The efficacy of epidermal growth factor receptor-specific antibodies against glioma xenografts is influenced by receptor levels, activation status, and heterodimerization

WZ-3146 acts as a novel small molecule inhibitor of KIF4A to inhibit glioma progression by inducing apoptosis

BACKGROUND

Glioma is considered the most common primary malignant tumor of the central nervous system. Although traditional treatments have not achieved satisfactory outcomes, recently, targeted therapies for glioma have shown promising efficacy. However, due to the single-target nature of targeted therapy, traditional targeted therapies are ineffective; thus, novel therapeutic targets are urgently needed.

METHODS

The gene expression data for glioma patients were derived from the GEO (GSE4290, GSE50161), TCGA and CGGA databases. Next, the upregulated genes obtained from the above databases were cross-analyzed, finally, 10 overlapping genes (BIRC5, FOXM1, EZH2, CDK1, KIF11, KIF4A, NDC80, PBK, RRM2, and TOP2A) were ultimately screened and only KIF4A expression has the strongest correlation with clinical characteristics in glioma patients. Futher, the TCGA and CGGA database were utilized to explore the correlation of KIF4A expression with glioma prognosis. Then, qRT-PCR and Western blot was used to detect the KIF4A mRNA and protein expression level in glioma cells, respectively. And WZ-3146, the small molecule inhibitor targeting KIF4A, were screened by Cmap analysis. Subsequently, the effect of KIF4A knockdown or WZ-3146 treatment on glioma was measured by the MTT, EdU, Colony formation assay and Transwell assay. Ultimately, GSEA enrichment analysis was performed to find that the apoptotic pathway could be regulated by KIF4A in glioma, in addition, the effect of WZ-3146 on glioma apoptosis was detected by flow cytometry and Western blot.

RESULTS

In the present study, we confirmed that KIF4A is abnormally overexpressed in glioma. In addition, KIF4A overexpression is a key indicator of glioma prognosis; moreover, suppressing KIF4A expression can inhibit glioma progression. We also discovered that WZ-3146, a small molecule inhibitor of KIF4A, can induce apoptosis in glioma cells and exhibit antiglioma effects.

CONCLUSION

In conclusion, these observations demonstrated that targeting KIF4A can inhibit glioma progression. With further research, WZ-3146, a small molecule inhibitor of KIF4A, could be combined with other molecular targeted drugs to cooperatively inhibit glioma progression.

A novel EGFR-specific recombinant ricin-panitumumab (scFv) immunotoxin against breast and colorectal cancer cell lines; in silico and in vitro analyses

The Epidermal Growth Factor Receptor (EGFR) has been of high importance as it is over expressed in a wide diversity of epithelial cancers, promoting cell proliferation and survival pathways. Recombinant immunotoxins (ITs) have emerged as a promising targeted therapy for cancer treatment. In this study, we aimed to investigate the antitumor activity of a novel recombinant immunotoxin designed against EGFR. Using an in silico approach, we confirmed the stability of the RTA-scFv fusion protein. The immunotoxin was successfully cloned and expressed in the pET32a vector, and the purified protein was analyzed by electrophoresis and western blotting. In vitro evaluations were conducted to assess the biological activities of the recombinant proteins (RTA-scFv, RTA, scFv). The novel immunotoxin demonstrated significant anti-proliferative and pro-apoptotic effects against cancer cell lines. The MTT cytotoxicity assay revealed a decrease in cell viability in the treated cancer cell lines. Additionally, Annexin V/Propidium iodide staining followed by flow cytometry analysis showed a significant induction of apoptosis in the cancer cell lines, with half maximal inhibitory concentration (IC50) values of 81.71 nM for MDA-MB-468 and 145.2 nM for HCT116 cells (P < 0.05). Furthermore, the EGFR-specific immunotoxin exhibited non-allergenic properties. The recombinant protein demonstrated high affinity binding to EGFR. Overall, this study presents a promising strategy for the development of recombinant immunotoxins as potential candidates for the treatment of EGFR-expressing cancers.

Alternative Splicing: Expanding the Landscape of Cancer Biomarkers and Therapeutics

Alternative splicing (AS) is a critical post-transcriptional regulatory mechanism used by more than 95% of transcribed human genes and responsible for structural transcript variation and proteome diversity. In the past decade, genome-wide transcriptome sequencing has revealed that AS is tightly regulated in a tissue- and developmental stage-specific manner, and also frequently dysregulated in multiple human cancer types. It is currently recognized that splicing defects, including genetic alterations in the spliced gene, altered expression of both core components or regulators of the precursor messenger RNA (pre-mRNA) splicing machinery, or both, are major drivers of tumorigenesis. Hence, in this review we provide an overview of our current understanding of splicing alterations in cancer, and emphasize the need to further explore the cancer-specific splicing programs in order to obtain new insights in oncology. Furthermore, we also discuss the recent advances in the identification of dysregulated splicing signatures on a genome-wide scale and their potential use as biomarkers. Finally, we highlight the therapeutic opportunities arising from dysregulated splicing and summarize the current approaches to therapeutically target AS in cancer.

EGFR as a clinical marker in glioblastomas and other gliomas

Epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein and a member of the tyrosine kinase superfamily receptor. Gliomas are tumors originating from glial cells, which show a range of aggressiveness depending on grade and stage. Many EGFR gene alterations have been identified in gliomas, especially glioblastomas, including amplifications, deletions and single nucleotide polymorphisms (SNPs). Glioblastomas are discussed as a separate entity due to their high correlation with EGFR mutants and the reported association of the latter with survival and response to treatment in this glioma subgroup. This review is a comprehensive report of EGFR gene alterations and their relations with several clinical factors in glioblastomas and other gliomas. It covers all EGFR gene alterations including point mutations, SNPs, methylations, copy number variations and amplifications, assessed with regard to different clinical variables, including response to therapy and survival. This review also discusses the current prognostic status of EGFR in glioblastomas and other gliomas, and highlights gaps in previous studies. This serves as an update for the medical community about the role of EGFR gene alterations in gliomas and specifically glioblastomas, as a means for targeted treatment and prognosis.

Highly Specific and Effective Targeting of EGFRvIII-Positive Tumors with TandAb Antibodies

To harness the cytotoxic capacity of immune cells for the treatment of solid tumors, we developed tetravalent, bispecific tandem diabody (TandAb) antibodies that recognize EGFRvIII, the deletion variant III of the epidermal growth factor receptor (EGFR), and CD3 on T-cells, thereby directing immune cells to eliminate EGFRvIII-positive tumor cells. Using phage display, we identified scFv antibodies selectively binding to EGFRvIII. These highly EGFRvIII-specific, fully human scFv were substantially improved by affinity maturation, achieving K_Ds in the picomolar range, and were used to construct a set of bispecific EGFRvIII-targeting TandAbs with a broad range of binding and cytotoxic properties. These antibodies exhibited an exquisite specificity for a distinguished epitope in the N-terminal portion of EGFRvIII, as shown on recombinant antigen in Western Blot, SPR, and ELISA, as well as on antigen-expressing cells in FACS assays, and did not bind to the wild-type EGFR. High-affinity EGFRvIII/CD3 TandAbs were most potent in killing assays, displaying cytotoxicity toward EGFRvIII-expressing CHO, F98 glioma, or human DK-MG cells with EC₅₀ values in the range of 1-10 pM in vitro. They also demonstrated dose-dependent growth control in vivo in an EGFRvIII-positive subcutaneous xenograft tumor model. Together with the tumor-exclusive expression of EGFRvIII, the EGFRvIII/CD3 TandAbs' high specificity and strictly target-dependent activation with no off-target activity provide an opportunity to target tumor cells and spare normal tissues, thereby reducing the side effects associated with other anti-EGFR therapies. In summary, EGFRvIII/CD3 TandAbs are highly attractive therapeutic antibody candidates for selective immunotherapy of EGFRvIII-positive tumors.

Aptamer targeting EGFRvIII mutant hampers its constitutive autophosphorylation and affects migration, invasion and proliferation of glioblastoma cells

Glioblastoma Multiforme (GBM) is the most common and aggressive human brain tumor, associated with very poor survival despite surgery, radiotherapy and chemotherapy.The epidermal growth factor receptor (EGFR) and the platelet-derived growth factor receptor β (PDGFRβ) are hallmarks in GBM with driving roles in tumor progression. In approximately half of the tumors with amplified EGFR, the EGFRvIII truncated extracellular mutant is detected. EGFRvIII does not bind ligands, is highly oncogenic and its expression confers resistance to EGFR tyrosine kinase inhibitors (TKIs). It has been demonstrated that EGFRvIII-dependent cancers may escape targeted therapy by developing dependence on PDGFRβ signaling, thus providing a strong rationale for combination therapy aimed at blocking both EGFRvIII and PDGFRβsignaling.We have recently generated two nuclease resistant RNA aptamers, CL4 and Gint4.T, as high affinity ligands and inhibitors of the human wild-type EGFR (EGFRwt) and PDGFRβ, respectively.Herein, by different approaches, we demonstrate that CL4 aptamer binds to the EGFRvIII mutant even though it lacks most of the extracellular domain. As a consequence of binding, the aptamer inhibits EGFRvIII autophosphorylation and downstream signaling pathways, thus affecting migration, invasion and proliferation of EGFRvIII-expressing GBM cell lines.Further, we show that targeting EGFRvIII by CL4, as well as by EGFR-TKIs, erlotinib and gefitinib, causes upregulation of PDGFRβ. Importantly, CL4 and gefitinib cooperate with the anti-PDGFRβ Gint4.T aptamer in inhibiting cell proliferation.The proposed aptamer-based strategy could have impact on targeted molecular cancer therapies and may result in progresses against GBMs.

Targeting a Cancer-Specific Epitope of the Epidermal Growth Factor Receptor in Triple-Negative Breast Cancer

BACKGROUND

Triple-negative breast cancers (TNBCs) are typically more aggressive and result in poorer outcomes than other breast cancers because treatment options are limited due to lack of hormone receptors or amplified human epidermal growth factor receptor 2 (HER2). Many TNBCs overexpress the epidermal growth factor receptor (EGFR) or manifest amplification of theEGFRgene, supporting EGFR as a therapeutic target. While EGFR-directed small molecule inhibitors have shown limited effectiveness in clinical settings, use of EGFR as a mechanism of delivering enzymatic cytotoxins to TNBC has not been demonstrated.

METHODS

Using the single-chain variable fragment (scFv) of the 806 antibody that binds only cells with overexpressed, misfolded, or mutant variants of the EGFR, a recombinant immunotoxin was engineered through gene fusion withPseudomonas aeruginosaExotoxin A (806-PE38). The potency of 806-PE38 on reducing TNBC cell growth in vitro and in xenograft models (n ≥ 6) was examined for six TNBC cell lines. All statistical tests were two-sided.

RESULTS

806-PE38 statistically significantly reduced the viability of all tested TNBC lines, with IC50values below 10 ng/mL for three of six cell lines, while not affecting cells with wild-type EGFR (IC50>300 ng/mL). Systemic treatments with 806-PE38 vs vehicle resulted in statistically significantly reduced tumor burdens (806-PE38 mean = 128 mm(3)[SD = 46 mm(3)] vs vehicle mean = 749 mm(3)[SD = 395 mm(3)], P = .001) and increased median survival (806-PE38 median = 82 days vs vehicle median = 50 days,P= .01) in a MDA-MB-468 TNBC mouse xenograft. Deletion of the catalytic residue eliminated both cytotoxic activity in vitro and the reduction in tumor burden and survival (P= .52).

CONCLUSIONS

These data support the further development of the 806-PE38 immunotoxin as a therapeutic agent for the treatment of patients with EGFR-positive TNBC. Follow-up experiments with combination therapies will be attempted to achieve full remissions.

Targeted therapy of glioblastoma stem-like cells and tumor non-stem cells using cetuximab-conjugated iron-oxide nanoparticles

Malignant gliomas remain aggressive and lethal primary brain tumors in adults. The epidermal growth factor receptor (EGFR) is frequently overexpressed in the most common malignant glioma, glioblastoma (GBM), and represents an important therapeutic target. GBM stem-like cells (GSCs) present in tumors are felt to be highly tumorigenic and responsible for tumor recurrence. Multifunctional magnetic iron-oxide nanoparticles (IONPs) can be directly imaged by magnetic resonance imaging (MRI) and designed to therapeutically target cancer cells. The targeting effects of IONPs conjugated to the EGFR inhibitor, cetuximab (cetuximab-IONPs), were determined with EGFR- and EGFRvIII-expressing human GBM neurospheres and GSCs. Transmission electron microscopy revealed cetuximab-IONP GBM cell binding and internalization. Fluorescence microscopy and Prussian blue staining showed increased uptake of cetuximab-IONPs by EGFR- as well as EGFRvIII-expressing GSCs and neurospheres in comparison to cetuximab or free IONPs. Treatment with cetuximab-IONPs resulted in a significant antitumor effect that was greater than with cetuximab alone due to more efficient, CD133-independent cellular targeting and uptake, EGFR signaling alterations, EGFR internalization, and apoptosis induction in EGFR-expressing GSCs and neurospheres. A significant increase in survival was found after cetuximab-IONP convection-enhanced delivery treatment of 3 intracranial rodent GBM models employing human EGFR-expressing GBM xenografts.

Challenges to targeting epidermal growth factor receptor in glioblastoma: escape mechanisms and combinatorial treatment strategies

Epidermal growth factor receptor (EGFR) gene amplification and activating mutations are common findings in glioblastomas. EGFR is at the top of a downstream signaling cascade that regulates important characteristics of glioblastoma cells, including cellular proliferation, migration, and survival. Targeting EGFR has therefore been regarded as a promising therapeutic strategy in glioblastoma for decades. However, although various pharmacological inhibitors and anti-EGFR antibodies are available, the antiglioma activity of these agents has been largely limited to preclinical models, whereas their administration to glioblastoma patients was characterized by lack of clinical benefit. Comprehensive efforts have been made within the last years to understand the underlying mechanisms that confer resistance to EGFR inhibition in glioma cells. The absence of well-known mutations that predict response to EGFR tyrosine kinase inhibitors (TKIs) in gliomas as well as the presence of redundant and alternative compensatory pathways are among the most important escape mechanisms that prevent potent antiglioma effects of EGFR-targeting drugs. Accordingly, an increasing number of in vitro and in vivo studies are aimed at overcoming this resistance by combinatorial approaches using anti-EGFR treatment together with one or more additional drugs. Novel insights into the molecular mechanisms mediating resistance to anti-EGFR treatment and promising combinatorial approaches may help to better define a future role for EGFR inhibition in the treatment of glioblastoma.

EGFRvIII-mediated transactivation of receptor tyrosine kinases in glioma: mechanism and therapeutic implications

A truncation mutant of the epidermal growth factor receptor, EGFRvIII, is commonly expressed in glioma, an incurable brain cancer. EGFRvIII is tumorigenic, in part, through its transactivation of other receptor tyrosine kinases (RTKs). Preventing the effects of this transactivation could form part of an effective therapy for glioma; however, the mechanism by which the transactivation occurs is unknown. Focusing on the RTK MET, we show that MET transactivation in U87MG human glioma cells in vitro is proportional to EGFRvIII activity and involves MET heterodimerization associated with a focal adhesion kinase (FAK) scaffold. The transactivation of certain other RTKs was, however, independent of FAK. Simultaneously targeting EGFRvIII (with panitumumab) and the transactivated RTKs themselves (with motesanib) in an intracranial mouse model of glioma resulted in significantly greater survival than with either agent alone, indicating that cotargeting these RTKs has potent antitumor efficacy and providing a strategy for treating EGFRvIII-expressing gliomas, which are usually refractory to treatment.

Advances and challenges in the molecular biology and treatment of glioblastoma-is there any hope for the future?

Malignant gliomas, such as glioblastoma multiforme (GBM), present some of the greatest challenges in the management of cancer patients worldwide. Even with aggressive surgical resections and recent advances in radiotherapy and chemotherapy, the prognosis for GBM patients remains dismal and quality of life is poor. Although new molecular pathways crucial to the biology and invasive ability of GBM are coming to light, translation of basic science achievements into clinical practice is slow. Optimal management requires a multidisciplinary approach and knowledge of potential complications arising from both disease and treatment. To help illustrate "where we are going" with GBM, we here include a detailed depiction of the molecular alterations underlying this fatal disease, as well as intensive research over the past two decades that has led to considerable advances in the understanding of basic GBM biology, pathogenesis and therapeutic approaches.

EGFR phosphorylates tumor-derived EGFRvIII driving STAT3/5 and progression in glioblastoma

EGFRvIII, a frequently occurring mutation in primary glioblastoma, results in a protein product that cannot bind ligand, but signals constitutively. Deducing how EGFRvIII causes transformation has been difficult because of autocrine and paracrine loops triggered by EGFRvIII alone or in heterodimers with wild-type EGFR. Here, we document coexpression of EGFR and EGFRvIII in primary human glioblastoma that drives transformation and tumorigenesis in a cell-intrinsic manner. We demonstrate enhancement of downstream STAT signaling triggered by EGFR-catalyzed phosphorylation of EGFRvIII, implicating EGFRvIII as a substrate for EGFR. Subsequent phosphorylation of STAT3 requires nuclear entry of EGFRvIII and formation of an EGFRvIII-STAT3 nuclear complex. Our findings clarify specific oncogenic signaling relationships between EGFR and EGFRvIII in glioblastoma.

Erlotinib resistance in EGFR-amplified glioblastoma cells is associated with upregulation of EGFRvIII and PI3Kp110δ

BACKGROUND

The treatment efficacy of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors like erlotinib has not met expectations for glioblastoma therapy, even for EGFR-overexpressing tumors. We determined possible mechanisms of therapy resistance using the unique BS153 glioblastoma cell line, which has retained amplification of the egfr gene and expression of EGFR variant (v)III.

METHODS

Functional effects of erlotinib, gefitinib, and cetuximab on BS153 proliferation, migration, and EGFR-dependent signal transduction were systematically compared in vitro. The tumor-initiating capacity of parental and treatment-resistant BS153 was studied in Naval Medical Research Institute/Foxn1(nu) mice. Potential mediators of resistance were knocked down using small interfering (si)RNA.

RESULTS

Erlotinib and gefitinib inhibited proliferation and migration of BS153 in a dose-dependent manner, whereas cetuximab had no effect. BS153 developed resistance to erlotinib (BS153(resE)) but not to gefitinib. Resistance was associated with strong upregulation of EGFRvIII and subsequent activation of the phosphatidylinositol-3-OH kinase (PI3K) pathway in BS153(resE) and an increased expression of the regulatory 110-kDa delta subunit of PI3K (p110δ). Knockdown of EGFRvIII in BS153(resE) largely restored sensitivity to erlotinib. Targeting PI3K pharmacologically caused a significant decrease in cell viability, and specifically targeting p110δ by siRNA partially restored erlotinib sensitivity in BS153(resE). In vivo, BS153 formed highly invasive tumors with an unusual growth pattern, displaying numerous satellites distant from the initial injection site. Erlotinib resistance led to delayed onset of tumor growth as well as prolonged overall survival of mice without changing tumor morphology.

CONCLUSIONS

EGFRvIII can mediate resistance to erlotinib in EGFR-amplified glioblastoma via an increase in PI3Kp110δ. Interfering with PI3Kp110δ can restore sensitivity toward the tyrosine kinase inhibitor.

Global protein profiling reveals anti-EGFR monoclonal antibody 806-modulated proteins in A431 tumor xenografts

An important mediator of tumorigenesis, the epidermal growth factor receptor (EGFR) is expressed in almost all non-transformed cell types, associated with tumor progression, angiogenesis and metastasis. The significance of the EGFR as a cancer therapeutic target is underscored by the clinical development of several different classes of EGFR antagonists, including monoclonal antibodies (mAb) and tyrosine kinase inhibitors. Extensive preclinical studies have demonstrated the anti-tumor effects of mAb806 against tumor xenografts overexpressing EGFR. EGF stimulation of A431 cells induces rapid tyrosine phosphorylation of intracellular signalling proteins which regulate cell proliferation and apoptosis. Detailed understanding of the intracellular signalling pathways and components modulated by mAbs (such as mAb806) to EGFR, and other growth factor receptors, remain limited. The use of fluorescence 2D difference gel electrophoresis (2D DIGE), coupled with sensitive MS-based protein profiling in A431 tumor (epidermoid carcinoma) xenografts, in combination with mAb806, revealed proteins modulating endocytosis, cell architecture, apoptosis, cell signalling pathways and cell cycle regulation, including Dynamin-1-like protein, cofilin-1 protein, and 14-3-3 protein zeta/delta. Further, we report various proteins, including Interferon-induced protein 53 (IFI53), and Oncogene EMS1 (EMS1) which have roles in the tumor microenvironment, regulating cancer cell invasiveness, angiogenesis and formation of metastases. These findings contribute to understanding the underlying biological processes associated with mAb806 therapy of EGFR-positive tumors, and identifying further potential protein markers that may contribute in assessment of the treatment response.

An EGFR wild type-EGFRvIII-HB-EGF feed-forward loop regulates the activation of EGFRvIII

EGFRvIII is a key oncogene in glioblastoma (GBM). EGFRvIII results from an in-frame deletion in the extracellular domain of EGFR, does not bind ligand and is thought to be constitutively active. Although EGFRvIII dimerization is known to activate EGFRvIII, the factors that drive EGFRvIII dimerization and activation are not well understood. Here we present a new model of EGFRvIII activation and propose that oncogenic activation of EGFRvIII in glioma cells is driven by co-expressed activated EGFR wild type (EGFRwt). Increasing EGFRwt leads to a striking increase in EGFRvIII tyrosine phosphorylation and activation while silencing EGFRwt inhibits EGFRvIII activation. Both the dimerization arm and the kinase activity of EGFRwt are required for EGFRvIII activation. EGFRwt activates EGFRvIII by facilitating EGFRvIII dimerization. We have previously identified HB-EGF, a ligand for EGFRwt, as a gene induced specifically by EGFRvIII. In this study, we show that HB-EGF is induced by EGFRvIII only when EGFRwt is present. Remarkably, altering HB-EGF recapitulates the effect of EGFRwt on EGFRvIII activation. Thus, increasing HB-EGF leads to a striking increase in EGFRvIII tyrosine phosphorylation while silencing HB-EGF attenuates EGFRvIII phosphorylation, suggesting that an EGFRvIII-HB-EGF-EGFRwt feed-forward loop regulates EGFRvIII activation. Silencing EGFRwt or HB-EGF leads to a striking inhibition of EGFRvIII-induced tumorigenicity, while increasing EGFRwt or HB-EGF levels resulted in accelerated EGFRvIII-mediated oncogenicity in an orthotopic mouse model. Furthermore, we demonstrate the existence of this loop in human GBM. Thus, our data demonstrate that oncogenic activation of EGFRvIII in GBM is likely maintained by a continuous EGFRwt-EGFRvIII-HB-EGF loop, potentially an attractive target for therapeutic intervention.

Targeted antiepidermal growth factor receptor (cetuximab) immunoliposomes enhance cellular uptake in vitro and exhibit increased accumulation in an intracranial model of glioblastoma multiforme

Therapeutic advances do not circumvent the devastating fact that the survival rate in glioblastoma multiforme (GBM) is less than 5%. Nanoparticles consisting of liposome-based therapeutics are provided against a variety of cancer types including GBM, but available liposomal formulations are provided without targeting moieties, which increases the dosing demands to reach therapeutic concentrations with risks of side effects. We prepared PEGylated immunoliposomes (ILs) conjugated with anti-human epidermal growth factor receptor (EGFR) antibodies Cetuximab (α-hEGFR-ILs). The affinity of the α-hEGFR-ILs for the EGF receptor was evaluated in vitro using U87 mg and U251 mg cells and in vivo using an intracranial U87 mg xenograft model. The xenograft model was additionally analyzed with respect to permeability to endogenous albumin, tumor size, and vascularization. The in vitro studies revealed significantly higher binding of α-hEGFR-ILs when compared with liposomes conjugated with isotypic nonimmune immunoglobulin. The uptake and internalization of the α-hEGFR-ILs by U87 mg cells were further confirmed by 3D deconvolution analyses. In vivo, the α-hEGFR-ILs accumulated to a higher extent inside the tumor when compared to nonimmune liposomes. The data show that α-hEGFR-ILs significantly enhance the uptake and accumulation of liposomes in this experimental model of GBM suggestive of improved specific nanoparticle-based delivery.

Antibody-functionalized porous silicon nanoparticles for vectorization of hydrophobic drugs

We describe the preparation of biodegradable porous silicon nanoparticles (pSiNP) functionalized with cancer cell targeting antibodies and loaded with the hydrophobic anti-cancer drug camptothecin. Orientated immobilization of the antibody on the pSiNP is achieved using novel semicarbazide based bioconjugate chemistry. To demonstrate the generality of this targeting approach, the three antibodies MLR2, mAb528 and Rituximab are used, which target neuroblastoma, glioblastoma and B lymphoma cells, respectively. Successful targeting is demonstrated by means of flow cytometry and immunocytochemistry both with cell lines and primary cells. Cell viability assays after incubation with pSiNPs show selective killing of cells expressing the receptor corresponding to the antibody attached on the pSiNP.

Epidermal growth factor receptor as a therapeutic target in glioblastoma

Glioblastoma represents one of the most challenging problems in neurooncology. Among key elements driving its behavior is the transmembrane epidermal growth factor receptor family, with the first member epidermal growth factor receptor (EGFR) centered in most studies. Engagement of the extracellular domain with a ligand activates the intracellular tyrosine kinase (TK) domain of EGFR, leading to autophosphorylation and signal transduction that controls proliferation, gene transcription, and apoptosis. Oncogenic missense mutations, deletions, and insertions in the EGFR gene are preferentially located in the extracellular domain in glioblastoma and cause constitutive activation of the receptor. The mutant EGFR may also transactivate other cell surface molecules, such as additional members of the EGFR family and the platelet-derived growth factor receptor, which ignite signaling cascades that synergize with the EGFR-initiated cascade. Because of the cell surface location and increased expression of the receptor along with its important biological function, EGFR has triggered much effort for designing targeted therapy. These approaches include TK inhibition, monoclonal antibody, vaccine, and RNA-based downregulation of the receptor. Treatment success requires that the drug penetrates the blood-brain barrier and has low systemic toxicity but high selectivity for the tumor. While the blockade of EGFR-dependent processes resulted in experimental and clinical treatment success, cells capable of using alternative signaling ultimately escape this strategy. A combination of interventions targeting tumor-specific cell surface regulators along with convergent downstream signaling pathways will likely enhance efficacy. Studies on EGFR in glioblastoma have revealed much information about the complexity of gliomagenesis and also facilitated the development of strategies for targeting drivers of tumor growth and combination therapies with increasing complexity.

Targeting EGFR for treatment of glioblastoma: molecular basis to overcome resistance

Glioblastoma (glioblastoma multiforme; GBM; WHO Grade IV) accounts for the majority of primary malignant brain tumors in adults. Amplification and mutation of the epidermal growth factor receptor (EGFR) gene represent signature genetic abnormalities encountered in GBM. A range of potential therapies that target EGFR or its mutant constitutively active form, ΔEGFR, including tyrosine kinase inhibitors (TKIs), monoclonal antibodies, vaccines, and RNA-based agents, are currently in development or in clinical trials for the treatment of GBM. Data from experimental studies evaluating these therapies have been very promising; however, their efficacy in the clinic has so far been limited by both upfront and acquired drug resistance. This review discusses the current status of anti-EGFR agents and the recurrent problem of resistance to these agents that strongly indicates that a multiple target approach will provide a more favorable future for these types of targeted therapies in GBM.

Targeting of a conformationally exposed, tumor-specific epitope of EGFR as a strategy for cancer therapy

Epidermal growth factor receptor (EGFR) and its most common extracellular mutant, EGFRvIII, are important therapeutic targets in multiple cancer types. A number of monoclonal antibodies and small-molecule inhibitors against these receptors are now used for anticancer treatments. New insights into the structure and function of these receptors illustrate how they can be targeted in novel ways, with expected improvements in the therapeutic efficacy. Monoclonal antibody 806 (mAb806) is an antibody that targets a conformationally exposed epitope of wild-type EGFR when it is overexpressed on tumor cells or in the presence of oncogenic mutations such as EGFRvIII. The mechanism of action of mAb806, which allows for EGFR inhibition without normal tissue toxicity, creates opportunities for combination therapy and strongly suggests mAb806 will be a superior targeted delivery system for antitumor agents. Targeting of the epitope for mAb806 also appears to be an improved strategy to inhibit tumors that express EGFRvIII. This concept of conformational epitope targeting by antibodies reflects an underlying interplay between the structure and biology of different conformational forms of the EGFR family.

Expression of EGFRvIII in glioblastoma: prognostic significance revisited

The epidermal growth factor receptor variant III (EGFRvIII) is associated with increased proliferation of glioma cells. However, the impact of EGFRvIII on survival of patients with glioblastoma (GBM) has not been definitively established. In the present study, we prospectively evaluated 73 patients with primary GBM treated with surgical resection and standard radio/chemotherapy. The EGFRvIII was assessed by reverse transcription-polymerase chain reaction (PCR), O(6)-methylguanine methyltransferase (MGMT) promoter methylation was assessed by methylation-specific PCR, and phosphatase and tension homolog (PTEN) expression was assessed by immunohistochemistry. In 14 patients of this series, who presented with tumor recurrence, EGFRvIII was determined by real-time PCR. Sensitivity to temozolomide (TMZ) was assessed in vitro on GBM neurosphere cell cultures with different patterns of EGFRvIII expression. Age 60 years or younger, preoperative Karnofsky Performance Status score of 70 or higher, recursive partitioning analysis score III and IV, methylated MGMT, and Ki67 index of 20% or less were significantly associated with longer overall survival (OS; P = .0069, P = .0035, P = .0007, P = .0437, and P = .0286, respectively). EGFRvIII identified patients with significantly longer OS (P = .0023) and the association of EGFRvIII/Ki67 of 20% or less, EGFRvIII/normal PTEN, EGFRvIII/methylated MGMT, and EGFRvIII/normal PTEN/methylated MGMT identified subgroups of GBM patients with better prognosis. In recurred GBMs, EGFRvIII expression was approximately two-fold lower than in primary tumors. In vitro, the EGFRvIII-negative GBM neurosphere cells were more resistant to TMZ than the positive ones. In conclusion, in contrast with previous studies, we found that EGFRvIII is associated with prolonged survival of GBM patients treated with surgery and radio/chemotherapy. Depletion of EGFRvIII in recurrent GBMs as well as differential sensitivity to TMZ in vitro indicates that the EGFRvIII-negative cell fraction is involved in resistance to radio/chemotherapy and tumor repopulation.

Lyn kinase mediates cell motility and tumor growth in EGFRvIII-expressing head and neck cancer

PURPOSE

EGF receptor variant III (EGFRvIII) has been detected in several cancers in which tumors expressing this truncated growth factor receptor show more aggressive behavior. The molecular mechanisms that contribute to EGFRvIII-mediated tumor progression that are amenable to targeted therapy are incompletely understood. The present study aimed to better define the role of Src family kinases (SFKs) in EGFRvIII-mediated cell motility and tumor growth of head and neck squamous cell carcinomas (HNSCC).

EXPERIMENTAL DESIGN

HNSCC models expressing EGFRvIII were treated with dasatinib, a pharmacologic inhibitor of SFKs.

RESULTS

SFK inhibition significantly decreased cell proliferation, migration, and invasion of EGFRvIII-expressing HNSCC cells. Administration of dasatinib to mice bearing EGFRvIII-expressing HNSCC xenografts resulted in a significant reduction of tumor volume compared with controls. Immunoprecipitation with anti-c-Src, Lyn, Fyn, and Yes antibodies followed by immunoblotting for phosphorylation of the SFK activation site (Y416) showed specific activation of Lyn kinase in EGFRvIII-expressing HNSCC cell lines and human HNSCC tumor specimens. Selective inhibition of Lyn using siRNA decreased cell migration and invasion of EGFRvIII-expressing HNSCCs compared with vector control cells.

CONCLUSIONS

These findings show that Lyn mediates tumor progression of EGFRvIII-expressing HNSCCs in which strategies to inhibit SFK may represent an effective therapeutic strategy.

Activation of Src induces mitochondrial localisation of de2-7EGFR (EGFRvIII) in glioma cells: implications for glucose metabolism

A common mutation of the epidermal growth factor receptor in glioma is the de2-7EGFR (or EGFRvIII). Glioma cells expressing de2-7EGFR contain an intracellular pool of receptor with high levels of mannose glycosylation, which is consistent with delayed processing. We now show that this delay occurs in the Golgi complex. Low levels of de2-7EGFR were also seen within the mitochondria. Src activation dramatically increased the amount of mitochondrial de2-7EGFR, whereas its pharmacological inhibition caused a significant reduction. Because de2-7EGFR is phosphorylated by Src at Y845, we generated glioma cells expressing a Y845F-modified de2-7EGFR. The de2-7EGFR(845F) mutant failed to show mitochondrial localisation, even when co-expressed with constitutive active Src. Low levels of glucose enhanced mitochondrial localisation of de2-7EGFR, and glioma cells expressing the receptor showed increased survival and proliferation under these conditions. Consistent with this, de2-7EGFR reduced glucose dependency by stimulating mitochondrial oxidative metabolism. Thus, the mitochondrial localisation of de2-7EGFR contributes to its tumorigenicity and might help to explain its resistance to some EGFR-targeted therapeutics.

Glioblastoma stem-like cell lines with either maintenance or loss of high-level EGFR amplification, generated via modulation of ligand concentration

PURPOSE

Despite the high incidence of epidermal growth factor receptor (EGFR) gene amplification and rearrangement in glioblastomas, no suitable cell line exists that preserves these alterations in vitro and is tumorigenic in immunocompromised mice. On the basis of previous observations that glioblastoma cells cultured with serum lose the EGFR amplification rapidly and that EGF can inhibit the growth of EGFR-amplified tumor cells, we hypothesized that serum-free and EGF-free culture conditions could promote maintenance of the EGFR amplification.

EXPERIMENTAL DESIGN

Cells from EGFR-amplified glioblastomas were taken into culture using neural stem cell conditions with modifications, including varying oxygen concentrations and omission of routine EGF supplementation.

RESULTS

High-level EGFR amplification was rapidly lost in 5 glioblastoma cultures supplemented with EGF, whereas it was preserved in cultures from the same tumors established without EGF. Cultures from 2 glioblastomas developed into pairs of cell lines, with either stable maintenance or irreversible loss of high-level EGFR amplification in the majority of cells. One EGFR-amplified cell line preserved expression of the receptor variant EGFRvIII. Cell lines with high-level EGFR amplification/EGFRvIII expression formed highly aggressive tumors in nude mice, whereas nonamplified cell lines were either nontumorigenic or grew significantly more slowly. In contrast, nonamplified cell lines proliferated faster in vitro. All cell lines responded to erlotinib, with inhibition of receptor activation and proliferation but partly different effects on downstream signaling and migration.

CONCLUSIONS

Isogenic glioblastoma cell lines maintaining stable differences in EGFR/EGFRvIII status can be derived by varying exposure to EGF ligand and reflect the intratumoral genetic heterogeneity.

Growth and metastasis suppression of glioma xenografts expressing exon 4-deletion variant of epidermal growth factor receptor by monoclonal antibody CH12-mediated receptor degradation

We recently isolated an exon-4-deleted epidermal growth factor receptor (EGFR) variant, termed de4 EGFR. Because the extracellular domain alteration of receptors often influences the antitumor effect of therapeutic antibodies, it is essential to test the sensitivity of de4 EGFR(+) tumors to anti-EGFR antibodies. Therefore, in this study, the antitumor activities of mAb CH12, an anti-EGFRvIII antibody developed in our laboratory, as well as a U.S. Food and Drug Administration-approved anti-EGFR antibody, cetuximab (C225), were characterized on de4 EGFR(+) models. The results of FACS assays showed that CH12 bound to de4 EGFR with a higher avidity than did C225. Interestingly, CH12, but not C225, significantly inhibited the metastasis and growth of U87MG-de4 EGFR xenografts, with a growth-inhibition ratio of 46.48% in vivo, and prolonged the survival of the tumor-bearing mice by 37.2%. Treatment with CH12 significantly suppressed tumor proliferation and angiogenesis with increased tumor apoptosis. Mechanistically, de4 EGFR protein expression was virtually undetectable in the U87MG-de4 EGFR xenografts treated with CH12. This may account for the observed reduction of Akt and Erk phosphorylation, cyclin D1, Bcl-2, and Bcl-x(L) expression and the increase of p27 and E-cadherin expression. Intriguingly, LAMP-1, a major component of the lysosome, was significantly up-regulated in the CH12-treated group but not in the C225-treated group, suggesting its contribution to the degradation of de4 EGFR. Taken together, our data demonstrated that mAb CH12 is a promising therapeutic agent for treating de4 EGFR(+) gliomas.

Bay846, a new irreversible small molecule inhibitor of EGFR and Her2, is highly effective against malignant brain tumor models

The epidermal growth factor receptor (EGFR) pathway is aberrantly activated in tumors and plays a key role in promoting tumor growth. Small molecule inhibitors which bind reversibly to EGFR have demonstrated limited clinical activity. Thus, there is a continued need to develop novel EGFR inhibitors with improved anti-tumor activity. Bay846 is a newly developed small molecule inhibitor that binds irreversibly to the tyrosine kinase domains of EGFR and Her2. The in vitro and in vivo efficacy of Bay846 was tested using a panel of nine human malignant brain tumor (glioma) models. Lapatinib, a reversible inhibitor of EGFR and Her2, was included for comparison. Six glioma cell lines were sensitive to Bay846 treatment. Bay846 strongly suppressed tumor cell growth in vitro by inducing cell lysis/death rather than cell cycle arrest. Consistent with this, Bay846 had potent anti-tumor activity which led to regressions in tumor size. The active, phosphorylated form of EGFR was reduced by Bay846 treatment in vitro and in tumors. Importantly, the efficacy of Bay846 was significantly greater than lapatinib in all assays. Bay846-sensitivity was associated with expression of a wild-type PTEN in conjunction with high levels of an oncogenic EGFR variant (A289V or EGFRvIII). These studies demonstrate that targeting the EGFR pathway with the irreversible inhibitor Bay846 has great potential to increase the efficacy of this cancer therapy.

Genomic and molecular characterization of malignant peripheral nerve sheath tumor identifies the IGF1R pathway as a primary target for treatment

PURPOSE

Malignant peripheral nerve sheath tumor (MPNST) is a rare sarcoma that lacks effective therapeutic strategies. We gain insight into the most recurrent genetically altered pathways with the purpose of scanning possible therapeutic targets.

EXPERIMENTAL DESIGN

We conducted a microarray-based comparative genomic hybridization profiling of two cohorts of primary MPNST tissue samples including 25 patients treated at The University of Texas MD Anderson Cancer Center and 26 patients from Tianjin Cancer Hospital. Immunohistochemistry (IHC) and cell biology detection and validation were carried out on human MPNST tissues and cell lines.

RESULTS

Genomic characterization of 51 MPNST tissue samples identified several frequently amplified regions harboring 2,599 genes and regions of deletion including 4,901 genes. At the pathway level, we identified a significant enrichment of copy number-altering events in the insulin-like growth factor 1 receptor (IGF1R) pathway, including frequent amplifications of the IGF1R gene itself. To validate the IGF1R pathway as a potential target in MPNSTs, we first confirmed that high IGF1R protein correlated with worse tumor-free survival in an independent set of samples using IHC. Two MPNST cell lines (ST88-14 and STS26T) were used to determine the effect of attenuating IGF1R. Inhibition of IGF1R in ST88-14 cells using siRNAs or an IGF1R inhibitor, MK-0646, led to significant decreases in cell proliferation, invasion, and migration accompanied by attenuation of the PI3K/AKT and mitogen-activated protein kinase pathways.

CONCLUSION

These integrated genomic and molecular studies provide evidence that the IGF1R pathway is a potential therapeutic target for patients with MPNST.

Src family kinases mediate epidermal growth factor receptor signaling from lipid rafts in breast cancer cells

Activation of the epidermal growth factor receptor (EGFR) regulates cellular proliferation, survival, and migration of breast cancer cells. In particular, EGFR recruits signaling proteins to the cell membrane leading to their phosphorylation and activation. However, EGFR also localizes to other cellular structures, including endosomes, mitochondrion, and nuclei. Recently, we demonstrated that lipid raft localization of EGFR in triple-negative breast cancer cell lines promotes EGFR protein-dependent, EGFR kinase-independent activation of Akt. Here, we further define the mechanism by which lipid rafts regulate EGFR signaling to Akt. Specifically, we show that the non-receptor tyrosine kinase c-Src co-localizes and co-associates with EGFR and lipid rafts. Breast cancer cells resistant to treatment with EGFR inhibitors, were also resistant to treatment with Src family kinase (SFK) inhibitors; however, the combination of EGFR and SFK inhibitors synergistically decreases cell viability. We found that this decrease in cell viability observed with EGFR and SFK inhibitor co-treatment correlates with loss of Akt phosphorylation. In addition, we found that in breast cancer cell lines with EGFR and c-Src co-localized to lipid rafts, phospho-inositide 3 kinase (PI3K) was also associated with lipid rafts. Together, the data herein suggest that lipid rafts provide a platform for the interaction of EGFR, c-Src, and PI3K, leading to activation of cellular survival signaling in breast cancer cells.

A simple guide screw method for intracranial xenograft studies in mice

The grafting of human tumor cells into the brain of immunosuppressed mice is an established method for the study of brain cancers including glioblastoma (glioma) and medulloblastoma. The widely used stereotactic approach only allows for the injection of a single animal at a time, is labor intensive and requires highly specialized equipment. The guide screw method, initially developed by Lal et al.,¹ was developed to eliminate cumbersome stereotactic procedures. We now describe a modified guide screw approach that is rapid and exceptionally safe; both of which are critical ethical considerations. Notably, our procedure now incorporates an infusion pump that allows up to 10 animals to be simultaneously injected with tumor cells.

To demonstrate the utility of this procedure, we established human U87MG glioma cells as intracranial xenografts in mice, which were then treated with AMG102; a fully human antibody directed to HGF/scatter factor currently undergoing clinical evaluation^2-5. Systemic injection of AMG102 significantly prolonged the survival of all mice with intracranial U87MG xenografts and resulted in a number of complete cures.

This study demonstrates that the guide screw method is an inexpensive, highly reproducible approach for establishing intracranial xenografts. Furthermore, it provides a relevant physiological model for validating novel therapeutic strategies for the treatment of brain cancers.

Complex oncogenic signaling networks regulate brain tumor-initiating cells and their progenies: pivotal roles of wild-type EGFR, EGFRvIII mutant and hedgehog cascades and novel multitargeted therapies

Complex signaling cross-talks between different growth factor cascades orchestrate the primary brain cancer development. Among the frequent deregulated oncogenic pathways, the ligand-activated wild-type epidermal growth factor receptor (EGFR), constitutively activated EGFRvIII mutant and sonic hedgehog pathways have attracted much attention because of their pivotal roles in pediatric medulloblastomas and adult glioblastoma multiformes (GBM) brain tumors. The enhanced expression levels and activation of EGFR, EGFRvIII mutant and hedgehog signaling elements can provide key roles for the sustained growth, migration and local invasion of brain tumor-initiating cells (BTICs) and their progenies, resistance to current therapies and disease relapse. These tumorigenic cascades also can cooperate with Wnt/β-catenin, Notch, platelet-derived growth factor (PDGF)/PDGF receptors (PDGFRs), hepatocyte growth factor (HGF)/c-Met receptor and vascular endothelial growth factor (VEGF)/VEGF receptors (VEGFRs) for the acquisition of a more malignant behavior and survival advantages by brain tumor cells during disease progression. Therefore, the simultaneous targeting of these oncogenic signaling components including wild-type EGFR, EGFRvIII mutant and hedgehog pathways may constitute a potential therapeutic approach of great clinical interest to eradicate BTICs and improve the efficacy of current clinical treatments by radiation and/or chemotherapy against aggressive and recurrent medulloblastomas and GBMs.

Differential and synergistic effects of epidermal growth factor receptor antibodies on unliganded ErbB dimers and oligomers

Antibodies directed against the epidermal growth factor receptor (EGFR) offer a potentially powerful therapeutic approach against cancers driven by the EGFR pathway. EGFR antibodies are believed to halt cell surface activation by blocking ligand-induced receptor tyrosine kinase activation, i.e., ligand binding, a change in conformation, or the monomer-dimer transition. In this work, we demonstrate that wild-type EGFR and the truncated de2-7-EGFR (tumor-associated mutant) formed unliganded homo-oligomers and examined the effects of two clinically relevant antibodies on the conformation and quaternary state of these ligand-free EGFR oligomers on the surface of cells. The EGFR antibodies were mAb528, a ligand-blocking antibody that binds domain III, and mAb806, a conformationally sensitive antibody that binds near the dimer interface in domain II. We used a model cellular system, BaF/3 cells, with GFP-tagged receptors in the absence of interference from secreted ligands or other erbB receptor members. Different antibody-mediated effects (conformational transition, receptor cross-linking, or receptor dissociation) were distinguished by combining two complementary biophysical techniques: image correlation spectroscopy (submicrometer scale clustering) and homo-Forster resonance energy transfer (association and/or conformation on a 1-10 nm scale). mAb528 cross-linked EGFR into an inactive EGFR dimer of dimers but had no effect when added to de2-7-EGFR oligomers. mAb806 had a minor effect on EGFR dimers as expected from its poor binding to a conformationally shielded epitope on wtEGFR but bound de2-7-EGFR oligomers, causing a conformational change in the intracellular C-terminal GFP-tagged tail. The combination of the two antibodies had synergistic effects, increasing the level of cross-linking of de2-7-EGFR, but did not lead to enhanced cross-linking of EGFR. The results reveal new modes of receptor-antibody interactions for EGFR and de2-7-EGFR.

Regulation of SRC family kinases in human cancers

The nonreceptor protein tyrosine kinase Src plays a crucial role in the signal transduction pathways involved in cell division, motility, adhesion, and survival in both normal and cancer cells. Although the Src family kinases (SFKs) are activated in various types of cancers, the exact mechanisms through which they contribute to the progression of individual tumors remain to be defined. The activation of Src in human cancers may occur through a variety of mechanisms that include domain interaction and structural remodeling in response to various activators or upstream kinases and phosphatastes. Because of Src's prominent roles in invasion and tumor progression, epithelial-to-mesenchymal transition, angiogenesis, and the development of metastasis, Src is a promising target for cancer therapy. Several small molecule inhibitors of Src are currently being investigated in clinical trials. In this article, we will summarize the mechanisms regulating Src kinase activity in normal and cancer cells and discuss the status of Src inhibitor development against various types of cancers.

Tumor heterogeneity is an active process maintained by a mutant EGFR-induced cytokine circuit in glioblastoma

Human solid tumors frequently have pronounced heterogeneity of both neoplastic and normal cells on the histological, genetic, and gene expression levels. While current efforts are focused on understanding heterotypic interactions between tumor cells and surrounding normal cells, much less is known about the interactions between and among heterogeneous tumor cells within a neoplasm. In glioblastoma multiforme (GBM), epidermal growth factor receptor gene (EGFR) amplification and mutation (EGFRvIII/DeltaEGFR) are signature pathogenetic events that are invariably expressed in a heterogeneous manner. Strikingly, despite its greater biological activity than wild-type EGFR (wtEGFR), individual GBM tumors expressing both amplified receptors typically express wtEGFR in far greater abundance than the DeltaEGFR lesion. We hypothesized that the minor DeltaEGFR-expressing subpopulation enhances tumorigenicity of the entire tumor cell population, and thereby maintains heterogeneity of expression of the two receptor forms in different cells. Using mixtures of glioma cells as well as immortalized murine astrocytes, we demonstrate that a paracrine mechanism driven by DeltaEGFR is the primary means for recruiting wtEGFR-expressing cells into accelerated proliferation in vivo. We determined that human glioma tissues, glioma cell lines, glioma stem cells, and immortalized mouse Ink4a/Arf(-/-) astrocytes that express DeltaEGFR each also express IL-6 and/or leukemia inhibitory factor (LIF) cytokines. These cytokines activate gp130, which in turn activates wtEGFR in neighboring cells, leading to enhanced rates of tumor growth. Ablating IL-6, LIF, or gp130 uncouples this cellular cross-talk, and potently attenuates tumor growth enhancement. These findings support the view that a minor tumor cell population can potently drive accelerated growth of the entire tumor mass, and thereby actively maintain tumor cell heterogeneity within a tumor mass. Such interactions between genetically dissimilar cancer cells could provide novel points of therapeutic intervention.

MAb 806 enhances the efficacy of ionizing radiation in glioma xenografts expressing the de2-7 epidermal growth factor receptor

PURPOSE

Mutations of the epidermal growth factor receptor (EGFR) are common in glioma. The most frequent mutation, de2-7 EGFR/EGFRvIII, occurs in approximately 40% of high-grade gliomas and confers resistance to ionizing radiation (IR). We have previously shown that mAb 806, a novel EGFR-specific antibody, is able to inhibit the growth of U87MG.Δ2-7 glioma xenografts expressing the de2-7 EGFR and may have potential as a therapeutic.

METHODS AND MATERIALS

Nude mice bearing U87MG.Δ2-7 xenografts were treated with mAb 806 and/or IR. Comparison of tumor volumes, the effect of treatment on angiogenesis as determined by mean vessel density, and expression changes in prosurvival protein pAkt between treatment groups were undertaken.

RESULTS

Treatment of mice bearing U87MG.Δ2-7 xenografts with mAb 806 and IR resulted in schedule-dependent radiosensitization. Maximal benefit was obtained when antibody treatment was given before irradiation, with the greatest inhibition of both tumor angiogenesis and tumor growth. Combination treatment mediated radiosensitization by selectively blocking the phosphorylation of the prosurvival protein Akt at serine 473, a process that is independent of DNA-dependent protein kinase catalytic subunit.

CONCLUSIONS

Our results provide a rationale for the use of mAb 806 in combination with IR for the treatment of glioma and potentially other solid tumors bearing the de2-7 EGFR.

Immuno-PET quantitation of de2-7 epidermal growth factor receptor expression in glioma using 124I-IMP-R4-labeled antibody ch806

Overexpression, activation, and mutations of the epidermal growth factor receptor (EGFR) are commonly found in solid tumors. The aim of this study was to develop a PET-based method for detecting the constitutively active mutant de2-7 EGFR, which is associated with disease progression and resistance to chemotherapy and radiotherapy in glioma.

METHODS

The chimeric antibody ch806, which selectively binds an epitope of the EGFR that is exposed only on overexpressed, mutant, or ligand-activated forms of the receptor, was conjugated to the radiohalogen (124)I via the residualizing ligand IMP-R4, and in vitro properties were characterized. In vivo biodistribution and small-animal PET studies were performed in BALB/c nude mice bearing U87MG.de2-7 glioma xenografts. Imaging results were correlated with measured tumor uptake of the radioconjugate.

RESULTS

(124)I-IMP-R4-ch806 had an immunoreactivity of 78.3% and was stable for 7 d when incubated in serum in vitro. The biodistribution analysis of (124)I-IMP-R4-ch806 demonstrated a maximal uptake of 30.95 +/- 6.01 percentage injected dose per gram (%ID/g) in U87MG.de2-7 xenografts at 48 h after injection, with prolonged tumor retention (6.07 +/- 0.80 %ID/g at 216 h after injection). The tumor-to-blood ratio increased from 0.44 at 4 h after injection to a maximum of 4.70 at 168 h after injection. PET of (124)I-IMP-R4-ch806 biodistribution was able to clearly detect the U87MG.de2-7 tumors at 24 h after injection and for at least 168 h after injection. Correlation between tumor PET image quantitation of (124)I-IMP-R4-ch806 and %ID/g determined from resected tissues (r = 0.9350) was excellent.

CONCLUSION

These results show that immuno-PET with (124)I-IMP-R4-ch806 is feasible and allows noninvasive quantitation of de2-7 EGFR expression in vivo.

The constitutive activity of epidermal growth factor receptor vIII leads to activation and differential trafficking of wild-type epidermal growth factor receptor and erbB2

A constitutively active epidermal growth factor receptor (EGFR) mutant, EGFR variant III (EGFRvIII), has been detected at high frequencies in certain human cancers. This study evaluated transactivation and trafficking of erbB family members as a result of constitutive EGFR activity in a cancer cell line. Expression of EGFRvIII modulated erbB family members through different mechanisms; the erbB3 mRNA level was reduced, whereas wild-type EGFR (wtEGFR) and erbB2 protein levels were diminished, with no change in their mRNA levels, and there was no change in the erbB4 expression level. Both EGFR and erbB2 were internalized as a result of EGFRvIII's activity and redistributed to the cell surface upon addition of AG1478, an inhibitor of wtEGFR/EGFRvIII catalytic activity. Acute activation of EGFRvIII by removing AG1478 from cells increased phosphorylation of both wtEGFR and erbB2 and caused differential trafficking of EGFRvIII's activation partners; wtEGFR was directed primarily to lysosomal compartments and partially to recycling compartments, whereas erbB2 was directed primarily to recycling compartments and partially to lysosomal compartments. Our data demonstrate that the constitutive activity of EGFRvIII is sufficient to trigger endocytosis and trafficking of wtEGFR and erbB2, which may play a role in activating signaling pathways that are triggered during receptor endocytosis.

A possible role for metallic ions in the carbohydrate cluster recognition displayed by a Lewis Y specific antibody

Background

Lewis Y (Le^y) is a blood group-related carbohydrate that is expressed at high surface densities on the majority of epithelial carcinomas and is a promising target for antibody-based immunotherapy. A humanized Le^y-specific antibody (hu3S193) has shown encouraging safety, pharmacokinetic and tumor-targeting properties in recently completed Phase I clinical trials.

Methodology/Principal Findings

We report the three-dimensional structures for both the free (unliganded) and bound (Le^y tetrasaccharide) hu3S193 Fab from the same crystal grown in the presence of divalent zinc ions. There is no evidence of significant conformational changes occurring in either the Le^y carbohydrate antigen or the hu3S193 binding site, which suggests a rigid fit binding mechanism. In the crystal, the hu3S193 Fab molecules are coordinated at their protein-protein interface by two zinc ions and in solution aggregation of Fab can be initiated by zinc, but not magnesium ions. Dynamic light scattering revealed that zinc ions could initiate a sharp transition from hu3S193 Fab monomers to large multimeric aggregates in solution.

Conclusions/Significance

Zinc ions can mediate interactions between hu3S193 Fab in crystals and in solution. Whether metallic ion mediated aggregation of antibody occurs in vivo is not known, but the present results suggest that similar clustering mechanisms could occur when hu3S193 binds to Le^y on cells, particularly given the high surface densities of antigen on the target tumor cells.

Fyn and SRC are effectors of oncogenic epidermal growth factor receptor signaling in glioblastoma patients

Activating epidermal growth factor receptor (EGFR) mutations are common in many cancers including glioblastoma. However, clinical responses to EGFR inhibitors are infrequent and short-lived. We show that the Src family kinases (SFK) Fyn and Src are effectors of oncogenic EGFR signaling, enhancing invasion and tumor cell survival in vivo. Expression of a constitutively active EGFR mutant, EGFRvIII, resulted in activating phosphorylation and physical association with Src and Fyn, promoting tumor growth and motility. Gene silencing of Fyn and Src limited EGFR- and EGFRvIII-dependent tumor cell motility. The SFK inhibitor dasatinib inhibited invasion, promoted tumor regression, and induced apoptosis in vivo, significantly prolonging survival of an orthotopic glioblastoma model expressing endogenous EGFRvIII. Dasatinib enhanced the efficacy of an anti-EGFR monoclonal antibody (mAb 806) in vivo, further limiting tumor growth and extending survival. Examination of a large cohort of clinical samples showed frequent coactivation of EGFR and SFKs in glioblastoma patients. These results establish a mechanism linking EGFR signaling with Fyn and Src activation to promote tumor progression and invasion in vivo and provide rationale for combined anti-EGFR and anti-SFK targeted therapies.

The deletion mutant EGFRvIII significantly contributes to stress resistance typical for the tumour microenvironment

BACKGROUND AND PURPOSE

The epidermal growth factor receptor (EGFR) is overexpressed or mutated in many tumour types. The truncated, constitutively active EGFRvIII variant has not been detected in normal tissues but is found in many malignancies. In the current study, we have investigated the hypothesis that EGFRvIII contributes to a growth and survival advantage under tumour microenvironment-related stress conditions.

MATERIALS AND METHODS

U373MG doxycycline-regulated isogenic cells expressing EGFRwt or EGFRvIII were created and validated using Western blot, FACS and qRT-PCR. In vitro proliferation was evaluated with standard growth assays. Cell survival was assayed using clonogenic survival. Animal experiments were performed using NMRI-nu-xenografted mice.

RESULTS

Inducible isogenic cell lines were created and showed high induction of EGFRwt and EGFRvIII upon doxycycline addition. Overexpression of EGFRvIII but not of EGFRwt in this model resulted in a growth and survival advantage upon different tumour microenvironment-related stress conditions in vitro. Induction of EGFRvIII increased tumour growth in vivo, which was reversible upon loss of expression.

CONCLUSIONS

Under conditions where nutrients are limited and stress is apparent, as in the tumour microenvironment, expression of EGFRvIII leads to a growth and survival advantage. These data indicate a potential selection of EGFRvIII-expressing tumour cells under such stress conditions.

The plasticity of oncogene addiction: implications for targeted therapies directed to receptor tyrosine kinases

A common mutation of the epidermal growth factor receptor (EGFR) in glioblastoma multiforme (GBM) is an extracellular truncation known as the de2-7 EGFR (or EGFRvIII). Hepatocyte growth factor (HGF) is the ligand for the receptor tyrosine kinase (RTK) c-Met, and this signaling axis is often active in GBM. The expression of the HGF/c-Met axis or de2-7 EGFR independently enhances GBM growth and invasiveness, particularly through the phosphatidylinositol-3 kinase/pAkt pathway. Using RTK arrays, we show that expression of de2-7 EGFR in U87MG GBM cells leads to the coactivation of several RTKs, including platelet-derived growth factor receptor beta and c-Met. A neutralizing antibody to HGF (AMG102) did not inhibit de2-7 EGFR-mediated activation of c-Met, demonstrating that it is ligand-independent. Therapy for parental U87MG xenografts with AMG 102 resulted in significant inhibition of tumor growth, whereas U87MG.Delta 2-7 xenografts were profoundly resistant. Treatment of U87MG.Delta 2-7 xenografts with panitumumab, an anti-EGFR antibody, only partially inhibited tumor growth as xenografts rapidly reverted to the HGF/c-Met signaling pathway. Cotreatment with panitumumab and AMG 102 prevented this escape leading to significant tumor inhibition through an apoptotic mechanism, consistent with the induction of oncogenic shock. This observation provides a rationale for using panitumumab and AMG 102 in combination for the treatment of GBM patients. These results illustrate that GBM cells can rapidly change the RTK driving their oncogene addiction if the alternate RTK signals through the same downstream pathway. Consequently, inhibition of a dominant oncogene by targeted therapy can alter the hierarchy of RTKs resulting in rapid therapeutic resistance.

Targeted therapy for malignant glioma patients: lessons learned and the road ahead

Molecularly targeted therapies are transforming the care of patients with malignant gliomas, including glioblastoma, the most common malignant primary brain tumor of adults. With an arsenal of small molecule inhibitors and antibodies that target key components of the signal transduction machinery that are commonly activated in gliomas, neuro-oncologists and neurosurgeons are poised to transform the care of these patients. Nonetheless, successful application of targeted therapies remains a challenge. Strategies are lacking for directing kinase inhibitor or other pathway-specific therapies to individual patients most likely to benefit. In addition, response to targeted agents is determined not only by the presence of the key mutant kinases, but also by other critical changes in the molecular circuitry of cancer cells, such as loss of key tumor suppressor proteins, the selection for kinase-resistant mutants, and the deregulation of feedback loops. Understanding these signaling networks, and studying them in patients, will be critical for developing rational combination therapies to suppress resistance for malignant glioma patients. Here we review the current status of molecular targeted therapies for malignant gliomas. We focus initially on identifying some of the insights gained to date from targeting the EGFR/PI3K/Akt/mTOR signaling pathway in patients and on how this has led toward a reconceptualization of some of the challenges and directions for targeted treatment. We describe how advances from the world of genomics have the potential to transform our approaches toward targeted therapy, and describe how a deeper understanding of the complex nature of cancer, and its adeptness at rewiring molecular circuitry to evade targeted agents, has raised new challenges and identified new leads.

Targeting a unique EGFR epitope with monoclonal antibody 806 activates NF-kappaB and initiates tumour vascular normalization

Monoclonal antibodies (mAbs) and tyrosine kinase inhibitors targeting the epidermal growth factor receptor (EGFR), which is often pathogenetically overexpressed or mutated in epithelial malignancies and glioma, have been modestly successful, with some approved for human use. MAb 806 was raised against de2–7EGFR (or EGFRvIII), a constitutively active mutation expressed in gliomas, but also recognizes a subset (<10%) of wild-type (wt) EGFR when it is activated by autocrine loop, overexpression or mutation. It does not bind inactive EGFR in normal tissues like liver. Glioma xenografts expressing the de2–7EGFR treated with mAb 806 show reduced receptor autophosphorylation, increased p27^KIP1 and reduced cell proliferation. Xenografts expressing the wtEGFR activated by overexpression or autocrine ligand are also inhibited by mAb 806, but the mechanism of inhibition has been difficult to elucidate, especially because mAb 806 does not prevent wtEGFR phosphorylation or downstream signalling in vitro. Thus, we examined the effects of mAb 806 on A431 xenograft angiogenesis. MAb 806 increases vascular endothelial growth factor (VEGF) and interleukin-8 production by activating NF-κB and normalizes tumour vasculature. Pharmacological inhibition of NF-κB completely abrogated mAb 806 activity, demonstrating that NF-κB activation is necessary for its anti-tumour function in xenografts. Given the increase in VEGF, we combined mAb 806 with bevacizumab in vivo, resulting in additive activity.

The EGFRvIII variant in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common brain tumour and has the worst prognosis. Epidermal growth factor receptor (EGFR) gene amplification, mutation and re-arrangement (all of which enhance tumour growth, survival, progression and resistance to therapy) are frequently observed in primary GBM. The most common EGFR variant in GBM, the EGFRvIII, is characterised by a deletion of 267 amino acids in the extracellular domain, leading to a receptor which is unable to bind ligand yet is constitutively active. Together with its impaired internalisation and degradation, the EGFRvIII enhances the tumourigenic potential of GBM by activating and sustaining mitogenic, anti-apoptotic and pro-invasive signalling pathways. This EGFRvIII-mediated enhanced tumourigenicity combined with the lack of EGFRvIII expression in normal tissue makes it an ideal candidate for targeted therapy. This review summarizes the current knowledge about the role of EGFRvIII in GBM and discusses therapeutic agents targeting EGFRvIII that are being evaluated as treatments for GBM.

Mechanisms of tumor resistance to EGFR-targeted therapies

BACKGROUND

Much effort has been devoted to development of cancer therapies targeting EGFR, based on its role in regulating cell growth. Small-molecule and antibody EGFR inhibitors have clinical roles based on their efficacy in a subset of cancers, generally as components of combination therapies. Many cancers are either initially resistant to EGFR inhibitors or become resistant during treatment, limiting the efficacy of these reagents.

OBJECTIVE/METHODS

To review cellular resistance mechanisms to EGFR-targeted therapies.

RESULTS/CONCLUSIONS

The best validated of these mechanisms include activation of classic ATP-binding casette (ABC) multidrug transporters; activation or mutation of EGFR; and overexpression or activation of signaling proteins operating in relation to EGFR. We discuss current efforts and potential strategies to override these sources of resistance. We describe emerging systems-biology-based concepts of alternative resistance to EGFR-targeted therapies, and discuss their implications for use of EGFR-targeted and other targeted therapies.

Molecular target approaches in head and neck cancer: epidermal growth factor receptor and beyond

Approximately 50,000 new cases of head and neck squamous cell carcinoma (HNSCC) will be diagnosed in the United States in 2009. Although the gradual decline in smoking rates in the United States is a highly favorable trend, the future global HNSCC incidence will likely reflect the increased marketing and penetration of tobacco products across several of our most populous countries. Although modern surgery, radiation, and conventional chemotherapy strategies for HNSCC continue to provide gradual improvement in outcome, the first molecular targeting approach to show a survival advantage for HNSCC patients has recently emerged in the context of epidermal growth factor receptor biology. The scientific background and current challenges accompanying this recent advance are described in this article as are several additional promising molecular targets for HNSCC. There is cautious anticipation that the logical advancement of molecular targeting agents in conjunction with radiation may afford increased cure rates and diminished normal tissue toxicity profiles for HNSCC patients over the years to come.

Inhibition of glioblastoma growth in a highly invasive nude mouse model can be achieved by targeting epidermal growth factor receptor but not vascular endothelial growth factor receptor-2

PURPOSE

Major shortcomings of traditional mouse models based on xenografted human glioblastoma cell lines are that tumor cells do not invade and that genetic alterations, such as amplification of the epidermal growth factor receptor (EGFR) gene, are not maintained. Such models are thus of limited value for preclinical studies. We established a highly invasive model to evaluate the effect of antibodies against EGFR (cetuximab) and vascular endothelial growth factor receptor-2 (antibody DC101).

EXPERIMENTAL DESIGN

After short-term culture, glioblastoma spheroids were implanted into the brains of nude mice. Animals were treated either i.c. with cetuximab or i.p. with DC101. Tumor burden was determined histologically using image analysis of 36 different landmark points on serial brain sections.

RESULTS

Invasive xenografts were obtained from nine different glioblastomas. Three of seven cases treated with cetuximab responded with significant tumor growth inhibition, whereas four did not. All responsive tumors were derived from glioblastomas exhibiting EGFR amplification and expression of the truncated EGFRvIII variant, which were maintained in the xenografts. All nonresponsive tumors lacked EGFR amplification and EGFRvIII expression. The proportion of apoptotic cells was increased, whereas proliferation and invasion were decreased in responsive tumors. None of four xenograft cases treated with DC101 responded to treatment, and the diffusely invading tumors grew independent of angiogenesis.

CONCLUSIONS

Inhibition of glioblastoma growth and invasion can be achieved using i.c. delivery of an anti-EGFR antibody, but tumor response depends on the presence of amplified and/or mutated EGFR. Antiangiogenic treatment with DC101 is not effective against diffusely invading tumors.