We previously demonstrated that the crude acetone extract of Bupleurum scorzonerifolium (BS-AE) 60 μg/ml has anti-proliferation activity and apoptotic effects on A549 non-small cell lung cancer (NSCLC). A novel lignan, isochaihulactone (4-benzo[1,3]dioxol-5-ylmethyl-3(3,4,5-trimethoxyl-benzylidene)-dihydro-furan-2-one), was isolated from BS-AE and identified from spectral evidence (1H NMR, 13C NMR, IR, and MS) and by comparison with authentic synthetic standards. Isochaihulactone was cytotoxic (IC50 = 10-50 μM) in a variety of human tumor cell lines. In in vitro and in vivo microtubule assembly assays, it inhibited tubulin polymerization in a concentration-dependent manner. As determined by flow cytometry, isochaihulactone caused G2/M phase arrest and apoptosis in a time- and concentration-dependent manner. G2/M arrest was correlated with increased p21/WAF1 levels, downregulation of the checkpoint proteins cyclin B1/cdc2 and mobility shift of cdc25C. Moreover, isochaihulactone (30 and 50 mg/kg) inhibited the growth of non-small cell lung carcinoma A549 xenograft in nude mice. These findings indicate isochaihulactone is a promising new antimitotic anticancer compound with potential for clinical application in the future.
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