Activation of mTORC1/mTORC2 signaling in pediatric low-grade glioma and pilocytic astrocytoma reveals mTOR as a therapeutic target

Advances in the management of low-grade gliomas

Low-grade gliomas (LGGs) represent the most common childhood brain tumors and are a histologically heterogenous group of tumors. Most LGGs are surgically resectable with excellent 10-year overall survival outcomes of more than 90 % with surgery alone. Tumors not amenable to surgical resection and those with an aggressive biology are more challenging to treat. Conventional radiotherapy is a more efficacious method of long-term tumor control than chemotherapy. However, radiation is associated with significant cognitive, endocrine, and cerebrovascular late effects, making chemotherapy an often-preferred modality over radiotherapy, especially in younger children. Multiple chemotherapy regimens have been evaluated over the past few decades with comparable survival outcomes and differing toxicity profiles. Newer regimens containing antiangiogenic agents also show promise. Recent molecular studies have implicated the BRAF oncogene, a key regulator of the MAPK pathway, and the AKT/mTOR pathway in pediatric LGG tumorigenesis. This has opened up promising new avenues for targeted therapy, with many agents currently under investigation.

Targeted therapy in pediatric low-grade glioma

Collectively, pediatric low-grade gliomas account for most brain tumors reported in children. Surgery is typically curable for operable lesions. However, more effective therapies are required for inaccessible tumors, both to overcome refractory disease and to minimize the toxicity associated with conventional adjuvant chemotherapy and radiotherapy regimens. Recent years have witnessed rapid improvements in our understanding of the molecular pathogenesis of several childhood tumors, including low-grade gliomas. As a result, several novel compounds targeting and inhibiting critical components of molecular signaling pathways purported to be overactive in the disease have been developed. This article summarizes the most recent literature evaluating such novel targeted agents in childhood low-grade gliomas.

Screening genes crucial for pediatric pilocytic astrocytoma using weighted gene coexpression network analysis combined with methylation data analysis

To identify novel genes associated with pediatric pilocytic astrocytoma (PA) for better understanding the molecular mechanism underlying the pediatric PA pathogenesis. Gene expression profile data of GSE50161 and GSE44971 and the methylation data of GSE44684 were downloaded from Gene Expression Omnibus. The differentially expressed genes (DEGs) between PA and normal control samples were screened using the limma package in R, and then used to construct weighted gene coexpression network (WGCN) using the WGCN analysis (WGCNA) package in R. Significant modules of DEGs were selected using the clustering analysis. Function enrichment analysis of the DEGs in significant modules were performed using the WGCNA package and clusterprofiler package in R. Correlation between methylation sites of DEGs and PA was analyzed using the CpGassoc package in R. Totally, 3479 DEGs were screened in PA samples. Thereinto, 3424 DEGs were used to construct the WGCN. Several significant modules of DEGs were selected based on the WGCN, in which the turquoise module was positively related to PA, whereas blue module was negatively related to PA. DEGs (for example, DOCK2 (dedicator of cytokinesis 2), DOCK8 and FCGR2A (Fc fragment of IgG, low affinity IIa)) in blue module were mainly involved in Fc gamma R-mediated phagocytosis pathway and natural killer cell-mediated cytotoxicity pathway. Methylations of 14 DEGs among the top 30 genes in blue module were related to PA. Our data suggest that DOCK2, DOCK8 and FCGR2A may represent potential therapeutic targets in PA that merits further investigation.

The mTOR signaling pathway as a treatment target for intracranial neoplasms

Inhibition of the mammalian target of rapamycin (mTOR) signaling pathway has become an attractive target for human cancer therapy. Hyperactivation of mTOR has been reported in both sporadic and syndromic (hereditary) brain tumors. In contrast to the large number of successful clinical trials employing mTOR inhibitors in different types of epithelial neoplasms, their use to treat intracranial neoplasms is more limited. In this review, we summarize the role of mTOR activation in brain tumor pathogenesis and growth relevant to new human brain tumor trials currently under way using mTOR inhibitors.