Sep 1 2009
The interaction between a network of altered genes appears to play an important role in the development and progression of brain tumors, according to a study in the July 15 issue of JAMA.
Malignant gliomas (brain tumors) are associated with disproportionately high illness and death and are among the most devastating of tumors. Particular genomic alterations are fundamental to both their formation and their malignant progression. "Chromosomal alterations presumably exert their tumor-promoting effect on glioma cells by modifying the expression or function of distinct genes, which map to those alterations, so as to deregulate growth factor signaling and survival pathways. For many chromosomal alterations, the biologically relevant target genes remain to be discovered," the authors write.
Oncogenic research on brain tumors has focused on the tumor-promoting or tumor-suppressive function of target genes within individual chromosomal alterations. However, these alterations do not exist in isolation, nor do single genes account for gliomagenesis. Rather, there may be mechanistic links to genes at other, coincident alterations, according to background information in the article.
Markus Bredel, M.D., Ph.D., of the Northwestern Brain Tumor Institute at Northwestern University Feinberg School of Medicine, Chicago, and colleagues examined the relationships of tumor-promoting genes in gliomas. The study included genomic profiles and clinical profiles of 501 patients with gliomas (45 tumors in an initial discovery set collected between 2001 and 2004 and 456 tumors in validation sets made public between 2006 and 2008) from multiple academic centers in the United States and The Cancer Genome Atlas Pilot Project (TCGA). The analysis included the identification of genes with coincident genetic alterations, correlated gene dosage (the copy number for a specific gene determined by certain analytic approaches) and gene expression, and multiple functional interactions; and the association between those genes and patient survival.
The researchers found: "The alteration of multiple networking genes by recurrent chromosomal aberrations in gliomas deregulates critical signaling pathways through multiple, cooperative mechanisms. These mutations, which are likely due to nonrandom selection of a distinct genetic landscape [a consistent pattern of chromosomal alterations] during gliomagenesis, are associated with patient prognosis."
The authors add that the identification of such gene alterations in gliomas prompts evaluation of their potential as therapeutic targets. "The network context of a gene likely affects the efficacy of therapies that target its protein. The complexity of our landscape model helps explain the lack of therapeutic efficacy of strategies targeting single gene products."
A multigene risk scoring model based on seven landscape genes was associated with the duration of overall survival in 189 glioblastoma patients from TCGA, an association that was confirmed in three additional malignant glioma patient populations.
"The current work provides a network model and biological rationale for the selection of a nonrandom genetic landscape in human gliomas," the authors write. "A multigene predictor model incorporating 7 landscape genes demonstrates how molecular insights emerging from our integrative multidimensional analysis could translate into relevant clinical end points affecting the future management of gliomas."