title: Coibamide A induces mTOR-independent autophagy and cell death in human glioblastoma cells.
abstract: Coibamide A is an N-methyl-stabilized depsipeptide that was isolated from a marine cyanobacterium as part of an International Cooperative Biodiversity Groups (ICBG) program based in Panama. Previous testing of coibamide A in the NCI in vitro 60 cancer cell line panel revealed a potent anti-proliferative response and "COMPARE-negative" profile indicative of a unique mechanism of action. We report that coibamide A is a more potent and efficacious cytotoxin than was previously appreciated, inducing concentration- and time-dependent cytotoxicity (EC50<100 nM) in human U87-MG and SF-295 glioblastoma cells and mouse embryonic fibroblasts (MEFs). This activity was lost upon linearization of the molecule, highlighting the importance of the cyclized structure for both anti-proliferative and cytotoxic responses. We show that coibamide A induces autophagosome accumulation in human glioblastoma cell types and MEFs via an mTOR-independent mechanism; no change was observed in the phosphorylation state of ULK1 (Ser-757), p70 S6K1 (Thr-389), S6 ribosomal protein (Ser-235/236) and 4EBP-1 (Thr-37/46). Coibamide A also induces morphologically and biochemically distinct forms of cell death according to cell type. SF-295 glioblastoma cells showed caspase-3 activation and evidence of apoptotic cell death in a pattern that was also seen in wild-type and autophagy-deficient (ATG5-null) MEFs. In contrast, cell death in U87-MG glioblastoma cells was characterized by extensive cytoplasmic vacuolization and lacked clear apoptotic features. Cell death was attenuated, but still triggered, in Apaf-1-null MEFs lacking a functional mitochondria-mediated apoptotic pathway. From the study of ATG5-null MEFs we conclude that a conventional autophagy response is not required for coibamide A-induced cell death, but likely occurs in dying cells in response to treatment. Coibamide A represents a natural product scaffold with potential for the study of mTOR-independent signaling and cell death mechanisms in apoptotic-resistant cancer cells.
authors.affiliation: Department of Pharmaceutical Sciences, Oregon State University, Corvallis, Oregon, United States of America.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Hau
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Greenwood
authors.forename: Christiane V
authors.initials: CV
authors.lastname: Löhr
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Serrill
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Proteau
authors.forename: Ian G
authors.initials: IG
authors.lastname: Ganley
authors.forename: Kerry L
authors.initials: KL
authors.lastname: McPhail
authors.forename: Jane E
authors.initials: JE
authors.lastname: Ishmael
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D053477:Apoptotic Protease-Activating Factor 1 / Q000172:deficiency / Q000235:genetics; D001343:Autophagy / Q000187:drug effects*; D000071187:Autophagy-Related Protein 5; D000071189:Autophagy-Related Protein-1 Homolog; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D003603:Cytotoxins / Q000494:pharmacology*; D047630:Depsipeptides / Q000494:pharmacology*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000172:deficiency / Q000235:genetics; D009928:Organ Specificity; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism
chemical_list: C506592:APAF1 protein, human; C502778:ATG5 protein, human; D048868:Adaptor Proteins, Signal Transducing; D053477:Apoptotic Protease-Activating Factor 1; D000071187:Autophagy-Related Protein 5; D018797:Cell Cycle Proteins; D003603:Cytotoxins; D047630:Depsipeptides; C087000:EIF4EBP1 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D008869:Microtubule-Associated Proteins; D010750:Phosphoproteins; C530036:coibamide A; D000071189:Autophagy-Related Protein-1 Homolog; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; C484754:ULK1 protein, human; D053148:Caspase 3