| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2002: ¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 2001: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Research Abstract |
We investigated the molecular pathways involved in death signals induced by combination treatment with TRAIL and DNA damaging chemotherapeutic agents in glioma cells. FADD was expressed in glioma cells and expression of a dominat-negtive form of FADD significantly suppressed the synergistic cytotoxicity of the combination treatment. An initiator caspase, caspase-8, which forms DISC with death receptors, was cleaved and activated by the combination treatment. An essential effector caspase, caspase-3, was also cleaved and activated, resulting in cleavage of PARP, an intrinsic substrate of caspase-3, suggesting that cell death induced by the combination treatment is mediated by direct caspase activation pathways through FADD. Bid cleavage and release of cytochrome c and apoptosis-inducing factor (AIF) into cytoplasm upon the combination treatment were also observed, suggesting that the mitochondrial apoptosis pathways play an important role in its synergistic cytotoxiciy. Combination of T
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RAIL and X-ray radiotherapy (XRT) exhibited similar enhanced cytotoxicity in human glioma cells. XRT at 10 Gy upregulated DR5 expression and the cytotoxicity was abrogated in the presence of TRAIL neutralizing DR5-Fc, indicating that DR5 induction may be important in this effect. Similar to chemotherapy, XRT/TRAIL combination treatment activated FADD/caspase-8 mediated direct activation of caspase cascade and mitochondrial apoptosis pathways as well. U87MG cells which is wild type for p53 showed resistance to TRAIL/XRT therapy. Introduction of a dominant-negative p53, p53DD, did not sensitize U87MG cells to the combination treatment, suggesting that wild-type p53 function is not required for the enhanced cytotoxicity. TRAIL/XRT combination treatment did not affect viability of normal human astrocytes. Function of a transcription factor NF-kB was not involved in the synergistic cytotoxic effects of both TRAIL/chemotherapy and TRAIL/XRT combination in glioma cells. Our results suggest that TRAIL could be effectively combined with both DNA damaging chemotherapy and XRT, conventional therapeutic modalities of human malignant gliomas, and thus provide evidence that such combination treatment could be potential novel therapeutics against intractable malignant gliomas. Less
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