title: Role of autophagy in temozolomide-induced cytotoxicity for malignant glioma cells.
abstract: Autophagy is originally named as a process of protein recycling. It begins with sequestering cytoplasmic organelles in a membrane vacuole called autophagosome. Autophagosomes then fuse with lysosomes, where the materials inside are degraded and recycled. To date, however, little is known about the role of autophagy in cancer therapy. In this study, we present that temozolomide (TMZ), a new alkylating agent, inhibited the viability of malignant glioma cells in a dose-dependent manner and induced G2/M arrest. At a clinically achievable dose (100 microM), TMZ induced autophagy, but not apoptosis in malignant glioma cells. After the treatment with TMZ, microtubule-associated protein light-chain 3 (LC3), a mammalian homologue of Apg8p/Aut7p essential for amino-acid starvation-induced autophagy in yeast, was recruited on autophagosome membranes. When autophagy was prevented at an early stage by 3-methyladenine, a phosphatidylinositol 3-phosphate kinase inhibitor, not only the characteristic pattern of LC3 localization, but also the antitumor effect of TMZ was suppressed. On the other hand, bafilomycin A1, a specific inhibitor of vacuolar type H(+)-ATPase, that prevents autophagy at a late stage by inhibiting fusion between autophagosomes and lysosomes, sensitized tumor cells to TMZ by inducing apoptosis through activation of caspase-3 with mitochondrial and lysosomal membrane permeabilization, while LC3 localization pattern stayed the same. These results indicate that TMZ induces autophagy in malignant glioma cells. Application of an autophagy inhibitor that works after the association of LC3 with autophagosome membrane, such as bafilomycin A1, is expected to enhance the cytotoxicity of TMZ for malignant gliomas.
authors.affiliation: Department of Neurosurgery, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors.forename: T
authors.initials: T
authors.lastname: Kanzawa
authors.forename: I M
authors.initials: IM
authors.lastname: Germano
authors.forename: T
authors.initials: T
authors.lastname: Komata
authors.forename: H
authors.initials: H
authors.lastname: Ito
authors.forename: Y
authors.initials: Y
authors.lastname: Kondo
authors.forename: S
authors.initials: S
authors.lastname: Kondo
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects / Q000502:physiology*; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005910:Glioma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D018942:Macrolides / Q000494:pharmacology; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D015388:Organelles / Q000378:metabolism; D000077204:Temozolomide
chemical_list: D018906:Antineoplastic Agents, Alkylating; C477012:MAP1LC3A protein, human; D018942:Macrolides; D008869:Microtubule-Associated Proteins; C025946:3-methyladenine; D003606:Dacarbazine; C040929:bafilomycin A1; D000225:Adenine; D000077204:Temozolomide