Antitumor effect of the cinnamaldehyde derivative CB403 through the arrest of cell cycle progression in the G2/M phase

Cinnamaldehydes have been shown to have inhibitory effects on farnesyl protein transferase (FPTase; EC 2.5.1.29) in vitro, angiogenesis, cell-cell adhesion, and tumor cell growth and to be immunomodulators. However, the mechanisms responsible for these effects remain unknown. To elucidate the molecular mechanism of the cinnamaldehyde derivative CB403 for growth inhibition, CB403 was synthesized from 2'-hydroxycinnamaldehyde. CB403-treated cells were weakly adherent to the culture dishes. In addition, CB403 inhibited tumor growth in these cells in a concentration-dependent manner. FACS analysis using human cancer cells treated with this compound showed cell cycle arrest in mitosis, which was correlated with a marked increase in the amount of cyclin B1. Furthermore, CB403 blocked in vivo growth of human colon and breast tumor xenografts without loss of body weight in nude mice. These results support the hypothesis that the cinnamaldehyde derivative CB403 exerts cytostatic properties by inducing mitotic arrest in cancer cells.     

Resveratrol modulates roscovitine-mediated cell cycle arrest of human MCF-7 breast cancer cells.

Human MCF-7 breast cancer cells are relatively resistant to anti-cancer drugs. Recently, we reported that roscovitine (ROSC), a selective cyclin-dependent kinase (CDK) inhibitor, arrested human MCF-7 breast cancer cells in G2 phase of the cell cycle and concomitantly induced apoptosis. Moreover, we observed that the effect of the CDK inhibitor was dependent on the content of the culture medium. The cell cycle inhibiting action of ROSC was markedly diminished in human MCF-7 cells cultivated in medium supplemented with phenol red. These observations indicated that the therapeutic effects of ROSC can be affected by the components of the tissue medium. Recently, a number of epidemiological and experimental studies indicated that polyphenols (e.g. resveratrol, epicatechins etc.), abundant micronutrients in food, are anti-oxidant agents and could have strong anti-mitotic as well as pro-apoptotic activities. In the present contribution we raised the question whether the ROSC-mediated cell cycle arrest could be additionally modulated by compounds of natural origin, especially by polyphenols. Considering the potential benefits of the dietary components during the post-chemotherapy period, we focused our attention on the effects of resveratrol administration after treatment with ROSC. We analyzed whether the combined treatment with resveratrol would exert any additional effect on the cell cycle status of ROSC-treated human cancer cells. Resveratrol exhibited low direct cytotoxicity. The combined treatment with ROSC enhanced the ROSC-mediated inhibition of cell proliferation and cell cycle arrest. These results indicate that targeted combination of anti-cancer drugs with distinct naturally occurring compounds could increase the efficacy of the therapy and concomitantly reduce the undesired side effects exerted by cytostatic drugs.     

Eupatilin, a dietary flavonoid, induces G2/M cell cycle arrest in human endometrial cancer cells

This study is the first to investigate the antiproliferative effect of eupatilin in human endometrial cancer cells. Eupatilin, a naturally occurring flavonoid isolated from Artemisia princeps, has anti-inflammatory, anti-oxidative, and anti-tumor activities. In the present study, we investigated the potential effect of eupatilin on cell growth and its molecular mechanism of action in human endometrial cancer cells. Eupatilin was more potent than cisplatin in inhibiting cell viability in the human endometrial cancer cell lines Hec1A and KLE. Eupatilin showed relatively low cytotoxicity in normal human endometrial cells HES and HESC cells when compared to cisplatin. Eupatilin induced G2/M phase cell cycle arrest in a time- and dose-dependent manner, as indicated by flow cytometry analysis. In addition, treatment of Hec1A cells with eupatilin resulted in a significant increase in the expression of p21^WAF1/CIP1 and in the phosphorylation of Cdc25C and Cdc2. Knockdown of p21 using specific siRNAs significantly compromised eupatilin-induced cell growth inhibition. Interestingly, levels of mutant p53 in Hec1A cells decreased markedly upon treatment with eupatilin, and p53 siRNA significantly increased p21 expression. Moreover, eupatilin modulated the phosphorylation of protein kinases ERK1/2, Akt, ATM, and Chk2. These results suggest that eupatilin inhibits the growth of human endometrial cancer cells via G2/M phase cell cycle arrest through the up-regulation of p21 by the inhibition of mutant p53 and the activation of the ATM/Chk2/Cdc25C/Cdc2 checkpoint pathway.     

Molecular mechanisms of ZD1839-induced G1-cell cycle arrest and apoptosis in human lung adenocarcinoma A549 cells

Epithelial growth factor receptor (EGFR) has been proposed as a target for anticancer therapy. ZD1839 (Iressa) is a quinazoline derivative that selectively inhibits the EGFR tyrosine kinase activity and is under clinical use in cancer patients. However, the molecular mechanisms involved in ZD1839-mediated anticancer effects remain largely uncharacterized. In this study, exposure of human lung adenocarcinoma A549 cells to ZD1839 caused G1 arrest, and subsequently induced apoptosis. Moreover, ZD1839 increased the protein levels of p27(KIP1) and retinoblastoma-related Rb2/p130 while decreased the expression of cyclin-dependent kinase-2 (CDK2), CDK4, CDK6 and cyclin-D1, cyclin-D3. In vitro kinase assay showed that ZD1839 decreased these CDKs expression in A549 cells, leading to significantly reduce their kinase activities. In addition, ZD1839-induced death of A549 cells with characteristics of apoptosis including apoptotic morphological changes, DNA fragmentation and enhancement of TUNEL-positive cell. These events were accompanied by a marked increase of Fas protein expression, and activation of caspase-2, -3, -8. Co-treatment of cells with Fas antagonist antibody significantly blocked ZD1839-induced apoptosis. Caspase-8 and caspase-3 inhibitors, but not a caspase-9 inhibitor, were also capable of restoring cell viability. Our results indicate that downregulation of the expression and function of CDK2, CDK4, CDK6, cyclin-D1 and cyclin-D3, as well as upregulation of p27(KIP1) and pRb2/p130, are strong candidates for the cell cycle regulator that arrests ZD1839-treated A549 cells at G1 phase. Furthermore, upregulation of Fas appears to play a major role in the initiation of ZD1839-induced apoptosis, activation of caspase-8/caspase-3 cascade is involved in the execution phase of this death program.     

N-Alkoxy derivatization of indole-3-carbinol increases the efficacy of the G1 cell cycle arrest and of I3C-specific regulation of cell cycle gene transcription and activity in human breast cancer cells

Indole-3-carbinol (I3C), a naturally occurring component of Brassica vegetables, such as cabbage, broccoli, and Brussels sprouts, induces a G1 cell cycle arrest of human breast cancer cells. Structure-activity relationships of I3C that mediate this anti-proliferative response were investigated using synthetic and natural I3C derivatives that contain substitutions at the indole nitrogen. Nitrogen substitutions included N-alkoxy substituents of one to four carbons in length, which inhibit dehydration and the formation of the reactive indolenine. Analysis of growth and cell cycle arrest of indole-treated human breast cancer cells revealed a striking increase in efficacy of the N-alkoxy I3C derivatives that is significantly enhanced by the presence of increasing carbon lengths of the N-alkoxy substituents. Compared to I3C, the half maximal growth arrest responses occurred at 23-fold lower indole concentration for N-methoxy I3C, 50-fold lower concentration for N-ethoxy I3C, 217-fold lower concentration for N-propoxy I3C, and 470-fold lower concentration for N-butoxy I3C. At these lower concentrations, each of the N-alkoxy substituted compounds induced the characteristic I3C response in that CDK6 gene expression, CDK6 promoter activity, and CDK2 specific enzymatic activity for its retinoblastoma protein substrate were strongly down-regulated. 3-Methoxymethylindole and 3-ethoxymethylindole were approximately as bioactive as I3C, whereas both tryptophol and melatonin failed to induce the cell cycle arrest, showing the importance of the C-3 hydroxy methyl substituent on the indole ring. Taken together, our study establishes the first I3C structure-activity relationship for cytostatic activities, and implicates I3C-based N-alkoxy derivatives as a novel class of potentially more potent experimental therapeutics for breast cancer.     

Tubulozole-induced G2/M cell cycle arrest in human colon cancer cells through formation of microtubule polymerization mediated by ERK1/2 and Chk1 kinase activation.

Our studies demonstrated that human colon cancer cells (COLO 205), with higher expression level of check point kinase 1 (Chk1), were more sensitive to microtubule damage agent Tubulozole (TUBU) induced G2/M phase arrest than normal human colon epithelial (CRL) cells. TUBU (10 microM, for 3h) treatment resulted in rapid and sustained phosphorylation of Cdc25C (Ser-216) leading to increased 14-3-3beta binding. This resulted in increased nuclear translocation. In addition, TUBU induced phosphorylation of the Cdc25C (Ser-216) and Bad (Ser-155) proteins were blocked by Chk1 SiRNA-transfection. Surprisingly, cellular apotosis was observed in cells treated with TUBU after Chk1 SiRNA inhibition. We further demonstrated that extracellular signal-regulated kinase (ERK) activation by TUBU was needed for Chk1 kinase activation and microtubule formation as shown by the attenuation of these responses by the ERK1/2 specific inhibitor PD98059. However, TUBU induced ERK1/2 phosphorylation was not blocked in the Chk1 SiRNA-transfected COLO 205 cells. These results imply that ERK1/2 mediated Chk1 activation may be play an important role in determining TUBU induced G2/M arrest or apoptosis in COLO 205 cells.     

Apoptosis in male germ cells in response to cyclin A1-deficiency and cell cycle arrest

Male mice homozygous for a mutated allele of the cyclin A1 gene (Ccna1) are sterile due to a block in cell cycle progression before the first meiotic division. Meiosis arrest in Ccna1(-/-) spermatocytes is associated with desynapsis abnormalities, lowered MPF activity, and apoptosis as evidenced by TUNEL-positive staining. With time, adult testicular tubules exhibit severe degeneration: some tubules in the older animals are almost devoid of germ cells at various stages of spermatogenesis. The mechanisms by which the cells sense the cell cycle arrest and the regulation of the decision to undergo cell death are under investigation.     

Anti-proliferation effect of 3-amino-2-imino-3,4-dihydro-2H-1,3-benzothiazin-4-one (BJ-601) on human vascular endothelial cells: G0/G1 p21-associated cell cycle arrest

The aim of this study was to examine the anti-proliferation effect of 3-amino-2-imino-3,4-dihydro-2H-1,3-benzothiazin-4-one (BJ-601) on human vascular endothelial cells and its possible molecular mechanism underlying. Our data showed that BJ-601 at a range of concentrations (0-40 microM) dose- and time-dependently decreased cell number in cultured human dermal microvascular endothelial cells (HDMVECs), but not human fibroblasts. The BJ-601-induced growth inhibition in HDMVECs was reversible. [3H]thymidine incorporation demonstrated that BJ-601 arrested the HDMVECs at the G0/G1 phase of the cell cycle. Western blot analysis revealed that BJ-601 (0-40 microM) dose-dependently increased the levels of the protein p21, but not of p27, p53, cyclins A, D1, D3 and E, cyclin-dependent kinase 2 (CDK2), and CDK4 in HDMVECs. Immunoprecipitation showed that the formation of the CDK2-p21 complex, but not CDK2-p27, CDK4-p21 and CDK4-p27 complexes, was increased in the BJ-601-treated HDMVECs. Kinase assay further demonstrated that CDK2, but not CDK4, kinase activity was decreased in a dose-dependent manner in the BJ-601-treated HDMVECs. Pretreatment of HDMVECs with a p21 antisense oligonucleotide, which blocked the expression of p21 protein, reversed the BJ-601-induced inhibition of [3H]thymidine incorporation into HDMVECs. Moreover, cotreatment of the endothelial cells with protein kinase C (PKC) inhibitor, staurosporine, prevented the BJ-601-induced decrease of [3H]thymidine incorporation into HDMVECs. Administration of BJ-601 dose-dependently inhibited capillary-like tube formation of HDMVECs in Matrigel. In conclusion, these data suggest that BJ-601 inhibits HDMVECs proliferation by increasing the level of p21 protein, which in turn inhibits CDK2 kinase activity, and finally causes retardation of the cell cycle at the G0/G1 phase.     

G1 cell cycle arrest by amlodipine, a dihydropyridine Ca2+ channel blocker, in human epidermoid carcinoma A431 cells

We demonstrated previously that amlodipine, a dihydropyridine Ca(2+) channel blocker, exhibits antitumor effects on human epidermoid carcinoma A431 cells both in vitro and in vivo, in part through inhibition of capacitative Ca(2+) entry. In this study, we examined the effects of amlodipine on cell cycle distribution and cell cycle regulatory molecules in A431 cells, since a rise in intracellular Ca(2+) is required at several points during cell cycle progression. Flow cytometric analysis revealed that treatment with amlodipine (20-30muM, for 24h) induced G1 phase cell accumulation. The amlodipine-induced G1 arrest was associated with a decrease in phosphorylation of retinoblastoma protein (pRB), a regulator of G1 to S phase transition, reduction of protein levels of cyclin D1 and cyclin dependent kinase 4 (CDK4), G1 specific cell cycle proteins, and increased expression of p21(Waf1/Cip1), an inhibitory protein of CDK/cyclin complexes. In vitro kinase assay revealed that amlodipine significantly decreased CDK2-, CDK4-, and their partners cyclin E- and cyclin D1-associated kinase activities. The amlodipine-induced reductions in cyclin D1 protein expression and in CDK2 kinase activity were reproduced by a dihydropyridine derivative, nicardipine, having an inhibitory effect on A431 cell growth, but not by nifedipine, lacking the antiproliferative activity. Our results demonstrate that amlodipine caused G1 cell cycle arrest and growth inhibition in A431 cells through induction of p21(Waf1/Cip1) expression, inhibition of CDK/cyclin-associated kinase activities, and reduced phosphorylation of pRB.     

Action of resveratrol alone or in combination with roscovitine, a CDK inhibitor, on cell cycle progression in human HL-60 leukemia cells

Results of a number of epidemiological and experimental studies indicate that polyphenols (e.g. resveratrol (RES), epicatechins etc.), antioxidant agents and abundant micronutrients in our food could have strong anti-mitotic as well as pro-apoptotic effects. In this study we raised the question whether roscovitine (ROSC), an inhibitor of cyclin-dependent kinases (CDKs) with increased selectivity towards CDK2, could be able to affect human leukemia HL-60 cells in which the p53 gene is inactivated and whether ROSC-induced effects could be additionally modulated by compounds of natural origin, especially by polyphenols e.g. RES. Exposure of HL-60 cells to ROSC for 24 h inhibited their proliferation. Flow cytometric analyses revealed that unlike MCF-7 cells, HL-60 cells were arrested in G₁ upon ROSC treatment. Furthermore, ROSC also induced apoptosis in HL-60 cells. After treatment with 40 μM ROSC for 24 h the frequency of hypoploid cells representing cells undergoing apoptosis reached approximately 50%. In the next step the action of RES alone or in combination with ROSC was examined. Interestingly, synergistic effects were observed after combined treatment for 24 h and sequential post-incubation for 48 h in the presence of RES. Such combined treatment resulted in a marked reduction of the frequency of the S- and G₂/M-phase cells and simultaneously increased the G₁ cell population up to 80% at a fourfold lower ROSC dose. Further analyses revealed that the combined treatment strongly activated caspase-3. These results clearly evidence that RES strongly potentiates ROSC-induced apoptosis.     

5-Methoxyflavanone induces cell cycle arrest at the G2/M phase, apoptosis and autophagy in HCT116 human colon cancer cells

Natural flavonoids have diverse pharmacological activities, including anti-oxidative, anti-inflammatory, and anti-cancer activities. In this study, we investigated the molecular mechanism underlying the action of 5-methoxyflavanone (5-MF) which has a strong bioavailability and metabolic stability. Our results show that 5-MF inhibited the growth and clonogenicity of HCT116 human colon cancer cells, and that it activated DNA damage responses, as revealed by the accumulation of p53 and the phosphorylation of DNA damage-sensitive proteins, including ataxia-telangiectasia mutated (ATM) at Ser1981, checkpoint kinase 2 (Chk2) at Thr68, and histone H2AX at Ser139. 5-MF-induced DNA damage was confirmed in a comet tail assay. We also found that 5-MF increased the cleavage of caspase-2 and -7, leading to the induction of apoptosis. Pretreatment with the ATM inhibitor KU55933 enhanced 5-MF-induced γ-H2AX formation and caspase-7 cleavage. HCT116 cells lacking p53 (p53^−/−) or p21 (p21^−/−) exhibited increased sensitivity to 5-MF compared to wild-type cells. 5-MF further induced autophagy via an ERK signaling pathway. Blockage of autophagy with the MEK inhibitor U0126 potentiated 5-MF-induced γ-H2AX formation and caspase-2 activation. These results suggest that a caspase-2 cascade mediates 5-MF-induced anti-tumor activity, while an ATM/Chk2/p53/p21 checkpoint pathway and ERK-mediated autophagy act as a survival program to block caspase-2-mediated apoptosis induced by 5-MF.     

Up-regulation of cyclin D1 by JNK1/c-Jun is involved in tumorigenesis of human embryo lung fibroblast cells induced by a low concentration of arsenite

Inorganic arsenic, a ubiquitous environmental contaminant, is associated with an increased risk of cancer. There are several hypotheses regarding arsenic-induced carcinogenesis. The mechanism of action remains obscure, although hyper-proliferation of cells is involved. In the present study, the molecular mechanisms underlying the proliferation and malignant transformation of human embryo lung fibroblast (HELF) cells induced by a low concentration of arsenite were investigated. The results reveal that a low concentration of arsenite induces cell proliferation and promotes cell cycle transition from the G₁ to the S phase. Moreover, arsenite activates the JNK1/c-Jun signal pathway, but not JNK2, which up-regulates the expression of cyclin D1/CDK4 and phosphorylates the retinoblastoma (Rb) protein. Blocking of the JNK1/c-Jun signal pathway suppresses the increases of cyclin D1 expression and Rb phosphorylation, which attenuates cell proliferation, reduces the transition from the G1 to the S phase, and thereby inhibits the neoplastic transformation of HELF cells induced by a low concentration of arsenite. Thus, activation of the JNK1/c-Jun pathway up-regulates the expression of cyclin D1, which is involved in the tumorigenesis caused by a low concentration of arsenite.     

Tebufenozide induces G1/S cell cycle arrest and apoptosis in human cells

Tebufenozide is a non-steroidal insect growth regulator and is extensively used to control pests, although it is considered to be safe for mammals and environmentally friendly. However, previous studies have found that tebufenozide is cytotoxic to man, although the exact mechanism remains elusive. This study will investigate the apoptotic molecular mechanisms which result from tebufenozide-induced DNA damage in HeLa cells. Our results demonstrate that tebufenozide could trigger arrest in G1/S phase related to a downregulation of cyclin E and cyclin-dependent kinase (CDK) 2 protein. In addition, Western blotting showed apoptosis was associated with the upregulation of p53, Bax and cleaved-PARP, as well as downregulation of Bcl-2 and PARP. Tebufenozide also regulated changes in mitochondrial permeability and reduced mitochondrial number and intracellular ATP production. Briefly, these results suggest that tebufenozide- induces cell cycle arrest and apoptosis through activating p53 protein in a Bax- and Bcl-2-triggered mitochondrial pathway. This work provides some scientific context for the safe use of tebufenozide in agriculture.     

Novel ferrocenyl derivatives exert anti-cancer effect in human lung cancer cells in vitro via inducing G1-phase arrest and senescence

Aim:

To investigate the effects of 7 novel 1-ferrocenyl-2-(5-phenyl-1H-1,2,4-triazol-3-ylthio) ethanone derivatives on human lung cancer cells in vitro and to determine the mechanisms of action.

Methods:

A549 human lung cancer cells were examined. Cell viability was analyzed with MTT assay. Cell apoptosis and senescence were examined using Hoechst 33258 and senescence-associated-β-galactosidase (SA-β-gal) staining, respectively. LDH release was measured using a detection kit. Cell cycle was analyzed using a flow cytometer. Intracellular ROS level was measured with the 2′,7′-dichlorodihydrofluorescein probe. Phosphorylation of p38 was determined using Western blot.

Results:

Compounds 5b, 5d, and 5e (40 and 80 μmol/L) caused significant decrease of A549 cell viability, while other 4 compounds had no effect on the cells. Compounds 5b, 5d, and 5e (80 μmol/L) induced G₁-phase arrest (increased the G₁ population by 22.6%, 24.23%, and 26.53%, respectively), and markedly increased SA-β-gal-positive cells. However, the compounds did not cause nuclear DNA fragmentation and chromatin condensation in A549 cells. Nor did they affect the release of LDH from the cells. The compounds significantly elevated the intracellular ROS level, decreased the mitochondrial membrane potential, and increased p38 phosphorylation in the cells. In the presence of the antioxidant and free radical scavenger N-acetyl-L-cysteine (10 mmol/L), above effects of compounds 5b, 5d, and 5e were abolished.

Conclusion:

The compounds 5b, 5d, and 5e cause neither apoptosis nor necrosis of A549 cells, but exert anti-cancer effect via inducing G₁-phase arrest and senescence through ROS/p38 MAP-kinase pathway.