PTEN mutation, EGFR amplification, and outcome in patients with anaplastic astrocytoma and glioblastoma multiforme

Gambogenic acid-induced time- and dose-dependent growth inhibition and apoptosis involving Akt pathway inactivation in U251 glioblastoma cells

Glioblastoma multiforme is the most common and aggressive type of primary brain tumor. Uncontrolled activation of the PI3K/Akt signaling pathway resulting from genetic alterations in phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and epidermal growth factor receptor (EGFR) correlates with poor prognosis and resistance to chemotherapy and radiotherapy of glioblastomas. In this study, we found that gambogenic acid (GNA), a polyprenylated xanthone isolated from the traditional medicine gamboge, efficiently arrested the cell cycle at the G(0)/G(1) phase by specifically repressing the expression of cyclin D1 and cyclin E, suppressed cell proliferation, colony formation and cell migration, and induced caspase-dependent apoptosis in U251 glioblastoma cells in a time- and dose-dependent manner. The pro-apoptotic effect of GNA on U251 cells was shown to be mediated through inactivation of the Akt pathway, because GNA efficiently suppressed the expression level of EGFR and reduced the phosphorylation of Akt (T308) and GSK3β (S9). Furthermore, the combined treatment with LY294002, a specific inhibitor of the PI3K/Akt kinase pathway, and GNA showed a synergistic or additive effect on the growth of U251 cells. Our results showed that GNA is a promising therapeutic agent for glioblastomas.

MicroRNAs involved in the EGFR/PTEN/AKT pathway in gliomas

Gliomas are the most common type of malignant primary brain tumor. Despite advances in surgery, radiation therapy, and chemotherapy, the prognosis of patients with gliomas has not significantly improved. MicroRNAs (miRNAs), a class of non-coding RNAs, 21-25 nucleotides long, negatively regulate the expression of target genes by interacting with specific sites in mRNAs, and play a critical role in the development of gliomas. The EGFR/PTEN/AKT pathway is a promising target for anti-glioma therapy. Recent studies have showed that regulation of the EGFR/PTEN/AKT pathway by miRNAs plays a major role in glioma progression, indicating a novel way to investigate the tumorigenesis, diagnosis, and therapy of gliomas. Here, we focus on recent findings of miRNAs with respect to the EGFR/PTEN/AKT pathway in gliomas.

Aberrant signaling pathways in glioma

Glioblastoma multiforme (GBM), a WHO grade IV malignant glioma, is the most common and lethal primary brain tumor in adults; few treatments are available. Median survival rates range from 12–15 months. The biological characteristics of this tumor are exemplified by prominent proliferation, active invasiveness, and rich angiogenesis. This is mainly due to highly deregulated signaling pathways in the tumor. Studies of these signaling pathways have greatly increased our understanding of the biology and clinical behavior of GBM. An integrated view of signal transduction will provide a more useful approach in designing novel therapies for this devastating disease. In this review, we summarize the current understanding of GBM signaling pathways with a focus on potential molecular targets for anti-signaling molecular therapies.

Molecular diagnostics of gliomas

CONTEXT

Gliomas are the most common primary brain tumors of adults and include a variety of histologic types and morphologies. Histologic evaluation remains the gold standard for glioma diagnosis; however, diagnostic difficulty may arise from tumor heterogeneity, overlapping morphologic features, and tumor sampling. Recently, our knowledge about the genetics of these tumors has expanded, and new molecular markers have been developed. Some of these markers have shown diagnostic value, whereas others are useful prognosticators for patient survival and therapeutic response.

OBJECTIVE

To review the most clinically useful molecular markers and their detection techniques in gliomas.

DATA SOURCES

Review of the pertinent literature and personal experience with the molecular testing in gliomas.

CONCLUSIONS

This article provides an overview of the most common molecular markers in neurooncology, including 1p/19q codeletion in oligodendroglial tumors, mutations in the isocitrate dehydrogenase 1 and 2 genes in diffuse gliomas, hypermethylation of the O(6)-methylguanine-DNA methyltransferase gene promoter in glioblastomas and anaplastic gliomas, alterations in the epidermal growth factor receptor and phosphatase and tensin homolog genes in high-grade gliomas, as well as BRAF alterations in pilocytic astrocytomas. Molecular testing of gliomas is increasingly used in routine clinical practice and requires that neuropathologists be familiar with these genetic markers and the molecular diagnostic techniques for their detection.

Treatment outcomes for patients with glioblastoma multiforme and a low Karnofsky Performance Scale score on presentation to a tertiary care institution. Clinical article

OBJECT

The object of this study was to determine the benefit of surgery, radiation, and chemotherapy for patients with glioblastoma multiforme (GBM) and a low Karnofsky Performance Scale (KPS) score.

METHODS

The authors retrospectively evaluated the records of patients who underwent primary treatment for pathologically confirmed GBM and with a KPS score ≤ 50 on initial evaluation for radiation therapy at a tertiary care institution between 1977 and 2006. Seventy-four patients with a median age of 69 years (range 19-88 years) and a median KPS score of 50 (range 20-50) were retrospectively grouped into the Radiation Therapy Oncology Group (RTOG) recursive partitioning analysis (RPA) Classes IV (11 patients), V (15 patients), and VI (48 patients). Patients underwent biopsy (38 patients) or tumor resection (36 patients). Forty-seven patients received radiation. Nineteen patients also received chemotherapy (53% temozolomide), initiated concurrently (47%) or after radiotherapy.

RESULTS

The median survival overall was 2.3 months (range 0.2-48 months). Median survival stratified by RPA Classes IV, V, and VI was 6.6, 6.6, and 1.8 months, respectively (p < 0.001, log-rank test). Median survival for patients receiving radiation (5.2 months) was greater than that for patients who declined radiation (1.6 months, p < 0.001). Patients in RPA Class VI appeared to benefit from radiotherapy only when tumor resection was also performed. The median survival from treatment initiation was greater for patients receiving chemotherapy concomitantly with radiotherapy (9.8 months) as compared with radiotherapy alone (1.7 months, p = 0.002). Of 20 patients seen for follow-up in the clinic at a median of 48 days (range 24-196 days) following radiotherapy, 70% were noted to have an improvement in the KPS score of between 10 and 30 points from the baseline score. On multivariate analysis, only RPA class (p = 0.01), resection (HR = 0.37, p = 0.001), and radiation therapy (HR = 0.39, p = 0.02) were significant predictors of a decreased mortality rate.

CONCLUSIONS

Patients with a KPS score ≤ 50 appear to have increased survival and functional status following tumor resection and radiation. The extent of benefit from concomitant chemotherapy is unclear. Future studies may benefit from reporting that utilizes a prognostic classification system such as the RTOG RPA class, which has been shown to be effective at separating outcomes even in patients with low performance status. Patients with GBMs and low KPS scores need to be evaluated in prospective studies to identify the extent to which different therapies improve outcomes.

Synthetic lethality of PARP inhibition in cancers lacking BRCA1 and BRCA2 mutations

Utilizing the concept of synthetic lethality has provided new opportunities for the development of targeted therapies, by allowing the targeting of loss of function genetic aberrations. In cancer cells with BRCA1 or BRCA2 loss of function, which harbor deficiency of DNA repair by homologous recombination, inhibition of PARP1 enzymatic activity leads to an accumulation of single strand breaks that are converted to double strand breaks but cannot be repaired by homologous recombination. Inhibition of PARP has therefore been advanced as a novel targeted therapy for cancers harboring BRCA1/2 mutations. Preclinical and preliminary clinical evidence, however, suggests a potentially broader scope for PARP inhibitors. Loss of function of various proteins involved in double strand break repair other than BRCA1/2 has been suggested to be synthetically lethal with PARP inhibition. Inactivation of these genes has been reported in a subset of human cancers and might therefore constitute predictive biomarkers for PARP inhibition. Here we discuss the evidence that the clinical use of PARP inhibition may be broader than targeting of cancers in BRCA1/2 germ-line mutation carriers.

[Morphological classification of glioblastomas]

BACKGROUND AND PURPOSE

In the 2007 WHO classification, glioblastomas are classified among the group of astrocytic tumors. They are highly malignant (grade IV). This group of tumors is morphologically heterogeneous. The WHO distinguishes between clinico-pathological entities, variants of entities and histological pattern. Variants are defined as being reliably indentified histologically and having some relevance for clinical outcome but as still being part of a previously defined overarching entity. Patterns of differentiation are identifiable by histological appearances but without clinical or pathological significance.

METHODS

The description of the histological and immunohistochemical features is based on the 2007 WHO classification.

RESULTS

In addition to the classic form of glioblastoma, two variants exist: the giant cell GBM and the gliosarcoma. The first but not the second would have a better outcome than the classic glioblastoma. The WHO classification also distinguishes several patterns of differentiation: small cells glioblastoma; glioblastoma with lipidized cells; glioblastoma with oligodendroglioma component; glioblastoma with heterologous differentiation. These patterns have to be recognized because they represent sometimes a diagnostic challenge. GFAP, Olig2 and Mib1/Ki67 are the most relevant immunohistochemical markers. Diagnostic value of neuronal markers is still controversial. EGFR or p53 expression can be detected and their prognosis value is discussed in this chapter. A systematic analysis of some markers in routine, for example IDH1 or internexin-a, could help to define more homogeneous groups of patients.

Age-dependent prognostic effects of EGFR/p53 alterations in glioblastoma: study on a prospective cohort of 140 uniformly treated adult patients

AIMS

To assess the prognostic influence of EGFR amplification/overexpression, p53 immunoreactivity and their age-dependent prognostic effects in a large prospective cohort of uniformly treated adult patients with newly diagnosed glioblastoma.

METHODS

Tumours from a uniformly treated prospective cohort of adult patients with newly diagnosed glioblastoma (n=140) were examined for EGFR amplification by fluorescence in situ hybridisation and EGFR/p53 expression by immunohistochemistry. Statistical methods were employed to assess the degree of association between EGFR amplification/overexpression and p53 immunopositivity. Survival analyses were performed by employing Cox proportional hazard models to assess the independent prognostic value of EGFR/p53 alterations and test the propensity for risk with age by assessing their interaction with patient age.

RESULTS

A strong positive correlation between EGFR amplification and EGFR overexpression (rho=0.5157; p<0.0001; CI 0.3783 to 0.6309) and a negative association of EGFR amplification (rho=-0.3417; p<0.0001; CI -0.4842 to -0.1816) and EGFR overexpression (rho=-0.3095; p<0.001; CI -0.4561 to -0.1465) with p53 immunopositivity was observed. Only patient age (HR: 1.029; p=0.004; CI 1.009 to 1.049) was associated with shorter survival by univariate Cox regression analysis. Multivariable Cox proportional hazards models revealed a statistically significant interaction between EGFR overexpression and age to be associated with shorter survival (HR: 1.001; p<0.0001; CI 1.000 to 1.002), thus predicting a higher hazard with increasing age. No age interaction of EGFR amplification status (HR: 1.001; p=0.642; CI 0.995 to 1.008) and p53 immunopositivity (HR: 1.000; p=0.841; CI 0.999 to 1.001) was noted in this cohort.

CONCLUSIONS

The prognostic value of EGFR overexpression is age-dependent, and there is a propensity for a higher hazard with increasing patient age. Identifying such groups of patients with more aggressive disease becomes mandatory, since they would benefit from intense therapeutic protocols targeting EGFR.

Sodium ion channel mutations in glioblastoma patients correlate with shorter survival

Background

Glioblastoma Multiforme (GBM) is the most common and invasive astrocytic tumor associated with dismal prognosis. Treatment for GBM patients has advanced, but the median survival remains a meager 15 months. In a recent study, 20,000 genes from 21 GBM patients were sequenced that identified frequent mutations in ion channel genes. The goal of this study was to determine whether ion channel mutations have a role in disease progression and whether molecular targeting of ion channels is a promising therapeutic strategy for GBM patients. Therefore, we compared GBM patient survival on the basis of presence or absence of mutations in calcium, potassium and sodium ion transport genes. Cardiac glycosides, known sodium channel inhibitors, were then tested for their ability to inhibit GBM cell proliferation.

Results

Nearly 90% of patients showed at least one mutation in ion transport genes. GBM patients with mutations in sodium channels showed a significantly shorter survival compared to patients with no sodium channel mutations, whereas a similar comparison based on mutational status of calcium or potassium ion channel mutations showed no survival differences. Experimentally, targeting GBM cells with cardiac glycosides such as digoxin and ouabain demonstrated preferential cytotoxicity against U-87 and D54 GBM cells compared to non-tumor astrocytes (NTAs).

Conclusions

These pilot studies of GBM patients with sodium channel mutations indicate an association with a more aggressive disease and significantly shorter survival. Moreover, inhibition of GBM cells by ion channel inhibitors such as cardiac glycosides suggest a therapeutic strategy with relatively safe drugs for targeting GBM ion channel mutations. Key Words: glioblastoma multiforme, ion channels, mutations, small molecule inhibitors, cardiac glycosides.

Epidermal growth factor receptor in glioma: signal transduction, neuropathology, imaging, and radioresistance

Aberrant epidermal growth factor receptor (EGFR) signaling is common in cancer. Increased expression of wild type and mutant EGFR is a widespread feature of diverse types of cancer. EGFR signaling in cancer has been the focus of intense investigation for decades primarily for two reasons. First, aberrant EGFR signaling is likely to play an important role in the pathogenesis of cancer, and therefore, the mechanisms of EGFR-mediated oncogenic signaling are of interest. Second, the EGFR signaling system is an attractive target for therapeutic intervention. EGFR gene amplification and overexpression are a particularly striking feature of glioblastoma (GBM), observed in approximately 40% of tumors. GBM is the most common primary malignant tumor of the central nervous system in adults. In approximately 50% of tumors with EGFR amplification, a specific EGFR mutant (EGFRvIII, also known as EGFR type III, de2-7, Delta EGFR) can be detected. This mutant is highly oncogenic and is generated from a deletion of exons 2 to 7 of the EGFR gene, which results in an in-frame deletion of 267 amino acids from the extracellular domain of the receptor. EGFRvIII is unable to bind ligand, and it signals constitutively. Although EGFRvIII has the same signaling domain as the wild type receptor, it seems to generate a distinct set of downstream signals that may contribute to an increased tumorigenicity. In this review, we discuss recent progress in key aspects of EGFR signaling in GBM, focusing on neuropathology, signal transduction, imaging of the EGFR, and the role of the EGFR in mediating resistance to radiation therapy in GBM.

Induction of CD8+ T-cell responses against novel glioma-associated antigen peptides and clinical activity by vaccinations with {alpha}-type 1 polarized dendritic cells and polyinosinic-polycytidylic acid stabilized by lysine and carboxymethylcellulose in patients with recurrent malignant glioma

PURPOSE

A phase I/II trial was performed to evaluate the safety and immunogenicity of a novel vaccination with α-type 1 polarized dendritic cells (αDC1) loaded with synthetic peptides for glioma-associated antigen (GAA) epitopes and administration of polyinosinic-polycytidylic acid [poly(I:C)] stabilized by lysine and carboxymethylcellulose (poly-ICLC) in HLA-A2(+) patients with recurrent malignant gliomas. GAAs for these peptides are EphA2, interleukin (IL)-13 receptor-α2, YKL-40, and gp100.

PATIENTS AND METHODS

Twenty-two patients (13 with glioblastoma multiforme [GBM], five with anaplastic astrocytoma [AA], three with anaplastic oligodendroglioma [AO], and one with anaplastic oligoastrocytoma [AOA]) received at least one vaccination, and 19 patients received at least four vaccinations at two αDC1 dose levels (1 × or 3 × 10(7)/dose) at 2-week intervals intranodally. Patients also received twice weekly intramuscular injections of 20 μg/kg poly-ICLC. Patients who demonstrated positive radiologic response or stable disease without major adverse events were allowed to receive booster vaccines. T-lymphocyte responses against GAA epitopes were assessed by enzyme-linked immunosorbent spot and HLA-tetramer assays.

RESULTS

The regimen was well-tolerated. The first four vaccines induced positive immune responses against at least one of the vaccination-targeted GAAs in peripheral blood mononuclear cells in 58% of patients. Peripheral blood samples demonstrated significant upregulation of type 1 cytokines and chemokines, including interferon-α and CXCL10. Nine (four GBM, two AA, two AO, and one AOA) achieved progression-free status lasting at least 12 months. One patient with recurrent GBM demonstrated sustained complete response. IL-12 production levels by αDC1 positively correlated with time to progression.

CONCLUSION

These data support safety, immunogenicity, and preliminary clinical activity of poly-ICLC-boosted αDC1-based vaccines.

Homozygous 10q23/PTEN deletion and its impact on outcome in glioblastoma: a prospective translational study on a uniformly treated cohort of adult patients

Tumors from a prospective cohort of adult patients with newly diagnosed glioblastoma (n=73), treated uniformly with radiochemotherapy, were examined for 10q23/PTEN deletion by fluorescence in situ hybridization (FISH). Statistical methods were employed to evaluate the degree of association between 10q23/PTEN deletion status and patient age. Survival analysis was performed using Kaplan-Meier log-rank test and multivariable Cox models to assess the prognostic value of 10q23/PTEN deletion. Interestingly, 10q23/PTEN homozygous deletion was frequent in patients >45 years of age (P=0.034) and the median age of patients harboring PTEN homozygous deletions was significantly higher than those with the retained status (P=0.019). 10q23/PTEN homozygous deletion was associated with shorter survival in the entire cohort as well in patients >45 years (P<0.05), indicating that loss of 10q23/PTEN showed clinical importance in elderly patients. Our study highlights the independent prognostic/predictive value of 10q23/PTEN deletion status as identified by FISH, particularly in glioblastoma patients aged >45 years.

Epidermal growth factor receptor expression modulates antitumor efficacy of vandetanib or cediranib combined with radiotherapy in human glioblastoma xenografts

PURPOSE

The purpose of this study was to determine the ability of radiation therapy (RT) combined with the tyrosine kinase inhibitors (TKI) vandetanib (antiepidermal growth factor receptor [EGFR] plus antivascular endothelial growth factor receptor [anti-VEGFR]) and cediranib (anti-VEGFR) to inhibit glioblastoma multiforme (GBM) growth. A secondary aim was to investigate how this regimen is modulated by tumor EGFR expression.

METHODS AND MATERIALS

Radiosensitivity was assessed by clonogenic cell survival assay. VEGF secretion was quantified by enzyme-linked immunosorbent assay. GBM (U87MG wild-type EGFR [wtEGFR] and U87MG EGFR-null) xenografts were treated with vandetanib, cediranib, and RT, alone or in combinations. Excised tumor sections were stained for proliferative and survival biomarkers.

RESULTS

In vitro, U87MG wtEGFR and U87 EGFR-null cells had similar growth kinetics. Neither TKI affected clonogenic cell survival following RT. However, in vivo, exogenous overexpression of wtEGFR decreased tumor doubling time (T2x) in U87MG xenografts (2.70 vs. 4.41 days for U87MG wtEGFR vs. U87MG vector, respectively). In U87MG EGFR-null cells, TKI combined with radiation was no better than radiation therapy alone. In U87MG wtEGFR, RT in combination with vandetanib (but not with cediranib) significantly increased tumor T2x compared with RT alone (T2x, 10.4 days vs. 4.8 days; p < 0.001). In vivo, growth delay correlated with suppression of pAkt, survivin, and Ki67 expression in tumor samples. The presence of EGFR augmented RT-stimulated VEGF release; this effect was inhibited by vandetanib.

CONCLUSIONS

EGFR expression promoted tumor growth in vivo but not in vitro, suggesting a microenvironmental effect. GBM xenografts expressing EGFR exhibited greater sensitivity to both cediranib and vandetanib than EGFR-null tumors. Hence EGFR status plays a major role in determining a tumor's in vivo response to radiation combined with TKI, supporting a "personalized" approach to GBM management.

PI3Kinase signaling in glioblastoma

Glioblastoma (GBM) is the most common primary tumor of the CNS in the adult. It is characterized by exponential growth and diffuse invasiveness. Among many different genetic alterations in GBM, e.g., mutations of PTEN, EGFR, p16/p19 and p53 and their impact on aberrant signaling have been thoroughly characterized. A major barrier to develop a common therapeutic strategy is founded on the fact that each tumor has its individual genetic fingerprint. Nonetheless, the PI3K pathway may represent a common therapeutic target to most GBM due to its central position in the signaling cascade affecting proliferation, apoptosis and migration. The read-out of blocking PI3K alone or in combination with other cancer pathways should mainly focus, besides the cytostatic effect, on cell death induction since sublethal damage may induce selection of more malignant clones. Targeting more than one pathway instead of a single agent approach may be more promising to kill GBM cells.

Molecular diagnostics of gliomas: state of the art

Modern neuropathology serves a key function in the multidisciplinary management of brain tumor patients. Owing to the recent advancements in molecular neurooncology, the neuropathological assessment of brain tumors is no longer restricted to provide information on a tumor's histological type and malignancy grade, but may be complemented by a growing number of molecular tests for clinically relevant tissue-based biomarkers. This article provides an overview and critical appraisal of the types of genetic and epigenetic aberrations that have gained significance in the molecular diagnostics of gliomas, namely deletions of chromosome arms 1p and 19q, promoter hypermethylation of the O6-methylguanine-methyl-transferase (MGMT) gene, and the mutation status of the IDH1 and IDH2 genes. In addition, the frequent oncogenic aberration of BRAF in pilocytic astrocytomas may serve as a novel diagnostic marker and therapeutic target. Finally, this review will summarize recent mechanistic insights into the molecular alterations underlying treatment resistance in malignant gliomas and outline the potential of genome-wide profiling approaches for increasing our repertoire of clinically useful glioma markers.

Cetuximab insufficiently inhibits glioma cell growth due to persistent EGFR downstream signaling

Overexpression and/or amplification of the epidermal growth factor receptor (EGFR) is present in 35-45% of primary glioblastoma multiforme tumors and has been correlated with a poor prognosis. In this study, we investigated the effect of cetuximab and intracellular signaling pathways downstream of EGFR, important for cell survival and proliferation. We show insufficient EGFR downregulation and competition with endogenous EGFR ligands upon cetuximab treatment. Dose-response experiments showed inhibition of EGFR phosphorylation without affecting two of the prominent downstream signaling pathways. Our results indicate that amplification and/or overexpression of EGFR is an unsatisfactory predictor for response to cetuximab.

Prospective evaluation of angiogenic, hypoxic and EGFR-related biomarkers in recurrent glioblastoma multiforme treated with cetuximab, bevacizumab and irinotecan

Several recent studies have demonstrated a beneficial effect of anti-angiogenic treatment with the vascular endothelial growth factor-neutralizing antibody bevacizumab in recurrent high-grade glioma. In the current study, immunohistochemical evaluation of biomarkers involved in angiogenesis, hypoxia and mediators of the epidermal growth factor receptor (EGFR) pathway were investigated. Tumor tissue was obtained from a previous phase II study, treating recurrent primary glioblastoma multiforme (GBM) patients with the EGFR inhibitor cetuximab in combination with bevacizumab and irinotecan. Of the 37 patients with available tumor tissue, 29 were evaluable for response. We concurrently performed immunohistochemical stainings on tumor tissue from 21 GBM patients treated with bevacizumab and irinotecan. We found a tendency of correlation between the hypoxia-related markers, indicating that they share the same regulatory mechanisms. None of the EGFR-related biomarkers showed any significant correlations with each other. None of the biomarkers tested alone or in combination could identify a patient population likely to benefit from bevacizumab and irinotecan, with or without the addition of cetuximab. There is still an urgent need for one or more reliable and reproducible biomarkers able to predict the efficacy of anti-angiogenic therapy.

Molecular pathology in adult gliomas: diagnostic, prognostic, and predictive markers

Over the past 10 years, there has been an increasing use of molecular markers in the assessment and management of adult malignant gliomas. Some molecular signatures are used diagnostically to help pathologists classify tumours, whereas others are used to estimate prognosis for patients. Most crucial, however, are those markers that are used to predict response to certain therapies, thereby directing clinicians to a particular treatment while avoiding other potentially deleterious therapies. Recently, large-scale genome-wide surveys have been used to identify new biomarkers that have been rapidly developed as diagnostic and prognostic tools. Given these developments, the pace of discovery of new molecular assays will quicken to facilitate personalised medicine in the setting of malignant glioma.

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.

A microfluidic platform for systems pathology: multiparameter single-cell signaling measurements of clinical brain tumor specimens

The clinical practice of oncology is being transformed by molecular diagnostics that will enable predictive and personalized medicine. Current technologies for quantitation of the cancer proteome are either qualitative (e.g., immunohistochemistry) or require large sample sizes (e.g., flow cytometry). Here, we report a microfluidic platform-microfluidic image cytometry (MIC)-capable of quantitative, single-cell proteomic analysis of multiple signaling molecules using only 1,000 to 2,800 cells. Using cultured cell lines, we show simultaneous measurement of four critical signaling proteins (EGFR, PTEN, phospho-Akt, and phospho-S6) within the oncogenic phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway. To show the clinical application of the MIC platform to solid tumors, we analyzed a panel of 19 human brain tumor biopsies, including glioblastomas. Our MIC measurements were validated by clinical immunohistochemistry and confirmed the striking intertumoral and intratumoral heterogeneity characteristic of glioblastoma. To interpret the multiparameter, single-cell MIC measurements, we adapted bioinformatic methods including self-organizing maps that stratify patients into clusters that predict tumor progression and patient survival. Together with bioinformatic analysis, the MIC platform represents a robust, enabling in vitro molecular diagnostic technology for systems pathology analysis and personalized medicine.

Akt activation is a common event in pediatric malignant gliomas and a potential adverse prognostic marker: a report from the Children's Oncology Group

Aberrant activation of Akt is a common finding in adult malignant gliomas, resulting in most cases from mutations or deletions involving PTEN, which allows constitutive Akt phosphorylation. In contrast, we have previously reported that pediatric malignant gliomas, which are morphologically similar to lesions arising in adults, have a substantially lower incidence of genomic alterations of PTEN. The objective of this study was to determine whether Akt activation was also an uncommon finding in childhood malignant gliomas and whether this feature was associated with survival. To address this issue, we examined the frequency of Akt activation, determined by overexpression of the activated phosphorylated form of Akt (Se(473)) on immunohistochemical analysis, in a series of 53 childhood malignant gliomas obtained from newly diagnosed patients treated on the Children's Oncology Group ACNS0126 and 0423 studies. The relationship between Akt activation and p53 overexpression, MIB1 labeling, and tumor histology was evaluated. The association between Akt activation and survival was also assessed. Overexpression of activated Akt was observed in 42 of 53 tumors, far in excess of the frequency of PTEN mutations we have previously observed. There was no association between Akt activation and either histology, p53 overexpression, or MIB1 proliferation indices. Although tumors that lacked Akt overexpression had a trend toward more favorable event-free survival and overall survival (p = 0.06), this association reflected that non-overexpressing tumors were significantly more likely to have undergone extensive tumor removal, which was independently associated with outcome. Activation of Akt is a common finding in pediatric malignant gliomas, although it remains uncertain whether this is an independent adverse prognostic factor. In view of the frequency of Akt activation, the evaluation of molecularly targeted therapies that inhibit this pathway warrants consideration for these tumors.

Epidermal growth factor receptor-mediated regulation of urokinase plasminogen activator expression and glioblastoma invasion via C-SRC/MAPK/AP-1 signaling pathways

One of the major pathophysiological features of malignant astrocytomas is their ability to infiltrate surrounding brain tissue. The epidermal growth factor receptor (EGFR) and proteases are known to be overexpressed in glioblastomas (GBMs), but the interaction between the activation of the EGFR and urokinase plasminogen activator (uPA) in promoting astrocytic tumor invasion has not been fully elucidated. Here, we characterized the signal transduction pathway(s) by which EGF regulates uPA expression and promotes astrocytoma invasion. We show that EGFR activation and constitutively active EGFR vIII in GBM cell lines upregulate uPA expression. Small-molecule inhibitors of mitogen-activated protein kinase, tyrosine kinase, and small interfering RNA targeting c-Src blocked uPA upregulation. Similarly, mutations in the activator protein 1 binding site of the uPA promoter reduced EGF-induced increases in uPA promoter activity. Treatment of GBM cells with EGF increased in vitro cell invasion, and the invasive phenotype was attenuated by gene silencing of uPA using small interfering RNA and short hairpin RNA. In addition, uPA knockdown clones formed smaller well-circumscribed tumors than nontarget U1242 control cells in a xenograft GBM mouse model in vivo. In summary, these results suggest that c-Src, mitogen-activated protein kinase, and a composite activator protein 1 on the uPA promoter are responsible for EGF-induced uPA expression and GBM invasion.

Update and developments in the treatment of glioblastoma multiforme - focus on bevacizumab

Glioblastoma is the most common primary brain tumor with a relatively poor prognosis. This article reviews the current standard therapy and discusses new developments in treatment of this disease. Surgical resection followed by radiation and chemotherapy has proven to be the most effective initial therapy. Recent advancement in molecular targeted therapies has led to the Food and Drug Administration (FDA) approval of bevacizumab in the setting of recurrent glioblastoma. The molecular pathways of glioblastoma growth are highlighted in this review. While numerous molecular targets are currently being intensely investigated, vascular endothelial growth factor (VEGF) receptor targeted therapy has been the only one to have shown clinical effect. The role of bevacizumab in this context provides a dynamic breakthrough in cancer therapy. Clinical trials have demonstrated significantly increased overall survival and six month progression free survival (PFS) in recurrent glioblastoma treated with bevacizumab alone or in combination with irinotecan. The use of this agent has also dramatically changed the imaging characteristics of glioblastoma. The anti-angiogenesis effects of bevacizumab have complicated the criterion for determining tumor growth. This may lead to redefinition of progressive disease based on non-invasive monitoring.

New pattern of EGFR amplification in glioblastoma and the relationship of gene copy number with gene expression profile

Gene amplification is a process that is characterized by an increase in the copy number of a restricted region in a chromosome arm, and is frequently associated with an overexpression of the corresponding amplified gene. Amplified DNA can be organized either as extrachromosomal elements, repeated units at a single locus or scattered throughout the genome. The amplification of the gene for epidermal growth factor receptor (EGFR) is a common finding in glioblastomas and the amplified gene copies appears as double minutes. The aim of this study was to investigate the different patterns of EGFR amplification in 40 cases of glioblastoma using FISH analysis in metaphases and paraffin sections, and to investigate the relationship of gene copy number with gene expression profile. The analysis of copy number alterations of EGFR was validated by quantitative PCR and SNP microarrays. We observed that in 42% of the cases, the type of amplification of EGFR was as double minute chromosomes. In addition, we detected another type of amplification, with extra copies of EGFR inserted in different loci of chromosome 7, present in 28% of cases. In this form of amplification, the number of copies is small, and the percentage of cells with EGFR amplification is rarely more than 15%. This model of amplification could correspond to a variant of the insertion mechanism, or a consequence of a process of duplication. Our results suggest that this mechanism could represent an early stage of amplification in glioblastomas. Overall, we found a close correlation between EGFR gene copy-number alterations and the level of EGFR protein expression. However, all cases with a high level of mRNA exhibited strong expression for the EGFR protein, and most cases with a low level of mRNA showed no overexpression of EGFR protein.

The role of the PTEN gene in malignant gliomas

This article focuses on the latest data about the role of the gene for phosphatase and tensin homologue located on chromosome 10 (PTEN) in malignant gliomas. PTEN acts as a tumour suppressor gene and plays a critical role in cell cycle progression, angiogenesis, migration, invasions and stem cell regulation. Furthermore, there is an interaction with other tumour suppressor genes. We discuss the role of miRNAs in modulating PTEN expression and also PTEN's role in the nucleus.

The clinicopathologic values of the molecules associated with the main pathogenesis of the glioblastoma

Glioblastoma (GBM) is a malignant CNS neoplasm. The prognosis of GBM may be influenced by the molecules of p53/MDM2/p14ARF, RB/p16INK4a, and the EGFR/PTEN/protein kinase B (PKB)/phosphoinositide 3-kinase (PI3K) pathways. We studied the expression status of specific molecular markers in GBMs by immunohistochemistry (IHC) and FISH in correlation with the clinical outcomes. The positivity of EGFR FISH and those of EGFR IHC by pharmDx and Zymed antibodies were 64.9%, 73.5%, and 43.4%, respectively. EGFR pharmDx antibody was more sensitive but less specific than EGFR Zymed antibody. p53 overexpression, MDM2 expression, p16 loss, PTEN loss, PKB and PI3K expression were found in 48.2%, 26.5%, 56.6%, 21.4%, 15.7% and 6.0%, respectively. EGFR IHC and FISH significantly, although not completely, correlated and EGFR and p53 immunoexpression also showed positive correlation. On multivariate survival studies, old age (> or =40 yrs) and bilaterality were independent unfavorable prognosis factors (p<0.05). Stratified by age, resectability and tumor size <5 cm were favorable survival factors in young (40<yrs) and old age groups (> or =40 yrs), respectively. Furthermore, the patients with supratentorial tumor lived longer than the patients with infratentorial tumor (p<0.05). Longer survival (survival length, > or =3 years) was statistically less frequent in the patients in the EGFR FISH-positive group (p=0.031).

Cetuximab, bevacizumab, and irinotecan for patients with primary glioblastoma and progression after radiation therapy and temozolomide: a phase II trial

The aim of this clinical trial was to investigate safety and efficacy when combining cetuximab with bevacizumab and irinotecan in patients with recurrent primary glioblastoma multiforme (GBM). Patients were included with recurrent primary GBM and progression within 6 months of ending standard treatment (radiotherapy and temozolomide). Bevacizumab and irinotecan were administered IV every 2 weeks. The first 10 patients received bevacizumab 5 mg/kg, but this was increased to 10 mg/kg after interim safety analysis. Irinotecan dose was based on whether patients were taking enzyme-inducing antiepileptic drugs or not: 340 and 125 mg/m(2), respectively. Cetuximab 400 mg/m(2) as loading dose followed by 250 mg/m(2) weekly was administered IV. Forty-three patients were enrolled in the trial, of which 32 were available for response. Radiographic responses were noted in 34%, of which 2 patients had complete responses and 9 patients had partial responses. The 6-month progression-free survival probability was 30% and median overall survival was 29 weeks (95% CI: 23-37 weeks). One patient had lacunar infarction, 1 patient had multiple pulmonary embolisms, and 3 patients had grade 3 skin toxicity, for which 1 patient needed plastic surgery. One patient was excluded due to suspicion of interstitial lung disease. Three patients had deep-vein thrombosis; all continued on study after adequate treatment. Cetuximab in combination with bevacizumab and irinotecan in recurrent GBM is well tolerated except for skin toxicity, with an encouraging response rate. However, the efficacy data do not seem to be superior compared with results with bevacizumab and irinotecan alone.

Epidermal growth factor receptor in glioblastomas: correlation between gene copy number and protein expression

Epidermal growth factor receptor is a transmembrane receptor involved in oncogenesis, including the development of glioblastoma. We studied the prognostic significance of epidermal growth factor receptor amplification as determined by fluorescence in situ hybridization, quantitative polymerase chain reaction, and protein expression by immunohistochemistry. Ninety-nine patients exhibiting glioblastoma were included. Immunohistochemistry was performed on microarray blocks with clone 25, which recognizes both epidermal growth factor receptor wild type and vIII, and scored using a semiquantitative approach. Quantitative polymerase chain reaction and fluorescence in situ hybridization techniques were performed on frozen section: 29.3% of cases had a high epidermal growth factor receptor immunohistochemistry score (score >/=200); and of these cases, 96.5% had gene amplification by fluorescence in situ hybridization and quantitative polymerase chain reaction. Conversely, of cases with a low immunohistochemistry score, 72.9% had normal karyotype or polysomy 7 by fluorescence in situ hybridization technique; but around 25% had gene amplification by fluorescence in situ hybridization and quantitative polymerase chain reaction. In the case of protein overexpression, quantitative polymerase chain reaction and fluorescence in situ hybridization could be avoided in first intention because their positive predictive value for amplification is 97%. In multivariate analysis, there was a trend toward an association between shorter overall survival time and epidermal growth factor receptor amplification as determined by fluorescence in situ hybridization analysis. However, cases with an immunohistochemistry score less 200 require further testing by fluorescence in situ hybridization or quantitative polymerase chain reaction.

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.

Reversing HOXA9 oncogene activation by PI3K inhibition: epigenetic mechanism and prognostic significance in human glioblastoma

HOXA genes encode critical transcriptional regulators of embryonic development that have been implicated in cancer. In this study, we documented functional relevance and mechanism of activation of HOXA9 in glioblastoma (GBM), the most common malignant brain tumor. Expression of HOXA genes was investigated using reverse transcription-PCR in primary gliomas and glioblastoma cell lines and was validated in two sets of expression array data. In a subset of GBM, HOXA genes are aberrently activated within confined chromosomal domains. Transcriptional activation of the HOXA cluster was reversible by a phosphoinostide 3-kinase (PI3K) inhibitor through an epigenetic mechanism involving histone H3K27 trimethylation. Functional studies of HOXA9 showed its capacity to decrease apoptosis and increase cellular proliferation along with tumor necrosis factor-related apoptosis-including ligand resistance. Notably, aberrant expression of HOXA9 was independently predictive of shorter overall and progression-free survival in two GBM patient sets and improved survival prediction by MGMT promoter methylation. Thus, HOXA9 activation is a novel, independent, and negative prognostic marker in GBM that is reversible through a PI3K-associated epigenetic mechanism. Our findings suggest a transcriptional pathway through which PI3K activates oncogenic HOXA expression with implications for mTOR or PI3K targeted therapies.

Suberoylanilide hydroxamic acid limits migration and invasion of glioma cells in two and three dimensional culture

High grade gliomas are aggressive cancers that are not well addressed by current chemotherapies, in large measure because these drugs do not curtail the diffuse invasion of glioma cells into brain tissue surrounding the tumor. Here, we investigate the effects of suberoylanilide hydroxamic acid (SAHA) on glioma cells in 2D and 3D in vitro assays, as SAHA has previously been shown to significantly increase apoptosis, decrease proliferation, and interfere with migration in other cell lines. We find that SAHA has significant independent effects on proliferation, migration, and invasion. These effects are seen in both 2D and 3D culture. In 3D culture, with glioma spheroids embedded in collagen I matrices, SAHA independently limits both glioma invasion and the reorganization of the tumor surroundings that usually proceeds such invasion. The decreased matrix reorganization and invasion is not accompanied by decreased production or activity of matrix-metalloproteases but instead may be related to increased cell-cell adhesion.

Joint NCCTG and NABTC prognostic factors analysis for high-grade recurrent glioma

The purpose of this study is to determine prognostic factors in patients with high-grade recurrent glioma for 3 outcome variables (overall survival, progression-free survival [PFS], and PFS rate 6 months after study registration [PFS6]). Data from 15 North Central Cancer Treatment Group (NCCTG) trials (n = 469, 1980-2004) and 12 North American Brain Tumor Consortium (NABTC) trials (n = 596, 1998-2002) were included. Eighteen prognostic variables were considered including type of treatment center (community/academic) and initial low-grade histology (yes/no). Recursive partitioning analysis (RPA), Cox proportional hazards, and logistic regression models with bootstrap resampling were used to identify prognostic variables. Longer survival was associated with last known grade (Grade) of III, younger age, ECOG performance score (PS) of 0, shorter time from initial diagnosis (DxTime), and no baseline steroid use. Factors associated with longer PFS were Grade III and shorter DxTime. For patients without temozolomide as part of the treatment regimen, the only factor associated with better PFS6 was Grade III, although DxTime was important in RPA and PS was important in logistic regression. Grade was the most important prognostic factor for all three endpoints regardless of the statistical method used. Other important variables for one or more endpoints included age, PS, and DxTime. Neither type of treatment center nor initial low-grade histology was identified as a major predictor for any endpoint.

The expression level of sphingosine-1-phosphate receptor type 1 is related to MIB-1 labeling index and predicts survival of glioblastoma patients

Although there are many reports on the clinical use of the MIB-1 labeling index (LI), which is a measure of proliferative activity in astrocytomas; its significance varies between studies. There are no known molecules that are directly linked to the MIB-1 LI in astrocytomas. We evaluated the clinical value of the MIB-1 LI in our human glioblastoma cases and determined the molecules that possibly influenced the MIB-1 LI. An immunohistochemical study of the MIB-1 protein was performed and MIB-1 LIs of 38 glioblastomas were determined. In the same cases, epidermal growth factor receptor (EGFR), platelet-derived growth factor receptor-alpha (PDGFRA), and sphingosine-1-phosphate receptor type 1 (S1P(1)), which are known regulators of glioma cell proliferation, were detected and quantified by quantitative real-time-PCR or western blotting. Kaplan-Meier survival curves for 38 patients with glioblastomas showed that a high MIB-1 LI correlated with poor survival (P < 0.05). Among the molecules tested, only the low expression of S1P(1) was significantly correlated with the high MIB-1 LI in glioblastomas (P < 0.05). Multivariate analysis revealed that the S1P(1) expression level was a significant prognostic factor. Our results indicate that the MIB-1 LI is an important prognostic factor in human glioblastomas. Furthermore, downregulation of S1P(1) expression increases proliferative activity, and thus enhances the malignancy of glioblastomas, resulting in a poor survival.

Combination therapy for malignant glioma based on PTEN status

The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is a central regulator of cell proliferation, migration, tumor growth, survival, angiogenesis and metabolism, contributing to the malignant phenotype of gliomas. Trials using targeted therapeutics against growth factor receptors and downstream signal mediators of the PI3K pathway have demonstrated only modest clinical benefit. Although recent clinical data suggests that malignant gliomas with PTEN are more likely to respond to EGF receptor inhibitors, gliomas have multiple concomitantly activated pathways, making them highly resistant to single-targeted therapy. This review discusses the importance of the PI3K pathway in glioma, the potential role of PTEN status in directing specific therapies, discusses clinical trial development of drug combinations to treat malignant gliomas and offers strategies for trial design that will be necessary to fully understand the successes and failures of current approaches to glioma therapy.

Robust detection of EGFR copy number changes and EGFR variant III: technical aspects and relevance for glioma diagnostics

Epidermal growth factor receptor (EGFR) is commonly affected in cancer, generally in the form of an increase in DNA copy number and/or as mutation variants [e.g., EGFR variant III (EGFRvIII), an in-frame deletion of exons 2-7]. While detection of EGFR aberrations can be expected to be relevant for glioma patients, such analysis has not yet been implemented in a routine setting, also because feasible and robust assays were lacking. We evaluated multiplex ligation-dependent probe amplification (MLPA) for detection of EGFR amplification and EGFRvIII in DNA of a spectrum of 216 diffuse gliomas. EGFRvIII detection was verified at the protein level by immunohistochemistry and at the RNA level using the conventionally used endpoint RT-PCR as well as a newly developed quantitative RT-PCR. Compared to these techniques, the DNA-based MLPA assay for EGFR/EGFRvIII analysis tested showed 100% sensitivity and specificity. We conclude that MLPA is a robust assay for detection of EGFR/EGFRvIII aberrations. While the exact diagnostic, prognostic and predictive value of such EGFR testing remains to be seen, MLPA has great potential as it can reliably and relatively easily be performed on routinely processed (formalin-fixed, paraffin-embedded) tumor tissue in combination with testing for other relevant glioma markers.

Long-term survivors of glioblastoma: clinical features and molecular analysis

BACKGROUND

Glioblastoma is a highly lethal neoplasm with a median survival of 12-14 months; only 2-5% of patients survive >3 years.

METHODS

At our institute, patients with glioblastoma are initially treated with maximum tumor resection followed by radiation and the intravenous injection of nimustine hydrochloride (ACNU).

RESULTS

Using this strategy, 18 of 123 (14.6%) patients treated at our hospital survived >3 years; 7 manifested no recurrence, and the other 11 had early recurrence and received additional therapies. To identify factors associated with prolonged survival, we compared these patients with 21 short-term (<1.5 years) glioblastoma survivors. In the long-term survivors, the MGMT promoter methylation was significantly more frequent. The rate of p53 mutation was lower, and the rate of PTEN mutations and the proliferation index were slightly higher in short-term survivors.

CONCLUSION

By multivariate analysis, we found that a younger age and MGMT promoter methylation were significant favorable factors in patients with glioblastoma.

Prognostic significance of molecular markers and extent of resection in primary glioblastoma patients

PURPOSE

Despite multimodal aggressive treatment glioblastoma patients still face a rather poor prognosis. Recent data indicate that certain molecular markers, in particular MGMT promoter hypermethylation, are associated with response to alkylating chemotherapy and longer survival. The clinical significance of other glioblastoma-associated molecular aberrations and their relationship to MGMT promoter hypermethylation is still poorly understood.

EXPERIMENTAL DESIGN

We conducted a translational study involving 67 newly diagnosed glioblastoma patients treated at our institution from 1998 to 2004. All patients were treated by open resection, followed by radiotherapy and adjuvant temozolomide chemotherapy. The tumors were investigated for MGMT promoter methylation, mRNA and protein expression, as well as presence of MGMT sequence polymorphisms. In addition, we screened for genetic aberrations of the EGFR, TP53, CDK4, MDM2, and PDGFRA genes as well as allelic losses on chromosomal arms 1p, 10q, and 19q.

RESULTS

Correlation of molecular findings with clinical data revealed significantly longer time to progression after onset of chemotherapy and longer overall survival of patients with MGMT-hypermethylated tumors. In contrast, MGMT protein expression, MGMT polymorphisms, and aberrations in any of the other genes and chromosomes were not significantly linked to patient outcome. Multivariate analysis identified MGMT promoter hypermethylation and near-complete tumor resection as the most important parameters associated with better prognosis.

CONCLUSION

Our study provides novel insights into the significance of molecular and clinical markers in predicting the prognosis of glioblastoma patients, which may improve stratification of patients into distinct prognostic subgroups.

Mechanisms of resistance to EGFR inhibitors in head and neck cancer

Epidermal growth factor receptor (EGFR), a receptor tyrosine kinase that activates multiple signaling pathways, including phosphatidylinositol-3-kinase/v-AKT murine thymoma viral oncogene homolog protein (Akt), has long been a target of novel therapies. Despite universal EGFR expression in head and neck squamous cell carcinoma (HNSCC), the majority of patients do not respond to EGFR inhibitors. This review focuses on mechanisms of resistance to these agents in HNSCC, and how these may be unique when compared with other malignancies such as non-small cell lung and colorectal cancers. Published studies and abstracts reveal that there are likely several mechanisms underlying resistance, suggesting that different strategies will be required to improve efficacy of EGFR inhibitors in HNSCC.

Radiosensitizing effects of temozolomide observed in vivo only in a subset of O6-methylguanine-DNA methyltransferase methylated glioblastoma multiforme xenografts

PURPOSE

Concurrent temozolomide (TMZ) and radiation therapy (RT) followed by adjuvant TMZ is standard treatment for patients with glioblastoma multiforme (GBM), although the relative contribution of concurrent versus adjuvant TMZ is unknown. In this study, the efficacy of TMZ/RT was tested with a panel of 20 primary GBM xenografts.

METHODS AND MATERIALS

Mice with intracranial xenografts were treated with TMZ, RT, TMZ/RT, or placebo. Survival ratio for a given treatment/line was defined as the ratio of median survival for treatment vs. placebo.

RESULTS

The median survival ratio was significantly higher for O6-methylguanine-DNA methyltransferase (MGMT) methylated tumors versus unmethylated tumors following treatment with TMZ (median survival ratio, 3.6 vs. 1.5, respectively; p = 0.008) or TMZ/RT (5.7 vs. 2.3, respectively; p = 0.001) but not RT alone (1.7 vs. 1.6; p = 0.47). In an analysis of variance, MGMT methylation status and p53 mutation status were significantly associated with treatment response. When we analyzed the additional survival benefit conferred specifically by combined therapy, only a subset (5 of 11) of MGMT methylated tumors derived substantial additional benefit from combined therapy, while none of the MGMT unmethylated tumors did. Consistent with a true radiosensitizing effect of TMZ, sequential treatment in which RT (week 1) was followed by TMZ (week 2) proved significantly less effective than TMZ followed by RT or concurrent TMZ/RT (survival ratios of 4.0, 9.6 and 12.9, respectively; p < 0.0001).

CONCLUSIONS

Concurrent treatment with TMZ and RT provides significant survival benefit only in a subset of MGMT methylated tumors and provides superior antitumor activity relative to sequential administration of RT and TMZ.

The drug-resistance to gefitinib in PTEN low expression cancer cells is reversed by irradiation in vitro

Background

Despite of the recent success of EGFR inhibitory agents, the primary drug-resistant becomes a major challenge for EGFR inhibitor therapies. PTEN gene is an important positive regulatory factor for response to EGFR inhibitor therapy. Low-expression of PTEN is clearly one of the important reasons why tumor cells resisted to tyrosine kinase inhibitors.

Methods

To investigate the drug-resistance reversal to gefitinb and the mechanism in PTEN low expression cells which radiated with X-rays in vitro, We demonstrated that H-157 lung cancer cells (low-expression of PTEN but phospho-EGFR overexpressed tumor cells) exposed to X-rays. The PTEN expressions and radiosensitizing effects of tyrosine kinase inhibitor before and after irradiation were observed. The cell-survival rates were evaluated by colony-forming assays. The cell apoptosis was investigated using FCM. The expressions of phospho-EGFR and PTEN were determined by Western blot analysis.

Results

The results showed that the PTEN expressions were significantly enhanced by X-rays. Moreover, the cell growth curve and survival curve were down-regulated in the gefitinib-treated groups after irradiation. Meanwhile, the radiation-induced apoptosis of tumor cells was increased by inhibition of the EGFR through up-regulation of PTEN.

Conclusion

These results suggested that PTEN gene is an important regulator on TKI inhibition, and the resistance to tyrosine kinase inhibitors might be reversed by irradiation in PTEN low expression cancer cells.

Status of PI3K inhibition and biomarker development in cancer therapeutics

The phosphatidylinositol 3-kinase (PI3K) signalling pathway is integral to diverse cellular functions, including cellular proliferation, differentiation and survival. The 'phosphate and tensin homologue deleted from chromosome 10' (PTEN) tumor suppressor gene plays a critical role as a negative regulator of this pathway. An array of genetic mutations and amplifications has been described affecting key components of this pathway, with implications not only for tumorigenesis but also for resistance to some classic cytotoxics and targeted agents. Emerging preclinical research has significantly advanced our understanding of the PI3K pathway and its complex machinations and interactions. This knowledge has enabled the evolution of rationally designed drugs targeting elements of this pathway. It is important that the development of suitable biomarkers continues in parallel to optimize use of these agents. A new generation of PI3K inhibitors is now entering early clinical trials, with much anticipation that they will add to the growing armamentarium of targeted cancer therapeutics.

Potential therapeutic effect of glycogen synthase kinase 3beta inhibition against human glioblastoma

PURPOSE

Glioblastoma represents the malignant brain tumor that is most refractory to treatment and in which the identification of molecular target(s) is urgently required. We investigated the expression, activity, and putative pathologic role of glycogen synthase kinase 3beta (GSK3beta), an emerging therapeutic target for neurodegenerative diseases, in human glioblastoma.

EXPERIMENTAL DESIGN

The active fraction of GSK3beta that is phosphorylated at the tyrosine 216 residue (pGSK3betaY216) was identified in glioblastoma cell lines. GSK3beta activity for phosphorylating its substrate was detected in these cells by nonradioisotopic in vitro kinase assay.

RESULTS

Higher expression levels of GSK3beta and pGSK3betaY216 were frequently detected in glioblastomas compared with nonneoplastic brain tissues. Inhibition of GSK3beta activity by escalating doses of a small-molecule inhibitor (AR-A014418) or inhibition of its expression by RNA interference induced the apoptosis and attenuated the survival and proliferation of glioblastoma cells in vitro. Inhibition of GSK3beta was associated with increased expression of p53 and p21 in glioblastoma cells with wild-type p53 and with decreased Rb phosphorylation and expression of cyclin-dependent kinase 6 in all glioblastoma cell lines. Administration of AR-A014418 at a low dose significantly sensitized glioblastoma cells to temozolomide and 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosourea, chemotherapeutic agents used in the clinical setting, as well as to ionizing radiation.

CONCLUSION

These results indicate that GSK3beta exerts a pathologic role by promoting the survival and proliferation of glioblastoma cells and by protecting them from apoptosis via the inactivation of p53- and/or Rb-mediated pathways. Consequently, we propose that GSK3beta provides a potential therapeutic target in glioblastoma.