syringolin-a and Ovarian-Neoplasms

Syrbactins belong to a new class of proteasome inhibitors which include syringolins and glidobactins. These small molecules are structurally distinct from other, well-established proteasome inhibitors, and bind the eukaryotic 20S proteasome by a novel mechanism. In this study, we examined the effects of syringolin A (SylA) and glidobactin A (GlbA) as well as two synthetic SylA-analogs (SylA-PEG and SylA-LIP) in human neuroblastoma (SK-N-SH), human multiple myeloma (MM1.S, MM1.RL, and U266), and human ovarian cancer (SKOV-3) cells. While all four syrbactins inhibited cell proliferation in a dose-dependent manner, GlbA was most potent in both dexamethasone-sensitive MM1.S cells (IC(50): 0.004microM) and dexamethasone-resistant MM1.RL cells (IC(50): 0.005microM). Syrbactins also inhibited the chymotrypsin-like proteasome activity in a dose-dependent fashion, and GlbA was most effective in SK-N-SH cells (IC(50): 0.015microM). The GlbA-promoted inhibition of proteasomal activity in SK-N-SH cells resulted in the accumulation of ubiquitinated proteins and tumor suppressor protein p53 and led to apoptotic cell death in a time-dependent manner. GlbA treatment also promoted the activation of Akt/PKB via phosphorylation at residue Ser(473) and induced autophagy as judged by the presence of the lipidated form of microtubule-associated protein 1 light chain 3 (LC3) and autophagosomes. Collectively, our data suggest that syrbactins belong to a new and effective proteasome inhibitor class which promotes cell death. Proteasome inhibition is a promising strategy for targeted anticancer therapy and syrbactins are a new class of inhibitors which provide a structural platform for the development of novel, proteasome inhibitor-based drug therapeutics.

Topics: Antineoplastic Agents; Apoptosis; Autophagy; Cell Line, Tumor; Cell Proliferation; Cell Survival; Child, Preschool; Dose-Response Relationship, Drug; Drug Screening Assays, Antitumor; Female; Humans; Infant; Male; Multiple Myeloma; Neuroblastoma; Ovarian Neoplasms; Peptides, Cyclic; Protease Inhibitors; Proto-Oncogene Proteins c-akt; Tumor Suppressor Protein p53

Syringolin A is a new plant elicitor produced by the plant pathogen Pseudomonas syringae pv. syringae. The goal of this study was to investigate whether syringolin A exhibits anti-proliferative properties in cancer cells. The treatment of human neuroblastoma (NB) cells (SK-N-SH and LAN-1) and human ovarian cancer cells (SKOV3) with syringolin A (0-100 microm) inhibited cell proliferation in a dose-dependent manner. The IC(50) (50% inhibition) for each cell line ranged between 20 microm and 25 microm. In SK-N-SH cells, the treatment with 20 microm syringolin A led to a rapid (24 h) increase of the apoptosis-associated tumour suppressor protein p53. In addition, we found that the treatment of SK-N-SH cells caused severe morphological changes after 48 h such as rounding of cells and loss of adherence, both conditions observed during apoptosis. The induction of apoptosis by syringolin A was confirmed by both poly (ADP-ribose) polymerase (PARP) cleavage and annexin V assay. Taken together, we show for the first time that the natural product syringolin A exhibits anti-proliferative activity and induces apoptosis. Syringolin A and structurally modified syringolin A derivatives may serve as new lead compounds for the development of novel anticancer drugs.

Topics: Animals; Antineoplastic Agents; Apoptosis; Caspase 3; Cell Division; Cell Line, Transformed; Cell Line, Tumor; Dose-Response Relationship, Drug; Female; Fibroblasts; Humans; Nervous System Neoplasms; Neuroblastoma; Ovarian Neoplasms; Peptides, Cyclic; Poly(ADP-ribose) Polymerases; Proto-Oncogene Proteins c-akt; Pseudomonas syringae; Rats; Tumor Suppressor Protein p53