Epidermal growth factor receptor (EGFR) ubiquitination as a mechanism of acquired resistance escaping treatment by the anti-EGFR monoclonal antibody cetuximab

Cetuximab is an epidermal growth factor receptor (EGFR)-blocking antibody that has been approved for treatment of patients with metastatic colorectal cancer. In this study, we investigated biochemical changes in signaling pathways of a cetuximab-resistant subline of DiFi colorectal cancer cells (DiFi5) that was developed by exposing the parental sensitive cells to subeffective doses of cetuximab over an extended period of time. Compared with parental DiFi cells that express high levels of EGFR and in which cetuximab induces apoptosis, the cetuximab-resistant DiFi5 cells showed markedly lower protein levels of EGFR, an increased association of EGFR with Cbl, and an increased ubiquitination of EGFR. DiFi5 cells also had a markedly higher level of Src-Y416 phosphorylation both at baseline and on EGF stimulation. Although EGFR levels were low, DiFi5 cells responded to EGF stimulation with robust phosphorylation of EGFR on Y845 and strong phosphorylation of Akt and extracellular signal-regulated kinase, comparable to those of parental cells. Most importantly, inhibition of Src kinase activity with PP2 reversed the resistance of DiFi5 cells to cetuximab-induced apoptosis without affecting the levels of EGFR in the cells. Our results indicate that colorectal cancer cells may develop acquired resistance to cetuximab via altering EGFR levels through promotion of EGFR ubiquitination and degradation and using Src kinase-mediated cell signaling to bypass their dependency on EGFR for cell growth and survival.     

Primary resistance to cetuximab therapy in EGFR FISH-positive colorectal cancer patients

The impact of KRAS mutations on cetuximab sensitivity in epidermal growth factor receptor fluorescence in situ hybridisation-positive (EGFR FISH+) metastatic colorectal cancer patients (mCRC) has not been previously investigated. In the present study, we analysed KRAS, BRAF, PI3KCA, MET, and IGF1R in 85 mCRC treated with cetuximab-based therapy in whom EGFR status was known. KRAS mutations (52.5%) negatively affected response only in EGFR FISH+ patients. EGFR FISH+/KRAS mutated had a significantly lower response rate (P=0.04) than EGFR FISH+/KRAS wild type patients. Four EGFR FISH+ patients with KRAS mutations responded to cetuximab therapy. BRAF was mutated in 5.0% of patients and none responded to the therapy. PI3KCA mutations (17.7%) were not associated to cetuximab sensitivity. Patients overexpressing IGF1R (74.3%) had significantly longer survival than patients with low IGF1R expression (P=0.006), with no difference in response rate. IGF1R gene amplification was not detected, and only two (2.6%) patients, both responders, had MET gene amplification. In conclusion, KRAS mutations are associated with cetuximab failure in EGFR FISH+ mCRC, even if it does not preclude response. The rarity of MET and IGF1R gene amplification suggests a marginal role in primary resistance. The potential prognostic implication of IGF1R expression merits further evaluation.     

EGFR单克隆抗体治疗转移性结直肠癌的耐药分子机制

靶向表皮生长因子受体（EGFR）的单克隆抗体是转移性结直肠癌（mCRC）的重要治疗药物,但有效率并不理想,主要原因是存在严重的原发性和继发性耐药。本文从分子改变的方面就靶向EGFR单克隆抗体（anti EGFR mAb）治疗mCRC的耐药分子机制作一综述,旨在为进一步研究anti EGFR mAb耐药机制提供参考,为mCRC患者实现临床个体化治疗提供理论依据。     

Successful challenge with the fully human EGFR antibody panitumumab following an infusion reaction with the chimeric EGFR antibody cetuximab.

Infusion reactions are serious complications associated withmodern antibody therapy. In order to reduce the incidence andseverity of such reactions, the newer generations of monoclonalantibodies contain less or no mouse-specific protein sequences.We describe the clinical course of a patient who experiencedan infusion     

Colorectal adenocarcinoma-derived EGFR mutants are oncogenic and sensitive to EGFR-targeted monoclonal antibodies,cetuximab and panitumumab

Somatic mutations of epidermal growth factor receptor (EGFR) occur in ~3% of colorectal cancer (CRC) patients. Here, through systematic functional screening of 21 recurrent EGFR mutations selected from public data sets, we show that 11 colon cancer-derived EGFR mutants (G63R, E114K, R165Q, R222C, S492R, P596L, K708R, E709K, G719S, G724S and L858R) are oncogenic and able to transform cells in a ligand-independent manner. We demonstrate that cellular transformation by these mutants requires receptor dimerization. Importantly, the EGF-induced and constitutive oncogenic potential of these EGFR mutants are inhibited by cetuximab or panitumumab in vivo and in vitro. Taken together, we propose that a subset of EGFR mutations can serve as genomic predictors for response to anti-EGFR antibodies and that metastatic CRC patients with such mutations may benefit from these drugs as part of the first-line therapy.     

Rituximab (monoclonal anti-CD20 antibody): mechanisms of action and resistance

Rituximab, a chimeric monoclonal antibody targeted against the pan-B-cell marker CD20, was the first monoclonal antibody to be approved for therapeutic use. Treatment with rituximab at standard weekly dosing is effective in more than 50% of patients with relapsed or refractory CD20-positive follicular non-Hodgkin's lymphoma, but is not curative. It is less effective in other subtypes of CD20-positive lymphoma and for retreatment, even with CD20 still expressed. Thus, binding of rituximab to CD20 is not sufficient to kill many lymphoma cells, indicating that there are mechanisms of resistance. Mechanisms of cell destruction that have been demonstrated to be activated by rituximab binding to CD20 include direct signaling of apoptosis, complement activation and cell-mediated cytotoxicity. The relative importance of each of these mechanisms in determining clinical response to rituximab treatment remains a matter of conjecture. Thus, the role of various resistance pathways, some documented in experimental systems and others still hypothetical, remains uncertain. Resistance could potentially be mediated by alterations in CD20 expression or signaling, elevated apoptotic threshold, modulation of complement activity or diminished cellular cytotoxicity. As the first of an expanding class of anticancer agents, lessons learned regarding the mechanism of rituximab action and resistance will be of increasing importance.     

Acquired resistance to EGFR inhibitors: mechanisms and prevention strategies

Potent and specific, or relatively specific, inhibitors of epidermal growth factor receptor (EGFR) signaling, including monoclonal antibodies and small molecular weight compounds, have been successfully developed. Both types of agent have been found to have significant antitumor activity, especially when used in combination with radio- hormone- and chemotherapy in preclinical studies. Because of the potentiation of the conventional drug activity in these combination settings, inhibitors of EGFR signaling have often been referred to as sensitizers for chemotherapy or radiation, as well as drug resistance reversal agents. Phase II clinical trials in head-and-neck as well as lung cancer suggested this concept of chemosensitization might translate into the clinic, but this remains to be definitively proven in randomized, double-blind Phase III trials. Given the extensive preclinical literature on EGFR blocking drugs and the advanced clinical development of such agents, it is surprising that the possibility of development of acquired resistance to the EGFR inhibitors themselves, a common clinical problem with virtually all other currently used anticancer drugs, remains a largely unexplored subject of investigation. Here we summarize some of the possible mechanisms that can result in acquired resistance to EGFR-targeting drugs. Alternative combination therapies to circumvent and delay this problem are suggested.     

HER2 signaling and resistance to the anti-EGFR monoclonal antibody cetuximab: a further step toward personalized medicine for patients with colorectal cancer

Primary and acquired resistance to anti-epidermal growth factor receptor (EGFR) drugs are clinically relevant problems in patients with metastatic colorectal carcinoma. A complex network of molecular alterations is involved in this phenomenon. Bertotti et al. report the development of serially transplantable groups of tumor xenografts in immune-deficient mice from patient-derived, genetically characterized metastatic colorectal carcinoma samples. These experimental models ("xenopatients") might represent a novel approach to discover and characterize the mechanisms of resistance to anti-EGFR therapy and other molecularly targeted therapies in metastatic colorectal carcinoma. In this respect, Bertotti et al. were able to identify HER2 gene amplification as one such mechanism of resistance to anti-EGFR therapy.     

Mechanism of action and resistance to monoclonal antibody therapy

Monoclonal antibodies (MoAbs) are increasingly used in the treatment of patients with hematological malignancies and autoimmune diseases. The most commonly employed humanized and chimeric MoAbs are rituximab, alemtuzumab (Campath-1H, Ilex Pharmaceuticals, San Antonio, TX), and gemtuzumab-ozogamicin (Mylotarg, Wyeth-Ayerst Laboratories, St Davids, PA). The mechanism of action of these antibodies, and host and cellular factors influencing the response, are not completely known. Induction of apoptosis, antibody-dependent cell cytotoxicity (ADCC), and complement-mediated cell death (CDC) is the proposed mechanism of action of these antibodies. We review the current understanding of the mechanism of action of and resistance to these MoAbs.     

Overcoming resistance to first generation EGFR TKIs with cetuximab in combination with chemotherapy in an EGFR mutated advanced stage NSCLC patient

We report the case of a female never-smoking patient with an epidermal growth factor receptor (EGFR) mutation positive advanced non-small cell lung cancer (NSCLC) who received multiple lines of treatment. When she evolved clinical resistance to first generation EGFR tyrosine kinase inhibitors (TKI), she was treated with a fifth-line combination therapy with cetuximab and vinorelbine. This combination was highly active with a treatment response lasting for 9 months supporting the hypothesis that EGFR monoclonal antibodies in combination with chemotherapy may play a role in reversing EGFR-TKI resistance in EGFR mutation-positive NSCLC.     

抗EGFR单抗联合EGFR酪氨酸激酶抑制剂对人肺腺癌细胞凋亡的影响及其机制

目的:目前抗表皮生长因子受体(epidermal growth factor receptor, EGFR)的小分子酪氨酸激酶抑制剂吉非替尼(gefitinib)和抗EGFR单克隆抗体西妥昔单抗(cetuximab)在肺癌的临床应用中颇为广泛.鉴于这两种药物均针对EGFR分子靶点,因此本研究旨在就上述两种药物联合用药对人肺腺癌细胞凋亡的影响及其分子机制进行探讨.方法:吉非替尼和西妥昔单抗单独或联合用药作用于人肺腺癌细胞株A549和SPC-A-1后,用碘化丙啶标记,采用流式细胞术观察细胞凋亡情况,活细胞计数试剂盒测定各组细胞增殖抑制情况,Western印迹法检测两种药物对EGFR下游信号通路蛋白[磷酸化蛋白激酶B(phosphorylated Akt, p-Akt)、磷酸化EGFR(phosphorylated EGFR,p-EGFR)和磷酸化丝裂原激活蛋白激酶(phosphorylated mitogen-activated protein kinase, p-MAPK)]在蛋白水平表达的影响.结果:吉非替尼或西妥昔单抗单独作用后,A549和SPC-A-1细胞均明显凋亡,同时细胞增殖受到不同程度的抑制.Western印迹法检测p-Akt、p-EGFR和p-MAPK蛋白表达量均较不用药对照组下降.吉非替尼和西妥昔单抗联合作用后,肺腺癌细胞的凋亡、增殖以及在EGFR分子层次表现出较单一用药更为显著的作用.结论:吉非替尼和西妥昔单抗两种药物之间具有良好的协同作用,联合用药可能在临床治疗非小细胞肺癌中具有较大的应用潜力.     

Molecular mechanisms of cisplatin resistance

Platinum-based drugs, and in particular cis-diamminedichloroplatinum(II) (best known as cisplatin), are employed for the treatment of a wide array of solid malignancies, including testicular, ovarian, head and neck, colorectal, bladder and lung cancers. Cisplatin exerts anticancer effects via multiple mechanisms, yet its most prominent (and best understood) mode of action involves the generation of DNA lesions followed by the activation of the DNA damage response and the induction of mitochondrial apoptosis. Despite a consistent rate of initial responses, cisplatin treatment often results in the development of chemoresistance, leading to therapeutic failure. An intense research has been conducted during the past 30 years and several mechanisms that account for the cisplatin-resistant phenotype of tumor cells have been described. Here, we provide a systematic discussion of these mechanism by classifying them in alterations (1) that involve steps preceding the binding of cisplatin to DNA (pre-target resistance), (2) that directly relate to DNA-cisplatin adducts (on-target resistance), (3) concerning the lethal signaling pathway(s) elicited by cisplatin-mediated DNA damage (post-target resistance) and (4) affecting molecular circuitries that do not present obvious links with cisplatin-elicited signals (off-target resistance). As in some clinical settings cisplatin constitutes the major therapeutic option, the development of chemosensitization strategies constitute a goal with important clinical implications.     

Molecular mechanisms of resistance of leukemia to imatinib mesylate

Despite high rates of hematologic and cytogenetic responses to imatinib therapy, the emergence of resistance to imatinib has been recognized as a major problem in the treatment of Ph-positive leukemia. The high frequency of BCR-ABL mutations and amplifications represents the high degree of heterogeneity in patients with advanced phase of CML, in whom multiple leukemic clones may exist. Therefore, a single inhibitor is unlikely to able to block all mutants.     

Molecular mechanisms of resistance to imatinib in Philadelphia-chromosome-positive leukaemias

Imatinib (STI571 or CGP57148B) is an innovative treatment for tumours with a constitutively activated form of c-ABL, c-KIT, or PDGFR. Such tumours include Philadelphia-chromosome-positive (Ph-positive) leukaemias, gastrointestinal stromal tumours, and PDGFR-positive leukaemias. Diseases such as primary hypereosinophilia and dermatofibrosarcoma protuberans also seem to respond to imatinib. Clinical trials assessing the therapeutic effects of imatinib have shown that the drug is highly effective with few associated side-effects, achieving durable cytogenetic responses in many patients with chronic-phase BCR-ABL-positive leukaemias. However, the emergence of resistance, particularly in patients with acute leukaemias, has prompted intense research, and many are concerned about the future prospects for imatinib. The resistance has been found in patients with acute-phase disease, but may also occur in patients with chronic-phase disease. Two cellular mechanisms for resistance to imatinib have been identified: amplification of BCR-ABL gene and mutations in the catalytic domain of the protein. In addition, suboptimum inhibition of BCR-ABL in vivo could contribute to the selection of resistant cells. We have summarised all currently available data on resistance to imatinib, both published and unpublished, including the mechanisms of resistance identified so far, and their clinical relevance to the different forms of Ph-positive leukaemias is discussed. Furthermore, we discuss strategies to overcome or prevent the development of resistance.     

The mechanisms of resistance to EGFR-TKIs and challenges to overcome resistance in EGFR mutant non-small cell lung cancer

Somatic activating mutations in the epidermal growth factor receptor (EGFR) gene were first identified in 2004 from tumor tissues of non-small cell lung cancer (NSCLC) patients and pulmonary adenocarcinoma cell lines. Although pulmonary adenocarcinoma patients harboring EGFR mutations have increased sensitivity to EGFR tyrosine kinase inhibitors (TKIs), gefitinib and erlotinib, the primary and acquired resistant cases remain major clinical problems. Therapeutic strategies for such oncogene-driven carcinomas were intensively investigated at both the clinical and preclinical levels. In this review, we focused on one particular molecularly-defined subset of NSCLC that harbors activating mutations in the EGFR gene. We summarized the rational dissection of the mechanisms of drug sensitivity and resistance to EGFR-TKIs, and the promising molecular-centric strategies for further improving the outcomes of NSCLC patients with EGFR activating mutations.     

西妥昔单抗治疗非小细胞肺癌耐药机制的研究进展

目的:总结国内外关于西妥昔单抗治疗非小细胞肺癌中耐药机制的研究进展.方法:应用Medline、PubMed、EMBASE及中国生物医学文献数据库检索系统,以"西妥昔单抗、非小细胞肺癌、表皮生长因子受体及耐药机制"为关键词,检索1990-01-2010-02的相关文献.纳入标准: 1)EGFR旁路信号传导通路与西妥昔单抗抵抗的关系;2)非小细胞肺癌患者EGFR基因突变与西妥昔单抗耐药;3)EGFR下游信号转导通路的活化与西妥昔单抗抵抗的关系.根据纳入标准分析34篇文献.结果:由于表皮生长因子受体(EGFR)调节多种细胞功能,EGFR抑制剂西妥昔单抗耐药现象可能与多个传导通路紊乱有关,包括旁路信号途径的激活、受体突变、配体自分泌/旁分泌的产生以及下游信号蛋白的组成性活化.结论:目前对西妥昔单抗产生耐药的确切机制尚不明确,要想解决其耐药问题,进一步提高西妥昔单抗治疗非小细胞肺癌的疗效,尚需进行更多项进一步的临床和基础研究来加以证实.     

Correlation of EGFR, IDH1 and PTEN status with the outcome of patients with recurrent glioblastoma treated in a phase II clinical trial with the EGFR-blocking monoclonal antibody cetuximab

Mutation and gene amplification of the epithelial growth factor receptor (EGFR) is one of the most common genetic alterations in glioblastoma (GB). EGFR is, therefore, an attractive molecular target for the treatment of GB. EGFR-targeted therapies however have been largely ineffective in clinical trials. In this study, we investigated the correlation between the EGFR gene amplification status, expression of the EGFR variant III (EGFRvIII) and EGFR variant IV (EGFRvIV) mutations, expression of the phosphatase and tensin homologue gene on chromosome 10 (PTEN) and mutation of the isocitrate dehydrogenase 1 (IDH1) gene and the survival of patients suffering from recurrent glioblastoma who were treated with the EGFR-targeted monoclonal antibody cetuximab in a prospective phase II clinical trial. EGFR amplification was detected in 19 out of 35 GB (54%), EGFRvIII expression in 11 (31.4%) and EGFRvIV expression in 7 (20%). The EGFRvIII and EGFRvIV mutations were exclusively found in GB with EGFR amplification and were almost mutually exclusive with IDH1 mutation (EGFRvIII mutation was found in 1 out of 11 GB with an IDH1 mutation). Patients with an EGFR amplification lacking EGFRvIII expression had a significantly superior progression free survival (PFS) and a numerical better overall survival (OS) following treatment with cetuximab [median PFS 3.03 vs. 1.63 months (p=0.006); median OS 5.57 vs. 3.97 months (p=0.12)]. Within the subgroup of patients with EGFR amplification, patients with EGFRvIII positive glioblastoma had a worse survival [median PFS 1.63 vs. 3.03 months (p=0.01); median OS 3.27 vs. 5.57 months (p=0.08)]. Our observations indicate that the type of EGFR mutation may determine the outcome of GB patients treated with cetuximab. Prospective investigation of both the EGFR amplification and mutation status in clinical trials with EGFR-targeted therapies for GB is indicated.     

Molecular mechanisms of acquired resistance to tyrosine kinase targeted therapy

In recent years, tyrosine kinases (TKs) have been recognized as central players and regulators of cancer cell proliferation, apoptosis, and angiogenesis, and are therefore considered suitable potential targets for anti-cancer therapies. Several strategies for targeting TKs have been developed, the most successful being monoclonal antibodies and small molecule tyrosine kinase inhibitors. However, increasing evidence of acquired resistance to these drugs has been documented, and extensive preclinical studies are ongoing to try to understand the molecular mechanisms by which cancer cells are able to bypass their inhibitory activity.