Mechanisms operative in the antitumor activity of temozolomide in glioblastoma multiforme

Development of immunotherapy for high-grade gliomas: Overcoming the immunosuppressive tumor microenvironment

The preclinical and clinical development of novel immunotherapies for the treatment of central nervous system (CNS) tumors is advancing at a rapid pace. High-grade gliomas (HGG) are aggressive tumors with poor prognoses in both adult and pediatric patients, and innovative and effective therapies are greatly needed. The use of cytotoxic chemotherapies has marginally improved survival in some HGG patient populations. Although several challenges exist for the successful development of immunotherapies for CNS tumors, recent insights into the genetic alterations that define the pathogenesis of HGG and their direct effects on the tumor microenvironment (TME) may allow for a more refined and targeted therapeutic approach. This review will focus on the TME in HGG, the genetic drivers frequently found in these tumors and their effect on the TME, the development of immunotherapy for HGG, and the practical challenges in clinical trials employing immunotherapy for HGG. Herein, we will discuss broadly the TME and immunotherapy development in HGG, with a specific focus on glioblastoma multiforme (GBM) as well as additional discussion in the context of the pediatric HGG diagnoses of diffuse midline glioma (DMG) and diffuse hemispheric glioma (DHG).

ITGA5 Predicts Dual-Drug Resistance to Temozolomide and Bevacizumab in Glioma

AIMS

Anti-angiotherapy (Bevacizumab) is currently regarded as a promising option for glioma patients who are resistant to temozolomide (TMZ) treatment. But ongoing clinical research failed to meet therapeutic expectations. This study aimed to explore the pivotal genetic feature responsible for TMZ and Bevacizumab resistance in glioma patients.

METHODS

We downloaded the transcriptomic and methylation data of glioma patients from The Cancer Genome Atlas (TCGA), Chinese Glioma Genome Atlas (CGGA), and Gene Expression Omnibus (GEO) databases and grouped these patients into resistant and non-resistant groups based on their clinical profiles. Differentially expressed genes and pathways were identified and exhibited with software in R platform. A TMZ-resistant cell line was constructed for validating the expression change of the candidate gene, ITGA5. An ITGA5-overexpressing cell line was also constructed to investigate its biological function using the CCK8 assay, Western blot, periodic acid-Schiff (PAS) staining, and transcriptional sequencing.

RESULTS

Change of the cell morphology and polarity was closely associated with TMZ mono-resistance and TMZ/Bevacizumab dual resistance in glioma patients. The expression level of ITGA5 was effective in determining drug resistance and the outcome of glioma patients, which is regulated by methylation on two distinct sites. ITGA5 was augmented in TMZ-resistant glioma cells, while overexpressing ITGA5 altered the cell-promoted TMZ resistance through enhancing vascular mimicry (VM) formation correspondingly.

CONCLUSIONS

Both the epigenetic and transcriptional levels of ITGA5 are effective in predicting TMZ and Bevacizumab resistance, indicating that ITGA5 may serve as a predictor of the treatment outcomes of glioma patients.

Myeloid-derived suppressor cells (MDSCs) in brain cancer: challenges and therapeutic strategies

The most fatal malignancy of the central nervous system (CNS) is glioblastoma. Brain cancer is a 'cold' tumor because of fewer immunoregulatory cells and more immunosuppressive cells. Due to the cold nature of brain cancers, conventional treatments which are used to manage glioma patients show little effectiveness. Glioma patients even showed resistance to immune checkpoint blockade (ICB) and no significant efficacy. It has been shown that myeloid-derived suppressor cells (MDSCs) account for approximately 30-50% of the tumor mass in glioma. This study aimed to review MDSC function in brain cancer, as well as possible treatments and related challenges. In brain cancer and glioma, several differences in the context of MDSCs have been reported, including disagreements about the MDSC subtype that has the most inhibitory function in the brain, or inhibitory function of regulatory B cells (Bregs). There are also serious challenges in treating glioma patients. In addition to the cold nature of glioma, there are reports of an increase in MDSCs following conventional chemotherapy treatments. As a result, targeting MDSCs in combination with other therapies, such as ICB, is essential, and recent studies with the combination therapy approach have shown promising therapeutic effects in brain cancer.

Antitumor Effects of 5-Aminolevulinic Acid on Human Malignant Glioblastoma Cells

5-Aminolevulinic acid (5-ALA) is a naturally occurring non-proteinogenic amino acid, which contributes to the diagnosis and therapeutic approaches of various cancers, including glioblastoma (GBM). In the present study, we aimed to investigate whether 5-ALA exerted cytotoxic effects on GBM cells. We assessed cell viability, apoptosis rate, mRNA expressions of various apoptosis-related genes, generation of reactive oxygen species (ROS), and migration ability of the human U-87 malignant GBM cell line (U87MG) treated with 5-ALA at different doses. The half-maximal inhibitory concentration of 5-ALA on U87MG cells was 500 μg/mL after 7 days; 5-ALA was not toxic for human optic cells and NIH-3T3 cells at this concentration. The application of 5-ALA led to a significant increase in apoptotic cells, enhancement of Bax and p53 expressions, reduction in Bcl-2 expression, and an increase in ROS generation. Furthermore, the application of 5-ALA increased the accumulation of U87MG cells in the SUB-G1 population, decreased the expression of cyclin D1, and reduced the migration ability of U87MG cells. Our data indicate the potential cytotoxic effects of 5-ALA on U87MG cells. Further studies are required to determine the spectrum of the antitumor activity of 5-ALA on GBM.

New Insights into the Multifaceted Role of Myeloid-Derived Suppressor Cells (MDSCs) in High-Grade Gliomas: From Metabolic Reprograming, Immunosuppression, and Therapeutic Resistance to Current Strategies for Targeting MDSCs

Cancer cells “hijack” host immune cells to promote growth, survival, and metastasis. The immune microenvironment of high-grade gliomas (HGG) is a complex and heterogeneous system, consisting of diverse cell types such as microglia, bone marrow-derived macrophages (BMDMs), myeloid-derived suppressor cells (MDSCs), dendritic cells, natural killer (NK) cells, and T-cells. Of these, MDSCs are one of the major tumor-infiltrating immune cells and are correlated not only with overall worse prognosis but also poor clinical outcomes. Upon entry from the bone marrow into the peripheral blood, spleen, as well as in tumor microenvironment (TME) in HGG patients, MDSCs deploy an array of mechanisms to perform their immune and non-immune suppressive functions. Here, we highlight the origin, function, and characterization of MDSCs and how they are recruited and metabolically reprogrammed in HGG. Furthermore, we discuss the mechanisms by which MDSCs contribute to immunosuppression and resistance to current therapies. Finally, we conclude by summarizing the emerging approaches for targeting MDSCs alone as a monotherapy or in combination with other standard-of-care therapies to improve the current treatment of high-grade glioma patients.

The Many Facets of Therapy Resistance and Tumor Recurrence in Glioblastoma

Glioblastoma (GBM) is the most lethal type of primary brain cancer. Standard care using chemo- and radio-therapy modestly increases the overall survival of patients; however, recurrence is inevitable, due to treatment resistance and lack of response to targeted therapies. GBM therapy resistance has been attributed to several extrinsic and intrinsic factors which affect the dynamics of tumor evolution and physiology thus creating clinical challenges. Tumor-intrinsic factors such as tumor heterogeneity, hypermutation, altered metabolomics and oncologically activated alternative splicing pathways change the tumor landscape to facilitate therapy failure and tumor progression. Moreover, tumor-extrinsic factors such as hypoxia and an immune-suppressive tumor microenvironment (TME) are the chief causes of immunotherapy failure in GBM. Amid the success of immunotherapy in other cancers, GBM has occurred as a model of resistance, thus focusing current efforts on not only alleviating the immunotolerance but also evading the escape mechanisms of tumor cells to therapy, caused by inter- and intra-tumoral heterogeneity. Here we review the various mechanisms of therapy resistance in GBM, caused by the continuously evolving tumor dynamics as well as the complex TME, which cumulatively contribute to GBM malignancy and therapy failure; in an attempt to understand and identify effective therapies for recurrent GBM.

Molecular biological investigation of temozolomide and KC7F2 combination in U87MG glioma cell line

Glioblastom Multiforme (GBM) is the most invasive and malignant member of the IV grade of the subclass Astrocytoma according to the last assessment of the 2016 WHO report. Due to the resistance to treatment and weak response, as well as the topographical structure of the blood brain barrier, the treatment is also difficult due to the severe clinical manifestation, and new treatment methods and new therapeutic agents are needed. Temozolomide (TMZ) is widely used in the treatment of glioblastoma and is considered as the primary treatment modality. TMZ, a member of the class of cognitive agents, is currently considered the most effective drug because it can easily pass through the blood brain barrier. Glucose metabolism is a complex energy producing machine that, a glucose molecule produces 38 molecules of ATP after full glycolytic catabolism. According to Otto Warburg's numerous studies cancer cells perform the first glycolytic step without entering the mitochondrial step. These cells produce lactic acid and make the micro-media more acidic even in aerobic conditions. This phenomenon is attributed to the Warburg hypothesis and either as aerobic glycolysis. Although glycolysis enzymes are the primary actors of this phenotypic expression, some genetic and epigenetic factors are no exception. We experimentally used KC7F2 active ingredient to target cancer metabolism. In our study, we evaluated cancer metabolism in combination with the effect of TMZ chemotherapeutic agent, examining the effect of two different agents separately and in combination to observe the effects of cancer cell proliferation, survival, apoptosis and expression of metabolism genes on expression. We observed that the combined effect of reduced the effective dose of the TMZ alkylating agent and that the effect was increased and the effect of the combined teraphy is assessed from a metabolic point of view and that it suppresses aerobic glycolysis.

Autocrine CXCL8-dependent invasiveness triggers modulation of actin cytoskeletal network and cell dynamics

Glioblastoma (GB) is the most representative form of primary malignant brain tumour. Several studies indicated a pleiotropic role of CXCL8 in cancer due to its ability to modulate the tumour microenvironment, growth and aggressiveness of tumour cell. Previous studies indicated that CXCL8 by its receptors (CXCR1 and CXCR2) induced activation of the PI3K/p-Akt pathway, a crucial event in the regulation of cytoskeleton rearrangement and cell mobilization. Human GB primary cell culture and U-87MG cell line were used to study the effects of CXCR1 and CXCR2 blockage, by a dual allosteric antagonist, on cell migration and cytoskeletal dynamics. The data obtained point towards a specific effect of autocrine CXCL8 signalling on GB cell invasiveness by the activation of pathways involved in cell migration and cytoskeletal dynamics, such as PI3K/p-Akt/p-FAK, p-cortactin, RhoA, Cdc42, Acetylated α-tubulin and MMP2. All the data obtained support the concept that autocrine CXCL8 signalling plays a key role in the activation of an aggressive phenotype in primary glioblastoma cells and U-87MG cell line. These results provide new insights about the potential of a pharmacological approach targeting CXCR1/CXCR2 pathways to decrease migration and invasion of GB cells in the brain parenchyma, one of the principal mechanisms of recurrence.

Temozolomide and Other Alkylating Agents in Glioblastoma Therapy

The alkylating agent temozolomide (TMZ) together with maximal safe bulk resection and focal radiotherapy comprises the standard treatment for glioblastoma (GB), a particularly aggressive and lethal primary brain tumor. GB affects 3.2 in 100,000 people who have an average survival time of around 14 months after presentation. Several key aspects make GB a difficult to treat disease, primarily including the high resistance of tumor cells to cell death-inducing substances or radiation and the combination of the highly invasive nature of the malignancy, i.e., treatment must affect the whole brain, and the protection from drugs of the tumor bulk—or at least of the invading cells—by the blood brain barrier (BBB). TMZ crosses the BBB, but—unlike classic chemotherapeutics—does not induce DNA damage or misalignment of segregating chromosomes directly. It has been described as a DNA alkylating agent, which leads to base mismatches that initiate futile DNA repair cycles; eventually, DNA strand breaks, which in turn induces cell death. However, while much is assumed about the function of TMZ and its mode of action, primary data are actually scarce and often contradictory. To improve GB treatment further, we need to fully understand what TMZ does to the tumor cells and their microenvironment. This is of particular importance, as novel therapeutic approaches are almost always clinically assessed in the presence of standard treatment, i.e., in the presence of TMZ. Therefore, potential pharmacological interactions between TMZ and novel drugs might occur with unforeseeable consequences.

OKN-007 Increases temozolomide (TMZ) Sensitivity and Suppresses TMZ-Resistant Glioblastoma (GBM) Tumor Growth

Treatment of glioblastoma (GBM) remains a challenge using conventional chemotherapy, such as temozolomide (TMZ), and is often ineffective as a result of drug resistance. We have assessed a novel nitrone-based agent, OKN-007, and found it to be effective in decreasing tumor volumes and increasing survival in orthotopic GBM xenografts by decreasing cell proliferation and angiogenesis and increasing apoptosis. In this study, we assessed combining OKN-007 with TMZ in vivo in a human G55 GBM orthotopic xenograft model and in vitro in TMZ-resistant and TMZ-sensitive human GBM cell lines. For the in vivo studies, magnetic resonance imaging was used to assess tumor growth and vascular alterations. Percent animal survival was also determined. For the in vitro studies, cell growth, IC50 values, RNA-seq, RT-PCR, and ELISA were used to assess growth inhibition, possible mechanism-of actions (MOAs) associated with combined OKN-007 + TMZ versus TMZ alone, and gene and protein expression levels, respectively. Microarray analysis of OKN-007-treated rat F98 glioma tumors was also carried out to determine possible MOAs of OKN-007 in glioma-bearing animals either treated or not treated with OKN-007. OKN-007 seems to elicit its effect on GBM tumors via inhibition of tumorigenic TGF-β1, which affects the extracellular matrix. When combined with TMZ, OKN-007 significantly increases percent survival, decreases tumor volumes, and normalizes tumor blood vasculature in vivo compared to untreated tumors and seems to affect TMZ-resistant GBM cells possibly via IDO-1, SUMO2, and PFN1 in vitro. Combined OKN-007 + TMZ may be a potentially potent treatment strategy for GBM patients.

A New Epigenetic Mechanism of Temozolomide Action in Glioma Cells

Temozolomide (TMZ) is an oral alkylating chemotherapeutic agent that prolongs the survival of patients with glioblastoma (GBM). Despite that high TMZ potential, progression of disease and recurrence are still observed. Therefore a better understanding of the mechanism of action of this drug is necessary and may allow more durable benefit from its anti-glioma properties. Using nucleotide post-labelling method and separation on thin-layer chromatography we measured of global changes of 5-methylcytosine (m5C) in DNA of glioma cells treated with TMZ. Although m5C is not a product of TMZ methylation reaction of DNA, we analysed the effects of the drug action on different glioma cell lines through global changes at the level of the DNA main epigenetic mark. The first effect of TMZ action we observed is DNA hypermethylation followed by global demethylation. Therefore an increase of DNA methylation and down regulation of some genes expression can be ascribed to activation of DNA methyltransferases (DNMTs). On the other hand hypomethylation is induced by oxidative stress and causes uncontrolled expression of pathologic protein genes. The results of brain tumours treatment with TMZ suggest the new mechanism of modulation epigenetic marker in cancer cells. A high TMZ concentration induced a significant increase of m5C content in DNA in the short time, but a low TMZ concentration at longer time hypomethylation is observed for whole range of TMZ concentrations. Therefore TMZ administration with low doses of the drug and short time should be considered as optimal therapy.

APE1/REF-1 down-regulation enhances the cytotoxic effects of temozolomide in a resistant glioblastoma cell line

Temozolomide (TMZ) is widely used for patients with glioblastoma (GBM); however, tumor cells frequently exhibit drug-resistance. Base excision repair (BER) has been identified as a possible mediator of TMZ resistance, and an attractive approach to sensitizing cells to chemotherapy. Human apurinic/apyrimidinic endonuclease/redox factor-1 (APE1) is an essential enzyme with a role in the BER pathway by repairing abasic sites, and it also acts as a reduction factor, maintaining transcription factors in an active reduced state. Thus, we aimed to investigate whether the down-regulation of APE1 expression by siRNA can interfere with the resistance of GBM to TMZ, being evaluated by several cellular and molecular parameters. We demonstrated that APE1 knockdown associated with TMZ treatment efficiently reduced cell proliferation and clonogenic survival of resistant cells (T98G), which appears to be a consequence of increased DNA damage, S-phase arrest, and H2AX phosphorylation, resulting in apoptosis induction. On the contrary, for those assays, the sensitization effects of APE1 silencing plus TMZ treatment did not occur in the TMZ-sensitive cell line (U87MG). Interestingly, TMZ-treatment and APE1 knockdown significantly reduced cell invasion in both cell lines, but TMZ alone did not reduce the invasion capacity of U87MG cells, as observed for T98G. We also found that VEGF expression was down-regulated by TMZ treatment in T98G cells, regardless of APE1 knockdown, but U87MG showed a different response, since APE1 silencing counteracted VEGF induction promoted by TMZ, suggesting that the APE1-redox function may play an indirect role, depending on the cell line. The present results support the contribution of BER in the GBM resistance to TMZ, with a greater effect in TMZ-resistant, compared with TMZ-sensitive cells, emphasizing that APE1 can be a promising target for modifying TMZ tolerance. Furthermore, genetic characteristics of tumor cells should be considered as critical information to select an appropriate therapeutic strategy.

Effect of temozolomide on livin and caspase-3 in U251 glioma stem cells

The aim of the present study was to analyze the effect of temozolomide (TMZ) on the antiapoptotic gene livin and the associated gene caspase-3. Cancer stem cells were isolated from U251 glioblastoma cells using immunomagnetic beads. The glioma cells and glioma stem cells were transfected with livin or small hairpin RNA (shRNA) against livin using lentiviral vectors. Quantitative PCR, flow cytometry and a Cell Counting kit-8 assay were used to detect the expression of livin and caspase-3, analyze the cell cycle and investigate cell proliferation, respectively, following treatment with various concentrations of TMZ (0, 25, 50, 100, 200 and 400 μmol/l) for different periods of time (24, 48 and 72 h). The expression levels of livin and caspase-3 in the U251 stem cells were significantly higher than those in the U251 cells (P<0.01). At the same intervention time, the expression levels of livin decreased and those of caspase-3 increased as the concentration of TMZ increased (P<0.05). The expression levels of livin and caspase-3 in the U251 cells were lower than those in the U251 stem cells with the same intervention time and concentration of TMZ (P<0.05). The cell cycle was arrested in the G2/M phase in the U251 cells following TMZ intervention; the proportion of cells in the G2/M phase increased as the concentration of TMZ increased (P<0.05). The U251 stem cells were arrested in the S phase following treatment with TMZ; the proportion of cells in the S phase increased as the concentration of TMZ increased (P<0.05). In conclusion, the expression levels of livin and caspase-3 were effectively inhibited and increased, respectively, in all cell models following treatment with TMZ. TMZ is able to arrest the cell cycle and enhance cell apoptosis. U251 stem cells are less vulnerable than U251 cells to TMZ.

Bortezomib overcomes MGMT-related resistance of glioblastoma cell lines to temozolomide in a schedule-dependent manner

Development of drug resistance after standard chemotherapy for glioblastoma multiforme (GBM) with temozolomide (TMZ) is associated with poor prognosis of GBM patients and is at least partially mediated by a direct DNA repair pathway involving O6-methylguanine methyltransferase (MGMT). This enzyme is under post-translational control by a multisubunit proteolytic cellular machinery, the 26S proteasome. Inhibition of the proteasome by bortezomib (BZ), a boronic acid dipeptide already in clinical use for the treatment of myeloma, has been demonstrated to induce growth arrest and apoptosis in GBM cells. In this study we investigated the effect of sequential treatment with BZ and TMZ on cell proliferation-viability and apoptosis of the human T98G and U87 GBM cell lines. We also tested for an effect of treatment on MGMT expression and important upstream regulators of the latter, including nuclear factor kappa B (NFκB), p44/42 mitogen-activated protein kinase (MAPK), p53, signal transducer and activator of transcription 3 (STAT3) and hypoxia-inducible factor 1α (HIF-1α). The sequence of drug administration for maximal cytotoxicity favored BZ prior to TMZ in T98G cells while the opposite was the case for U87 cells. Maximal efficacy was associated with downregulation of MGMT, reduced IκBα-mediated proteasome-dependent nuclear accumulation of NFκB, attenuation of p44/42 MAPK, AKT and STAT3 activation, and stabilization of p53 and inactive HIF-1α. Collectively, these results suggest that proteasome inhibition by BZ overcomes MGMT-mediated GBM chemoresistance, with scheduling of administration being critical for obtaining the maximal tumoricidal effect of combination with TMZ.

Treating brain tumor-initiating cells using a combination of myxoma virus and rapamycin

BACKGROUND

Intratumoral heterogeneity in glioblastoma multiforme (GBM) poses a significant barrier to therapy in certain subpopulation such as the tumor-initiating cell population, being shown to be refractory to conventional therapies. Oncolytic virotherapy has the potential to target multiple compartments within the tumor and thus circumvent some of the barriers facing conventional therapies. In this study, we investigate the oncolytic potential of myxoma virus (MYXV) alone and in combination with rapamycin in vitro and in vivo using human brain tumor-initiating cells (BTICs).

METHODS

We cultured fresh GBM specimens as neurospheres and assayed their growth characteristics in vivo. We then tested the susceptibility of BTICs to MYXV infection with or without rapamycin in vitro and assessed viral biodistribution/survival in vivo in orthotopic xenografts.

RESULTS

The cultured neurospheres were found to retain stem cell markers in vivo, and they closely resembled human infiltrative GBM. In this study we determined that (i) all patient-derived BTICs tested, including those resistant to temozolomide, were susceptible to MYXV replication and killing in vitro; (ii) MYXV replicated within BTICs in vivo, and intratumoral administration of MYXV significantly prolonged survival of BTIC-bearing mice; (iii) combination therapy with MYXV and rapamycin improved antitumor activity, even in mice bearing "advanced" BTIC tumors; (iv) MYXV treatment decreased expression of stem cell markers in vitro and in vivo.

CONCLUSIONS

Our study suggests that MYXV in combination with rapamycin infects and kills both the BTICs and the differentiated compartments of GBM and may be an effective treatment even in TMZ-resistant patients.

Neural precursor cells induce cell death of high-grade astrocytomas through stimulation of TRPV1

Primary astrocytomas of World Health Organization grade 3 and grade 4 (HG-astrocytomas) are preponderant among adults and are almost invariably fatal despite multimodal therapy. Here, we show that the juvenile brain has an endogenous defense mechanism against HG-astrocytomas. Neural precursor cells (NPCs) migrate to HG-astrocytomas, reduce glioma expansion and prolong survival by releasing a group of fatty acid ethanolamides that have agonistic activity on the vanilloid receptor (transient receptor potential vanilloid subfamily member-1; TRPV1). TRPV1 expression is higher in HG-astrocytomas than in tumor-free brain and TRPV1 stimulation triggers tumor cell death via the activating transcription factor-3 (ATF3) controlled branch of the ER stress pathway. The anti-tumorigenic response of NPCs is lost with aging. NPC-mediated tumor suppression can be mimicked in the adult brain by systemic administration of the synthetic vanilloid Arvanil, suggesting that TRPV1 agonists hold potential as new HG-astrocytoma therapeutics.

Temozolomide and other potential agents for the treatment of glioblastoma multiforme

This article provides historical and recent perspectives related to the use of temozolomide for the treatment of glioblastoma multiforme. Temozolomide has quickly become part of the standard of care for the modern treatment of stage IV glioblastoma multiforme since its approval in 2005. Yet despite its improvements from previous therapies, median survival remains approximately 15 months, with a 2-year survival rate of 8% to 26%. The mechanism of action of this chemotherapeutic agent, conferred advantages and limitations, treatment resistance and rescue, and potential targets of future research are discussed.

The impact of bevacizumab on temozolomide concentrations in intracranial U87 gliomas

PURPOSE

An important question in the sequencing of anti-cancer therapies in patients with glioblastoma (GBM) is whether concurrent anti-angiogenesis therapies improve or impair brain concentrations of concomitantly administered cytotoxic therapies. The purpose of this study is to assess the intratumoral disposition of temozolomide (TMZ) via microdialysis before and after bevacizumab in an intracranial GBM xenograft model.

METHODS

Microdialysis probes were placed within tumor and contralateral brain in athymic rats bearing U87 intracerebral gliomas. TMZ (50 mg/kg oral) was administered 10 days thereafter. Extracellular fluid (ECF) was collected for 6 h. BEV was administered (10 mg/kg IV), and TMZ was re-dosed (50 mg/kg oral) 36 h thereafter with additional ECF collection. All ECF samples were assessed for TMZ concentration with liquid chromatography-tandem mass spectrometry.

RESULTS

Tumor TMZ mean area under the concentration-time curve (AUC(0-∞)) was 3.35 μg h/mL pre-BEV. Post-BEV, tumor mean TMZ AUC(0-∞) was 3.98 μg h/mL. In non-tumor brain, mean TMZ AUC(0-∞) pre-BEV was 3.22 μg h/mL and post-BEV was 3.34 μg h/mL.

CONCLUSIONS

There were no statistically significant changes in TMZ pharmacokinetics before or after BEV in the athymic rat U87 intracranial glioma model. BEV and TMZ are being investigated as a combination therapy in several ongoing studies for patients with glioma. These data reassuringly suggest that BEV does not significantly change the ECF tumor concentrations of TMZ in either tumor-bearing or normal brain when dosed 36 h prior to TMZ.

Cediranib enhances control of wild type EGFR and EGFRvIII-expressing gliomas through potentiating temozolomide, but not through radiosensitization: implications for the clinic

Glioblastomas (GBM) frequently overexpress the epidermal growth factor receptor (wtEGFR) or its mutant, EGFRvIII, contributing to chemo- and radioresistance. The current standard of care is surgery followed by radiation therapy with concurrent temozolomide (TMZ) followed by adjuvant TMZ. New treatment strategies for GBM include blockade of EGFR signaling and angiogenesis. Cediranib is a highly potent receptor tyrosine kinase inhibitor that inhibits all three VEGF receptors. This study investigated the radiosensitizing potential of cediranib in combination with TMZ in U87 GBM xenografts expressing wtEGFR or EGFRvIII. U87 GBM cells stably transfected with either wtEGFR or EGFRvIII were injected into the hind limbs of nude mice. Cediranib was dosed at 3 mg/kg daily five times a week orally for 2 weeks. TMZ was dosed at 10 mg/kg once only on day 0. Radiotherapy (RT) consisted of 3 fractions of 5 Gy (days 0-2). Cediranib did not radiosensitize either tumor type; however, cediranib did enhance the effectiveness of TMZ in both transfectants. Our results suggest that combining cediranib with temozolomide in the clinic will lead to improved tumor control.

Temozolomide modifies caveolin-1 expression in experimental malignant gliomas in vitro and in vivo

BACKGROUND

Caveolin-1 is a protein that displays promotive versus preventive roles in cancer progression according to circumstances. Temozolomide (TMZ) is the standard chemotherapeutic to treat glioma patients. The present work aims to characterizeTMZ-induced effects on caveolin-1 expression in glioma cells.

METHODS

Human astroglioma (U373 and T98G) and oligodendroglioma (Hs683) cell lines were used in vitro as well as in vivo orthotopic xenografts (Hs683 and U373) into the brains of immunocompromisedmice. In vitro TMZ-induced effects on protein expression and cellular localization were determined by Western blot analysis and on the actin cytoskeleton organization by means of immunofluorescence approaches. In vivo TMZ-induced effects in caveolin-1 expression in human glioma xenografts were monitored by means of immunohistochemistry.

RESULTS

TMZ modified caveolin-1 expression and localization in vitro and in vivo after an administration schedule that slightly, if at all, impaired cell growth characteristics in vitro. Caveolin-1 by itself (at a 100-ng/ml concentration) was able to significantly reduce invasiveness (Boyden chambers) of the three human glioma cell lines. The TMZ-inducedmodification in caveolin-1 expression in flotation/raft compartments was paralleled by altered Cyr61 and β(1) integrin expression, two elements that have already been reported to collaborate with caveolin-1 in regulating glioma cell biology, and all these features led to profound reorganization of the actin cytoskeleton. An experimental Src kinase inhibitor, AZD0530, almost completely antagonized the TMZ-induced modulation in caveolin-1 expression.

CONCLUSION

TMZ modifies caveolin-1 expression in vitro and in vivo in glioma cells, a feature that directly affects glioma cell migration properties.

Anti-angiogenic therapy: adapting strategies to overcome resistant tumors

Healthy cells, as well as benign and malignant tumors, depend upon the body's blood supply to bring in oxygen and nutrients and carry away waste products. Using this property against tumors, anti-angiogenic therapy targets the tumor vasculature with the aim of starving the tumor, and has demonstrated exceptional clinical efficacy against a number of tumors. This review discusses the current state of knowledge regarding anti-angiogenic therapies presently available to patients, and garners from both preclinical and clinical literature the benefits and side effects associated with anti-angiogenic therapies, the unfortunate mechanisms of acquired resistance to these novel therapeutics, and highlights promising next generation anti-angiogenics that may overcome the limitations encountered with first generation therapies.

Trans-sodium crocetinate enhancing survival and glioma response on magnetic resonance imaging to radiation and temozolomide

Object

Glioblastoma (GB) tumors typically exhibit regions of hypoxia. Hypoxic areas within the tumor can make tumor cells less sensitive to chemotherapy and radiation therapy. Trans-sodium crocetinate (TSC) has been shown to transiently increase oxygen to hypoxic brain tumors. The authors examined whether this improvement in intratumor oxygenation translates to a therapeutic advantage when delivering standard adjuvant treatment to GBs.

Methods

The authors used C6 glioma cells to create a hypoxic GB model. The C6 glioma cells were stereotactically injected into the rat brain to create a tumor. Fifteen days later, MR imaging was used to confirm the presence of a glioma. The animals were randomly assigned to 1 of 3 groups: 1) temozolomide alone (350 mg/m2/day for 5 days); 2) temozolomide and radiation therapy (8 Gy); or 3) TSC (100 μg/kg for 5 days), temozolomide, and radiation therapy. Animals were followed through survival studies, and tumor response was assessed on serial MR images obtained at 15-day intervals during a 2-month period.

Results

Mean survival (± SEM) of the temozolomide-alone and the temozolomide/radiotherapy groups was 23.2 ± 0.9 and 29.4 ± 4.4 days, respectively. Mean survival in the TSC/temozolomide/radiotherapy group was 39.8 ± 6 days, a statistically significant improvement compared with either of the other groups (p < 0.05).

Although tumor size was statistically equivalent in all groups at the time of treatment initiation, the addition of TSC to temozolomide and radiotherapy resulted in a statistically significant reduction in the MR imaging–documented mean tumor size at 30 days after tumor implantation. The mean tumor size in the TSC/temozolomide/radiotherapy group was 18.9 ± 6.6 mm2 compared with 42.1 ± 2.7 mm2 in the temozolomide-alone group (p = 0.047) and 35.8 ± 5.1 mm2 in the temozolomide/radiation group (p = 0.004).

Conclusions

In a hypoxic GB model, TSC improves the radiological and clinical effectiveness of temozolomide and radiation therapy. Further investigation of this oxygen diffusion enhancer as a radiosensitizer for hypoxic brain tumors seems warranted.

Long-term temozolomide treatment induces marked amino metabolism modifications and an increase in TMZ sensitivity in Hs683 oligodendroglioma cells

Gliomas account for more than 50% of all primary brain tumors. The worst prognosis is associated with gliomas of astrocytic origin, whereas gliomas with an oligodendroglial origin offer higher sensitivity to chemotherapy, especially when oligodendroglioma cells display 1p19q deletions. Temozolomide (TMZ) provides therapeutic benefits and is commonly used with radiotherapy in highly malignant astrocytic tumors, including glioblastomas. The actual benefits of TMZ during long-term treatment in oligodendroglioma patients have not yet been clearly defined. In this study, we have investigated the effects of such a long-term TMZ treatment in the unique Hs683 oligodendroglioma model. We have observed increased TMZ sensitivity of Hs683 orthotopic tumors that were previously treated in vitro with months of progressive exposure to increasing TMZ concentrations before being xenografted into the brains of immunocompromised mice. Whole-genome and proteomic analyses have revealed that this increased TMZ sensitivity of Hs683 oligodendroglioma cells previously treated for long periods with TMZ can be explained, at least partly, by a TMZ-induced p38-dependant dormancy state, which in turn resulted in changes in amino acid metabolism balance, in growth delay, and in a decrease in Hs683 oligodendroglioma cell-invasive properties. Thus, long-term TMZ treatment seems beneficial in this Hs683 oligodendroglioma model, which revealed itself unable to develop resistance against TMZ.

Combining bevacizumab with temozolomide increases the antitumor efficacy of temozolomide in a human glioblastoma orthotopic xenograft model

PURPOSE

The aims of the present work were to investigate the in vitro and in vivo antiangiogenic effects of chronic temozolomide treatment on various glioma models and to demonstrate whether bevacizumab (Avastin) increased the therapeutic benefits contributed by temozolomide in glioma.

EXPERIMENTAL DESIGN

The expression levels of various antiangiogenic factors in four glioma cell lines were evaluated after chronic in vitro treatment with temozolomide by Western blot. Proliferation and migration assays were performed on human endothelial cells incubated with supernatants of glioma cells treated with and without temozolomide. Orthotopic glioma models were used to evaluate the antiangiogenic effects of temozolomide in vivo and the therapeutic benefits of different temozolomide treatment schedules used alone or in combination with bevacizumab.

RESULTS

Temozolomide, a proautophagic and proapoptotic drug, decreased the expression levels of HIF-1alpha, ID-1, ID-2, and cMyc in the glioma models investigated, all of which playing major roles in angiogenesis and the switch to hypoxic metabolism. These changes could be, at least partly, responsible for the impairment of angiogenesis observed in vitro and in vivo. Moreover, combining bevacizumab with temozolomide increased the survival of glioma-bearing mice in comparison to each compound administered alone.

CONCLUSIONS

In addition to the numerous mechanisms of action already identified for temozolomide, we report here that it also exerts antitumor effects by impairing angiogenic processes. We further emphasize that bevacizumab, which is an antiangiogenic drug with a different mechanism of action, could be useful in combination with temozolomide to increase the latter's therapeutic benefit in glioma patients.

Use of FDA approved methamphetamine to allow adjunctive use of methylnaltrexone to mediate core anti-growth factor signaling effects in glioblastoma

Methylnaltrexone (MNTX) was recently FDA approved to treat opiate induced constipation. It happens to also indirectly reduce Src activity. Src is a 54 kDa tyrosine kinase, crucial in signaling of, and link between, vascular endothelial growth factor (VEGF), and epidermal growth factor (EGF). Glioblastomas use both EGF and VEGF signaling to enhance growth and neo-angiogenesis. Stem cell sub-fractions of glioblastomas are enriched for high VEGF synthesizing cells so this is a particularly valuable adjunctive target during cytotoxic treatment with drugs like temozolomide. MNTX does not cross the blood-brain barrier (BBB). Methamphetamine (MA) temporarily opens the BBB and therefore may allow methylnaltrexone entry into glioblastoma tissue. MA is FDA approved, marketed to treat attention problems in children. MA-MNTX combination should be tested as glioblastoma treatment adjunct. Temozolomide CSF levels are 10-20% of blood levels. Thus MA may also allow greater brain tissue temozolomide levels yet with lower systemic exposure.

Differential sensitivity of human glioblastoma LN18 (PTEN-positive) and A172 (PTEN-negative) cells to Taxol for apoptosis

Glioblastoma is the most malignant brain tumor in humans and an average survival of glioblastoma patients hardly exceeds 12 months. Taxol is a plant-derived anti-cancer agent, which has been used in the treatments of many solid tumors. Deletion or mutation of phosphatase and tension homolog located on chromosome ten (PTEN) occurs in more than 80% of glioblastomas. We examined the sensitivity of human glioblastoma LN18 (PTEN-positive) and A172 (PTEN-negative) cells to Taxol for induction of apoptosis. Wright staining showed morphological features of apoptosis after treatment with different doses of Taxol for 24 h. Significant amount of apoptosis occurred in LN18 cells after treatment with 25 nM Taxol, while in A172 cells only after treatment with 50 nM Taxol. Western blotting with an antibody that could specifically detect activation or phosphorylation of Akt (p-Akt) did not show any p-Akt in LN18 cells but an increase in p-Akt in A172 cells. Activation of Akt in A172 cells could be reversed by pre-treatment of the cells with the phosphatidylinositol-3-kinase (PI3K) inhibitor LY294002, indicating involvement of PI3K activity in this process. Apoptosis occurred with an increase in Bax:Bcl-2 and mitochondrial release of cytochrome c into the cytosol leading to activation of mitochondria-dependent caspase cascade. Taxol did not cause upregulation of vascular endothelial growth factor (VEGF), a key mediator of angiogenesis, in LN18 cells but substantial upregulation of VEGF in A172 cells. After treatment with Taxol, increases in p-Akt and VEGF could maintain survival and angiogenesis, respectively, in PTEN-negative glioblastoma. As a single chemotherapy, Taxol might be more efficacious in PTEN-positive glioblastoma than in PTEN-negative glioblastoma. Thus, our study showed differential sensitivity of PTEN-positive and PTEN-negative glioblastoma cells to Taxol.