Cell-cycle dysregulation and anticancer therapy

Kaempferol-7-O-beta-D-glucoside (KG) isolated from Smilax china L. rhizome induces G2/M phase arrest and apoptosis on HeLa cells in a p53-independent manner

Kaempferol-7-O-beta-D-glucoside (KG), a flavonoid glycoside, isolated from Smilax china L. rhizome, displayed marked anticancer activity on a panel of established cancer cells, of which, HeLa human cervix carcinoma cells were the most sensitive. Meanwhile, the cytotoxic effects of KG on normal human cells (HEK293 embryonic kidney cells and L-02 embryonic liver cells) were much smaller than on cancer cells. This work studied the molecular mechanisms underlying KG induced growth inhibition in HeLa cells. The results showed that KG induced G2/M phase growth arrest correlated with Cyclin B1 and Cdk1 decrease in a p53-independent manner, and also caused an increase in apoptosis, which was confirmed by characteristic morphological changes, evident DNA fragmentation, increased apoptotic sub-G1 population. Furthermore, inhibition of NF-kappaB nuclear translocation, up-regulation of Bax and down-regulation of Bcl-2, were observed in HeLa cells treated with KG, which indicated that the mitochondrial pathway was involved in the apoptosis signal pathway. In summary, KG displayed a significant anti-tumor effect through cell cycle arrest and apoptotic induction in HeLa cells, which suggested that KG might have therapeutic potential against cervix carcinoma.

Anticancer activity and mechanisms of norcantharidin-Nd3II on hepatoma

Norcantharidin (NCTD), a demethylated form of cantharidin, is currently used as an anticancer drug in China, but five newly synthesized derivatives have not been tested for antitumor efficacy. In this study, we investigated the in-vitro and in-vivo activity of five derivatives on Bel-7402, HeLa and PC-3M1E8 cell lines on a sulfarhodamine B assay. All of the derivatives showed significant antiproliferative activity, hence we elected to study further one of them, NCTD-Nd3II, in an in-vivo mouse model, and to examine its effects on cell cycle and protein expression. NCTD-Nd3II inhibited H22 tumors in mice in a dose-dependent manner with low toxicity. Flow cytometry results showed that apoptosis and G2/M cell cycle arrest contributed to the cytotoxic and cytostatic effects of NCTD-Nd3II. Further studies showed that Bax and p21 protein expression was upregulated, whereas cyclin B1, Cdc-2 and Bcl-2 protein expression was downregulated. Our findings show that NCTD-Nd3II might be a promising chemotherapeutic agent for hepatomas.

A phenomenological approach to the simulation of metabolism and proliferation dynamics of large tumour cell populations

A major goal of modern computational biology is to simulate the collective behaviour of large cell populations starting from the intricate web of molecular interactions occurring at the microscopic level. In this paper we describe a simplified model of cell metabolism, growth and proliferation, suitable for inclusion in a multicell simulator, now under development (Chignola R and Milotti E 2004 Physica A 338 261-6). Nutrients regulate the proliferation dynamics of tumour cells which adapt their behaviour to respond to changes in the biochemical composition of the environment. This modelling of nutrient metabolism and cell cycle at a mesoscopic scale level leads to a continuous flow of information between the two disparate spatiotemporal scales of molecular and cellular dynamics that can be simulated with modern computers and tested experimentally.

Targeted MYCN expression affects cytotoxic potential of chemotherapeutic drugs in neuroblastoma cells

Neuroblastoma (NB) is a solid childhood tumour that exhibits heterogeneous biological and clinical phenotypes. Multiple drug resistance marks a major complication especially in high-risk patients with advanced tumour stages and specific genetic aberrations, such as MYCN amplification and lp deletion. As an approach to further address the mechanisms of chemotherapeutic responsiveness of NB, we used a MYCN-inducible in vitro system and tested the susceptibility of NB cells to anti-tumour drugs currently included in NB treatment protocols dependent on MYCN expression. We observed cytotoxic effects using drug concentrations corresponding to blood plasma levels achieved in NB patients. The most potent drugs were microtubule inhibitors vindesin, paclitaxel and vincristin. Less effective were doxorubicine, arsenic trioxide, cisplatin, etoposide and carboplatin. Exposed to anti-tumour agents, NB cells with induced MYCN expression exhibited higher specific apoptosis than NB cells lacking MYCN expression. Anti-tumour drugs in MYCN-on cells accelerated G1-S phase transition, led to enhanced accumulation of cell populations in G2/M phase, and increased levels of apoptosis. In contrast, MYCN-off cell populations arrested in G1 and, to a smaller extent, in G2/M and exhibited delayed onset of apoptosis. In summary, apoptosis profiles and anti-proliferative potential of chemotherapeutic drugs, used at in vivo tolerable doses, are affected by MYCN overexpression and deregulated cell cycle in SH-EP(MYCN) cells.

2-(3-Fluorophenyl)-6-methoxyl-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (YJC-1) induces mitotic phase arrest in A549 cells

A 2-phenyl-4-quinolone (2-PQ) derivative, 2-(3-fluorophenyl)-6-methoxyl-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (YJC-1), was synthesized in our laboratory. In this study, we delineated the growth-inhibitory effect of YJC-1 in human lung carcinoma A549 cells. YJC-1 inhibited cell growth with an IC(50) value of about 4.8 microM via microtubule polymerization, causing growth arrest in the mitotic phase. Immunoblotting analysis revealed a dramatic induction of cyclin-dependent kinase (CDK) inhibitor p21(Cip1/Waf1) and down-regulation of Cdc25C phosphatase to inhibit the protein expression of cyclin B1 and CDK1. We also found that YJC-1 induced a profound time-dependent elevation in p21(Cip1/Waf1) gene expression in comparison with the negative control. In vivo, we also found that YJC-1 significantly suppressed tumor growth in mice inoculated with A549 cells. These findings suggest that YJC-1 can suppress A549 cell growth via mitotic phase arrest.

Caffeine Promotes Apoptosis in Mitotic Spindle Checkpoint-arrested Cells

The spindle assembly checkpoint arrests cells in mitosis when defects in mitotic spindle assembly or partitioning of the replicated genome are detected. This checkpoint blocks exit from mitosis until the defect is rectified or the cell initiates apoptosis. In this study we have used caffeine to identify components of the mechanism that signals apoptosis in mitotic checkpoint-arrested cells. Addition of caffeine to spindle checkpoint-arrested cells induced >40% apoptosis within 5 h. It also caused proteasome-mediated destruction of cyclin B1, a corresponding reduction in cyclin B1/cdk1 activity, and reduction in MPM-2 reactivity. However, cells retained MAD2 staining at the kinetochores, an indication of continued spindle checkpoint function. Blocking proteasome activity did not block apoptosis, but continued spindle checkpoint function was essential for apoptosis. After systematically eliminating all known targets, we have identified p21-activated kinase PAK1, which has an anti-apoptotic function in spindle checkpoint-arrested cells, as a target for caffeine inhibition. Knockdown of PAK1 also increased apoptosis in spindle checkpoint-arrested cells. This study demonstrates that the spindle checkpoint not only regulates mitotic exit but apoptosis in mitosis through the activity of PAK1.

Inhibitory effect of snake venom toxin fromVipera lebetina turanicaon hormone-refractory human prostate cancer cell growth: induction of apoptosis through inactivation of nuclear factor κB

We investigated whether the snake venom toxin (SVT) from Vipera lebetina turanica inhibits cell growth of human prostate cancer cells by inducing apoptosis and also studied possible signaling pathways involved in this cell death. SVT inhibited growth of PC-3 and DU145 cells, androgen-independent prostate cancer cells, but not LNCaP cells, a human androgen-dependent prostate cancer cell. Cells were arrested in the G(2)-M phase by SVT with a concomitant decrease in the expression of the G(2)-M phase regulatory protein cyclin B1 and were also arrested in the G(1)-S phase with decreasing expression of cyclin-dependent kinase 4, cyclin D1 and cyclin E. In addition to the growth-inhibitory effect, SVT increased the induction of apoptotic cell death. Untreated PC-3 cells show high DNA binding activity of nuclear factor kappaB (NF-kappaB), an antiapoptotic transcriptional factor, but this was inhibited by SVT and accompanied by a significant inhibition of p50 translocation into the nucleus, as well as phosphorylation of inhibitory kappaB. Consistent with the induction of apoptosis and inhibition of NF-kappaB, this toxin increased the expression of proapoptotic proteins such as p53, Bax, caspase-3, and caspase-9, but down-regulated antiapoptotic protein Bcl-2. However, SVT did not show an inhibitory effect on cell growth and caspase-3 activity in cells carrying mutant p50 and inhibitory kappaB kinase plasmids. Confocal microscopy analysis showed that SVT is taken up into the nucleus of the cells. These findings suggest that a nanogram concentration range of SVT from V. lebetina turanica could inhibit hormone-refractory human prostate cancer cell growth, and the effect may be related to NF-kappaB signal-mediated induction of apoptosis.

Cruciferous vegetables and human cancer risk: epidemiologic evidence and mechanistic basis

Cruciferous vegetables are a rich source of glucosinolates and their hydrolysis products, including indoles and isothiocyanates, and high intake of cruciferous vegetables has been associated with lower risk of lung and colorectal cancer in some epidemiological studies. Glucosinolate hydrolysis products alter the metabolism or activity of sex hormones in ways that could inhibit the development of hormone-sensitive cancers, but evidence of an inverse association between cruciferous vegetable intake and breast or prostate cancer in humans is limited and inconsistent. Organizations such as the National Cancer Institute recommend the consumption of five to nine servings of fruits and vegetables daily, but separate recommendations for cruciferous vegetables have not been established. Isothiocyanates and indoles derived from the hydrolysis of glucosinolates, such as sulforaphane and indole-3-carbinol (I3C), have been implicated in a variety of anticarcinogenic mechanisms, but deleterious effects also have been reported in some experimental protocols, including tumor promotion over prolonged periods of exposure. Epidemiological studies indicate that human exposure to isothiocyanates and indoles through cruciferous vegetable consumption may decrease cancer risk, but the protective effects may be influenced by individual genetic variation (polymorphisms) in the metabolism and elimination of isothiocyanates from the body. Cooking procedures also affect the bioavailability and intake of glucosinolates and their derivatives. Supplementation with I3C or the related dimer 3,3'-diindolylmethane (DIM) alters urinary estrogen metabolite profiles in women, but the effects of I3C and DIM on breast cancer risk are not known. Small preliminary trials in humans suggest that I3C supplementation may be beneficial in treating conditions related to human papilloma virus infection, such as cervical intraepithelial neoplasia and recurrent respiratory papillomatosis, but larger randomized controlled trials are needed.

N-methylformamide and 9-hydroxystearic acid: two anti-proliferative and differentiating agents with different modes of action in colon cancer cells

N-methylformamide (NMF) is an anti-proliferative, differentiating agent studied in several cell lines as well as in preclinical and clinical trials, whose mechanisms of action are still unclear. 9-Hydroxystearic acid (9-HSA) is an endogenous product of lipid peroxidation recently identified as a new histone deacetylase 1 inhibitor. Both agents show the same anti-proliferative effects by arresting colon cancer cell growth in G0/G1. We addressed two questions. (i) Do they act by regulating G0/G1 checkpoint proteins? (ii) Does 9-HSA have differentiating effects comparable to those of NMF? The effects of NMF and 9-HSA on growth, differentiation and invasiveness of HT29, a colon cancer cell line, have been compared by using immunoprecipitation analysis, confocal microscopy, enzyme assays and invasiveness tests. The results show that the G1 arrest caused by NMF is a cell cycle exit due to p27 induction, whereas 9-HSA has no effect on the induction of this inhibitor. Evidence is presented that the arrest in early G0/G1 induced by 9-HSA is associated with the conversion of HT29 characteristics to those of a more benign phenotype, whereas the arrest in the late G1 in response to NMF is not followed by a decrease in tumorigenicity. The failure of NMF in cancer therapy indicates that both anti-proliferative and differentiating characteristics are required for an anti-tumoral agent to be effective.

Cytotoxic activity and cytostatic mechanism of novel 2-arylbenzo[b]furans

The aims of this study were to screen cytotoxic compounds from 14 newly-synthesized 2-arylbenzo[b]furans and explore their mechanisms of action. Cytotoxicity was determined by the MTT method. Cell-cycle distribution was detected by flow cytometry. Wright-Giemsa staining was performed to demonstrate the morphological features of cells in mitotic phase. Polymerization of tubulin was detected by tubulin assembly assay, and the cellular microtubule network was observed by immunocytochemical study. Among the 14 compounds screened, 4-formyl-2-(4-hydroxy-3-methoxyphenyl)-5-(2-methoxycarbonyethyl)-7-methoxy-benzo[b]furan (ERJT-12) showed significant cytotoxicity. Our results demonstrated that ERJT-12 exhibited anti-cancer activity in a variety of tumour cell lines with an IC50 value (concentration resulting in 50% inhibition of cell growth) of 5.75 approximately 17.29 microM. Cell cycle analysis showed a concentration-dependent accumulation of tumour cells in G2/M phase after treatment with ERJT-12. Further investigation indicated that ERJT-12 blocked the cell cycle in M phase, with separation and dispersion of chromosomes. ERJT-12 inhibited tubulin polymerization in-vitro. Changes of the cellular microtubule network caused by ERJT-12 were also detected, which were similar to the changes caused by colchicine. These results suggested that the anti-cancer activity of ERJT-12 is worth further investigation.

Diallyl disulfide increases CDKN1A promoter-associated histone acetylation in human colon tumor cell lines

Diallyl disulfide (DADS) is an organosulfur compound from garlic, which inhibits colon tumor cell proliferation. In a previous study, we have shown that in Caco-2 and HT-29 cells DADS (200 microM) increases global histone acetylation, CDKN1A mRNA, and p21(waf1) protein levels and induces G2/M cell cycle arrest. These results suggested that DADS could inhibit cell proliferation through at least in part a transcriptional activation of CDKN1A expression involving histone acetylation. In this study, using chromatin immunoprecipitation assays, we demonstrate that in Caco-2 and HT-29 cells histone H4 and/or H3 acetylation is increased within CDKN1A promoter after 3 and 6 h treatments with DADS. These results strongly suggest that histone acetylation, a molecular mechanism implicated in the regulation of gene expression, could account for the induction of CDKN1A expression and the antiproliferating effects of DADS in colon tumor cells.

Methyl protodioscin induces G2/M cell cycle arrest and apoptosis in HepG2 liver cancer cells

Methyl protodioscin (NSC-698790) is one of the main bioactive components in the traditional Chinese medicine Dioscorea collettii var. hypoglauca (Dioscoreaceae). In this study, we investigated the anti-proliferative effect of methyl protodioscin on the HepG2 cells and the mechanism of the induced cytotoxicity. Treatment of methyl protodioscin resulted in G2/M arrest and apoptosis in HepG2 cells. These effects were attributed to down-regulation of Cyclin B1 and the signaling pathways leading to up-regulation of Bax and down-regulation of BCL2, suggesting that methyl protodioscin may be a novel anti-mitotic agent.

Centrosome-, chromosomal-passenger- and cell-cycle-associated mRNAs are differentially regulated in the development of sporadic colorectal cancer

Dysregulation of the centrosome complex and chromosomal segregation has been associated with aneuploid cells and aggressive solid tumours, but the relevance of this mechanism to the adenoma-carcinoma sequence of sporadic colorectal cancer (sCRC), especially tumours showing chromosomal instability (CIN), is still unknown. In a series of matching normal epithelial cells (n = 41), dysplastic cells (n = 18), and invasive carcinoma cells (n = 41) from cases with sCRC, mRNA levels of the centrosomal kinase Aurora-A/STK15 and the chromosomal passenger- and cell cycle-associated molecules Incenp, Survivin, Mad-2, and Cyclin-D1 were therefore measured with specific reference to the type of genetic instability. Compared with normal epithelium, significant up-regulation of mRNAs was already present for Aurora-A/STK15 (p = 0.0313) in dysplastic cells and for all investigated markers in invasive carcinoma. Whereas Aurora-A/STK15 mRNA levels were similarly up-regulated in dysplastic and invasive carcinoma cells (p = 0.0797), Survivin (p = 0.0046) and Cyclin-D1 (p = 0.0017) mRNA levels increased from dysplastic to invasive carcinoma cells. In carcinomas, Incenp mRNA correlated with T category (p = 0.0149), and Survivin (p = 0.0382) and Cyclin-D1 (p = 0.0185) were associated with tumour differentiation. Importantly, a significantly higher (p = 0.0419) fold-change of Aurora-A/STK15 mRNA (p = 0.0419), but not Incenp, Survivin, Mad-2 or Cyclin-D1, was observed in sCRC cases with CIN (n = 29) when compared with tumours showing microsatellite instability (MIN, n = 10). The present data are the first to show an early increase of the centrosomal kinase Aurora-A/STK15 in the adenoma-carcinoma sequence of sCRC. The regulation of this kinase differs in CIN- and MIN-type sCRCs and the pattern of changes is different from those of the cell-cycle-associated markers Survivin, Mad-2, and Cyclin-D1. This reinforces the concept of preferential dysregulation of the centrosome complex in CIN-type (aneuploid), compared with MIN-type, sporadic colorectal cancers and may influence the response to and efficiency of novel therapeutics targeting Aurora kinases.

Threshold effects of nitric oxide-induced toxicity and cellular responses in wild-type and p53-null human lymphoblastoid cells

Toxicity induced by nitric oxide (NO(*)) has been extensively investigated in many in vitro and in vivo experimental models. Recently, our laboratories found that both concentration and cumulative total dose are critical determinants of cell death caused by NO(*). Here, we report results of studies designed to define total dose thresholds and threshold effects for several NO(*)-induced toxicity and cellular responses and to determine impacts of p53 on them. We exposed human lymphoblastoid TK6 cells harboring wild-type p53 and isogenic p53-null NH32 cells to NO(*) delivered by a membrane delivery system. Cells were exposed at a steady state concentration of 0.6 microM for varying lengths of time to deliver increasing cumulative doses (expressed in units of microM min), and several end points of cytotoxicity and mutagenesis were quantified. Threshold doses for NO(*)-induced cytotoxicity were 150 microM min in TK6 cells and 300 microM min in NH32 cells, respectively. Threshold doses for NO(*)-induced apoptosis were identical to those for cytotoxicity, but mitochondrial depolarization thresholds were lower than those for cytotoxicity and apoptosis in both cell types. To gain insight into underlying mechanisms, cells of both types were exposed to sublethal (33% of cytotoxicity threshold), cytotoxicity threshold, or toxic (twice the cytotoxicity threshold) doses of NO(*). In TK6 cells (p53), the sublethal threshold dose induced DNA double-strand breaks, but nucleobase deamination products (xanthine, hypoxanthine, and uracil) in DNA were increased only modestly (<50%) by toxic doses. Increased mutant fraction at the thymidine kinase gene (TK1) locus was observed only at the toxic dose of NO(*). Treatment of NH32 cells with NO(*) at the threshold or toxic dose elevated mutagenesis of the TK1 gene, but did not cause detectable levels of DNA double-strand breaks. At similar levels of cell viability, the frequency of DNA recombinational repair was higher in p53-null NH32 cells than in wild-type TK6 cells. NO(*) treatment induced p53-independent cell cycle arrest predominately at the S phase. Akt signaling pathway and antioxidant proteins were involved in the modulation of toxic responses of NO(*). These findings indicate that exposure to doses of NO(*) at or above the cytotoxicity threshold dose induces DNA double-strand breaks, mutagenesis, and protective cellular responses to NO(*) damage. Furthermore, recombinational repair of DNA may contribute to resistance to NO(*) toxicity and potentially increase the risk of mutagenesis. The p53 plays a central role in these responses in human lymphoblastoid cells.

YC-1 Induces S Cell Cycle Arrest and Apoptosis by Activating Checkpoint Kinases

Hypoxia-inducible factor-1alpha (HIF-1alpha) seems central to tumor growth and progression because it up-regulates genes essential for angiogenesis and the hypoxic adaptation of cancer cells, which is why HIF-1alpha inhibition is viewed as a cancer therapy strategy. Paradoxically, HIF-1alpha also leads to cell cycle arrest or the apoptosis of cancer cells. Thus, the possibility cannot be ruled out that HIF-1alpha inhibitors unlock cell cycle arrest under hypoxic conditions and prevent cell death, which would limit the anticancer effect of HIF-1alpha inhibitors. Previously, we reported on the development of YC-1 as an anticancer agent that inhibits HIF-1alpha. In the present study, we evaluated the effects of YC-1 on hypoxia-induced cell cycle arrest and cell death. It was found that YC-1 does not reverse the antiproliferative effect of hypoxia, but rather that it induces S-phase arrest and apoptosis at therapeutic concentrations that inhibit HIF-1alpha and tumor growth; however, YC-1 did not stimulate cyclic guanosine 3',5'-monophosphate production in this concentration range. It was also found that YC-1 activates the checkpoint kinase-mediated intra-S-phase checkpoint, independently of ataxia-telangiectasia mutated kinase or ataxia-telangiectasia mutated and Rad3-related kinase. These results imply that YC-1 does not promote the regrowth of hypoxic tumors because of its cell cycle arrest effect. Furthermore, YC-1 may induce the combined anticancer effects of HIF-1alpha inhibition and cell growth inhibition.

Carboxyamido-triazole inhibits proliferation of human breast cancer cells via G(2)/M cell cycle arrest and apoptosis

Carboxyamido-triazole (CAI), a voltage-independent calcium channel inhibitor, has been shown to be able to induce growth inhibition and apoptosis in cancer cells. In the present study, we demonstrate that CAI significantly inhibits proliferation of cultured MCF-7 human breast cancer cells in a dose-dependent manner with an IC(50) of approximately 26 microM. Reduced proliferation of MCF-7 cells in the presence of CAI correlated with accumulation of cells in G(2)/M phase and induction of apoptosis. A treatment of MCF-7 cells with 30 microM CAI caused a time-dependent decrease in the levels of proteins that regulate G(2)/M progression, including Cdk1, Cyclin B1, and Cdc25C. A simultaneous increase in the expression of p21 protein was observed. We also demonstrated a concurrent decrease of the mitochondrial membrane potential (DeltaPsi(m)), and down-regulation of anti-apoptotic protein Bcl-2. In conclusion, it seems reasonable to hypothesize that the antitumor effect of CAI in MCF-7 cells is based on G(2)/M cell cycle arrest and inducing apoptosis.

Equivalent effect of DNA damage-induced apoptotic cell death or long-term cell cycle arrest on colon carcinoma cell proliferation and tumour growth

Knowledge of the type of biological reaction to chemotherapy is a prerequisite for its rational enhancement. We previously showed that irinotecan-induced DNA damage triggers in the HCT116p53(wt) colon carcinoma cell line a long-term cell cycle arrest and in HCT116p53(-/-) cells apoptosis (Magrini et al., 2002). To compare the contribution of long-term cell cycle arrest and that of apoptosis to inhibition of cell proliferation after irinotecan-induced DNA damage, we used this isogenic system as well as the cell lines LS174T (p53(wt)) and HT-29 (p53(mut)). Both p53(wt) cell lines responded to damage by undergoing a long-term tetraploid G1 arrest, whereas the p53(mut) cell lines underwent apoptosis. Cell cycle arrest as well as apoptosis caused a similar delay in cell proliferation. Irinotecan treatment also induced in mouse tumours derived from the p53(wt) cell lines a tetraploid G1 arrest and in those derived from the p53-deficient cell lines a transient G2/M arrest and apoptosis. The delay of tumour growth was in the same range in both groups, that is, arrest- and apoptosis-mediated tumour growth inhibition was comparable. In conclusion, cell cycle arrest as well as apoptosis may be equipotent mechanisms mediating the chemotherapeutic effects of irinotecan.

Interaction between Polyamines and the Mitogen-Activated Protein Kinase Pathway in the Regulation of Cell Cycle Variables in Breast Cancer Cells

Inhibition of polyamine biosynthesis with alpha-difluoromethylornithine (DFMO) has been shown to inhibit proliferation of breast cancer cells although its mechanism of action has not been fully elucidated. To address this issue, we tested the effects of DFMO on cell cycle variables of MDA-MB-435 human breast cancer cells in culture. We also focused on the possible mediatory role of the mitogen-activated protein kinase (MAPK) pathway on the cell cycle effects of DFMO because this compound has been shown to activate MAPK signaling. We found that DFMO caused a p53-independent increase in p21 and its association with cyclin-dependent kinase (cdk)-2 and decreased cdk-2 protein as well as its phosphorylation on Thr160. In addition, DFMO markedly suppressed the expression of the full-length and low molecular weight forms of cyclin E. These effects of DFMO were reversible with exogenous putrescine, thus indicating that they are specifically mediated through polyamine depletion. Cdk-2 activity was drastically reduced in DFMO-treated breast cancer cells which exhibited a reduction in retinoblastoma (Rb) phosphorylation and protein. As a predictable consequence of these effects, DFMO caused a G1-S block. In addition, DFMO inhibited G2-M transition, most likely as a result of its induction of p21 expression. Inhibition of the MAPK pathway with PD98059 or U0126 blocked the DFMO-induced induction of p21 and the reduction of cdk-2 protein. PD98059 reversed the G2-M block induced by DFMO (probably as a result of suppression of p21) but not the G1-S arrest. MDA-MB-435 cells treated with PD98059 or U0126 in the presence and absence of DFMO exhibited a marked increase in the expression of p27 and its association with cdk-2, a decrease in phosphorylation of cdk-2 on Thr160, and a decrease in cyclin E expression. As predicted, PD98059 treatment reduced cdk-2 activity and Rb phosphorylation while reversing the decrease in Rb protein induced by DFMO. Neither DFMO nor PD98059, either alone or in combination, reduced cdk-4 activity despite a marked induction in p15 expression caused by DFMO. Our results indicate that activation of the MAPK pathway accounts for some of the effects of DFMO on cell cycle events of breast cancer cells. Inhibition of the MAPK pathway, however, does not reverse the cell cycle arrest induced by DFMO because of activation of alternative mechanisms leading to suppression of cdk-2 activity.

Dynamic Green Fluorescent Protein Sensors for High‐Content Analysis of the Cell Cycle

We have developed two dynamic sensors that report cell cycle position in living mammalian cells. The sensors use well-characterized components from proteins that are spatially and temporally regulated through the cell cycle. Coupling of these components to Enhanced Green Fluorescent Protein (EGFP) has been used to engineer fusion proteins that report G1/S and G2/M transitions during the cell cycle without perturbing cell cycle progression. Expression of these sensors in stable cell lines allows high content analysis of the effects of drugs and gene knockdown on the cell cycle using automated image analysis to determine cell cycle position and to abstract correlative data from multiplexed sensors and morphological analysis.

Xanthones induce cell-cycle arrest and apoptosis in human colon cancer DLD-1 cells

We investigated the antiproliferative effects of four structurally similar prenylated xanthones, alpha-mangostin, beta-mangostin, gamma-mangostin, and methoxy-beta-mangostin, in human colon cancer DLD-1 cells. These xanthones differ in the number of hydroxyl and methoxy groups. Except for methoxy-beta-mangostin, the other three xanthones strongly inhibited cell growth at 20 microM and their antitumor efficacy was correlated with the number of hydroxyl groups. Hoechst 33342 nuclear staining and nucleosomal DNA-gel electrophoresis revealed that the antiproliferative effects of alpha- and gamma-mangostin, but not that of beta-mangostin, were associated with apoptosis. It was also shown that their antiproliferative effects were associated with cell-cycle arrest by affecting the expression of cyclins, cdc2, and p27; G1 arrest was by alpha-mangostin and beta-mangostin, and S arrest by gamma-mangostin. These findings provide a relevant basis for the development of xanthones as an agent for cancer prevention and combination therapy with anti-cancer drugs.

1-(3,4-dimethoxyphenyl)-3,5-dodecenedione (I6) induces G1 arrest and apoptosis in human promyelocytic leukemia HL-60 cells

1-(3,4-dimethoxyphenyl)-3,5-dodecenedione (I6), a gingerdione derivative, was synthesized in our laboratory, has been demonstrated to be an effective anti-tumor agent in human leukemia cells. Gingerdione is one of the components from ginger. In the present study, we found that I6 could inhibit cell proliferation in the time- and dose-dependent manner in human promyelocytic leukemia HL-60 cells. To investigate the anti-proliferation mechanism of I6, cell cycle analysis was performed. Results showed that I6 induced significant G1 arrest and apoptosis in HL-60 cells. It was proved by the reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of regulatory on G1 arrest that the levels of p15 and p27 increased after treatment and mRNA levels of cyclin D2, cyclin E, and cdc25A were decreased. The I6-induced apoptosis was further confirmed by DNA fragmentation assay. The DNA gel electrophoresis showed that I6 induced DNA fragmentation, a biochemical hallmark of apoptosis, in HL-60 cells. I6-induced apoptosis was accompanied by an apparent up-regulation of caspase-3, and down-regulation of Bcl-2. Taken together, these results suggest that markedly down-regulation of G1 associated cyclin D2, cyclin E and cdc25A and up-regulation of CDKI, p15 and p27, and may contribute to I6-mediated cell cycle arrest. Furthermore, the Bcl-2 expression decrease and caspase-3 activation may be the plausible mechanism by which I6 induced apoptosis. These results suggest that I6 is a potent anti-HL-60 drug and possess a significant action on cell cycle before commitment for apoptosis occurrence.

Regulation of the INK4a/ARF locus by histone deacetylase inhibitors

Despite the importance of the INK4a/ARF locus in tumor suppression, its modulation by histone deacetylase inhibitors (HDACis) remains to be characterized. Here, we have shown that the levels of p16INK4a are decreased in human and murine fibroblasts upon exposure to relatively high concentrations of trichostatin A and sodium butyrate. Interestingly, the levels of p19ARF are strongly upregulated in murine cells even at low concentrations of HDACis. Using ARF-deficient cells, we have demonstrated that p19ARF plays an active role in HDACi-triggered cytostasis and the contribution of p19ARF to this arrest is of higher magnitude than that of the well established HDACi target p21Waf1/Cip. Moreover, chemically induced fibrosarcomas in ARF-null mice are more resistant to the therapeutic effect of HDACis than similar tumors in wild type or p21Waf1/Cip-null mice. Together, our results have established the tumor suppressor ARF as a relevant target for HDACi chemotherapy.

Selective and irreversible cell cycle inhibition by diphenyleneiodonium

Because cell proliferation is subject to checkpoint-mediated regulation of the cell cycle, pharmacophores that target cell cycle checkpoints have been used clinically to treat human hyperproliferative disorders. It is shown here that the flavoprotein inhibitor diphenyleneiodionium can block cell proliferation by targeting of cell cycle checkpoints. Brief exposure of mitotically arrested cells to diphenyleneiodonium induces a loss of the mitotic cell morphology, and this corresponds with a decrease in the levels of the mitotic markers MPM2 and phospho-histone H3, as well as a loss of centrosome maturation, spindle disassembly, and redistribution of the chromatin remodeling helicase ATRX. Surprisingly, this mitotic exit resulted in a tetraploidization that persisted long after drug release. Analogously, brief exposure to diphenyleneiodonium also caused prolonged arrest in G(1) phase. By contrast, diphenyleneiodonium exposure did not abrogate S phase, although it did result in a subsequent block of G(2) cell cycle progression. This indicates that diphenyleneiodonium selectively targets components of the cell cycle, thereby either causing cell cycle arrest, or checkpoint override followed by cell cycle arrest. These irreversible effects of diphenyleneiodonium on the cell cycle may underlie its potent antiproliferative activity.

Differential effects of histone deacetylase inhibitors in tumor and normal cells-what is the toxicological relevance?

Histone deacetylase (HDAC) inhibitors target key steps of tumor development: They inhibit proliferation, induce differentiation and/or apoptosis, and exhibit potent antimetastatic and antiangiogenic properties in transformed cells in vitro and in vivo. Preliminary studies in animal models have revealed a relatively high tumor selectivity of HDAC inhibitors, strenghtening their promising potential in cancer chemotherapy. Until now, preclinical in vitro research has almost exclusively been performed in cancer cell lines and oncogene-transformed cells. However, as cell proliferation and apoptosis are essential for normal tissue and organ homeostasis, it is important to investigate how HDAC inhibitors influence the regulation of and interplay between proliferation, differentiation, and apoptosis in primary cells as well. This review highlights the discrepancies in molecular events triggered by trichostatin A, the reference compound of hydroxamic acid-containing HDAC inhibitors, in hepatoma cells and primary hepatocytes (which are key targets for drug-induced toxicity). The implications of these differential outcomes in both cell types are discussed with respect to both toxicology and drug development. In view of the future use of HDAC inhibitors as cytostatic drugs, it is highly recommended to include both tumor cells and their healthy counterparts in preclinical developmental studies. Screening the toxicological properties of compounds early in their development process, using a battery of different cell types, will enable researchers to discard those compounds bearing undesirable adverse activity before entering into expensive clinical trials. This will not only reduce the risk for harmful exposure of patients but also save time and money.

Antisense-Mediated Suppression of Hyaluronan Synthase 2 Inhibits the Tumorigenesis and Progression of Breast Cancer

The progression of several cancers is correlated with the increased synthesis of the glycosaminoglycan, hyaluronan. Hyaluronan is synthesized at the plasma membrane by various isoforms of hyaluronan synthases (HAS). The importance of HAS2 expression in highly invasive breast cancer was characterized by the antisense inhibition of HAS2 (ASHAS2). The effect of HAS2 inhibition on cell proliferation, migration, hyaluronan metabolism, and receptor status was characterized in vitro, whereas the effect on tumorigenicity and metastasis was established in vivo. HAS2 inhibition resulted in a 24-hour lag in proliferation that was concomitant to transient arrest of 79% of the cell population in G0-G1. Inhibition of HAS2 did not alter the expression of the other HAS isoforms, whereas hyaluronidase (HYAL2) and the hyaluronan receptor, CD44, were significantly down-regulated. ASHAS2 cells accumulated greater amounts of high molecular weight hyaluronan (>10,000 kDa) in the culture medium, whereas mock and parental cells liberated less hyaluronan of three distinct molecular weights (100, 400, and 3,000 kDa). The inhibition of HAS2 in the highly invasive MDA-MB-231 breast cancer cell line inhibited the initiation and progression of primary and secondary tumor formation following s.c. and intracardiac inoculation into nude mice, whereas controls readily established both primary and secondary tumors. The lack of primary and secondary tumor formation was manifested by increased survival times where ASHAS2 animals survived 172% longer than the control animals. Collectively, these unique results strongly implicate the central role of HAS2 in the initiation and progression of breast cancer, potentially highlighting the co-dependency between HAS2, CD44, and HYAL2 expression.

Novel indication for cancer therapy: Chk1 inhibition sensitizes tumor cells to antimitotics

Paclitaxel (Taxol) is the most-prescribed anti-mitotic agent for a variety of advanced metastatic cancers. It induces mitotic arrest leading to apoptosis through microtubule stabilization. Chk1 is the major cell-cycle checkpoint kinase mediating S- and G2-arrests in response to various DNA-damages. Chk1 inhibitor is anticipated and has been demonstrated to potentiate the cytotoxicity of DNA-damaging agents through abrogation of cell-cycle checkpoints. Paclitaxel does not, however, induce Chk1 activation, and Chk1 has not been shown to function in mitotic checkpoint. Thus, Chk1 inhibitor is not expected to enhance the toxicity of paclitaxel. Here we show that downregulation of Chk1 sensitizes tumor cells to the toxicity of paclitaxel in cell proliferation assay. Fluorescence microscopy showed that Chk1 knockdown augments mitotic catastrophe and apoptosis in paclitaxel-treated cancer cells. Further, we elucidated the mechanism of this sensitization. Chk1 inhibition facilitates paclitaxel-induced M-phase entry by activation of Cdc2 kinase and accumulation of cyclin B1, the required cofactor for Cdc2 kinase activity. Moreover, Chk1 downregulation inhibits M phase exit through induction of the anaphase inhibitor, securin/PDS1. Collectively, Chk1 elimination sustains a more effective mitotic arrest as demonstrated by the more efficient accumulation of M-phase marker phospho-histone H3. We show that Chk1 elimination attenuates the paclitaxel-induced activation of the anti-apoptotic p42/p44 (ERK1/2) MAP kinase pathway, additionally contributing to the sensitization. Our results suggest that in addition to its well-established role as an enforcer of S and G2-checkpoints in response to genotoxic stress, Chk1 also plays a protective role in mitotic checkpoint to lessen mitotic catastrophe and thereby limits cell-death. Therefore Chk1 downregulation can not only potentiate DNA-damaging agents, but also enhance the toxicity of anti-microtubule agents, which significantly broadens its therapeutic applications.

Dopamine inhibits cell growth and cell cycle by blocking ribonucleotide reductase

Dopamine (DA) is a classical neurotransmitter modulating various brain functions by acting on its specific receptors. In addition, DA is a reactive molecule that has been implicated in neurodegeneration, especially in Parkinson's disease. Here we show that DA inhibited cell growth of dopamine transporter transfected cells by intracellularly blocking cell cycle progression. To pinpoint the site of this effect, we measured DNA distribution and 5-bromo-2'-deoxyuridine (BrdU) incorporation, as well as the levels of the key cell cycle proteins. DA increased number of cells with a G1 DNA content, decreased BrdU incorporation and simultaneously increased cyclin A but had no effect on cyclin D2, D3, E, nor on cdk4 and p21. These results narrowed down the DA effect to the beginning of S phase, suggesting inhibition of the ribonucleotide reductase, an enzyme essential for DNA synthesis. Indeed, measurement of enzyme activity in situ revealed that DA, within 1h of addition to cells labelled with [3H]cytidine, strongly reduced the cell content of [3H]2'-deoxycytidine 5'-triphophate. The time course of this DA effect preceded the cell cycle progression. This novel molecular mechanism of intracellular DA action independent of plasmamembrane receptors may be involved in processes controlling the development and survival of brain dopaminergic neurons.

A glyphosate-based pesticide impinges on transcription

Widely spread chemicals used for human benefits may exert adverse effects on health or the environment, the identification of which are a major challenge. The early development of the sea urchin constitutes an appropriate model for the identification of undesirable cellular and molecular targets of pollutants. The widespread glyphosate-based pesticide affected sea urchin development by impeding the hatching process at millimolar range concentration of glyphosate. Glyphosate, the active herbicide ingredient of Roundup, by itself delayed hatching as judged from the comparable effect of different commercial glyphosate-based pesticides and from the effect of pure glyphosate addition to a threshold concentration of Roundup. The surfactant polyoxyethylene amine (POEA), the major component of commercial Roundup, was found to be highly toxic to the embryos when tested alone and therefore could contribute to the inhibition of hatching. Hatching, a landmark of early development, is a transcription-dependent process. Correlatively, the herbicide inhibited the global transcription, which follows fertilization at the 16-cell stage. Transcription inhibition was dose-dependent in the millimolar glyphosate range concentration. A 1257-bp fragment of the hatching enzyme transcript from Sphaerechinus granularis was cloned and sequenced; its transcription was delayed by 2 h in the pesticide-treated embryos. Because transcription is a fundamental basic biological process, the pesticide may be of health concern by inhalation near herbicide spraying at a concentration 25 times the adverse transcription concentration in the sprayed microdroplets.

Antitumor mechanism of evodiamine, a constituent from Chinese herb Evodiae fructus, in human multiple-drug resistant breast cancer NCI/ADR-RES cells in vitro and in vivo

Drug resistance is one of the main obstacles to the successful treatment of cancer. The availability of agents that are highly effective against drug-resistant cancer cells is therefore essential. The present study was performed to examine the anticancer effects of evodiamine, a major constituent of the Chinese herb Evodiae fructus, in adriamycin-resistant human breast cancer NCI/ADR-RES cells. Evodiamine inhibited the proliferation of NCI/ADR-RES cells in a concentration-dependent manner with a GI50 of 0.59 +/- 0.11 microM. This agent also caused a substantial apoptosis at 1 microM. FACScan flow cytometric analysis of cell cycle progression revealed that a G2/M arrest was initiated after a 12-h exposure to the drug. Evodiamine increased tubulin polymerization as determined by the immunocytochemical and in vivo tubulin polymerization analyses. In a time- and concentration-dependent manner, evodiamine also promoted the phosphorylations of Raf-1 kinase and Bcl-2. The phosphorylation site of Raf-1 kinase was identified to be serine338. The in vivo anticancer effects of evodiamine were evaluated in Balb-c/nude mice following a tumor xenograft implantation of NCI/ADR-RES cells. The antitumor activity of evodiamine against the human multiple-drug resistant tumor xenograft was found to be superior to that of paclitaxel. Evodiamine therefore represents a highly promising chemotherapeutic agent in the treatment of human multiple-drug resistant cancer cells.

Inhibition of IκB Kinase Activity by Acetyl-boswellic Acids Promotes Apoptosis in Androgen-independent PC-3 Prostate Cancer Cells in Vitro and in Vivo

Signaling through NF-kappaB has been implicated in the malignant phenotype as well as the chemoresistance of various cancers. Here we show that the natural compounds acetyl-beta-boswellic acid and acetyl-11-keto-beta-boswellic acid (AKbetaBA) inhibit proliferation and elicit cell death in chemoresistant androgen-independent PC-3 prostate cancer cells in vitro and in vivo. Induction of apoptosis was demonstrated in cultured PC-3 cells by several parameters including mitochondrial cytochrome c release and DNA fragmentation. At the molecular level these compounds inhibit constitutively activated NF-kappaB signaling by intercepting the IkappaB kinase (IKK) activity; signaling through the interferon-stimulated response element remained unaffected, suggesting specificity for IKK inhibition. The impaired phosphorylation of p65 and the reduced nuclear translocation of NF-kappaB proteins were associated with down-regulation of the constitutively overexpressed and NF-kappaB-dependent antiapoptotic proteins Bcl-2 and Bcl-x(L). In addition, expression of cyclin D1, a crucial cell cycle regulator, was reduced as well. Down-regulation of IKK by antisense oligodeoxynucleotides confirmed the essential role of IKK inhibition for the proliferation of the PC-3 cells. Both compounds tested were active in vivo, yet AKbetaBA proved to be far superior. Indeed, topical application of water-soluble AKbetaBA-gamma-cyclodextrin on PC-3 tumors xenografted onto chick chorioallantoic membranes induced concentration-dependent inhibition of proliferation as well as apoptosis. Similarly, in nude mice carrying PC-3 tumors, systemic application of AKbetaBA-gamma-cyclodextrin inhibited tumor growth and triggered apoptosis in the absence of detectable systemic toxicity. Thus, AKbetaBA and related compounds acting on IKK might provide a novel approach for the treatment of chemoresistant human tumors such as androgen-independent human prostate cancers.

Denbinobin-mediated anticancer effect in human K562 leukemia cells: role in tubulin polymerization and Bcr-Abl activity

Denbinobin (5-hydroxy-3,7-dimethoxy-1,4-phenanthraquinone) has been reported to exhibit anti-tumor and anti-inflammatory activity. Nevertheless, the anti-tumor mechanism of denbinobin remains unclear. In the present study, we evaluated the anticancer activity of denbinobin in human myelogenous K562 leukemia cells. In accordance with the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay, we demonstrated that denbinobin inhibited cell viability in a concentration-dependent manner with an IC50 value of 1.84 microM. Cell cycle analysis illustrated that exposure of denbinobin caused a G2/M phase accumulation in a time-dependent manner. Tubulin polymerization in cells was apparently enhanced by denbinobin, implying that denbinobin might have a regulatory role in tubulin/microtubule. Furthermore, denbinobin significantly suppressed the expression of Bcr-Abl and phosphorylation of CrkL, a crucial tyrosine kinase and an adaptor protein in chronic myeloid leukemia, respectively. Denbinobin also markedly enhanced CD11b expression after a long-term treatment, suggesting that denbinobin might play a role in facilitating differentiation in K562 cells. In summary, we have demonstrated that denbinobin displays anticancer effects in K562 cells through the increase of levels of tubulin polymerization and deregulation of Bcr-Abl signaling. Our data demonstrate that denbinobin could be a potential anticancer lead compound for further development.

NPM/ALK downregulates p27Kip1 in a PI-3K-dependent manner

OBJECTIVES

Anaplastic large-cell lymphomas (ALCL) are frequently associated with the chromosomal translocation t(2;5) (p23;q35) resulting in the NPM/ALK fusion gene that encodes a constitutively activated tyrosine kinase. We showed that NPM/ALK stimulated cell proliferation and that PI-3K/AKT pathway played an important role in this effect. p27Kip1 is a member of the CDK family inhibitory proteins regulating the entry into S phase. It was reported that p27Kip1 function is impaired in many tumors. In this study we investigated the role of PI-3K/AKT in NPM/ALK-dependent downregulation of p27Kip1 protein.

MATERIALS AND METHODS

To investigate this phenomenon the pro-B cell line BaF3, BaF3 cell line stably expressing NPM/ALK, and ALCL SUP-M2 cell line were used. The p27Kip1 protein expression before and after LY294002, wortmannin, or epoxomicin treatment and phosphorylation status of AKT were measured in parental and NPM/ALK+ cells by Western analysis. Also, the localization of p27Kip1 protein was analyzed by fractionation and immunoblotting.

RESULTS

p27Kip1 was found to be downregulated in NPM/ALK-transformed hematopoietic cells, but inhibition of proteasome-dependent degradation pathway by epoxomicin reversed this effect. In addition, treatment of NPM/ALK+ cells with LY294002, the PI-3K inhibitor, caused elevation of p27Kip1 protein expression and its nuclear localization.

CONCLUSIONS

Taken together, we postulate that NPM/ALK-PI-3K pathway stimulates cell proliferation by regulation of the expression and nuclear localization of p27Kip1.

YC-1 [3-(5'-Hydroxymethyl-2'-furyl)-1-benzyl Indazole] exhibits a novel antiproliferative effect and arrests the cell cycle in G0-G1 in human hepatocellular carcinoma cells

This study delineates the antiproliferative activities and in vivo efficacy of YC-1 [3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole] in human hepatocellular carcinoma cells. YC-1 inhibited the growth of HA22T and Hep3B cells in a concentration-dependent manner without significant cytotoxicity. YC-1 induced G(1) phase arrest in the cell cycle, as detected by an increase in the proportion of cells in the G(1) phase using FAC-Scan flow cytometric analysis. It was further shown that cGMP, p42/p44 mitogen-activated protein kinase, or AKT kinase-mediated signaling pathways did not contribute to the YC-1-induced effect. Of note, YC-1 induced a dramatic increase in the expression of cyclin-dependent kinase (CDK)-inhibitory protein, p21(CIP1/WAP1), and a modest increase in p27(KIP1). The association of p21(CIP1/WAP1) with CDK2 was markedly increased in cells responsive to YC-1. YC-1 did not modify the expression of cyclin D1, cyclin E, CDK2, or CDK4. In a corollary in vivo study, YC-1 induced dose-dependent inhibition of tumor growth in mice inoculated with HA22T cells. Immunohistochemical analysis revealed an inverse relationship between the staining of p21(CIP1/WAF) and the staining of Ki-67, a cell proliferation marker. Based on the results reported herein, we suggest that YC-1 induces cell cycle arrest and inhibits tumor growth both in vitro and in vivo via the up-regulation of p21(CIP1/WAP1) expression in HA22T cells. Because of this, YC-1 is a potential antitumor agent worthy of further investigation.

In Vivo Measurement of Microtubule Dynamics Using Stable Isotope Labeling with Heavy Water

Microtubules are dynamic polymers with central roles in the mitotic checkpoint, mitotic spindle assembly, and chromosome segregation. Agents that block mitotic progression and cell proliferation by interfering with microtubule dynamics (microtubule-targeted tubulin-polymerizing agents (MTPAs)) are powerful antitumor agents. Effects of MTPAs (e.g. paclitaxel) on microtubule dynamics have not yet been directly demonstrated in intact animals, however. Here we describe a method that measures microtubule dynamics as an exchange of tubulin dimers into microtubules in vivo. The incorporation of deuterium ((2)H(2)) from heavy water ((2)H(2)O) into tubulin dimers and polymers is measured by gas chromatography/mass spectrometry. In cultured human lung and breast cancer cell lines, or in tumors implanted into nude mice, tubulin dimers and polymerized microtubules exhibited nearly identical label incorporation rates, reflecting their rapid exchange. Administration of paclitaxel during 24 h of (2)H(2)O labeling in vivo reduced (2)H labeling in polymers while increasing (2)H in dimers, indicating diminished flux of dimers into polymers (i.e. inhibition of microtubule dynamic equilibrium). In vivo inhibition of microtubule dynamics was dose-dependent and correlated with inhibition of DNA replication, a stable isotopic measure of tumor cell growth. In contrast, microtubule polymers from sciatic nerve of untreated mice were not in dynamic equilibrium with tubulin dimers, and paclitaxel increased label incorporation into polymers. Our results directly demonstrate altered microtubule dynamics as an important action of MTPAs in vivo. This sensitive and quantitative in vivo assay of microtubule dynamics may prove useful for pre-clinical and clinical development of the next generation of MTPAs as anticancer drugs.

N2-substituted O6-cyclohexylmethylguanine derivatives: potent inhibitors of cyclin-dependent kinases 1 and 2

The adenosine 5'-triphosphate (ATP) competitive cyclin-dependent kinase inhibitor O(6)-cyclohexylmethylguanine (NU2058, 1) has been employed as the lead in a structure-based drug discovery program resulting in the discovery of the potent CDK1 and -2 inhibitor NU6102 (3, IC(50) = 9.5 nM and 5.4 nM vs CDK1/cyclinB and CDK2/cyclinA3, respectively). The SAR for this series have been explored further by the synthesis and evaluation of 45 N(2)-substituted analogues of NU2058. These studies have confirmed the requirement for the hydrogen bonding N(2)-NH group and the requirement for an aromatic N(2)-substituent to confer potency in the series. Additional potency is conferred by the presence of a group capable of donating a hydrogen bond at the 4'-position, for example, the 4'-hydroxy derivative (25, IC(50) = 94 nM and 69 nM vs CDK1/cyclinB and CDK2/cyclinA3, respectively), 4'-monomethylsulfonamide derivative (28, IC(50) = 9 nM and 7.0 nM vs CDK1/cyclinB and CDK2/cyclinA3, respectively), and 4'-carboxamide derivative (34, IC(50) = 67 nM and 64 nM vs CDK1/cyclinB and CDK2/cyclinA3, respectively). X-ray crystal structures have been obtained for key compounds and have been used to explain the observed trends in activity.

Genistein inversely affects tubulin-binding agent-induced apoptosis in human breast cancer cells

Genistein, a natural isoflavone phytoestrogen present in soybeans, has been extensively studied as a chemopreventive or therapeutic agent in several types of cancer. The traditional Asian diet is rich in soy products may explain in part why the incidence of breast cancer in Asian women is relatively low. To improve therapeutic benefits, we investigated the combination of genistein with chemotherapeutic agents in phenotypically dissimilar human breast cancer cells, MCF-7 and MDA-MB-231, in which estrogen receptor expression is positive and negative, respectively. In the present study, genistein significantly decreased cell apoptosis induced by tubulin-binding agents, paclitaxel and vincristine. FACScan analysis revealed that genistein also diminished the accumulation of the G2/M phase in the cell cycle caused by tubulin-binding agents. In situ staining of microtubules revealed that genistein could decrease paclitaxel-induced tubulin polymerization. However, in vivo tubulin polymerization assay revealed that simultaneous treatment of genistein did not change the tubulin/microtubule dynamic. Genistein reduced Bcl-2 phosphorylation triggered by paclitaxel and vincristine without changing Bax protein expression. p53 and p21 expression, monitored by Western blotting, was not altered by genistein. However, the expression of cyclin B1 and CDC2 kinase was markedly decreased in combination with genistein. In conclusion, genistein inversely affected tubulin-binding agent-induced apoptosis via down-regulation of cyclin B1/CDC2 kinase expression resulting in reduced Bcl-2 phosphorylation.

Characterization of the cytotoxic mechanism of Mana-Hox, an analog of manzamine alkaloids

Mana-Hox is a synthetic analog of manzamines, which are beta-carboline alkaloids isolated from marine sponges. Mana-Hox exhibited cytotoxicity against various tumor cell lines with the IC(50) range from 1 to 5 microM. Cell cycle synchronization and flow cytometric analysis showed that Mana-Hox delayed cell cycle progression at mitosis. At the concentration that delayed mitotic progression, bipolar spindle with lagged chromosomes and multipolar spindle with disorganized chromosomes were detected. The presence of such aberrant mitotic cells accompanied by the activation of spindle checkpoint that delayed cells exit from mitosis. However, after a short delay, lagged chromosomes were able to display in the abnormal metaphase plates, and subsequent cell division resulting in chromosome missegregation. Furthermore, the aberrant mitotic cells showed lower viability, indicating that Mana-Hox-induced cell death resulting from chromosome missegregation. This study is the first to explore cytotoxic mechanism of a manzamine-related compound and understand its potential as a lead compound for the development of future anticancer agents.

Induction of mitotic arrest and apoptosis by evodiamine in human leukemic T-lymphocytes

Leukemias are a heterogenous group of diseases characterized by uncontrolled proliferation of abnormal blood cells of hematopoietic system. Evodiamine, a characteristic alkaloid extracted from Evodia fruits, has been reported to exhibit inhibitory effect on cell proliferation and migration in several types of cancer cells. However, there is no report elucidating the action target and anti-cancer mechanism of this potential natural compound. In this study, we have defined the anti-proliferative and apoptotic mechanisms of evodiamine in human acute leukemia CCRF-CEM cells. According to the MTT assay, the cell viability was inhibited by evodiamine in a concentration-dependent manner with an IC50 of 0.57 +/- 0.05 microM. Flow cytometry analysis showed that the apoptotic cell death proceeded by evodiamine was accompanied with a cell cycle arrest at the G2/M phase. Using Wright-Giemsa staining, we observed that evodiamine caused the cells to arrest in mitosis. It also profoundly caused an increase in polymerized tubulin levels and Bcl-2 phosphorylation on serine 70 in these cells. These data imply that the microtubular cytoskeleton appears to be one of the cellular targets in response to evodiamine. Moreover, treatment of CCRF-CEM cells with evodiamine was associated with increased levels of pro-apoptotic protein Bax, activation of caspase-3, and proteolytic cleavage of poly (ADP-ribose) polymerase, an endogenous caspase-3 substrate. Taken together, we demonstrate that evodiamine causes the mitotic arrest and a consequent apoptosis in CCRF-CEM cells through the enhancement of polymerized tubulin levels. Furthermore, several biological events including the Bcl-2 phosphorylation, Bax up-regulation and increase of caspase-3 activity could explain evodiamine-induced cell apoptosis.

A Novel Synthetic Inhibitor of CDC25 Phosphatases

CDC25 dual-specificity phosphatases are essential regulators that dephosphorylate and activate cyclin-dependent kinase/cyclin complexes at key transitions of the cell cycle. CDC25 activity is currently considered to be an interesting target for the development of new antiproliferative agents. Here we report the identification of a new CDC25 inhibitor and the characterization of its effects at the molecular and cellular levels, and in animal models. BN82002 inhibits the phosphatase activity of recombinant human CDC25A, B, and C in vitro. It impairs the proliferation of tumoral cell lines and increases cyclin-dependent kinase 1 inhibitory tyrosine phosphorylation. In synchronized HeLa cells, BN82002 delays cell cycle progression at G1-S, in S phase and at the G2-M transition. In contrast, BN82002 arrests U2OS cell cycle mostly in the G1 phase. Selectivity of this inhibitor is demonstrated: (a) by the reversion of the mitotic-inducing effect observed in HeLa cells upon CDC25B overexpression; and (b) by the partial reversion of cell cycle arrest in U2OS expressing CDC25. We also show that BN82002 reduces growth rate of human tumor xenografts in athymic nude mice. BN82002 is a original CDC25 inhibitor that is active both in cell and animal models. This greatly reinforces the interest in CDC25 as an anticancer target.

Analysis of cell-cycle kinetics and sulfur amino acid metabolism in methionine-dependent tumor cell lines; the effect of homocysteine supplementation

Methionine dependence is a feature unique to cancer cells, exhibited as inability to grow in a methionine-depleted environment supplemented with homocysteine, the immediate metabolic precursor of methionine. This study explores the effect of methionine depletion and homocysteine supplementation on the viability, sulfur amino acid metabolism and cell-cycle kinetics of normal and cancer cells, as well as their ability to recover from the treatments. An array of cells including hepatomas (HTC, Phi-1), prostate adenocarcinomas (PC-3) and transformed (3T3) and normal (HS-27) fibroblasts, has been used aiming to evaluate the importance of tissue specificity. All cell lines proliferated well in methionine-complete media (M+H-), whilst only the normal fibroblasts HS-27 grew in methionine-depleted homocysteine-supplemented media (M-H+). None of the tested cell lines were able to grow in media without methionine or homocysteine (M-H-). HTC was the only cell line that did not recover from the M-H+ treatment whilst PC-3 did not recover from the M-H- treatment. Methionine and homocysteine depletion (M-H+ and M-H-) were found to induce arrest at different phases of the cell cycle, depending on the cell line: the methionine-dependent HTC, PC-3 and 3T3 arrested at the S and G2/M phase, whilst Phi-1 and the methionine-independent HS-27 accumulated in the G1 phase. The cell-cycle kinetics showed that the observed blockades were reversible. The information resulting from these studies is important for not only the behavior of cancer cells, but also for appreciating the potential of developing cancer therapies based on methionine-depletion strategies.

Cell cycle and no end

Our knowledge about the molecular circuits regulating the duplication of the genetic material and the subsequent division of a cell into two daughter cells has exploded over the last decade. Aberrations in the regulation of the cell cycle belong to the hallmarks of malignant transformation, leading, in turn, to the development of tumours. After introducing the basics of eukaryotic cell-cycle regulation and describing the four phases of the cell cycle (namely, G1, S, G2 and M) in more detail, alterations of key components of the cell-cycle machinery in human malignancies and their functional consequences are presented. Principally, deregulation of the cell cycle can be caused by unrestricted activity of cell-cycle promoting factors (many oncogenes fall into this class) or by inactivation of inhibitory factors (many tumour suppressor genes belong to this class). Both types of deregulation have been described in human tumours and are discussed in detail. Perspectives concerning the translation of this knowledge into daily routine practice and future applications are discussed at the end. The molecular mechanisms of actual cell division (sister chromatid segregation and cytokinesis) are mentioned only briefly.