Cladosporol A triggers apoptosis sensitivity by ROS-mediated autophagic flux in human breast cancer cells

Background

Endophytes have proven to be an invaluable resource of chemically diverse secondary metabolites that act as excellent lead compounds for anticancer drug discovery. Here we report the promising cytotoxic effects of Cladosporol A (HPLC purified >98%) isolated from endophytic fungus Cladosporium cladosporioides collected from Datura innoxia. Cladosporol A was subjected to in vitro cytotoxicity assay against NCI60 panel of human cancer cells using MTT assay. We further investigated the molecular mechanism(s) of Cladosporol A induced cell death in human breast (MCF-7) cancer cells. Mechanistically early events of cell death were studied using DAPI, Annexin V-FITC staining assay. Furthermore, immunofluorescence studies were carried to see the involvement of intrinsic pathway leading to mitochondrial dysfunction, cytochrome c release, Bax/Bcl-2 regulation and flowcytometrically measured membrane potential loss of mitochondria in human breast (MCF-7) cancer cells after Cladosporol A treatment. The interplay between apoptosis and autophagy was studied by microtubule dynamics, expression of pro-apoptotic protein p21 and autophagic markers monodansylcadaverine staining and LC3b expression.

Results

Among NCI60 human cancer cell line panel Cladosporol A showed least IC₅₀ value against human breast (MCF-7) cancer cells. The early events of apoptosis were characterized by phosphatidylserine exposure. It disrupts microtubule dynamics and also induces expression of pro-apoptotic protein p21. Moreover treatment of Cladosporol A significantly induced MMP loss, release of cytochrome c, Bcl-2 down regulation, Bax upregulation as well as increased monodansylcadaverine (MDC) staining and leads to LC3-I to LC3-II conversion.

Conclusion

Our experimental data suggests that Cladosporol A depolymerize microtubules, sensitize programmed cell death via ROS mediated autophagic flux leading to mitophagic cell death.

Graphical abstract

The proposed mechanism of Cladosporol A -triggered apoptotic as well as autophagic death of human breast cancer (MCF-7) cells. The figure shows that Cladosporol A induced apoptosis through ROS mediated mitochondrial pathway and increased p21 protein expression in MCF-7 cells in vitro.

Electronic supplementary material

The online version of this article (doi:10.1186/s12860-017-0141-0) contains supplementary material, which is available to authorized users.

Novel Beta-Tubulin-Immobilized Nanoparticles Affinity Material for Screening β-Tubulin Inhibitors from a Complex Mixture

In order to efficiently screen and isolate β-tubulin inhibitors, β-tubulin was immobilized on core-shell PMMA/CS (poly(methyl methacrylate)/Chitosan) nanoparticles to produce a new type of immobilized affinity material named β-tubulin-immobilized nanoparticles (β-TIN). The selectivity and adsorption performance of β-TIN were characterized using various control drugs. The β-TIN, the paclitaxel molecularly imprinted ploymers (MIP), and the C18 adsorbing material were compared for selectivity and enrichment ratio. Microtubule-targeting antitumor compounds were screened and isolated from a typical Chinese medicine, Chloranthus multistachys, by β-TIN. Three active compounds (curcolnol, zedoarofuran, and codonolactone) in Chloranthus multistachys extract were captured successfully. Microscale thermophoresis demonstrated that these three compounds strongly bind to β-tubulin, and the dissociation constants (K_d) between the three active compounds and β-tubulin were 1820 ± 0.68 nM, 1640 ± 0.52 nM, and 284 ± 1.00 nM, respectively. Moreover, the binding affinity between codonolactone and β-tubulin was greater than that between paclitaxel and β-tubulin. The antitumor activities of the three compounds were confirmed by the microtubule inhibition model, and the results showed a similar antitumor mechanism as paclitaxel. Molecular dynamics simulations were performed to preliminarily investigate the potential binding sites and the structure-activity relationship between the three active molecules and β-tubulin. Our study is the first to report the use of this novel material which is highly efficient in capturing low-content β-tubulin inhibitors from a complex mixture. The three screened compounds exhibited potential antineoplastic activity, and these lead compounds utilize a new mechanism of action with promising development prospects. Because β-TIN is easily prepared, displays excellent adsorption and selectivity for targets, and can effectively maintain the steric conformation and activities of target proteins, it will be very useful in the screening of lead compounds for different drug target proteins.

PCL-based thermo-gelling polymers for in vivo delivery of chemotherapeutics to tumors

The synthesis of a multiblock poly(ether ester urethane)s comprising poly(ε-caprolactone), poly(ethylene glycol), and poly(propylene glycol) segments is described. We found that this polymer possessed a critical thermo-gelation concentration of 4wt%. Molecular characterization of the polymer was performed in terms of molecular weight determination, chemical composition elucidation and functional group determination using GPC, NMR, and FTIR. We carried out in vitro paclitaxel and doxorubicin release studies and demonstrated that sustained therapeutic release of about 2weeks can be obtained with this system. A nude mice model of tumor was developed and intratumoral injection of therapeutic-loaded thermo-gel demonstrated that PTX-loaded thermo-gel effectively inhibited the growth of tumors.

Synthesis and biological evaluation of simplified pironetin analogues with modifications in the side chain and the lactone ring

The stereoselective syntheses and the biological evaluation of several structurally modified pironetin analogues are discussed. Like the parent compound, some of these analogues have found to be cytotoxic. However, and unlike pironetin, they do not interact with tubulin.

Large-Scale Off-Target Identification Using Fast and Accurate Dual Regularized One-Class Collaborative Filtering and Its Application to Drug Repurposing

Target-based screening is one of the major approaches in drug discovery. Besides the intended target, unexpected drug off-target interactions often occur, and many of them have not been recognized and characterized. The off-target interactions can be responsible for either therapeutic or side effects. Thus, identifying the genome-wide off-targets of lead compounds or existing drugs will be critical for designing effective and safe drugs, and providing new opportunities for drug repurposing. Although many computational methods have been developed to predict drug-target interactions, they are either less accurate than the one that we are proposing here or computationally too intensive, thereby limiting their capability for large-scale off-target identification. In addition, the performances of most machine learning based algorithms have been mainly evaluated to predict off-target interactions in the same gene family for hundreds of chemicals. It is not clear how these algorithms perform in terms of detecting off-targets across gene families on a proteome scale. Here, we are presenting a fast and accurate off-target prediction method, REMAP, which is based on a dual regularized one-class collaborative filtering algorithm, to explore continuous chemical space, protein space, and their interactome on a large scale. When tested in a reliable, extensive, and cross-gene family benchmark, REMAP outperforms the state-of-the-art methods. Furthermore, REMAP is highly scalable. It can screen a dataset of 200 thousands chemicals against 20 thousands proteins within 2 hours. Using the reconstructed genome-wide target profile as the fingerprint of a chemical compound, we predicted that seven FDA-approved drugs can be repurposed as novel anti-cancer therapies. The anti-cancer activity of six of them is supported by experimental evidences. Thus, REMAP is a valuable addition to the existing in silico toolbox for drug target identification, drug repurposing, phenotypic screening, and side effect prediction. The software and benchmark are available at https://github.com/hansaimlim/REMAP.

High-throughput techniques have generated vast amounts of diverse omics and phenotypic data. However, these sets of data have not yet been fully explored to improve the effectiveness and efficiency of drug discovery, a process which has traditionally adopted a one-drug-one-gene paradigm. Consequently, the cost of bringing a drug to market is astounding and the failure rate is daunting. The failure of the target-based drug discovery is in large part due to the fact that a drug rarely interacts only with its intended receptor, but also generally binds to other receptors. To rationally design potent and safe therapeutics, we need to identify all the possible cellular proteins interacting with a drug in an organism. Existing experimental techniques are not sufficient to address this problem, and will benefit from computational modeling. However, it is a daunting task to reliably screen millions of chemicals against hundreds of thousands of proteins. Here, we introduce a fast and accurate method REMAP for large-scale predictions of drug-target interactions. REMAP outperforms state-of-the-art algorithms in terms of both speed and accuracy, and has been successfully applied to drug repurposing. Thus, REMAP may have broad applications in drug discovery.

PHB-Based Gels as Delivery Agents of Chemotherapeutics for the Effective Shrinkage of Tumors

Injectable thermogel to deliver chemotherapeutics in a minimally invasive manner and to achieve their long term sustained release at tumor sites to minimize side effects is attractive for chemotherapy and precision medicine, but its rational design remains a challenge. In this work, a copolymer with natural biodegradable poly[(R)-3-hydroxybutyrate] (PHB), hydrophilic poly(ethylene glycol), and temperature sensitive poly(propylene glycol) blocks linked by urethane linkages is designed to show thermogelling characteristics which are beneficial for minimally invasive injection and safe degradation. This thermogelling polymer possesses in vitro biocompatibility with very low cyto-toxicity in HEK293 cells. Furthermore, it is able to form the gel to achieve the controllable release of paclitaxel (PTX) and doxorubicin (DOX) by adjusting polymer concentrations. A rodent model of hepatocarcinoma has been performed to demonstrate the in vivo applications of this PHB-based thermogel. The drug-loaded thermogel has been intratumorally injected and both PTX-loaded and DOX-loaded thermogel have significantly slowed down tumor growth. This work represents the first time that injectable PHB thermogels have possessed good controllable release effect of chemotherapeutics against the in vivo model of tumors and will benefit various applications, including on-demand drug delivery and personalized medicine.

Leveraging a high resolution microfluidic assay reveals insights into pathogenic fungal spore germination

Germination of spores into actively growing cells is a process essential for survival and pathogenesis of many microbes. Molecular mechanisms governing germination, however, are poorly understood in part because few tools exist for evaluating and interrogating the process. Here, we introduce an assay that leverages developments in microfluidic technology and image processing to quantitatively measure germination with unprecedented resolution, assessing both individual cells and the population as a whole. Using spores from Cryptococcus neoformans, a leading cause of fatal fungal disease in humans, we developed a platform to evaluate spores as they undergo morphological changes during differentiation into vegetatively growing yeast. The assay uses pipet-accessible microdevices that can be arrayed for efficient testing of diverse microenvironmental variables, including temperature and nutrients. We discovered that temperature influences germination rate, a carbon source alone is sufficient to induce germination, and the addition of a nitrogen source sustains it. Using this information, we optimized the assay for use with fungal growth inhibitors to pinpoint stages of germination inhibition. Unexpectedly, the clinical antifungal drugs amphotericin B and fluconazole did not significantly alter the process or timing of the transition from spore to yeast, indicating that vegetative growth and germination are distinct processes in C. neoformans. Finally, we used the high temporal resolution of the assay to determine the precise defect in a slow-germination mutant. Combining advances in microfluidics with a robust fungal molecular genetic system allowed us to identify and alter key temporal, morphological, and molecular events that occur during fungal germination.

Targeting of tubulin polymerization and induction of mitotic blockage by Methyl 2-(5-fluoro-2-hydroxyphenyl)-1H-benzo[d]imidazole-5-carboxylate (MBIC) in human cervical cancer HeLa cell

Background

Microtubule Targeting Agents (MTAs) including paclitaxel, colchicine and vinca alkaloids are widely used in the treatment of various cancers. As with most chemotherapeutic agents, adverse effects and drug resistance are commonly associated with the clinical use of these agents. Methyl 2-(5-fluoro-2-hydroxyphenyl)-1H- benzo[d]imidazole-5-carboxylate (MBIC), a benzimidazole derivative displays greater toxicity against various cancer compared to normal human cell lines. The present study, focused on the cytotoxic effects of MBIC against HeLa cervical cancer cells and possible actions on the microtubule assembly.

Methods

Apoptosis detection and cell-cycle assays were performed to determine the type of cell death and the phase of cell cycle arrest in HeLa cells. Tubulin polymerization assay and live-cell imaging were performed to visualize effects on the microtubule assembly in the presence of MBIC. Mitotic kinases and mitochondrial-dependent apoptotic proteins were evaluated by Western blot analysis. In addition, the synergistic effect of MBIC with low doses of selected chemotherapeutic actions were examined against the cancer cells.

Results

Results from the present study showed that following treatment with MBIC, the HeLa cells went into mitotic arrest comprising of multi-nucleation and unsegregated chromosomes with a prolonged G₂-M phase. In addition, the HeLa cells showed signs of mitochondrial-dependant apoptotic features such as the release of cytochrome c and activation of caspases. MBIC markedly interferes with tubulin polymerization. Western blotting results indicated that MBIC affects mitotic regulatory machinery by up-regulating BubR1, Cyclin B1, CDK1 and down-regulation of Aurora B. In addition, MBIC displayed synergistic effect when given in combination with colchicine, nocodazole, paclitaxel and doxorubicin.

Conclusion

Taken together, our study demonstrated the distinctive microtubule destabilizing effects of MBIC against cervical cancer cells in vitro. Besides that, MBIC exhibited synergistic effects with low doses of selected anticancer drugs and thus, may potentially reduce the toxicity and drug resistance to these agents.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0332-0) contains supplementary material, which is available to authorized users.

PLA-based thermogel for the sustained delivery of chemotherapeutics in a mouse model of hepatocellular carcinoma

This work represents the first time that poly(PEG/PPG/PLA urethane) has been used for the delivery of drugs to tumours in vivo and the encouraging results point to the potential for further development of this thermogel platform for anti-cancer applications.

A deterministic oscillatory model of microtubule growth and shrinkage for differential actions of short chain fatty acids

Short-chain fatty acids have distinct effects on cytoskeletal proteins at the level of expression and organisation. We report a new oscillatory, deterministic model which accounts for different actions and predicts response according to fatty acid chain length.

Empirical analysis of BMD metrics in genetic toxicology part I: in vitro analyses to provide robust potency rankings and support MOA determinations

Genetic toxicity testing has traditionally been used for hazard identification, with dichotomous classification of test results serving to identify genotoxic agents. However, the utility of genotoxicity data can be augmented by employing dose-response analysis and point of departure determination. Via interpolation from a fitted dose-response model, the benchmark dose (BMD) approach estimates the dose that elicits a specified (small) effect size. BMD metrics and their confidence intervals can be used for compound potency ranking within an endpoint, as well as potency comparisons across other factors such as cell line or exposure duration. A recently developed computational method, the BMD covariate approach, permits combined analysis of multiple dose-response data sets that are differentiated by covariates such as compound, cell type or exposure regime. The approach provides increased BMD precision for effective potency rankings across compounds and other covariates that pertain to a hypothesised mode of action (MOA). To illustrate these applications, the covariate approach was applied to the analysis of published in vitro micronucleus frequency dose-response data for ionising radiations, a set of aneugens, two mutagenic azo compounds and a topoisomerase II inhibitor. The ionising radiation results show that the precision of BMD estimates can be improved by employing the covariate method. The aneugen analysis provided potency groupings based on the BMD confidence intervals, and analyses of azo compound data from cells lines with differing metabolic capacity confirmed the influence of endogenous metabolism on genotoxic potency. This work, which is the first of a two-part series, shows that BMD-derived potency rankings can be employed to support MOA evaluations as well as facilitate read across to expedite chemical evaluations and regulatory decision-making. The follow-up (Part II) employs the combined covariate approach to analyse in vivo genetic toxicity dose-response data focussing on how improvements in BMD precision can impact the reduction and refinement of animal use in toxicological research.

Synthesis of phenstatin/isocombretastatin-chalcone conjugates as potent tubulin polymerization inhibitors and mitochondrial apoptotic inducers

A series of phenstatin/isocombretastatin–chalcones were synthesized and screened for their cytotoxic activity against various human cancer cell lines. Some representative compounds exhibited significant antiproliferative activity against a panel of sixty human cancer cell lines of the NCI, with GI50 values in the range of 0.11 to 19.0 μM. Three compounds (3b, 3c and 3e) showed a broad spectrum of antiproliferative efficacy on most of the cell lines in the sub-micromolar range. In addition, all the synthesized compounds (3a–l and 4a–l) displayed moderate to excellent cytotoxicity against breast cancer cells such as MCF-7 and MDA-MB-231 with IC50 values in the range of 0.5 to 19.9 μM. Moreover, the tubulin polymerization assay and immunofluorescence analysis results suggest that some of these compounds like 3c and 3e exhibited significant inhibitory effect on the tubulin assembly with an IC50 value of 0.8 μM and 0.6 μM respectively. A competitive binding assay suggested that these compounds bind at the colchicine-binding site of tubulin. A cell cycle assay revealed that these compounds arrest at the G2/M phase and lead to apoptotic cell death. Furthermore, this was confirmed by Hoechst 33258 staining, activation of caspase 9, DNA fragmentation, Annexin V-FITC and mitochondrial membrane depolarization. Molecular docking studies indicated that compounds like 3e occupy the colchicine binding site of tubulin.

A STRIPAK component Strip regulates neuronal morphogenesis by affecting microtubule stability

During neural development, regulation of microtubule stability is essential for proper morphogenesis of neurons. Recently, the striatin-interacting phosphatase and kinase (STRIPAK) complex was revealed to be involved in diverse cellular processes. However, there is little evidence that STRIPAK components regulate microtubule dynamics, especially in vivo. Here, we show that one of the core STRIPAK components, Strip, is required for microtubule organization during neuronal morphogenesis. Knockdown of Strip causes a decrease in the level of acetylated α-tubulin in Drosophila S2 cells, suggesting that Strip influences the stability of microtubules. We also found that Strip physically and genetically interacts with tubulin folding cofactor D (TBCD), an essential regulator of α- and β-tubulin heterodimers. Furthermore, we demonstrate the genetic interaction between strip and Down syndrome cell adhesion molecule (Dscam), a cell surface molecule that is known to work with TBCD. Thus, we propose that Strip regulates neuronal morphogenesis by affecting microtubule stability.

Overexpression of SCLIP promotes growth and motility in glioblastoma cells

SCLIP, a microtubule-destabilizing phosphoprotein, is known to be involved in the development of the central nervous system (CNS). It has been well established that there are notable parallels between normal development and tumorigenesis, especially in glioma. However, no studies have examined the significance of SCLIP in gliomagenesis. To address this, we investigated the expression of SCLIP and its roles in the development of gliomas. Notably, we found that SCLIP was highly expressed in various grades of glioma samples, as compared with normal brain tissues. Overexpression of SCLIP dramatically stimulated tumor cell migration and invasion as well as proliferation and downregulation of SCLIP showed opposite effects, establishing an important oncogenic role for this gene. Furthermore, we revealed that STAT3 was required to maintain SCLIP stability, suggesting that overexpression of STAT3 may be a critical step to facilitate microtubule dynamics and subsequently promotes migration and invasion of glioma cells. Taken together, our findings demonstrate that SCLIP plays an important role in glioma pathology, and may represent a novel therapeutic strategy against human glioma.

Death-associated protein kinase 2 mediates nocodazole-induced apoptosis through interaction with tubulin

Death-associated protein kinase 2 (DAPK2) is a positive regulator of apoptosis. Although we recently reported that 14-3-3 proteins inhibit DAPK2 activity and its subsequent apoptotic effects via binding to DAPK2, the molecular mechanisms underlying the DAPK2-mediated apoptotic pathway remain unclear. Therefore, we attempted to further identify DAPK2-interacting proteins using pull-down assays and mass spectrometry. The microtubule β-tubulin was identified as a novel DAPK2-binding protein in HeLa cells. Pull-down assays revealed that DAPK2 interacted with the α/β-tubulin heterodimer, and that the C-terminal region of DAPK2, which differs from that of other DAPK family members, was sufficient for the association with β-tubulin. Although the microtubule-depolymerizing agent nocodazole induced apoptosis in HeLa cells, the level of apoptosis was significantly decreased in the DAPK2 knockdown cells. Furthermore, we found that treatment with nocodazole resulted in an increased binding of DAPK2 to β-tubulin. These findings indicate that DAPK2 mediates nocodazole-induced apoptosis via binding to tubulin.

Interferon inducible antiviral MxA is inversely associated with prostate cancer and regulates cell cycle, invasion and Docetaxel induced apoptosis

BACKGROUND

The interferon inducible Myxovirus (influenza virus) resistance A (MxA) is considered as a key mediator of the interferon-induced antiviral response. Mx proteins contain the typical GTP-binding motif and show significant homology to dynamin family of GTPases. Strong interaction of MxA with tubulin suggests that Mx proteins could be involved in mitosis. Studies have shown that MxA inhibit tumor motility/metastasis and virus induced apoptosis. However, the clear association between MxA expression and cancer remains unknown. Meta-analysis suggested that MxA expression was inversely correlated with prostate cancer (PCa). In this study, we demonstrate the expression MxA in PCa and its functional significance on the cancer phenotype.

METHODS

The expression of MxA protein in prostate cancer was examined by immuno-histochemistry. MxA was knocked down (shMxA) or over-expressed (pMxA) in DU145 or LNCaP PCa cell lines respectively. These cell lines were used to study proliferation, apoptosis, invasion, migration, and anchorage independent growth. Co-localization of MxA with tubulin was performed by immuno-cytochemistry following Docetaxel treatment.

RESULTS

The expression of MxA protein was significantly decreased in PCa as compared to the normal tissues. DU145 cells lacking MxA (DU145 + chMxA) showed significant increase in proliferation, associated with decreased expression of CDKN1A and B. Increased migration, anchorage independent growth in DU145 + shMxA cells was associated with increased MMP13 expression. Tubulin organization was also dependent on MxA expression. Tubulin polymerizing agents such as Docetaxel was less effective in promoting apoptosis in cells lacking MxA due to altered tubulin organization. Gain of MxA expression in LNCaP cells (LNCaP + pMxA) resulted in cell cycle arrest that was associated with increased expression of CDKN1A. MxA expression was also down-regulated by dihydrotestosterone in LNCaP cells.

CONCLUSIONS

MxA expression is inversely correlated with prostate cancer. Down-regulation of MxA in LNCaP cells by DHT suggests that MxA could play a significant role in disease progression. Loss of MxA expression results in increased metastasis and decreased sensitivity to Docetaxel suggesting that MxA expression could determine the outcome of chemo-therapeutic treatment. Additional studies will be required to fully establish the cross-talk between androgen receptor-IFN pathway in regulating MxA expression in the normal prostate and prostate cancer. Prostate 75:266-279, 2015. © 2014 Wiley Periodicals, Inc.

LC-based targeted metabolomics analysis of nucleotides and identification of biomarkers associated with chemotherapeutic drugs in cultured cell models

Treatment of mammalian cells with chemotherapeutic drugs can result in perturbations of nucleotide pools. Monitoring these perturbations in cultured tumor cells from human sources is useful for assessment of the effect of drug therapy and a better understanding of the mechanism of action of these drugs. In this study, three classes of chemotherapeutic drugs with different mechanisms of action were used in the development of drug-treated cell models. The LC-based targeted metabolomics analysis of nucleotides in cells of the control group and the drug-treated group was carried out. Several data processing methods were combined for the identification of potential biomarkers associated with the action of drugs, including one-way analysis of variance, principal component analysis, and receiver operating characteristic curves. Intriguingly, tumor cells of both the control group and the drug-treated groups can be distinguished from each other, and several variables were recognized as potential biomarkers, such as ATP, GMP, and UDP for antimetabolite agents, ATP, GMP, and CTP for DNA-damaging agents, as well as GMP, ATP, UDP, and GDP for the mitotic spindle agents. Further validation of the potential biomarkers was performed using the receiver operating characteristic curve. Considering their corresponding area under the curve, which was larger than 0.9, it can be concluded that GMP and ATP are the best potential biomarkers for DNA-damaging drugs, as well as GMP, ATP, and UDP for the other two classes of drugs. This limited nucleotide approach cannot completely distinguish the mechanisms of the nine drugs, but it provides preliminary evidence for the role of pharmacometabolomics in the preclinical development of drugs at least.

Synthesis, biological evaluation and molecular modeling of 1H-benzo[d]imidazole derivatives as novel anti-tubulin polymerization agents

A series of novel compounds (8a–21b) were designed and synthesized based on 2-phenyl-1H-benzo[d]imidazole. Compound 18b showed the most potent in vitro growth inhibitory activity and significant tubulin polymerization inhibitory activity.

Inhibition of JNK2 and JNK3 by JNK inhibitor IX induces prometaphase arrest-dependent apoptotic cell death in human Jurkat T cells

Exposure of human Jurkat T cells to JNK inhibitor IX (JNKi), targeting JNK2 and JNK3, caused apoptotic DNA fragmentation along with G2/M arrest, phosphorylation of Bcl-2, Mcl-1, and Bim, Δψm loss, and activation of Bak and caspase cascade. These JNKi-induced apoptotic events were abrogated by Bcl-2 overexpression, whereas G2/M arrest, cyclin B1 up-regulation, Cdk1 activation, and phosphorylation of Bcl-2 family proteins were sustained. In the concomitant presence of the G1/S blocking agent aphidicolin and JNKi, the cells underwent G1/S arrest and failed to induce all apoptotic events. The JNKi-induced phosphorylation of Bcl-2 family proteins and mitochondrial apoptotic events were suppressed by the Cdk1 inhibitor. Immunofluorescence microscopic analysis revealed that mitotic spindle defect and prometaphase arrest were the underlying factors for the G2/M arrest. These results demonstrate that JNKi-induced mitochondrial apoptosis was caused by microtubule damage-mediated prometaphase arrest, prolonged Cdk1 activation, and phosphorylation of Bcl-2 family proteins in Jurkat T cells.

Parthenolide and costunolide reduce microtentacles and tumor cell attachment by selectively targeting detyrosinated tubulin independent from NF-κB inhibition

Introduction

Detyrosinated tubulin, a post-translational modification of α-tubulin and a hallmark of stable microtubules, has gained recent attention given its association with tumor progression, invasiveness, and chemoresistance. We also recently reported that epithelial-to-mesenchymal transition (EMT) promotes tubulin detyrosination through tubulin tyrosine ligase (TTL) suppression. Furthermore, detyrosinated tubulin-enriched membrane protrusions, termed microtentacles (McTN), facilitate tumor cell reattachment to endothelial layers. Given the induction of EMT associated with inflammation and cancer progression, we tested anti-inflammatory nuclear factor-kappaB (NF-κB) inhibitors on a panel of human breast carcinoma cells to examine their effects on detyrosinated tubulin to identify more specific tubulin-directed anti-cancer treatments.

Methods

Using metastatic human breast carcinoma cells MDA-MB-157, MDA-MB-436, and Bt-549, we measured the impact of NF-κB inhibitors parthenolide, costunolide, and resveratrol on detyrosinated tubulin using protein expression analysis and immunofluorescence. A luciferase reporter assay and a viability screen were performed to determine if the effects were associated with their NF-κB inhibitory properties or were a result of apoptosis. Real-time monitoring of cell-substratum attachment was measured utilizing electrical impedance across microelectronic sensor arrays. We compared the selectivity of the NF-κB inhibitors to specifically target detyrosinated tubulin with traditional tubulin-targeted therapeutics, paclitaxel and colchicine, throughout the study.

Results

Sesquiterpene lactones, parthenolide and costunolide, selectively decrease detyrosinated tubulin independent of their inhibition of NF-κB. Live-cell scoring of suspended cells treated with parthenolide and costunolide show reduction in the frequency of microtentacles and inhibition of reattachment. Structural analysis shows that parthenolide and costunolide can decrease detyrosinated microtubules without significantly disrupting the overall microtubule network or cell viability. Paclitaxel and colchicine display indiscriminate disruption of the microtubule network.

Conclusions

Our data demonstrate that selective targeting of detyrosinated tubulin with parthenolide and costunolide can reduce McTN frequency and inhibit tumor cell reattachment. These actions are independent of their effects on NF-κB inhibition presenting a novel anti-cancer property and therapeutic opportunity to selectively target a stable subset of microtubules in circulating tumor cells to reduce metastatic potential with less toxicity in breast cancer patients.

Prometaphase arrest-dependent phosphorylation of Bcl-2 and Bim reduces the association of Bcl-2 with Bak or Bim, provoking Bak activation and mitochondrial apoptosis in nocodazole-treated Jurkat T cells

Treatment of Jurkat T cells with the microtubule-depolymerizing agent nocodazole (NOC) caused prometaphase arrest and apoptosis. NOC-induced mitochondrial apoptotic events including Bak activation, Δψm loss, cytochrome c release, and caspase cascade activation were blocked by Bcl-2 overexpression. However, mitotic arrest, Cdc25C activation, upregulation of cyclin B1 levels, Cdk1 activation, Bcl-2 phosphorylation at Thr-56 and Ser-70, and Bim phosphorylation were retained. The treatment of Jurkat T cells concomitantly with NOC and the G1/S-blocking agent hydroxyurea resulted in G1/S arrest and complete abrogation of all apoptotic events. The association of Bcl-2 with Bim or Bak declined after the prometaphase arrest-dependent phosphorylation of Bcl-2 and Bim, whereas the association of Bcl-2 with Bax remained relatively constant. Although Bax was redistributed from the cytosol to the mitochondria, resulting in an increase in the mitochondrial level of Bax following NOC treatment, the subcellular localization of Bcl-2, Bim, Bak and apoptosis-inducing factor was confined to the mitochondrial fraction irrespective of NOC treatment. Experiments using selective caspase inhibitors showed that mitochondria-dependent activation of caspase-9 and -3 was crucial for NOC-induced apoptosis. NOC-induced phosphorylation of Bcl-2 and Bim, Δψm loss, and mitochondria-dependent apoptotic events were significantly suppressed by a Cdk1 inhibitor roscovitine, but not by the JNK inhibitor SP600125 or the p38 MAPK inhibitor SB203580. These results show that the prometaphase arrest-dependent phosphorylation of Bcl-2 and Bim, which was mediated by Cdk1, could reduce the association of Bcl-2 with Bak or Bim to allow Bak activation and mitochondrial apoptotic events in Jurkat T cells exposed to NOC.

Synthesis and biological evaluation of truncated α-tubulin-binding pironetin analogues lacking alkyl pendants in the side chain or the dihydropyrone ring

The preparation of several new truncated analogues of the natural dihydropyrone pironetin is described. They differ from the natural product mainly in the suppression of some of the alkyl pendants in either the side chain or the dihydropyrone ring. Their cytotoxic activity and their interactions with tubulin have been investigated. It has been found that all analogues are cytotoxic towards two either sensitive or resistant tumoral cell lines with similar IC50 values in each case, thus strongly suggesting that, like natural pironetin, they also display a covalent mechanism of action. Their cytotoxicity is, however, lower than that of the parent compound. This indicates that all alkyl pendants are necessary for the full biological activity, with the ethyl group at C-4 seemingly being particularly relevant. Most likely, the alkyl groups cause a restriction in the conformational mobility of the molecule and reduce the number of available conformations. This makes it more probable that the molecule preferentially adopts a shape which fits better into the binding point in α-tubulin.

Docking, synthesis and antiproliferative activity of N-acylhydrazone derivatives designed as combretastatin A4 analogues

Cancer is the second most common cause of death in the USA. Among the known classes of anticancer agents, the microtubule-targeted antimitotic drugs are considered to be one of the most important. They are usually classified into microtubule-destabilizing (e.g., Vinca alkaloids) and microtubule-stabilizing (e.g., paclitaxel) agents. Combretastatin A4 (CA-4), which is a natural stilbene isolated from Combretum caffrum, is a microtubule-destabilizing agent that binds to the colchicine domain on β-tubulin and exhibits a lower toxicity profile than paclitaxel or the Vinca alkaloids. In this paper, we describe the docking study, synthesis, antiproliferative activity and selectivity index of the N-acylhydrazone derivatives (5a-r) designed as CA-4 analogues. The essential structural requirements for molecular recognition by the colchicine binding site of β-tubulin were recognized, and several compounds with moderate to high antiproliferative potency (IC50 values ≤18 µM and ≥4 nM) were identified. Among these active compounds, LASSBio-1586 (5b) emerged as a simple antitumor drug candidate, which is capable of inhibiting microtubule polymerization and possesses a broad in vitro and in vivo antiproliferative profile, as well as a better selectivity index than the prototype CA-4, indicating improved selective cytotoxicity toward cancer cells.

Synthesis, biological evaluation, and molecular docking studies of novel chalcone oxime derivatives as potential tubulin polymerization inhibitors

Compounds of novel chalcone oxime derivatives containing different substituent groups were designed, synthesized and evaluated for the inhibitory activity against tubulin polymerization and cancer cell inhibitory activity.

Docking and molecular dynamics studies of the binding between Peloruside A and tubulin

The molecular docking, MD simulation and binding free energy calculation were performed to explore the probable binding modes between PLA and tubulin. Through docking study, three possible binding sites for PLA were speculated as follows: the taxane site, the alternative site and a new site in α-tubulin. Then, 12.0 ns MD simulations show that these binding modes predicted by docking have been changed more or less, whereas the MD simulations offer more reliable binding details. The MM-PBSA binding free-energy calculations reasonably identify that the taxane site is the most favorable binding site of PLA and the alternative site is the secondary one, which can be used to explain some experimental facts. These studies theoretically resolve the priority of binding sites for PLA and offer the reliable binding modes between PLA and tubulin, and thus help to understanding the action mechanism for this kind of inhibitor.

Phosphorylation of eIF4GII and 4E-BP1 in response to nocodazole treatment: a reappraisal of translation initiation during mitosis

Translation mechanisms at different stages of the cell cycle have been studied for many years, resulting in the dogma that translation rates are slowed during mitosis, with cap-independent translation mechanisms favored to give expression of key regulatory proteins. However, such cell culture studies involve synchronization using harsh methods, which may in themselves stress cells and affect protein synthesis rates. One such commonly used chemical is the microtubule de-polymerization agent, nocodazole, which arrests cells in mitosis and has been used to demonstrate that translation rates are strongly reduced (down to 30% of that of asynchronous cells). Using synchronized HeLa cells released from a double thymidine block (G 1/S boundary) or the Cdk1 inhibitor, RO3306 (G 2/M boundary), we have systematically re-addressed this dogma. Using FACS analysis and pulse labeling of proteins with labeled methionine, we now show that translation rates do not slow as cells enter mitosis. This study is complemented by studies employing confocal microscopy, which show enrichment of translation initiation factors at the microtubule organizing centers, mitotic spindle, and midbody structure during the final steps of cytokinesis, suggesting that translation is maintained during mitosis. Furthermore, we show that inhibition of translation in response to extended times of exposure to nocodazole reflects increased eIF2α phosphorylation, disaggregation of polysomes, and hyperphosphorylation of selected initiation factors, including novel Cdk1-dependent N-terminal phosphorylation of eIF4GII. Our work suggests that effects on translation in nocodazole-arrested cells might be related to those of the treatment used to synchronize cells rather than cell cycle status.

Pyrrolizidine alkaloids and fatty acids from the endemic plant species Rindera umbellata and the effect of lindelofine-N-oxide on tubulin polymerization

The examination of the aerial parts, roots, and seeds of the endemic plant Rindera umbellata is reported in this paper for the first time. Phytochemical investigation of R. umbellata led to the isolation and characterization of ten pyrrolizidine alkaloids and eleven fatty acids in the form of triglycerides. Pyrrolizidine alkaloids 1-9 were found in the aerial parts, 7 and 8 in the roots, and 6-10, together with eleven fatty acids, in the seeds of this plant species. The structures of compounds 1-10 were established based on spectroscopic studies (¹H- and ¹³C-NMR, 2D NMR, IR and CI-MS). After trans-esterification, methyl esters of the fatty acids were analyzed using GC-MS. The effect of lindelofine-N-oxide (7) on tubulin polymerization was determined.

Alkylphospholipids deregulate cholesterol metabolism and induce cell-cycle arrest and autophagy in U-87 MG glioblastoma cells

Glioblastoma is the most common malignant primary brain tumour in adults and one of the most lethal of all cancers. Growing evidence suggests that human tumours undergo abnormal lipid metabolism, characterised by an alteration in the mechanisms that regulate cholesterol homeostasis. We have investigated the effect that different antitumoural alkylphospholipids (APLs) exert upon cholesterol metabolism in the U-87 MG glioblastoma cell line. APLs altered cholesterol homeostasis by interfering with its transport from the plasma membrane to the endoplasmic reticulum (ER), thus hindering its esterification. At the same time they stimulated the synthesis of cholesterol from radiolabelled acetate and its internalisation from low-density lipoproteins (LDLs), inducing both 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) and LDL receptor (LDLR) genes. Fluorescent microscopy revealed that these effects promoted the accumulation of intracellular cholesterol. Filipin staining demonstrated that this accumulation was not confined to the late endosome/lysosome (LE/LY) compartment since it did not colocalise with LAMP2 lysosomal marker. Furthermore, APLs inhibited cell growth, producing arrest at the G2/M phase. We also used transmission electron microscopy (TEM) to investigate ultrastructural alterations induced by APLs and found an abundant presence of autophagic vesicles and autolysosomes in treated cells, indicating the induction of autophagy. Thus our findings clearly demonstrate that antitumoural APLs interfere with the proliferation of the glioblastoma cell line via a complex mechanism involving cholesterol metabolism, cell-cycle arrest or autophagy. Knowledge of the interrelationship between these processes is fundamental to our understanding of tumoural response and may facilitate the development of novel therapeutics to improve treatment of glioblastoma and other types of cancer.

Tubulin-interactive stilbene derivatives as anticancer agents

Microtubules are dynamic polymers that occur in eukaryotic cells and play important roles in cell division, motility, transport and signaling. They form during the process of polymerization of α- and β-tubulin dimers. Tubulin is a significant and heavily researched molecular target for anticancer drugs. Combretastatins are natural cis-stilbenes that exhibit cytotoxic properties in cultured cancer cells in vitro. Combretastatin A-4 (3′-hydroxy-3,4,4′, 5-tetramethoxy-cis-stilbene; CA-4) is a potent cytotoxic cis-stilbene that binds to β-tubulin at the colchicine-binding site and inhibits tubulin polymerization. The prodrug CA-4 phosphate is currently in clinical trials as a chemotherapeutic agent for cancer treatment. Numerous series of stilbene analogs have been studied in search of potent cytotoxic agents with the requisite tubulin-interactive properties. Microtubule-interfering agents include numerous CA-4 and transresveratrol analogs and other synthetic stilbene derivatives. Importantly, these agents are active in both tumor cells and immature endothelial cells of tumor blood vessels, where they inhibit the process of angiogenesis. Recently, computer-aided virtual screening was used to select potent tubulin-interactive compounds. This review covers the role of stilbene derivatives as a class of antitumor agents that act by targeting microtubule assembly dynamics. Additionally, we present the results of molecular modeling of their binding to specific sites on the α- and β-tubulin heterodimer. This has enabled the elucidation of the mechanism of stilbene cytotoxicity and is useful in the design of novel agents with improved anti-mitotic activity. Tubulin-interactive agents are believed to have the potential to play a significant role in the fight against cancer.

Metagenomic profiles of free-living archaea, bacteria and small eukaryotes in coastal areas of Sichang island, Thailand

Background

Tha Wang and Tham Phang coasts, though situated at similar oceanographic positions on Sichang island, Chonburi province, Thailand, are different in bay geography and amount of municipal disturbances. These affect the marine ecosystems. The study used metagenomics combined with 16S and 18S rDNA pyrosequencing to identify types and distributions of archaea, bacteria, fungi and small eukaryotes of sizes ranges 0.45 and ~30 μm.

Results

Following the open bay geography and minimal municipal sewages, Tham Phang coast showed the cleaner water properties, described by color, salinity, pH, conductivity and percent dissolved oxygen. The 16S and 18S rDNA metagenomic profiles for Tha Wang and Tham Phang coasts revealed many differences, highlighting by low Lennon and Yue & Clayton theta similarity indices (66.03-73.03% for 16S rDNA profiles, 2.85-25.38% for 18S rDNA profiles). For 16S rDNA, the percent compositions of species belonging to Proteobacteria, Bacteroidetes, Cyanobacteria, Firmicutes, Verrucomicrobia, Gammatimonadetes, Tenericutes, Acidobacteria, Spirochaetes, Chlamydiae, Euryarchaeota, Nitrospirae, Planctomycetes, Thermotogae and Aquificae were higher or distinctly present in Tha Wang. In Tham Phang, except Actinobacteria, the fewer number of prokaryotic species existed. For 18S rDNA, fungi represented 74.745% of the species in Tha Wang, whereas only 6.728% in Tham Phang. Basidiomycota (71.157%) and Ascomycota (3.060%) were the major phyla in Tha Wang. Indeed, Tha Wang-to-Tham Phang percent composition ratios for fungi Basidiomycota and Chytridiomycota were 1264.701 and 25.422, respectively. In Tham Phang, Brachiopoda (lamp shells) and Mollusca (snails) accounted for 80.380% of the 18S rDNA species detected, and their proportions were approximately tenfold greater than those in Tha Wang. Overall, coastal Tham Phang comprised abundant animal species.

Conclusions

Tha Wang contained numerous archaea, bacteria and fungi, many of which could synthesize useful biotechnology gas and enzymes that could also function in high-saline and high-temperature conditions. Tham Phang contained less abundant archaea, bacteria and fungi, and the majority of the extracted metagenomes belonged to animal kingdom. Many microorganisms in Tham Phang were essential for nutrient-recycling and pharmaceuticals, for instances, Streptomyces, Pennicilium and Saccharomyces. Together, the study provided metagenomic profiles of free-living prokaryotes and eukaryotes in coastal areas of Sichang island.

Induction of tumor cell death through targeting tubulin and evoking dysregulation of cell cycle regulatory proteins by multifunctional cinnamaldehydes

Multifunctional trans-cinnamaldehyde (CA) and its analogs display anti-cancer properties, with 2-benzoyloxycinnamaldehyde (BCA) and 5-fluoro-2-hydroxycinnamaldehyde (FHCA) being identified as the ortho-substituted analogs that possess potent anti-tumor activities. In this study, BCA, FHCA and a novel analog 5-fluoro-2-benzoyloxycinnamaldehyde (FBCA), were demonstrated to decrease growth and colony formation of human colon-derived HCT 116 and mammary-derived MCF-7 carcinoma cells under non-adhesive conditions. The 2-benzoyloxy and 5-fluoro substituents rendered FBCA more potent than BCA and equipotent to FHCA. The cellular events by which these cinnamaldehydes caused G(2)/M phase arrest and halted proliferation of HCT 116 cells were thereby investigated. Lack of significant accumulation of mitosis marker phospho-histone H3 in cinnamaldehyde-treated cells indicated that the analogs arrested cells in G(2) phase. G(2) arrest was brought about partly by cinnamaldehyde-mediated depletion of cell cycle proteins involved in regulating G(2) to M transition and spindle assembly, namely cdk1, cdc25C, mad2, cdc20 and survivin. Cyclin B1 levels were found to be increased, which in the absence of active cdk1, would fail to drive cells into M phase. Concentrations of cinnamaldehydes that brought about dysregulation of levels of cell cycle proteins also caused tubulin aggregation, as evident from immunodetection of dose-dependent tubulin accumulation in the insoluble cell lysate fractions. In a cell-free system, reduced biotin-conjugated iodoacetamide (BIAM) labeling of tubulin protein pretreated with cinnamaldehydes was indicative of drug interaction with the sulfhydryl groups in tubulin. In conclusion, cinnamaldehydes treatment at proapoptotic concentrations caused tubulin aggregation and dysegulation of cell cycle regulatory proteins cdk1 and cdc25C that contributed at least in part to arresting cells at G(2) phase, resulting in apoptotic cell death characterized by emergence of cleaved forms of caspase 3 and poly (ADP-ribose) polymerase (PARP). Results presented in this study have thus provided further insights into the intricate network of cellular events by which cinnamaldehydes induce tumor cell death.

Discovery of novel tubulin inhibitors via structure-based hierarchical virtual screening

To discover novel tubulin inhibitors, we performed structure-based virtual screening against the colchicine binding pocket. In combination with a hierarchical docking and scoring procedure, the structural information of an additional subpocket in colchicine site was applied to filter out the undesired docking hits. This strategy automatically resulted in 63 candidates meeting the structural and energetic criteria from a screening library containing approximately 100,000 diverse druglike compounds. Among them, nine molecules were chosen for experimental validation, which all share the similar binding pose and contain an enriched scaffold bearing thiophene core. Encouragingly, five compounds are active in tubulin polymerization assay. The most potent inhibitor, 2-(2-fluorobenzamido)-3-carboxamide-4,5-dimethylthiophene, is structurally distinct to any known colchicine site binders and has higher ligand efficiency than colchicine. On the basis of its predicted binding pose, we systematically probed its binding characteristics by testing series of structural modifications. The obtained structure-activity relationship results are consistent with our binding model, and the inhibition activities of two analogues are improved by 2-fold. We expect that the novel structure discovered in the present study may serve as a starting point for developing tubulin inhibitors with improved efficacy and fewer side effects. We also expect that our hierarchical strategy may be generally applicable in structure-based virtual screening campaigns.

An antitubulin agent BCFMT inhibits proliferation of cancer cells and induces cell death by inhibiting microtubule dynamics

Using cell based screening assay, we identified a novel anti-tubulin agent (Z)-5-((5-(4-bromo-3-chlorophenyl)furan-2-yl)methylene)-2-thioxothiazolidin-4-one (BCFMT) that inhibited proliferation of human cervical carcinoma (HeLa) (IC₅₀, 7.2±1.8 µM), human breast adenocarcinoma (MCF-7) (IC₅₀, 10.0±0.5 µM), highly metastatic breast adenocarcinoma (MDA-MB-231) (IC₅₀, 6.0±1 µM), cisplatin-resistant human ovarian carcinoma (A2780-cis) (IC₅₀, 5.8±0.3 µM) and multi-drug resistant mouse mammary tumor (EMT6/AR1) (IC₅₀, 6.5±1µM) cells. Using several complimentary strategies, BCFMT was found to inhibit cancer cell proliferation at G2/M phase of the cell cycle apparently by targeting microtubules. In addition, BCFMT strongly suppressed the dynamics of individual microtubules in live MCF-7 cells. At its half maximal proliferation inhibitory concentration (10 µM), BCFMT reduced the rates of growing and shortening phases of microtubules in MCF-7 cells by 37 and 40%, respectively. Further, it increased the time microtubules spent in the pause (neither growing nor shortening detectably) state by 135% and reduced the dynamicity (dimer exchange per unit time) of microtubules by 70%. In vitro, BCFMT bound to tubulin with a dissociation constant of 8.3±1.8 µM, inhibited tubulin assembly and suppressed GTPase activity of microtubules. BCFMT competitively inhibited the binding of BODIPY FL-vinblastine to tubulin with an inhibitory concentration (K_i) of 5.2±1.5 µM suggesting that it binds to tubulin at the vinblastine site. In cultured cells, BCFMT-treatment depolymerized interphase microtubules, perturbed the spindle organization and accumulated checkpoint proteins (BubR1 and Mad2) at the kinetochores. BCFMT-treated MCF-7 cells showed enhanced nuclear accumulation of p53 and its downstream p21, which consequently activated apoptosis in these cells. The results suggested that BCFMT inhibits proliferation of several types of cancer cells including drug resistance cells by suppressing microtubule dynamics and indicated that the compound may have chemotherapeutic potential.

Discrimination of ligands with different flexibilities resulting from the plasticity of the binding site in tubulin

Tubulin, an α,β heterodimer, has four distinct ligand binding sites (for paclitaxel, peloruside/laulimalide, vinca, and colchicine). The site where colchicine binds is a promising drug target for arresting cell division and has been observed to accommodate compounds that are structurally diverse but possess comparable affinity. This investigation, using two such structurally different ligands as probes (one being colchicine itself and another, TN16), aims to provide insight into the origin of this diverse acceptability to provide a better perspective for the design of novel therapeutic molecules. Thermodynamic measurements reveal interesting interplay between entropy and enthalpy. Although both these parameters are favourable for TN16 binding (ΔH < 0, ΔS > 0), but the magnitude of entropy has the determining role for colchicine binding as its enthalpic component is destabilizing (ΔH > 0, ΔS > 0). Molecular dynamics simulation provides atomistic insight into the mechanism, pointing to the inherent flexibility of the binding pocket that can drastically change its shape depending on the ligand that it accepts. Simulation shows that in the complexed states both the ligands have freedom to move within the binding pocket; colchicine can switch its interactions like a "flying trapeze", whereas TN16 rocks like a "swing cradle", both benefiting entropically, although in two different ways. Additionally, the experimental results with respect to the role of solvation entropy correlate well with the computed difference in the hydration: water molecules associated with the ligands are released upon complexation. The complementary role of van der Waals packing versus flexibility controls the entropy-enthalpy modulations. This analysis provides lessons for the design of new ligands that should balance between the "better fit" and "flexibility"', instead of focusing only on the receptor-ligand interactions.

ROS-independent JNK activation and multisite phosphorylation of Bcl-2 link diallyl tetrasulfide-induced mitotic arrest to apoptosis

Garlic-derived organosulfur compounds including diallyl polysulfides are well known for various health-beneficial properties and recent reports even point to a potential role of diallyl polysulfides as chemopreventive and therapeutic agents in cancer treatment due to their selective antiproliferative effects. In this respect, diallyl tri- and tetrasulfide are reported as strong inducers of an early mitotic arrest and subsequent apoptosis, but the underlying molecular mechanisms and the link between these two events are not yet fully elucidated. Our data revealed that diallyl tetrasulfide acts independently of reactive oxygen species and tubulin represents one of its major cellular targets. Tubulin depolymerization prevents the formation of normal spindle microtubules, thereby leading to G2/M arrest. Here, we provide evidence that c-jun N-terminal kinase, which is activated early in response to diallyl tetrasulfide treatment, mediates multisite phosphorylation and subsequent proteolysis of the anti-apoptotic protein B-cell lymphoma 2. As the latter event occurs concomitantly with the onset of apoptosis and the chemical c-jun N-terminal kinase inhibitor SP600125 not only prevented B-cell lymphoma 2 phosphorylation and proteolysis but also apoptosis following diallyl tetrasulfide treatment, we suggest that these c-jun N-terminal kinase-mediated modulations of B-cell lymphoma 2 represent the missing link connecting early microtubule inactivation to the induction of apoptosis.

Kinetic stabilization of microtubule dynamics by indanocine perturbs EB1 localization, induces defects in cell polarity and inhibits migration of MDA-MB-231 cells

Cell motility is an essential aspect of metastatic spread of cancer. Microtubule-targeted agents exhibit anti-metastatic properties, the underlying mechanism of which remains understudied. In this study, we have investigated the role of microtubule dynamics in migration of cancer cells using indanocine, a synthetic small molecule inhibitor of tubulin. We found that indanocine, at concentrations that did not visibly affect microtubule organization, suppressed dynamic instability of microtubules and reduced the rate of migration of highly metastatic MDA-MB-231 cells. Indanocine-treated cells were defective in lamellipodium formation and could not develop polarized morphology. The kinetic stabilization of microtubules was associated with a marked increase in their acetylation level and a perturbation in the localization of EB1, a microtubule plus end binding protein. Using standard scratch wound healing assay and immunofluorescence analysis; we found that microtubule acetylation occurred in the direction of migration in vehicle-treated cells, whereas indanocine treatment led to a global acetylation of microtubules. The results together suggested that selective stabilization of microtubules was perturbed in the presence of indanocine that possibly resulted in lack of cell polarization and a concurrent reduction in migration of cells. Moreover, microtubule stabilization by indanocine affected adhesion turnover and impaired the polarized pattern of adhesion sites in cells. Together the results indicated that the regulation of microtubule dynamics is required to coordinate cell polarization as well as adhesion asymmetry and support the hypothesis that the perturbation of microtubule dynamics by tubulin-targeted agents can be exploited to restrict the migration of tumor cells.