Geoditin A induces oxidative stress and apoptosis on human colon HT29 cells.

Geoditin A, an isomalabaricane triterpene isolated from the marine sponge Geodia japonica, has been demonstrated to dissipate mitochondrial membrane potential, activate caspase 3, decrease cytoplasmic proliferating cell nuclear antigen (PCNA), and induce apoptosis of leukemia cells, but the underlying mechanism remains unclear [1]. In this study, we found fragmentation of Golgi structure, suppression of transferrin receptor expression, production of oxidants, and DNA fragmentation in human colon cancer HT29 cells after treatment with geoditin A for 24 h. This apoptosis was not abrogated by chelation of intracellular iron with salicylaldehyde isonicotinoyl hydrazone (SIH), but suppressed by N-acetylcysteine (NAC), a thiol antioxidant and GSH precursor, indicating that the cytotoxic effect of geoditin A is likely mediated by a NAC-inhibitable oxidative stress. Our results provide a better understanding of the apoptotic properties and chemotherapeutical potential of this marine triterpene.

Involvement of p21 and FasL in induction of cell cycle arrest and apoptosis by neochamaejasmin A in human prostate LNCaP cancer cells.

Neochamaejasmin A ( 1), a biflavonoid isolated from the roots of a traditional Chinese medicine, Stellera chamaejasme L., was shown to inhibit cellular (3)H-thymidine incorporation (IC 50 12.5 microg/mL) and subsequent proliferation of human prostate cancer LNCaP cells. Treatment of LNCaP cells with low doses of 1 (< or =6.25 microg/mL) suppressed DNA-binding activities of the transcription factors NFkappaB and AP-1 to the promoter of cyclin D and also inhibited expression of the cell cycle regulatory proteins cyclin D, proliferating cell nuclear antigen, and nucleolin, thus arresting cells in G 1 phase of the cell cycle. A lengthy exposure with higher doses of 1 (> or =12.5 microg/mL) revealed the production of reactive oxygen species, dissipation of the mitochondrial membrane potential, up-regulation of cyclin-dependent kinase inhibitor p21, and induction of cell apoptosis. An aggregation of Fas-procaspase 8-procaspase 3 and p21-procaspase 3 proteins by coimmunoprecipitation, immunoblotting analysis, and MALDI-mass spectrometry indicated the involvement of Fas and p21 in 1-mediated cytotoxicity, and pretreatment of cells with antisense FasL oligonucleotides partially abolished apoptosis. Thus, 1 blocked cell cycle progression at the G 1 phase by activating the p21 protein and ultimately promoting the Fas-caspase 8-caspase 3 apoptotic machinery.

Apoptotic activity of betulinic acid derivatives on murine melanoma B16 cell line.

The mitochondrion plays a crucial role in the process of apoptosis and has thus become one of the targets for the search for potential chemotherapeutic agents. Betulinic acid [3beta-hydroxy-lup-20(19)lupaen-28-carbonic acid], a lupane-type triterpene which is abundant in many plant species, has been shown to exert a direct effect on the mitochondria and subsequent apoptosis in melanoma cells. Chemical synthesis and modification of betulinic acid are being explored to develop more potent derivatives. We present here the apoptotic activity of several natural derivatives of betulinic acid which were isolated from the roots of a Chinese medicinal herb, Pulsatilla chinensis (Bge) Regel [Ye, W., Ji, N.N., Zhao, S.X., Liu, J.H., Ye, T., McKervey, M.A., Stevenson, P., 1996. Triterpenoids from Pulsatilla chinensis. Phytochemistry 42, 799-802]. Of the five compounds tested, 3-oxo-23-hydroxybetulinic acid was the most cytotoxic on murine melanoma B16 cells (IC50=22.5 microg/ml), followed by 23-hydroxybetulinic acid and betulinic acid (IC50=32 and 76 microg/ml, respectively), with lupeol and betulin exhibiting the weakest cytotoxicity (IC50> or =100 microg/ml). Exposure of B16 cells to betulinic acid, 23-hydroxybetulinic acid and 3-oxo-23-hydroxybetulinic acid caused a rapid increase in reactive oxidative species production and a concomitant dissipation of mitochondrial membrane potential in a dose- and time-dependent manner, which resulted in cell apoptosis, as demonstrated by fluorescence microscopy, gel electrophoresis and flow-cytometric analysis. Cell cycle analysis further demonstrated that both 3-oxo-23-hydroxybetulinic acid and 23-hydroxybetulinic acid dramatically increased DNA fragmentation at the expense of G1 cells at doses as low as 12.5 and 25 microg/ml, respectively, thereby showing their potent apoptotic properties. Our results showed that hydroxylation at the C3 position of betulinic acid is likely to enhance the apoptotic activity of betulinic acid derivatives (23-hydroxybetulinic acid and 3-oxo-23-hydroxybetulinic acid) on murine melanoma B16 cells.