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: Andrew M Hau, Jeffrey A Greenwood, Christiane V Löhr, Jeffrey D Serrill, Philip J Proteau, Ian G Ganley, Kerry L McPhail, Jane E Ishmael
• Journal: PloS one (PLoS One) Vol. 8 Issue 6 Pg. e65250 ( 2013) ISSN: 1932-6203 [Electronic] United States
• PMID: 23762328 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• APAF1 protein, human
• ATG5 protein, human
• Adaptor Proteins, Signal Transducing
• Apoptotic Protease-Activating Factor 1
• Autophagy-Related Protein 5
• Cell Cycle Proteins
• Cytotoxins
• Depsipeptides
• EIF4EBP1 protein, human
• Intracellular Signaling Peptides and Proteins
• Microtubule-Associated Proteins
• Phosphoproteins
• coibamide A
• Autophagy-Related Protein-1 Homolog
• Protein Serine-Threonine Kinases
• Ribosomal Protein S6 Kinases
• TOR Serine-Threonine Kinases
• ULK1 protein, human
• Caspase 3

Topics

• Adaptor Proteins, Signal Transducing (genetics, metabolism)
• Animals
• Apoptosis (drug effects)
• Apoptotic Protease-Activating Factor 1 (deficiency, genetics)
• Autophagy (drug effects)
• Autophagy-Related Protein 5
• Autophagy-Related Protein-1 Homolog
• Caspase 3 (genetics, metabolism)
• Cell Cycle Proteins
• Cell Line, Tumor
• Cytotoxins (pharmacology)
• Depsipeptides (pharmacology)
• Fibroblasts (cytology, drug effects, metabolism)
• Gene Expression Regulation, Neoplastic (drug effects)
• Humans
• Intracellular Signaling Peptides and Proteins (genetics, metabolism)
• Mice
• Microtubule-Associated Proteins (deficiency, genetics)
• Organ Specificity
• Phosphoproteins (genetics, metabolism)
• Protein Serine-Threonine Kinases (genetics, metabolism)
• Ribosomal Protein S6 Kinases (genetics, metabolism)
• Signal Transduction (drug effects)
• TOR Serine-Threonine Kinases (genetics, metabolism)