Oncogenic transformation by inhibitor-sensitive and -resistant EGFR mutants

Pharmacological characterization of MP-412 (AV-412), a dual epidermal growth factor receptor and ErbB2 tyrosine kinase inhibitor

Epidermal growth factor receptor (EGFR) and ErbB2 are currently recognized as validated target molecules in cancer treatment strategies. MP-412 (AV-412) is a potent dual inhibitor of EGFR and ErbB2 tyrosine kinases, including the mutant EGFR(L858R,T790M), which is clinically resistant to the EGFR-specific kinase inhibitors erlotinib and gefitinib. In an enzyme assay, MP-412 inhibited the EGFR variants and ErbB2 in the nanomolar range with over 100-fold selectivity compared with other kinases, apart from abl and flt-1, which were both moderately sensitive to the compound. In cells, MP-412 inhibited autophosphorylation of EGFR and ErbB2 with IC(50) of 43 and 282 nM, respectively. It also inhibited epidermal growth factor (EGF)-dependent cell proliferation with an IC(50) of 100 nM. Moreover, MP-412 abrogated EGFR signaling in the gefitinib-resistant H1975 cell line, which harbors a double mutation of L858R and T790M in EGFR. In animal studies using cancer xenograft models, MP-412 (30 mg/kg) demonstrated complete inhibition of tumor growth of the A431 and BT-474 cell lines, which overexpress EGFR and ErbB2, respectively. MP-412 suppressed autophosphorylation of EGFR and ErbB2 at the dose corresponding to its antitumor efficacy. When various dosing schedules were applied, MP-412 showed significant effects with daily and every-other-day schedules, but not with a once-weekly schedule, suggesting that frequent dosing is preferable for this compound. Furthermore, MP-412 showed a significant antitumor effect on the ErbB2-overexpressing breast cancer KPL-4 cell line, which is resistant to gefitinib. These studies indicate that MP-412 has potential as a therapeutic agent for the treatment of cancers expressing EGFR and ErbB2, especially those resistant to the first generation of small-molecule inhibitors.

The HER family and cancer: emerging molecular mechanisms and therapeutic targets

The human epidermal growth factor receptor (HER) family of transmembrane tyrosine kinases regulates diverse cellular functions in response to extracellular ligands. The deregulation of HER signaling through gene amplification or mutation is seen in many human tumors and an abundance of experimental evidence supports the etiological role of these events in cancer pathogenesis. In addition, the fact that they are feasible targets for both antibody and small-molecule therapeutics has made them highly pursued targets for the development of rationally designed anticancer drugs. Several HER-targeting agents have entered clinical practice and this has led to novel discoveries regarding the mechanisms of resistance, which has defined a new generation of challenges for targeted cancer therapies. Here, we review recent advances in our understanding of HER signaling and targeting in cancer.

EGFR exon 20 insertion mutation in Japanese lung cancer

Mutations of the epidermal growth factor receptor (EGFR) gene have been reported in non-small cell lung cancer (NSCLC), especially in female, never smoker patients with adenocarcinoma. Some common somatic mutations in EGFR, including deletion mutations in exon 19 and leucine to arginine substitution at amino acid position 858 (L858R) in exon 21, have been examined for their ability to predict sensitivity to gefitinib or erlotinib. On the other hand, previous report has shown that the insertion mutation at exon 20 is related to gefitinib resistance. We investigated the exon 20 EGFR mutation statuses in 322 surgically treated non-small cell lung cancer cases. Two hundred and five adenocarcinoma cases were included. The presence or absence of EGFR mutations of kinase domains was analyzed by direct sequences. EGFR insertion mutations at exon 20 were found from 7 of 322 (2.17%) lung cancer patients. We also detected the 18 deletion type mutations in exon 19, and 25 L858R type mutations in exon 21. There was a tendency towards higher exon 20 insertion ratio in never smoker (never smoker 4.4% versus smoker 1.3%, p=0.0996) and female (female 4.5% versus male 1.3%, p=0.0917). Two exon 20 insertion cases were treated with gefitinib and failed to response. EGFR insertion mutation in exon 20 could not be ignored from Japanese lung cancers.

Mutations of the epidermal growth factor receptor gene and related genes as determinants of epidermal growth factor receptor tyrosine kinase inhibitors sensitivity in lung cancer

Recent discovery of mutations in the tyrosine kinase domain of the epidermal growth factor receptor (EGFR) gene in lung adenocarcinoma greatly stimulated biomarker research on predictive factors for EGFR tyrosine kinase inhibitors (TKI), such as gefitinib and erlotinib. Although patients with activating mutations of the EGFR generally respond to EGFR TKIs very well, it is natural to assume that there is no sole determinant, considering great complexity and redundancy of the EGFR pathway. Subsequently, roles of different types of EGFR mutations or mutations of genes that are members of the EGFR pathway such as KRAS and HER2 have been evaluated. In this review, we summarize the recent findings about how mutations of the EGFR and related genes affect sensitivity to EFGR-TKIs. We also discuss molecular mechanisms of acquired resistance to EGFR-TKIs that is almost inevitable in EGFR-TKI therapy. The door for genotype-based treatment of lung cancer is beginning to open, and through these efforts, it will be possible to slow the progression of lung cancer and eventually, to decrease mortality from lung cancer.

Exon 19 deletion mutations of epidermal growth factor receptor are associated with prolonged survival in non-small cell lung cancer patients treated with gefitinib or erlotinib

PURPOSE

Somatic mutations in the epidermal growth factor receptor (EGFR) have been detected in patients with non-small cell lung cancer (NSCLC) and are associated with sensitivity to treatment with gefitinib or erlotinib. Our study explored the relationship between the two most common types of somatic EGFR mutations, exon 19 deletions and the L858R point mutation, and outcomes of patients following treatment with gefitinib or erlotinib.

EXPERIMENTAL DESIGN

Tumor specimens obtained before treatment with gefitinib or erlotinib were analyzed for EGFR mutations. Patients with exon 19 deletion or L858R mutations were identified. The response rate, time to progression, and overall survival were determined for the two groups.

RESULTS

We identified 36 patients with NSCLC and an EGFR mutation who were treated with gefitinib or erlotinib. Patients with an exon 19 deletion had a significantly longer overall survival compared with patients with an L858R mutation (38 versus 17 months; P = 0.04). There were also trends toward higher response rate (73% versus 50%) and improved time to progression (24 versus 10 months) for the patients with an exon 19 deletion, although these were not independently significant in a multivariate analysis. A difference in response rate for patients treated with gefitinib compared with erlotinib was also noted [18 of 23 (78%) versus 3 of 9 (33%); P = 0.04]. No obvious difference in time to progression or overall survival was noted between gefitinib- and erlotinib-treated patients.

CONCLUSIONS

Patients with NSCLC and EGFR exon 19 deletions have a longer survival following treatment with gefitinib or erlotinib compared with those with the L858R mutation. Pooling of greater numbers of patients and completion of prospective trials are needed to further define the predictive and prognostic roles of different EGFR mutations with respect to treatment with gefitinib, erlotinib, and other EGFR inhibitors.

Transcriptional profiling of non-small cell lung cancer cells with activating EGFR somatic mutations

Background

Activating somatic mutations in epidermal growth factor receptor (EGFR) confer unique biologic features to non-small cell lung cancer (NSCLC) cells, but the transcriptional mediators of EGFR in this subgroup of NSCLC have not been fully elucidated.

Methodology/Principal Findings

Here we used genetic and pharmacologic approaches to elucidate the transcriptomes of NSCLC cell lines. We transcriptionally profiled a panel of EGFR-mutant and -wild-type NSCLC cell lines cultured in the presence or absence of an EGFR tyrosine kinase inhibitor. Hierarchical analysis revealed that the cell lines segregated on the basis of EGFR mutational status (mutant versus wild-type), and expression signatures were identified by supervised analysis that distinguished the cell lines based on mutational status (wild-type versus mutant) and type of mutation (L858R versus Δ746-750). Using an EGFR mutation-specific expression signature as a probe, we mined the gene expression profiles of two independent cohorts of NSCLC patients and found the signature in a subset. EGFR tyrosine kinase inhibitor treatment regulated the expression of multiple genes, and pharmacologic inhibition of the protein products of two of them (PTGS2 and EphA2) inhibited anchorage-independent growth in EGFR-mutant NSCLC cells.

Conclusions/Significance

We have elucidated genes not previously associated with EGFR-mutant NSCLC, two of which enhanced the clonogenicity of these cells, distinguishing these mediators from others previously shown to maintain cell survival. These findings have potential clinical relevance given the availability of pharmacologic tools to inhibit the protein products of these genes.

Induction of BIM is essential for apoptosis triggered by EGFR kinase inhibitors in mutant EGFR-dependent lung adenocarcinomas

BACKGROUND

Mutations in the epidermal growth factor receptor (EGFR) gene are associated with increased sensitivity of lung cancers to kinase inhibitors like erlotinib. Mechanisms of cell death that occur after kinase inhibition in these oncogene-dependent tumors have not been well delineated. We sought to improve understanding of this process in order to provide insight into mechanisms of sensitivity and/or resistance to tyrosine kinase inhibitors and to uncover new targets for therapy.

METHODS AND FINDINGS

Using a panel of human lung cancer cell lines that harbor EGFR mutations and a variety of biochemical, molecular, and cellular techniques, we show that EGFR kinase inhibition in drug-sensitive cells provokes apoptosis via the intrinsic pathway of caspase activation. The process requires induction of the proapoptotic BH3-only BCL2 family member BIM (i.e., BCL2-like 11, or BCL2L11); erlotinib dramatically induces BIM levels in sensitive but not in resistant cell lines, and knockdown of BIM expression by RNA interference virtually eliminates drug-induced cell killing in vitro. BIM status is regulated at both transcriptional and posttranscriptional levels and is influenced by the extracellular signal-regulated kinase (ERK) signaling cascade downstream of EGFR. Consistent with these findings, lung tumors and xenografts from mice bearing mutant EGFR-dependent lung adenocarcinomas display increased concentrations of Bim after erlotinib treatment. Moreover, an inhibitor of antiapoptotic proteins, ABT-737, enhances erlotinib-induced cell death in vitro.

CONCLUSIONS

In drug-sensitive EGFR mutant lung cancer cells, induction of BIM is essential for apoptosis triggered by EGFR kinase inhibitors. This finding implies that the intrinsic pathway of caspase activation may influence sensitivity and/or resistance of EGFR mutant lung tumor cells to EGFR kinase inhibition. Manipulation of the intrinsic pathway could be a therapeutic strategy to enhance further the clinical outcomes of patients with EGFR mutant lung tumors.

EGFR polymorphism of the kinase domain in Japanese lung cancer

BACKGROUND

Mutations of the epidermal growth factor receptor (EGFR) gene at kinase domain have been reported in non-small-cell lung cancer (NSCLC), and some common somatic mutations in EGFR have been examined for their ability to predict sensitivity to gefitinib or erlotinib. However, EGFR mutations at exon 20 have been reported to predict resistance to gefitinib therapy.

MATERIALS AND METHODS

We investigated the EGFR mutations and/or polymorphism statuses at kinase domain in 303 surgically treated non-small cell lung cancer (NSCLC) cases. One hundred ninety-four adenocarcinoma cases were included. The presence or absence of EGFR polymorphism of kinase domains was analyzed by direct sequences. We have also investigated EGFR polymorphism status at exon 20 for 23 NSCLC patients who had undergone surgery followed by treatment with gefitinib at the National Hospital Organization, Kinki-chuo Chest Medical Center.

RESULTS

EGFR mutations at kinase domain were found in 75 of 303 lung cancer patients. During sequencing of EGFR tyrosine kinase domain in tumors, 86 EGFR polymorphism (G2607A) cases were identified at exon 20. G2067A polymorphism was significantly higher in nonadenocarcinomas (37.4%) than in adenocarcinoma (25.3%, P = 0.0415). The polymorphism status did not correlate with gender, smoking (never smoker versus smoker), and EGFR mutations. In 46 total gefitinib treated NSCLC patients, there was a tendency toward better prognosis in EGFR wild type (GG) patients than AG + AA patients. EGFR polymorphism in Japanese lung cancers seemed to be less frequent than Caucasian lung cancers.

CONCLUSIONS

EGFR-tyrosine kinase polymorphism might be associated with clinicopathological background of lung cancers.

Emergence of epidermal growth factor receptor T790M mutation during chronic exposure to gefitinib in a non small cell lung cancer cell line

The epidermal growth factor receptor (EGFR)-specific tyrosine kinase inhibitor gefitinib may provide dramatic clinical responses in some patients with pulmonary adenocarcinoma carrying activating mutations of the EGFR. However, prolonged administration of gefitinib may eventually induce acquired resistance in such patients. To gain insight into the mechanisms of this phenomenon, we placed PC-9, a cell line derived from pulmonary adenocarcinoma that has a 15-bp deletion in EGFR exon 19, under the continuous selective pressure of low levels of gefitinib without any mutagen, and established a subline that was able to grow in the presence of 2 micromol/L of gefitinib (designated RPC-9). In this cell line, about half of the reverse transcription-PCR products from mutated EGFR also carried an additional mutation (T790M). In keeping with the proposed role of T790M in abrogating gefitinib binding with EGFR, gefitinib-treated RPC-9 hardly displayed any decrease in the constitutive phosphorylation of EGFR, Akt, or Erk1/2 unlike in PC-9 cells. Interestingly, transfection of the EGFR carrying only a 15-bp deletion reversed the resistance to gefitinib in RPC-9 cells. Thus, the balance of expression levels between gefitinib-sensitive or gefitinib-resistant EGFR may govern the response to gefitinib in lung cancer.

The Impact of Sex and Smoking Status on the Mutational Spectrum of Epidermal Growth Factor Receptor Gene in Non–small Cell Lung Cancer

PURPOSE

Mutation of epidermal growth factor receptor (EGFR) gene has been reported to be present in non-small cell lung cancer (NSCLC) and significantly associated with female sex and never-smoking status. In this study, we extensively investigated the impact of sex and smoking on the EGFR mutation.

EXPERIMENTAL DESIGN

We examined EGFR exons 18 to 21 status in 1,467 NSCLC patients by direct sequencing to study the impact of sex and smoking status on the EGFR mutational spectrum.

RESULTS

Among 1,467 patients, 197 mutations were found at exon 19, 176 at exon 21, 21 at exon 18, and 24 at exon 20. To examine the independent effect of sex and smoking, the mutational status of each exon was compared between smokers and never smokers in each sex and between males and females stratified by smoking status. In females, exon 19 (P = 0.001) and exon 21 (P < 0.001) mutations were significantly less frequent in ever smokers compared with never smokers. In males, exon 19 (P < 0.001), exon 21 (P < 0.001), and exon 18 (P = 0.003) mutations were significantly less frequent in ever smokers compared with never smokers. In analysis stratified by smoking, there was no difference in sex among never smokers. However, exon 19 mutations were significantly less frequent in males compared with females among ever smokers (P = 0.003). In addition, the interactive effect of male sex and ever smoking status significantly decreased the frequency of exon 19 mutations (P = 0.047) when female never smoker was set as a reference.

CONCLUSION

Both sex and smoking status could influence the EGFR mutational spectrum. Our findings suggest that individual EGFR exons may have differing susceptibilities for mutagenesis.

Detection of epidermal growth factor receptor gene mutations in cytology specimens from patients with non-small cell lung cancer utilising high-resolution melting amplicon analysis

Background:

Activating epidermal growth factor receptor (EGFR) mutations have been implicated in non-small cell lung cancer (NSCLC), and have also been clinically correlated with patient sensitivity to targeted EGFR inhibitors.

Aim:

To describe a technique for determining EGFR mutation status on archival fine needle aspirate (FNA) specimens from advanced NSCLC patients.

Methods:

Eleven archival FNA slides from patients with advanced NSCLC were examined for diagnostic material to identify tumour cell-enriched regions. EGFR mutation status was determined using a slide-scrape DNA extraction protocol of selected tumour cell regions on the smear slides, followed by real time PCR and high resolution melt analysis (HRMAA) of EGFR exons 18, 19, 20, and 21, followed by sequence analysis.

Results:

All DNA samples were successfully amplified by PCR. Three adenocarcinoma patient samples contained EGFR mutations in exon 19 (L747-P753insS). One of the three had an additional exon 19 mutation (A755D).

Conclusions:

Archival cytology slides from patients with NSCLC can be used to determine EGFR mutation status by PCR, HRMAA, and sequencing. The ability to use archival cytology slides greatly increases the potential material available for molecular analysis in diagnosis and selection of patients for targeted therapeutic agents.

Clinical significance of epidermal growth factor receptor gene mutations on treatment outcome after first-line cytotoxic chemotherapy in Japanese patients with non-small cell lung cancer

INTRODUCTION

The relationship between the EGFR gene mutation status and clinical outcome has not fully been assessed in patients with non-small cell lung cancer (NSCLC) who received cytotoxic agents. The aim of this study was to clarify its association. We also examined whether this association could be affected by previous gefitinib treatment.

METHODS

Patients with advanced or postoperative recurrent NSCLC who received both cytotoxic chemotherapy and gefitinib monotherapy in their treatment course were included in this study. An EGFR mutation was determined in exons 19 and 21 by direct sequencing.

RESULTS

Of 194 Japanese patients with advanced or relapsed NSCLC assessable for mutation analysis, 60 received both cytotoxic chemotherapy and gefitinib monotherapy through their treatment courses. EGFR mutations significantly affected progression-free survival (PFS) in the first-line cytotoxic chemotherapy regimens in the multivariate analysis (hazard ratio for PFS = 0.422; p = 0.0422). In contrast, in 28 (47%) of the 60 patients who also received cytotoxic chemotherapy after the relapse to gefitinib monotherapy, there were no differences in PFS stratified by EGFR mutation status. The sensitivity to gefitinib was, however, correlated with EGFR mutation status, and its sensitivity was retained even in the second-line treatment setting in patients with EGFR mutations.

CONCLUSIONS

EGFR mutations were therefore significantly associated with a better PFS in the first-line cytotoxic chemotherapy regimens. However, its association was not observed in the cytotoxic regimens administered after the relapse to gefitinib monotherapy, whereas gefitinib sensitivity was associated with an EGFR mutation even in the second-line or later treatment settings.

Functional analysis of cancer-associated EGFR mutants using a cellular assay with YFP-tagged EGFR intracellular domain

BACKGROUND

The presence of EGFR kinase domain mutations in a subset of NSCLC patients correlates with the response to treatment with the EGFR tyrosine kinase inhibitors gefitinib and erlotinib. Although most EGFR mutations detected are short deletions in exon 19 or the L858R point mutation in exon 21, more than 75 different EGFR kinase domain residues have been reported to be altered in NSCLC patients. The phenotypical consequences of different EGFR mutations may vary dramatically, but the majority of uncommon EGFR mutations have never been functionally evaluated.

RESULTS

We demonstrate that the relative kinase activity and erlotinib sensitivity of different EGFR mutants can be readily evaluated using transfection of an YFP-tagged fragment of the EGFR intracellular domain (YFP-EGFR-ICD), followed by immunofluorescence microscopy analysis. Using this assay, we show that the exon 20 insertions Ins770SVD and Ins774HV confer increased kinase activity, but no erlotinib sensitivity. We also show that, in contrast to the common L858R mutation, the uncommon exon 21 point mutations P848L and A859T appear to behave like functionally silent polymorphisms.

CONCLUSION

The ability to rapidly obtain functional information on EGFR variants of unknown relevance using the YFP-EGFR-ICD assay might prove important in the future for the management of NSCLC patients bearing uncommon EGFR mutations. In addition, our assay may be used to determine the response of resistant EGFR mutants to novel second-generation TKIs.

Oncogenic activity of epidermal growth factor receptor kinase mutant alleles is enhanced by the T790M drug resistance mutation

Activating mutations in the epidermal growth factor receptor (EGFR) characterize a subset of non-small cell lung cancers (NSCLC) with extraordinary sensitivity to targeted tyrosine kinase inhibitors (TKI). A single secondary EGFR mutation, T790M, arising in cis with the primary activating mutation, confers acquired resistance to these drugs. However, the T790M mutation is also detected in the absence of drug selection, suggesting that it may provide a growth advantage. We show here that although T790M alone has only a modest effect on EGFR function, when combined with the characteristic activating mutations L858R or del746-750, it results in a dramatic enhancement of EGFR activity. The double mutants show potent ligand-independent receptor autophosphorylation associated with altered cellular phenotypes, soft agar colony formation, and tumorigenesis in nude mice. The significant gain-of-function properties of these double mutants may explain their initial presence before drug selection and their rapid selection as the single drug resistance mutation during therapy with gefitinib/erlotinib, and suggests that they may contribute to the adverse clinical course of TKI-resistant NSCLC.

Ligand-independent phosphorylation of Y869 (Y845) links mutant EGFR signaling to stat-mediated gene expression

Activating mutants of EGFR have been identified in a subset of non-small-cell lung cancers. To investigate mutant-driven signaling, we focused on Y869, a residue in the same activation loop where the L858R and L861Q mutations are located. We observed ligand-independent phosphorylation of Y869 in 32D cells EGFR(L858R) and EGFR(L861Q). The EGFR tyrosine kinase inhibitor (TKI) erlotinib inhibited Y869 P-EGFR in intact cells as well as in a cell-free kinase reaction. Expression of kinase domain of EGFR(L858R) and EGFR(L861Q) exhibited auto-phosphorylation of Y869; this was inhibited by EGFR TKIs but not by Src kinase inhibitor. P-Y859 of EGFR-mediated downstream component, STAT5, was also analyzed. Y694 P-STAT5 was eliminated by erlotinib treatment. Analysis of immune-complexes showed constitutive association of mutant EGFRs with STAT5 and Src which was unaffected by erlotinib or PP1. On the other hand, 32D-EGFR(WT) exhibited constitutive STAT5 phosphorylation and association of EGFR with JAK2. In these cells, a JAK2 inhibitor abrogated P-STAT5 whereas mutant EGFRs did not associate with JAK2. Expression of c-myc was regulated by EGFR/STAT5 signaling in cells expressing EGFR(L858R) and EGFR(L861Q). Our results suggest that ligand-independent and Src activity-independent phosphorylation of Y869 in mutant EGFR regulates STAT5 activation and c-myc expression.

Pharmacogenomics of lung cancer: with a view to address EGFR-targeted therapies

Epidermal growth factor receptor (EGFR)-targeted therapies have demonstrated variable success in treating individuals with non-small-cell lung cancer. Understanding the molecular mechanisms of response and resistance to this class of treatment has led to patient selection strategies that may improve outcomes. The second generation of EGFR-targeted therapies is now under clinical evaluation and may prove to be successful at circumventing a portion of primary or acquired resistance to first-generation tyrosine kinase inhibitors. These principles are generally applicable to the field of targeted therapy and predictive pharmacogenomics.

Development of new mouse lung tumor models expressing EGFR T790M mutants associated with clinical resistance to kinase inhibitors

Background

The EGFR T790M mutation confers acquired resistance to kinase inhibitors in human EGFR mutant lung adenocarcinoma, is occasionally detected before treatment, and may confer genetic susceptibility to lung cancer.

Methodology/Principal Findings

To study further its role in lung tumorigenesis, we developed mice with inducible expression in type II pneumocytes of EGFR^T790M alone or together with a drug-sensitive L858R mutation. Both transgenic lines develop lung adenocarcinomas that require mutant EGFR for tumor maintenance but are resistant to an EGFR kinase inhibitor. EGFR^L858R+T790M-driven tumors are transiently targeted by hsp90 inhibition. Notably, EGFR^T790M-expressing animals develop tumors with longer latency than EGFR^L858R+T790M-bearing mice and in the absence of additional kinase domain mutations.

Conclusions/Significance

These new mouse models of mutant EGFR-dependent lung adenocarcinomas provide insight into clinical observations. The models should also be useful for developing improved therapies for patients with lung cancers harboring EGFR^T790M alone or in conjunction with drug-sensitive EGFR kinase domain mutations.

Sensitivity of epidermal growth factor receptor and ErbB2 exon 20 insertion mutants to Hsp90 inhibition

The mature epidermal growth factor receptor (EGFR) neither associates with nor requires the molecular chaperone heat-shock protein 90 (Hsp90). Mutations in EGFR exons 18, 19, and 21 confer Hsp90 chaperone dependence. In non-small cell lung cancer (NSCLC), these mutations are associated with enhanced sensitivity to EGFR inhibitors in vitro and with clinical response in vivo. Although less prevalent, insertions in EGFR exon 20 have also been described in NSCLC. These mutations, however, confer resistance to EGFR inhibitors. In NSCLC, exon 20 insertions have also been identified in the EGFR family member ErbB2. Here, we examined the sensitivity of exon 20 insertion mutants to an Hsp90 inhibitor currently in the clinic. Our data demonstrate that both EGFR and ErbB2 exon 20 insertion mutants retain dependence on Hsp90 for stability and downstream-signalling capability, and remain highly sensitive to Hsp90 inhibition. Use of Hsp90 inhibitors should be considered in NSCLC harbouring exon 20 insertions in either EGFR or ErbB2.

Mutational activation of ErbB family receptor tyrosine kinases: insights into mechanisms of signal transduction and tumorigenesis

Signaling by the Epidermal Growth Factor Receptor (EGFR) and related ErbB family receptor tyrosine kinases can be deregulated in human malignancies as the result of mutations in the genes that encode these receptors. The recent identification of EGFR mutations that correlate with sensitivity and resistance to EGFR tyrosine kinase inhibitors in lung and colon tumors has renewed interest in such activating mutations. Here we review current models for ligand stimulation of receptor dimerization and for activation of receptor signaling by receptor dimerization. In the context of these models, we discuss ErbB receptor mutations that affect ligand binding and those that cause constitutive receptor phosphorylation and signaling as a result of constitutive receptor dimerization. We discuss mutations in the cytoplasmic regions that affect enzymatic activity, substrate specificity and coupling to effectors and downstream signaling pathways. Finally, we discuss how emergent mechanisms of ErbB receptor mutational activation could impact the search for clinically relevant ErbB receptor mutations.

Selecting Patients for Treatment with Epidermal Growth Factor Tyrosine Kinase Inhibitors

Identification of objective tumor regressions with epidermal growth factor receptor tyrosine kinases (EGFR TKI) in non-small cell lung cancer (NSCLC) patients has resulted in intense, worldwide clinical and basic research directed toward finding the optimal use of EGFR TKIs in NSCLC. EGFR TKI clinical trials have shown that higher response rates and longer survival are associated with specific patient characteristics and that using conventional chemotherapy simultaneously with EGFR TKIs in unselected patients does not increase survival. Molecular studies have revealed that EGFR-activating mutations and high EGFR gene copy number are frequently found in patients who have the best outcomes with EGFR TKIs. More recent studies suggest that KRAS mutations may identify the subset of patients who have the worst outcome with the EGFR TKI treatment. Currently, investigators are trying to determine the optimal approach to selecting patients for treatment with EGFR TKIs. Studies that have evaluated the potential predictive value of clinical features and/or molecular profiles in EGFR TKI-treated NSCLC patients are discussed in this review.

Diagnosis and treatment of bronchioloalveolar carcinoma

PURPOSE OF REVIEW

Bronchioloalveolar carcinoma accounts for 5% of lung cancers, although histologically mixed bronchioloalveolar carcinoma and adenocarcinoma account for up to 20%. Bronchioloalveolar carcinoma histology is present in a majority of tumors found on lung-cancer screening by computed tomography. We review issues surrounding the diagnosis and treatment of bronchioloalveolar carcinoma, which often differs from other types of lung cancer.

RECENT FINDINGS

A spectrum of disease from histologically pure bronchioloalveolar carcinoma to adenocarcinoma exists. The approach to treatment of diseases within this spectrum is still evolving. Evidence on the role of sub-lobar resection, resection of multifocal disease, and pulmonary transplantation is reviewed. We also discuss epidermal growth factor receptor tyrosine kinase inhibitors, and their role in patients with bronchioloalveolar carcinoma.

SUMMARY

An understanding of recent developments in the diagnosis and treatment of patients with bronchioloalveolar carcinoma histology is important as early detection of lung cancer becomes more common. Ongoing clinical trials will provide important information on the role of limited resection. The use of epidermal growth factor receptor tyrosine kinase inhibitors should currently be limited to patients with advanced or recurrent disease who have failed cytotoxic chemotherapy. New targeted therapies are emerging for patients with bronchioloalveolar carcinoma histology.

Gefitinib-sensitive EGFR lacking residues 746-750 exhibits hypophosphorylation at tyrosine residue 1045, hypoubiquitination, and impaired endocytosis

Gefitinib-sensitive nonsmall cell lung cancers (NSCLC) are characterized by somatic mutations in the kinase domain of epidermal growth factor receptor (EGFR). The mutant EGFR forms are reported to mediate characteristic signal transduction pathways that are different from those mediated by the wild-type EGFR and are involved in transformation in vivo. We have examined signal transduction pathways initiated from a frequently identified gefitinib-sensitizing mutant EGFR lacking residues 746-750 by employing a mouse fibroblast cell line that is free of endogenous EGFR and transiently transfected COS-7 cells. Upon EGF stimulation, the deletion-mutant EGFR mediated prolonged downstream signals. The analysis of the phosphotyrosine patterns of the receptor revealed that the deletion-mutant EGFR lacked phosphorylation at tyrosine residue 1045, which is the major binding site of Cbl. The EGF-induced endocytosis of the deletion-mutant EGFR was impaired. The ubiquitination and downregulation of the deletion-mutant EGFR were also reduced. On the other hand, another mutant, EGFR, possessing a L858R substitution, exhibited phosphorylation at 1045 and its downstream signalings were not prolonged. These data suggest that the signal transduction pathways initiated from these mutant forms are different, and that impaired endocytosis might be responsible for the prolonged signals mediated by the deletion-mutant EGFR.

Tumor growth inhibition with cetuximab and chemotherapy in non-small cell lung cancer xenografts expressing wild-type and mutated epidermal growth factor receptor

PURPOSE

Targeting the epidermal growth factor receptor (EGFR) is a validated approach to treat cancer. In non-small cell lung cancer (NSCLC), EGFR contains somatic mutations in 10% of patients, which correlates with increased response rates to small molecule inhibitors of EGFR. We analyzed the effects of the monoclonal IgG1 antibody Erbitux (cetuximab) in NSCLC xenografts with wild-type (wt) or mutated EGFR.

EXPERIMENTAL DESIGN

NSCLC cell lines were grown s.c. in nude mice. Dose-dependent efficacy was established for cetuximab. To determine whether combination therapy produces tumor regressions, cetuximab was dosed at half-maximal efficacy with chemotherapy used at maximum tolerated dose.

RESULTS

Cetuximab showed antitumor activity in wt (A549, NCI-H358, NCI-H292) and mutated [HCC-827 (delE746-A750), NCI-H1975 (L858R, T790M)] EGFR-expressing xenografts. In the H292 model, cetuximab and docetaxel combination therapy was more potent to inhibit tumor growth than cetuximab or docetaxel alone. Cisplatin augmented efficacy of cetuximab to produce 6 of 10 regressions, whereas 1 of 10 regressions was found with cetuximab and no regression was found with cisplatin. Using H1975 xenografts, gemcitabine increased efficacy of cetuximab resulting in 12 of 12 regressions. Docetaxel with cetuximab was more efficacious with seven of nine regressions compared with single treatments. Cetuximab inhibited autophosphorylation of EGFR in both H292 and H1975 tumor lysates. Exploring the underlying mechanism for combination effects in the H1975 xenograft model, docetaxel in combination with cetuximab added to the antiproliferative effects of cetuximab but was the main component in this drug combination to induce apoptosis.

CONCLUSIONS

Cetuximab showed antitumor activity in NSCLC models expressing wt and mutated EGFR. Combination treatments increased the efficacy of cetuximab, which may be important for the management of patients with chemorefractory NSCLC.

Epidermal growth factor receptor mutations in lung cancers

In 2004, two groups reported somatic mutations in the gene for the epidermal growth factor receptor (EGFR) in patients with non-small cell lung cancer (NSCLC), which were highly correlated with the clinical response to the anticancer drug, gefitinib. Since then, a tremendous amount of knowledge has accumulated, and sheds light on significant oncological properties as well as the clinical relevance of this mutation, which could be applicable to other malignancies. The EGFR mutations are distributed throughout the kinase domain, but a deletion in exon 19 and the point mutation L858R in exon 21 account for approximately 90%, which confer a greater response to gefitinib treatment, compared with other types of EGFR mutations. These EGFR mutations in the tyrosine kinase domain are seldom acquired in cancers of the other organs and the mutations preferentially involve a subset of lung cancers, which are clinicopathologically characterized by female sex, non-smoking, adenocarcinoma histology and East Asian ethnicity. In Japan, the EGFR mutations are detected in approximately 30% of overall NSCLC and approximately 40% of surgically resected adenocarcinomas. The morphological features of adenocarcinomas harboring the mutations were reported to be frequent in those with bronchioloalveolar features, but it is suggested that the cellular lineage of the putative original cells of the cancers refines the subset more clearly. In the present study the current knowledge of EGFR mutations is reviewed, insights from which raise many further questions, and thus suggest new directions for future research.

Correlation between EGFR gene mutation pattern and Akt phosphorylation in pulmonary adenocarcinomas

The detection of gene mutation of epithelial growth factor receptor (EGFR) is important to predict the therapeutic effect of gefitinib. Recently, it was reported that examination of the activation of the downstream protein of EGFR is useful in the same way as the EGFR mutation. Therefore the purpose of the present paper was to determine whether activation of Akt and Erk, which are downstream proteins, and the EGFR gene mutation pattern was correlated. A total of 130 pulmonary adenocarcinomas were studied for the gene mutations of EGFR in exon 19 and 21, and the phosphorylation of Akt and Erk was investigated by immunostaining. The EGFR mutation was detected in 32%, the positivity of p-Akt was 51%, and the rate of p-Erk was 27%. The EGFR mutation-positive cases were the minority in p-Akt-negative cases, and the p-Akt expression was significantly associated with the mutation of EGFR (P=0.0014). In addition, there was a significant correlation between the L858R mutation and the expression of p-Akt (P=0.040). It is suggested that the activation of Akt is dependent on EGFR mutation pattern.

Defining clinically relevant molecular subsets of lung cancer

The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs), gefitinib and erlotinib, induce dramatic responses in certain patients with non-small cell lung cancer (NSCLC). As such, the drugs provide an unexpected tool to dissect clinically relevant molecular subsets of NSCLC. For example, using mutational profiling of tumor DNA from patients with sensitivity, primary resistance, and secondary resistance to these agents, we and others have demonstrated that somatic mutations in the tyrosine kinase domain of EGFR are associated with sensitivity to gefitinib and erlotinib, while mutations in KRAS, which encodes a GTPase downstream of EGFR, are associated with primary resistance. Furthermore, second site mutations in the EGFR kinase domain are commonly found in patients with acquired resistance. We are now using a variety of molecular and biological approaches to help further define molecular subsets of lung cancer that have relevance in the clinic.

The impact of epidermal growth factor receptor gene status on gefitinib-treated Japanese patients with non-small-cell lung cancer

We investigated the relationships between genetic factors and clinical outcome in Japanese non-small-cell lung cancer (NSCLC) patients treated with gefitinib. Ninety-eight NSCLC patients who had been treated with gefitinib, were screened for mutations in epidermal growth factor receptor (EGFR) exons 18-21, KRAS exon2, and polymorphisms including the CA simple sequence repeat in intron1 (CA-SSR1) and single nucleotide polymorphisms in the promoter region (-216G/T and -191C/A), using a PCR-based assay and direct sequencing. The EGFR copy number status was also evaluated using a fluorescence in situ hybridization assay. EGFR and KRAS mutations were found in 38 (38.8%) and 8 (8.2%) of the 98 patients, respectively. A high EGFR copy number status was identified in 31 (41.3%) of the 75 assessable patients. Drug-sensitive EGFR mutations limited to exon19 deletions and L858R were independent predictive factors of a stronger sensitivity to gefitinib (p = 0.0002), the overall survival (OS) (p = 0.0036), and prolonged progression-free survival (PFS) (p < 0.0001). The EGFR copy number status was not related to a sensitivity to gefitinib and prolonged OS and PFS. Regarding polymorphisms, patients with a short CA-SSR1 showed a prolonged OS as compared with those with a long length in patients with a drug-sensitive EGFR mutation, although this difference was not significant (p = 0.13). Thus, drug-sensitive EGFR mutations predict a favorable clinical outcome and a high EGFR copy number may not be related to clinical benefits in gefitinib-treated Japanese patients with NSCLC. Our findings also suggest that the CA-SSR1 length may influence the clinical outcome in patients with a drug-sensitive EGFR mutation.

Epidermal growth factor receptor mutants from human lung cancers exhibit enhanced catalytic activity and increased sensitivity to gefitinib

Somatic mutations within the epidermal growth factor receptor (EGFR) kinase domain are detected in 10% to 30% of human non-small cell lung cancers and are correlated with striking clinical responses in a subset of patients treated with EGFR kinase inhibitors, such as gefitinib and erlotinib. Cell-based studies suggest that these mutant EGFRs promote increased autophosphorylating activity on a subset of EGFR COOH-terminal tyrosines and the consequent engagement of a subset of downstream effectors. Because EGFR function is regulated at multiple levels in vivo, and it is therefore difficult to assess the direct consequences of these mutations on EGFR enzyme function, we measured EGFR catalytic activity in in vitro kinase assays using purified recombinant proteins corresponding to the cytoplasmic domain of wild-type and two frequently detected EGFR mutants (DelL747-P753insS and L858R). Both mutants exhibit substantially increased autophosphorylating activity relative to wild-type EGFR, and they exhibit distinct reaction kinetics. In addition, the mutant kinases are more sensitive to kinase inhibition by gefitinib, which seems to reflect their increased drug affinity. These findings suggest that the altered signaling properties and drug sensitivity of these EGFR mutants that have been observed in vivo largely result from differences in the catalytic properties of the kinase. In addition, we find that the T790M secondary "drug resistance mutation" of EGFR, which frequently arises in relapsed patients that initially responded to treatment, confers enhanced kinase activity to primary activating EGFR alleles and may, therefore, be oncogenic in some contexts.

Differential constitutive activation of the epidermal growth factor receptor in non-small cell lung cancer cells bearing EGFR gene mutation and amplification

The identification of somatic mutations in the tyrosine kinase domain of the epidermal growth factor receptor (EGFR) in patients with non-small cell lung cancer (NSCLC) and the association of such mutations with the clinical response to EGFR tyrosine kinase inhibitors (TKI), such as gefitinib and erlotinib, have had a substantial effect on the treatment of this disease. EGFR gene amplification has also been associated with an increased therapeutic response to EGFR-TKIs. The effects of these two types of EGFR alteration on EGFR function have remained unclear, however. We have now examined 16 NSCLC cell lines, including eight newly established lines from Japanese NSCLC patients, for the presence of EGFR mutations and amplification. Four of the six cell lines that harbor EGFR mutations were found to be positive for EGFR amplification, whereas none of the 10 cell lines negative for EGFR mutation manifested EGFR amplification, suggesting that these two types of EGFR alteration are closely associated. Endogenous EGFRs expressed in NSCLC cell lines positive for both EGFR mutation and amplification were found to be constitutively activated as a result of ligand-independent dimerization. Furthermore, the patterns of both EGFR amplification and EGFR autophosphorylation were shown to differ between cell lines harboring the two most common types of EGFR mutation (exon 19 deletion and L858R point mutation in exon 21). These results reveal distinct biochemical properties of endogenous mutant forms of EGFR expressed in NSCLC cell lines and may have implications for treatment of this condition.

Understanding the new genetics of responsiveness to epidermal growth factor receptor tyrosine kinase inhibitors

The epidermal growth factor receptor (EGFR) is implicated in cancer progression and development and, being overexpressed in a variety of human malignancies, is an attractive target for selective anticancer therapy. EGFR tyrosine kinase inhibitors (TKIs) have been demonstrated to produce dramatic and durable responses in a fraction of non-small cell lung cancer patients. During the last few years, clinical and biological predictors for TKI sensitivity have been identified. Among clinical features, never-smoking history seemed the most critical factor, probably because of the different spectrum of molecular abnormalities associated with cigarette-smoking exposure. Among biological predictors, several studies indicate that EGFR mutations and increased EGFR gene copy number are implicated in response to TKI therapy, with conflicting results in survival. Mutations in the EGFR gene as well as in K-ras and HER2 genes seemed to impair TKI effects, leading to TKI resistance. Because most available data come from retrospective studies, there is an urgent need to validate these results in prospective trials. Several studies have been recently completed, and these data could indicate how to properly select patients who are candidates for TKI therapy.

Response to treatment and survival of patients with non-small cell lung cancer undergoing somatic EGFR mutation testing

Somatic mutations in the epidermal growth factor receptor (EGFR) gene are associated with clinical response and prolonged survival in patients with non-small cell lung cancer (NSCLC) treated with EGFR tyrosine kinase inhibitors (TKIs). We began screening patients for somatic EGFR mutations by DNA sequencing as part of clinical care in 2004. We performed a retrospective cohort study of 278 patients with NSCLC referred for EGFR testing over a 10-month period. Tumor samples underwent direct DNA sequence analyses of EGFR exons 18 through 24. We determined the clinical characteristics and EGFR mutation status of the patients and analyzed their response to therapy and survival. EGFR somatic mutations were identified in 68 (24%) of patients. A minimal smoking history was the strongest clinical predictor of harboring a mutation. In multivariable analyses, each pack-year of smoking corresponded to a 5% decreased likelihood of having an EGFR mutation. Among 92 patients with unresectable disease undergoing subsequent systemic therapy, EGFR mutations were associated with an increased response rate to EGFR TKIs (p < .0001) but not chemotherapy. Overall survival was significantly prolonged in EGFR mutation-positive patients (p = .001), with a median survival of 3.1 years compared with 1.6 years in mutation-negative patients, after adjusting for age, gender, and stage at diagnosis. Integrating molecular profiling into clinical care is feasible in NSCLC patients and provides useful clinical information.

Update on epidermal growth factor receptor mutations in non-small cell lung cancer

In 2004, several investigators reported that somatic mutations in the epidermal growth factor receptor gene were associated with clinical responses to erlotinib and gefitinib in patients with non-small cell lung cancer. Since then, multiple groups have examined the biological properties that such mutations confer as well as the clinical relevance of these mutations in patients with non-small cell lung cancer. Although a tremendous amount of knowledge has been gained in the past 2 years, there remain a number of important epidemiologic, biological, and clinical questions.

Molecular predictors of response to epidermal growth factor receptor antagonists in non-small-cell lung cancer

In the last 5 years the epidermal growth factor receptor (EGFR) has emerged as one of the most important targets for drug development in oncology. Monoclonal antibodies targeting the external domain of EGFR have been shown to have clinical benefit in colorectal and head and neck cancer when combined with chemotherapy and/or radiation. Small molecules that inhibit the tyrosine kinase (TK) domain of EGFR have become critical new weapons in the treatment of non-small-cell lung cancer (NSCLC). The discovery that mutations in the TK domain are associated with dramatic and sustained responses to EGFR TK inhibitors (TKIs) has allowed the design of trials to test these agents as potential first-line therapies and has provided a fascinating window into the future of genotype-directed targeted therapy. Recent advances in understanding the biologic basis of acquired resistance to these agents have great potential to improve the clinical effectiveness of this class of drugs. This review summarizes the biology of EGFR in NSCLC, the clinical and molecular predictors of benefit from treatment with EGFR TKIs, the use of patient-specific molecular profiling, and future directions of clinical and basic scientific research.

EGFR kinase domain mutations - functional impact and relevance for lung cancer therapy

In 2004 remarkable clinical responses in non-small-cell lung cancer (NSCLC) patients treated with the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor gefitinib were reported to correlate with the presence of certain somatic EGFR kinase domain mutations in tumors. Since then, a surge of enthusiasm has been encountered in the field of molecular and clinical oncology. Beyond the promise of a tailored medicine, questions about the molecular mechanisms underlying the observed effects have arisen. In vitro analysis of NSCLC cells with endogenous EGFR mutations, recombinant expression of EGFR variants by transfection of several cell lines and the generation of transgenic mice expressing mutant EGFR were applied to study the impact of these genetic alterations on cellular signaling and cell fate. This review outlines the current mechanistic knowledge derived from such studies and discusses the relevance of EGFR kinase domain mutations for EGFR-directed therapies, including monoclonal antibodies.

Activation of downstream epidermal growth factor receptor (EGFR) signaling provides gefitinib-resistance in cells carrying EGFR mutation

Patients with pulmonary adenocarcinoma carrying the epidermal growth factor receptor (EGFR) mutation tend to display dramatic clinical response to treatment with the EGFR tyrosine kinase inhibitor gefitinib. Unfortunately, in many cases the cancer cells eventually acquire resistance, and this limits the duration of efficacy. To gain insight into these acquired resistance mechanisms, we first prepared HEK293T cell line stably transfected with either wild-type (WT) or mutant (L858R) EGFR, and then expressed oncogenic K-Ras12V mutant in the latter transfectant. Although 293T cells expressing wild-type EGFR did not show any growth inhibition by gefitinib treatment similarly to the non-transfected cells, the cells expressing the EGFR-L858R were exquisitely sensitive. Consistently, phospho-Akt levels were decreased in response to gefitinib in cells expressing EGFR-L858R but not in cells with EGFR-WT. In contrast, 293T cells expressing both EGFR-L858R and oncogenic K-Ras were able to proliferate even in the presence of high concentration of gefitinib probably by inducing Erk1/2 activation. We also expressed K-Ras12V in the gefitinib-sensitive pulmonary adenocarcinoma cell line PC-9, which harbors an in-frame deletion in the EGFR gene. The activated K-Ras inhibited the effects of gefitinib treatment on cell growth, cell death induction and levels of phospho-Akt, as well as phospho-Erk. These data indicate that activated Ras could substitute most of the upstream EGFR signal, and are consistent with the hypothesis that mutational activation of targets immediately downstream from the EGFR could induce the secondary resistance to gefitinib in patients with lung cancer carrying EGFR mutation.

Epidermal growth factor receptor mutations in lung cancer

The development and clinical application of inhibitors that target the epidermal growth factor receptor (EGFR) provide important insights for new lung cancer therapies, as well as for the broader field of targeted cancer therapies. We review the results of genetic, biochemical and clinical studies focused on somatic mutations of EGFR that are associated with the phenomenon of oncogene addiction, describing 'oncogenic shock' as a mechanistic explanation for the apoptosis that follows the acute treatment of susceptible cells with kinase inhibitors. Understanding the genetic heterogeneity of epithelial tumours and devising strategies to circumvent their rapid acquisition of resistance to targeted kinase inhibitors are essential to the successful use of targeted therapies in common epithelial cancers.

Structures of lung cancer-derived EGFR mutants and inhibitor complexes: mechanism of activation and insights into differential inhibitor sensitivity

Mutations in the EGFR kinase are a cause of non-small-cell lung cancer. To understand their mechanism of activation and effects on drug binding, we studied the kinetics of the L858R and G719S mutants and determined their crystal structures with inhibitors including gefitinib, AEE788, and a staurosporine. We find that the mutations activate the kinase by disrupting autoinhibitory interactions, and that they accelerate catalysis as much as 50-fold in vitro. Structures of inhibitors in complex with both wild-type and mutant kinases reveal similar binding modes for gefitinib and AEE788, but a marked rotation of the staurosporine in the G719S mutant. Strikingly, direct binding measurements show that gefitinib binds 20-fold more tightly to the L858R mutant than to the wild-type enzyme.

Which biomarker predicts benefit from EGFR-TKI treatment for patients with lung cancer?

Subsets of patients with non-small cell lung cancer respond remarkably well to small molecule tyrosine kinase inhibitors (TKI) specific for epidermal growth factor receptor (EGFR) such as gefitinib or erlotinib. In 2004, it was found that EGFR mutations occurring in the kinase domain are strongly associated with EGFR-TKI sensitivity. However, subsequent studies revealed that this relationship was not perfect and various predictive markers have been reported. These include EGFR gene copy numbers, status of ligands for EGFR, changes in other HER family genes or molecules downstream to EGFR including KRAS or AKT. In this review, we would like to review current knowledge of predictive factors for EGFR-TKI. As all but one phase III trials failed to show a survival advantage of the treatment arm involving EGFR-TKIs, it is necessary to select patients by these biomarkers in future clinical trials. Through these efforts, it would be possible to individualise EGFR-TKI treatment for patients suffering from lung cancer.

The major lung cancer-derived mutants of ERBB2 are oncogenic and are associated with sensitivity to the irreversible EGFR/ERBB2 inhibitor HKI-272

Mutations in the ERBB2 gene were recently found in approximately 2% of primary non-small cell lung cancer (NSCLC) specimens; however, little is known about the functional consequences and the relevance to responsiveness to targeted drugs for most of these mutations. Here, we show that the major lung cancer-derived ERBB2 mutants, including the most frequent mutation, A775insYVMA, lead to oncogenic transformation in a cellular assay. Murine cells transformed with these mutants were relatively resistant to the reversible epidermal growth factor receptor (EGFR) inhibitor erlotinib, resembling the resistant phenotype found in cells carrying the homologous mutations in exon 20 of EGFR. However, the same cells were highly sensitive to the irreversible dual-specificity EGFR/ERBB2 kinase inhibitor HKI-272, as were those overexpressing wild-type ERBB2. Finally, the NSCLC cell line, Calu-3, overexpressing wild-type ERBB2 owing to a high-level amplification of the ERBB2 gene were highly sensitive to HKI-272. These results provide a rationale for treatment of patients with ERBB2-mutant or ERBB2-amplified lung tumors with HKI-272.

Erlotinib effectively inhibits JAK2V617F activity and polycythemia vera cell growth

JAK2(V617F), a mutant of tyrosine kinase JAK2, is found in most patients with polycythemia vera (PV) and a substantial proportion of patients with idiopathic myelofibrosis or essential thrombocythemia. The JAK2 mutant displays a much increased kinase activity and generates a PV-like phenotype in mouse bone marrow transplant models. This study shows that the anti-cancer drug erlotinib (Tarceva) is a potent inhibitor of JAK2(V617F) activity. In vitro colony culture assays revealed that erlotinib at micro-molar concentrations effectively suppresses the growth and expansion of PV hematopoietic progenitor cells while having little effect on normal cells. Furthermore, JAK2(V617F)-positive cells from PV patients show greater susceptibility to the inhibitor than their negative counterparts. Similar inhibitory effects were found with the JAK2(V617F)-positive human erythroleukemia HEL cell line. These data suggest that erlotinib may be used for treatment of JAK2(V617F)-positive PV and other myeloproliferative disorders.

PTEN-Mediated Resistance to Epidermal Growth Factor Receptor Kinase Inhibitors

Molecularly targeted therapies are transforming the treatment of cancer. Elucidating the dynamic signaling networks that underlie sensitivity and resistance to these inhibitors is critical for successful clinical application. There is considerable evidence to suggest that constitutively activating mutations in kinases that regulate cellular growth may result in tumor cell "addiction" and favorable response to targeted inhibition. However, there is emerging evidence to suggest that clinical response may also be determined by other changes in the molecular circuitry of cancer cells, such as loss of key tumor-suppressor proteins. Here, we will discuss resistance to epidermal growth factor receptor tyrosine kinase inhibitors in glioblastoma patients that is mediated by loss of the PTEN tumor-suppressor protein.

Somatic mutations of the epidermal growth factor receptor and non-small-cell lung cancer

Frequent overexpression of epidermal growth factor receptor (EGFR) in non-small-cell lung cancer (NSCLC) makes EGFR a new therapeutic target. Two specific EGFR tyrosine kinase inhibitors, gefitinib (ZD1839, Iressa) and erlotinib (OSI-774, Tarceva), have been developed and approved by the US Food and Drug Administration for second-line and third-line treatment of advanced NSCLC. Clinical trials have shown considerable variability in the response rate between different patients with NSCLC, which led to the discovery of somatic EGFR-activating mutations. This brief review summarises the discovery and functional consequences of the mutations, their clinicopathological features and significant implications in the treatment and prognosis of NSCLC.