Induction of Apoptosis in Human Cancer Cells by Candidaspongiolide, a Novel Sponge Polyketide

• Published in: JNCI : Journal of the National Cancer Institute Vol. 100; no. 17; pp. 1233 - 1246
• Main Authors: Trisciuoglio, Daniela, Uranchimeg, Badarch, Cardellina, John H., Meragelman, Tamara L., Matsunaga, Shigeki, Fusetani, Nobuhiru, Del Bufalo, Donatella, Shoemaker, Robert H., Melillo, Giovanni
• Format: Journal Article
• Language: English
• Published: Cary, NC Oxford University Press 03.09.2008; Oxford Publishing Limited (England)
• Subjects: Animals; Antineoplastic agents; Antineoplastic Agents - pharmacology; Apoptosis; Apoptosis - drug effects; Biological and medical sciences; Blotting, Western; Brain cancer; Caspase 12 - metabolism; Cell culture; Cell Line, Tumor; Chemotherapy; Colorectal cancer; Dose-Response Relationship, Drug; eIF-2 Kinase - metabolism; Enzyme Activation - drug effects; Eukaryotic Initiation Factor-2 - metabolism; Flow Cytometry; General aspects; Glioma - etiology; HCT116 Cells; Humans; Macrolides - pharmacology; MAP Kinase Kinase 4 - metabolism; Marine biology; Medical research; Medical sciences; Oncology; p38 Mitogen-Activated Protein Kinases - metabolism; Pharmacology. Drug treatments; Phosphorylation - drug effects; Porifera; RNA, Small Interfering; Transfection; Tumors; Antineoplastic agent; Human; Nervous system diseases; Rectal disease; Colorectal cancer; Animal origin; Malignant tumor; In vitro; Biological activity; Colonic disease; Polyketide; Malignant glioma; Cancerology; Cell death; Protein synthesis; Central nervous system disease; Established cell line; Digestive diseases; Intestinal disease; Cancer; Apoptosis
• ISSN: 0027-8874; 1460-2105
• DOI: 10.1093/jnci/djn239

Background Candidaspongiolide (CAN), a novel polyketide from a marine sponge, is the active component of a mixture that was found to be potently cytotoxic in the National Cancer Institute’s 60-cell-line screen. Methods Effects of CAN on U251 glioma and HCT116 colorectal cancer cells and on normal fibroblasts were assessed using radiolabeling studies to measure protein synthesis, clonogenic assays to measure cell survival, flow cytometry of annexin V– and propidium iodide–stained cells to measure apoptosis, and western blots in the presence or absence of specific inhibitors to assess accumulation and phosphorylation of potential downstream target proteins. Results CAN inhibited protein synthesis and potently induced apoptosis in both U251 and HCT116 cells, the latter in part by a caspase 12–dependent pathway. For example, 25%–30% of U251 or HCT116 cells became apoptotic after 24 hours of treatment with 100 nM CAN. CAN also rapidly induced sustained phosphorylation of eukaryotic translation initiation factor-2 (eIF2)-α at Ser51 and of the translation elongation factor eEF2 at Thr56, which could contribute to its dose-dependent inhibition of protein synthesis. Stable expression of dominant-negative eIF2α was sufficient to prevent CAN-induced eIF2α phosphorylation and induction of apoptosis but insufficient to prevent inhibition of protein synthesis. CAN induction of eIF2α phosphorylation did not occur by a classic endoplasmic reticulum stress pathway. However, an inhibitor of and small-interfering RNAs to the double-stranded RNA–dependent protein kinase PKR prevented CAN-mediated eIF2α phosphorylation and apoptosis, respectively. Although CAN inhibited protein synthesis in both cancer cells and normal human fibroblasts, it induced eIF2α phosphorylation and apoptosis only in cancer cells. Conclusions CAN triggers PKR/eIF2α/caspase 12–dependent apoptosis and inhibits protein synthesis in cancer cells but only inhibits protein synthesis in normal cells.