- Primary research
- Open Access
Antiproliferative activity and apoptosis-inducing mechanism of constituents from Toona sinensis on human cancer cells
© Yang et al.; licensee BioMed Central Ltd. 2013
- Received: 16 December 2012
- Accepted: 4 February 2013
- Published: 9 February 2013
Natural products, including plants, microorganisms and marines, have been considered as valuable sources for anticancer drug discovery. Many Chinese herbs have been discovered to be potential sources of antitumor drugs.
In the present study, we investigated the antitumor efficacy of the compounds isolated from Toona sinensis, an important herbal medicine. The inhibitory activities of these compounds were investigated on MGC-803, PC3, A549, MCF-7, and NIH3T3 cells in vitro by MTT assay. The mechanism of the antitumor action of active compounds was investigated through AO/EB staining, Hoechst 33258 staining, TUNEL assay, flow cytometry analysis, and western blotting analysis.
Fifteen compounds were isolated from the roots of Toona sinensis. Betulonic acid (BTA) and 3-oxours-12-en-28-oic acid (OEA) isolated from the plant inhibited the proliferation of MGC-803 and PC3 cells, with IC50 values of 17.7 μ M and 13.6 μ M, 26.5 μ M and 21.9 μ M, respectively. Both could lead to cell apoptosis, and apoptosis ratios reached 27.3% and 24.5% in MGC-803 cells at 72 h after treatment at 20 μ M, respectively. Moreover, the study of cancer cell apoptotic signaling pathway indicated that both of them could induce cancer cell apoptosis through the mitochondrial pathway, involving the expressions of p53, Bax, caspase 9 and caspase 3.
The study shows that most of the compounds obtained from Toona sinensis could inhibit the growth of human cancer cells. Furthermore, BTA and OEA exhibited potent antitumor activities via induction of cancer cell apoptosis.
- Toona sinensis
Among the conventional antitumor cytotoxic chemotherapies, many compounds are derived from natural products[1–3]. Over 60% of the current anticancer drugs have their origin in one way or another from natural sources[4, 5]. Natural compounds had attracted considerable attention as cancer chemopreventive agents and also as cancer therapeutics[6, 7]. As cancer cells have evolved multiple mechanisms to resist the induction of programmed cell death (apoptosis), the modulation of apoptosis signaling pathways by natural compounds have been demonstrated to constitute a key event in these antitumor activities[8, 9]. Toona sinensis, an important herb medicine, belongs to the Meliaceae family which comprises approximately 50 genera and 1400 species throughout the world, and is widely distributed in China except Xinjiang and Inner Mongolia Autonomous Regions. The objective of present study was to evaluate the potency of the components from the plant for growth inhibiting of human cancer cell lines and to study their antitumor mechanism. Fifteen compounds were isolated from the plant, and these compounds were bioassayed on human gastric cancer cell line MGC-803, prostatic cancer cell line PC3, lung cancer cell line A549, breast cancer cell line MCF-7, and mouse embryonic fibroblast cell line NIH3T3 in vitro by MTT assay. Interestingly, it was found that betulonic acid (BTA) and 3-oxours-12-en-28-oic acid (OEA) had the potent inhibitory activities against MGC-803 and PC3 cell lines, and were less toxic on normal cells than on the investigated cancer cell lines. Also, BTA and OEA are betulinic acid (BA) and ursolic acid (UA) derivatives, respectively. BA and UA are naturally occurring pentacyclic triterpenoids which are widely distributed in the plant kingdom[11, 12]. It was found that BA could inhibit growth of cancer cells[13, 14], without affecting normal cells[15, 16], and it was a highly selective growth inhibitor of human melanoma, neuroectodermal and malignant tumor cells. UA has also been reported to show significant cytotoxicity against some tumor cell lines[13, 18–21]. There are a few reports on the anticancer effects of BTA and OEA on various tumor cells recently. Some studies have shown that BTA could inhibit the growth of various types of human tumor cell lines, including SGC-7901, HepG-2, LNCaP, and DU-145 cells. In 1999, Min et al. found that OEA possessed antitumor activity on A549, SK-OV-3, SK-MEL-2, XF498, and HCT15 cells, with low IC50 values (< 5 μ g/mL). However, no report was found on the antitumor mechanism of the two compounds. Thus, the mechanism of action needs to be further clarified. Further investigation of BTA and OEA was carried out on MGC-803 and PC3 cells, and experimental results of fluorescent staining and flow cytometry analysis indicated that the two compounds could induce cell apoptosis. In addition, the mechanism underlying apoptosis of BTA and OEA was also investigated in this study. To the best of our knowledge, this is the first report on apoptosis inducing of BTA and OEA in MGC-803 and PC3 cells.
Fresh samples of Toona sinensis were collected from Bijie, Guizhou Province in China, in August 2011. Prof. Qingde Long, Department of Medicine, Guiyang Medical University, identified the plant material. A voucher specimen was deposited at Guiyang Medical University, Guiyang, China.
MGC-803, PC3, A549. MCF-7, and NIH3T3 cell lines were obtained from the Institute of Biochemistry and Cell Biology, China Academy of Science. MGC-803 is human gastric cancer cell line, PC3 is prostatic cancer cell line, A549 is lung cancer cell line, MCF-7 is breast cancer cell line, and NIH3T3 is mouse embryonic fibroblast cell line. The entire cancer cell lines were maintained in the RPMI 1640 medium and NIH3T3 was maintained in the DMEM medium. They were supplemented with 10% heat-inactivated fetal bovine serum (FBS) in a humidified atmosphere of 5% CO2 at 37°C. All cell lines were maintained at 37°C in a humidified 5% carbon dioxide and 95% air incubator.
The antitumor activities of the compounds were determined by MTT assay. All tested compounds were dissolved in DMSO and subsequently diluted in the culture medium before treatment of the cultured cells. When the cells were 80-90% confluent, they were harvested by treatment with a solution containing 0.25% trypsin, thoroughly washed and resuspended in supplemented growth medium. Cells (1×104/well) were plated in 100 μ L of medium/well in 96-well plate. After incubations overnight, the cells were treated with different concentrations of extracts or compounds for 72 h. Thereafter, 100 μ L of MTT (Beyotime Co., Jiangsu, China) solution was added to each well and then incubated for 4 h. The colored MTT-formazan crystals which were produced from MTT were dissolved in SDS for 12 h. And then the OD values were measured at 595 nm with a microplate reader (BIO-RAD, model 680), which is directly proportional to the number of living cells in culture[24–26].
The active compounds were investigated for apoptotic activity by AO/EB staining. When the cells were 80-90% confluent, they were harvested by treatment with a solution containing 0.25% trypsin, thoroughly washed and resuspended in supplemented growth medium. The cells were seeded in 6-well tissue culture plates (5×104 cell/mL, 0.6 mL/well). After incubations overnight, the medium was removed and replaced with fresh medium plus 10% FBS and then supplemented with compounds (20 μ mol/L). After the treatment period, 20 μ L of the AO/EB dye mix (Beyotime Co., Shanghai, China) were added to each well, and the apoptotic cells were viewed and counted under the fluorescent microscope (OLYMPUS Co., Tokyo Met, Japan)[27, 28].
Hoechst 33258 staining
Morphological assessment of apoptotic cells was performed using Hoechst 33258 staining method. The cells were seeded in 6-well tissue culture plates (5×104 cell/mL, 0.6 mL/well). After incubations overnight, the medium was removed and replaced with fresh medium plus 10% FBS and then supplemented with compounds (20 μ mol/L) for a certain range of treatment time. The culture medium containing compounds was removed, and the cells were fixed in 4% paraformaldehyde for 10 min. The cells were washed twice with PBS, and were consequently stained with 0.5 mL of Hoechst 33258 staining (Beyotime Co., Jiangsu, China) for 5 min. The stained nuclei were washed twice with PBS, and were consequently observed under an IX71SIF-3 fluorescence microscope at 350 nm excitation and 460 nm emissions.
The cells (5×104 cell/mL, 0.6 mL/well) were seeded in 6-well tissue culture plates. Following incubation, the medium was removed and replaced with fresh medium plus 10% FBS and then supplemented with compounds (20 μ mol/L). TUNEL assays were performed using a colorimetric TUNEL apoptosis assay kit according to the manufacturer’s instructions. (1) After the treatment period, cells were washed with 1×PBS and fixed in 4% paraformaldehyde for 40 min. The cells were washed once with PBS, and were consequently permeabilized with immunol staining wash buffer for 2 min on ice. (2) The cells were rewashed once with PBS, and were consequently incubated in 0.3% H2O2 in methanol at room temperature for 20 min to inactivate the endogenous peroxidases, after which the cells were washed thrice with PBS. (3) The cells were incubated with 2 μ L of TdT-enzyme and 48 μ L of Biotin-dUTP per specimen for 60 min at 37°C. The cells were terminated for 10 min, and were consequently incubated with streptavidin-HRP (50 μ L per specimen) conjugate diluted at 1:50 in sample diluent for 30 min. (4) The cells were washed three times with PBS, and were consequently incubated with diaminobenzidine solution (200 μ L per specimen) for 10 min. At last, the cells were rewashed twice with PBS, and were consequently imaged under an XDS-1B inverted biological microscope.
Flow cytometry analysis
Prepared MGC-803 cells (1×106/mL) were washed twice with cold PBS and then re-suspended gently in 500 μ L binding buffer. Thereafter, cells were stained in 5 μ L Annexin V-FITC and shaked well. Finally, 5 μ L PI was added to these cells and incubated for 20 min in a dark place, analyzed by FACS Calibur, Becton Dickinson[31, 32].
Caspase 3 enzyme assay
Cells were collected after treatment with BTA and OEA at 2.5, 5, and 10 μ M for 12 h, respectively. Prepared MGC-803 cells (1×106/mL, 5 ml) were washed twice with cold PBS. Then, 100 μ L of lysis buffer was added to the cells for 25 min on ice and centrifuged at 16000 g for 15 min. 80 μ L of reaction buffer and 10 μ L of Ac-DEVED-p NA were added to 10 μ L of supernatant liquid. After incubating at 37°C for 2–3 h in darkness, the absorbance was measured at 405 nm, with the lysis buffer and reaction buffer as control
Caspase 9 enzyme assay
Cells were collected after treatment with BTA and OEA at 2.5, 5, and 10 μ M for 12 h, respectively. Prepared MGC-803 cells (1×106/mL, 5 ml) were washed twice with cold PBS. Then, 100 μ L of lysis buffer was added to the cells for 25 min on ice and centrifuged at 16000 g for 15 min. 80 μ L of reaction buffer and 10 μ L of Ac-LEHD-pNA were added to 10 μ L of supernatant liquid. After incubating at 37°C for 2–3 h in darkness, the absorbance was measured at 405 nm, with the lysis buffer and reaction buffer as control.
Western botting analysis
Cells were collected after treatment with BTA and OEA at 2.5, 5, and 10 μ M for 12 h, respectively. Western blotting analysis was performed as previously described, using the following antibodies at dilutions of 1:500 to 1:1000: anti-p53, anti-Bax, and anti-β actin (Cell signaling technology, Beverly, MA).
All statistical analyses were performed using SPSS 10.0, and the data were analyzed using one-way ANOVA. The mean separations were performed using the least significant difference method. Each experiment was performed in triplicate, and all experiments were run thrice and yielded similar results. Measurements from all the replicates were combined, and the treatment effects were analyzed.
The roots of Toona sinensis collected from Guizhou province were studied, and fifteen compounds were isolated from the plants. The extraction and purification process of the compounds from the plant and their NMR data are presented in Additional file1.
Antitumor activities of the isolated compounds on the proliferation of different cell lines
Inhibitory Rate for Different Cell Lines (%, mean ± SD)a
23.5 ± 2.1
16.5 ± 2.3
12.6 ± 3.1
18.9 ± 1.7
5.6 ± 2.4
23.5 ± 5.4
17.8 ± 4.9
7.8 ± 1.5
10.4 ± 1.8
7.6 ± 4.5
12.3 ± 4.1
9.8 ± 3.6
4.5 ± 1.8
7.2 ± 5.2
4.3 ± 2.3
17.2 ± 1.7
22.7 ± 1.4
16.9 ± 2.4
42.2 ± 1.6
4.2 ± 2.5
52.1 ± 5.7
49.6 ± 2.3
45.3 ± 3.2
37.6 ± 3.9
28.9 ± 4.3
45.5 ± 4.1
50.6 ± 1.6
47.1 ± 1.1
43.2 ± 3.6
58.2 ± 3.0
46.1 ± 5.9
42.0 ± 2.2
39.2 ± 6.8
11.1 ± 6.7
3-Oxours-12-en-28-oic acid (8)
45.2 ± 2.0
42.5 ± 1.4
35.9 ± 0.8
37.2 ± 1.5
23.6 ± 1.3
Ursolic acid (9)
52.1 ± 2.2
55.6 ± 2.4
37.6 ± 1.7
47.8 ± 1.2
21.7 ± 4.9
Betulonic acid (10)
56.1 ± 2.6
63.4 ± 4.2
35.2 ± 2.4
51.2 ± 4.4
22.1 ± 6.2
Gallic acid (11)
55.7± 1. 9
40.2 ± 4.2
46.3 ± 3.6
33.1 ± 1.4
13.6 ± 2.2
Betulinic acid (13)
36.9 ± 1.6
23.6 ± 3.4
33.5 ± 2.3
41.6 ± 3.7
23.4 ± 2.9
92.1 ± 1.3
93.4 ± 2.6
96.2 ± 0.8
91.1 ± 2.2
99.4 ± 0.4
Apoptosis is a physiological pattern of cell death characterized by morphological features and extensive DNA fragmentation. Thus, to determine whether the grown inhibitory activities of BTA and OEA were related to the induction of apoptosis, the morphological changes of MGC-803 and PC3 cells were investigated using acridine orange/ethidium bromide (AO/EB) staining and Hoechst 33258 staining, and Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay to confirm cell apoptosis. Moreover, the apoptosis ratios induced by BTA and OEA caused apoptosis in MGC-803 cells were quantitatively assessed by flow cytometry (FCM). Interestingly, whether the cancer cell apoptosis by the two compounds was though the mitochondrial pathway was also studied.
In conclusion, studies on the chemical constituents from Toona sinensis, and their biological activities have assumed significance for the rational development and utilization of this plant. In this study, fifteen compounds were isolated and identified. Meanwhile, the tumor cell growth inhibition effects of these constituents on MGC-803, PC3, A549 and MCF-7 cells were carried out by MTT assay. Among these compounds, BTA and OEA, which were isolated from Toona sinensis, showed potent activities on MGC-803 and PC3 cell lines in a dose-dependent manner. The IC50 values of BTA and OEA on MGC-803 and PC3 cells were determined to be 17.7 μ M and 13.6 μ M, 26.5 μ M and 21.9 μ M, respectively, all of which were lower than that on NIH3T3 cells (IC50 > 50 μ M). The apoptosis inducing activities of BTA and OEA on MGC-803 and PC3 cell lines were investigated through AO/EB staining, Hoechst 33258 staining, and TUNEL assay. In addition, the apoptosis ratios induced by BTA and OEA caused apoptosis of MGC-803 cells were quantitatively assessed by flow cytometry, with apoptosis ratios of 27.3% and 24.5% after 72 h of treatment at 20 μ M, respectively. Interestingly, the BTA and OEA induced cell apoptosis through the mitochondrial pathway in MGC-803 cells. Our findings have implied that BTA and OEA has potential therapeutic value for treatment of cancer.
The authors wish to thank the National Key Program for Basic Research (Nos.2010CB126105, 2010CB134504), the National Natural Science Foundation of China (Nos. 21132003, 21172048), Guizhou Province S&T Program (No. 20103052) for the financial support.
- Demain AL, Vaishnav P: Natural products for cancer chemotherapy. Microb Biotechnol. 2011, 4: 687-699. 10.1111/j.1751-7915.2010.00221.x.PubMed CentralView ArticlePubMedGoogle Scholar
- Massaoka MH, Matsuo AL, Figueiredo CR, Farias CF, Girola N, Arruda DC, Scutti JAB, Romoff P, Favero OA, Ferreira MJP, Lago JHG, Travassos LR: Jacaranone induces apoptosis in melanoma cells via ROS-mediated downregulation of Akt and p38 MAPK activation and displays antitumor activity in vivo. PLoS One. 2012, 7: 1-11.View ArticleGoogle Scholar
- Patel B, Prakash R, Yasir M, Sattwik das: Natural bioactive compound with anticancer potential. Int J Adv Pharm Sci. 2010, 1: 32-41. 10.5138/ijaps.2010.0976.1055.01003.View ArticleGoogle Scholar
- Cragg GM, Newman J: Nature: a vital source of leads for anticancer drug development. Phytochem Rev. 2009, 8: 313-331. 10.1007/s11101-009-9123-y.View ArticleGoogle Scholar
- Cragg GM, Newman J: Plants as a source of anti-cancer and anti-HIV agents. Ann Appl Biol. 2003, 143: 127-133. 10.1111/j.1744-7348.2003.tb00278.x.View ArticleGoogle Scholar
- Nobili S, Lippi D, Witort E, Donnini M, Bausi L, Mini E, Capaccioli S: Natural compounds for cancer treatment and prevention. Pharmacol Res. 2009, 59: 365-378. 10.1016/j.phrs.2009.01.017.View ArticlePubMedGoogle Scholar
- Fulda S, Debatin KM: Sensitization for tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis by the chemopreventive agent resveratrol. Cancer Res. 2004, 64: 337-346. 10.1158/0008-5472.CAN-03-1656.View ArticlePubMedGoogle Scholar
- Fulda S: Modulation of apoptosis by natural products for cancer therapy. Planta Med. 2010, 76: 1075-1079. 10.1055/s-0030-1249961.View ArticlePubMedGoogle Scholar
- Solary E, Droin N, Bettaieb A, Corcos L, Dimanche-Boitrel MT, Garrido C: Positive and negative regulation of apoptotic pathways by cytotoxic agents in hematological malignancies. Leukemia. 2000, 14: 1833-1849. 10.1038/sj.leu.2401902.View ArticlePubMedGoogle Scholar
- Castellanos L, Correa RS, Martinez E, Calderon JS: Oleanane triterpenoids from Cedrela montana (Meliaceae). Z Naturforsch C. 2002, 57: 575-578.PubMedGoogle Scholar
- Kommera H, Dittrich S, Kalbitz J, Dräger B, Mueller T, Paschke R, Kalud-erovic’GN: Carbamate derivatives of betulinic acid and betulin with selective cytotoxic activity. Bioorg Med Chem Lett. 2010, 20: 3409-3412. 10.1016/j.bmcl.2010.04.004.View ArticlePubMedGoogle Scholar
- Rao VS, de Melo CL, Queiroz MGR, Lemos TLG, Menezes DB, Melo TS, Santos FA: Ursolic acid, a pentacyclic triterpene from Sambucus australis, prevents abdominal adiposity in mice fed a high-fat diet. J Med Food. 2011, 14: 1375-1382. 10.1089/jmf.2010.0267.View ArticlePubMedGoogle Scholar
- Ryu SY, Choi SU, Lee SH, Lee CO, No Z, Ahn JW: Antitumor triterpenes from medicinal plants. Arch Pharm Res. 1994, 17: 375-377. 10.1007/BF02974180.View ArticleGoogle Scholar
- Cichewicz RH, Kouzi SA: Chemistry, biological activity, and chemotherapeutic potential of betulinic acid for the prevention and treatment of cancer and HIV infection. Med Res Rev. 2004, 24: 90-114. 10.1002/med.10053.View ArticlePubMedGoogle Scholar
- Chintharlapalli S, Papineni S, Lei P, Pathi S, Safe S: Betulinic acid inhibits colon cancer cell and tumor growth and induces proteasome-dependent and -independent downregulation of specificity proteins (Sp) transcription factors. BMC Cancer. 2011, 11: 371-383. 10.1186/1471-2407-11-371.PubMed CentralView ArticlePubMedGoogle Scholar
- Fulda S: Betulinic acid for cancer treatment and prevention. Int J Mol Sci. 2008, 9: 1096-1107. 10.3390/ijms9061096.PubMed CentralView ArticlePubMedGoogle Scholar
- Pisha E, Chai H, Lee IS, Chagwedera TE, Farnsworth NR, Cordell GA, Beecher CW, Fong HH, Kinghorn AD, Brown DM: Discovery of betulinic acid as a selective inhibitor of human melanoma that functions by induction of apoptosis. Nat Med. 1995, 1: 1046-1051. 10.1038/nm1095-1046.View ArticlePubMedGoogle Scholar
- Min BS, Kim YH, Lee SM, Jung HJ, Lee JS, Na MK, Lee CO, Lee JP, Bae K: Cytotoxic Triterpenes from Crataegus pinnatifida. Arch Pharm Res. 2000, 23: 155-158. 10.1007/BF02975505.View ArticlePubMedGoogle Scholar
- Ma CM, Cai SQ, Cui JR, Wang RQ, Tu PF, Hattori M, Daneshtalab M: The cytotoxic activity of ursolic acid derivatives. Eur J Med Chem. 2005, 40: 582-589. 10.1016/j.ejmech.2005.01.001.View ArticlePubMedGoogle Scholar
- Kim DK, Baek JH, Kang CM, Yoo MA, Sung JW, Chung HY, Kim ND, Choi YH, Lee SH, Kim KW: Apoptotic activity of ursolic acid may correlate with the inhibition of initiation of DNA replication. Int J Cancer. 2000, 87: 629-836. 10.1002/1097-0215(20000901)87:5<629::AID-IJC2>3.0.CO;2-P.View ArticlePubMedGoogle Scholar
- Andersson D, Liu JJ, Nilsson A, Duan RD: Ursolic acid inhibits proliferation and stimulates apoptosis in HT29 cells following activation of alkaline sphingomyelinase. Anticancer Res. 2003, 23: 3317-3322.PubMedGoogle Scholar
- Zhang X, Li H, Jin Y, Fang G: Effects of betulonic acid on SGC-7901, HepG-2 and mice of bearing S180 tumor cells. Nat Prod Res Dev. 2009, 21: 766-770.Google Scholar
- Saxena BB, Zhu L, Hao M, Kisilis E, Katdare M, Oktem O, Bomshteyna A, Rathnam P: Boc-lysinated-betulonic acid: a potent, anti-prostate cancer agent. Bioorg Med Chem. 2006, 14: 6349-6358. 10.1016/j.bmc.2006.05.048.View ArticlePubMedGoogle Scholar
- Guo L, Wu JZ, Han T, Cao T: Chemical composition, antifugal and antitumor properties of ether extracts of Scapania verrucosa Heeg. and its endophytic fungus Chaetomium fusiforme. Molecules. 2008, 13: 2114-2125. 10.3390/molecules13092114.View ArticlePubMedGoogle Scholar
- Dellai A, Deghrigue M, Laroche-Clary A, Masour HB, Chouchane N, Robert J, Bouraoui A: Evaluation of antiproliferative and anti-inflammatory activities of methanol extract and its fractions from the Mediterranean sponge. Cancer Cell Int. 2012, 12: 18-10.1186/1475-2867-12-18.PubMed CentralView ArticlePubMedGoogle Scholar
- Kjellström J, Oredsson SM, Wennerberg J: Increased toxicity of a trinuclear Pt-compound in a human squamous carcinoma cell line by polyamine depletion. Cancer Cell Int. 2012, 12: 20-10.1186/1475-2867-12-20.View ArticlePubMedGoogle Scholar
- Wei HB, Hu BG, Han XY, Zheng ZH, Wei B, Huang JL: Effect of all-trans retinoic acid on drug sensitivity and expression of survivin in LoVo cells. Chin Med J. 2008, 4: 331-335.Google Scholar
- Jiang Z, Wu W, Qian M: Cellular damage and apoptosis along with changes in NF-kappa B expression were induced with contrast agent enhanced ultrasound in gastric cancer cells and hepatoma cells. Cancer Cell Int. 2012, 12: 8-10.1186/1475-2867-12-8.PubMed CentralView ArticlePubMedGoogle Scholar
- Holmquist G: Hoechst 33258 fluorescent staining of Drosophila chromosomes. Chromosoma. 1975, 49: 333-356.View ArticlePubMedGoogle Scholar
- Liu MC, Yang SJ, Jin LH, Hu DY, Wu ZB, Yang S: Chemical constituents of the ethyl acetate extract of Belamcanda chinensis (L.) DC roots and their antitumor activities. Molecules. 2012, 5: 6156-6169.View ArticleGoogle Scholar
- Orozco AF, Lewis DE: Flow cytometric analysis of circulating microparticles in plasma. Cytom A. 2010, 77: 502-514.View ArticleGoogle Scholar
- Ishikawa J, Takahashi Y, Hazawa M, Fukushi Y, Yoshizawa A, Kashiwakura I: Suppressive effects of liquid crystal compounds on the growth of U937 human leukemic monocyte lymphoma cells. Cancer Cell Int. 2012, 12: 3-10.1186/1475-2867-12-3.PubMed CentralView ArticlePubMedGoogle Scholar
- Liu J, Uematsu H, Tsuchida N, Ikeda MA: Essential role of caspase-8 in p53/p73-dependent apoptosis induced by etoposide in head and neck carcinoma cells. Mol Cancer. 2011, 10: 1-13. 10.1186/1476-4598-10-1.View ArticleGoogle Scholar
- Collins JA, Schandl CA, Young KK, Vesely J, Willingham MC: Major DNA fragmentation is a late event in apoptosis. J Histochem Cytochem. 1997, 45: 923-934. 10.1177/002215549704500702.View ArticlePubMedGoogle Scholar
- Liu MC, Yang SJ, Jin LH, Hu DY, Xue W, Song BA, Yang S: Synthesis and cytotoxicity of novel ursolic acid derivatives containing an acyl piperazine moiety. Eur J Med Chem. 2012, 58: 128-135.View ArticlePubMedGoogle Scholar
- Wu J, Yi WS, Jin LH, Hu DY, Song BA: Antiproliferative and cell apoptosis-inducing activities of compounds from Buddleja davidii in MGC-803 cells. Cell Div. 2012, 7: 1-20. 10.1186/1747-1028-7-1.View ArticleGoogle Scholar
- Xu XQ, Gao XH, Jin LH, Yuan K, Hu DY, Song BA, Yang S: Antiproliferation and cell apoptosis inducing bioactivities of constituents from Dysosma versipellis in PC3 and Bcap-37 cell lines. Cell Div. 2011, 6: 1-14. 10.1186/1747-1028-6-1.View ArticleGoogle Scholar
- Yuan K, Song BA, Jin LH, Xu S, Hu DY, Xu XQ, Yang S: Synthesis and biological evaluation of novel 1-aryl, 5-(phenoxy-substituted) aryl-1,4-pentadien-3-one derivatives. Med Chem Commn. 2011, 2: 585-589. 10.1039/c1md00038a.View ArticleGoogle Scholar
- Cui H, Schroering A, Ding HF: p53 mediates DNA damaging drug-induced apoptosis through a caspase-9-dependent pathway in SH-SY5Y neuroblastoma cells. Mol Cancer Ther. 2002, 1: 679-686.PubMedGoogle Scholar
- Juin P, Hunt A, Littlewood T, Griffiths B, Swigart BL, Korsmeyer S, Evan G: c-Myc functionally cooperates with Bax to induce apoptosis. Mol Cell Biol. 2002, 22: 6158-6169. 10.1128/MCB.22.17.6158-6169.2002.PubMed CentralView ArticlePubMedGoogle Scholar
- Brunelle JK, Letai A: Control of mitochondrial apoptosis by the Bcl-2 family. J Cell Sci. 2009, 122: 437-441. 10.1242/jcs.031682.PubMed CentralView ArticlePubMedGoogle Scholar
- Basu A, Haldar S: The relationship between Bcl2, Bax and p53: consequences for cell cycle progression and cell death. Mol Hum Reprod. 1998, 1998: 1099-1109.View ArticleGoogle Scholar
- Gross A, McDonnell JM, Korsmeyer SJ: BCL-2 family members and the mitochondria in apoptosis. Gene Dev. 1999, 13: 1899-1911. 10.1101/gad.13.15.1899.View ArticlePubMedGoogle Scholar
- Rodriguez J, Lazebnik Y: Caspase-9 and APAF-1 form an active holoenzyme. Gene Dev. 1999, 13: 3179-3184. 10.1101/gad.13.24.3179.PubMed CentralView ArticlePubMedGoogle Scholar
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