l-663536 and Glioma

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) triggers specific apoptosis in tumor cells and is one of the most promising candidates for cancer gene therapy. However, resistance to TRAIL is one of the main impediments to use of TRAIL in cancer treatment. We showed previously that the lipoxygenase inhibitor MK886 in combination with TRAIL exhibits enhanced antitumor activities compared with each agent alone in human glioma cells. In this study, we elucidated the molecular mechanisms responsible for MK886-mediated sensitization to TRAIL-induced apoptosis. We found that MK886 sensitized glioma cells to TRAIL-induced apoptosis by upregulating the death receptor 5 (DR5) and that specific knockdown of DR5 attenuated cell death. The mechanisms underlying this sensitization involved activation of the MK886-induced p38 mitogen-activated protein kinase (MAPK) pathway and subsequent DR5 overexpression. However, treatment with a specific inhibitor or gene silencing of p38 MAPK abolished both the DR5 induction and the increase in apoptosis caused by TRAIL. Taken together, our findings indicate that the increased expression of DR5 in a p38 MAPK-dependent manner plays an important role in the sensitization of MK886 to TRAIL-induced apoptosis.

Topics: Apoptosis; Drug Resistance, Neoplasm; Drug Synergism; Gene Knockdown Techniques; Glioma; Humans; Indoles; Lipoxygenase Inhibitors; p38 Mitogen-Activated Protein Kinases; Receptors, TNF-Related Apoptosis-Inducing Ligand; TNF-Related Apoptosis-Inducing Ligand; Transcription Factor CHOP; Up-Regulation

The apoptotic ligand TRAIL is believed to have promise as a cancer gene therapy, yet many types of cancer, including gliomas, have exhibited resistance to TRAIL-induced apoptosis. Here, we show that therapeutic combination of the lipoxygenase inhibitor MK886 and TRAIL-secreting human mesenchymal stem cells (MSC-TRAIL) provide targeted and prolonged delivery of TRAIL both in vitro and in orthotopic mouse models of glioma. Treatment of either TRAIL-sensitive or TRAIL-resistant human glioma cells with MK886 and MSC-TRAIL resulted in significantly enhanced apoptosis compared with each agent alone. MK886 effectively increased the sensitivity to TRAIL-induced apoptosis via upregulation of the death receptor 5 and downregulation of the antiapoptotic protein survivin in human glioma cell lines and in primary glioma cells. This regulation was accompanied by a substantial increase in caspase activation after combined treatment. Furthermore, in vivo survival experiments and imaging analysis in orthotopic xenografted mice showed that MSC-based TRAIL gene delivery combined with MK886 into the tumors had greater therapeutic efficacy than single-agent treatment. Together, our findings indicate that MK886 combined with MSC-based TRAIL gene delivery may represent a novel strategy for improving the treatment of malignant gliomas.

Topics: Animals; Antineoplastic Agents; Blotting, Western; Brain Neoplasms; Cell Line, Tumor; Combined Modality Therapy; Flow Cytometry; Genetic Therapy; Glioma; Humans; Immunohistochemistry; Indoles; Male; Mesenchymal Stem Cell Transplantation; Mesenchymal Stem Cells; Mice; Mice, Nude; RNA, Small Interfering; TNF-Related Apoptosis-Inducing Ligand; Transfection; Xenograft Model Antitumor Assays

Mounting evidence suggests that lipoxygenase (LO)-catalyzed products may play a key role in the development and progression of human cancers. In this study, we analyzed the effects of a 5-LO inhibitor, which inhibits the conversion of arachidonic acid to leukotrienes, on cell proliferation and apoptosis in human malignant glioma cells, including 5-LO-expressing cells U-87MG, A172 and 5-LO non-expressing cell U373. Growth of U-87MG and A172 cells, but not that of U373 cells, was inhibited in a dose-dependent manner by treatment with MK886. Similarly, specific 5-LO silencing by small interfering RNA reduced the growth of U-87MG and A172 cells. MK886 treatment reduced 5-LO activity independently of 5-LO-activating protein (FLAP) in human malignant glioma cells. MK886 treatment also induced cell apoptosis, measured by DNA fragmentation and nuclear condensation, in U-87MG and A172 cells but there were no signs in U373 cells. Moreover, this treatment reduced ERKs phosphorylation and anti-apoptotic molecule Bcl-2 expression, and increased Bax expression in U-87MG and A172 cells. In summary, our results show there is a link between the 5-LO expression status and the extent of MK886-inhibited cell proliferation and apoptosis. Taken together, this study suggest that 5-LO is a possible target for treating patients with gliomas, and 5-LO inhibition might be potent therapy for patients with 5-LO-expressing malignant gliomas.

Topics: Apoptosis; Apoptosis Regulatory Proteins; Arachidonate 5-Lipoxygenase; Cell Line, Tumor; Cell Proliferation; DNA Fragmentation; Dose-Response Relationship, Drug; Flow Cytometry; Gene Expression Regulation, Neoplastic; Glioma; Humans; Indoles; Lipoxygenase Inhibitors; Mutation; RNA, Small Interfering; Time Factors; Transfection; Tumor Suppressor Protein p53