EGFR overexpression and radiation response in glioblastoma multiforme

Molecular neuro-oncology and development of targeted therapeutic strategies for brain tumors. Part 1: Growth factor and Ras signaling pathways

Brain tumors are a diverse group of malignancies that remain refractory to conventional treatment approaches, including radiotherapy and cytotoxic chemotherapy. Molecular neuro-oncology has now begun to clarify the transformed phenotype of brain tumors and identify oncogenic pathways that may be amenable to targeted therapy. Growth factor signaling pathways are often upregulated in brain tumors and may contribute to oncogenesis through autocrine and paracrine mechanisms. Excessive growth factor receptor stimulation can also lead to overactivity of the Ras signaling pathway, which is frequently aberrant in brain tumors. Receptor tyrosine kinase inhibitors, antireceptor monoclonal antibodies and antisense oligonucleotides are targeted approaches under investigation as methods to regulate aberrant growth factor signaling pathways in brain tumors. Several receptor tyrosine kinase inhibitors, including imatinib mesylate (Gleevec), gefitinib (Iressa) and erlotinib (Tarceva), have entered clinical trials for high-grade glioma patients. Farnesyl transferase inhibitors, such as tipifarnib (Zarnestra), which impair processing of proRas and inhibit the Ras signaling pathway, have also entered clinical trials for patients with malignant gliomas. Further development of targeted therapies and evaluation of these new agents in clinical trials will be needed to improve survival and quality of life of patients with brain tumors.

Time and dose-dependent radiosensitization of the glioblastoma multiforme U251 cells by the EGF receptor tyrosine kinase inhibitor ZD1839 (‘Iressa’)

Hyperactive epidermal growth factor receptor (EGFR) signaling, which promotes unregulated cell growth and inhibits apoptosis, is believed to contribute to clinical radiation resistance of glioblastoma multiforme (GBM). Blockage of the EGFR signalling pathways may offer an attractive therapeutic target to increase the cytotoxic effects of radiotherapy. We report the effects of ZD1839 ('Iressa'), a selective EGFR tyrosine kinase inhibitor on the radiation sensitivity of the U251 GBM cell line, which expresses high levels of EGFR. In radiation survival experiments, 5 microM of ZD1839 had a significant radiosensitizing effect and increased cell death was observed at doses of 5Gy in the presence of ZD1839. Dose and schedule of drug administration in combination with radiation appeared to be a crucial element to obtain radiosensitization of the cells. These studies suggest novel therapeutic strategies in the treatment of GBM.

Combined effect of gefitinib ('Iressa', ZD1839) and targeted radiotherapy with 211At-EGF

The EGFR-TKI (epidermal growth factor receptor tyrosine kinase inhibitor) gefitinib ['Iressa' (trademark of the AstraZeneca group of companies), ZD1839] increases the cellular uptake of radiolabelled epidermal growth factor (EGF). We investigated gefitinib treatment combined with astatine-211 EGF targeting in vitro using two cell lines expressing high levels of EGFR: A431 (sensitive to gefitinib) and U343MGaCl2:1 (resistant to gefitinib). In both cell lines, the uptake of 211At-EGF was markedly increased by concomitant treatment with gefitinib. Survival was investigated using both a clonogenic survival assay and a cell growth assay. Combined gefitinib and 211At-EGF treatment reduced the survival of U343 cells 3.5-fold compared with 211At-EGF alone. In A431 cells, 211At-EGF treatment resulted in very low survival, but combined treatment with gefitinib increased the survival by about 20-fold. These results indicate that combined treatment with gefitinib might increase the effect of ligand-mediated radionuclide therapy in gefitinib-resistant tumours and decrease the effect of such therapy in gefitinib-sensitive tumours.

Molecular markers in clinical radiation oncology

Radiation therapy plays a critical role in the management of a majority of patients diagnosed with cancer. Identification of factors that help predict which patients are at risk for relapse within the irradiated field remains an active area of investigation. Although conventional clinical and pathologic factors have been helpful in identifying risk and guiding clinical decision-making for both local and systemic management, there is clearly a need to identify additional prognostic markers, which can aid in refining our treatment strategies and improving outcomes. A substantial amount of research efforts have been devoted to identifying molecular markers for prognostic and therapeutic strategies. The recent emergence of a powerful armamentarium of molecular tools has resulted in rapid expansion of our fund of knowledge and understanding of the molecular biology underlying tumor behavior and response. While a majority of these efforts have been focused on risk factors for metastatic disease and survival, there is a rapidly growing body of literature focused on molecular factors associated with radiation resistance and locoregional failure. In this review, we summarize recent advances and the available literature evaluating molecular markers as they relate to radiation sensitivity of solid tumors. Literature regarding the potential application of expression of genes related to apoptosis, angiogenesis, cell cycle, DNA repair and growth factors will be reviewed. Some of the basic biology and laboratory evidence demonstrating how the marker relates to radiation response and available correlative clinical studies employing these markers as prognostic tools are presented. The majority of molecular markers that have potential clinical significance with respect to radiation sensitivity and local control will be highlighted.

[111In]Bz-DTPA-hEGF: Preparation andIn VitroCharacterization of a Potential Anti-Glioblastoma Targeting Agent

The overexpression of epidermal growth factor receptors, EGFR, in glioblastomas is well documented. Hence, the EGFR can be used as target structure for a specific targeting of glioblastomas. Both radiolabeled anti-EGFR antibodies and the natural ligand EGF are candidate agents for targeting. However, EGF, which has a rather low molecular weight (6 kDa), might have better tissue penetration properties through both normal tissue and tumors in comparison with anti-EGF antibodies and their fragments. The aim of this study was to prepare and evaluate in vitro an EGF-based antiglioma conjugate with residualizing label. Human recombinant EGF (hEGF) was coupled to isothiocyanate-benzyl-DTPA. The conjugate was purified from unreacted chelator using solid-phase extraction and labeled with (111)In. The labeling yield was 87% +/- 7%. The label was reasonably stable; the transchelation of (111)In to serum proteins was about 5% after incubation at 37 degrees C during 24 hours. The obtained [(111)In]benzyl-DTPA-hEGF conjugate was characterized in vitro using the EGFR expressing glioma cell line U343MGaCl2:6. The binding affinity, internalization, and retention of the conjugate were studied. The conjugate had receptor specific binding and the radioactivity was quickly internalized. The intracellular retention of radioactivity after interrupted incubation with conjugate was 71% +/- 1% and 59% +/- 1.5% at 24 and 45 hours, respectively. The dissociation constant was estimated to 2.0 nM. The results indicate that [(111)In]benzyl-DTPA-hEGF is a potential candidate for targeting glioblastoma cells, possibly using locoregional injection.

Recent advances in the molecular genetics of primary gliomas

Primary brain tumors, particularly glioblastomas, remain a challenge for oncology. Uncontrolled cellular proliferation, lack of apoptosis, invasion, and angiogenesis are among the biologic processes that render these tumors both aggressive and difficult to treat. An understanding of the genetics and molecular events regulating these aggressive tumors is beginning to emerge, partly because of recent knowledge in genomics, gene expression analysis, and mouse tumor models. As a result, it is now generally accepted that brain tumors, particularly those arising from cells of glial lineage, result from stepwise accumulation of deleterious genetic alterations. Several genetic abnormalities have been described, and current research is aimed at elucidating their causal association with brain tumor formation and progression. The purpose of this review is to summarize some of the most important recently published findings on the molecular genetics of primary gliomas.

Treatment of cultured glioma cells with the EGFR-TKI gefitinib ("Iressa", ZD1839) increases the uptake of astatinated EGF despite the absence of gefitinib-mediated growth inhibition

The EGFR-TKI (epidermal growth factor receptor tyrosine kinase inhibitor) gefitinib ("Iressa", ZD1839), a reversible growth inhibitor of EGFR-expressing tumour cells, has been shown to enhance the antitumour effect of ionising radiation, and also to increase the uptake of radioiodinated EGF. Thus, combination of gefitinib treatment and radionuclide targeting is an interesting option for therapy of brain tumours that are difficult to treat with conventional methods. The aim of this study was to evaluate how pre-treatment with gefitinib affects binding of astatinated EGF ((211)At-EGF) to cultured glioma U343 cells, which express high levels of EGFR. The growth of U343 cells in the presence of gefitinib was investigated, and it was found that gefitinib does not significantly inhibit the growth of these cells. Nevertheless, the uptake of (211)At-EGF in U343 cells was markedly increased (up to 3.5 times) in cells pre-treated with gefitinib (1 microM). This indicates that a combination of gefitinib treatment and radionuclide targeting to EGFR might be a useful therapeutic modality, even for patients who do not respond to treatment with gefitinib alone.

Identification of molecular subtypes of glioblastoma by gene expression profiling

Epidermal growth factor receptor (EGFR) overexpression occurs in nearly 50% of cases of glioblastoma (GBM), but its clinical and biological implications are not well understood. We have used Affymetrix high-density oligonucleotide arrays to demonstrate that EGFR-overexpressing GBMs (EGFR+) have a distinct global gene transcriptional profile. We show that the expression of 90 genes can distinguish EGFR+ from EGFR nonexpressing (EGFR-) GBMs, including a number of genes known to act as growth/survival factors for GBMs. We have also uncovered two additional novel molecular subtypes of GBMs, one of which is characterized by coordinate upregulation of contiguous genes on chromosome 12q13-15 and expression of both astrocytic and oligodendroglial genes. These results define distinct molecular subtypes of GBMs that may be important in disease stratification, and in the discovery and assessment of GBM treatment strategies.

Genetic alterations of human brain tumors as molecular prognostic factors

Despite a number of basic and clinical studies, it is still very difficult to improve the prognosis of patients with high-grade astrocytoma. However, the recent success of procarbazine, N-(2-chloroethyl)-N'-cyclohexyl-N-nitrosourea and vincristine (PCV) chemotherapy for oligodendrogliomas that have lost chromosomes 1p and 19q has encouraged the authors to evaluate the biological behavior of brain tumors by means of genetic analysis. Both the disorders of the p53/MDM2/p14(ARF) and the p16(INK4a)/RB signaling pathways have been found to play an essential role in tumorigenesis of various brain tumors. Herein, the authors summarize the genetic alterations of brain tumors by mainly focusing on two pathways that appear to affect significantly the patient prognosis.

EGFR blockade with ZD1839 ("Iressa") potentiates the antitumor effects of single and multiple fractions of ionizing radiation in human A431 squamous cell carcinoma. Epidermal growth factor receptor

PURPOSE

Signaling pathways initiated by the epidermal growth factor receptor (EGFR) play important roles in the response to ionizing radiation. In this study the consequences of inhibiting the EGFR on the response of A431 cells (human vulvar squamous cell carcinoma cells that overexpress EGFR) to radiation, were investigated in vitro and in vivo, using the selective EGFR-tyrosine kinase inhibitor, ZD1839 ("Iressa").

METHODS AND MATERIALS

The effect of ZD1839 on proliferation, apoptosis, and clonogenic survival after radiation was determined in vitro. For in vivo studies, athymic nude mice with established subcutaneous A431 xenografts (approximately 100 mm(3)) were treated with either a single 10 Gy fraction or 4 daily 2.5 Gy fractions of radiation with or without ZD1839 (75 mg/kg/day intraperitoneally for 10 days) to determine effects on tumor growth delay.

RESULTS

Treatment of A431 cells with ZD1839 in vitro reduced proliferation, increased apoptosis, and reduced clonogenic survival after radiation. Strikingly greater than additive effects of ZD1839 in combination with radiation on tumor growth delay were observed in vivo after either a single 10 Gy fraction (enhancement ratio: 1.5) or multiple 4 x 2.5 Gy fractions (enhancement ratio: 4). ZD1839 reduced tumor vascularity, as well as levels of vascular endothelial growth factor (VEGF) protein and mRNA induced by stimulation with epidermal growth factor (EGF), suggesting a possible role of inhibition of angiogenesis in the effect.

CONCLUSIONS

Inhibiting EGFR-mediated signal transduction cascades with ZD1839 potentiates the antitumor effect of single and multiple fractions of radiation. These data provide preclinical rationale for clinical trials of EGFR inhibitors including ZD1839 in combination with radiation.

Molecular epidemiology of glioblastoma

Glioblastoma (GBM) is the most important primary brain tumor, both in terms of its incidence and its devastating impact on the unfortunate patients who have it. Although several well-defined hereditary syndromes predispose to malignant gliomas, most cases occur in the absence of a such a syndrome. The role of environmental factors, based on the known associations to date, also appears limited when compared with the total number of patients affected. It is clear that much remains to be discovered to better elucidate the causes of GBM, but the increasing recognition of molecular subtypes may help advance this field. This review highlights current insights into the molecular epidemiology of GBM.

Epidermal growth factor family receptors and inhibitors: radiation response modulators

Growing evidence suggests that epidermal growth factor family receptors (HERs) play a significant role in radiation response. EGFR expression levels and activation by ligand correlate with radioresistance, and exogenous HER2 expression alters radiation response. Preclinical studies of anti-EGFR anti-HER2 antibodies, and kinase inhibitors that inhibit EGFR, both EGFR and HER2, or all 4 family members show potential for clinical radiosensitization. Early-phase clinical trials of the anti-EGFR antibody, C225, prove the combination of C225 and radiotherapy to be well tolerated and promising. A phase 3 randomized trial in head and neck cancer is underway, and clinical investigation of other HER inhibitors is in progress. The mechanisms(s) of radiation response modulation by HERs appear complex and diverse. Signal transduction initiated by receptor activation promotes survival and proliferation after ionizing radiation, and HER inhibitors affect cellular responses to ionizing radiation (IR) in diverse ways, including inducing apoptosis, cell cycle arrest, and impeding DNA repair. HER signaling and inhibition also affect tumor-stroma interactions, particularly angiogenesis and endothelial survival after IR. Further investigation of the radiation response modulation by EGFR family members and their inhibitors will lead to optimization of this promising therapeutic approach.

Molecular targets as therapeutic strategies in the management of breast cancer

Therapy directed against specific biologic targets has long been used in the treatment of breast cancer; the estrogen receptor is a validated prognostic and therapeutic target, and antiestrogen therapy has been used effectively for decades. Recently, scientific progress and increased comprehension of mechanisms of breast cancer pathogenesis have led to the proliferation of both potential molecular targets and new therapeutic agents. The success of traztuzumab (Herceptin, Genentech, South San Francisco, CA), an anti-HER2 antibody, has spurred the development of other biologically directed therapeutics. In this overview, I discuss three targets relevant to breast cancer (the epidermal growth factor receptor family, angiogenesis, and NF-kappa B), and therapeutic approaches directed against these targets are discussed.

Immunohistochemical markers for prognosis of cerebral glioblastomas

Glioblastoma is the commonest neuroectodermal tumor and the most malignant in the range of cerebral astrocytic gliomas. The prognostic utility of various biological markers for glioblastomas has been broadly tested but the results obtained are regarded as controversial. In the present study, 302 glioblastoma specimens were studied to evaluate a possible association between clinical outcome and expression of some immunohistochemical variables. Furthermore, tumors examined were subdivided on the three cytological subsets--small-cell (SGB), pleomorphic-cell (PGB) and gemistocytic (GGB). Immunohistochemical variables differed between various subsets: the number of p53-positive tumors was found to be prevailed among the PGB, whereas the number of tumors with EGFR and mdm2 positivity was significantly greater in SGB. GGB contained significantly lowest mean proliferating cell nuclear antigen (PCNA) labeling index (LI), greater number of p21ras positive cases, and higher mean apoptotic index (AI). Survival time in patients with SGB, EGFR and mdm2-positivity and PCNA LI >40% was found to be significantly shorter, whereas presence of p21ras and AI >0.5% were associated with prolonged survival. Multivariate analysis revealed that survival time is associated with SGB, EGFR-positivity, and AI (p = 0.0023, p = 0.0035 and p = 0.0029 respectively). We conclude that although some immunohistochemical variables were found to be significant for glioblastoma outcome, they appear to be closely related to biology of single cytological subsets. Furthermore, these variables exhibited no prognostic value when they were analyzed within each cytological subset separately. Therefore, the glioblastoma subdivision on three cytological subsets proposed by us is carrying some element of rationality but, undoubtedly, requires further prospective studies.

Non-cytotoxic therapies for malignant gliomas

Malignant gliomas cause 2% of cancer deaths in western countries, and even the most intensive combinations of radiotherapy and chemotherapy cannot be curative. New chemotherapeutic drugs and alternative therapeutic modalities are strongly needed. Huge efforts are directed towards the development of innovative strategies for targeting and mending the specific molecular alterations in tumor cells (translational research). This review aims to summarize the most promising lines of investigational research in the field of neuro-oncology, such as non-cytotoxic drugs, immunotoxins, inhibitors of angiogenesis and gene therapy approaches, which will probably offer new therapy options for brain tumor patients.