Epidermal growth factor receptor (EGFR) antibody down-regulates mutant receptors and inhibits tumors expressing EGFR mutations

Activating mutations in the kinase domain of the EGF receptor have been reported in non-small cell lung cancer. The majority of tumors expressing these mutants are sensitive to ATP mimetics that inhibit the EGFR tyrosine kinase. The effect of antibodies that bind to the ectodomain of the receptor is less clear. We report herein the effects and mechanisms of action of the antibody cetuximab in lung cancer cells that naturally express receptor mutations and in ErbB-null 32D hematopoietic cells transfected with mutant EGFR. Treatment with cetuximab down-regulated EGFR levels and inhibited cell growth both in vitro and in vivo. This was associated with inhibition of ligand-independent EGFR signaling. These effects were seen in 32D cells arguing the growth inhibitory action was not because of the blockade of autocrine ligand action. Both antibody-induced EGFR down-regulation and inhibition of growth required receptor dimerization as monovalent Fab fragments only eliminated receptor levels or reduced cell proliferation in the presence of antihuman IgG. Finally, cetuximab inhibited growth of H1975 lung cancer cells and xenografts, which expressed L858R/T790M EGFR and were resistant to EGFR tyrosine kinase inhibitors. These data suggest that cetuximab is an effective therapy against mutant EGFR-expressing cancer cells and thus can be considered in combination with other anti-EGFR molecules.     

Atomistic probing of aptameric binding of CD19 outer membrane domain reveals an “aptamer walking” mechanism

We propose an integrated structural approach to search potential aptamer molecules for targeting cancer receptor proteins. We used the outer cellular domain of the B-lymphocyte antigen, CD19, as the target for this study. First, using available protein-aptamer structures deposited in the protein data bank as resources, structural annotation was performed to seek the most probable binding aptamer and its potential initial configuration to the CD19 structure. Using this initial structure, molecular dynamics (MD) simulations were performed for adjustment of the aptamer-binding. During this process, we observed an “aptamer walking” mechanism of the binding of the single-stranded RNA-aptamer to CD19: the aptamer molecule gradually adjusts its configurations and shifts toward favorable binding positions. However, the target molecule CD19 maintained a relatively stable conformation during this process. The interface area between the RNA-aptamer and CD19 increased from less than 8 nm² to over 12 nm² during a 2-μs MD simulation. Using a stable binding pose as the starting structure, we manually mutated the RNA-aptamer to a DNA-aptamer and found that the interface area was further increased to over 16 nm², indicating a stronger affinity compared to the RNA-aptamer. The RNA- and DNA-aptamers and their stable binding-poses to the CD19 molecule may be used as templates in designing potential aptamer molecules that target the B-cell marker molecule CD19 with enhanced specificity and stability.     

Synergistic anti-proliferative and pro-apoptotic activity of combined therapy with bortezomib, a proteasome inhibitor, with anti-epidermal growth factor receptor (EGFR) drugs in human cancer cells

The proteasome plays a pivotal role in the turnover of regulatory transduction proteins induced by activated cell membrane growth factor receptors. The epidermal growth factor receptor (EGFR) pathway is crucial in the development and progression of human epithelial cancers. Proteasome inhibition may sensitize human cancer cell lines to EGFR inhibitors. We investigated the growth inhibitory and pro-apoptotic effects of the proteasome inhibitor bortezomib in combination with anti-EGFR drugs, such as gefitinib, vandetanib, and cetuximab in EGFR-expressing human cancer cell lines. Bortezomib determined dose-dependent growth inhibition in a nine cancer cell line panel (IC(50) values, range 6-42 nM). A significant synergistic growth inhibitory effect was observed with the combination of bortezomib and each EGFR inhibitor in all cell lines (combination index, CI, range 0.10-0.55), which was accompanied by a significant induction in apoptosis by the combined treatment with bortezomib, cetuximab and vandetanib. In HCT-116 colon cancer and A549 lung adenocarcinoma cells, bortezomib plus EGFR inhibitor treatment induced a more effective inhibition of EGFR-activated down-stream signals, including a marked suppression in activated, phosphorylated Akt (P-Akt). In contrast, overexpression of a constitutively active P-Akt protected A549 cells by cell growth inhibition and apoptosis following treatment with bortezomib and EGFR inhibitors. The combined treatment with bortezomib and EGFR inhibitors has a synergistic growth inhibitory and pro-apoptotic activity in different human cancer cells which possess a functional EGFR-dependent autocrine growth pathway through to a more efficient and sustained inhibition of Akt.     

Roles of autophagy in cetuximab-mediated cancer therapy against EGFR

Cetuximab is an epidermal growth factor receptor (EGFR)-blocking antibody that is approved to treat several types of solid cancers in patients. We recently showed that cetuximab can induce autophagy in cancer cells by both inhibiting the class I phosphatidylinositol 3-kinase (PtdIns3K)/Akt/mammalian target of rapamycin (mTOR) pathway and activating the class III PtdIns3K (hVps34)/beclin 1 pathway. In the current study, we investigated the relationship between cetuximab-induced autophagy and apoptosis and the biological roles of autophagy in cetuximab-mediated cancer therapy. We found that cetuximab induced autophagy in cancer cells that show strong or weak induction of apoptosis after cetuximab treatment but not in those that show only cytostatic growth inhibition. Inhibition of cetuximab-induced apoptosis by a caspase inhibitor prevented the induction of autophagy. Conversely, inhibition of cetuximab-induced autophagy by silencing the expression of autophagy-related genes (Atg) or treating the cancer cells with lysosomal inhibitors enhanced the cetuximab-induced apoptosis, suggesting that autophagy was a protective cellular response to cetuximab treatment. On the other hand, cotreatment of cancer cells with cetuximab and the mTOR inhibitor rapamycin resulted in an Atg-dependent and lysosomal inhibition-sensitive death of cancer cells that show only growth inhibition or weak apoptosis after cetuximab treatment, indicating that cell death may be achieved by activating the autophagy pathway in these cells. Together, our findings may guide the development of novel clinical strategies for sensitizing cancer cells to EGFR-targeted therapy.Key words: EGFR, cetuximab, autophagy, apoptosis, cancer therapy     

Treatment of HNSCC cell lines with the EGFR-specific inhibitor cetuximab (Erbitux) results in paradox phosphorylation of tyrosine 1173 in the receptor

Overexpression of the epidermal growth factor receptor (EGFR, ErbB1, HER1) is frequent in head and neck squamous cell carcinomas (HNSCCs) and correlates with disease progression. Inhibition of EGFR with the kinase inhibitor AG1478 abolished receptor phosphorylation and reduced cell proliferation. However, treatment of HNSCC cells with cetuximab (Erbitux), a monoclonal antibody designed to block the EGFR ligand binding site, led to paradox EGFR activation due to hyperphosphorylation of tyrosine 1173, however, with a concomitant reduction in Erk1/2 phosphorylation levels. No pronounced influence on cell proliferation levels could be observed after treatment with this antibody. Since cetuximab appears able to activate EGFR in HNSCC cell lines, it is necessary to rethink the exact mechanisms by which cetuximab that recently was approved for the treatment of advanced head and neck cancer, inhibits tumor growth.     

Vaccine-induced ErbB (EGFR/HER2)-specific immunity in spontaneous canine cancer

Epidermal Growth Factor Receptor (EGFR) is overexpressed on a number of human cancers, and often is indicative of a poor outcome. Treatment of EGFR/HER2 overexpressing cancers includes monoclonal antibody therapy (cetuximab/trastuzumab) either alone or in conjunction with other standard cancer therapies. While monoclonal antibody therapy has been proven to be efficacious in the treatment of EGFR/HER2 overexpressing tumors, drawbacks include the lack of long-lasting immunity and acquired resistance to monoclonal therapy. An alternative approach is to induce a polyclonal anti-EGFR/HER2 tumor antigen response by vaccine therapy. In this phase I/II open-label study, we examined anti-tumor immunity in companion dogs with spontaneous EGFR expressing tumors. Canine cancers represent an outbred population in which the initiation, progression of disease, mutations and growth factors closely resemble that of human cancers. Dogs with EGFR expressing tumors were immunized with a short peptide of the EGFR extracellular domain with sequence homology to HER2. Serial serum analyses demonstrated high titers of EGFR/HER2 binding antibodies with biological activity similar to that of cetuximab and trastuzumab. Canine antibodies bound both canine and human EGFR on tumor cell lines and tumor tissue. CD8 T cells and IgG deposition were evident in tumors from immunized dogs. The antibodies inhibited EGFR intracellular signaling and inhibited tumor growth in vitro. Additionally, we illustrate objective responses in reducing tumors at metastatic sites in host animals. The data support the approach of amplifying anti-tumor immunity that may be relevant in combination with other immune modifying therapies such as checkpoint inhibitors.     

Synergistic Effect of Afatinib with Su11274 in Non-Small Cell Lung Cancer Cells Resistant to Gefitinib or Erlotinib

Epidermal growth factor receptor (EGFR) and c-MET receptors are expressed on many non-small cell lung cancer (NSCLC) cells. Current single agent therapeutic targeting of a mutant EGFR has a high efficacy in the clinic, but is not curative. Here, we investigated the combination of targeting EGFR and c-MET pathways in NSCLC cells resistant to receptor tyrosine kinase inhibitors (TKIs), using RNA interference and inhibition by TKIs. Different NSCLC cell lines with various genomic characteristics (H358, H1650 and H1975) were transfected with EGFR-specific-siRNA, T790M-specific-siRNA, c-MET siRNA or the combination. Subsequently EGFR TKIs (gefitinib, erlotinib or afatinib) or monoclonal antibody cetuximab were combined respectively with the c-MET-specific TKI su11274 in NSCLC cell lines. The cell proliferation, viability, caspase−3/7 activity and apoptotic morphology were monitored by spectrophotometry, fluorimetry and fluorescence microscopy. The combined effect of EGFR TKIs, or cetuximab and su11274, was evaluated using a combination index. The results showed that the cell lines that were relatively resistant to EGFR TKIs, especially the H1975 cell line containing the resistance T790M mutation, were found to be more sensitive to EGFR-specific-siRNA. The combination of EGFR siRNA plus c-MET siRNA enhanced cell growth inhibition, apoptosis induction and inhibition of downstream signaling in EGFR TKI resistant H358, H1650 and H1975 cells, despite the absence of activity of the c-MET siRNA alone. EGFR TKIs or cetuximab plus su11274 were also consistently superior to either agent alone. The strongest biological effect was observed when afatinib, an irreversible pan-HER blocker was combined with su11274, which achieved a synergistic effect in the T790M mutant H1975 cells. In a conclusion, our findings offer preclinical proof of principle for combined inhibition as a promising treatment strategy for NSCLC, especially for patients in whom current EGFR-targeted treatments fail due to the presence of the T790M-EGFR-mutation or high c-MET expression.     

A fibronectin scaffold approach to bispecific inhibitors of epidermal growth factor receptor and insulin-like growth factor-I receptor

Engineered domains of human fibronectin (Adnectins?) were used to generate a bispecific Adnectin targeting epidermal growth factor receptor (EGFR) and insulin-like growth factor-I receptor (IGF-IR), two transmembrane receptors that mediate proliferative and survival cell signaling in cancer. Single-domain Adnectins that specifically bind EGFR or IGF-IR were generated using mRNA display with a library containing as many as 10¹³ Adnectin variants. mRNA display was also used to optimize lead Adnectin affinities, resulting in clones that inhibited EGFR phosphorylation at 7 to 38 nM compared to 2.6 μM for the parental clone. Individual, optimized, Adnectins specific for blocking either EGFR or IGF-IR signaling were engineered into a single protein (EI-Tandem Adnectin). The EI-Tandems inhibited phosphorylation of EGFR and IGF-IR, induced receptor degradation, and inhibited down-stream cell signaling and proliferation of human cancer cell lines (A431, H292, BxPC3 and RH41) with IC₅₀ values ranging from 0.1 to 113 nM. Although Adnectins bound to EGFR at a site distinct from those of anti-EGFR antibodies cetuximab, panitumumab and nimotuzumab, like the antibodies, the anti-EGFR Adnectins blocked the binding of EGF to EGFR. PEGylated EI-Tandem inhibited the growth of both EGFR and IGF-IR driven human tumor xenografts, induced degradation of EGFR, and reduced EGFR phosphorylation in tumors. These results demonstrate efficient engineering of bispecific Adnectins with high potency and desired specificity. The bispecificity may improve biological activity compared to monospecific biologics as tumor growth is driven by multiple growth factors. Our results illustrate a technological advancement for constructing multi-specific biologics in cancer therapy.     

Rational identification of an optimal antibody mixture for targeting the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) is frequently dysregulated in human malignancies and a validated target for cancer therapy. Two monoclonal anti-EGFR antibodies (cetuximab and panitumumab) are approved for clinical use. However, the percentage of patients responding to treatment is low and many patients experiencing an initial response eventually relapse. Thus, the need for more efficacious treatments remains. Previous studies have reported that mixtures of antibodies targeting multiple distinct epitopes are more effective than single mAbs at inhibiting growth of human cancer cells in vitro and in vivo. The current work describes the rational approach that led to discovery and selection of a novel anti-EGFR antibody mixture Sym004, which is currently in Phase 2 clinical testing. Twenty-four selected anti-EGFR antibodies were systematically tested in dual and triple mixtures for their ability to inhibit cancer cells in vitro and tumor growth in vivo. The results show that targeting EGFR dependent cancer cells with mixtures of antibodies is superior at inhibiting their growth both in vitro and in vivo. In particular, antibody mixtures targeting non-overlapping epitopes on domain III are efficient and indeed Sym004 is composed of two monoclonal antibodies targeting this domain. The superior growth inhibitory activity of mixtures correlated with their ability to induce efficient EGFR degradation.     

Expression of Epidermal Growth Factor Receptor Detected by Cetuximab Indicates Its Efficacy to Inhibit In Vitro and In Vivo Proliferation of Colorectal Cancer Cells

Cetuximab is a chimeric mouse–human monoclonal antibody that targets the human epidermal growth factor receptor (EGFR). However, EGFR expression determined by immunohistochemistry does not predict clinical outcomes of colorectal cancer (CRC) patients treated with cetuximab. Therefore, we evaluated the correlation between EGFR levels detected by cetuximab and drug sensitivities of CRC cell lines (Caco-2, WiDR, SW480, and HCT116) and the A431 epidermoid carcinoma cell line. We used flow cytometry (FCM) to detect EGFR-binding of biotinylated cetuximab on the cell surface. Subcloned cell lines showing the highest and lowest EGFR expression levels were chosen for further study. Cytotoxic assays were used to determine differential responses to cetuximab. Xenograft models treated with cetuximab intraperitoneally to assess sensitivity to cetuximab. Strong responses to cetuximab were specifically exhibited by subcloned cells with high EGFR expression levels. Furthermore, cetuximab inhibited the growth of tumors in xenograft models with high or low EGFR expression levels by 35% and 10%–20%, respectively. We conclude that detection of EGFR expression by cetuximab promises to provide a novel, sensitive, and specific method for predicting the sensitivity of CRC to cetuximab.     

Daidzein Synergizes with Gefitinib to Induce ROS/JNK/c-Jun Activation and Inhibit EGFR-STAT/AKT/ERK Pathways to enhance Lung Adenocarcinoma cells chemosensitivity

Lung cancer is the major cause of cancer associated mortality. Mutations in EGFR have been implicated in lung cancer pathogenesis. Gefitinib (GF) is a RTKI (receptor tyrosine kinase inhibitor) first-choice drug for EGFR mutated advanced lung cancer. However, drug toxicity and cancer cell resistance lead to treatment failure. Consequently, new therapeutic strategies are urgently required. Therefore, this study was aimed at identifying tumor suppressive compounds that can synergistically improve Gefitinib chemosensitivity in the lung cancer treatment. Medicinal plants offer a vast platform for the development of novel anticancer agents. Daidzein (DZ) is an isoflavone compound extracted from soy plants and has been shown to possess many medicinal benefits. The anticancer potential of GF and DZ combination treatment was investigated using MTT, western blot, fluorescent microscopy imaging, flow cytometry and nude mice tumor xenograft techniques. Our results demonstrate that DZ synergistically induces c-Jun nuclear translocation through ROS/ASK1/JNK and downregulates EGFR-STAT/AKT/ERK pathways to activate apoptosis and a G0/G1 phase cell cycle blockade. In in-vivo, the combination treatment significantly suppressed A549 lung cancer cells tumor xenograft growth without noticeable toxicity. Daidzein supplements with current chemotherapeutic agents may well be an alternative strategy to improve the treatment efficacy of lung adenocarcinoma.     

靶点药物Cetuximab(C225)研究新进展

在许多肿瘤组织中均有表皮生长因子受体(epidermal growthfactor receptor,EGFR)的过表达,它的失调与肿瘤对化疗和放疗的耐受以及不良预后相关,为肿瘤的治疗提供了一个理想的分子靶点.Cetuximab(C225)是特异性EGFR单克隆抗体,与化疗或放疗联合应用时具有协同作用,具有毒副作用少、靶向性好等优点.Cetuximab(C225)已被批准用于对伊利替康抵抗的结直肠癌和头颈部鳞癌的治疗,对非小细胞肺癌、乳腺癌、胰腺癌等具有EGFR高表达肿瘤治疗的临床试验正在进行之中,为肿瘤治疗开辟了一个全新的领域.     

Roles of autophagy in cetuximab-mediated cancer therapy against EGFR

Cetuximab is an epidermal growth factor receptor (EGFR)-blocking antibody that is approved to treat several types of solid cancers in patients. We recently showed that cetuximab can induce autophagy in cancer cells by both inhibiting the class I phosphatidylinositol 3-kinase (PtdIns3K)/Akt/mammalian target of rapamycin (mTOR) pathway and activating the class III PtdIns3K (hVps34)/beclin 1 pathway. In the current study, we investigated the relationship between cetuximab-induced autophagy and apoptosis and the biological roles of autophagy in cetuximab-mediated cancer therapy. We found that cetuximab induced autophagy in cancer cells that show strong or weak induction of apoptosis after cetuximab treatment but not in those that show only cytostatic growth inhibition. Inhibition of cetuximab-induced apoptosis by a caspase inhibitor prevented the induction of autophagy. Conversely, inhibition of cetuximab-induced autophagy by silencing the expression of autophagy-related genes (Atg) or treating the cancer cells with lysosomal inhibitors enhanced the cetuximab-induced apoptosis, suggesting that autophagy was a protective cellular response to cetuximab treatment. On the other hand, cotreatment of cancer cells with cetuximab and the mTOR inhibitor rapamycin resulted in an Atg-dependent and lysosomal inhibition-sensitive death of cancer cells that show only growth inhibition or weak apoptosis after cetuximab treatment, indicating that cell death may be achieved by activating the autophagy pathway in these cells. Together, our findings may guide the development of novel clinical strategies for sensitizing cancer cells to EGFR-targeted therapy.     

Anti-tumor activity of the combination of cetuximab, an anti-EGFR blocking monoclonal antibody and ZD6474, an inhibitor of VEGFR and EGFR tyrosine kinases

PURPOSE: The epidermal growth factor receptor (EGFR) autocrine pathway plays an important role in cancer cell growth. Vascular endothelial growth factor A (VEGF-A) is a key regulator of tumor-induced endothelial cell proliferation and vascular permeability. ZD6474 is an orally available, small molecule inhibitor of VEGF receptor-2 (VEGFR-2), EGFR and RET tyrosine kinase activity. We investigated the activity of ZD6474 in combination with cetuximab, an anti-EGFR blocking monoclonal antibody, to determine the anti-tumor activity of EGFR blockade through the combined use of two agents targeting the receptor at different molecular sites in cancer cells and of VEGFR-2 blockade in endothelial cells. EXPERIMENTAL DESIGN: The anti-tumor activity in vitro and in vivo of ZD6474 and/or cetuximab was tested in human cancer cell lines with a functional EGFR autocrine pathway. RESULTS: The combination of ZD6474 and cetuximab determined synergistic growth inhibition in all cancer cell lines tested as assessed by the Chou and Talalay method. In nude mice bearing established human colon carcinoma (GEO) or lung adenocarcinoma (A549) xenografts and treated with ZD6474 and/or cetuximab for 4 weeks, a reversible tumor growth inhibition was caused by each drug. In contrast, a more significant tumor growth delay resulted from the combination of the two agents with an approximately 100-110 days increase in mice median overall survival as compared to single agent treatment. CONCLUSIONS: This study provides a rationale for evaluating in a clinical setting the double blockade of EGFR in combination with inhibition of VEGFR-2 signaling as cancer therapy.     

Rational identification of an optimal antibody mixture for targeting the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) is frequently dysregulated in human malignancies and a validated target for cancer therapy. Two monoclonal anti-EGFR antibodies (cetuximab and panitumumab) are approved for clinical use. However, the percentage of patients responding to treatment is low and many patients experiencing an initial response eventually relapse. Thus, the need for more efficacious treatments remains. Previous studies have reported that mixtures of antibodies targeting multiple distinct epitopes are more effective than single mAbs at inhibiting growth of human cancer cells in vitro and in vivo. The current work describes the rational approach that led to discovery and selection of a novel anti-EGFR antibody mixture Sym004, which is currently in Phase 2 clinical testing. Twenty-four selected anti-EGFR antibodies were systematically tested in dual and triple mixtures for their ability to inhibit cancer cells in vitro and tumor growth in vivo. The results show that targeting EGFR dependent cancer cells with mixtures of antibodies is superior at inhibiting their growth both in vitro and in vivo. In particular, antibody mixtures targeting non-overlapping epitopes on domain III are efficient and indeed Sym004 is composed of two monoclonal antibodies targeting this domain. The superior growth inhibitory activity of mixtures correlated with their ability to induce efficient EGFR degradation.Key words: EGFR, antibody synergy, functional screening, epitope binning, antibody combinations     

以EGFR为靶点的肿瘤分子靶向药物研究进展

随着分子生物学研究的进展,分子靶向治疗已成为除手术、放疗、化疗之外的第4种治疗方法,越来越多的用于临床治疗恶性肿瘤。分子靶向药物进入体内能够特异地选择致癌位点,杀伤肿瘤细胞,而不会波及周围正常的组织细胞,因此分子靶向治疗又被称为"生物导弹"。与传统化疗药物相比,分子靶向药物具有特异性强、疗效明显、副作用少等优点。按照分子靶向药物的性质主要归为两大类:一类是单克隆抗体,如西妥昔单抗等;另一类是单靶点或多靶点的小分子抑制剂,如吉非替尼等。表皮生长因子受体(EGFR)对肿瘤的生长、发展以及肿瘤干细胞的维持都有着非常重要的作用,并且在多种实体瘤中存在过表达或异常表达,因此在肿瘤治疗中,EGFR成为一个非常重要的用药靶点。现主要对目前国内已上市的针对EGFR的分子靶向药物最新的临床研究进展作一简要综述。     

A fibronectin scaffold approach to bispecific inhibitors of epidermal growth factor receptor and insulin-like growth factor-I receptor

Engineered domains of human fibronectin (Adnectins™) were used to generate a bispecific Adnectin targeting epidermal growth factor receptor (EGFR) and insulin-like growth factor-I receptor (IGF-IR), two transmembrane receptors that mediate proliferative and survival cell signaling in cancer. Single-domain Adnectins that specifically bind EGFR or IGF-IR were generated using mRNA display with a library containing as many as 10¹³ Adnectin variants. mRNA display was also used to optimize lead Adnectin affinities, resulting in clones that inhibited EGFR phosphorylation at 7 to 38 nM compared to 2.6 µM for the parental clone. Individual optimized Adnectins specific for blocking either EGFR or IGF-IR signaling were engineered into a single protein (EI-Tandem Adnectin). The EI-Tandems inhibited phosphorylation of EGFR and IGF-IR, induced receptor degradation and inhibited down-stream cell signaling and proliferation of human cancer cell lines (A431, H292, BxPC3 and RH41) with IC₅₀ values ranging from 0.1 to 113 nM. Although Adnectins bound to EGFR at a site distinct from those of anti-EGFR antibodies cetuximab, panitumumab and nimotuzumab, like the antibodies, the anti-EGFR Adnectins blocked the binding of EGF to EGFR. PEGylated EI-Tandem inhibited the growth of both EGFR and IGF-IR driven human tumor xenografts, induced degradation of EGFR and reduced EGFR phosphorylation in tumors. These results demonstrate efficient engineering of bispecific Adnectins with high potency and desired specificity. The bispecificity may improve biological activity compared to monospecific biologics as tumor growth is driven by multiple growth factors. Our results illustrate a technological advancement for constructing multi-specific biologics in cancer therapy.Key words: Adnectin, biologics, EGFR, IGF-IR, bispecific     

Primary and acquired resistance to anti-EGFR targeted drugs in cancer therapy

In recent years, the epidermal growth factor receptor (EGFR) has been recognized as a central player and regulator of cancer cell proliferation, apoptosis and angiogenesis and, therefore, as a potentially relevant therapeutic target. Several strategies for EGFR targeting have been developed, the most succesful being represented by monoclonal antibodies, that directly interfere with ligand-receptor binding and small molecule tyrosine kinase inhibitors, that interfere with activation/phosphorylation of EGFR. These agents have been authorized in advanced chemorefractory cancers, including colorectal cancer, non-small-cell lung cancer and head and neck cancer. However, evidence of resistance to these drugs has been described and extensive studies have been performed to investigate whether resistance to EGFR-targeted therapy is primary or secondary. Cellular levels of EGFR do not always correlate with response to the EGFR inhibitors. Indeed, in spite of the over expression and efficient inhibition of EGFR, resistance to EGFR inhibitors may occur. Moreover, given the genetic instability of cancer cells, genetic modifications could enable them to acquire a resistant phenotype to anti-EGFR therapies. Taken together, these findings support the importance of understanding the molecular mechanisms affecting cancer cell sensitivity or resistance to such inhibitors. This review will focus on the most relevant mechanisms contributing to the acquisition of sensitivity/resistance to EGFR inhibitors.     

Structural basis for EGF receptor inhibition by the therapeutic antibody IMC-11F8

Therapeutic anticancer strategies that target and inactivate the epidermal growth factor receptor (EGFR) are under intense study in the clinic. Here we describe the mechanism of EGFR inhibition by an antibody drug IMC-11F8. IMC-11F8 is a fully human antibody that has similar antitumor potency as the chimeric cetuximab/Erbitux and might represent a safer therapeutic alternative. We report the X-ray crystal structure of the Fab fragment of IMC-11F8 (Fab11F8) in complex with the entire extracellular region and with isolated domain III of EGFR. We compare this to our previous study of the cetuximab/EGFR interaction. Fab11F8 interacts with a remarkably similar epitope, but through a completely different set of interactions. Both the similarities and differences in binding of these two antibodies have important implications for the development of inhibitors that could exploit this same mechanism of EGFR inhibition.