Heregulins and the ErbB-2/3/4 receptors in gliomas

Integrative Analysis of Neuregulin Family Members-Related Tumor Microenvironment for Predicting the Prognosis in Gliomas

Gliomas, including brain lower grade glioma (LGG) and glioblastoma multiforme (GBM), are the most common primary brain tumors in the central nervous system. Neuregulin (NRG) family proteins belong to the epidermal growth factor (EGF) family of extracellular ligands and they play an essential role in both the central and peripheral nervous systems. However, roles of NRGs in gliomas, especially their effects on prognosis, still remain to be elucidated. In this study, we obtained raw counts of RNA-sequencing data and corresponding clinical information from 510 LGG and 153 GBM samples from The Cancer Genome Atlas (TCGA) database. We analyzed the association of NRG1-4 expression levels with tumor immune microenvironment in LGG and GBM. GSVA (Gene Set Variation Analysis) was performed to determine the prognostic difference of NRGs gene set between LGG and GBM. ROC (receiver operating characteristic) curve and the nomogram model were constructed to estimate the prognostic value of NRGs in LGG and GBM. The results demonstrated that NRG1-4 were differentially expressed in LGG and GBM in comparison to normal tissue. Immune score analysis revealed that NRG1-4 were significantly related to the tumor immune microenvironment and remarkably correlated with immune cell infiltration. The investigation of roles of m⁶A (N6-methyladenosine, m⁶A)-related genes in gliomas revealed that NRGs were prominently involved in m⁶A RNA modification. GSVA score showed that NRG family members are more associated with prognosis in LGG compared with GBM. Prognostic analysis showed that NRG3 and NRG1 can serve as potential independent biomarkers in LGG and GBM, respectively. Moreover, GDSC drug sensitivity analysis revealed that NRG1 was more correlated with drug response compared with other NRG subtypes. Based on these public databases, we preliminarily identified the relationship between NRG family members and tumor immune microenvironment, and the prognostic value of NRGs in gliomas. In conclusion, our study provides comprehensive roles of NRG family members in gliomas, supporting modulation of NRG signaling in the management of glioma.

Exploiting cancer's phenotypic guise against itself: targeting ectopically expressed peptide G-protein coupled receptors for lung cancer therapy

Lung cancer, claiming millions of lives annually, has the highest mortality rate worldwide. This advocates the development of novel cancer therapies that are highly toxic for cancer cells but negligibly toxic for healthy cells. One of the effective treatments is targeting overexpressed surface receptors of cancer cells with receptor-specific drugs. The receptors-in-focus in the current review are the G-protein coupled receptors (GPCRs), which are often overexpressed in various types of tumors. The peptide subfamily of GPCRs is the pivot of the current article owing to the high affinity and specificity to and of their cognate peptide ligands, and the proven efficacy of peptide-based therapeutics. The article summarizes various ectopically expressed peptide GPCRs in lung cancer, namely, Cholecystokinin-B/Gastrin receptor, the Bombesin receptor family, Bradykinin B1 and B2 receptors, Arginine vasopressin receptors 1a, 1b and 2, and the Somatostatin receptor type 2. The autocrine growth and pro-proliferative pathways they mediate, and the distinct tumor-inhibitory effects of somatostatin receptors are then discussed. The next section covers how these pathways may be influenced or 'corrected' through therapeutics (involving agonists and antagonists) targeting the overexpressed peptide GPCRs. The review proceeds on to Nano-scaled delivery platforms, which enclose chemotherapeutic agents and are decorated with peptide ligands on their external surface, as an effective means of targeting cancer cells. We conclude that targeting these overexpressed peptide GPCRs is potentially evolving as a highly promising form of lung cancer therapy.

The Under-Appreciated Promiscuity of the Epidermal Growth Factor Receptor Family

Each member of the epidermal growth factor receptor (EGFR) family plays a key role in normal development, homeostasis, and a variety of pathophysiological conditions, most notably in cancer. According to the prevailing dogma, these four receptor tyrosine kinases (RTKs; EGFR, ERBB2, ERBB3, and ERBB4) function exclusively through the formation of homodimers and heterodimers within the EGFR family. These combinatorial receptor interactions are known to generate increased interactome diversity and therefore influence signaling output, subcellular localization and function of the heterodimer. This molecular plasticity is also thought to play a role in the development of resistance toward targeted cancer therapies aimed at these known oncogenes. Interestingly, many studies now challenge this dogma and suggest that the potential for EGFR family receptors to interact with more distantly related RTKs is much greater than currently appreciated. Here we discuss how the promiscuity of these oncogenic receptors may lead to the formation of many unexpected receptor pairings and the significant implications for the efficiency of many targeted cancer therapies.

A structural perspective on the regulation of the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that plays a critical role in the pathogenesis of many cancers. The structure of intact forms of this receptor has yet to be determined, but intense investigations of fragments of the receptor have provided a detailed view of its activation mechanism, which we review here. Ligand binding converts the receptor to a dimeric form, in which contacts are restricted to the receptor itself, allowing heterodimerization of the four EGFR family members without direct ligand involvement. Activation of the receptor depends on the formation of an asymmetric dimer of kinase domains, in which one kinase domain allosterically activates the other. Coupling between the extracellular and intracellular domains may involve a switch between alternative crossings of the transmembrane helices, which form dimeric structures. We also discuss how receptor regulation is compromised by oncogenic mutations and the structural basis for negative cooperativity in ligand binding.

RNAi-mediated inhibition of presenilin 2 inhibits glioma cell growth and invasion and is involved in the regulation of Nrg1/ErbB signaling

Gliomas are the leading cause of death among adults with primary brain malignancies. Treatment for malignant gliomas remains limited, and targeted therapies have been incompletely explored. In this study, we found that the protein expression of presenilin 2 (PS2) was significantly increased in glioma tissues, at least partially because of promoter demethylation. We further evaluated the biological functions of PS2 in U251 glioma cell proliferation, migration, invasion, and tumor growth in vivo by specific inhibition of PS2 using short hairpin RNA (shRNA). We found that PS2 depletion inhibited glioma cell growth as the result of inhibited proliferation and induced apoptosis. PS2 depletion also decreased the invasive capability of glioma cells and anchorage-independent colony formation in soft agar. Moreover, suppression of PS2 expression significantly impaired the growth of glioma xenografts in nude mice. Finally, the decrease in glioma cell growth caused by PS2 depletion seems to involve Nrg1/ErbB signaling. In summary, our data highlight the use of RNA interference (RNAi) as a tool to better understand the molecular basis of PS2 in glioma progression and to uncover new targets for the treatment of glioma.

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.

c-erbB-2 protein expression in astrocytic tumors of the brain

Background

Astrocytic tumors are the primary brain tumors, which often progress to glioblastoma, a highly malignant neoplasm of the central nervous system. There is much new data regarding to the formation and progression of these tumors; however, glioblastoma remains one of the most fatal neoplasms in humans.

The aim of the study was to evaluate the role of c-erbB-2 protein expression in various groups of astrocytic tumors.

Material/Methods

65 cases of astrocytic tumors were divided into 3 groups: diffuse astrocytoma (group I; n=17 cases), anaplastic astrocytoma (group II; n=23 cases) and glioblastoma (group III; n=25 cases). C-erbB-2 protein expression was estimated semiquantitatively on immunohistochemically stained tissue sections using antibodies against c-erbB-2 protein. Statistical analysis was performed in all examined groups.

Results

The c-erbB-2 protein expression was observed in 15 out of 17 cases (88.3%) in group I, 22 out of 25 cases (88%) cases in group II, and in 19 out of 23 cases (82.6%) in group III. There were no statistically significant differences between the examined groups. The strongest c-erbB-2 immunoexpression was observed in low grade astrocytomas (diffuse astrocytomas G2); in the glioblastoma group the c-erbB-2 protein expression was weak and 17.4% of cases were negative.

Conclusions

C-erbB-2 protooncogene alteration is an early phenomenon in glial tumor development and progression.

Overexpression of c-erbB2 is a negative prognostic factor in anaplastic astrocytomas

The epidermal growth factor receptor (EGFR) family, consisting of four tyrosine kinase receptors, c-erbB1-4, seems to be influential in gliomagenesis. The aim of this study was to investigate EGFR gene amplification and expression of c-erbB1-4 receptor proteins in human anaplastic astrocytomas. Formalin-fixed and paraffin-embedded sections from 31 cases were investigated by standard immunohistochemical procedures for expression of c-erbB1-4 receptor proteins using commercial antibodies. EGFR gene amplification was studied by fluorescence in situ hybridization using paraffin-embedded tissues. Two monoclonal antibodies, NCL-EGFR-384 and NCL-EGFR, were used for EGFR detection and they displayed positive immunoreactivity in 97% and 71%, respectively. For c-erbB2 detection three monoclonal antibodies, CB11, 3B5, and 5A2, were applied and they displayed positive immunoreactivity in 45%, 100%, and 52%, respectively. Positive immunostaining for c-erbB3 and c-erbB4 was encountered in 97% and 74%, respectively. The EGFR gene was amplified in 9 out of 31 tumors (29%). After adjusting for age, Karnofsky performance status, and extent of surgical resection, Cox multiple regression analysis with overall survival as the dependent variable revealed that c-erbB2 overexpression detected by the monoclonal antibody clone CB11 was a statistically significant poor prognostic factor (P = 0.004). This study shows the convenience and feasibility of immunohistochemistry when determining the expression of receptor proteins in tissue sections of human astrocytomas. The synchronous overexpression of c-erbB1-4 proteins in anaplastic astrocytomas supports their role in the pathogenesis of these tumors. Further, c-erbB2 overexpression seems to predict aggressive behaviour.

The ERBB3 receptor in cancer and cancer gene therapy

ERBB3, a member of the epidermal growth factor receptor (EGFR) family, is unique in that its tyrosine kinase domain is functionally defective. It is activated by neuregulins, by other ERBB and nonERBB receptors as well as by other kinases, and by novel mechanisms. Downstream it interacts prominently with the phosphoinositol 3-kinase/AKT survival/mitogenic pathway, but also with GRB, SHC, SRC, ABL, rasGAP, SYK and the transcription regulator EBP1. There are likely important but poorly understood roles for nuclear localization and for secreted isoforms. Studies of ERBB3 expression in primary cancers and of its mechanistic contributions in cultured cells have implicated it, with varying degrees of certainty, with causation or sustenance of cancers of the breast, ovary, prostate, certain brain cells, retina, melanocytes, colon, pancreas, stomach, oral cavity and lung. Recent results link high ERBB3 activity with escape from therapy targeting other ERBBs in lung and breast cancers. Thus a wide and centrally important role for ERBB3 in cancer is becoming increasingly apparent. Several approaches for targeting ERBB3 in cancers have been tested or proposed. Small inhibitory RNA (siRNA) to ERBB3 or AKT is showing promise as a therapeutic approach to treatment of lung adenocarcinoma.

Low HER2-expressing glioblastomas are more often secondary to anaplastic transformation of low-grade glioma

BACKGROUND

Anti-Human Epithelial Receptor Type 2 (HER2) antibodies have the ability to induce in vitro apoptosis of glioblastoma (GBM) cells. This study was designed to evaluate the variability of HER2 expression in GBM and its role as a possible prognosis factor.

METHODS

Data of 57 patients with GBM and 16 patients with grade III gliomas were retrospectively analyzed. The expression of HER2 was determined by immunohistochemistry and intensity was noted from 0+ to 3+. We compared the HER2 expression in de novo GBM and in GBM resulting from anaplastic transformation of low-grade glioma ("secondary GBM"). Statistical analysis was performed using univariate analysis and the Kaplan-Meier method.

FINDINGS

All GBM expressing highly HER2 (2+ and 3+) were de novo GBM. All secondary GBM expressed HER2 with low intensity (0+ and 1+). Survival time was significantly longer when HER2 expression was low (Log Rank test P = 0.04). The patterns of HER2 expression were similar between grade III gliomas and secondary GBM.

CONCLUSIONS

To our best knowledge, our study showed for the first time a significant association between HER2 expression and the type of GBM, with subsequent influence on survival rate. GBM with low-HER2 expression are more likely to be secondary GBM, carrying a better prognosis than de novo GBM.

Localization of neuregulin-1α (heregulin-α) and one of its receptors, ErbB-4 tyrosine kinase, in developing and adult human brain

Using immunohistochemistry, Western blot analysis, and RT-polymerase chain reaction, we studied the distribution of neuregulin-1 splice variant alpha (NRG-1alpha) and one of its putative receptors, ErbB-4 tyrosine kinase, in human brain. In the pre- and perinatal human brain immunoreactivity was confined to numerous neurons, with the highest cell density found in cortical gray matter, hypothalamus and cerebellum. In the adult brain, single cortical gray and white matter neurons showed NRG-1alpha immunoreactivity. Occasionally, immunoreactive oligodendrocytes were observed. NRG-1alpha-expressing neurons were also found in the hypothalamus, hippocampus, basal ganglia and brain stem. Application of two antibodies recognizing alpha and beta isoforms revealed a different distribution pattern in that many cortical and hippocampal pyramidal neurons were labeled. ErbB-4 immunoreactivity was expressed in both neurons and oligodendrocytes. Our data show that NRG-1alpha expression is lower in the adult human brain than in the developing brain, and, therefore, support a role for NRG-1alpha in brain development.

Increasing of HER2 Membranar Density in Human Glioblastoma U251MG Cell Line Established in a New Nude Mice Model

Glioblastoma multiform (GBM) remains the most devastating primary tumour in neuro-oncology. Human Epithelial Receptor Type 2 (HER2) is a transmembrane tyrosine/kinase receptor that is important for cancer growth. HER2 is not expressed in adult glial cells, but its expression increases with the degree of astrocytomas anaplasia. We have recently demonstrated the ability of anti-HER2 antibodies to induce in vitro apoptosis GBM cell lines; this ability is correlated to HER2 density. A decreasing of tyrosine/kinase receptors density during in vitro culture was reported. No information exists about the variation of HER2 expression after in vivo implantation. For that, the two cell lines in vitro tested (U251MG, A172) were in vivo implanted. We established a U251MG in vivo model in balb/c nude mice showing an important increasing of HER2 density. The HER2 density is correlated to anti-HER2 antibody efficiency so this model will be useful for the evaluation of in vivo anti-HER2 antibody treatment.

Neuregulin-1 enhances survival of human astrocytic glioma cells

Malignant astrocytic gliomas, referred to as astrocytomas, represent the most commonly diagnosed adult primary brain tumor. These tumors are characterized by unrelenting growth that is often resistant to chemotherapy and radiation therapy. Tumor expansion into the healthy surrounding brain tissue produces severe and often fatal consequences. In this study, we examine the potential for the neuregulin-1/erbB receptor signaling cascade to contribute to this process by modulating glioma cell growth. Using antibodies specific for the erbB receptors, we demonstrate the expression patterns for the erbB2, erbB3, and erbB4 receptors in human glioma biopsy samples. We then verify receptor expression in a panel of human glioma cell lines. Next, we investigate the status of the erbB2 and erbB3 receptors in the human glioma cell lines and find that they are constitutively tyrosine-phosphorylated and heterodimerized. Subsequently, we demonstrate that theses same cell lines express membrane bound and released forms of neuregulins, the erbB receptor ligands, suggesting a possible autocrine or paracrine signaling network. Furthermore, we show that exogenous activation of erbB2 and erbB3 receptors in U251 glioma cells by recombinant Nrg-1beta results in enhanced glioma cell growth under conditions of serum-deprivation. This enhancement is due to an increase in cell survival rather than an increase in cell proliferation and is dependent on the activation of erbB2 and phosphatidylinositol-3 kinase (PI3K). Moreover, Nrg-1beta activates an inhibitor of apoptosis, Akt, implying a possible role for this kinase in mediating Nrg-1beta effects in gliomas. This data suggests that glioma cells may use autocrine or paracrine neuregulin-1/erbB receptor signaling to enhance cell survival under conditions where growth would otherwise be limited.

Roles for neuregulins in human cancer

The human epidermal growth factor (EGF) receptor (HER) family of receptor tyrosine kinases has frequently been implicated in cancer. Apart from overexpression or mutation of these receptors, also the aberrant autocrine or paracrine activation of HERs by EGF-like ligands may be important in cancer progression. Neuregulins constitute a family of EGF-like ligands that bind to HER3 or HER4, preferably forming heterodimers with the orphan receptor HER2. Mesenchymal neuregulin typically serves as a pro-survival and pro-differentiation signal for adjacent epithelia. Disruption of the balance between proliferation and differentiation, because of autocrine production by the epithelial cells, increased sensitivity to paracrine signals or disruption of the spatial organization, may lead to constitutive receptor activation, in the absence of receptor overexpression. Consequently, the analysis of ligand expression and/or activated receptors in tumor samples may broaden the group of patients that can benefit from targeted therapies.

Recombinant humanised anti-HER2/neu antibody (Herceptin) induces cellular death of glioblastomas

Glioblastoma multiforme (GBM) remains the most devastating primary tumour in neuro-oncology. Targeting of the human epithelial receptor type 2 (HER2)-neu receptor by specific antibodies is a recent well-established therapy for breast tumours. Human epithelial receptor type 2/neu is a transmembrane tyrosine/kinase receptor that appears to be important for the regulation of cancer growth. Human epithelial receptor type 2/neu is not expressed in the adult central nervous system, but its expression increases with the degree of astrocytoma anaplasia. The specificity of HER2/neu for tumoral astrocytomas leads us to study in vitro treatment of GBM with anti-HER2/neu antibody. We used human GBM cell lines expressing HER2/neu (A172 express HER2/neu more than U251MG) or not (U87MG) and monoclonal humanised antibody against HER2/neu (Herceptin®). Human epithelial receptor type 2/neu expression was measured by immunohistochemistry and flow cytometry. Direct antibody effect, complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity were evaluated by different cytometric assays. We have shown, for the first time, the ability of anti-HER2/neu antibodies to induce apoptosis and cellular-dependent cytotoxicity of HER2/neu-expressing GBM cell lines. The results decreased from A172 to U251 and were negative for U87MG, in accordance with the decreasing density of HER2/neu receptors.

Role for calcium-activated potassium channels (BK) in growth control of human malignant glioma cells

Voltage-dependent large-conductance Ca(2+)-activated K(+) channels, often referred to as BK channels, are a unique class of ion channels coupling intracellular chemical signaling to electrical signaling. BK channel expression has been shown to be up-regulated in human glioma biopsies, and expression levels correlate positively with the malignancy grade of the tumor. Glioma BK channels (gBK) are a splice variant of the hslo gene, are characterized by enhanced sensitivity to [Ca(2+)](i), and are the target of modulation by growth factors. By using the selective pharmacological BK channel inhibitor iberiotoxin, we examined the potential role of these channels in tumor growth. Cell survival assays examined the ability of glioma cells to grow in nominally serum-free medium. Under such conditions, BK channel inhibition by iberiotoxin caused a dose- and time-dependent decrease in cell number discernible as early as 72 hr after exposure and maximal growth inhibition after 4-5 days. FACS analysis shows that IbTX treatment arrests glioma cells in S phase of the cell cycle, whereupon cells undergo cell death. Interestingly, IbTX effects were nullified when cells were maintained in 7% fetal calf serum. Electrophysiological analysis, in conjunction with biotinylation studies, demonstrates that serum starvation caused a significant translocation of BK channel protein to the plasma membrane, corresponding to a two- to threefold increase in whole-cell conductance, but without a change in total gBK protein. Hence, expression of functional gBK channels appears to be regulated in a growth-factor-dependent manner, with enhanced surface expression promoting tumor cell growth under conditions of growth factor deprivation as might occur under in vivo conditions.

Neuregulin-1 enhances motility and migration of human astrocytic glioma cells

Gliomas are the most frequently diagnosed adult primary brain malignancy. These tumors have a tendency to invade diffusely into the surrounding healthy brain tissue, thereby precluding their successful surgical removal. In this report, we examine the potential for the neuregulin-1/erbB receptor signaling network to contribute to this process by modulating glioma cell motility. Neuregulin-1 is expressed throughout the immature and adult central nervous system and has been demonstrated to influence the migration of a variety of cell types in the developing brain. In addition, erbB2, an integral member of the heterodimeric neuregulin-1 receptor, has been shown to be overexpressed in human glioma biopsies. Using antibodies specific for erbB2 and erbB3, we show that these receptors localize preferentially in regions of the plasma membrane which are involved in facilitating cellular movement. Here, erbB2 colocalizes and coimmunoprecipitates with members of the focal complex including beta1-integrin and focal adhesion kinase. Further, erbB receptor activation by neuregulin-1 enhances cell motility in two-dimensional scratch motility assays and stimulates cell invasion in three-dimensional Transwell migration assays. These effects of neuregulin-1 appear to involve the activation of focal adhesion kinase, which occurs downstream from erbB2 receptor stimulation. Taken together these data suggest that neuregulin-1 plays an important modulatory role in glioma cell invasion.

Tumour-endothelium interactions in co-culture: coordinated changes of gene expression profiles and phenotypic properties of endothelial cells

Tumour angiogenesis is a complex process based upon a sequence of interactions between tumour cells and endothelial cells. To model tumour/endothelial-cell interactions, we co-cultured U87 human glioma cells with human umbilical vein endothelial cells (HUVECs). U87 cells induced an 'activated' phenotype in HUVECs, including an increase in proliferation, migration and net-like formation. Activation was observed in co-cultures where cells were in direct contact and physically separated, suggesting an important role for soluble factor(s) in the phenotypic and genotypic changes observed. Expressional profiling of tumour-activated endothelial cells was evaluated using cDNA arrays and confirmed by quantitative PCR. Matching pairs of receptors/ligands were found to be coordinately expressed, including TGFbetaRII with TGFbeta3, FGFRII and cysteine-rich fibroblast growth factor receptor (CRF-1) with FGF7 and FGF12, CCR1, CCR3, CCR5 with RANTES and calcitronin receptor-like gene (CALCRL) with adrenomedullin. Consistent with cDNA array data, immunohistochemical staining of expressed proteins revealed the upregulation of Tie-2 receptor in vitro and in vivo. Our data suggest that tumour-induced activation of quiescent endothelial cells involves the expression of angiogenesis-related receptors and the induction of autocrine growth loops. We suggest that tumour cells release growth factors that induce endothelial cells to express specific ligands and their cognate receptors coordinately.

Ligand liposomes and boron neutron capture therapy

Boron neutron capture therapy (BNCT) has been used both experimentally and clinically for the treatment of gliomas and melanomas, with varying results. However, the therapeutic effects on micro-invasive tumor cells are not clear. The two drugs that have been used clinically, p-boronophenylalanine, (BPA), and the sulfhydryl borane, (BSH), seem to be taken up preferentially in solid tumor areas but it is uncertain whether enough boron is taken up by micro-invasive tumor cells. To increase the selective uptake of boron by such cells, would be to exploit tumor transformation related cellular changes such as over-expression of growth factor receptors. However, the number of receptors varies from small to large and the uptake of large amounts of boron for each receptor interaction is necessary in order to deliver sufficient amounts of boron. Therefore, each targeting moiety must deliver large number of boron atoms. One possible way to meet these requirements would be to use receptor-targeting ligand liposomes, containing large number of boron atoms. This will be the subject of this review and studies of boron containing liposomes, with or without ligand, will be discussed. Two recent examples from the literature are ligand liposomes targeting either folate or epidermal growth factor (EGF) receptors on tumor cells. Other potential receptors on gliomas include PDGFR and EGFRvIII. Besides the appropriate choice of target receptor, it is also important to consider delivery of the ligand liposomes, their pharmacodynamics and pharmacokinetics and cellular processing, subjects that also will be discussed in this review.

Epidermal growth factor receptor as a genetic therapy target for carcinoma cell radiosensitization

BACKGROUND

Exposure of human cancer cells to ionizing radiation activates the epidermal growth factor receptor (EGFR), which, in turn, mediates a cytoprotective response that reduces the cells' sensitivity to ionizing radiation. Overexpression of a dominant-negative EGFR mutant, EGFR-CD533, disrupts the cytoprotective response by preventing radiation-induced activation of the receptor and its downstream effectors. To investigate whether gene therapy with EGFR-CD533 has the potential to increase tumor cell radiosensitivity, we introduced an adenoviral vector containing EGFR-CD533 into xenograft tumors in nude mice and evaluated the tumor response to ionizing radiation.

METHODS

Xenograft tumors established from the human mammary carcinoma cell line MDA-MB-231 were transduced via infusion with the adenoviral vector Ad-EGFR-CD533 or a control vector containing the beta-galactosidase gene, Ad-LacZ. The transduced tumors were then exposed to radiation in the therapeutic dose range, and radiation-induced EGFR activation was assessed by examining the tyrosine phosphorylation of immunoprecipitated EGFR. Radiosensitization was determined in vitro by colony-formation assays. All statistical tests were two-sided.

RESULTS

The transduction efficiency of MDA-MB-231 tumors by Ad-LacZ was 44%. Expression of EGFR-CD533 in tumors reduced radiation-induced EGFR activation by 2.94-fold (95% confidence interval [CI] = 2.23 to 4.14). The radiosensitivity of Ad-EGFR-CD533-transduced tumors was statistically significantly higher (46%; P<.001) than that of Ad-LacZ-transduced tumors, yielding a dose-enhancement ratio of 1.85 (95% CI = 1.54 to 2.51).

CONCLUSIONS

Transduction of MDA-MB-231 xenograft tumors with Ad-EGFR-CD533 conferred a dominant-negative EGFR phenotype and induced tumor radiosensitization. Therefore, disruption of EGFR function through overexpression of EGFR-CD533 may hold promise as a gene therapeutic approach to enhance the sensitivity of tumor cells to ionizing radiation.

Implications for Src kinases in hematopoiesis: signal transduction therapeutics

Signal transduction therapeutics is now the dominant theme of drug discovery, and its most immediate impact will be in cancer therapeutics. Blood cell proliferation, differentiation, and activation are controlled by cytokines, whose receptors contain tyrosine kinase catalytic domains or recruit cytosolic tyrosine kinases. Among the most important cytosolic protein tyrosine kinases are the Src and Jak families. Receptor or cytosolic protein tyrosine kinases activate a similar set of intracellular signaling molecules. In blood cells, excessive tyrosine kinase activity is associated with either cancer or autoreactive diseases. Therefore, tyrosine kinases and their substrates serve as excellent candidates for drug intervention. Herceptin has been approved for use in breast cancer. Other agents, such as SU101 and CGP 57418B, are well into phase I-III trials. Newer, more selective tyrosine kinase inhibitors are being evaluated for future use in the treatment of hematologic and solid tumors as well as a wide range of inflammatory or autoimmune diseases.

Retroviral vectors pseudotyped with lymphocytic choriomeningitis virus

Pseudotyping can improve retroviral vector stability and transduction efficiency. Here, we describe a novel pseudotype of murine leukemia virus packaged with lymphocytic choriomeningitis virus (LCMV). This pseudotype was stable during ultracentrifugation and infected several cell lines from different species. Moreover, LCMV glycoproteins were not cell toxic.