longikaurin-a and Liver-Neoplasms

Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer, and is also highly resistant to conventional chemotherapy treatments. In this study, we report that Longikaurin A (LK-A), an ent-kaurane diterpenoid isolated from the plant Isodon ternifolius, induced cell cycle arrest and apoptosis in human HCC cell lines. LK-A also suppressed tumor growth in SMMC-7721 xenograft models, without inducing any notable major organ-related toxicity. LK-A treatment led to reduced expression of the proto-oncogene S phase kinase-associated protein 2 (Skp2) in SMMC-7721 cells. Lower Skp2 levels correlated with increased expression of p21 and p-cdc2 (Try15), and a corresponding decrease in protein levels of Cyclin B1 and cdc2. Overexpression of Skp2 significantly inhibited LK-A-induced cell cycle arrest in SMMC-7721 cells, suggesting that LK-A may target Skp2 to arrest cells at the G2/M phase. LK-A also induced reactive oxygen species (ROS) production and apoptosis in SMMC-7721 cells. LK-A induced phosphorylation of c-Jun N-terminal kinase (JNK), but not extracellular signal-regulated kinase and P38 MAP kinase. Treatment with, the JNK inhibitor SP600125 prevented LK-A-induced apoptosis in SMMC-7721 cells. Moreover, the antioxidant N-acetylcysteine prevented phosphorylation of both JNK and c-Jun. Taken together, these data indicate that LK-A induces cell cycle arrest and apoptosis in cancer cells by dampening Skp2 expression, and thereby activating the ROS/JNK/c-Jun signaling pathways. LK-A is therefore a potential lead compound for development of antitumor drugs targeting HCC.

Topics: Animals; Antineoplastic Agents, Phytogenic; Apoptosis; Carcinoma, Hepatocellular; CDC2 Protein Kinase; Cyclin B; Cyclin B1; Cyclin-Dependent Kinase Inhibitor p21; Cyclin-Dependent Kinases; Diterpenes, Kaurane; Dose-Response Relationship, Drug; Down-Regulation; G2 Phase Cell Cycle Checkpoints; Hep G2 Cells; Humans; JNK Mitogen-Activated Protein Kinases; Liver Neoplasms; Male; Mice; Mice, Inbred BALB C; Mice, Nude; Phosphorylation; Protein Kinase Inhibitors; Proto-Oncogene Mas; Proto-Oncogene Proteins c-jun; Reactive Oxygen Species; S-Phase Kinase-Associated Proteins; Signal Transduction; Time Factors; Transfection; Tumor Burden; Xenograft Model Antitumor Assays