Epidermal growth factor receptor mutations in non-small cell lung cancer: a basic science discovery with immediate clinical impact

A large body of preclinical work suggested that the epidermal growth factor receptor (EGFR) would be a successful target for therapy against non-small cell lung cancer (NSCLC), and this led to the development of oral, selective EGFR tyrosine kinase inhibitors (TKI) that improve symptoms and survival in patients with advanced NSCLC. However, not all patients benefit from this treatment, and there has been great interest in identifying the molecular correlates that predict for response to these agents. The recent detection of somatic mutations in EGFR that predict for response to the EGFR tyrosine kinase inhibitors has excited the scientific community. This discovery has far-reaching implications, not only for lung cancer patients treated with an EGFR TKI but also for future drug development in all malignancies.     

非小细胞肺癌表皮生长因子受体基因突变与分子靶向治疗

肺癌分子靶向治疗近年来取得较大进展.特别是针对表皮生长因子受体(EGFR)分子靶向药物表现出确定的临床效果.临床应用表明,EGFR基因酪氨酸激酶域体细胞突变与非小细胞肺癌患者对酪氨酸激酶抑制剂吉非替尼的敏感性相关.本文就EGFR生物学特点、EGFR在肺癌中的表达、EGFR基因突变率、EGFR基因突变与EGFR酪氨酸激酶抑制剂疗效的关系作一综述.     

Targeting the MET gene for the treatment of non-small-cell lung cancer

Recently, a better understanding of the specific mechanisms of oncogene addiction has led to the development of antitumor strategies aimed at blocking these abnormalities in different malignancies, including lung cancer. These abnormalities trigger constitutive activation of tyrosine kinase receptors (RTKs) involved in fundamental cell mechanisms such as proliferation, survival, differentiation and migration, and consequently the aberrant signaling of RTKs leads to cancer growth and survival. The inhibition of aberrant RTKs and downstream signaling pathways has opened the door to the targeted therapy era.In non-small-cell lung cancer (NSCLC), molecular research has allowed the discrimination of different aberrant RTKs in lung cancer tumorigenesis and progression, and thus the identification of several targetable oncogenic drivers. Following the development of small molecules (gefitinib/erlotinib and crizotinib) able to reversibly inhibit the epidermal growth factor receptor (EGFR) and signaling pathways mediated by anaplastic lymphoma kinase (ALK), respectively, the MET signaling pathway has also been recognized as a potential target. Moreover, according to current knowledge, MET could be considered both as a secondary oncogenic mechanism and as a prognostic factor. Several therapeutic strategies for inhibiting activated hepatocyte growth factor receptor (HGFR) and the subsequent downstream signaling transduction have been improved in order to block tumor growth. This review will focus on the MET pathway and its role in resistance to EGFR TK (tyrosine kinase) inhibitors, the different strategies of its inhibition, and the potential approaches to overcoming acquired resistance.     

New biological treatments for lung cancer

Therapies targeted on cell signal pathways that control cell division and tumor angiogenesis have been developed over the last five years for non small cell lung cancer (NSCLC) with some amazing results, in subgroups of selected patients, predicting more significant success in the upcoming years. Compounds targeted on EGF tyrosine kinase receptor have been tested in large clinical phase 2 and 3 trials including thousands of patients. Their efficacy has been proved, in second and third line trials, after first line cisplatin-based chemotherapy for non-mucinous adenocarcinoma in non-smokers, women and Asian patients. Response rates vary from 10% in non selected Caucasian patients to 40% in non-smoking Asian patients with long survivals. Therapeutic targeting improves success rates, either relying on EGFR gene amplification detection by FISH, or search for EGFR tyrosine kinase domain mutations. Commercial kits are available for routine molecular diagnosis of domain mutations potentially enabling molecular targeting in addition to clinical targeting. Angiogenesis inhibitors, especially monoclonal antibody to VEGF, bevacizumab, have also been developed in the last few years. Bevacizumab associated with classical cytotoxic chemotherapy led, in selected patients (with non squamous cell lung cancer and no past history of cardiovascular disease) to an increase of median survival to more than 12 months with tolerable toxicity. Other drugs that have both anti-EGFR activity and anti-angiogenic properties will be soon developed, since future bioactive anti-cancer drugs will probably be multi-targeted drugs.     

A simple view on lung cancer biology: The EGFR pathway

Epidermal growth factor receptor (EGFR) is a cell membrane tyrosine kinase receptor. Activating mutations at exon 19?and 21?of the EGFR gene are associated with the occurrence and development of lung adenocarcinoma. These gain of function mutations predict responsiveness to EGFR tyrosine kinase inhibitors (TKis), erlotinib or gefitinib and are also a favorable prognostic factor in lung cancer. Sequencing is the recommended technique to detect the mutations, but other more sensitive technics are under evaluation. Treatment as first line therapy by gefitinib is limited to lung cancer patients harboring an EGFR mutation. Erlotinib can be given regardless of the EGFR status as second or third line therapy, as well as maintenance therapy in patients with a stable disease after platinum based chemotherapy. In EGFR mutated tumors, most patients present a recurrence of the disease, despite an initial response on EGFR TKis. Two mechanisms of secondary resistance have been identified, the selection of the T790M mutation in EGFR exon 20?and the MET amplification. Other molecular anomalies as the ras mutations or the EMLA-ALK protein fusion are mutually exclusive with the EGFR mutations and are associated with primary resistance to EGFR TKis.     

Targeted therapy: An evolving world of lung cancer

Lung cancer remains one of the most fatal illnesses. Recent development in cancer genomics and molecular targeted therapy leads to a paradigm shift in management of advanced‐stage non‐small cell lung cancer. Patients with activated mutation of epidermal growth factor receptor (EGFR) responded dramatically to EGFR tyrosine kinase inhibitor such as gefitinib or erlotinib. Multiple randomized studies have showed EGFR tyrosine kinase inhibitor to be superior to standard first‐line chemotherapy in this biomarker‐selected population. As the vasculature is considered to be the ‘Achillus heel’ of the tumour, anti‐angiogenic treatment is considered to be a suitable target. Inhibition of vascular endothelial growth factor may improve the efficacy of chemotherapy, although a practical biomarker has not been identified. We have entered an era of personalized therapy for lung cancer and this evolvement holds great promises for better treatment in future.     

From combinatorial peptide selection to drug prototype (II): Targeting the epidermal growth factor receptor pathway

The epidermal growth factor receptor (EGFR), a tyrosine kinase, is central to human tumorigenesis. Typically, three classes of drugs inhibit tyrosine kinase pathways: blocking antibodies, small kinase inhibitors, and soluble ligand receptor traps/decoys. Only the first two types of EGFR-binding inhibitory drugs are clinically available; notably, no EGFR decoy has yet been developed. Here we identify small molecules mimicking EGFR and that functionally behave as soluble decoys for EGF and TGFα, ligands that would otherwise activate downstream signaling. After combinatorial library selection on EGFR ligands, a panel of binding peptides was narrowed by structure–function analysis. The most active motif was CVRAC (EGFR 283–287), which is necessary and sufficient for specific EGFR ligand binding. Finally, a synthetic retro-inverted derivative, _D(CARVC), became our preclinical prototype of choice. This study reveals an EGFR-decoy drug candidate with translational potential.     

Acquired resistance of non-small cell lung cancer to epidermal growth factor receptor tyrosine kinase inhibitors

Activation of epidermal growth factor receptor (EGFR) triggers anti-apoptotic signaling, proliferation, angiogenesis, invasion, metastasis, and drug resistance, which leads to development and progression of human epithelial cancers, including non-small cell lung cancer (NSCLC). Inhibition of EGFR by tyrosine kinase inhibitors such as gefitinib and erlotinib has provided a new hope for the cure of NSCLC patients. However, acquired resistance to gefitinib and erlotinib via EGFR-mutant NSCLC has occurred through various molecular mechanisms such as T790M secondary mutation, MET amplification, hepatocyte growth factor (HGF) overexpression, PTEN downregulation, epithelial-mesenchymal transition (EMT), and other mechanisms. This review will discuss the biology of receptor tyrosine kinase inhibition and focus on the molecular mechanisms of acquired resistance to tyrosine kinase inhibitors of EGFR-mutant NSCLC.     

Epidermal growth factor receptor inhibition strategies in oncology

Molecular targeting strategies for cancer therapy are distinct from conventional chemotherapy and radiotherapy in their potential to provide increased tumor specificity. One particular molecular target of high promise in oncology is the epidermal growth factor receptor (EGFR). The EGFR is overexpressed, dysregulated or mutated in many epithelial malignancies, and EGFR activation appears important in tumor growth and progression. Advances in signal transduction biology continue to sharpen our understanding regarding specific contributions of EGFR signaling networks to cancer behavior. Two predominant classes of EGFR inhibitors have been developed including monoclonal antibodies (mAbs) that target the extracellular domain of EGFR, such as cetuximab (Erbitux), and small molecule tyrosine kinase inhibitors (TKIs) that target the receptor catalytic domain of EGFR, such as gefitinib (Iressa) and erlotinib (Tarceva). Mechanisms of action for EGFR inhibitors have been investigated in preclinical model systems. Safety, activity, pharmacokinetics and pharmacodynamics have been assessed in clinical trials. The anti-EGFR mAbs and TKIs have partially overlapping toxicity profiles, but distinct routes of administration, serum half-lives and therefore dosing schedules. Both classes of agents show clear antitumor activity, and cetuximab and gefitinib have been recently FDA approved for colorectal and lung cancer indications respectively. However, the absence of survival benefit for EGFR TKIs in combination with chemotherapy in large-scale phase III lung cancer trials in 2003 underscores a major challenge in anti-EGFR oncology therapeutics; namely to identify those tumors and patients that will respond predictably to EGFR inhibitor approaches. Newly identified mutations in the EGFR catalytic domain that appear to confer sensitivity to EGFR TKIs promise to open new doors of investigation regarding response prediction. Advances will also require enhanced molecular understanding of the overall EGFR signaling network, and improved methods to gauge the dependence of individual tumors on EGFR signaling pathways for growth advantage. Results from newly reported phase III trials in 2004 now confirm a survival advantage for the use of EGFR inhibitors in combination with high-dose radiation in head and neck cancer, and in refractory lung cancer respectively. It appears likely that EGFR inhibitors (and other rationally designed molecular growth inhibitors) will play a meaningful role in cancer therapy in the years to come.     

Role of constitutively activated protein tyrosine kinases in malignant myeloproliferative disorders: an update

Modern molecular technology helped identify more than 10 protein tyrosine kinases related to myeloid malignancies, which allowed the development of small molecule inhibitors targeting deregulated protein tyrosine kinase activity. Protein tyrosine kinase deregulation can occur as a consequence of fusion gene formation because of chromosomal translocations, or as distinct gain-of-function point mutations. Although the tyrosine kinase inhibitor imatinib mesylate (Gleevec) targeting the ABL protein tyrosine kinase has revolutionized current chronic myeloid leukemia therapy, it became rapidly evident that overcoming the multiple cellular resistance mechanisms will be very challenging. To develop efficient therapeutic alternatives, one must understand the complex signal transduction mechanisms involved in transformation by deregulated protein tyrosine kinases. This article reviews the most recently identified molecular mechanisms involved in cell transformation by the BCR/ABL protein tyrosine kinase fusion and presents new members of the increasing family of deregulated protein tyrosine kinases involved in myeloproliferative disorders. In addition, the article discusses new, promising small molecule protein tyrosine kinase inhibitors and the molecular mechanism that may lead to resistance to these drugs. Finally, the article highlights putative alternative strategies that could be used to block signal transduction pathways of deregulated protein tyrosine kinase activity.     

Targeting non-small cell lung cancer with epidermal growth factor tyrosine kinase inhibitors: where do we stand, where do we go

Cytotoxic chemotherapy has only yielded modest gains in survival in lung cancer in the past decade. However, the development of agents targeting specific signaling pathways that drive carcinogenesis has heralded a major paradigm shift in the approach to treatment of cancer. In non-small cell lung cancer (NSCLC), many researchers have focused on the epidermal growth factor receptor (EGFR) because this protein is present on a relatively high proportion of non-small cell lung cancers and its intracellular tyrosine kinase activates a signaling cascade that drives tumor growth. Blockade of the EGFR by small molecule inhibitors of the tyrosine kinase, such as gefitinib and erlotinib, causes tumor regressions in NSCLC. Phase II monotherapy trials of EGFR tyrosine kinase inhibitors in patients with previously treated advanced NSCLC demonstrated anti-tumor activity with objective response rates of 10–19% with acceptable toxicities and an associated improvement in lung cancer symptomatology. Gefitinib is now an FDA approved treatment for advanced NSCLC previously treated with platinum and docetaxel-based therapies. However, phase III trials of gefitinib and erlotinib in combination with chemotherapy doublets have failed to demonstrate a survival advantage when compared with chemotherapy alone. It remains unclear why these drugs work so effectively in certain patients and so poorly in combination with chemotherapy. The goal of ongoing and future investigation is to identify which patients may benefit from this new therapeutic approach.     

Biomarkers and targeted therapies in non-small cell lung cancer: present and future treatments

Since several years, the perception of lung cancer has considerably evolved. Indeed, we have proceeded from a simple classification based on histology to a molecular dismemberment, with a lot of subtypes of tumors according to there molecular alteration profile. Mutations of the EGFR receptor define so a group of cancers particularly sensitive to EGFR tyrosine kinase inhibitors (TKI). Gefitinib has shown its efficacy in term of response and survival in first line treatment of NSCLC arboring EGFR mutations. Recently, the ALK-AML4 translocation has been found in approximately 5% of NSCLC, accessible to a specified targeted therapy (crizotinib) with response rate around 60%. NSCLC with HER2 mutation or amplification could be treated with trastuzumab, whereas treatments targeting Met pathway are currently in development. At last, several drugs active in case of DNA repair dysfunction, like PARP inhibitors, have already shown there efficacy in particular types of NSCLC. In a very near future, molecular screening of these molecular alterations should be systematic from the diagnostic, to allow a personalized treatment according to the mutation profile.     

Second-generation irreversible epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs): a better mousetrap? A review of the clinical evidence

The discovery of activating epidermal growth factor receptor (EGFR) mutations in non-small cell lung cancer (NSCLC) in 2004 heralded the era of molecular targeted therapy in NSCLC. First-generation small molecule, reversible tyrosine kinase inhibitors (TKIs) of EGFR, gefitinib and erlotinib, had been approved for second- or third-line treatment of NSCLC prior to the knowledge of these mutations. However, resistance to gefitinib and erlotinib invariably develops after prolonged clinical use. Two second-generation irreversible EGFR TKIs, afatinib (BIBW 2992) and dacomitinib (PF-00299804), that can potentially overcome the majority of these resistances are in late stage clinical development. Here I will review the clinical data of EGFR TKIs and discuss the appropriate future role of afatinib and dacomitinib in NSCLC: whether as replacement of erlotinib or gefitinib or only after erlotinib or gefitinib failure and whether different subgroups would benefit from different approaches.     

Clinical aspects of epidermal growth factor receptor inhibitors: benefit and risk

Gefitinib and erlotinib are small molecules that selectively inhibit epidermal growth factor receptor (EGFR) tyrosine kinase activity. Developmental studies of either drug have failed to show synergistic effects when combined with cytotoxic drugs as the first line treatment in patients with advanced non-small cell lung cancer, but erlotinib has shown survival prolongation when compared with best supportive care in patients with recurrence. Female gender, adenocarcinoma histology and lack of smoking history are considered to be clinical factors predicting response. Being positive for EGFR mutations in exons 18-24 in cancer cells has a strong correlation with response. On the other hand, preceding idiopathic pulmonary fibrosis, male gender and history of smoking appear to be risk factors for EGFR tyrosine kinase inhibitor-induced interstitial lung disease in the Japanese population. Reports on these factors predicting response or risk for interstitial lung disease have attracted great interest in the relation between cancer genetics and drugs, as well as the relation between ethnicity and genetics. In clinical practice, EGFR tyrosine kinase inhibitor should be prescribed with careful consideration and it is essential to assess benefit and risk of the drug.     

Therapeutic strategy for advanced EGFR mutant non-small-cell lung carcinoma

Activating mutation in exons 19 or 21 of epidermal growth factor receptor (EGFR) in non-small-cell lung cancers (NSCLC) are associated with increased sensitivity to EGFR tyrosine kinase inhibitors (EGFR-TKIs), such as gefitinib and erlotinib. Cancer patients harboring activating EGFR mutations benefit from first-line TKI therapy. Yet 10% of patients present a primary TKI resistance, while 50% of the others develop a secondary resistance within 9–12 months after starting TKI. The RECIST's definition of progression appears flawed when applied to EGFR-mutated NSCLC patients. Most often, tumor volume shrinking widely exceeds 30% during TKI response and kinetics of growth is low during relapse. At present, secondary resistance mechanisms associated with progression are better known: clonal selection of EGFR resistance mutation (T790M mutation in exon 20), amplification of transmembrane receptors for other growth factors (c-met, HER family, IGF1R, or AXL), downstream molecular alterations in EGFR signaling pathway (PI3K or PTEN), and epithelial–mesenchymal transition or transdifferentiation to small-cell cancer. The best strategy for secondary resistance is not well-defined: maintaining TKI therapy, switching to chemotherapy, combining both treatments, or using new therapies targeting other signaling pathways.     

Epidermal growth factor receptor targeted therapies for solid tumours

The majority of human epithelial cancers is frequently characterized by a functional activation of the epidermal growth factor receptor (EGFR)-driven-pathways. Today, two classes of EGFR inhibitors are routinely used in the clinic: anti-EGFR monoclonal antibodies such as cetuximab and panitumumab and small-molecule inhibitors of the EGFR tyrosine kinase activity such as erlotinib and gefitinib. Anti-EGFR therapies have been approved in several countries for the treatment of metastatic nonsmall-cell lung cancer, colorectal cancer, squamous-cell carcinoma of the head and neck, and pancreatic cancer. This article summarizes the clinical evidence of the anticancer activity of anti-EGFR treatment, and considers the current, and controversial, clinical issues with respect to their optimal use in the treatment of patients with cancer. Mechanisms of resistance to anti-EGFR treatment are also briefly discussed.     

Gefitinib prevents bleomycin-induced lung fibrosis in mice

RATIONALE: Transforming growth factor-alpha and epidermal growth factor (EGF), the ligands for EGF receptor (EGFR), stimulate fibroblast proliferation and play an important role in the pathogenesis of pulmonary fibrosis. Therefore, inhibition of the EGFR signal by an EGFR tyrosine kinase inhibitor (EGFR-TKI) may prevent pulmonary fibrosis. However, there is a possibility that blocking the EGFR signal may inhibit epithelial cell repair, thereby exaggerating lung fibrosis. OBJECTIVE: To investigate the effect of EGFR-TK inhibition on lung fibrosis. METHODS: We looked at the effects of the EGFR-TKIs gefitinib (20, 90, 200 mg/kg) and AG1478 (12 mg/kg) on a bleomycin-induced lung fibrosis model in mice. MEASUREMENTS AND MAIN RESULTS: Gefitinib prevented lung fibrosis at all three doses. Furthermore, in those mice that did not receive bleomycin treatment, gefitinib at 200 mg/kg did not induce lung fibrosis. Immunohistochemistry revealed that phosphorylation of EGFR in lung mesenchymal cells induced by bleomycin was inhibited by gefitinib. AG1478 also attenuated the lung fibrosis. In vitro studies further demonstrated that the addition of gefitinib or AG1478 suppressed the EGFR ligand-induced proliferation of lung fibroblasts. CONCLUSIONS: These findings suggest that, in the preclinical setting, EGFR-TKIs may have a protective effect on lung fibrosis induced by bleomycin. Because these molecular targeted drugs may have differing effects depending on species and individuals, a cautious interpretation is warranted.     

非小细胞肺癌表皮生长因子受体酪氨酸激酶抑制剂耐药机制研究进展

以吉非替尼和厄罗替尼为代表的表皮生长因子受体酪氨酸激酶抑制剂在部分非小细胞肺癌患者中的治疗效果显著,但几乎所有患者最终均表现为耐药.因此,为提高该类药物的效用,对耐药性的研究便显得至关重要.基因突变、细胞表型改变、受体内化、信号通路成分及其调节因子的基因表达改变等都可以导致肿瘤细胞摆脱对表皮生长因子受体信号通路的专一性依赖而产生耐药.     

Overview of tyrosine kinase inhibitors in clinical breast cancer

Studies of cell models and profiling of clinical breast cancer material to reveal the mechanisms of resistance to anti-oestrogen therapy, and to tamoxifen in particular, have reported that this phenomenon can be associated with increased expression and signalling through erbB Type 1 growth factor receptors, notably the epidermal growth factor receptor (EGFR) and HER2. Further molecular studies have revealed an intricate interlinking between such growth factor receptor pathways and oestrogen receptor (ER) signalling. Inhibition of receptor tyrosine kinase activity involved in the EGFR signalling cascade forms the basis for the use of EGFR specific tyrosine kinase inhibitors exemplified by gefitinib (ZD1839, Iressa) and erlotinib (OSI-774, Tarceva). Such agents have proved promising in pre-clinical studies and are currently in clinical trials in breast cancer, where gefitinib has been studied more extensively to date. Here, we present an overview of the current development of gefitinib in clinical breast cancer. This includes results from our clinical breast cancer trial 1839IL/0057 that demonstrate the efficacy of gefitinib within ER-positive, tamoxifen-resistant patients with locally advanced/metastatic disease, where parallel decreases in EGFR signal transduction and the Ki67 (MIB1) proliferation marker can be detected as predicted from model system studies. We also consider trials examining combination treatment with gefitinib and anti-hormonal strategies that will begin to address the clinically important question of whether gefitinib can delay/prevent onset of anti-hormone resistance.     

Cross-talk between MET and EGFR in non-small cell lung cancer involves miR-27a and Sprouty2

In the past decade, we have observed exciting advances in lung cancer therapy, including the development of targeted therapies. However, additional strategies for early detection and tumor-based therapy are still essential in improving patient outcomes. EGF receptor (EGFR) and MET (the receptor tyrosine kinase for hepatocyte growth factors) are cell-surface tyrosine kinase receptors that have been implicated in diverse cellular processes and as regulators of several microRNAs (miRNAs), thus contributing to tumor progression. Here, we demonstrate a biological link between EGFR, MET, and the miRNA cluster 23a∼27a∼24–2. We show that miR-27a regulates MET, EGFR, and Sprouty2 in lung cancer. In addition, we identify both direct and indirect mechanisms by which miR-27a can regulate both MET and EGFR. Thus, we propose a mechanism for MET and EGFR axis regulation that may lead to the development of therapeutics in lung cancer.