Molecular neuro-oncology and the development of targeted therapeutic strategies for brain tumors Part 4: p53 signaling pathway

Differential transcriptomic analysis of crayfish (Procambarus clarkii) from a rice coculture system challenged by Vibrio parahaemolyticus

Rice-crayfish (Procambarus clarkii) coculture is an effective farming mode and has been promoted in various regions of China. However, infection in crayfish can be a significant economic drain. We found crayfish infected with Vibrio parahemolyticus (VP), and to understand the molecular mechanisms of the immune responses of crayfish to VP infection, Illumina sequencing was employed to identify changes in the mRNA of hepatopancreatic tissue. A total of 47.30 and 43.01million high-quality transcriptome reads were generated from the hepatopancreatic samples of the experimental group (EG) and control group (CG), respectively. We found 5559 genes were significantly differentially expressed, including 2521 up-regulated genes (45.35%) and 3038 down-regulated genes (54.65%). These genes were enriched in 126 GO terms and 76 KEGG pathways (P ≤ 0.05), including the MAPK and PI3K-Akt signaling pathways and cell adhesion molecules, with 23 up-regulated genes and 3 down-regulated genes related to immune responses in the EG relative to the CG. Histopathological analysis revealed that the epithelial cells of the hepatopancreatic tubules in the EG were severely atrophic, necrotic, and exfoliated, resulting in thin and collapsing hepatopancreatic tubules. The expression patterns of 8 differentially expressed genes involved in immune responses were validated by quantitative real-time RT-PCR. These results provide a valuable basis for the immune responses of crayfish to acute hepatopancreatic necrosis disease at transcriptome level.

Molecularly targeted therapies for malignant gliomas: advances and challenges

The identification of molecular markers associated with tumor but not with normal tissue has allowed the development of highly specific, targeted therapies for the treatment of cancer. Over the last several years, tremendous advances in our understanding of the genetic and molecular changes involved in the progression of malignant gliomas have triggered a large effort in the development of targeted therapies to treat these tumors. However, to date only a modest clinical benefit, limited to subsets of patients, has been demonstrated. Furthermore, despite a high degree of target selectivity, the use of targeted therapies often has systemic toxicity. The reasons behind this limited clinical success are complex and include the intricacy of the signaling pathways in gliomas and the heterogeneity of the disease process, compounded by existing limitations in assessing the efficacy of these novel agents when conventional end points and clinical trial designs are utilized. However, despite these difficulties targeted therapies remain a very attractive avenue of treatment for malignant gliomas. Three basic approaches are needed to overcome the hurdles associated with targeted therapies: first, further development of genetic profiling techniques will help to better determine the genetic changes and molecular pathways involved in gliomas and will potentially allow the design of individualized therapies based on the genetic and molecular signature of each tumor. Second, there is a need for the development of better combination strategies (complementary targeted agents or targeted agents with chemotherapy drugs) directed towards disease heterogeneity. Third, we need to optimize the design of preclinical and clinical trials to obtain the maximum amount of information in the shortest period of time.

Effects of Gamma Knife surgery on C6 glioma in combination with adenoviral p53 in vitro and in vivo

OBJECT

The authors sought to study the combined potential of wild-type p53 gene transfer and Gamma Knife surgery (GKS) for the treatment of glioblastomas multiforme. Modification of the radiation response in C6 glioma cells in vitro and in vivo by the wild-type p53 gene was investigated.

METHODS

Stable expression of wild-type p53 in C6 cells was achieved by transduction of the cells with adenoviral p53. Two days later, some cells were treated with GKS. Forty-eight hours after irradiation, the comparative survival rate was assessed by monotetrazolium (MTT) assays. Treated and control C6 glioma cells (4 x 10(3) per well) were plated into a 96-well plate in octuplicate and tested every 24 hours. Meanwhile, immunohistopathological examination of proliferating cell nuclear antigen (PCNA) and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (TUNEL) assays were performed. The MTT assays indicated the p53, GKS, and combined treated cells proliferated at a significantly lower rate than those of the control group (p < 0.01, Days 2-6) and the positive fraction of PCNA in p53-treated group and GKS-treated group was 70.18 +/- 3.61 and 50.71 +/- 2.61, respectively, whereas the percentage in the combined group was 30.68 +/- 1.49 (p < 0.01). Fifty-six male Sprague-Dawley rats were anesthetized and inoculated with 10(6) cultured C6 glioma cells into the cerebrum. Forty-eight hours after transduction with adenoviral p53, some rats underwent GKS. A margin dose of 15 Gy was delivered to the 50% isodose line. Two days later, six rats in each group were killed. Their brains were removed and paraffin-embedded section were prepared for immunohistopathological examination and TUNEL assays. The remaining rats were observed for the duration of the survival period. The survival curve indicated that a modest but significant enhancement of survival duration was seen in the p53-treated or GKS alone groups, whereas a more marked and highly significant enhancement of survival duration was achieved when these two treatment modalities were combined. When PCNA expression was downregulated, apoptotic cells become obvious after TUNEL staining.

CONCLUSIONS

The findings of this study suggest that p53-based gene therapy in combination with GKS may be superior to single-modality treatment of C6 glioma.

Isoform-specific expression of 14-3-3 proteins in human astrocytoma

BACKGROUND

14-3-3 protein plays crucial roles in tumorigenesis, including the maintenance of cell cycle and DNA repair, the prevention of apoptosis, among others. In mammalian cells, seven 14-3-3 isoforms (beta, epsilon, zeta, eta, theta, gamma and sigma) have been identified and each of these seems to have distinct tissue localizations and isoform-specific functions. In the present study, the levels of all seven 14-3-3 isoforms were examined in astrocytoma.

METHODS

The expression of 14-3-3 isoforms and their protein expression levels were examined in five glioma cell lines by western blotting. Then in astrocytoma tissues, we investigated expression percentages of each isoform by immunohistochemistry. The protein and mRNA expression levels of each isoform were also detected by western blotting and RT-PCR, respectively.

RESULTS

14-3-3beta and eta were specifically expressed in astrocytoma, and their expression frequencies and levels increased with the increase of astrocytoma malignancy. The result from glioma cell lines was consistent with that from astrocytoma tissue.

CONCLUSIONS

In our study, we found two tumor-specific isoforms of 14-3-3 in astrocytoma. They might be involved in astrocytoma tumorigenesis and may be useful as targets for therapy.

Recent advances in the medical therapy of high-grade gliomas

Malignant glial neoplasms, including glioblastoma, are amongst the most devastating and intractable of solid tumors. Until recently the standard of care for newly diagnosed glioblastoma was surgical resection to the extent feasible followed by conventional fractionated radiotherapy. When administered for disease progression, chemotherapy had modest benefit and its use in the adjuvant setting was controversial. Temozolomide, an oral alkylating chemotherapeutic agent, has now been demonstrated to increase survival time in patients with newly diagnosed glioblastoma when used concurrently with radiotherapy and as adjuvant or maintenance treatment for six cycles thereafter. Correlative molecular studies suggested that the benefit of temozolomide is largely restricted to patients whose tumor has silenced the gene for methylguanine methyltransferase, a repair enzyme implicated in resistance to alkylator chemotherapy. Use of temozolomide chemotherapy upfront in the management of glioblastoma is now considered the standard of care. This significant advance has also stimulated development of therapeutic strategies that incorporate temozolomide, and other agents, in the initial management of most high-grade gliomas. Furthermore, our increased understanding of the molecular derangements that underlie gliomagenesis has identified a number of putative molecular targets against which novel therapeutics have been tested with encouraging preliminary results. Finally, the challenges presented by the blood–brain barrier to adequate drug delivery have stimulated the development of unique locoregional delivery techniques that are currently undergoing clinical evaluation. This review summarizes these recent advances, and speculates on how the field is likely to evolve in the near future.

Diagnosis and treatment of recurrent high-grade astrocytoma

High-grade gliomas represent a significant source of cancer-related death, and usually recur despite treatment. In this analysis of current brain tumor medicine, we review diagnosis, standard treatment, and emerging therapies for recurrent astrocytomas. Difficulties in interpreting radiographic evidence, especially with regard to differentiating between tumor and necrosis, present a formidable challenge. The most accurate diagnoses come from tissue confirmation of recurrent tumor, but a combination of imaging techniques, such as magnetic resonance spectroscopy imaging, may also be relevant for diagnosis. Repeat resection can prolong life, but repeat irradiation of the brain poses serious risks and results in necrosis of healthy brain tissue; therefore, reirradiation is usually not offered to patients with recurrent tumors. We describe the use of conventional radiotherapy, intensity-modulated radiotherapy, brachytherapy, radiosurgery, and photodynamic therapy for recurrent high-grade glioma. The use of chemotherapy is limited by drug distribution and toxicity, but the development of new drug-delivery techniques such as convection-enhanced delivery, which delivers therapeutic molecules at an effective concentration directly to the brain, may provide a way to reduce systemic exposure to cytotoxic agents. We also discuss targeted therapies designed to inhibit aberrant cell-signaling pathways, as well as new experimental therapies such as immunotherapy. The treatment of this devastating disease has so far been met with limited success, but emerging knowledge of neuroscience and the development of novel therapeutic agents will likely give patients new options and require the neuro-oncology community to redefine clinical trial design and strategy continually.

Molecular neuro-oncology and the development of targeted therapeutic strategies for brain tumors. Part 5: apoptosis and cell cycle

Brain tumors are a diverse group of malignancies that remain refractory to conventional treatment approaches. Molecular neuro-oncology has now begun to clarify the transformed phenotype of brain tumors and identify oncogenic pathways that might be amenable to targeted therapy. Abnormalities of the apoptotic and cell cycle signaling pathways are key molecular features of many brain tumors and are currently under evaluation for potential therapeutic intervention. The apoptosis pathway has numerous targets for molecular therapeutic development, including p53, Bax, Bcl-2, cFLIP, effector caspases, growth factor receptors, phosphatidylinositol-3-kinase, Akt and apoptosis inhibitors. Current molecular treatment approaches include antisense techniques, gene therapy and small-molecule modulators and inhibitors. Potential targets of the cell cycle pathway include the cyclins, cyclin-dependent kinases, p53, retinoblastoma, E2F and the cyclin-dependent kinase inhibitors. Developmental molecular therapeutics for this pathway include adenoviral and gene therapy, small-peptide cyclin-dependent kinase modulators, proteasomal inhibitors and small-molecule cyclin-dependent kinase inhibitors. Several of these recently identified agents have begun evaluation in clinical trials. Further development of targeted therapies designed to modulate apoptosis and the cell cycle, and evaluation of these new agents in clinical trials, will be needed to improve survival and quality of life for patients with brain tumors.

Immunocytochemical detection of 14-3-3 in primary nervous system tumors

14-3-3 proteins have attracted much recent interest in the etiopathogenesis of human cancers owing to their involvement in the prevention of apoptosis. However, the expression of 14-3-3 in primary nervous system tumors has not been previously characterized. In this paper, Immunohistochemistry using a specific anti-14-3-3 antibody was performed on formalin-fixed, paraffin embedded archival tissue from 124 primary human nervous system tumors and 10 normal brain tissues. In the normal control brains, 14-3-3 immunoreactivity was localized mainly in the neuronal somata and processes, and some glial cells showed only weak immunoreactivity. However, 14-3-3 immunoreactivity was seen in the majority of astrocytomas [grade I (9/11), II (16/21), III (13/17), IV (17/21)]. There was no difference between the positive expression rates of 14-3-3 in different grades of astrocytomas (P = 0.968). But the intensity and degree of 14-3-3 immunoreactivity in diffuse astrocytomas, anaplastic astrocytoma, and glioblastoma multiformes showed trends with tumor grade, with glioblastomas having the highest positivity (P = 0.048). The 14-3-3 immunoreactivity was also seen in the majority of other gliomas [oligodendroglioma (2/3), anaplastic oligodendroglioma (4/4), ependymoma (1/2), anaplastic ependymoma (2/2), choroid plexus papilloma (3/3), pineocytoma (2/2), medulloblastoma (5/8)]. All meningiomas [syncytical (3), fibrous/fibroblastic (4), angiomatous (4), transitional/mixed (3)] were intensely and diffusely positive. All schwannomas (4), neurofibromas (2), pituitary adenomas (6) and craniopharyngiomas(4) also showed intense positive staining. These results showed that 14-3-3 is expressed in the majority of the primary human nervous system tumors. The up-regulated expression of 14-3-3 may be a common mechanism for evading apoptosis in most primary human nervous system tumors, and targeting 14-3-3 may be a novel promising strategy for the treatment of these tumors, especially for malignant tumors.