Pharmacological and Genetic Inhibitions of PI3K/Akt Activity to Treat Malignant Brain Tumors

• Main Authors: Tsung-ching Lai, 賴宗慶
• Other Authors: Hong-sheng Hsiao
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/79371509046769699381

碩士 === 國立中山大學 === 生物科學系研究所 === 93 === Gliomblastoma is a highly malignant tumor of the central nervous system that is resistant to radiation and chemotherapy. Evidences accumulated over recent years have indicated the phosphoinositide 3-kinase/Akt signal transduction pathway as one of the major factors implicated in cancer resistance to conventional therapies. In this study we determined whether inhibition of PI3K/Akt signal pathway through pharmacological and/or genetic manipulation could enhance radiation sensitivity in glioma cells. Our results showed 6 of 12 glioma cell lines with activated Akt mostly due to reciprocal down-regulation of PTEN activity (loss-of-function mutations) but not by PIK3CA gain-of-function mutations. U87 and U373 glioma cell lines with PTEN mutation showing strong Akt Ser473 phopshorylation were treated with PI3K inhibitor LY294002 and irradiated with 0, 2.5, 5 and 7.5 Gy of radiation dosages. The results showed LY294002 inhibited Akt actvation in the glioma cells and decreased clonogenic survival in a radiation dose-dependent manner. Expression of dominant-negative Akt and PTEN through adenovirus mediated gene delivery in U87 and U373 glioma cells sensitized tumor cells to radiation treatment. Furthermore, PDK1 and mTOR inhibitors were also used on radiation sensitivity test. But both inhibitors had no radiosensitization in glioma cells. Glioma invasion was linked to advanced tumor stages. Recently, Type 1 insulin-like growth factor regulates tumor invasion have been showed to be mediated through the PI3K/Akt signaling pathway. In this study, we treated glioma cells with LY294002 to analyze its effects on invasion and migration potentials of the tumor cells. The results showed LY294002 inhibited both abilities in most glioma cell lines in vitro. In addition we used adv-PTEN and adv-dnAkt to confirm these results. Adv-PTEN performed dramatic decrease in glioma cell invasion potentials. Furthermore, we investigated whehter PI3K downstream PDK1, and mTOR involved in tumor cell invasion. We used PDK1 and mTOR inhibitors in glioma and determined their effects on invasion by Boyden chamber assay. Unfortunately, both of inhibitors had only limited inhibition on glioma invasion. Take together, our results indicate the feasibility of using PI3K/Akt inhibiting genetic and pharmacological agents to induce glioma cells to become more sensitive to radiation treatment and reduced invasion potentials. However, glioma radiosensitization and invasion may also be regulated by other signaling pathway.