Investigation of the component of Lycopodium serratum extract that inhibits proliferation and mediates apoptosis of human HL-60 leukemia cells

In this study, we investigate a plant commonly used in herbal medicines, Lycopodium serratum, which is believed to have anti-cancer properties. An alcoholic extract of L. serratum (LSE) was investigated for its ability to induce apoptosis in cultured human promyelocytic leukemia HL-60 cells. Treatment of HL-60 cells with various concentrations of LSE (6–100 μg/mL) resulted in a sequence of events characteristic of apoptosis, including loss of cell viability, morphological changes, and increased sub-G₁ DNA content. Serratenediol (SE), a known biologically active agent, was isolated from MC fraction of LSE and was able to demonstrate significant and dose-dependent growth inhibitory effects on HL-60 cells. Similar to the effects observed with the crude LSE, the SE-related effects included the formation of apoptotic bodies and fragmented DNA, as well as the accumulation of DNA in the sub-G₁ phase of the cell cycle. Analysis of the mechanism of these events indicated that SE treated cells had an increased ratio of Bax/Bcl-xL, released the cytochrome c, activated caspase-9, -3, and cleaved poly-ADP-ribose polymerase (PARP); these observations are hallmarks of apoptotic events. Thus, the results suggest that SE can induce apoptosis via regulating the ratio of Bax/Bcl-xL in HL-60 cell lines.     

Caspases家族成员促进DADAG诱导的人白血病HL—60细胞凋亡

目的:研究caspases家族成员在二乙酰二脱水卫矛醇(DADAG)诱导人白血病HL-60细胞凋亡中的作用.方法:MTT法观察DADAG的体外抗增殖作用;透射电镜、DNA梯形条带和流式细胞仪检测HL-60细胞凋亡;caspase-3检测试剂盒和Western blot法分析caspases家族成员.结果:DADAG明显抑制HL-60细胞增殖和诱导细胞凋亡.DADAG处理HL-60细胞24h后,caspase-3酶活性达峰值,同时聚腺苷二磷酸核糖聚合酶(PARP)、lamin B和DFF45蛋白开始出现断裂片段.Caspase-3抑制剂z-DEVD·fmk可部分逆转DADAG诱导的HL-60细胞凋亡,而caspases广谱抑制剂z-VAD·fmk可完全逆转此作用.结论:Caspases在DADAG诱导HL-60细胞凋亡中起重要作用,它们通过酶解底物PARP、DFF45和lamin B促进细胞凋亡.     

DNA引物酶抑制剂碘化-3,3′-二乙基-9-甲基-硫杂羰花青诱导人白血病HL-60细胞凋亡

目的研究DNA引物酶抑制剂碘化-3,3′-二乙基-9-甲基-硫杂羰花青(DMTCCI)诱导人粒细胞性白血病HL-60细胞凋亡并探索其机制。方法分别采用不同浓度的DMTCCI处理培养于RPMI-1640培养基的HL-60细胞。采用MTT法检测DMTCCI对HL-60细胞的生长抑制作用。采用流式细胞仪和DNA琼脂糖凝胶电泳方法检测细胞凋亡。采用蛋白免疫印迹(Western blotting)法观察凋亡相关蛋白survivin， Bcl-xL， Bad， Bax， Bcl-2， caspase-9， caspase-3， caspase-6， PARP， DFF45和lamin B的表达。采用ApoAlert Caspase-3分析试剂盒检测caspase-3的活性。结果DMTCCI具有抑制人白血病HL-60细胞增殖的作用，其IC₅₀值为0.24 μmol·L^-1。流式细胞仪和DNA琼脂糖凝胶电泳结果显示，DMTCCI可诱导HL-60细胞凋亡。在经DMTCCI处理的HL-60细胞中，survivin和Bcl-xL蛋白的表达水平下调，Bad和Bax蛋白的表达水平上调，Bcl-2蛋白的表达水平无变化，caspase-9，caspase-3，caspase-6，PARP，DFF45和lamin B被分别裂解，产生相应裂解产物。在HL-60细胞中，caspase-3的活性在1 μmol·L^-1 DMTCCI处理3 h时明显升高，在处理12 h时达到最高峰。结论DMTCCI可抑制人白血病HL-60细胞的增殖并诱导其发生细胞凋亡。Bcl-2家族蛋白、survivin和caspases家族蛋白可能参与了上述诱导HL-60细胞凋亡的过程。     

DNA引物酶抑制剂碘化-3,3''-二乙基-9-甲基-硫杂羰花青诱导人白血病HL-60细胞凋亡

目的 研究DNA引物酶抑制剂碘化-3,3'-二乙基-9-甲基-硫杂羰花青(DMTCCI)诱导人粒细胞性白血病HL-60细胞凋亡并探索其机制.方法 分别采用不同浓度的DMTCCI处理培养于RPMI-1640培养基的HL-60细胞.采用MTT法检测DMTCCI对HL-60细胞的生长抑制作用.采用流式细胞仪和DNA琼脂糖凝胶电泳方法检测细胞凋亡.采用蛋白免疫印迹(Western blotting)法观察捌亡相关蛋白survivin,Bcl-xL,Bad,Bax,Bcl-2,caspase-9,caspase-3,caspase-6,PARP,DFF45和lamin B的表达.采用ApoAlert Caspase-3分析试剂盒检测caspase-3的活性.结果 DMTCCI具有抑制人白血病HL-60细胞增殖的作用,其IC50值为0.24μmol·L-1.流式细胞仪和DNA琼脂糖凝胶电泳结果显示,DMTCCI可诱导HL-60细胞凋亡.在经DMTCCI处理的HL-60细胞中,survivin和Bcl-xL蛋白的表达水平下调,Bad和Bax蛋白的表达水平上调,Bcl-2蛋白的表达水平无变化,caspase-9,caspase-3,caspase-6,PARP, DFF45和lamin B被分别裂解,产生相应裂解产物.在HL-60细胞中,caspase-3的活性在1μmol·L-1 DMTCCI处理3 h时明显升高,在处理12 h时达到最高峰.结论 DMTCCI可抑制人白血病HL-60细胞的增殖并诱导其发生细胞凋亡.Bcl-2家族蛋白、survivin和caspases家族蛋白可能参与了上述诱导HL-60细胞凋亡的过程.     

Fucoxanthin induces apoptosis in human leukemia HL-60 cells through a ROS-mediated Bcl-xL pathway

Fucoxanthin, a natural biologically active substance isolated from Ishige okamurae, evidences antitumor activity in human leukemia cell HL-60 cells via the induction of apoptosis. However, the mechanism underlying fucoxanthin-induced apoptosis in HL-60 cells remains unclear. In this study, we focused on the effect of fucoxanthin induction on the accumulation of reactive oxygen species (ROS), and on the triggering of Bcl-xL signaling pathway in HL-60 cells. We determined that ROS are generated during fucoxanthin-induced cytotoxicity and apoptosis in HL-60 cells, and that N-acetylcysteine (NAC), a ROS scavenger, suppressed fucoxanthin-induced cytotoxicity and apoptosis. Moreover, fucoxanthin-induced the cleavage of caspases -3 and -7, and poly-ADP-ribose polymerase (PARP) and a decrease of Bcl-xL levels, whereas NAC pre-treatment significantly inhibited caspase-3, -7, and PARP cleavage and the reduction in Bcl-xL levels. In this study, it was demonstrated for the first time that fucoxanthin generated ROS and that the accumulation of ROS performed a crucial role in the fucoxanthin-induced Bcl-xL signaling pathway.     

Ellagitannins from Terminalia calamansanai induced apoptosis in HL-60 cells

Terminalia calamansanai (Blanco) Rolf. (Combretaceae) is used medicinally as lithontriptic in Philippines. The 70% acetone extracts of T. calamansanai leaves inhibited the viability of human promyelocytic leukemia HL-60 cells. 1-α-O-Galloylpunicalagin, punicalagin, 2-O-galloylpunicalin, sanguiin H-4, and methyl gallate were the main components isolated from T. calamansanai with the IC₅₀ values of 65.2, 74.8, 42.2, 38.0 and >100 μM, respectively, for HL-60 cells. Apoptosis of HL-60 cells treated with 1-α-O-galloylpunicalagin, punicalagin, 2-O-galloylpunicalin, and sanguiin H-4 was noted by the appearance of a sub-G₁ peak in flow cytometric analysis and DNA fragmentation by gel electrophoresis. 2-O-Galloylpunicalin and sanguiin H-4 induced a decrease of the human poly(ADP-ribose)polymerase (PARP) cleavage-related procaspase-3 and elevated activity of caspase-3 in HL-60 cells, but not normal human peripheral blood mononuclear cells (PBMCs), suggesting that both compounds may be new candidates for drug development in the prevention and treatment of cancer.     

N,N-dimethyl phytosphingosine induces caspase-8-dependent cytochrome c release and apoptosis through ROS generation in human leukemia cells

N,N-dimethyl phytosphingosine (DMPS) blocks the conversion of sphingosine to sphingosine-1-phosphate (S1P) by the enzyme sphingosine kinase (SK). In this study, we elucidated the apoptotic mechanisms of DMPS action on a human leukemia cell line using functional pharmacologic and genetic approaches. First, we demonstrated that DMPS-induced apoptosis is evidenced by nuclear morphological change, distinct internucleosomal DNA fragmentation, and an increased sub-G1 cell population. DMPS treatment led to the activation of caspase-9 and caspase-3, accompanied by the cleavage of poly(ADP-ribose) polymerase (PARP) and led to cytochrome c release, depolarization of the mitochondrial membrane potential, and downregulation of the anti-apoptotic members of the bcl-2 family. Ectopic expression of bcl-2 and bcl-xL conferred resistance of HL-60 cells to DMPS-induced cell death, suggesting that DMPS-induced apoptosis occurs predominantly through the activation of the intrinsic mitochondrial pathway. We also observed that DMPS activated the caspase-8–Bid–Bax pathway and that the inhibition of caspase-8 by z-IETD-fmk or small interfering RNA suppressed the cleavage of Bid, cytochrome c release, caspase-3 activation, and apoptotic cell death. In addition, cells subjected to DMPS exhibited significantly increased reactive oxygen species (ROS) generation, and ROS scavengers, such as quercetin and Tiron, but not N-acetylcysteine (NAC), inhibited DMPS-induced activations of caspase-8, -3 and subsequent apoptotic cell death, indicating the role of ROS in caspase-8-mediated apoptosis. Taken together, these results indicate that caspase-8 acts upstream of caspase-3, and that the caspase-8-mediated mitochondrial pathway is important in DMPS-induced apoptosis. Our results also suggest that ROS are critical regulators of caspase-8-mediated apoptosis in DMPS-treated leukemia cells.     

Wogonin and fisetin induce apoptosis in human promyeloleukemic cells, accompanied by a decrease of reactive oxygen species, and activation of caspase 3 and Ca(2+)-dependent endonuclease

Seven structurally related flavonoids including luteolin, nobiletin, wogonin, baicalein, apigenin, myricetin and fisetin were used to study their biological activities on the human leukemia cell line, HL-60. On MTT assay, wogonin, baicalein, apigenin, myricetin and fisetin showed obvious cytotoxic effects on HL-60 cells, with wogonin and fisetin being the most-potent apoptotic inducers among them. The cytotoxic effects of wogonin and fisetin were accompanied by the dose- and time-dependent appearance of characteristics of apoptosis including DNA fragmentation, apoptotic bodies and the sub-G1 ratio. Treatment with an apoptosis-inducing concentration of wogonin or fisetin causes rapid and transient induction of caspase 3/CPP32 activity, but not caspase 1 activity. Further, cleavage of poly(ADP-ribose) polymerase (PARP) and decrease of pro-caspase 3 protein were detected in wogonin- and fisetin-treated HL-60 cells. An increase in the pro-apoptotic protein, bax, and a decrease in the anti-apoptotic protein, Mcl-1, were detected in fisetin- and wogonin-treated HL-60 cells. However, Bcl-2, Bcl-XL, and Bad all remained unchanged in wogonin- and fisetin-treated HL-60 cells. In vitro chromatin digestion revealed that endonuclease activity was profoundly enhanced in wogonin- and fisetin-treated HL-60 cells, and the addition of ethylenediaminetetraacetic acid (EDTA) or ethyleneglycoltetraacetic acid (EGTA) into the reaction blocked endonuclease activation and at an optimum pH of 7.5. The caspase 3 inhibitor, Ac-DEVD-CHO, but not the caspase 1 inhibitor, Ac-YVAD-CHO, attenuated wogonin- and fisetin-induced DNA ladders, PARP cleavage, and endonuclease activation. Pretreatment of HL-60 cells with N-acetyl-cysteine or catalase efficiently inhibited H(2)O(2) (200 microM)-induced apoptosis, but showed no inhibitory effect on wogonin- and fisetin-induced DNA ladders, caspase 3 activation, or bax protein induction. Decrease in endogenous ROS production was detected in wogonin- and fisetin-treated HL-60 cells by DCHF-DA assay. In conclusion, our experiments indicate that a decrease in intracellular peroxide level was involved in wogonin- and fisetin-induced apoptosis; activation of caspase 3 and endonuclease, induction of bax protein and suppression of Mcl-1 protein were detected in the process.     

Hexahydro-β-acids induce apoptosis through mitochondrial pathway, GADD153 expression, and caspase activation in human leukemia cells

Hexahydro-β-acids (HBA) and β-acids (BA) displayed strong growth inhibitory effects against human leukemia HL-60 cells and were able to induce apoptosis in a concentration- and time-dependent manner and the morphological changes associated with apoptotic cell death; however, BA was less effective. Treatment with HBA caused a rapid loss of mitochondrial trans-membrane potential, release of mitochondrial cytochrome c into cytosol. The levels of Bad and Bax were dramatically increased in cells treated with HBA. In addition, the results showed that HBA promoted the up-regulation of Fas prior to the processing and activation of pro-caspase-8 and cleavage of Bid, suggesting the involvement of a Fas-mediated pathway in HBA-induced cells. Moreover, the changes occurred after single breaks in DNA were detected, suggesting that HBA induced irreparable DNA damage, which in turn triggered the process of apoptosis. HBA markedly enhanced the growth arrest DNA damage-inducible gene 153 (GADD153) protein in a concentration- and time-dependent manner. These findings suggest that HBA creates an oxidative cellular environment that induces DNA damage and GADD153 gene activation, which in turn triggers apoptosis in HL-60 cells. Our study identified the novel mechanisms of HBA-induced apoptosis and indicated that HBA may be used as a potential chemopreventive and chemotherapeutic agent.     

Inhibition of topoisomerase II by the marine alkaloid ascididemin and induction of apoptosis in leukemia cells

Ascididemin (ASC) is a pentacyclic DNA-intercalating agent isolated from the Mediterranean ascidian Cystodytes dellechiajei. This marine alkaloid exhibits marked cytotoxic activities against a range of tumor cells, but its mechanism of action remains poorly understood. We investigated the effects of ASC on DNA cleavage by human topoisomerases I and II. Relaxation assays using supercoiled DNA showed that ASC stimulated double-stranded cleavage of DNA by topoisomerase II, but exerted only a very weak effect on topoisomerase I. ASC is a conventional topoisomerase II poison that significantly promoted DNA cleavage, essentially at sites having a C on the 3' side of the cleaved bond (-1 position), as observed with etoposide. The stimulation of DNA cleavage by topoisomerase I in the presence of ASC was considerably weaker than that observed with camptothecin. Cytotoxicity measurements showed that ASC was even less toxic to P388 leukemia cells than to P388CPT5 cells resistant to camptothecin. In addition, the marine alkaloid was found to be equally toxic to HL-60 leukemia cells sensitive or resistant to mitoxantrone. It is therefore unlikely that topoisomerases are the main cellular targets for ASC. This alkaloid was found to strongly induce apoptosis in HL-60 and P388 leukemia cells. Cell cycle analysis showed that ASC treatment was associated with a loss of cells in the G1 phase accompanied with a large increase in the sub-G1 region. Cleavage experiments with poly(ADP-ribose) polymerase (PARP) revealed that caspase-3 was a mediator of the apoptotic pathway induced by ASC. The DNA of ASC-treated cells was severely fragmented. Collectively, these findings indicate that ASC is a potent inducer of apoptosis in leukemia cells.     

Celastrol isolated from Tripterygium regelii induces apoptosis through both caspase-dependent and -independent pathways in human breast cancer cells

The aim of the present study was to evaluate the underlying apoptotic mechanisms of celastrol, a major biologically active component of Tripterygium regelii, in human breast adenocarcinoma MCF-7 cells. Celastrol was isolated from T. regelii chloroform extract by silica gel column chromatography, and its chemical structure was identified via ¹H NMR and ¹³C NMR. Celastrol significantly inhibited cell growth in dose- and time-dependent manners. Celastrol induced sub-G1 DNA accumulation, formation of apoptotic bodies, nuclear condensation, and a DNA ladder in MCF-7 cells. Celastrol triggered the activation of caspase family proteins. Celastrol caused activation of caspase-7, -8, and -9, PARP cleavage, caspase-8-mediated bid cleavage, and release of cytochrome c and AIF. In addition, celastrol decreased the expression of anti-apoptotic Bcl-2 protein and increased expression of pro-apoptotic Bax protein. These results suggest that celastrol inhibits the proliferation of MCF-7 cells through induction of apoptosis, which is mediated by a mitochondrial-dependent caspase pathway.     

A novel aminosteroid of the 5α-androstane-3α,17β-diol family induces cell cycle arrest and apoptosis in human promyelocytic leukemia HL-60 cells

RM, a novel aminosteroid synthesized by our research group, shows a broad spectrum of antitumor activity against nine cancer cell lines and limited toxicity against two normal cell lines. However, its related mechanism of action has not yet been elucidated. In this study, we investigated the cellular and molecular events underlying the cytotoxicity of RM in human acute promyelocytic leukemia HL-60 cells. RM was found to induce a G0/G1 cell cycle block of HL-60 cells but not terminal myeloid differentiation. Interestingly, typical apoptotic morphological changes were exhibited by HL-60 cells treated with RM stained with Hoechst 33342 and examined by fluorescence microscopy. Apoptotic death assay using annexin-V/propidium iodide dual staining flow cytometry demonstrated a dose-dependent apoptotic effect of RM on HL-60 cells. In addition, RM induced the cleavage of caspase-3, caspase-8 and PARP, but not the cleavage of caspase-9. Our findings suggest that RM reduces HL-60 cells survival through a caspase-dependent death receptor pathway.     

Fluoride induces apoptosis by caspase-3 activation in human leukemia HL-60 cells

Even though fluoride toxicity is increasingly being considered to be important, very little information is available on the mechanism of action of fluoride. In the present study, the toxicity of fluoride on human leukemia (HL-60) cells was investigated and the involvement of caspase-3 was also studied. Fluoride induced apoptosis in HL-60 cells in a dose- and time-dependent manner. Annexin staining and DNA ladder formation on agarose gel electrophoresis further revealed that HL-60 cells underwent apoptosis on exposure to 2-5 mM fluoride. Western blotting using polyclonal anti-caspase-3 antibody and mouse anti-human poly(ADP-ribose) polymerase (PARP) monoclonal antibody was performed to investigate caspase-3 and PARP activity. Fluoride led to the activation of caspase-3 which was evident by the loss of the 32 kDa precursor and appearance of the 17 kDa subunit. Furthermore, intact 116 kDa PARP was cleaved by fluoride treatment as shown by the appearance of a cleaved 89 kDa fragment. The results clearly suggest that fluoride causes cell death in HL-60 cells by causing the activation of caspase-3 which in turn cleaves PARP leading to DNA damage and ultimately cell death.     

The cytotoxicity of eutigosides fromEurya emarginata against HL-60 promyelocytic leukemia cells

Two phenolic glucosides, eutigoside B and eutigoside C were isolated from the fresh leaves of Eurya emarginata. These two phenolic glucosides exerted a significant inhibitory effect on the growth of HL-60 promyelocytic leukemia cells. Furthermore, when the HL-60 cells were treated with eutigoside C, several apoptotic characteristics such as DNA fragmentation, morphologic changes, and increase of the population of sub-G1 hypodiploid cells were observed. In order to understand the mechanism of apoptosis induction by eutigoside C, we examined the changes of Bcl-2 and Bax expression levels. The eutigoside C reduced Bcl-2 protein and mRNA levels, but slightly increased Bax protein and mRNA levels in a time-dependent manner. When we examined the activation of caspase-3, an effector of apoptosis, the eutigoside C increased the expression of active form (19-kDa) of caspase-3 and the increase of their activities was demonstrated by the cleavage of poly (ADP-ribose) polymerase, a substrate of caspase-3, to 85-kDa. The results suggest that the inhibitory effect of eutigoside C from E. emarginata on the growth of HL-60 appears to arise from the induction of apoptosis via the down-regulation of Bcl-2 and the activation of caspase.     

Decursin from Angelicagigas Nakai induces apoptosis in RC-58T/h/SA#4 primary human prostate cancer cells via a mitochondria-related caspase pathway

Decursin is a major biological active component of Angelicagigas Nakai and is known to induce apoptosis of metastatic prostatic cancer cells. However, the apoptotic mechanism of decursin using primary malignant tumor (RC-58T/h/SA#4)-derived human prostate cells is not known. In the present study, we show that treatment of prostate cancer cells with decursin inhibited cell proliferation in a dose-dependent manner. Decursin also induced apoptosis in RC-58T/h/SA#4 cells, as determined by flow cytometry, Hoechst 33258 staining, and DNA fragmentation. Decursin caused activation of caspases-8, -9, and -3 and promoted the apoptotic action of caspase-8-mediated Bid cleavage. Decursin increased the protein levels of Bax and cytosolic cytochrome c as well as cleavage of PARP while decreasing the protein levels of Bcl-2. Furthermore, the caspase-independent mitochondrial apoptosis factor, apoptosis-inducing factor (AIF), was upregulated by treatment with decursin. Taken together, these findings indicate that decursin inhibited the proliferation of RC-58T/h/SA#4 cells through induction of apoptosis, which is mediated by both caspase-dependent and -independent apoptotic pathways.     

Toosendanin induces apoptosis through suppression of JNK signaling pathway in HL-60 cells

Toosendanin (TSN), a triterpenoid isolated from Melia toosendan Sieb. et Zucc., has been found to suppress proliferation and induce apoptosis in a variety of human cancer cells. However, the mechanism how TSN induces apoptosis remains poorly understood. In this study, we examined the effects of TSN on the growth, cell cycle arrest, induction of apoptosis and the involved signaling pathway in human promyelocytic leukemia HL-60 cells. Proliferation of HL-60 cells was inhibited in a dose-dependent manner with the IC_{50 (48h)} of 28 ng/mL. The growth inhibition was due primarily to the S phase arrest and cell apoptosis. Cell apoptosis induced by TSN was confirmed by Annexin V-FITC/propidium iodide staining. The increase of the pro-apoptotic protein Bax, cleaved PARP and caspase-3, and the decrease of anti-apoptotic protein Bcl-2 were observed. Western blot analysis indicated that TSN inhibits the CDC42/MEKK1/JNK pathway. Taken together, our study suggested, for the first time, that the pro-apoptotic effects of TSN on HL-60 cells were mediated through JNK signaling pathway.     

Baicalein induced in vitro apoptosis undergo caspases activity in human promyelocytic leukemia HL-60 cells.

In this study, we evaluated the potential apoptosis effects of baicalein on human promyelocytic leukemia HL-60 cells in vitro. Apoptosis induction, cell viability, morphology and caspase-3 activity were then performed to determine by flow cytometric assay, DNA gel electrophoresis, anti-ADP-ribose stain and determination of caspase-3 activity. There is a significant difference in cell death of HL-60 cells that was detected between baicalein-treated and untreated groups. Furthermore, there was a further significant increase in apoptosis induction when cells were treated with baicalein compared to without baicalein treated groups. Flow cytometric assays and DNA fragmentation gel electrophoresis also confirmed baicalein induced apoptosis in HL-60 cells. Baicalein also promoted caspase-3 activity then leading to cleavage of poly-ADP-ribose polymerase finally leading to DNA fragmentation occurrence. Furthermore, the baicalein-induced apoptosis was markedly blocked by the broad-spectrum caspase inhibitor, z-VAD-fmk. Taken together, these results suggest that treatment of human leukemia HL-60 cells with baicalein induced apoptosis through activation of caspase-3 activity.     

Disruption of the PI3K/AKT/mTOR signaling cascade and induction of apoptosis in HL-60 cells by an essential oil from Monarda citriodora

We have isolated an essential oil from Monarda citriodora (MC) and characterized its 22 chemical constituents with thymol (82%), carvacrol (4.82%), β-myrcene (3.45%), terpinen-4-ol (2.78%) and p-cymene (1.53%) representing the major constituents. We have reported for the first time the chemotherapeutic potential of MC in human promyelocytic leukemia HL-60 cells by means of apoptosis and disruption of the PI3K/AKT/mTOR signaling cascade. MC and its major constituent, thymol, inhibit the cell proliferation in different types of cancer cell lines like HL-60, MCF-7, PC-3, A-549 and MDAMB-231. MC was found to be more cytotoxic than thymol in HL-60 cells with an IC₅₀ value of 22 μg/ml versus 45 μg/ml for thymol. Both MC and thymol induce apoptosis in HL-60 cells, which is evident by Hoechst staining, cell cycle analysis and immuno-expression of Bcl-xL, caspase-3,-8,-9 and PARP-1 cleavage. Both induce apoptosis by extrinsic and intrinsic apoptotic pathways that were confirmed by enhanced expression of death receptors (TNF-R1, Fas), caspase-9, loss of mitochondrial membrane potential and regression of Bcl-2/Bax ratio. Interestingly, both MC and thymol inhibit the downstream and upstream signaling of PI3K/AKT/mTOR pathway. The degree of apoptosis induction and disruption of the PI3K signaling cascade by MC was significantly higher when compared to thymol.