Obtusilactone A and (−)‐sesamin induce apoptosis in human lung cancer cells by inhibiting mitochondrial Lon protease and activating DNA damage checkpoints

Abstract

Several compounds from Cinnamomum kotoense show anticancer activities. However, the detailed mechanisms of most compounds from C. kotoense remain unknown. In this study, we investigated the anticancer activity of obtusilactone A (OA) and ())-sesamin in lung cancer. Our results show that human Lon is upregulated in non-small-cell lung cancer (NSCLC) cell lines, and downregulation of Lon triggers caspase-3 mediated apoptosis. Through enzymebased screening, we identified two small-molecule compounds, obtusilactone A (OA) and ())-sesamin from C. kotoense, as potent Lon protease inhibitors. Obtusilactone A and ())-sesamin interact with Ser855 and Lys898 residues in the active site of the Lon protease according to molecular docking analysis. Thus, we suggest that cancer cytotoxicity of the compounds is partly due to the inhibitory effects on Lon protease. In addition, the compounds are able to cause DNA double-strand breaks and activate checkpoints. Treatment with OA and ())-sesamin induced p53-independent DNA damage responses in NSCLC cells, including G 1 ⁄ S checkpoint activation and apoptosis, as evidenced by phosphorylation of checkpoint proteins (H2AX, Nbs1, and Chk2), caspase-3 cleavage, and sub-G 1 accumulation. In conclusion, OA and ())-sesamin act as both inhibitors of human mitochondrial Lon protease and DNA damage agents to activate the DNA damage checkpoints as well induce apoptosis in NSCLC cells. These dual functions open a bright avenue to develop more selective chemotherapy agents to overcome chemoresistance and sensitize cancer cells to other chemotherapeutics. (Cancer Sci 2010; 101: 2612-2620 L ung cancer is a leading cause of cancer-related death in both men and women in the USA (1) and Taiwan. The survival rate after chemotherapy regimens and the drug development of molecular-targeted agents for lung cancer therapy is still challenging. (2,3) Lon is a highly conserved ATP-dependent serine protease that has been identified from prokaryotes and to mitochondria of eukaryotes.(4) In vivo studies show that Lon plays an important role in mitochondrial DNA maintenance and expression (5)(6)(7) and regulation of mitochondria function.(8) Mitochondrial function is a crucial determinant of cellular sensitivity to cancer therapeutic drugs because of its roles in mediating apoptosis.(9) Enhanced mitochondrial biogenesis as well as tumorigenesis are linked to overexpression and increased proteolytic activity of Lon. (8,10) Downregulation of Lon leads to loss of mitochondrial function, reduced cell proliferation capacity, and apoptosis. (11,12) Deregulation of Lon leading to tumorigenesis has raised its potential as a target in the development of a novel drug in cancer therapy.To date, very few small-molecule inhibitors of Lon protease have been found, although several peptide-based proteasome inhibitors have been reported. (13,14) Cell cycle checkpoints are sophisticated surveillance mechanisms that are used to monitor the integrity of DNA.(15,16) After DNA lesions are sensed by sensor proteins, the kinase activ...

Mitochondrial dysfunction in cancer: Potential roles of ATF5 and the mitochondrial UPR

“…For instance, inhibition of mitochondrial protease LONP1 by obtusilactone A or CDDO selectively kills non-small-cell lung carcinoma and lymphoma cells, respectively [139, 140]. Also, inhibition of ClpP can selectively kill human leukemic cells by disturbing the folding of mitochondrial metabolic proteins [132].…”

Mitochondrial Lon protease in human disease and aging: Including an etiologic classification of Lon-related diseases and disorders

“…Obtusilactone A and (−)-sesamin, compounds derived from Cinnamomum kotoense are potent Lon protease inhibitors, which interact with Ser855 and Lys898 residues in the active site of the Lon protease [107]. Lon is upregulated in non-small-cell lung cancer (NSCLC) cell lines, and downregulation of Lon with either Obtusilactone A or (−)-sesamin triggers caspase-3 mediated apoptosis [107].…”

“…Lon is upregulated in non-small-cell lung cancer (NSCLC) cell lines, and downregulation of Lon with either Obtusilactone A or (−)-sesamin triggers caspase-3 mediated apoptosis [107]. …”

Differentiation therapy: sesamin as an effective agent in targeting cancer stem-like side population cells of human gallbladder carcinoma

“…Regarding its antitumor effects, sesamin has been demonstrated to inhibit the growth of a variety of cancer cells both in vivo and in vitro , including breast cancer [13,14], human lung cancer [15] and colon cancer [16]. The mechanisms by which sesamin exerts antitumor effects are not fully understood, but its role in suppression of NF-κB and interleukin 6 (IL-6) have been clarified [12,17].…”