Cyclooxygenase in the treatment of glioma: its complex role in signal transduction

Identification of Hub Genes and Key Pathways Associated with Anti-VEGF Resistant Glioblastoma Using Gene Expression Data Analysis

Anti-VEGF therapy is considered to be a useful therapeutic approach in many tumors, but the low efficacy and drug resistance limit its therapeutic potential and promote tumor growth through alternative mechanisms. We reanalyzed the gene expression data of xenografts of tumors of bevacizumab-resistant glioblastoma multiforme (GBM) patients, using bioinformatics tools, to understand the molecular mechanisms of this resistance. An analysis of the gene set data from three generations of xenografts, identified as 646, 873 and 1220, differentially expressed genes (DEGs) in the first, fourth and ninth generations, respectively, of the anti-VEGF-resistant GBM cells. Gene Ontology (GO) and pathway enrichment analyses demonstrated that the DEGs were significantly enriched in biological processes such as angiogenesis, cell proliferation, cell migration, and apoptosis. The protein–protein interaction network and module analysis revealed 21 hub genes, which were enriched in cancer pathways, the cell cycle, the HIF1 signaling pathway, and microRNAs in cancer. The VEGF pathway analysis revealed nine upregulated (IL6, EGFR, VEGFA, SRC, CXCL8, PTGS2, IDH1, APP, and SQSTM1) and five downregulated hub genes (POLR2H, RPS3, UBA52, CCNB1, and UBE2C) linked with several of the VEGF signaling pathway components. The survival analysis showed that three upregulated hub genes (CXCL8, VEGFA, and IDH1) were associated with poor survival. The results predict that these hub genes associated with the GBM resistance to bevacizumab may be potential therapeutic targets or can be biomarkers of the anti-VEGF resistance of GBM.

Biological effects of selective COX-2 inhibitor NS398 on human glioblastoma cell lines

Background

Cyclooxygenase-2 (COX-2), an inflammation-associated enzyme, has been implicated in tumorigenesis and progression of glioblastoma (GBM). The poor survival of GBM was mainly associated with the presence of glioma stem cells (GSC) and the markedly inflammatory microenvironment. To further explore the involvement of COX-2 in glioma biology, the effects of NS398, a selective COX-2 inhibitor, were evaluated on GSC derived from COX-2 expressing GBM cell lines, i.e., U87MG and T98G, in terms of neurospheres' growth, autophagy, and extracellular vesicle (EV) release.

Methods

Neurospheres' growth and morphology were evaluated by optical and scanning electron microscopy. Autophagy was measured by staining acidic vesicular organelles. Extracellular vesicles (EV), released from neurospheres, were analyzed by transmission electron microscopy. The autophagic proteins Beclin-1 and LC3B, as well as the EV markers CD63 and CD81, were analyzed by western blotting. The scratch assay test was used to evaluate the NS398 influence on GBM cell migration.

Results

Both cell lines were strongly influenced by NS398 exposure, as showed by morphological changes, reduced growth rate, and appearance of autophagy. Furthermore, the inhibitor led to a functional change of EV released by neurospheres. Indeed, EV secreted by NS398-treated GSC, but not those from control cells, were able to significantly inhibit adherent U87MG and T98G cell migration and induced autophagy in recipient cells, thus leading to effects quite similar to those directly caused by NS398 in the same cells.

Conclusion

Despite the intrinsic diversity and individual genetic features of U87MG and T98G, comparable effects were exerted by the COX-2 inhibitor NS398 on both GBM cell lines. Overall, our findings support the crucial role of the inflammatory-associated COX-2/PGE2 system in glioma and glioma stem cell biology.

Radiosensitivity enhancement by Co-NMS-mediated mitochondrial impairment in glioblastoma

We investigated the radiosensitizing effects of Co-NMS, a derivative of nimesulide based on a cobalt carbonyl complex, on malignant glioma cells. In the zebrafish exposed to Co-NMS ranging from 5 to 20 μM, cell death and heat shock protein 70 expression in the brain and neurobehavioral performance were evaluated. Our data showed that Co-NMS at 5 μM did not cause the appreciable neurotoxicity, and thereby was given as a novel radiation sensitizer in further study. In the U251 cells, Co-NMS combined with irradiation treatment resulted in significant inhibition of cell growth and clonogenic capability as well as remarkable increases of G2/M arrest and apoptotic cell population compared to the irradiation alone treatment. This demonstrated that the Co-NMS administration exerted a strong potential of sensitizing effect on the irradiated cells. With regard to the tumor radiosensitization of Co-NMS, it could be primarily attributed to the Co-NMS-derived mitochondrial impairment, reflected by the loss of mitochondrial membrane potential, the disruption of mitochondrial fusion and fission balance as well as redox homeostasis. Furthermore, the energy metabolism of the U251 cells was obviously suppressed by cotreatment with Co-NMS and irradiation through repressing mitochondrial function. Taken together, our findings suggested that Co-NMS could be a desirable drug to enhance the radiotherapeutic effects in glioblastoma patients.

The Effect of Biotinylated PAMAM G3 Dendrimers Conjugated with COX-2 Inhibitor (celecoxib) and PPARγ Agonist (Fmoc-L-Leucine) on Human Normal Fibroblasts, Immortalized Keratinocytes and Glioma Cells in Vitro

Glioblastoma multiforme (GBM) is the most malignant type of central nervous system tumor that is resistant to all currently used forms of therapy. Thus, more effective GBM treatment strategies are being investigated, including combined therapies with drugs that may cross the blood brain barrier (BBB). Another important issue considers the decrease of deleterious side effects of therapy. It has been shown that nanocarrier conjugates with biotin can penetrate BBB. In this study, biotinylated PAMAM G3 dendrimers substituted with the recognized anticancer agents cyclooxygenase-2 (COX-2) inhibitor celecoxib and peroxisome proliferator-activated receptor γ (PPARγ) agonist Fmoc-L-Leucine (G3-BCL) were tested in vitro on human cell lines with different p53 status: glioblastoma (U-118 MG), normal fibroblasts (BJ) and immortalized keratinocytes (HaCaT). G3-BCL penetrated efficiently into the lysosomal and mitochondrial compartments of U-118 MG cells and induced death of U-118 MG cells via apoptosis and inhibited proliferation and migration at low IC₅₀ = 1.25 µM concentration, considerably lower than either drug applied alone. Comparison of the effects of G3-BCL on expression of COX-2 and PPARγ protein and PGE₂ production of three different investigated cell line phenotypes revealed that the anti-glioma effect of the conjugate was realized by other mechanisms other than influencing PPAR-γ expression and regardless of p53 cell status, it was dependent on COX-2 protein level and high PGE₂ production. Similar G3-BCL cytotoxicity was seen in normal fibroblasts (IC₅₀ = 1.29 µM) and higher resistance in HaCaT cells (IC₅₀ = 4.49 µM). Thus, G3-BCL might be a good candidate for the targeted, local glioma therapy with limited site effects.

Small-molecule inhibition of prostaglandin E receptor 2 impairs cyclooxygenase-associated malignant glioma growth

BACKGROUND AND PURPOSE

An up-regulation of COX-2 in malignant gliomas causes excessive synthesis of PGE₂ , which is thought to facilitate brain tumour growth and invasion. However, which downstream PGE₂ receptor subtype (i.e., EP₁ -EP₄ ) directly contributes to COX activity-promoted glioma growth remains largely unknown.

EXPERIMENTAL APPROACH

Using a publicly available database from The Cancer Genome Atlas research network, we compared the expression of PGE₂ signalling-associated genes in human lower grade glioma and glioblastoma multiforme (GBM) samples. The Kaplan-Meier analysis was performed to determine the relationship between their expression and survival probability. A time-resolved FRET method was used to identify the EP subtype that mediates COX-2/PGE₂ -initiated cAMP signalling in human GBM cells. Taking advantage of a recently identified novel selective bioavailable brain-permeable small-molecule antagonist, we studied the effect of pharmacological inhibition of the EP₂ receptor on glioma cell growth in vitro and in vivo.

KEY RESULTS

The EP₂ receptor is a key Gα_s -coupled receptor that mediates COX-2/PGE₂ -initiated cAMP signalling pathways in human malignant glioma cells. Inhibition of EP₂ receptors reduced COX-2 activity-driven GBM cell proliferation, invasion, and migration and caused cell cycle arrest at G0-G1 and apoptosis of GBM cells. Glioma cell growth in vivo was also substantially decreased by post-treatment with an EP₂ antagonist in both subcutaneous and intracranial tumour models.

CONCLUSION AND IMPLICATIONS

Taken together, our results suggest that PGE₂ signalling via the EP₂ receptor increases the malignant potential of human glioma cells and might represent a novel therapeutic target for GBM.

The Process and Regulatory Components of Inflammation in Brain Oncogenesis

Central nervous system tumors comprising the primary cancers and brain metastases remain the most lethal neoplasms and challenging to treat. Substantial evidence points to a paramount role for inflammation in the pathology leading to gliomagenesis, malignant progression and tumor aggressiveness in the central nervous system (CNS) microenvironment. This review summarizes the salient contributions of oxidative stress, interleukins, tumor necrosis factor-α(TNF-α), cyclooxygenases, and transcription factors such as signal transducer and activator of transcription 3 (STAT3) and nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-κB) and the associated cross-talks to the inflammatory signaling in CNS cancers. The roles of reactive astrocytes, tumor associated microglia and macrophages, metabolic alterations, microsatellite instability, O⁶-methylguanine DNA methyltransferase (MGMT) DNA repair and epigenetic alterations mediated by the isocitrate dehydrogenase 1 (IDH1) mutations have been discussed. The inflammatory pathways with relevance to the brain cancer treatments have been highlighted.

Cyclooxygenase-2 in glioblastoma multiforme

Glioblastoma multiforme (GBM) represents the most prevalent brain primary tumor, yet there is a lack of effective treatment. With current therapies, fewer than 5% of patients with GBM survive more than 5 years after diagnosis. Mounting evidence from epidemiological studies reveals that the regular use of nonsteroidal anti-inflammatory drugs (NSAIDs) is correlated with reduced incidence of GBM, suggesting that cyclooxygenase-2 (COX-2) and its major product within the brain, prostaglandin E2 (PGE₂), are involved in the development and progression of GBM. Here, we highlight our current understanding of COX-2 in GBM proliferation, apoptosis, invasion, angiogenesis, and immunosuppression by focusing on recent in vitro and in vivo experimental data. We also discuss the feasibility of COX-2 as a therapeutic target for GBM in light of the latest human studies.

Diacetyloxyl derivatization of the fibroblast growth factor inhibitor dobesilate enhances its anti-inflammatory, anti-angiogenic and anti-tumoral activities

BACKGROUND

Dobesilate (2,5-dihydroxyphenyl sulfonate, DHPS) was recently identified as the most potent member of a family of fibroblast growth factor (FGF) inhibitors headed by gentisic acid, one of the main catabolites of aspirin. Although FGFs were first described as inducers of angiogenesis, they were soon recognized as broad spectrum mitogens. Furthermore, in the last decade these proteins have been shown to participate directly in the onset of inflammation, and their potential angiogenic activity often contributes to the inflammatory process in vivo. The aim of this work was to evaluate the anti-inflammatory, anti-angiogenic and anti-tumoral activities of the derivative of DHPS obtained by acetoxylation of its two hydroxyl groups (2,5-diacetoxyphenyl sulfonate; DAPS).

METHODS

Anti-inflammatory, anti-angiogenic and anti-tumoral activities of DHPS and DAPS were compared using in vivo assays of dermatitis, angiogenesis and tumorigenesis. The effects of both compounds on myeloperoxidase (MPO) and cyclooxygenase (COX) activities, cytokine production and FGF-induced fibroblast proliferation were also determined.

RESULTS

Topical DAPS is more effective than DHPS in preventing inflammatory signs (increased vascular permeability, edema, leukocyte infiltration, MPO activation) caused by contact dermatitis induction in rat ears. DAPS, but not DHPS, effectively inhibits COX-1 and COX-2 activities. DAPS also reduces the increase in serum cytokine concentration induced by lipopolysaccharide in rats. Furthermore, DAPS displays higher in vivo efficacy than DHPS in inhibiting FGF-induced angiogenesis and heterotopic glioma progression, with demonstrated oral efficacy to combat both processes.

CONCLUSIONS

By inhibiting both FGF-signaling and COX-mediated prostaglandin synthesis, DAPS efficiently breaks the vicious circle created by the reciprocal induction of FGF and prostaglandins, which probably sustains undesirable inflammation in many circumstances. Our findings define the enhancement of anti-inflammatory, anti-angiogenic and anti-tumoral activities by diacetyloxyl derivatization of the FGF inhibitor, dobesilate.

Effect of α-tocopheryl succinate on the molecular damage induced by indomethacin in C6 glioma cells

Indomethacin is a member of the non-steroidal anti-inflammatory drug (NSAID) class, which has great potential for use in the treatment of glioma. However, it induces the generation of reactive oxygen species (ROS) and causes molecular damage while inducing its effects. Vitamin E is widely used in the complementary therapy of cancers. The main goal of the present study was to investigate the effects of α-tocopheryl succinate (α-TOS) against the oxidative damage induced by indomethacin in C6 glioma cells. Cells were treated with 10 μM α-TOS alone or in combination with 200 μM indomethacin for two days. The intracellular ROS level, molecular damage as revealed by lipid peroxidation and protein carbonyl formation, and the COX activity in C6 glioma cells were measured. Treatment of the cells with α-TOS and indomethacin, alone or in combination, caused the levels of ROS generation and protein damage to increase, but protected against lipid peroxidation and reduced COX activity.

Plausible role of naringenin against cerebrally implanted C6 glioma cells in rats

Gliomas encompass a significant percentage of intrinsic neoplasms of the central nervous system in both adults and children. The constitutive activation of phosphatidylinositol 3-kinase (PI3K) and protein kinase B is the hallmark of glioma. The up-regulated protein kinase B could influence the expression of cyclooxygenase-2, an indicator of aggressive glioma. The present study was embarked to demonstrate the effect of naringenin (50 mg/kg bw for 30 days administrated orally) on PI3K, protein kinase B, and cyclooxygenase-2 in cerebrally implanted rat C6 glioma model. After the experimental period of 30 days, the animals were sacrificed and excised brain tissues were subjected to study the expressions of PI3K, protein kinase B, and cyclooxygenase-2 by reverse transcriptase polymerase chain reaction followed Western blot analysis. The activity of COX-2 (production of prostaglandin-E(2)) was also determined by high pressure liquid chromatography. The results showed that the naringenin could down-regulate the expressions of PI3K and protein kinase B along with activity and expression of cyclooxygenase-2 in C6 glioma cells implanted rat brain. In conclusion, it can be argued that the reduced expressions of phosphatidylinositol 3-kinase and protein kinase B in naringenin-treated glioma-induced rat brain might be involved in the down-regulation of cyclooxygenase-2 expression and activity. Thus, fine-tuned investigation of which will be helpful for targeted drug discovery against glioma.

Concanavalin-A triggers inflammatory response through JAK/STAT3 signalling and modulates MT1-MMP regulation of COX-2 in mesenchymal stromal cells

Pharmacological targeting of inflammation through STAT3 and NF-κB signaling pathways is, among other inflammatory biomarkers, associated with cyclooxygenase (COX)-2 inhibition and is believed to play a crucial role in prevention and therapy of cancer. Recently, inflammatory factors were found to impact on mesenchymal stromal cells (MSC) contribution to tumor angiogenesis. Given MSC chemotaxis and cell survival are regulated, in part, by the membrane type-1 matrix metalloproteinase (MT1-MMP), an MMP also involved in transducing NF-κB intracellular signaling pathways, we tested whether STAT3 regulation by MT1-MMP may also contribute to the expression balance of COX-2 in MSC. We demonstrate that STAT3 phosphorylation was triggered in MSC treated with the MT1-MMP inducer lectin Concanavalin-A (ConA), and that this phosphorylation was abrogated by the JAK2 inhibitor AG490. MT1-MMP gene silencing significantly inhibited ConA-induced STAT3 phosphorylation and this was correlated with reduced proMMP-2 activation and COX-2 expression. On the other hand, STAT3 gene silencing potentiated ConA-induced COX-2 expression, providing evidence for a new MT1-MMP/JAK/STAT3 signaling axis that may, in part, explain how MT1-MMP contributes to proinflammatory intracellular signaling. Given that MSC are avidly recruited within inflammatory microenvironments and within experimental vascularizing tumors, these mechanistic observations support a possible dual control of cell adaptation to inflammation by MT1-MMP and that may enable MSC to be active participants within inflamed tissues.

The lectin concanavalin-A signals MT1-MMP catalytic independent induction of COX-2 through an IKKgamma/NF-kappaB-dependent pathway

The lectin from Canavalia ensiformis (Concanavalin-A, ConA), one of the most abundant lectins known, enables one to mimic biological lectin/carbohydrate interactions that regulate extracellular matrix protein recognition. As such, ConA is known to induce membrane type-1 matrix metalloproteinase (MT1-MMP) which expression is increased in brain cancer. Given that MT1-MMP correlated to high expression of cyclooxygenase (COX)-2 in gliomas with increasing histological grade, we specifically assessed the early proinflammatory cellular signaling processes triggered by ConA in the regulation of COX-2. We found that treatment with ConA or direct overexpression of a recombinant MT1-MMP resulted in the induction of COX-2 expression. This increase in COX-2 was correlated with a concomitant decrease in phosphorylated AKT suggestive of cell death induction, and was independent of MT1-MMP's catalytic function. ConA- and MT1-MMP-mediated intracellular signaling of COX-2 was also confirmed in wild-type and in Nuclear Factor-kappaB (NF-kappaB) p65(-/-) mutant mouse embryonic fibroblasts (MEF), but was abrogated in NF-kappaB1 (p50)(-/-) and in I kappaB kinase (IKK) gamma(-/-) mutant MEF cells. Collectively, our results highlight an IKK/NF-kappaB-dependent pathway linking MT1-MMP-mediated intracellular signaling to the induction of COX-2. That signaling pathway could account for the inflammatory balance responsible for the therapy resistance phenotype of glioblastoma cells, and prompts for the design of new therapeutic strategies that target cell surface carbohydrate structures and MT1-MMP-mediated signaling. Concise summary Concanavalin-A (ConA) mimics biological lectin/carbohydrate interactions that regulate the proinflammatory phenotype of cancer cells through yet undefined signaling. Here we highlight an IKK/NF-kappaB-dependent pathway linking MT1-MMP-mediated intracellular signaling to the induction of cyclooxygenase-2, and that could be responsible for the therapy resistance phenotype of glioblastoma cells.

Prostaglandin E2 released from activated microglia enhances astrocyte proliferation in vitro

Microglial activation has been implicated in many astrogliosis-related pathological conditions including astroglioma; however, the detailed mechanism is not clear. In this study, we used primary enriched microglia and astrocyte cultures to determine the role of microglial prostaglandin E(2) (PGE(2)) in the proliferation of astrocytes. The proliferation of astrocytes was measured by BrdU incorporation. The level of PGE(2) was measured by ELISA method. Pharmacological inhibition or genetic ablation of COX-2 in microglia were also applied in this study. We found that proliferation of astrocytes increased following lipopolysaccharide (LPS) treatment in the presence of microglia. Furthermore, increased proliferation of astrocytes was observed in the presence of conditioned media from LPS-treated microglia. The potential involvement of microglial PGE(2) in enhanced astrocyte proliferation was suggested by the findings that PGE(2) production and COX-2 expression in microglia were increased by LPS treatment. In addition, activated microglia-induced increases in astrocyte proliferation were blocked by the PGE(2) antagonist AH6809, COX-2 selective inhibitor DuP-697 or by genetic knockout of microglial COX-2. These findings were further supported by the finding that addition of PGE(2) to the media significantly induced astrocyte proliferation. These results indicate that microglial PGE(2) plays an important role in astrocyte proliferation, identifying PGE(2) as a key neuroinflammatory molecule that triggers the pathological response related to uncontrollable astrocyte proliferation. These findings are important in elucidating the role of activated microglia and PGE(2) in astrocyte proliferation and in suggesting a potential avenue in the use of anti-inflammatory agents for the therapy of astroglioma.

A MT1-MMP/NF-kappaB signaling axis as a checkpoint controller of COX-2 expression in CD133+ U87 glioblastoma cells

Background

The CD133(+) stem cell population in recurrent gliomas is associated with clinical features such as therapy resistance, blood-brain barrier disruption and, hence, tumor infiltration. Screening of a large panel of glioma samples increasing histological grade demonstrated frequencies of CD133(+) cells which correlated with high expression of cyclooxygenase (COX)-2 and of membrane type-1 matrix metalloproteinase (MT1-MMP).

Methods

We used qRT-PCR and immunoblotting to examine the molecular interplay between MT1-MMP and COX-2 gene and protein expression in parental, CD133(+), and neurospheres U87 glioma cell cultures.

Results

We found that CD133, COX-2 and MT1-MMP expression were enhanced when glioma cells were cultured in neurosphere conditions. A CD133(+)-enriched U87 glioma cell population, isolated from parental U87 cells with magnetic cell sorting technology, also grew as neurospheres and showed enhanced COX-2 expression. MT1-MMP gene silencing antagonized COX-2 expression in neurospheres, while overexpression of recombinant MT1-MMP directly triggered COX-2 expression in U87 cells independent from MT1-MMP's catalytic function. COX-2 induction by MT1-MMP was also validated in wild-type and in NF-κB p65^-/- mutant mouse embryonic fibroblasts, but was abrogated in NF-κB1 (p50^-/-) mutant cells.

Conclusion

We provide evidence for enhanced COX-2 expression in CD133(+) glioma cells, and direct cell-based evidence of NF-κB-mediated COX-2 regulation by MT1-MMP. The biological significance of such checkpoint control may account for COX-2-dependent mechanisms of inflammatory balance responsible of therapy resistance phenotype of cancer stem cells.

Radiosensitization of human glioma cells by cyclooxygenase-2 (COX-2) inhibition: independent on COX-2 expression and dependent on the COX-2 inhibitor and sequence of administration

PURPOSE

Patients with a malignant glioma have a very poor prognosis. Cyclooxygenase-2 (COX-2) protein is regularly upregulated in gliomas and might be a potential therapeutic target. The effects of three selective COX-2 inhibitors were studied on three human glioma cell lines.

MATERIALS AND METHODS

The selective COX-2 inhibitors NS-398, Celecoxib and Meloxicam and three human glioma cell lines (D384, U251 and U87) were used. Cell growth was assessed by a proliferation assay, the interaction with radiation (0 - 6 Gy) was studied using the clonogenic assay and cell cycle distribution was determined by FACS (fluorescence-activated cell sorting) analysis.

RESULTS

All COX-2 inhibitors reduced proliferation of the glioma cell lines irrespective of their COX-2 expression level. Incubation with 200 microM NS-398 24 h before radiation enhanced radiation-induced cell death of D384 cells and 750 microM Meloxicam resulted in radiosensitization of D384 and U87 cells. No radiosensitization was observed with COX-2 inhibitor administration after radiotherapy. Treatment of D384 with NS-398 (200 microM) or Celecoxib (50 microM) and U87 with NS-398 (200 microM) after radiation resulted even in radioprotection.

CONCLUSIONS

Effectiveness of COX-2 inhibitors on cell proliferation and radio-enhancement was independent of COX-2 protein expression. The sequence of COX-2 inhibitor addition and irradiation is very important.

Radiosensitizing potential of the selective cyclooygenase-2 (COX-2) inhibitor meloxicam on human glioma cells

The COX-2 protein is frequently overexpressed in human malignant gliomas. This expression has been associated with their aggressive growth characteristics and poor prognosis for patients. Targeting the COX-2 pathway might improve glioma therapy. In this study, the effects of the selective COX-2 inhibitor meloxicam alone and in combination with irradiation were investigated on human glioma cells in vitro. A panel of three glioma cell lines (D384, U87 and U251) was used in the experiments from which U87 cells expressed constitutive COX-2. The response to meloxicam and irradiation (dose-range of 0-6 Gy) was determined by the clonogenic assay, cell proliferation was evaluated by growth analysis and cell cycle distribution by FACS. 24-72 h exposure to 250-750 microM meloxicam resulted in a time and dose dependent growth inhibition with an almost complete inhibition after 24 h for all cell lines. Exposure to 750 microM meloxicam for 24 h increased the fraction of cells in the radiosensitive G(2)/M cell cycle phase in D384 (18-27%) and U251 (17-41%) cells. 750 microM meloxicam resulted in radiosensitization of D384 (DMF:2.19) and U87 (DMF:1.25) cells, but not U251 cells (DMF:1.08). The selective COX-2 inhibitor meloxicam exerted COX-2 independent growth inhibition and radiosensitization of human glioma cells.

Therapeutic advances in the treatment of glioblastoma: rationale and potential role of targeted agents

Despite advances in standard therapy, including surgical resection followed by radiation and chemotherapy, the prognosis for patients with glioblastoma multiforme (GBM) remains poor. Unfortunately, most patients die within 2 years of diagnosis of their disease. Molecular abnormalities vary among individual patients and also within each tumor. Indeed, one of the distinguishing features of GBM is its marked genetic heterogeneity. Nonetheless, recent developments in the field of tumor biology have elucidated signaling pathways and genes involved in the development of GBM, and several novel agents that target these signaling pathways are being developed. As new details on the genetic characteristics of this disease become available, innovative treatment regimens, including a variety of traditional treatment modalities such as surgery, radiation, and cytotoxic chemotherapy, will be combined with newer targeted therapies. This review introduces these new targeted therapies in the context of current treatment options for patients with GBM. It is hoped that this combined approach will overcome the current limitations in the treatment of patients with GBM and result in a better prognosis for these patients.

COX-2 inhibitors act as radiosensitizer in tumor treatment

Since cyclooxygenase-2 (COX-2) is overexpressed in malignant tissues, the COX-2 mediated signaling pathway has been recognized as potential target for therapeutic intervention. In most human tumors, COX-2 overexpression has been associated with tumor aggressiveness and poor clinical outcome. In vitro studies show inhibition of cell proliferation by selective COX-2 inhibitors alone, and enhancement of the response to irradiation. In vivo experimental reports demonstrate enhanced tumor response and impediment of tumor neovascularization following radiotherapy combined with COX-2 inhibition. Clinical studies on the combination of irradiation with COX-2 inhibitors are emerging. Taken together, the perspective for the combined approach of radiotherapy with COX-2 inhibition yields clinical significance since preclinical data demonstrate selective COX-2 inhibitors to act as radiosensitizer in tumor treatment.

Expression of cyclooxygenase-2 and epidermal growth factor receptor in primary and recurrent glioblastoma multiforme

PURPOSE

To investigate the pattern and level of cyclooxygenase-2 (COX-2) expression in a series of high grade primary and recurrent glioblastoma multiforme (GBM) and correlation with time to recurrence and patients' survival following therapy. The relationship between COX-2 and epidermal growth factor receptor (EGFR) immunoreactivities was evaluated.

MATERIALS AND METHODS

Specimens of 14 primary and 14 recurrent GBMs (eight pairs) following surgery and full course radiation therapy were processed for immunostaining on COX-2 and EGFR. Tumor cell positivity was semi-quantitatively scored. COX-2 scores of the primary tumor and recurrence were correlated with the time to radiological tumor progression and patients' survival.

RESULTS

COX-2 positive tumor cells were disseminated throughout the tumor parenchyma. The intensity and pattern of COX-2 expression were heterogeneous, with predominant expression in areas surrounding tumor necrosis. Scoring of COX-2 positivity revealed values between 1 and 80% of the cells. Primary GBMs with COX-2 expression levels between 25% and 70% of the tumor cells showed a shorter time to radiological recurrence than GBMs with <10% COX-2 positive tumor cells (respectively, 219 +/- 50 and 382 +/- 77 days). No correlation was found between the COX-2 expression in the primary tumor and patients' survival (r (s) = -0.073) following therapy. No correlation was found either between COX-2 and EGFR immunoreactivity.

CONCLUSIONS

Immunohistochemical expression of COX-2 in GBM showed large variation. Hence, determination of COX-2 expression in tumor specimen for each individual might be relevant for selection of those patients, who could benefit from adjuvant therapy with selective COX-2 inhibitors.

The cyclooxygenase inhibitor indomethacin modulates gene expression and represses the extracellular matrix protein laminin γ1 in human glioblastoma cells

The induction of cyclooxygenase-2 (COX-2) expression is associated with more aggressive gliomas and poor survival. Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit COX activity and have antitumorigenic properties. In this report, our initial aim was to determine if indomethacin would alter gene expression as measured by suppression subtractive hybridization (SSH). Three up-regulated and four down-regulated genes by indomethacin treatment were identified. Laminin gamma1, an extracellular matrix molecule, was the most significantly repressed gene. The repression of laminin gamma1 by indomethacin was confirmed by Northern and Western blot analyses and occurred in a concentration- and time-dependent manner at the protein level. Among several NSAIDs tested, only sulindac sulfide and indomethacin suppressed laminin gamma1 protein expression, and this repression was observed in both COX-expressing and -deficient cell lines, suggesting that laminin gamma1 repression by COX inhibitors was independent of COX. Indomethacin, at a concentration that represses laminin gamma1, inhibited glioblastoma cell invasion that was partially restored with additional human laminin protein containing gamma1 chain. The repression of laminin gamma1 by NSAIDs may be related to attenuation of invasion of brain tumors. These findings are important in understanding the chemopreventive activity of some NSAIDs and could be relevant for designing therapeutic strategies against glioblastoma.