Enhancing proteasomal processing improves survival for a peptide vaccine used to treat glioblastoma

Despite its essential role in antigen presentation, enhancing proteasomal processing is an unexploited strategy for improving vaccines. pepVIII, an anticancer vaccine targeting EGFRvIII, has been tested in several trials for glioblastoma. We examined 20 peptides in silico and experimentally, which showed that a tyrosine substitution (Y6-pepVIII) maximizes proteasome cleavage and survival in a subcutaneous tumor model in mice. In an intracranial glioma model, Y6-pepVIII showed a 62 and 31% improvement in median survival compared to control animals and pepVIII-vaccinated mice. Y6-pepVIII vaccination altered tumor-infiltrating lymphocyte subsets and expression of PD-1 on intratumoral T cells. Combination with anti-PD-1 therapy cured 45% of the Y6-pepVIII-vaccinated mice but was ineffective for pepVIII-treated mice. Liquid chromatography-tandem mass spectrometry analysis of proteasome-digested pepVIII and Y6-pepVIII revealed that most fragments were similar but more abundant in Y6-pepVIII digests and 77% resulted from proteasome-catalyzed peptide splicing (PCPS). We identified 10 peptides that bound human and murine MHC class I. Nine were PCPS products and only one peptide was colinear with EGFRvIII, indicating that PCPS fragments may be a component of MHC class I recognition. Despite not being colinear with EGFRvIII, two of three PCPS products tested were capable of increasing survival when administered independently as vaccines. We hypothesize that the immune response to a vaccine represents the collective contribution from multiple PCPS and linear products. Our work suggests a strategy to increase proteasomal processing of a vaccine that results in an augmented immune response and enhanced survival in mice.

Development and Evaluation of a Web-Based Resource for Suicidal Thoughts: NowMattersNow.org

Background

Nearly half of people who die by suicide see a health care provider in the month before their death. With the release of new care guidelines, detection of suicidal patients will likely increase. Providers need access to suicide-specific resources that can be used as part of immediate, brief interventions with a suicidal patient. Web-based suicide prevention resources have the potential to address this need.

Objective

This study aimed to describe the development of the NowMattersNow.org website as a resource for individuals with suicidal thoughts and to evaluate the utility of the site via user experience surveys.

Methods

NowMattersNow.org is an online video-based free public resource that provides evidence-based teachings, examples, and resources for managing suicidal thoughts and intense emotions focused largely around skills from dialectical behavior therapy. Developed with assistance from mental health consumers, it is intended to address gaps in access to services for suicidal patients in health care systems. Visitors stay an average of a minute and a half on the website. From March 2015 to December 2017, a user experience survey measured self-reported changes on a 1 (not at all) to 5 (completely overwhelming) scale regarding intensity of suicidal thoughts and negative emotions while on the website. Longitudinal regression analyses using generalized estimating equations evaluated the magnitude and statistical significance of user-reported changes in suicidal ideation and negative emotion. In secondary analyses, user-reported changes specific to subgroups, including men aged 36 to 64 years, mental health care providers, and other health care providers were evaluated.

Results

During the period of analysis, there were 138,386 unique website visitors. We analyzed surveys (N=3670) collected during that time. Subsamples included men aged 36 to 64 years (n=512), mental health providers (n=460), and other health care providers (n=308). A total of 28% (1028/3670) of survey completers rated their suicidal thoughts as a 5 or “completely overwhelming” when they entered the website. We observed significant reductions in self-reported intensity of suicidal thoughts (–0.21, P<.001) and negative emotions (–0.32, P<.001), including decreases for users with the most severe suicidal thoughts (–6.4%, P<.001), most severe negative emotions (–10.9%, P<.001), and for middle-aged men (–0.13, P<001). Results remained significant after controlling for length of visit to website (before the survey) and technology type (mobile, desktop, and tablet).

Conclusions

Survey respondents reported measurable reductions in intensity of suicidal thoughts and emotions, including those rating their suicidal thoughts as completely or almost completely overwhelming and among middle-aged men. Although results from this user-experience survey administered at one point in time to a convenience sample of users must be interpreted with caution, results provide preliminary support for the potential effectiveness of the NowMattersNow.org website as a tool for short-term management of suicidal thoughts and negative emotions.

Targeting a glioblastoma cancer stem-cell population defined by EGF receptor variant III

The relationship between mutated proteins and the cancer stem-cell population is unclear. Glioblastoma tumors frequently express EGFRvIII, an EGF receptor (EGFR) variant that arises via gene rearrangement and amplification. However, expression of EGFRvIII is restricted despite the prevalence of the alteration. Here, we show that EGFRvIII is highly coexpressed with CD133 and that EGFRvIII(+)/CD133(+) defines the population of cancer stem cells (CSC) with the highest degree of self-renewal and tumor-initiating ability. EGFRvIII(+) cells are associated with other stem/progenitor markers, whereas markers of differentiation are found in EGFRvIII(-) cells. EGFRvIII expression is lost in standard cell culture, but its expression is maintained in tumor sphere culture, and cultured cells also retain the EGFRvIII(+)/CD133(+) coexpression, self-renewal, and tumor initiating abilities. Elimination of the EGFRvIII(+)/CD133(+) population using a bispecific antibody reduced tumorigenicity of implanted tumor cells better than any reagent directed against a single epitope. This work demonstrates that a mutated oncogene can have CSC-specific expression and be used to specifically target this population.

Chimeric antigen receptor containing ICOS signaling domain mediates specific and efficient antitumor effect of T cells against EGFRvIII expressing glioma

Background

Adoptive transfer of chimeric antigen receptor (CAR)-modified T cells appears to be a promising immunotherapeutic strategy. CAR combines the specificity of antibody and cytotoxicity of cytotoxic T lymphocytes, enhancing T cells’ ability to specifically target antigens and to effectively kill cancer cells. Recent efforts have been made to integrate the costimulatory signals in the CAR to improve the antitumor efficacy. Epidermal growth factor receptor variant III (EGFRvIII) is an attractive therapeutic target as it frequently expresses in glioma and many other types of cancers. Our current study aimed to investigate the specific and efficient antitumor effect of T cells modified with CAR containing inducible costimulator (ICOS) signaling domain.

Methods

A second generation of EGFRvIII/CAR was generated and it contained the EGFRvIII single chain variable fragment, ICOS signaling domain and CD3ζ chain. Lentiviral EGFRvIII/CAR was prepared and human CD3⁺ T cells were infected by lentivirus encoding EGFRvIII/CAR. The expression of EGFRvIII/CAR on CD3⁺ T cells was confirmed by flow cytometry and Western blot. The functions of EGFRvIII/CAR⁺ T cells were evaluated using in vitro and in vivo methods including cytotoxicity assay, cytokine release assay and xenograft tumor mouse model.

Results

Chimeric EGFRvIIIscFv-ICOS-CD3ζ (EGFRvIII/CAR) was constructed and lentiviral EGFRvIII/CAR were made to titer of 10⁶ TU/ml. The transduction efficiency of lentiviral EGFRvIII/CAR on T cells reached around 70% and expression of EGFRvIII/CAR protein was verified by immunoblotting as a band of about 57 kDa. Four hour ⁵¹Cr release assays demonstrated specific and efficient cytotoxicity of EGFRvIII/CAR⁺ T cells against EGFRvIII expressing U87 cells. A robust increase in the IFN-γ secretion was detected in the co-culture supernatant of the EGFRvIII/CAR⁺ T cells and the EGFRvIII expressing U87 cells. Intravenous and intratumor injection of EGFRvIII/CAR⁺ T cells inhibited the in vivo growth of the EGFRvIII expressing glioma cells.

Conclusions

Our study demonstrates that the EGFRvIII/CAR-modified T cells can destroy glioma cells efficiently in an EGFRvIII specific manner and release IFN-γ in an antigen dependent manner. The specific recognition and effective killing activity of the EGFRvIII-directed T cells with ICOS signaling domain lays a foundation for us to employ such approach in future cancer treatment.

Breakpoint analysis of transcriptional and genomic profiles uncovers novel gene fusions spanning multiple human cancer types

Gene fusions, like BCR/ABL1 in chronic myelogenous leukemia, have long been recognized in hematologic and mesenchymal malignancies. The recent finding of gene fusions in prostate and lung cancers has motivated the search for pathogenic gene fusions in other malignancies. Here, we developed a “breakpoint analysis” pipeline to discover candidate gene fusions by tell-tale transcript level or genomic DNA copy number transitions occurring within genes. Mining data from 974 diverse cancer samples, we identified 198 candidate fusions involving annotated cancer genes. From these, we validated and further characterized novel gene fusions involving ROS1 tyrosine kinase in angiosarcoma (CEP85L/ROS1), SLC1A2 glutamate transporter in colon cancer (APIP/SLC1A2), RAF1 kinase in pancreatic cancer (ATG7/RAF1) and anaplastic astrocytoma (BCL6/RAF1), EWSR1 in melanoma (EWSR1/CREM), CDK6 kinase in T-cell acute lymphoblastic leukemia (FAM133B/CDK6), and CLTC in breast cancer (CLTC/VMP1). Notably, while these fusions involved known cancer genes, all occurred with novel fusion partners and in previously unreported cancer types. Moreover, several constituted druggable targets (including kinases), with therapeutic implications for their respective malignancies. Lastly, breakpoint analysis identified new cell line models for known rearrangements, including EGFRvIII and FIP1L1/PDGFRA. Taken together, we provide a robust approach for gene fusion discovery, and our results highlight a more widespread role of fusion genes in cancer pathogenesis.

Gene fusions represent an important class of cancer genes, created by rearrangements of the genome that bring together two different genes. Because they are unique to cancer cells, gene fusions are ideal diagnostic markers and therapeutic targets. While gene fusions were once thought restricted mainly to blood cancers, recent discoveries suggest they are more widespread. Here, we have developed an approach for mining DNA microarray data to detect the tell-tale signatures of gene fusions, as “breakpoints” occurring within the encoding DNA or expressed transcripts. We apply this approach to a large collection of nearly 1,000 human cancer specimens. From this analysis, we discover and verify twelve new gene fusions occurring in diverse cancer types. We verify that some of these rearrangements recur in other samples of the same cancer type (supporting a causal role) and that the cancers show dependency on the fusion for cancer cell growth. Notably, some of these fusions (e.g. CEP85L/ROS1 in angiosarcoma) represent the first for that cancer type and thus provide important new biological insight. Some are also good drug targets (including rearrangements of ROS1, RAF1, and CDK6 kinases), with clear implications for therapy.

Abstract 3733: Defining and targeting a Glioblastoma cancer stem cell population with EGF Receptor Variant III

The relationship between mutated proteins and the relatively rare cancer stem cell population is unclear since driver mutations are present throughout a tumor. Glioblastoma (GBM) tumors frequently express EGFRvIII, an EGFR variant that arises via gene rearrangement and amplification. The expression of EGFRvIII is restricted despite the prevalence of the alteration. Here we show that EGFRvIII is expressed in a population of human GBM cancer stem cells. EGFRvIII positive cancer stem cells demonstrate greater self-renewal and tumor initiation than the more abundant EGFRvIII negative cells. EGFRvIII positive cells are associated with stem/progenitor markers while markers of differentiation are found in EGFRvIII negative cells. EGFRvIII is highly co-expressed with CD133, and the EGFRvIII positive/CD133 positive sub-population defines the highest self-renewal and tumor initiating population. Surprisingly, wildtype EGFR was infrequently co-expressed with EGFRvIII but present in the majority of cells, both in primary GBM and cultured GBM neurospheres. Elimination of the EGFRvIII positive or the EGFRvIII/CD133 dual positive population with an engineered anti-EGFRvIII/CD133 bi-specific antibody reduced tumorigenicity of implanted tumor cells. This work demonstrates that a mutated oncogene can have CSC specific expression and be used to specifically target this population.

Citation Format: David R. Emlet, Catherine Del Vecchio, Puja Gupta, Siddhartha Mitra, Shuang-Yin Han, Marina Holgado-Madruga, Gordon Li, Kristen Jensen, Hannes Vogel, Stephen Skirboll, Albert J. Wong. Defining and targeting a Glioblastoma cancer stem cell population with EGF Receptor Variant III. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3733. doi:10.1158/1538-7445.AM2013-3733

Targeting EGF receptor variant III: tumor-specific peptide vaccination for malignant gliomas

Glioblastoma multiforme (GBM) is the most common and deadly of the human brain cancers. The EGF receptor is often amplified in GBM and provides a potential therapeutic target. However, targeting the normal receptor is complicated by its nearly ubiquitous and high level of expression in certain tissues. A naturally occurring deletion mutant of the EGF receptor, EGFRvIII, is a constitutively active variant originally identified in a high percentage of brain cancer cases, and more importantly is rarely found in normal tissue. A peptide vaccine, rindopepimut (CDX-110, Celldex Therapeutics), is directed against the novel exon 1-8 junction produced by the EGFRvIII deletion, and it has shown high efficacy in preclinical models. Recent Phase II clinical trials in patients with newly diagnosed GBM have shown EGFRvIII-specific immune responses and significantly increased time to progression and overall survival in those receiving vaccine therapy, as compared with published results for standard of care. Rindopepimut therefore represents a very promising therapy for patients with GBM.

Abstract 10: Oncogenic variant EGFRvIII defines a hierarchy in glioblastoma and expression is restricted by epigenetic mechanisms despite the presence of gene amplification

Glioblastoma multiforme (GBM) is the most common and deadly primary brain tumor. Amplification and rearrangements of the epidermal growth factor receptor (EGFR) gene are frequently found in GBM. The most common variant is EGFRvIII, an exon 2-7 deletion mutant resulting from amplification and rearrangement of the EGFR locus. We have hypothesized that EGFRvIII could mark a cancer stem cell or tumor initiating cell population. If amplification and rearrangement are early events in tumorigenesis, this implies that they should be preserved throughout the tumor. However, in primary GBM EGFRvIII expression was focal and sporadic. To understand the relationship between EGFRvIII expression and the underlying genomic alterations, we utilized manual dissection to separate EGFRvIII positive and negative cells and a quantitative PCR assay that detects independently both EGFR amplification and rearrangement. Unexpectedly, we found EGFR amplification and rearrangement throughout the tumor, including regions with no EGFRvIII expression. This supports our hypothesis and further suggests that mechanisms exist to modulate EGFRvIII expression even in the presence of high gene amplification. To study this phenomenon, we characterized three GBM cell lines with endogenous EGFRvIII expression and corresponding EGFR amplification and rearrangement, confirmed by Western blot, RT-PCR and FISH. By flow cytometry analysis EGFRvIII expression was heterogeneous, with 9-50% EGFRvIII positive cells in each cell line. Both positive and negative populations maintained the genetic alterations, recapitulating what we observed in primary GBM. Importantly, EGFRvIII defined a hierarchy where EGFRvIII-positive cells gave rise to additional positive and negative cells. However, only cells that had recently lost EGFRvIII expression could re-express EGFRvIII. Epigenetic mechanisms played a role in modulating EGFRvIII expression to maintain a heterogeneous population. Demethylation induced a 20-60% increase in the percentage of EGFRvIII-positive cells, indicating that some cells could re-express EGFRvIII. Surprisingly, inhibition of histone deacetylation resulted in a 50-80% reduction in EGFRvIII expression. Collectively, this data demonstrates that EGFRvIII does follow a stem cell model for hierarchical expression and sheds light on the existence of a transient population that is able to re-express EGFRvIII, an important buffer for maintaining EGFRvIII-positive cell numbers. Furthermore, we provide the first evidence that EGFRvIII expression can be silenced by epigenetic mechanisms, suggesting that drugs which modulate the epigenome might be used successfully in glioblastoma tumors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 10. doi:1538-7445.AM2012-10

Expression of epidermal growth factor variant III (EGFRvIII) in pediatric diffuse intrinsic pontine gliomas

Despite numerous clinical trials over the past 2 decades, the overall survival for children diagnosed with diffuse intrinsic pontine glioma (DIPG) remains 9-10 months. Radiation therapy is the only treatment with proven effect and novel therapies are needed. Epidermal growth factor receptor variant III (EGFRvIII) is the most common variant of the epidermal growth factor receptor and is expressed in many tumor types but is rarely found in normal tissue. A peptide vaccine targeting EGFRvIII is currently undergoing investigation in phase 3 clinical trials for the treatment of newly diagnosed glioblastoma (GBM), the tumor in which this variant receptor was first discovered. In this study, we evaluated EGFRvIII expression in pediatric DIPG samples using immunohistochemistry with a double affinity purified antibody raised against the EGFRvIII peptide. Staining of pediatric DIPG histological samples revealed expression in 4 of 9 cases and the pattern of staining was consistent with what has been seen in EGFRvIII transfected cells as well as GBMs from adult trials. In addition, analysis of tumor samples collected immediately post mortem and of DIPG cells in culture by RT-PCR, western blot analysis, and flow cytometry confirmed EGFRvIII expression. We were therefore able to detect EGFRvIII expression in 6 of 11 DIPG cases. These data suggest that EGFRvIII warrants investigation as a target for these deadly pediatric tumors.

Immunohistochemical discrimination of wild-type EGFR from EGFRvIII in fixed tumour specimens using anti-EGFR mAbs ICR9 and ICR10

Background:

The human epidermal growth factor receptor (EGFR) is an important therapeutic target in oncology, and three different types of EGFR inhibitors have been approved for the treatment of cancer patients. However, there has been no clear association between the expression levels of EGFR protein in the tumours determined by the FDA-approved EGFR PharmDx kit (Dako) or other standard anti-EGFR antibodies and the response to the EGFR inhibitors.

Method:

In this study, we investigated the potential of our anti-EGFR monoclonal antibodies (mAbs; ICR9, ICR10, ICR16) for immunohistochemical diagnosis of wild-type EGFR and/or the type-III deletion mutant form of EGFR (EGFRvIII) in formalin-fixed, paraffin-embedded human tumour specimens.

Results:

We found that the anti-EGFR mAb in the EGFR PharmDx kit stained both wild-type and EGFRvIII-expressing cells in formalin-fixed, paraffin-embedded sections. This pattern of EGFR immunostaining was also found with our anti-EGFR mAb ICR16. In contrast, mAbs ICR10 and ICR9 were specific for the wild-type EGFR.

Conclusion:

We conclude that mAbs ICR9 and ICR10 are ideal tools for investigating the expression patterns of wild-type EGFR protein in tumour specimens using immunohistochemistry, and to determine their prognostic significance, as well as predictive value for response to therapy with EGFR antibodies.

A novel epidermal growth factor receptor variant lacking multiple domains directly activates transcription and is overexpressed in tumors

The epidermal growth factor receptor (EGFR) is essential to multiple physiological and neoplastic processes via signaling by its tyrosine kinase domain and subsequent activation of transcription factors. EGFR overexpression and alteration, including point mutations and structural variants, contribute to oncogenesis in many tumor types. In this study, we identified an in-frame splice variant of the EGFR called mini-LEEK (mLEEK) that is more broadly expressed than the EGFR and is overexpressed in several cancers. Unlike previously characterized EGFR variants, mLEEK lacks the extracytoplasmic, transmembrane and tyrosine kinase domains. mLEEK localizes in the nucleus and functions as a transcription factor to regulate target genes involved in the cellular response to endoplasmic reticulum (ER) stress, including the master regulator of the unfolded protein response (UPR) pathways, molecular chaperone GRP78/Bip. We demonstrated that mLEEK regulates GRP78 transcription through direct interaction with a cis-regulatory element within the gene promoter. Several UPR pathways were interrogated and mLEEK expression was found to attenuate the induction of all pathways upon ER stress. Conversely, knockdown of mLEEK resulted in caspase-mediated cell death and sensitization to ER stress. These findings indicate that mLEEK levels determine cellular responses to unfavorable conditions that cause ER stress. This information, along with the overexpression of mLEEK in tumors, suggests unique strategies for therapeutic intervention. Furthermore, the identification of mLEEK expands the known mechanisms by which the EGFR gene contributes to oncogenesis and represents the first link between two previously disparate areas in cancer cell biology: EGFR signaling and the UPR.

Measuring the constitutive activation of c-Jun N-terminal kinase isoforms

The c-Jun N-terminal kinases (JNK) are important regulators of cell growth, proliferation, and apoptosis. JNKs are typically activated by a sequence of events that include phosphorylation of its T-P-Y motif by an upstream kinase, followed by homodimerization and translocation to the nucleus. Constitutive activation of JNK has been found in a variety of cancers including non-small cell lung carcinomas, gliomas, and mantle cell lymphoma. In vitro studies show that constitutive activation of JNK induces a transformed phenotype in fibroblasts and enhances tumorigenicity in a variety of cell lines. Interestingly, a subset of JNK isoforms was recently found to autoactivate rendering the proteins constitutively active. These constitutively active JNK proteins were found to play a pivotal role in activating transcription factors that increase cellular growth and tumor formation in mice. In this chapter, we describe techniques and methods that have been successfully used to study the three components of JNK activation. Use of these techniques may lead to a better understanding of the components of JNK pathways and how JNK is activated in cancer cells.

Rindopepimut, a 14-mer injectable peptide vaccine against EGFRvIII for the potential treatment of glioblastoma multiforme

Celldex Therapeutics is developing rindopepimut (CDX-110), a 14-mer injectable peptide vaccine for the potential treatment of glioblastoma multiforme (GBM). Rindopepimut specifically targets a novel junctional epitope of the EGFR deletion mutant EGFRvIII, which is a constitutively active receptor that is expressed in approximately 60 to 70% of patients with GBM. EGFRvIII expression is correlated with worse prognosis and reduced overall survival. Importantly, EGFRvIII is not expressed in normal brain tissue, making it an excellent therapeutic target. Preclinical studies demonstrated lasting tumor regression and increased survival times, as well as efficient generation of EGFRvIII-specific humoral and cellular immune responses, in animals expressing EGFRvIII and vaccinated with rindopepimut. Phase I and II clinical trials in patients with GBM demonstrated significantly increased median time to progression and overall survival time in those vaccinated with rindopepimut compared with matched historical controls. Only limited side effects have been observed in patients. Given these results, rindopepimut is an extremely promising therapy for patients with GBM. Phase I and II clinical trials in patients with GBM were ongoing at the time of publication. In the future, it may be beneficial to combine rindopepimut with other treatment modalities to further prolong survival.

Development of an EGFRvIII specific recombinant antibody

BACKGROUND

EGF receptor variant III (EGFRvIII) is the most common variant of the EGF receptor observed in human tumors. It results from the in frame deletion of exons 2-7 and the generation of a novel glycine residue at the junction of exons 1 and 8. This novel juxtaposition of amino acids within the extra-cellular domain of the EGF receptor creates a tumor specific and immunogenic epitope. EGFRvIII expression has been seen in many tumor types including glioblastoma multiforme (GBM), breast adenocarcinoma, non-small cell lung carcinoma, ovarian adenocarcinoma and prostate cancer, but has been rarely observed in normal tissue. Because this variant is tumor specific and highly immunogenic, it can be used for both a diagnostic marker as well as a target for immunotherapy. Unfortunately many of the monoclonal and polyclonal antibodies directed against EGFRvIII have cross reactivity to wild type EGFR or other non-specific proteins. Furthermore, a monoclonal antibody to EGFRvIII is not readily available to the scientific community.

RESULTS

In this study, we have developed a recombinant antibody that is specific for EGFRvIII, has little cross reactivity for the wild type receptor, and which can be easily produced. We initially designed a recombinant antibody with two anti-EGFRvIII single chain Fv's linked together and a human IgG1 Fc component. To enhance the specificity of this antibody for EGFRvIII, we mutated tyrosine H59 of the CDRH2 domain and tyrosine H105 of the CDRH3 domain to phenylalanine for both the anti-EGFRvIII sequence inserts. This mutated recombinant antibody, called RAb(DMvIII), specifically detects EGFRvIII expression in EGFRvIII expressing cell lines as well as in EGFRvIII expressing GBM primary tissue by western blot, immunohistochemistry (IHC) and immunofluorescence (IF) and FACS analysis. It does not recognize wild type EGFR in any of these assays. The affinity of this antibody for EGFRvIII peptide is 1.7 × 10⁷ M⁻¹ as determined by enzyme-linked immunosorbent assay (ELISA).

CONCLUSION

This recombinant antibody thus holds great potential to be used as a research reagent and diagnostic tool in research laboratories and clinics because of its high quality, easy viability and unique versatility. This antibody is also a strong candidate to be investigated for further in vivo therapeutic studies.

The role of the c-Jun N-terminal kinase 2-α-isoform in non-small cell lung carcinoma tumorigenesis

The c-Jun N-terminal kinases (JNKs) are members of the mitogen-activated protein kinase family and have been implicated in tumorigenesis. One isoform in particular, JNK2α, has been shown to be frequently activated in primary brain tumors, to enhance several tumorigenic phenotypes and to increase tumor formation in mice. As JNK is frequently activated in non-small cell lung carcinoma (NSCLC), we investigated the role of the JNK2α isoform in NSCLC formation by examining its expression in primary tumors and by modulating its expression in cultured cell lines. We discovered that 60% of the tested primary NSCLC tumors had three-fold higher JNK2 protein and two- to three-fold higher JNK2α mRNA expression than normal lung control tissue. To determine the importance of JNK2α in NSCLC progression, we reduced JNK2α expression in multiple NSCLC cell lines using short hairpin RNA. Cell lines deficient in JNK2α had decreased cellular growth and anchorage-independent growth, and the tumors were four-fold smaller in mass. To elucidate the mechanism by which JNK2α induces NSCLC growth, we analyzed the JNK substrate, signal transducer and activator of transcription 3 (STAT3). Our data demonstrates for the first time that JNK2α can regulate the transcriptional activity of STAT3 by phosphorylating the Ser727 residue, thereby regulating the expression of oncogenic genes, such as c-Myc. Furthermore, reintroduction of JNK2α2 or STAT3 restored the tumorigenicity of the NSCLC cells, demonstrating that JNK2α is important for NSCLC progression. Our studies reveal a novel mechanism in which phosphorylation of STAT3 is mediated by a constitutively active JNK2 isoform, JNK2α.

Pineal parenchymal tumor of intermediate differentiation: clinicopathological report and analysis of epidermal growth factor receptor variant III expression

OBJECTIVE

Epidermal growth factor receptor (EGF) receptor gene amplification is commonly seen in cancer and is the target of many therapies. EGF receptor variant III (EGFRvIII) is the most common variant of the EGF receptor and has been detected in a large percentage of patients with glioblastoma multiforme but not in normal brain. Therapies targeting EGFRvIII are currently being investigated in clinical and preclinical trials.

METHODS

A 14-year-old girl who presented with headaches was found to have a pineal parenchymal tumor of intermediate differentiation. We review the histopathological properties that led to the diagnosis of this tumor. EGF receptor gene amplification and EGFRvIII expression have not been analyzed in pineal tumors. We investigated EGF receptor gene status and EGFRvIII expression in this patient's tumor.

RESULTS

Tumor tissue was obtained and analyzed with flow cytometry, reverse-transcriptase polymerase chain reaction, and Western blot analysis. EGFRvIII was detected by all 3 methods. The tumor was further analyzed by fluorescence in situ hybridization, which did not reveal EGF receptor gene amplification.

CONCLUSION

This is the first report of EGFRvIII expression in a pineal tumor. It is interesting that this variant is detected in the absence of EGF receptor gene amplification. A larger study evaluating the presence of EGFRvIII in pineal tumors is needed.

Abstract 694: Immunohistochemical discrimination of wild type EGFR from EGFRvIII in fixed tumor specimens using anti-EGFR mAbs ICR9 and ICR10

Abnormal expression of the epidermal growth factor receptor (EGFR) has been reported in a wide range of human epithelial malignancies and in some studies has been associated with poor prognosis and treatment resistance. Currently, three different types of EGFR inhibitors have been approved by the FDA for the treatment of patients with head and neck, metastatic colorectal, pancreatic or breast cancers: anti-EGFR monoclonal antibodies [(mAbs), cetuximab and panitumumab], small molecule EGFR tyrosine kinase inhibitors [(TKIs) gefitinib, erlotinib] or a dual EGFR and HER-2 tyrosine kinase inhibitor (lapatinib) However, there has been no clear association between the expression levels of EGFR in the tumours determined by the FDA approved EGFR PharmDx™ kit (DakoCytomation) or other standard anti-EGFR antibodies and the response to the EGFR inhibitors. One reason could be that the antibody used in the diagnosis of EGFR is not specific to the wild type EGFR and can also bind to the type-III mutant form of EGFR (EGFRvIII). We have extensively profiled our unique panel of high affinity rat anti-EGFR mAbs for use in the diagnosis and therapy of human cancers. The aim of the present investigation was to evaluate the potential of several of these antibodies (ICR9, ICR10, ICR16) for immunohistochemical diagnosis of wild type EGFR and/or EGFRvIII in formalin fixed paraffin embedded tumour specimens. We prepared 10% (v/v) neutral buffered formalin paraffin embedded sections of HN5 and HC2 20d2/c pelleted cells, which overexpress wild type EGFR and EGFRvIII respectively. Tumour sections were incubated with primary anti-EGFR mAbs followed by HRP linked secondary antibody (ABD Serotec Ltd., UK). The sections were then treated with DAB+ substrate-chromogen solution (Dako), counterstained with haematoxylin and mounted. The EGFR PharmDx™ kit, containing positive and negative control cell lines was purchased from Dako (UK) and the immunostaining of sections was conducted according to the manufacturer's protocol. We found that the mouse anti-EGFR mAb in the EGFR pharmDx™ kit stained both wild type and EGFRvIII expressing cells in the formalin fixed paraffin embedded sections. This pattern of EGFR immunostaining was also found with our anti-EGFR mAb ICR16. In contrast, mAbs ICR9 and ICR10, which are directed against two distinct epitopes on the external domain of the EGFR, were specific for wild-type EGFR in formalin-fixed paraffin embedded tumour specimens. We conclude that mAbs ICR9 and ICR10 are ideal tools for investigating the expression patterns of wild type EGFR (membranous, nuclear, and cytoplasmic) in tumour specimens using immunohistochemistry and to determine their prognostic significance as well as predictive value for response to therapy with EGFR antibodies.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 694.

Abstract 314: Characterization of the Y83C Gab1 mutation in breast cancer

Following addition of various growth factors and cytokines, the Gab1 docking protein is tyrosine phosphorylated, which then activates different signaling pathways. A screening of human breast cancers revealed a mutation in the Pleckstrin homology domain of Gab1, at the 83rd amino acid changing the tyrosine to a cysteine. To explore the impact of this mutation in human breast cancer, the mutation was overexpressed in the MDA-MB 468 cell line. Upon addition of EGF there was a significant higher increase in tyrosine phosphorylation of the mutant versus the wild type that correlated with an increased association with Shc, Shp2, Grb2 and p85. Pull down experiments with the GST/RBD (Ras binding domain of Raf) fusion protein detected higher activity levels of Ras in the mutant form in comparison with the wild type. Soft agar colony formation assays indicated a 2-3 fold increase in the number of colonies in the Y83C mutation with respect to the wt Gab1. The information understood from this study can help to characterize a mutant of Gab1 and this plays an important role in the context of personalized medicine by elucidating a specific target against tumors which express the mutation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 314.

The epidermal growth factor variant III peptide vaccine for treatment of malignant gliomas

Epidermal growth factor variant III (EGFRvIII) is the most common alteration of the epidermal growth factor (EGF) receptor found in human tumors. It is commonly expressed in glioblastoma multiforme (GBM), where it was initially identified. This constitutively active mutant receptor leads to unregulated growth, survival, invasion, and angiogenesis in cells that express it. EGFRvIII results from an in-frame deletion of exons 2 to 7 resulting in the fusion of exon 1 to exon 8 of the EGF receptor gene creating a novel glycine at the junction in the extracellular amino terminal domain. The juxtaposition of ordinarily distant amino acids in combination with the glycine that forms at the junction leads to a novel tumor-specific epitope that would make an ideal tumor-specific target. A peptide derived from the EGFRvIII junction can be used as a vaccine to prevent or induce the regression of tumors. This peptide vaccine has now proceeded to phase 1 and 2 clinical trials where it has been highly successful and is now undergoing investigation in a larger human clinical trial for patients who have newly diagnosed GBM. In this article, the authors discuss the preclinical data that led to the human trials and the exciting preliminary data from the clinical trials.

EGF receptor variant III as a target antigen for tumor immunotherapy

The EGF receptor (EGFR) is the first tyrosine kinase receptor ever cloned and remains at the forefront of targeted therapies against cancer. Currently, there are four US FDA-approved drugs and several more in Phase III studies that target the EGFR. These drugs, while resulting in some dramatic remissions, have not resulted in strong nor consistent improvements in survival. EGFR variant III (EGFRvIII) is the most common variant of the EGFR and is present in many different cancer types but not in normal tissue. It results from the fusion of exon 1 to exon 8 of the EGFR gene, which results in a novel glycine at the junction. This mutant receptor is constitutively active in these tumors and can lead directly to cancer phenotypes due to its oncogenic properties. EGFRvIII is an attractive target antigen for cancer immunotherapy because it is not expressed in normal tissue and because cells producing EGFRvIII have an enhanced capacity for dysregulated growth, survival, invasion and angiogenesis. In this review, we will discuss preclinical and clinical data from studies using EGFRvIII as the target antigen for immunotherapy, with a focus on the potential for greatly improved survival for patients diagnosed with glioblastoma multiforme.

Constitutive activity of JNK2 alpha2 is dependent on a unique mechanism of MAPK activation

c-Jun N-terminal kinases (JNKs) are part of the mitogen-activated protein kinase (MAPK) family and are important regulators of cell growth, proliferation, and apoptosis. Typically, a sequential series of events are necessary for MAPK activation: phosphorylation, dimerization, and then subsequent translocation to the nucleus. Interestingly, a constitutively active JNK isoform, JNK2alpha2, possesses the ability to autophosphorylate and has been implicated in several human tumors, including glioblastoma multiforme. Because overexpression of JNK2alpha2 enhances several tumorigenic phenotypes, including cell growth and tumor formation in mice, we studied the mechanisms of JNK2alpha2 autophosphorylation and autoactivation. We find that JNK2alpha2 dimerization in vitro and in vivo occurs independently of its autophosphorylation but is dependent on nine amino acids, known as the alpha-region. Alanine scanning mutagenesis of the alpha-region reveals that five specific mutants (L218A, K220A, G221A, I224A, and F225A) prevent JNK2alpha2 dimerization rendering JNK2alpha2 inactive and incapable of stimulating tumor formation. Previous studies coupled with additional mutagenesis of neighboring isoleucines and leucines (I208A, I214A, I231A, and I238A) suggest that a leucine zipper may play an important role in JNK2alpha2 homodimerization. We also show that a kinase-inactive JNK2alpha2 mutant can interact with and inhibit wild type JNK2alpha2 autophosphorylation, suggesting that JNK2alpha2 undergoes trans-autophosphorylation. Together, our results demonstrate that JNK2alpha2 differs from other MAPK proteins in two major ways; its autoactivation/autophosphorylation is dependent on dimerization, and dimerization most likely precedes autophosphorylation. In addition, we show that dimerization is essential for JNK2alpha2 activity and that prevention of dimerization may decrease JNK2alpha2 induced tumorigenic phenotypes.

A variant epidermal growth factor receptor protein is similarly expressed in benign hyperplastic and carcinomatous prostatic tissues in black and white men

BACKGROUND AND OBJECTIVE

Anti-epidermal growth factor receptor strategies are now established in cancer treatment We have recently described the presence of EGFRvIII (a variant EGFR) in prostatic tumours from UK white men and this is now a target for anti-prostate cancer treatments. However, there has been no report on the expression of this abnormal protein in black men.

MATERIALS AND METHODS

We determined EGFRvIII expression in sections of normal, benign hyperplastic (BPH) and carcinomatous (CaP) prostatic archival tissues from Nigerian men and UK white men using streptavidin immunohistochemical techniques. The EGFRvIII immunoreactivity was scored visually using a semi-quantitative method and the results compared statistically.

RESULTS

EGFRvIII expression increased with increasing malignancy in both study populations (CaP > BPH > Normal p, <0.0001). Furthermore, EGFRvIII expression was similar in both BPH and CaP tissues in black and white men (p, 0.86 and 0.31 respectively).

CONCLUSION

These results demonstrate that EGFRvIII immunoreactivity in prostatic tumours in black men is similar to that in white men. Anti-cancer treatments directed at the EGFRvIII should be equally effective in men from both subpopulations.

The scaffolding adapter Gab1 mediates vascular endothelial growth factor signaling and is required for endothelial cell migration and capillary formation

Vascular endothelial growth factor (VEGF) is involved in the promotion of endothelial cell proliferation, migration, and capillary formation. These activities are mainly mediated by the VEGFR2 receptor tyrosine kinase that upon stimulation, promotes the activation of numerous proteins including phospholipase Cgamma (PLCgamma), phosphatidylinositol 3-kinase (PI3K), Akt, Src, and ERK1/2. However, the VEGFR2-proximal signaling events leading to the activation of these targets remain ill defined. We have identified the Gab1 adapter as a novel tyrosine-phosphorylated protein in VEGF-stimulated cells. In bovine aortic endothelial cells, Gab1 associates with VEGFR2, Grb2, PI3K, SHP2, Shc, and PLCgamma, and its overexpression enhances VEGF-dependent cell migration. Importantly, silencing of Gab1 using small interfering RNAs leads to the impaired activation of PLCgamma, ERK1/2, Src, and Akt; blocks VEGF-induced endothelial cell migration; and perturbs actin reorganization and capillary formation. In addition, co-expression of VEGFR2 with Gab1 mutants unable to bind SHP2 or PI3K in human embryonic kidney 293 cells and bovine aortic endothelial cells mimics the defects observed in Gab1-depleted cells. Our work thus identifies Gab1 as a novel critical regulatory component of endothelial cell migration and capillary formation and reveals its key role in the activation of VEGF-evoked signaling pathways required for angiogenesis.

c-Jun NH(2)-terminal kinase 2alpha2 promotes the tumorigenicity of human glioblastoma cells

c-Jun NH(2)-terminal kinases (JNK) are members of the mitogen-activated protein kinase family and have been implicated in the formation of several human tumors, especially gliomas. We have previously shown that a 55 kDa JNK isoform is constitutively active in 86% of human brain tumors and then showed that it is specifically a JNK2 isoform and likely to be either JNK2alpha2 or JNK2beta2. Notably, we found that only JNK2 isoforms possess intrinsic autophosphorylation activity and that JNK2alpha2 has the strongest activity. In the present study, we have further explored the contribution of JNK2 isoforms to brain tumor formation. Analysis of mRNA expression by reverse transcription-PCR revealed that JNK2alpha2 is expressed in 91% (10 of 11) of glioblastoma tumors, whereas JNK2beta2 is found in only 27% (3 of 11) of tumors. Both JNK2alpha2 and JNK2beta2 mRNAs are expressed in normal brain (3 of 3). Using an antibody specific for JNK2alpha isoforms, we verified that JNK2alpha2 protein is expressed in 88.2% (15 of 17) of glioblastomas, but, interestingly, no JNK2alpha2 protein was found in six normal brain samples. To evaluate biological function, we transfected U87MG cells with green fluorescent protein-tagged versions of JNK1alpha1, JNK2alpha2, and JNK2alpha2APF (a dominant-negative mutant), and derived cell lines with stable expression. Each cell line was evaluated for various tumorigenic variables including cellular growth, soft agar colony formation, and tumor formation in athymic nude mice. In each assay, JNK2alpha2 was found to be the most effective in promoting that phenotype. To identify effectors specifically affected by JNK2alpha2, we analyzed gene expression. Gene profiling showed several genes whose expression was specifically up-regulated by JNK2alpha2 but down-regulated by JNK2alpha2APF, among which eukaryotic translation initiation factor 4E (eIF4E) shows the greatest change. Because AKT acts on eIF4E, we also examined AKT activation. Unexpectedly, we found that JNK2alpha2 could specifically activate AKT. Our data provides evidence that JNK2alpha2 is the major active JNK isoform and is involved in the promotion of proliferation and growth of human glioblastoma tumors through specific activation of AKT and overexpression of eIF4E.

β1Integrins Modulate Cell Adhesion by Regulating Insulin-Like Growth Factor-II Levels in the Microenvironment

The interactions between cancer cells and the extracellular matrix (ECM) regulate cancer progression. The beta1C and beta1A integrins, two cytoplasmic variants of the beta1 integrin subfamily, are differentially expressed in prostate cancer. Using gene expression analysis, we show here that the beta1C variant, an inhibitor of cell proliferation, which is down-regulated in prostate cancer, up-regulates insulin-like growth factor-II (IGF-II) mRNA and protein levels. In contrast, beta1A does not affect IGF-II levels. We provide evidence that beta1C-mediated up-regulation of IGF-II levels increases adhesion to Laminin-1, a basement membrane protein down-regulated in prostate cancer, and that the beta1C cytoplasmic domain contains the structural motif sufficient to increase cell adhesion to Laminin-1. This autocrine mechanism that locally supports cell adhesion to Laminin-1 via IGF-II is selectively regulated by the beta1 cytoplasmic domain via activation of the growth factor receptor binding protein 2-associated binder-1/SH2-containing protein-tyrosine phosphatase 2/phosphatidylinositol 3-kinase pathway. Thus, the concurrent local loss of beta1C integrin, of its ligand Laminin-1, and of IGF-II in the tumor microenvironment may promote prostate cancer cell invasion and metastasis by reducing cancer cell adhesive properties. It is, therefore, conceivable that reexpression of beta1C will be sufficient to revert a neoplastic phenotype to a nonproliferative and highly adherent normal phenotype.

Identification of a Specific Domain Responsible for JNK2α2 Autophosphorylation

c-Jun N-terminal kinases (JNKs) are a group of mitogen-activated protein kinase family members that are important in regulating cell growth, proliferation, and apoptosis. Activation of the JNK pathway has been implicated in the formation of several human tumors. We have previously demonstrated that a 55-kDa JNK isoform is constitutively activated in 86% of human brain tumors and more recently demonstrated that this isoform is either JNK2alpha2 or JNK2beta2. Importantly, we have also found that among the 10 known JNK isoforms, the JNK2 isoforms are unique in their ability to autophosphorylate in vitro and in vivo. This does not require the participation of any upstream kinases and also leads to substrate kinase activity in vitro and in vivo. To clarify the mechanism of JNK2alpha2 autoactivation, we have generated a series of chimeric cDNAs joining portions of JNK1alpha2, which does not have detectable autophosphorylation activity, with portions of JNK2alpha2, which has the strongest autophosphorylation activity. Through in vivo and in vitro kinase assays, we were able to define a domain ranging from amino acids 218 to 226 within JNK2alpha2 that is required for its autophosphorylation. Mutation of JNK2alpha2 to its counterpart of JNK1alpha2 in this region abrogated the autophosphorylation activity and c-Jun substrate kinase activity in vivo and in vitro. Notably, switching of JNK1alpha2 to JNK2alpha2 at this 9-amino acid site enabled JNK1alpha2 to gain the autophosphorylation activity in vivo and in vitro. We also found two other functional sites that participate in JNK2alpha2 activity. One site ranging from amino acids 363 to 382 of JNK2alpha2 is required for efficient c-Jun binding in vitro, and a site ranging from amino acids 383 to 424 enhances autophosphorylation intensity, although it is not required for triggering the autophosphorylation in vitro. These findings have uncovered the regions required for JNK2alpha2 autophosphorylation, and this information could be used as potential targets to block JNK2alpha2 activation.

Alterations in the expression of androgen receptor, wild type-epidermal growth factor receptor and a mutant epidermal growth factor receptor in human prostate cancer

Prostatic carcinogenesis has been associated with alterations in the expression of the androgen receptor (AR) and the epidermal growth factor receptor (WT-EGFR), and over-expression of the constitutively active variant epidermal growth factor receptor (EGFRvIII). Changes in the expression of AR, WT-EGFR and EGFRvIII were evaluated in serial sections from 26 normal and 26 benign hyperplastic and 50 prostate cancer tissues using specific immunostaining techniques. The loss of AR expression in peri-epithelial stroma as prostatic tissues de-differentiated correlated strongly with the depletion of WT-EGFR and with increasing expression of the EGFRvIII in the adjacent epithelium. In contrast, changes in epithelial AR immunopositivity in these tissues correlated weakly with the changes in normal and variant EGFR levels. This is the first report correlating the changes in the expression of these three proteins in archival material from the different human prostatic tissue histotypes. The loss of expression of proteins that contribute to the regulation of prostatic homeostasis (AR and WT-EGFR) correlates strongly with the expression of a constitutively active variant EGF receptor (EGFRvIII) in human prostate cancer. These changes occur at an early stage of neoplastic transformation and may contribute to the progression of the disease to hormone independence.

Role of the Grb2-associated binder 1/SHP-2 interaction in cell growth and transformation

Grb2-associated binder 1 (Gab1) is a docking protein that is tyrosine phosphorylated following the activation of multiple cytokine receptors and receptor tyrosine kinases. Its function then is to recruit and activate multiple signaling molecules. In our previous work, we showed that Gab1 enhances cell growth and induces the transformed phenotype in NIH3T3 cells downstream of the epidermal growth factor (EGF) receptor. In this report, we analyze how it produces these effects. Because SHP-2 is the major binding partner of Gab1, we mutated its binding site in the Gab1 cDNA (Gab1/DeltaSHP-2). This construct was stably overexpressed in NIH3T3 cells (3T3-Gab1/DeltaSHP-2) and in the wild-type Gab1 cDNA (3T3-Gab1) or an empty expression vector (3T3-CTR). Our findings show that after EGF stimulation, Gab1/DeltaSHP-2 has a higher level of tyrosine phosphorylation at early time points than Gab1. Gab1/DeltaSHP-2 recruits more phosphatidylinositol 3'-kinase than Gab1 after EGF triggering, which accounts for a higher and more sustained AKT activation in 3T3-Gab1/DeltaSHP-2 cells relative to 3T3-Gab1 fibroblasts. Moreover, 3T3-Gab1/DeltaSHP-2 cells demonstrate a higher level of extracellular-regulated kinase 1 activation at early time points of EGF stimulation. However, there was an unexpected decrease in c-fos promoter induction in 3T3-Gab1/DeltaSHP-2 cells when compared with 3T3-Gab1 cells. Additionally, the 3T3-Gab1/DeltaSHP-2 cells show a reversion of the transformed phenotype, including fewer morphologic changes, an increase in stress fiber cytoskeletal organization, and a decrease in cell proliferation and anchorage independent growth. These results reveal that the Gab1/SHP-2 interaction is essential for cell growth and transformation but that this must occur through a novel pathway that is independent of extracellular-regulated kinase or AKT. On the basis of its role in growth and transformation, the Gab1/SHP-2 interaction may become an attractive target for the pharmacologic intervention of malignant cell growth.

Gab1 is an integrator of cell death versus cell survival signals in oxidative stress

Upon the addition of different growth factors and cytokines, the Gab1 docking protein is tyrosine phosphorylated and in turn activates different signaling pathways. On the basis of the large body of evidence concerning cross talk between the signaling pathways activated by growth factors and oxidative stress, we decided to investigate the role of Gab1 in oxidative injury. We stimulated wild-type mouse embryo fibroblasts (MEF) or MEF with a homozygous deletion of the Gab1 gene (-/- MEF) with H(2)O(2). Our results show that Gab1 is phosphorylated in a dose- and time-dependent manner after H(2)O(2) triggering. Gab1 then recruits molecules such as SHP2, phosphatidylinositol 3-kinase (PI3K), and Shc. Gab1 phosphorylation is sensitive to the Src family kinase inhibitor PP2. Furthermore, we demonstrate that Gab1 is required for H(2)O(2)-induced c-Jun N-terminal kinase (JNK) activation but not for ERK2 or p38 activation. Reconstitution of Gab1 in -/- MEF rescues JNK activation, and we find that this is dependent on the SHP2 binding site in Gab1. Cell viability assays reveal that Gab1 has a dual role in cell survival: a positive one through its interaction with PI3K and a negative one through its interaction with SHP2. This is the first report identifying Gab1 as a component in oxidative stress signaling and one that is required for JNK activation.

Targeting of cells expressing wild-type EGFR and type-III mutant EGFR (EGFRvIII) by anti-EGFR MAb ICR62: a two-pronged attack for tumour therapy

With a view to their use in cancer therapy, we have produced rat monoclonal antibodies (MAbs) directed against 5 distinct epitopes (A-E) on the external domain of the wild-type human EGF receptor (EGFR). Here, we have investigated the relative binding and anti-tumour activity of our anti-EGFR MAbs against HC2 20d2/c cells, which have been engineered to overexpress the type-III mutated form of the human EGFR (EGFRvIII). We found that anti-EGFR MAbs that are the most effective antagonists of EGFR ligands (e.g., ICR16, ICR62 and ICR80) also bind to cells that overexpress the EGFRvIII. Although these antibodies are potent inhibitors of the growth of cells which express wild-type EGFR, they did not directly inhibit the growth in vitro of EGFRvIII expressing HC2 20d2/c cells, or the constitutive tyrosine kinase activity of this receptor. However, in the presence of human peripheral blood mononuclear cells (PBMC), the rat IgG2b MAb ICR62 induced strong antibody-dependent cell-mediated cytotoxicity (ADCC) against HC2 20d2/c cells in culture. Interestingly, MAb ICR62 also inhibited very effectively experimental lung metastases of HC2 20d2/c cells in athymic nude mice. Our results suggest that anti-EGFR MAb ICR62, which binds to the EGFRvIII, may have potential in the treatment of tumors which overexpress the EGFRvIII via immunological mechanisms such as ADCC. Since tumours that are EGFRvIII positive may also overexpress the wild-type EGFR, the use of anti-EGFR MAbs that target both wild-type and mutant receptors may have advantages over those that target only1form.

Constitutively active forms of c-Jun NH2-terminal kinase are expressed in primary glial tumors

The c-Jun NH(2)-terminal kinases (JNKs) have a role both in promoting apoptosis and tumorigenesis. The JNKs are encoded by three separate genes (JNK1, 2, and 3), which are spliced alternatively to create 10 JNK isoforms that are either M(r) 55,000 or 46,000 in size. However, the functional significance and distinct role for each splice variant remains unclear. We have noted previously that 86% of primary human glial tumors show activation of almost exclusively the M(r) 55,000 isoforms of JNK. To further study which isoforms are involved, we constructed glutathione S-transferase fusion proteins for all 10 JNK isoforms and examined kinase activity with or without the activating upstream kinase. Surprisingly, five JNK isoforms demonstrate autophosphorylation activity, and in addition, all four JNK2 isoforms (either M(r) 55,000 or 46,000) show a high basal level of substrate kinase activity in the absence of the upstream kinase, especially a M(r) 55,000 JNK2 isoform. Examination revealed autophosphorylation activity at the T-P-Y motif, which is critical for JNK activation, because a mutant lacking the dual phosphorylation sites did not show autophosphorylation or basal kinase activity. Using green fluorescence protein-JNK expression vectors, transient transfection into U87MG cells demonstrates that although the JNK1 isoforms localize predominantly to the cytoplasm, the JNK2 isoforms localize to the nucleus and are phosphorylated, confirming the constitutive activation seen in vitro. We then examined which JNK isoforms are active in glial tumors by performing two-dimensional electrophoresis. This revealed that the M(r) 55,000 isoforms of JNK2 are the principal active JNK isoforms present in tumors. Collectively, these results suggest that these constitutively active JNK isoforms play a significant role in glial tumors. Aside from epidermal growth factor receptor vIII, this is the only other kinase that has been shown to be basally active in glioma. The presence of constitutively active JNK isoforms may have implications for the design of inhibitors of the JNK pathway.

Expression of constitutively activated EGFRvIII in non-small cell lung cancer

The epidermal growth factor receptor (EGFR) variant type III (variously called EGFRvIII, de2-7 EGFR or deltaEGFR) has an in-frame deletion of the extracellular domain and is found in numerous types of human tumors. Since EGFRvIII has been reported to be tumor-specific and has oncogenic potential, it is being investigated as a potential therapeutic target. Because the cell-specific expression of EGFRvIII in lung has not been well documented, we examined the expression of EGFRvIII in 76 non-small cell lung cancers (NSCLCs) and 10 non-neoplastic lung tissues by immunohistochemistry using a new monoclonal antibody specific for this variant receptor. We found a higher incidence (30 of 76, 39%) of enhanced EGFRvIII expression in NSCLC than previously described. Interestingly, the presence of EGFRvIII was also observed in several normal tissue components of lung (e.g., normal bronchial epithelium). Given the high prevalence of EGFRvIII in NSCLC, a newly developed phospho-specific (activated) EGFR antibody was employed for immunohistochemical analysis that permitted visualization of activated EGFR and/or EGFRvIII in tumors. This study presents evidence, for the first time, that EGFRvIII expressed in human tumors is phosphorylated and hence activated. Our results suggest that the sustained activation of EGFRvIII is implicated in the pathogenesis of NSCLC and thus EGFRvIII is a potential therapeutic target in this challenging disease.

Elevated JNK activation contributes to the pathogenesis of human brain tumors

The ERK pathway is typically associated with activation of the EGF receptor and has been shown to play a major role in promoting several tumor phenotypes. An analogous signaling module, the JNK pathway, has not been shown to be consistently activated by the EGF receptor but is instead more uniformly stimulated by cellular stresses and cytokines. The function of the JNK pathway in primary tumors is unclear as it has been implicated in both promoting apoptosis and cell growth in vitro, which may be a reflection of the cell lines chosen. Primary human brain tumors frequently show overexpression of the EGF receptor. To clarify the role of JNK in tumorigenesis, we have investigated the role of JNK in a large panel of primary human brain tumors and tumor derived cell lines. Here we present evidence that JNK has a major role in promoting tumorigenesis both in vivo and in vitro. Western blot analysis demonstrated that 86% (18 of 21) of primary brain tumors showed evidence of JNK activation but only 38% (8 of 21) showed evidence of ERK activation. Kinase assays revealed that 77% of brain tumor cell lines activated JNK in response to EGF (7 of 13) or had high levels of basal activity (3 of 13), whereas none of six normal cell lines analysed, including astrocytes, had these properties. Of several growth factors examined, EGF produced the highest level of JNK induction in tumor cell lines and the duration of activation was greater than that seen for ERK. Expression of a dominant-negative (dn) form of JNK potently inhibited EGF mediated anchorage independent growth and protection from cell death in two glial tumor cell lines. These findings demonstrate that enhanced JNK activation is frequently found in primary brain tumors and that this activation contributes to phenotypes related to transformation.

Proteolytic release of CD44 intracellular domain and its role in the CD44 signaling pathway

CD44 is a widely distributed cell surface adhesion molecule and is implicated in diverse biological processes. However, the nature of intracellular signaling triggered by CD44 remains to be elucidated. Here, we show that CD44 undergoes sequential proteolytic cleavage in the ectodomain and intracellular domain, resulting in the release of a CD44 intracellular domain (ICD) fragment. Consequently, CD44ICD acts as a signal transduction molecule, where it translocates to the nucleus and activates transcription mediated through the 12-O-tetradecanoylphorbol 13-acetate-responsive element, which is found in numerous genes involved in diverse cellular processes. Expression of an uncleavable CD44 mutant as well as metalloprotease inhibitor treatment blocks CD44-mediated transcriptional activation. In search of the underlying mechanism, we have found that CD44ICD potentiates transactivation mediated by the transcriptional coactivator CBP/p300. Furthermore, we show that cells expressing CD44ICD produce high levels of CD44 messenger RNA, suggesting that the CD44 gene is one of the potential targets for transcriptional activation by CD44ICD. These observations establish a novel CD44 signaling pathway and shed new light on the functional link between proteolytic processing of an adhesion molecule at the cell surface and transcriptional activation in the nucleus.

Further characterization of storage-related alterations in immunoreactivity of archival tissue sections and its implications for collaborative multicenter immunohistochemical studies

Storage of unstained paraffin slides may lead to the deterioration of specimens and failure to detect cellular proteins immunohistochemically. Although the implication of age-induced alterations on multicenter immunohistochemical studies would be considerable, they have not been investigated previously. The current study was undertaken to examine the effect of this factor further and to explore new ways of overcoming the resultant shortcomings. The authors now report on the immunodetection of a host of antigens in similarly preserved unstained serial paraffin slides obtained from three centers using a panel of eight antibodies. Staining of recently prepared sections from the authors' centers resulted in similar strong patterns in seven of eight antibodies, with one antibody demonstrating variable immunoreactivity. However, storage of unstained paraffin sections at room temperature resulted in a variable but progressive decrease in expression of several tissue antigens. Although the loss in antigenicity was proportional to the length of storage, the effect was reversible if super antibody concentrations were used. The authors conclude that recently prepared paraffin sections from centers with similar fixation protocols have similar immunoreactivity and are suitable for use in comparative multicenter studies. However, in view of the delays that may attend tissue transportation during these projects, the authors suggest that test systems should be checked for age-induced antigen degradation by incubating sections with higher antibody concentrations.

The Gab1 docking protein links the b cell antigen receptor to the phosphatidylinositol 3-kinase/Akt signaling pathway and to the SHP2 tyrosine phosphatase

B cell antigen receptor (BCR) signaling causes tyrosine phosphorylation of the Gab1 docking protein. This allows phosphatidylinositol 3-kinase (PI3K) and the SHP2 tyrosine phosphatase to bind to Gab1. In this report, we tested the hypothesis that Gab1 acts as an amplifier of PI3K- and SHP2-dependent signaling in B lymphocytes. By overexpressing Gab1 in the WEHI-231 B cell line, we found that Gab1 can potentiate BCR-induced phosphorylation of Akt, a PI3K-dependent response. Gab1 expression also increased BCR-induced tyrosine phosphorylation of SHP2 as well as the binding of Grb2 to SHP2. We show that the pleckstrin homology (PH) domain of Gab1 is required for BCR-induced phosphorylation of Gab1 and for Gab1 participation in BCR signaling. Moreover, using confocal microscopy, we show that BCR ligation can induce the translocation of Gab1 from the cytosol to the plasma membrane and that this requires the Gab1 PH domain as well as PI3K activity. These findings are consistent with a model in which the binding of the Gab1 PH domain to PI3K-derived lipids brings Gab1 to the plasma membrane, where it can be tyrosine-phosphorylated and then act as an amplifier of BCR signaling.

Grb-2-associated binder-1 is involved in insulin-induced egr-1 gene expression through its phosphatidylinositol 3'-kinase binding site

The Grb2-associated binder-1 (Gab1) is one of the major adapter molecules downstream of growth factor receptor signaling. Even though insulin causes tyrosine phosphorylation of Gab1, its role in insulin signaling has not been identified yet. We have demonstrated that insulin increased expression of early growth response gene-1 (egr-1), which is one of the most important transcription factors involved in cell proliferation and differentiation. In the present study, the possible role of Gab1 in insulin-induced egr-1 expression was studied using Rat1 fibroblasts expressing human insulin receptors and wildtype Gab1 (HIRc/Gab1(WT)), Gab1 with three tyrosines in the phosphatidylinositol (PI) 3'-kinase binding domain mutated to phenylalanine (HIRc/Gab1(DeltaPI3K)), or histidinol resistance only (HIRc/HIS). Insulin-induced egr-1 expression in HIRc/Gab1(DeltaPI3K) cells was much lower than in the other cells, as determined by Northern blot analysis. These results suggest that Gab1 is involved in the signaling pathway for insulin-induced egr-1 expression through increasing PI3'-kinase activity. The MAP kinase activity increased less with insulin treatment in HIRc/Gab1(DeltaPI3K) cells than in other cells. Inhibition of MAP kinase by the MEK inhibitor completely abolished insulin-induced egr-1 expression. These results suggest that Gab1 increases MAP kinase activity through its PI3'-kinase binding site, which then leads to egr-1 expression. Our results indicate that Gab1 is involved in the control of egr-1 expression regulated by insulin.

The tyrosine phosphatase SHP-2 is required for sustained activation of extracellular signal-regulated kinase and epithelial morphogenesis downstream from the met receptor tyrosine kinase

Epithelial morphogenesis is critical during development and wound healing, and alterations in this program contribute to neoplasia. Met, the hepatocyte growth factor (HGF) receptor, promotes a morphogenic program in epithelial cell lines in matrix cultures. Previous studies have identified Gab1, the major phosphorylated protein following Met activation, as important for the morphogenic response. Gab1 is a docking protein that couples the Met receptor with multiple signaling proteins, including phosphatidylinositol-3 kinase, phospholipase Cgamma, the adapter protein Crk, and the tyrosine specific phosphatase SHP-2. HGF induces sustained phosphorylation of Gab1 and sustained activation of extracellular signal-regulated kinase (Erk) in epithelial Madin-Darby canine kidney cells. In contrast, epidermal growth factor fails to promote a morphogenic program and induces transient Gab1 phosphorylation and Erk activation. To elucidate the Gab1-dependent signals required for epithelial morphogenesis, we undertook a structure-function approach and demonstrate that association of Gab1 with the tyrosine phosphatase SHP-2 is required for sustained Erk activation and for epithelial morphogenesis downstream from the Met receptor. Epithelial cells expressing a Gab1 mutant protein unable to recruit SHP-2 elicit a transient activation of Erk in response to HGF. Moreover, SHP-2 catalytic activity is required, since the expression of a catalytically inactive SHP-2 mutant, C/S, abrogates sustained activation of Erk and epithelial morphogenesis by the Met receptor. These data identify SHP-2 as a positive modulator of Erk activity and epithelial morphogenesis downstream from the Met receptor.

Epidermal growth factor receptor vIII enhances tumorigenicity in human breast cancer

Epidermal growth factor receptor vIII (EGFRvIII) is a tumor-specific, ligand-independent, constitutively active variant of the EGFR. Its expression has been detected in gliomas and various other human malignancies. To more fully characterize the function and potential biological role of EGFRvIII in regulating cell proliferation and in tumorigenesis, we transfected EGFRvIII cDNA into a nontumorigenic, interleukin 3 (IL-3)-dependent murine hematopoietic cell line (32D cells). We observed 32D cells expressing high levels of EGFRvIII (32D/EGFRvIII P5) to be capable of abrogating the IL-3-dependent pathway in the absence of ligands. In contrast, the parental cells, 32D/EGFR, 32D/ErbB-4, and 32D/ErbB-2+ErbB-3 cells, all depended on IL-3 or EGF-like ligands for growth. 32D/EGFRvIII P5 cells subjected to long-term culture conditions in the absence of IL-3 revealed further elevation of EGFRvIII expression levels. These results suggested that the IL-3-independent phenotype is mediated by EGFRvIII. The level of expression is a critical driving force for the IL-3-independent phenotype. Dose-response analysis revealed 32D/EGFRvIII cells to require 500-fold higher concentrations (50 ng/ml) of EGF to further stimulate the EGF-mediated proliferation than in the 32D/EGFR cells (100 pg/ml). Similar effects were also observed in beta-cellulin-mediated proliferation. Moreover, 32D cells expressing high levels of EGFRvIII formed large tumors in nude mice, even when no exogenous EGF ligand was administered. In contrast, no tumors grew in mice injected with 32D/EGFR, 32D/ErbB-4, and 32D/ErbB-2+ErbB-3 cells or low-expressing clone 32D/EGFRvIII C2 cells or the parental 32D cells. The changes of the ligand specificity support the notion for an altered conformation of EGFRvIII to reveal an activated ligand-independent oncoprotein with tumorigenic activity analogous to v-erbB. These studies clearly demonstrate that EGFRvIII is capable of transforming a nontumorigenic, IL-3-dependent murine hematopoietic cell line (32D cells) into an IL-3-independent and ligand-independent malignant phenotype in vitro and in vivo. To delineate the biological significance of EGFRvIII in human breast cancer, we expressed EGFRvIII in the MCF-7 human breast cancer cell line. Expression of EGFRvIII in MCF-7 cells produced a constitutively activated EGFRvIII receptor. Expression of EGFRvIII in MCF-7 cells also elevated ErbB-2 phosphorylation, presumably through heterodimerization and cross-talk. These MCF-7/EGFRvIII transfectants exhibited an approximately 3-fold increase in colony formation in 1% serum with no significant effect observed at higher percentages of serum. A similar result was also seen in anchorage-dependent assays. Furthermore, EGFRvIII expression significantly enhanced tumorigenicity of MCF-7 cells in athymic nude mice with P < 0.001. Collectively, these results provide the first evidence that EGFRvIII could play a pivotal role in human breast cancer progression.

Evidence for the differential expression of a variant EGF receptor protein in human prostate cancer

Earlier studies have demonstrated an unexplained depletion of the epidermal growth factor receptor (EGFR) protein expression in prostatic cancer. We now attribute this phenomenon to the presence of a variant EGFR (EGFRvIII) that is highly expressed in malignant prostatic neoplasms. In a retrospective study, normal, benign hyperplastic and malignant prostatic tissues were examined at the mRNA and protein levels for the presence of this mutant receptor. The results demonstrated that whilst EGFRvIII was not present in normal prostatic glands, the level of expression of this variant protein increased progressively with the gradual transformation of the tissues to the malignant phenotype. The selective association of high EGFRvIII levels with the cancer phenotype underlines the role that this mutant receptor may maintain in the initiation and progression of malignant prostatic growth, and opens the way for new approaches in the management of this disease including gene therapy.

Gab1 mediates neurite outgrowth, DNA synthesis, and survival in PC12 cells

The Gab1-docking protein has been shown to regulate phosphatidylinositol 3-kinase PI3K activity and potentiate nerve growth factor (NGF)-induced survival in PC12 cells. Here, we investigated the potential of Gab1 to induce neurite outgrowth and DNA synthesis, two other important aspects of NGF-induced neuronal differentiation of PC12 cells and NGF-independent survival. We generated a recombinant adenovirus encoding hemagglutinin (HA)-epitope-tagged Gab1 and expressed this protein in PC12 cells. HA-Gab1 was constitutively tyrosine-phosphorylated in PC12 cells and induced the phosphorylation of Akt/protein kinase B and p44/42 mitogen-activated protein kinase. HA-Gab1-stimulated a 10-fold increase in neurite outgrowth in the absence of NGF and a 5-fold increase in NGF-induced neurite outgrowth. HA-Gab1 also stimulated DNA synthesis and caused NGF-independent survival in PC12 cells. Finally, we found that HA-Gab1-induced neuritogenesis was completely suppressed by pharmacological inhibition of mitogen-activated protein kinase kinase (MEK) activity and 50% suppressed by inhibition of PI3K activity. In contrast, HA-Gab1-stimulated cell survival was efficiently suppressed only by inhibition of both PI3K and MEK activities. These results indicate that Gab1 is capable of mediating differentiation, DNA synthesis, and cell survival and uses both PI3K and MEK signaling pathways to achieve its effects.

A conserved inositol phospholipid binding site within the pleckstrin homology domain of the Gab1 docking protein is required for epithelial morphogenesis

Stimulation of the hepatocyte growth factor receptor tyrosine kinase, Met, induces the inherent morphogenic program of epithelial cells. The multisubstrate binding protein Gab1 (Grb2-associated binder-1) is the major phosphorylated protein in epithelial cells following activation of Met. Gab1 contains a pleckstrin homology domain and multiple tyrosine residues that act to couple Met with multiple signaling proteins. Met receptor mutants that are impaired in their association with Gab1 fail to induce a morphogenic program in epithelial cells, which is rescued by overexpression of Gab1. The Gab1 pleckstrin homology domain binds to phosphatidylinositol 3,4, 5-trisphosphate and contains conserved residues, shown from studies of other pleckstrin homology domains to be crucial for phospholipid binding. Mutation of conserved phospholipid binding residues tryptophan 26 and arginine 29, generates Gab1 proteins with decreased phosphatidylinositol 3,4,5-trisphosphate binding, decreased localization at sites of cell-cell contact, and reduced ability to rescue Met-dependent morphogenesis. We conclude that the ability of the Gab1 pleckstrin homology domain to bind phosphatidylinositol 3,4,5-trisphosphate is critical for subcellular localization of Gab1 and for efficient morphogenesis downstream from the Met receptor.

The Gab1 PH domain is required for localization of Gab1 at sites of cell-cell contact and epithelial morphogenesis downstream from the met receptor tyrosine kinase

Stimulation of the hepatocyte growth factor (HGF) receptor tyrosine kinase, Met, induces mitogenesis, motility, invasion, and branching tubulogenesis of epithelial and endothelial cell lines in culture. We have previously shown that Gab1 is the major phosphorylated protein following stimulation of the Met receptor in epithelial cells that undergo a morphogenic program in response to HGF. Gab1 is a member of the family of IRS-1-like multisubstrate docking proteins and, like IRS-1, contains an amino-terminal pleckstrin homology domain, in addition to multiple tyrosine residues that are potential binding sites for proteins that contain SH2 or PTB domains. Following stimulation of epithelial cells with HGF, Gab1 associates with phosphatidylinositol 3-kinase and the tyrosine phosphatase SHP2. Met receptor mutants that are impaired in their association with Gab1 fail to induce branching tubulogenesis. Overexpression of Gab1 rescues the Met-dependent tubulogenic response in these cell lines. The ability of Gab1 to promote tubulogenesis is dependent on its pleckstrin homology domain. Whereas the wild-type Gab1 protein is localized to areas of cell-cell contact, a Gab1 protein lacking the pleckstrin homology domain is localized predominantly in the cytoplasm. Localization of Gab1 to areas of cell-cell contact is inhibited by LY294002, demonstrating that phosphatidylinositol 3-kinase activity is required. These data show that Gab1 is an important mediator of branching tubulogenesis downstream from the Met receptor and identify phosphatidylinositol 3-kinase and the Gab1 pleckstrin homology domain as crucial for subcellular localization of Gab1 and biological responses.

The Gab1 protein is a docking site for multiple proteins involved in signaling by the B cell antigen receptor

Gab1 is a member of the docking/scaffolding protein family which includes IRS-1, IRS-2, c-Cbl, p130(cas), and p62(dok). These proteins contain a variety of protein-protein interaction motifs including multiple tyrosine residues that when phosphorylated can act as binding sites for Src homology 2 (SH2) domain-containing signaling proteins. We show in the RAMOS human B cell line that Gab1 is tyrosine-phosphorylated in response to B cell antigen receptor (BCR) engagement. Moreover, tyrosine phosphorylation of Gab1 correlated with the binding of several SH2-containing signaling proteins to Gab1 including Shc, Grb2, phosphatidylinositol 3-kinase, and the SHP-2 tyrosine phosphatase. Far Western analysis showed that the SH2 domains of Shc, SHP-2, and the p85 subunit of phosphatidylinositol 3-kinase could bind directly to tyrosine-phosphorylated Gab1 isolated from activated RAMOS cells. In contrast, the Grb2 SH2 domain did not bind directly to Gab1 but instead to the Shc and SHP-2 associated with Gab1. We also show that Gab1 is present in the membrane-enriched particulate fraction of RAMOS cells and that Gab1/signaling protein complexes are found in this fraction after BCR engagement. Thus, tyrosine-phosphorylated Gab1 may recruit cytosolic signaling proteins to cellular membranes where they can act on membrane-bound targets. This may be a critical step in the activation of multiple BCR signaling pathways.

Determination of Gab1 (Grb2-associated binder-1) interaction with insulin receptor-signaling molecules

The newly identified insulin receptor (IR) substrate, Gab1 [growth factor receptor bound 2 (Grb2)-associated binder-1] is rapidly phosphorylated on several tyrosine residues by the activated IR. Phosphorylated Gab1 acts as a docking protein for Src homology-2 (SH2) domain-containing proteins. These include the regulatory subunit p85 of phosphatidylinositol 3-kinase and phosphotyrosine phosphatase, SHP-2. In this report, using a modified version of the yeast two-hybrid system, we localized which Gab1 phospho-tyrosine residues are required for its interaction with phosphatidylinositol 3-kinase and with SHP-2. Our results demonstrate that to interact with p85 or SHP-2 SH2 domains, Gab1 must be tyrosine phosphorylated by IR. Further, we found that Gab1 tyrosine 472 is the major site for association with p85, while tyrosines 447 and 589 are participating in this process. Concerning Gab1/SHP-2 interaction, only mutation of tyrosine 627 prevents binding of Gab1 to SHP-2 SH2 domains, suggesting the occurrence of a monovalent binding event. Finally, we examined the role of Gab1 PH (Pleckstrin homology) domain in Gab1/IR interaction and in Gab1 tyrosine phosphorylation by IR. Using the modified two-hybrid system and in vitro experiments, we found that the Gab1 PH domain is not important for IR/ Gab1 interaction and for Gab1 tyrosine phosphorylation. In contrast, in intact mammalian cells, Gab1 PH domain appears to be crucial for its tyrosine phosphorylation and association with SHP-2 after insulin stimulation.