Induction of cell cycle arrest and apoptosis in human cervix carcinoma cells during therapy by cisplatin

The aim of the therapy of human malignancies is the inhibition of cell proliferation and/or induction of apoptosis. We studied the kinetics of the morphological and biochemical changes in HeLa cells during chemotherapy by cisplatin (CP). Apoptosis was evaluated by scoring of cells exhibiting changes characteristic for early and late stages of apoptosis as determined by Hoechst 33258 staining and by examination of positive reaction for activated caspase-3. Expression and intracellular localization of distinct proteins was analyzed by immunoblotting of subcellular fractions and segregation of nucleoli by immunocytochemistry. Chromatin fragmentation characteristic for apoptosis was observed in single cells after 3h cisplatin. A strong cytoplasmic accumulation of cytochrome C detected by immunoblotting 6h post-treatment was accompanied by an activation of caspase-9. Neither inhibition of cell division nor blocking of DNA replication preceded the onset of apoptosis. Our results show that after short treatment by CP, cell proliferation and apoptosis concomitantly occurred.     

A selective cyclooxygenase-2 inhibitor, NS398, inhibits cell growth and induces cell cycle arrest in the G2/M phase in human esophageal squamous cell carcinoma cells

It is well known that cyclooxygenase (COX) -2 is expressed in a variety of human malignant solid tumors, associated with tumor angiogenesis, cell proliferation and inhibition of apoptosis. Here, we examined the effect of NS398, a selective COX-2 inhibitor, on two human esophageal squamous cell carcinoma (SCC) cell lines, TE-1 and TE-12. Western blot analysis confirmed the expression of COX-2 in TE-12, but not in TE-1. Treatment with 100microM NS398 suppressed the cell viability in TE-12 (48.6% of control) after 48 hours, in contrast to showing no effects in TE-1. The apoptotic index was extremely low in both cell lines after the treatment. NS398 clearly increased the number of cells in the G2/M phase and decreased the cells in the G1 and S phases in TE-12, but not TE-1. A pre-G1 fraction was not noted in either cell line. Moreover, TE-12 cells showed a decrease in the expression levels of cyclin B1 and an increase in p27Kip1. These findings suggest that NS398 inhibits cell growth and induces G2/M arrest in human SCC cells expressing COX-2.     

Resveratrol inhibits oral squamous cell carcinoma through induction of apoptosis and G2/M phase cell cycle arrest

The present study was performed to investigate the effect of resveratrol (trans-3,4′,5-trihydroxystilbene) present as a natural phytoalexin in grapes, peanuts, and red wine on oral squamous cancer cell lines, SCC-VII, SCC-25, and YD-38. MTS assay and flow cytometry, respectively, were used for the analysis of inhibition of cell proliferation and apoptosis. Western blot analysis was performed to examine the effect of resveratrol on the expression of proteins associated with cell cycle regulation. The results revealed a concentration- and time-dependent inhibition of proliferation in all the three tested cell lines on treatment with resveratrol. The IC₅₀ of resveratrol for SCC-VII, SCC-25, and YD-38 cell lines was found to be 0.5, 0.7, and 1.0 μg/ml, respectively, after 48-h treatment. Examination of the cell cycle analysis showed that resveratrol treatment induced cell cycle arrest in the G2/M phase and enhanced the expression of phospho-cdc2 (Tyr 15), cyclin A2, and cyclin B1 in the oral squamous cell carcinoma (OSCC) cells. It also caused a marked increase in the percentage of apoptotic cells as revealed by the fluorescence-activated cell sorting analysis. Thus, resveratrol exhibits inhibitory effect on the proliferation of OSCC oral cancer cells through the induction of apoptosis and G2/M phase cell cycle arrest.     

Induction of cell cycle arrest and apoptosis in human breast cancer cells by quercetin

Quercetin, a widely distributed bioflavonoid, has been shown to induce growth inhibition in certain cancer cell types. In the present study we have pursued the mechanism of growth inhibition in MCF-7 human breast cancer cells. Quercetin treatment resulted in the accumulation of cells specifically at G2/M phase of the cell cycle. Mitotic index measured by MPM2 staining clearly showed that cells were transiently accumulated in M phase, 24 h after treatment. The transient M phase accumulation was accompanied by a transient increase in the levels of cyclin B1 and Cdc2 kinase activity. However, 24 h or longer treatment caused a marked accumulation of cells in G2 instead of M phase. Levels of cyclin B1 and cyclin B1-associated Cdc2 kinase activity were also decreased. We also found that quercetin markedly increased Cdk-inhibitor p21CIP1/WAF1 protein level after treatment for 48 h or longer, and the induction of p21CIP1/WAF1 increased its association with Cdc2-cyclin B1 complex, however, up-regulation of p53 by quercetin was not observed. Quercetin also induced significant apoptosis in MCF-7 cells in addition to cell cycle arrest, and the induction of apoptosis was markedly blocked by antisense p21CIP1/WAF1 expression. The present data, therefore, demonstrate that a flavonoid quercetin induces growth inhibition in the human breast carcinoma cell line MCF-7 through at least two different mechanisms; by inhibiting cell cycle progression through transient M phase accumulation and subsequent G2 arrest, and by inducing apoptosis.     

Monensin inhibits the growth of renal cell carcinoma cells via cell cycle arrest or apoptosis

Previously, we showed that monensin, Na+ ionophore, potently inhibited the growth of acute myelogenous leukemia and lymphoma cells. Here, we demonstrate that monensin inhibited the proliferation of renal cell carcinoma cells with IC50 of about 2.5 micro M. Monensin induced a G1 or a G2-M phase arrest in these cells. When we examined the effects of this drug on ACHN cells, monensin decreased the levels of CDK2, CDK6, cdc2, cyclin A and cyclin B1 proteins. p21 and p27 proteins were increased by monensin. In addition, monensin markedly enhanced the binding of p21 with CDK2 and the binding of p27 with CDK6. Furthermore, the activities of CDK2- and CDK6-associated kinase were reduced in association with hypophosphorylation of Rb protein. Monensin also induced the apoptosis in several renal cell carcinoma cells. Apoptotic process of Caki-2 cells was associated with the changes of Bcl-2, Bcl-XL, caspase-9, caspase-3, caspase-7 proteins as well as mitochondria transmembrane potential (DeltaPsim) loss. Taken together, these results demonstrate for the first time that monensin inhibits the growth of renal cell carcinoma cells via cell cycle arrest or apoptosis.     

5'-nitro-indirubinoxime induces G2/M cell cycle arrest and apoptosis in human KB oral carcinoma cells

Our previous study demonstrated that the novel indirubin derivative, 5'-nitro-indirubinoxime (5'-NIO), effectively arrested the tumor growth through the inhibition of cell proliferation and the induction of apoptosis. However, the precise molecular mechanisms underlying 5'-NIO-induced antitumor activity remain unclear. Here, we report that 5'-NIO inhibits the proliferation of human KB oral carcinoma cells via the cell cycle arrest in G2/M phase. 5'-NIO reduced the activity of Cdc2/cyclin B complex through the inhibition of the PLK1 expression. Partially, 5'-NIO also arrested cell cycle in G1/S phase via the reduction of CDK4 and cyclin D1/D3 levels by p16 and induction of the level of p21waf1. Using flow cytometry analysis, we showed that 5'-NIO-induced cell cycle arrest is followed by apoptosis. We determined further that 5'-NIO-induced apoptosis is accomplished by the mitochondria-dependent activation of the caspase cascade. Overall, these observations suggest the potential value of 5'-NIO as a candidate for a therapeutic modality for the treatment of oral cancer.     

Triptolide-induced cell cycle arrest and apoptosis in human renal cell carcinoma cells

Renal cell carcinoma (RCC) is the most frequent type of renal-originated malignancy. Although nephrectomy is successfully used to save the lives of patients with localized RCC, treatment of advanced and other refractory RCCs is poor and still inadequate. Here, we show that triptolide, a small molecule and a well-known anti-inflammatory and anti-immunity agent used in the clinic, is capable of inducing cell apoptosis via the mitochondrial pathway in the 786-0 RCC cell line. This induction occurred in concert with reduced expression of genes related to the stabilization of mitochondria such as Bcl-2 and Bcl-XL. Cell cycle analysis showed that exposure to triptolide decreased the proportion of cells in the G0/G1 and G2/M phases, and increased the proportion of cells in the S phase. Cell accumulation in the S phase can be attributed to reduced expression of cell cycle checkpoint regulators such as cyclin A, cyclin B, CDK1, CDK2 and retinoblastoma proteins (Rb). These results raise the possibility that triptolide-induced apoptosis is mediated by cell cycle arrest. Similarly, in another human RCC cell line, OS-RC-2, triptolide-induced apoptosis and cell accumulation in S phase were also observed. Therefore, triptolide emerges as a stimulator of apoptosis by influencing coordinate regulation of proliferation and apoptosis, and may be applicable to the treatment of human renal cell carcinoma.     

Survivin deficiency induces apoptosis and cell cycle arrest in HepG2 hepatocellular carcinoma cells

The postulated dual roles of survivin as an anti-apoptotic factor and a mitotic inducer have placed this factor in the spotlight of cancer research. The purpose of this study was to investigate whether survivin might connect the cell cycle with apoptosis. Here, by simultaneously monitoring survivin deficiency-induced morphological changes of HepG2 cells using time-lapse imaging as well as determining apoptosis progression, we observed synchronized defective mitosis characterized by multinucleated and polyploid cells and cell cycle arrest at S phase or G2/M phase followed by apoptosis, the processes of which depended on the simultaneous destruction of specialized subcellular compartments of survivin and activation of caspase-3-like protease. These findings showed that the survivin protein acted as mitotic regulator and apoptosis inhibitor, but may also possess the role of a bridge in integrating apoptosis and cell division. An essential prerequisite of this pathway was the specialized subcellular localization of survivin. The overexpression of survivin was required to maintain cell viability and proper cell cycle transitions, and to preserve genetic fidelity during cell division in HepG2 cells.     

2'-Nitroflavone induces cell cycle arrest and apoptosis in HeLa human cervical carcinoma cells

The mechanism of antitumor action of a synthetic nitroflavone derivative, 2'-nitroflavone, was evaluated in vitro in HeLa human cervix adenocarcinoma cells. We showed that the nitroflavone derivative slowed down the cell cycle at the S phase and increase the population of cells at the G(2)/M phase after 24h of incubation. The treatment with 2'-nitroflavone also induced an apoptotic response, characterized by an increase of the sub-G1 fraction of cells, by cells with chromatin condensation and membrane blebbing, by a typical ladder of DNA fragmentation and by detection of apoptotic cells stained with Annexin V. The observed apoptosis was regulated by caspase-8 and -9, both contributing to the activation of the effector caspase-3. In addition, inhibitors of caspase-8 or -9 partially protected HeLa cells from 2'-nitroflavone-induced cell death. We also found that 2'-nitroflavone did not affect the total amount of Bax and Bcl-2 proteins, although a translocation of Bax from cytosol to mitochondria was evident after 6h of exposure. Furthermore, 2'-nitroflavone decreased the expression of the anti-apoptotic Bcl-X(L) protein, induced the release of cytochrome C to cytosol and increased the levels of Fas and Fas-L. Our results indicated that both death receptor and mitochondria-dependent pathways are involved in the apoptotic cell death triggered by 2'-nitroflavone and suggest that this derivative could be a potentially useful agent for the treatment of certain malignancies.     

Induction of G0/G1 cell cycle arrest in ovarian carcinoma cells by the anti-inflammatory drug NS-398, but not by COX-2-specific RNA interference

Cyclooxygenases, particularly COX-2, play an important role in tumor development and progression. We have previously shown that COX-2 expression is an independent prognostic factor in human ovarian carcinoma. In this study, we investigated the effects of the inhibition of COX isoforms by the NSAID NS-398 as well as by COX-isoform-specific RNA interference (RNAi) in the human ovarian carcinoma cell lines OVCAR-3 and SKOV-3. OVCAR-3 cells showed a constitutive expression of COX-1 and an induction of high levels of COX-2 and PGE(2) after stimulation with interleukin-1beta. In contrast, SKOV-3 cells were negative for both COX isoforms. In OVCAR-3 cells, PGE(2) production was inhibited by NS-398 in concentrations of 1 microM and by a COX-2-specific silencing RNA (siRNA), while a COX-1-specific siRNA did not have an effect. This suggests that COX-2 is the major source of PGE(2) in this cell line. To dissociate COX-2-specific and non-COX-2-specific effects on cell proliferation, a proliferation assay was performed after incubation of cells with NS-398 and COX siRNAs. NS-398 induced an inhibition of cell proliferation at concentrations of 50-500 microM, which are above the concentrations needed for the inhibition of PGE(2) production. This inhibitory effect was present in the COX-positive cell line OVCAR-3 as well as in the COX-negative cell line SKOV-3 and could not be reverted by addition of exogenous PGE(2). Neither COX-1- nor COX-2-specific siRNAs had an effect on cell proliferation of OVCAR-3 cells. Cell cycle analysis showed an increased accumulation of cells in the G0/G1 phase after treatment with NS-398, but not with COX siRNAs. These experiments suggest that NS-398 reduced cell proliferation in ovarian carcinoma cells by induction of G0/G1 cell cycle arrest independent of COX-2 inhibition. Our study shows that specific inhibition of COX isoforms by RNAi could be used to dissociate effects of NSAIDs. Furthermore, our results suggest that cell cycle arrest is one of the primary mechanisms responsible for the antiproliferative effects of NS-398 on ovarian carcinoma cells.     

Induction of apoptosis and G2/M cell cycle arrest by DCC.

The Deleted in Colorectal Cancer gene (DCC) encodes a cell surface receptor that belongs to the Ig superfamily. Inactivation of the DCC gene has been implicated in human tumor progression. However, little is known about the biological function of the DCC protein. In the present study, we demonstrated that expression of DCC activated caspase-3 and programmed cell death, or induced G2/M cell cycle arrest in tumor cells. In some cell lines, apoptosis was evident within 24 h of DCC expression. Timing of the appearance of apoptotic cells coincided with that of the cleavage of poly (ADP-ribose) polymerase, a substrate of caspase-3. Expression of the apoptosis inhibitory gene Bcl-2 was not able to abrogate the DCC-induced apoptosis. In the G2/M cycle arrest cells, cdk1 activity was inhibited. Our results suggest that the DCC protein may transduce signals resulting in activation of caspases or inhibition of Cdk1. These data provide a possible mechanism by which DCC suppresses tumorigenesis.     

Induction of cell cycle arrest and apoptosis in myeloma cells by cepharanthine, a biscoclaurine alkaloid

Cepharanthine (CEP), a biscoclaurine alkaloid extracted from Stephania Cepharantha Hayata, has been used in Japan for treating patients with radiation-induced leucopenia or thrombocytopenia. We treated a patient with multiple myeloma (MM), who was not responding to preceding chemotherapy, who coincidently received therapy with CEP due to thrombocytopenia. Since the case showed a marked reduction of tumor load, direct anti-tumor effects of CEP to myeloma cells were investigated in vitro. Anti-tumor effects were observed in all myeloma cell lines tested, including a line resistant to melphalan. Exposure to CEP of a myeloma cell line induced the production of reactive oxygen species, activated the caspase-3 pathway and eventually induced apoptosis. Pre-exposure of cells to a pan-caspase inhibitor, Z-VAD-FMK, or a free radical scavenger, Tiron, effectively blocked CEP-induced apoptosis. Interestingly, CEP also inhibited cell growth of myeloma cells by inducing CDK inhibitors. These data show, for the first time, that CEP has anti-myeloma effects by the activation of apoptotic pathways and blocking cell cycle progression via CDK inhibitors. Although analysis of these two pathways should be clarified further, the use of CEP may be considered as a potential therapeutic agent for a subset of MM.     

PPARγ活化诱导细胞凋亡和周期阻滞来抑制结肠癌细胞生长

目的探讨过氧化物酶体增殖物激活受体γ(peroxisome proliferator activated receptorγ,PPARγ)在结肠癌细胞株HT-29中的表达及其活化后对结肠癌细胞生长的影响。方法通过RT-PCR和Western blot检测HT-29中PPARγmRNA及蛋白质的表达,四甲基偶氮唑盐(MTT)微量酶反应比色法检测PPARγ配体罗格列酮(rosiglitazone,Rosi)和15d-PGJ2对HT-29细胞生长的影响,荧光显微镜、TUNEL法观察Rosi和15d-PGJ2激活PPARγ后诱导HT-29细胞凋亡形态和生化改变,流式细胞仪(FCM)以碘化丙啶(PI)单染法检测细胞周期。结果RT-PCR及Western blot检测结果表明结肠癌细胞HT-29中存在PPARγmRNA及蛋白质的表达。MTT结果显示Rosi和15d-PGJ2可抑制HT-29细胞生长,且具有时间、剂量依赖效应。荧光显微镜、TUNEL检测显示PPARγ活化后HT-29细胞出现典型的凋亡现象,10μmol/L Rosi或15d-PGJ2作用48h后的细胞凋亡率分别为(17.3±1.9)%及(20.8±2.9)%,与对照组(3.86±0.49)%相比差异均具有统计学意义(P<0.05)。FCM结果显示Rosi和15d-PGJ2激活PPARγ后诱导细胞周期阻滞于G0/G1期,与对照组相比差异有统计学意义(P<0.05)。结论结肠癌细胞HT-29表达PPARγ,其活化可通过诱导细胞凋亡及细胞周期阻滞,抑制结肠癌细胞增长。因此,PPARγ可能为结肠癌治疗的一个新靶点。     

Induction of apoptosis and cell cycle arrest in mouse colon 26 cells by benastatin A.

Benastatin A, isolated from Streptomyces bacteria, is reported to inhibit mammalian glutathione transferases (GSTs). Since GST inhibitors such as ethacrynic acid are suggested to induce apoptosis in some cell lines, the effect of benastatin A on the survival of mouse colon 26 adenocarcinoma cells was compared with that of ethacrynic acid. When cells in stationary phase were treated with benastatin A, viable cells were found to be dose-dependently decreased after 3 days. In the case of ethacrynic acid, this became apparent within 24 h. Electrophoretic analysis revealed DNA fragmentation, indicating that cell loss was due to apoptosis in both cases. The dominant GST in colon 26 cells was identified as the class Pi-form (GST-II), and the activities in crude extracts as well as purified GST-II were almost completely inhibited by 50 microM ethacrynic acid. Immunoblot and northern blot analyses revealed increased GST-II protein and mRNA levels in cells treated with ethacrynic acid. Benastatin A did not significantly affect the activity in the crude extract even at 20 microM, a 10-fold higher concentration than that which almost completely inhibited the activity of purified GST-II. However, GST activity and GST-II protein were decreased in colon 26 cells treated with benastatin A for 5 days, no significant activity being detected in the range of 16 - 20 microM. In addition, beta-actin and bax mRNAs were also decreased in a dose-dependent manner. Furthermore, flow cytometric analysis of colon 26 cells revealed that benastatin A blocked the cell cycle at the G1/G0 phase. Thus, benastatin A also induces apoptosis of colon 26 cells, but this is unlikely to be due to inhibition of GST activity.     

Monensin-mediated growth inhibition of SNU-C1 colon cancer cells via cell cycle arrest and apoptosis

Previously, we showed that monensin, Na+ ionophore, potently inhibited the growth of acute myelogenous leukemia and lymphoma cells. Here, we demonstrate that monensin inhibited the proliferation of solid tumor cells with IC50 of about 2.5 micro M. Monensin induced a G1 or a G2-M phase arrest in these cells. When we examined the effects of this drug on SNU-C1 cells, monensin decreased the levels of CDK2, CDK4, CDK6, cyclin D1 and cyclin A proteins. While p27 was increased by monensin, p21 was not. In addition, monensin markedly enhanced the binding of p27 with CDK2, CDK4 and CDK6. Furthermore, the activities of CDK2-, CDK4- and CDK6-associated kinase were reduced in association with hypophosphorylation of Rb protein. Monensin also induced apoptosis in solid tumor cells. Apoptotic process of SNU-C1 cells was associated with the changes of Bax, caspase-3 and mitochondria transmembrane potential (deltapsim). Taken together, these results demonstrated for the first time that monensin inhibited the growth of solid tumor cells, especially SNU-C1 cells, via cell cycle arrest and apoptosis.     

Induction of apoptosis by cyclo-oxygenase-2 inhibitor NS398 through a cytochrome C-dependent pathway in esophageal cancer cells.

Non-steroidal anti-inflammatory drugs (NSAIDs) can induce tumor cells to undergo apoptosis in vitro. They have also shown cancer-preventive activity in vivo. The mechanism of their effects is, however, not well defined. We investigated the mechanism by which a new NSAID, NS398, induces apoptosis in esophageal cancer cell lines. NS398 decreased cell viability in 2 cyclo-oxygenase-2-positive (COX-2(+)) esophageal cancer cell lines but not in a COX-2(-) cell line. DNA fragmentation and TUNEL assays demonstrated that NS398 induced the 2 COX-2(+) cancer cell lines to undergo apoptosis. The percentage of apoptosis induced by NS398 was associated with the level of COX-2 expression. Further investigation showed that the cytochrome c pathway was responsible for NS398-induced apoptosis; i.e., cytochrome c was released from mitochondria, caspase-9 and caspase-3 were activated and finally poly(ADP-ribose)polymerase (PARP) was cleaved. Furthermore, the effect of NS398 was inhibited by the caspase inhibitor Z-DEVD-FMK and prostaglandin E(2). In contrast, bcl-2, bax, c-myc, Fas and Fas-ligand showed minor changes. Altogether, our data suggest that induction of apoptosis by NS398 is associated with COX-2 expression and occurs through the cytochrome c-dependent pathway, which sequentially activates caspase-9 and caspase-3 and cleaves PARP.