TKI-R Plus 1 mM gefitinib (6 mths)

Characterization of gefitinib (1mM) resistant breast cells (1) Moderate expression of EGFR No detectable basal pEGFR and low levels of ERK1/2 Growth stimulation by IGF-I, IGF-II, heregulin-b and bFGF pEGFR1173 pERK1/2 Total EGFR TAM-R TAM/ TKI-R b-actin 50 100 150 200 250 300 350 EGF TGF-a IGF-I IGF-II Her-b bFGF PDGF Cell growth (% of control) * *Significant at p<0.05 IGF, insulin-like growth factor; bFGF, basic fibroblast growth factor TGF, transforming growth factor; PDGF, platelet-derived growth factor Jones et al., Endocrine-related Cancer 11: 1-22, 2004

Characterization of gefitinib-resistant breast cells (2) Production of IGF-II by RT-PCR Small reduction in IGF-1R expression but elevation in pIGF-1R Increased sensitivity to growth inhibition by the IGF-1R inhibitor AG1024 IGF-II TAM-R TAM/ TKI-R b-actin 20 40 60 80 100 120 1 5 10 AG1024 (mM) * Cell growth (% of control) TAM-R TAM/TKI-R pIGF-1R Total IGF-1R b-actin

Downstream targets of IGF-1R signalling Gefitinib resistant breast cells show elevated basal levels of activated AKT and PKCd Phosphorylation of AKT and PKCd was reduced in the presence of the IGF-1R inhibitor AG1024 42 kD 0 1 5 mM AG1024 60 kD pAKT b-actin 77 kD pPKCd TAM/TKI-R TAM-R TAM/TKI-R pPKCd pAKT b-actin

Despite elevated HER-2, TAM/TKI-R cells were insensitive to challenge with trastuzumab TAM-R TAM/TKI-R TAM/ TKI-R 140 TAM-R Total HER-2 120 Cell growth (% of control) 100 * b-actin 80 * * 60 * * 40 pHER-2 20 b-actin 1 5 10 50 100 Trastuzumab (nM) * Significant at p<0.05

Other studies have shown that: IGF-1R signalling is central in modulating the responses to trastuzumab in MCF7/HER-18 cells (Lu et al., JNCI 2001;93(24):1852) HER-2 can be activated by the IGF-1R which involves a physical association of the two receptors (Balana et al., Oncogene 2001;20:34)

Evidence of physical association between IGF-1R and HER-2, and co-localisation at tumour cell membranes IP: pIGF-1R WB: total HER-2 IP: total HER-2 WB: pIGF-1R TAM/TKI-R cells IGF-1R HER-2 IP, immunoprecipitation WB, Western blot IGF-1R / HER-2

Investigating the possible interaction between IGF-1R and HER-2 Concentrations of AG1024 that blocked IGF-1R phosphorylation also inhibited HER-2 phosphorylation TAM/TKI-R cells 1 h 24 h AG1024 (mM) 0 10 20 0 10 20 pIGF-1R pHER-2

Summary Type II receptors i.e. IGF1-R and/or InsR are important in both acquired and de novo gefitinib resistance in breast cancer and other cancer types. Via EGFR blockade, gefitinib can faciliate Type II receptor signalling which in turn can modulate EGFR phosphorylation. EGFR expression/activation can increase with long-term exposure to gefitinib which in turn may contribute to growth.

TAM-R cell Growth rate as % of control Treatment period (weeks) Strategies to improve gefitinib response Delay gefitinib resistance in breast cancer: combine gefitinib plus the resistance mechanism inhibitor e.g. Treat tamoxifen resistant breast cancer cells with gefitinib and an IGF-1R inhibitor Gefitinib (1mM) Gefitinib + AG1024 (5mM) 100 TAM-R cell Growth rate as % of control 50 Total cell kill 3 5 20 3 5 12 Treatment period (weeks)

Conclusions Single blockade of EGFR (or any growth factor) signalling through monotherapy is unlikely to be sufficient for maximum anti-tumour activity. Identification of components involved in resistance mechanisms is essential and the subsequent co-targeting of these elements in combinatorial strategies.