CBER/Food & Drug Administration, Bethesda, MD

Human glioblastoma tumors over expressing high levels of interleukin-13 receptor (IL-13R) are being targeted by a recombinant cytotoxin, composed of IL-13 and a truncated form of Pseudomonas exotoxin. 
Preclinical animal studies have demonstrated remarkable antitumor activity in glioblastoma tumor models and based on these studies three clinical trials are currently ongoing for the treatment of recurrent glioma. 
IL-13 cytotoxin exhibits strong cytotoxic activity leading to apoptotic and/or necrotic cell death of target cells. 
To elucidate the significance of IL-13 receptor in glioblastoma cells and molecular mechanisms of cell death induced by IL-13 toxin, cDNA microarray technology is employed to examine the gene expression profiles belonging to various pathways. 
Total RNA isolated from U251 glioma cells after treatment with IL-13 cytotoxin for various time points was labeled and hybridized with a high quality cDNA microarray chip provided by Advanced Technology Center, NCI. 
The gene expression profile was compared between untreated control and IL-13 cytotoxin (10ng/ml) treated (1h, 4h, 8h, and 24h) groups. 
The results were analyzed by GenePix software, and by microarray database (mAdb) software tools provided by Center for Information Technology/NIH. 
The experiments were repeated at least 2-4 times. 
Several important gene expression patterns were identified as a result of treatment with IL-13 cytotoxin. 
Type I induced 24 hours after IL-13 cytotoxin treatment showed up-regulation of genes belonging to cell cycle arrest and apoptosis. 
Type II pattern showed up-regulation of genes belonging to cell proliferation, cytokines, inflammatory response, and cellular processes and cell signaling within 4h of IL-13 cytotoxin treatment. 
Type III pattern showed down regulation of gene expression belonging to angiogenesis, DNA synthesis, metabolism, adhesion molecules and receptors. 
Gene expression was confirmed by RT-PCR analysis for various genes. 
Our study demonstrates that IL-13 cytotoxin modulates a large number of genes belonging to various pathways. 
Our study provides important insights into the association of IL-13 receptor with various molecules and mechanism of cell death leading to antitumor activity of IL13 cytotoxin.

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