Microtubule targeting agents: from biophysics to proteomics

The marine-derived HIF-1α inhibitor, Yardenone 2, reduces prostate cancer cell proliferation by targeting HIF-1 target genes

BACKGROUND

Prostate cancer (PCa) ranks as the second most prevalent cancer in men, with advanced stages posing significant treatment challenges. Given its solid tumor nature, PCa is highly susceptible to hypoxia, a condition associated with resistance to radiation and chemotherapy, metastasis, and unfavorable patient outcomes. Hypoxia-inducible factors (HIFs) play a pivotal role in cancer cell adaptation to hypoxic environments, contributing to treatment resistance. Consequently, inhibitors targeting HIFs hold promise for cancer therapy.

METHODS

In this study, we aimed to characterize novel HIF-1α inhibitors including Sodwanones A (1), B (2), C (3), G (4) and Yardenone 2 (5) isolated from marine sponges belonging to the Axinella genus. Our investigation evaluated the impact of these compounds on various aspects of HIF-1α regulation, including stabilization, nuclear localization, expression of HIF-1 target genes (while sparing HIF-2 target genes), cellular metabolism, as well as cell proliferation and viability in prostate cells under hypoxic conditions.

RESULTS

Our findings revealed that among the compounds tested, Yardenone 2 exhibited notable effects in hypoxia: it destabilized HIF-1α at the protein level, decreased its nuclear localization, selectively altered the expression of HIF-1 target genes, and restrained cell proliferation in aggressive PC3 prostate cancer cells as well as in an MSK-PCa3 patient-derived organoid line. Moreover, it affected the morphology of these organoid. Yardenone 2 was also compared to Docetaxel, a specific microtubule inhibitor and a drug used in the treatment of prostate cancer. The comparison between the two compounds revealed notable differences, such as a lack of specificity to hypoxic cells of Docetaxel.

CONCLUSION

These results mark the first demonstration that Yardenone 2 functions as a cytostatic-like inhibitor impacting microtubules, specifically targeting hypoxic cancer cells. This discovery suggests a promising avenue for novel therapeutic interventions in prostate cancer.

Mechanism of regulation of KIF23 on endometrial cancer cell growth and apoptosis

OBJECTIVE

The global incidence of endometrial cancer, a malignant tumor in females, is on the rise. It is one of the most common gynecological cancers. Early-stage endometrial cancers can often be treated successfully with uterine extirpation. However, those diagnosed at a later stage have a poor prognosis and encounter treatment challenges. Therefore, additional research is necessary to develop primary prevention strategies for high-risk women and improve survival rates among patients with endometrial cancer. Hence, gene therapy targeting KIF23 shows promise as an advanced strategy for the treatment of endometrial cancer.

METHODS

Immunohistochemistry, Western blotting, and PCR were used to examine the expression of KIF23 and its associated pathway factors in endometrial cancer tissue (specifically Ishikawa and SNGM cells, respectively). We investigated the functional roles of KIF23 using CCK-8, colony-forming proliferation assays, Transwell migration assays, and xenotransplantation in mice.

RESULTS

Immunohistochemistry analysis showed variations in the expression levels of KIF23 between endometrial cancer tissue and normal endometrium tissue. KIF23 downregulated BAX and caspase-3 protein expression while upregulating BCL-2 protein expression. Additionally, knocking out KIF23 inhibits endometrial cancer cell proliferation and migration while promoting cell death. Mechanistically, our study provides evidence that KIF23 promotes endometrial cancer cell proliferation by activating the ERK and AKT/PI3K pathways, while simultaneously inhibiting programmed cell death in endometrial cancer.

CONCLUSION

Our study provides evidence to support the inhibition of endometrial cancer by KIF23 knockdown. This offers valuable insights for future research on potential therapeutic strategies for this type of cancer.

Kinesin-7 CENP-E in tumorigenesis: Chromosome instability, spindle assembly checkpoint, and applications

Kinesin motors are a large family of molecular motors that walk along microtubules to fulfill many roles in intracellular transport, microtubule organization, and chromosome alignment. Kinesin-7 CENP-E (Centromere protein E) is a chromosome scaffold-associated protein that is located in the corona layer of centromeres, which participates in kinetochore-microtubule attachment, chromosome alignment, and spindle assembly checkpoint. Over the past 3 decades, CENP-E has attracted great interest as a promising new mitotic target for cancer therapy and drug development. In this review, we describe expression patterns of CENP-E in multiple tumors and highlight the functions of CENP-E in cancer cell proliferation. We summarize recent advances in structural domains, roles, and functions of CENP-E in cell division. Notably, we describe the dual functions of CENP-E in inhibiting and promoting tumorigenesis. We summarize the mechanisms by which CENP-E affects tumorigenesis through chromosome instability and spindle assembly checkpoints. Finally, we overview and summarize the CENP-E-specific inhibitors, mechanisms of drug resistances and their applications.

Discovery of a Dual Tubulin and Neuropilin-1 (NRP1) Inhibitor with Potent In Vivo Anti-Tumor Activity via Pharmacophore-based Docking Screening, Structure Optimization, and Biological Evaluation

Dual inhibition of tubulin and neuropilin-1 (NRP1) may become an effective method for cancer treatment by simultaneously killing tumor cells and inhibiting tumor angiogenesis. Herein, we identified dual tubulin/NRP1-targeting inhibitor TN-2, which exhibited good inhibitory activity against both tubulin polymerization (IC50 = 0.71 ± 0.03 μM) and NRP1 (IC50 = 0.85 ± 0.04 μM). Importantly, it significantly inhibited the viability of several human prostate tumor cell lines. Further mechanism studies indicated that TN-2 could inhibit tubulin polymerization and cause G2/M arrest, thereby inducing cell apoptosis. It could also suppress cell tube formation, migration, and invasion. Moreover, TN-2 showed obvious antitumor effects on the PC-3 cell-derived xenograft model with negligible side effects and good pharmacokinetic profiles. These data demonstrate that TN-2 could be a promising dual-target chemotherapeutic agent for the treatment of prostate cancer.

KCNQ1OT1 promotes retinoblastoma progression by targeting miR-339-3p that suppresses KIF23

BACKGROUND

Long noncoding RNAs (lncRNAs) are involved in tumor formation and development. KCNQ1OT1 regulates the malignant proliferation of retinoblastoma (RB), but the specific mechanism remains to be further investigated.

METHODS

The KCNQ1OT1, miR-339-3p and KIF23 expression levels in RB were detected by qRT-PCR and western blotting. The cell viability, proliferation, migration ability and caspase-3 activity of RB cells were evaluated by CCK-8, BrdU, transwell and caspase-3 activity analysis. Western blot was used to detect the Bax and Bcl-2 protein expression in RB cells. The binding relationship between KCNQ1OT1, miR-339-3p and KIF23 was detected by luciferase, RIP and RNA pull-down assay.

RESULTS

KCNQ1OT1 and KIF23 were up-regulated frequently in RB, and miR-339-3p was down-regulated. Functional studies showed that downregulation of KCNQ1OT1 or KIF23 inhibited the survival and migration of RB cells, and facilitated apoptosis. Interference with miR-339-3p showed the opposite effect. Mechanisms suggested that KCNQ1OT1 exited its oncogenic activity by positively regulating the expression of KIF23 and sponging miR-339-3p.

CONCLUSION

KCNQ1OT1/miR-339-3p/KIF23 may be a new biomarker for the diagnosis and treatment of RB.

Myotoxin-3 from the Pacific Rattlesnake Crotalus oreganus oreganus Venom Is a New Microtubule-Targeting Agent

Microtubule targeting agents (MTA) are anti-cancer molecules that bind tubulin and interfere with the microtubule functions, eventually leading to cell death. In the present study, we used an in vitro microtubule polymerization assay to screen several venom families for the presence of anti-microtubule activity. We isolated myotoxin-3, a peptide of the crotamine family, and three isoforms from the venom of the Northern Pacific rattlesnake Crotalus oreganus oreganus, which was able to increase tubulin polymerization. Myotoxin-3 turned out to be a cell-penetrating peptide that slightly diminished the viability of U87 glioblastoma and MCF7 breast carcinoma cells. Myotoxin 3 also induced remodeling of the U87 microtubule network and decreased MCF-7 microtubule dynamic instability. These effects are likely due to direct interaction with tubulin. Indeed, we showed that myotoxin-3 binds to tubulin heterodimer with a Kd of 5.3 µM and stoichiometry of two molecules of peptide per tubulin dimer. Our results demonstrate that exogenous peptides are good candidates for developing new MTA and highlight the richness of venoms as a source of pharmacologically active molecules.

KIF23 enhances cell proliferation in pancreatic ductal adenocarcinoma and is a potent therapeutic target

Background

In recent research, high expression of kinesin family member 23 (KIF23), one of the kinesin motor proteins involved in the regulation of cytokinesis, has been shown to be related to poor prognosis in glioma and paclitaxel-resistant gastric cancer, as a results of the enhancement of proliferation, migration, and invasion. In this study, we analyzed the role of KIF23 in the progression of pancreatic ductal adenocarcinoma.

Methods

A bioinformatic method was used to analyze the KIF23 mRNA level in pancreatic tumor tissues compared with normal pancreatic tissues and to analyze the connection between high KIF23 expression and prognosis. We examined the expression of KIF23 using immunohistochemistry and analyzed the connection between the expression of KIF23 and clinicopathological features in pancreatic ductal adenocarcinoma patients. In addition, a colony formation assay, MTT assay, and western blot assay were performed in vitro, along with a mouse xenograft model in vivo, to analyze the effect of KIF23 on proliferation. Further, the correlation between KIF23 and CDCA8 was analyzed by TCGA and immunohistochemical data.

Results

Bioinformatic results showed that KIF23 mRNA expression was higher in pancreatic tumor tissues than in normal pancreatic tissues and a poor prognosis has been linked to the high expression of KIF23. Immunohistochemistry revealed that KIF23 was highly expressed at the protein level and high expression of KIF23 correlated with adverse clinicopathological features. Our experimental results demonstrated that knockdown of KIF23 could inhibit the proliferation of pancreatic cells. Further, a positive correlation between KIF23 and CDCA8 expression existed, and KIF23 might promote pancreatic cancer proliferation by affecting CDCA8 expression.

Conclusions

Our data showed that high expression of KIF23 is associated with a poor prognosis, and KIF23 might be a potential therapeutic target for pancreatic ductal adenocarcinoma.

Paxillin family of focal adhesion adaptor proteins and regulation of cancer cell invasion

The paxillin family of proteins, including paxillin, Hic-5, and leupaxin, are focal adhesion adaptor/scaffolding proteins which localize to cell-matrix adhesions and are important in cell adhesion and migration of both normal and cancer cells. Historically, the role of these proteins in regulating the actin cytoskeleton through focal adhesion-mediated signaling has been well documented. However, studies in recent years have revealed additional functions in modulating the microtubule and intermediate filament cytoskeletons to affect diverse processes including cell polarization, vesicle trafficking and mechanosignaling. Expression of paxillin family proteins in stromal cells is also important in regulating tumor cell migration and invasion through non-cell autonomous effects on the extracellular matrix. Both paxillin and Hic-5 can also influence gene expression through a variety of mechanisms, while their own expression is frequently dysregulated in various cancers. Accordingly, these proteins may serve as valuable targets for novel diagnostic and treatment approaches in cancer.

Multi-Scale Procedural Animations of Microtubule Dynamics Based on Measured Data

Biologists often use computer graphics to visualize structures, which due to physical limitations are not possible to image with a microscope. One example for such structures are microtubules, which are present in every eukaryotic cell. They are part of the cytoskeleton maintaining the shape of the cell and playing a key role in the cell division. In this paper, we propose a scientifically-accurate multi-scale procedural model of microtubule dynamics as a novel application scenario for procedural animation, which can generate visualizations of their overall shape, molecular structure, as well as animations of the dynamic behaviour of their growth and disassembly. The model is spanning from tens of micrometers down to atomic resolution. All the aspects of the model are driven by scientific data. The advantage over a traditional, manual animation approach is that when the underlying data change, for instance due to new evidence, the model can be recreated immediately. The procedural animation concept is presented in its generic form, with several novel extensions, facilitating an easy translation to other domains with emergent multi-scale behavior.

4(1H)-quinolone derivatives overcome acquired resistance to anti-microtubule agents by targeting the colchicine site of β-tubulin

Developing new therapeutic strategies to overcome drug resistance of cancer cells is an ongoing endeavor. From among 2 million chemicals, we identified ethyl 4-oxo-2-phenyl-1,4-dihydroquinoline-6-carboxylate (AS1712) as a low-toxicity inhibitor of lung cancer cell proliferation and xenograft tumor growth. We show that AS1712 is active against broad cancer cell lines and is able to bind in the colchicine-binding pocket of β-tubulin, thereby inhibiting microtubule assembly and, consequently, inducing mitotic arrest and apoptosis. Our cell-based structure-activity relationship study identified a new lead compound, RJ-LC-15-8, which had a greater anti-proliferative potency for H1975 cells than did AS1712, while maintaining a similar mechanism of action. Notably, AS1712 and RJ-LC-15-8 overcame P-glycoprotein efflux pump and β-tubulin alterations that lead to acquired resistance against microtubule-targeting drugs of cancer cells. AS1712 and RJ-LC-15-8 may be lead compounds that overcome acquired resistance to microtubule-targeting agents of cancer cells.

Characterization of Microtubule-Associated Proteins (MAPs) and Tubulin Interactions by Isothermal Titration Calorimetry (ITC)

Microtubules are highly dynamic structures which play a central role in many cellular processes such as cell division, intracellular transport, and migration. Their dynamics is tightly regulated by stabilizing and destabilizing microtubule-associated proteins (MAPs), such as tau and stathmin. Many approaches have been developed to study interactions between tubulin and MAPs. However, isothermal titration calorimetry (ITC) is the only direct thermodynamic method that enables a full thermodynamic characterization of the interaction after a single titration experiment. We provide here the protocols to apply ITC to tubulin interaction with either stathmin or tau, which will help to avoid the common pitfalls in this very powerful and sensitive method.

Transcriptome analysis on chlorpyrifos detoxification in Uronema marinum (Ciliophora, Oligohymenophorea)

Chlorpyrifos (CPF) pollution has drawn widespread concerns in aquatic environments due to its risks to ecologic system, however, the response mechanisms of ciliates to CPF pollution were poorly studied. In our current work, the degradation of CPF by ciliates and the morphological changes of ciliates after CPF exposure were investigated. In addition, the transcriptomic profiles of the ciliate Uronema marinum, with and without exposure with CPF, were detected using digital gene expression technologies. De novo transcriptome assembly 166,829,634 reads produced from three groups (untreated, CPF treatment at 12 h and 24 h) by whole transcriptome sequencing (RNA-Seq). Gene ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathways were analyzed in all unigenes and different expression genes to identify their biological functions and processes. Furthermore, the results indicated that genes related to the stress response, cytoskeleton and cell structure proteins, and antioxidant systems might play an important role in the resistance mechanism of ciliates. The enzyme activities of SOD and GST after CPF stress were also analyzed, and the result showed the good antioxidant capacity of SOD and GST in ciliates inferred from the increase of the activities of the two enzymes. The ciliate Uronema marinum showed a resistance response to chlorpyrifos stress at the transcriptomic level in the present work, which indicates that ciliates can be considered as a potential bioremediation agent.

KIF23 is an independent prognostic biomarker in glioma, transcriptionally regulated by TCF-4

Kinesin family member 23 (KIF23), a nuclear protein and a key regulator of cellular cytokinesis, has been found to be overexpressed as an oncogene in glioma. However, the prognostic and clinicopathological features of glioma with KIF23 expression was not clear yet. Here, we analyzed KIF23 expression pattern by using whole genome mRNA expression microarray data from Chinese Glioma Genome Atlas (CGGA) database (http://www.cgga.org.cn), and found that KIF23 overexpression was significantly associated with high grade glioma as well as the higher mortality in survival analysis (log-rank test, p<0.01). The results of the three other validation datasets showed similar findings. Furthermore, KIF23 also served as an independent prognostic biomarker in glioma patients. Finally, functional assay showed that reduction of KIF23 suppressed glioma cell proliferation both in vivo and vitro. Additionally, we found that KIF23 was regulated by TCF-4 at transcriptionally level. Therefore, this evidence indicates KIF23 over-expression is associated with glioma malignancy and conferred a worse survival time in glioma, which suggests KIF23 is a new novel prognostic biomarker with potential therapeutic implications in glioma.

Different transcriptomic responses of two marine copepods, Tigriopus japonicus and Pseudodiaptomus annandalei, to a low dose of mercury chloride (HgCl2)

Mercury (Hg) pollution is a ubiquitous and serious concern in marine environments, but the response mechanisms of marine animals to Hg pollution (i.e., toxicity/tolerance) are poorly understood. To compare the global responses of two marine copepods (Tigriopus japonicus and Pseudodiaptomus annandalei), we analyzed whole transcriptomes using RNA-seq technology in response to Hg treatment (a nominal 10μg/L HgCl₂ in seawater) for 5h. Hg was strikingly accumulated in both copepods under treatment. The Hg concentration in P. annandalei was higher under metal exposure by approximately 1.4-fold compared with treated T. japonicus. Among transcriptomic data, 101 genes in T. japonicus and 18 genes in P. annandalei were differentially regulated in response to Hg exposure. The up-regulated genes in T. japonicus were concerned with stress, growth, and development, while the down-regulated ones were mainly related to immune response. In P. annandalei, most of the differentially expressed genes were up-regulated, and all were involved in stress response. Our work indicated that Hg exhibits endocrine-disrupting potential at the transcriptomic level in marine copepods. Overall, our study demonstrates the species-specific molecular responses of these two copepods to Hg pollution.

Anthelmintic drug albendazole arrests human gastric cancer cells at the mitotic phase and induces apoptosis

As microtubules have a vital function in the cell cycle, oncologists have developed microtubule inhibitors capable of preventing uncontrolled cell division, as in the case of cancer. The anthelmintic drug albendazole (ABZ) has been demonstrated to inhibit hepatocellular, ovarian and prostate cancer cells via microtubule targeting. However, its activity against human gastric cancer (GC) cells has remained to be determined. In the present study, ABZ was used to treat GC cells (MKN-45, SGC-7901 and MKN-28). A a CCK-8 cell proliferation assay was performed to assess the effects of ABZ on cell viability and cell cycle changes were assessed using flow cytometry. SGC-7901 cells were selected for further study, and flow cytometry was employed to determine the apoptotic rate, immunofluorescence analysis was employed to show changes of the microtubule structure as well as the subcellular localization and expression levels of cyclin B1, and western blot analysis was used to identify the dynamics of microtubule assembly. The expression levels of relevant proteins, including cyclin B1 and Cdc2, the two subunits of mitosis-promoting factor as well as apoptosis-asociated proteins were also assessed by western blot analysis. The results showed that ABZ exerted its anti-cancer activity in GC cell lines by disrupting microtubule formation and function to cause mitotic arrest, which is also associated with the accumulation of cyclin B1, and consequently induces apoptosis.

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.

Interactions of long-chain homologues of colchicine with tubulin

Several colchicine analogues in which the N-acetyl residue has been replaced by aliphatic, straight-chain acyl moieties, have been synthesized. These compounds show high cytotoxic activity at the nanomolar level against the tumoral cell lines HT-29, MCF-7 and A549. Some of them exhibit activities in the picomolar range against the HT-29 line and are thus two to three orders of magnitude more cytotoxic than colchicine. In this specific cell line, the activities were found to be closely related to the length of the acyl carbon chain, an increase in the latter giving rise to an increase in the cytotoxicity with a maximum in the range of 10-12 carbon atoms, followed by a decrease in activity with still longer chains. Some of the compounds inhibit microtubule assembly and induce the formation of abnormal polymers and present in most cases better apparent affinity constants than colchicine. In addition, at IC₅₀ concentrations the analogues block the cell cycle of A549 cells in the G2/M phase. Molecular docking studies suggest that, while interactions of the colchicine analogues with the colchicine binding site at β-tubulin are still present, the increase in the acyl chain length leads to the progressive development of new interactions, not present in colchicine itself, with the neighboring α-tubulin subunit. Indeed, sufficiently long acyl chains span the intradimer interface and contact with a hydrophobic groove in α-tubulin. It is worth noting that some of the compounds show cytotoxicity at concentrations three orders of magnitude lower than colchicine. Their pharmacological use in cancer therapy could possibly be performed with lower dosages and be thus endowed with less acute toxicity problems than in the case of colchicine.

Microtubule destabilising agents: far more than just antimitotic anticancer drugs

Vinca alkaloids have been approved as anticancer drugs for more than 50 years. They have been classified as cytotoxic chemotherapy drugs that act during cellular mitosis, enabling them to target fast growing cancer cells. With the evolution of cancer drug development there has been a shift towards new "targeted" therapies to avoid the side effects and general toxicities of "cytotoxic chemotherapies" such as the vinca alkaloids. Due to their original classification, many have overlooked the fact that vinca alkaloids, taxanes and related drugs do have a specific molecular target: tubulin. They continue to be some of the most effective anticancer drugs, perhaps because their actions upon the microtubule network extend far beyond the ability to halt cells in mitosis, and include the induction of apoptosis at all phases of the cell cycle. In this review, we highlight the numerous cellular consequences of disrupting microtubule dynamics, expanding the textbook knowledge of microtubule destabilising agents and providing novel opportunities for their use in cancer therapy.

A microtubule inhibitor, ABT-751, induces autophagy and delays apoptosis in Huh-7 cells

The objective was to investigate the upstream mechanisms of apoptosis which were triggered by a novel anti-microtubule drug, ABT-751, in hepatocellular carcinoma-derived Huh-7 cells. Effects of ABT-751 were evaluated by immunocytochemistry, flow cytometric, alkaline comet, soft agar, immunoblotting, CytoID, green fluorescent protein-microtubule associated protein 1 light chain 3 beta detection, plasmid transfection, nuclear/cytosol fractionation, coimmunoprecipitation, quantitative reverse transcription-polymerase chain reaction, small-hairpin RNA interference and mitochondria/cytosol fractionation assays. Results showed that ABT-751 caused dysregulation of microtubule, collapse of mitochondrial membrane potential, generation of reactive oxygen species (ROS), DNA damage, G₂/M cell cycle arrest, inhibition of anchorage-independent cell growth and apoptosis in Huh-7 cells. ABT-751 also induced early autophagy via upregulation of nuclear TP53 and downregulation of the AKT serine/threonine kinase (AKT)/mechanistic target of rapamycin (MTOR) pathway. Through modulation of the expression levels of DNA damage checkpoint proteins and G₂/M cell cycle regulators, ABT-751 induced G₂/M cell cycle arrest. Subsequently, ABT-751 triggered apoptosis with marked downregulation of B-cell CLL/lymphoma 2, upregulation of mitochondrial BCL2 antagonist/killer 1 and BCL2 like 11 protein levels, and cleavages of caspase 8 (CASP8), CASP9, CASP3 and DNA fragmentation factor subunit alpha proteins. Suppression of ROS significantly decreased ABT-751-induced autophagic and apoptotic cells. Pharmacological inhibition of autophagy significantly increased the percentages of ABT-751-induced apoptotic cells. The autophagy induced by ABT-751 plays a protective role to postpone apoptosis by exerting adaptive responses following microtubule damage, ROS and/or impaired mitochondria.

Semi-automated microplate monitoring of protein polymerization and aggregation

Static light scattering (SLS) is a commonly used technique for monitoring dynamics of high molecular weight protein complexes such as protein oligomers or aggregates. However, traditional methods are limited to testing a single condition and typically require large amounts of protein and specialized equipment. We show that a standard microplate reader can be used to characterize the molecular dynamics of different types of protein complexes, with the multiple advantages of microscale experimental volumes, semi-automated protocols and highly parallel processing.

Screening Anti-Cancer Drugs against Tubulin using Catch-and-Release Electrospray Ionization Mass Spectrometry

Tubulin, which is the building block of microtubules, plays an important role in cell division. This critical role makes tubulin an attractive target for the development of chemotherapeutic drugs to treat cancer. Currently, there is no general binding assay for tubulin-drug interactions. The present work describes the application of the catch-and-release electrospray ionization mass spectrometry (CaR-ESI-MS) assay to investigate the binding of colchicinoid drugs to αβ-tubulin dimers extracted from porcine brain. Proof-of-concept experiments using positive (ligands with known affinities) and negative (non-binders) controls were performed to establish the reliability of the assay. The assay was then used to screen a library of seven colchicinoid analogues to test their binding to tubulin and to rank their affinities.

Proteomic and Microscopic Strategies towards the Analysis of the Cytoskeletal Networks in Major Neuropsychiatric Disorders

Mental health disorders have become worldwide health priorities. It is estimated that in the next 20 years they will account for a 16 trillion United State dollars (US$) loss. Up to now, the underlying pathophysiology of psychiatric disorders remains elusive. Altered cytoskeleton proteins expression that may influence the assembly, organization and maintenance of cytoskeletal integrity has been reported in major depressive disorders, schizophrenia and to some extent bipolar disorders. The use of quantitative proteomics, dynamic microscopy and super-resolution microscopy to investigate disease-specific protein signatures holds great promise to improve our understanding of these disorders. In this review, we present the currently available quantitative proteomic approaches use in neurology, gel-based, stable isotope-labelling and label-free methodologies and evaluate their strengths and limitations. We also reported on enrichment/subfractionation methods that target the cytoskeleton associated proteins and discuss the need of alternative methods for further characterization of the neurocytoskeletal proteome. Finally, we present live cell imaging approaches and emerging dynamic microscopy technology that will provide the tools necessary to investigate protein interactions and their dynamics in the whole cells. While these areas of research are still in their infancy, they offer huge potential towards the understanding of the neuronal network stability and its modification across neuropsychiatric disorders.

A Quantitative Method for Microtubule Analysis in Fluorescence Images

Microtubule analysis is of significant value for a better understanding of normal and pathological cellular processes. Although immunofluorescence microscopic techniques have proven useful in the study of microtubules, comparative results commonly rely on a descriptive and subjective visual analysis. We developed an objective and quantitative method based on image processing and analysis of fluorescently labeled microtubular patterns in cultured cells. We used a multi-parameter approach by analyzing four quantifiable characteristics to compose our quantitative feature set. Then we interpreted specific changes in the parameters and revealed the contribution of each feature set using principal component analysis. In addition, we verified that different treatment groups could be clearly discriminated using principal components of the multi-parameter model. High predictive accuracy of four commonly used multi-classification methods confirmed our method. These results demonstrated the effectiveness and efficiency of our method in the analysis of microtubules in fluorescence images. Application of the analytical methods presented here provides information concerning the organization and modification of microtubules, and could aid in the further understanding of structural and functional aspects of microtubules under normal and pathological conditions.

Thematic Minireview Series: The State of the Cytoskeleton in 2015

The study of cytoskeletal polymers has been an active area of research for more than 70 years. However, despite decades of pioneering work by some of the brightest scientists in biochemistry, cell biology, and physiology, many central questions regarding the polymers themselves are only now starting to be answered. For example, although it has long been appreciated that the actin cytoskeleton provides contractility and couples biochemical responses with mechanical stresses in cells, only recently have we begun to understand how the actin polymer itself responds to mechanical loads. Likewise, although it has long been appreciated that the microtubule cytoskeleton can be post-translationally modified, only recently have the enzymes responsible for these modifications been characterized, so that we can now begin to understand how these modifications alter the polymerization and regulation of microtubule structures. Even the septins in eukaryotes and the cytoskeletal polymers of prokaryotes have yielded new insights due to recent advances in microscopy techniques. In this thematic series of minireviews, these topics are covered by some of the very same scientists who generated these recent insights, thereby providing us with an overview of the State of the Cytoskeleton in 2015.

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.

Induction of the intrinsic apoptotic pathway via a new antimitotic agent in an esophageal carcinoma cell line

Background

2-Ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (ESE-16) is a unique, in silico-designed compound with possible anticancer properties, which were identified in our laboratory. This compound is capable of interfering with microtubule dynamics and is believed to have potential carbonic anhydrase IX inhibiting activity.

In this study, it was investigated whether ESE-16 is capable of inducing apoptosis in vitro in the esophageal carcinoma SNO cell line via the intrinsic pathway at a concentration of 0.2 μM with an exposure time of 24 hours.

Results

Qualitative results were obtained via light microscopy, transmission electron microscopy and confocal microscopy. Results showed hallmarks of apoptosis in the ESE-16-treated cells. In addition, data revealed an increase in the number of ESE-16-treated cells blocked in metaphase. Cell death via apoptosis in the ESE-16-treated cells was confirmed by studying the internal ultrastructure of the cells via transmission electron microscopy, while confocal microscopy revealed abnormal spindle formation and condensed chromatin in ESE-16-treated cells, thus confirming metaphase block.

Quantitative results were obtained via flow cytometry and spectrophotometry. Cell death via apoptosis in ESE-16-treated cells was quantitatively confirmed by the Annexin V-FITC apoptosis detection assay. Flow cytometry and spectrophotometry revealed dissipation of mitochondrial membrane potential and an increase in superoxide levels in the ESE-16-treated cells when compared to the relevant controls. Both initiator caspase 9 and effector caspase 3 activities were increased, which demonstrates that ESE-16 causes cell death in a caspase-dependent manner.

Conclusions

This was the first in vitro study conducted to investigate the action mechanism of ESE-16 on an esophageal carcinoma cell line. The results provided valuable information on the action mechanism of this potential anticancer agent. It can be concluded that the novel in silico-designed compound exerts an anti-proliferative effect on the esophageal carcinoma SNO cell line by disrupting microtubule function resulting in metaphase block. This culminates in apoptotic cell death via the intrinsic apoptotic pathway. This research provided cellular targets warranting in vivo assessment of ESE-16’s potential as an anticancer agent.

CKD-516 displays vascular disrupting properties and enhances anti-tumor activity in combination with chemotherapy in a murine tumor model

PURPOSE

CKD-516 is a benzophenone analog in which the B ring is modified by replacement with a carbonyl group. The study assessed CKD-516 as a vascular disrupting agent or anti-cancer drug.

METHODS

To assess the effect of S516 on vascularization, we analyzed the effect on human umbilical vein endothelial cells (HUVECs). To determine the inhibition of cell proliferation of S516, we used H460 lung carcinoma cells. The alteration of microtubules was analyzed using immunoblot, RT-PCR and confocal imaging. To evaluate the anti-tumor effects of gemcitabine and/or CKD-516, H460 xenograft mice were treated with CKD-516 (2.5 mg/kg) and/or gemcitabine (40 mg/kg), and tumor growth was compared with vehicle-treated control. For histologic analysis, liver, spleen and tumor tissues from H460 xenograft mice were obtained 12 and 24 h after CKD-516 injection.

RESULTS

Cytoskeletal changes of HUVECs treated with 10 nM S516 were assessed by immunoblot and confocal imaging. S516 disrupted tubulin assembly and resulted in microtubule dysfunction, which induced cell cycle arrest (G2/M). S516 markedly enhanced the depolymerization of microtubules, perhaps due to the vascular disrupting properties of S516. Interestingly, S516 decreased the amount of total tubulin protein in HUVECs. Especially, S516 decreased mRNA expression α-tubulin (HUVECs only) and β-tubulin (HUVECs and H460 cells) at an early time point (4 h). Immunocytochemical analysis showed that S516 changed the cellular microtubule network and inhibited the formation of polymerized microtubules. Extensive central necrosis of tumors was evident by 12 h after treatment with CKD-516 (2.5 mg/kg, i.p.). In H460 xenografts, CKD-516 combined with gemcitabine significantly delayed tumor growth up to 57 % and 36 % as compared to control and gemcitabine alone, respectively.

CONCLUSION

CKD-516 is a novel agent with vascular disrupting properties and enhances anti-tumor activity in combination with chemotherapy.

NMK-TD-100, a novel microtubule modulating agent, blocks mitosis and induces apoptosis in HeLa cells by binding to tubulin

Thiadiazoles are one of the most widely utilized agents in medicinal chemistry, having a wide range of pharmacologic activity. Microtubules (MTs) have always remained a sought-after target in rapidly proliferating cancer cells. We screened for the growth inhibitory effect of synthetic 5-(3-indolyl)-2-substituted-1,3,4-thiadiazoles on cancer cells and identified NMK-TD-100, as the most potent agent. Cell viability experiments using human cervical carcinoma cell line (HeLa cells) indicated that the IC50 value was 1.42±0.11 µM for NMK-TD-100 for 48 h treatment. In further study, we examined the mode of interaction of NMK-TD-100 with tubulin and unraveled the cellular mechanism responsible for its anti-tumor activity. NMK-TD-100 induced arrest in mitotic phase of cell cycle, caused decline in mitochondrial membrane potential and induced apoptosis in HeLa cells. Immunofluorescence studies using an anti-α-tubulin antibody showed a significant depolymerization of the interphase microtubule network and spindle microtubule in HeLa cells in a concentration-dependent manner. However, the cytotoxicity of NMK-TD-100 towards human peripheral blood mononuclear cells (PBMC) was lower compared to that in cancer cells. Polymerization of tissue purified tubulin into microtubules was inhibited by NMK-TD-100 with an IC50 value of 17.5±0.35 µM. The binding of NMK-TD-100 with tubulin was studied using NMK-TD-100 fluorescence enhancement and intrinsic tryptophan fluorescence of tubulin. The stoichiometry of NMK-TD-100 binding to tubulin is 1:1 (molar ratio) with a dissociation constant of ~1 µM. Fluorescence spectroscopic and molecular modeling data showed that NMK-TD-100 binds to tubulin at a site which is very near to the colchicine binding site. The binding of NMK-TD-100 to tubulin was estimated to be ~10 times faster than that of colchicine. The results indicated that NMK-TD-100 exerted anti-proliferative activity by disrupting microtubule functions through tubulin binding and provided insights into its potential of being a chemotherapeutic agent.

Azaindole derivatives are inhibitors of microtubule dynamics, with anti-cancer and anti-angiogenic activities

BACKGROUND AND PURPOSE

Drugs targeting microtubules are commonly used for cancer treatment. However, the potency of microtubule inhibitors used clinically is limited by the emergence of resistance. We thus designed a strategy to find new cell-permeable microtubule-targeting agents.

EXPERIMENTAL APPROACH

Using a cell-based assay designed to probe for microtubule polymerization status, we screened a chemical library and identified two azaindole derivatives, CM01 and CM02, as cell-permeable microtubule-depolymerizing agents. The mechanism of the anti-tumour effects of these two compounds was further investigated both in vivo and in vitro.

KEY RESULTS

CM01 and CM02 induced G2/M cell cycle arrest and exerted potent cytostatic effects on several cancer cell lines including multidrug-resistant (MDR) cell lines. In vitro experiments revealed that the azaindole derivatives inhibited tubulin polymerization and competed with colchicines for this effect, strongly indicating that tubulin is the cellular target of these azaindole derivatives. In vivo experiments, using a chicken chorioallantoic xenograft tumour assay, established that these compounds exert a potent anti-tumour effect. Furthermore, an assay probing the growth of vessels out of endothelial cell spheroids showed that CM01 and CM02 exert anti-angiogenic activities.

CONCLUSIONS AND IMPLICATIONS

CM01 and CM02 are reversible microtubule-depolymerizing agents that exert potent cytostatic effects on human cancer cells of diverse origins, including MDR cells. They were also shown to inhibit angiogenesis and tumour growth in chorioallantoic breast cancer xenografts. Hence, these azaindole derivatives are attractive candidates for further preclinical investigations.

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.

The microtubule depolymerizing agent CYT997 effectively kills acute myeloid leukemia cells via activation of caspases and inhibition of PI3K/Akt/mTOR pathway proteins

The orally active microtubule-depolymerizing agent CYT997 is potently cytotoxic to a variety of tumors in vitro and in vivo. However, the effects of this agent on acute myeloid leukemia (AML) cells and its mechanisms are unknown. The present study demonstrated that CYT997 effectively inhibited the growth of AML cells in vitro. Treatment of AML cells with CYT997 resulted in G2/M phase cell cycle arrest, and induced apoptosis through the activation of extrinsic and intrinsic apoptotic pathways. Furthermore, CYT997 induced cell death in CD123⁺ leukemia cells and significantly reduced leukemia colony formation. CYT997 was also demonstrated to exert dual effects on the expression of PI3K/Akt and mechanistic target of rampamycin (mTOR) signaling pathway proteins. Therefore, CTY997, used alone or in combination with chemotherapy, may represent a promising approach for the treatment of AML.

End-binding proteins sensitize microtubules to the action of microtubule-targeting agents

Microtubule-targeting agents (MTAs) are widely used for treatment of cancer and other diseases, and a detailed understanding of the mechanism of their action is important for the development of improved microtubule-directed therapies. Although there is a large body of data on the interactions of different MTAs with purified tubulin and microtubules, much less is known about how the effects of MTAs are modulated by microtubule-associated proteins. Among the regulatory factors with a potential to have a strong impact on MTA activity are the microtubule plus end-tracking proteins, which control multiple aspects of microtubule dynamic instability. Here, we reconstituted microtubule dynamics in vitro to investigate the influence of end-binding proteins (EBs), the core components of the microtubule plus end-tracking protein machinery, on the effects that MTAs exert on microtubule plus-end growth. We found that EBs promote microtubule catastrophe induction in the presence of all MTAs tested. Analysis of microtubule growth times supported the view that catastrophes are microtubule age dependent. This analysis indicated that MTAs affect microtubule aging in multiple ways: destabilizing MTAs, such as colchicine and vinblastine, accelerate aging in an EB-dependent manner, whereas stabilizing MTAs, such as paclitaxel and peloruside A, induce not only catastrophes but also rescues and can reverse the aging process.

Combination of albendazole and 2-methoxyestradiol significantly improves the survival of HCT-116 tumor-bearing nude mice

Background

Albendazole (ABZ) is a microtubule-targeting anthelmintic with a remarkable activity against a variety of human cancer cells. In this study, we examined if the antitumor activity of ABZ could be enhanced by its combination with other microtubule-binding agents.

Methods

The interactions between ABZ and microtubule-binding agents, paclitaxel, vinblastine, colchicine, and 2-methoxyestradiol were characterized using median effect analysis method in HCT-116 colorectal cancer cells and DU145 prostate cancer cell line. The mechanism underlying the synergistic interaction related to tubulin polymerization and apoptosis was then investigated. Finally, the effect of the combination therapy on the survival of HCT-116 tumor-bearing nude mice was evaluated.

Results

Among the tested drugs, a synergistic anti-proliferative effect was observed with the combination of low concentrations of ABZ plus colchicine and ABZ plus 2-methoxyestradiol (2ME). Exploring the mechanism of the interaction between ABZ and 2ME revealed that the combination therapy synergistically activated the extrinsic pathway of apoptosis. Consistent with in vitro results, the combination of low concentration of ABZ with 2ME prolonged the survival of mice-bearing HCT-116 tumors. High concentration of ABZ in combination with 2ME, however, proved to be less effective than ABZ alone.

Conclusions

The combination of low doses of ABZ and 2ME has shown promising results in our pre-clinical model. Additionally, the finding that the combination of two microtubule-binding agents that share the same binding site can act synergistically may lead to the development of new therapeutic strategies in cancer treatment.

Microtubule-associated proteins and tubulin interaction by isothermal titration calorimetry

Microtubules play an important role in a number of vital cell processes such as cell division, intracellular transport, and cell architecture. The highly dynamic structure of microtubules is tightly regulated by a number of stabilizing and destabilizing microtubule-associated proteins (MAPs), such as tau and stathmin. Because of their importance, tubulin-MAPs interactions have been extensively studied using various methods that provide researchers with complementary but sometimes contradictory thermodynamic data. Isothermal titration calorimetry (ITC) is the only direct thermodynamic method that enables a full thermodynamic characterization (stoichiometry, enthalpy, entropy of binding, and association constant) of the interaction after a single titration experiment. This method has been recently applied to study tubulin-MAPs interactions in order to bring new insights into molecular mechanisms of tubulin regulation. In this chapter, we review the technical specificity of this method and then focus on the use of ITC in the investigation of tubulin-MAPs binding. We describe technical issues which could arise during planning and carrying out the ITC experiments, in particular with fragile proteins such as tubulin. Using examples of stathmin and tau, we demonstrate how ITC can be used to gain major insights into tubulin-MAP interaction.

MiR-328 expression is decreased in high-grade gliomas and is associated with worse survival in primary glioblastoma

MicroRNAs, a group of small endogenous, noncoding RNAs, are aberrantly expressed in many human cancers and can act as oncogene or anti-oncogene. Recent evidence suggests that some miRNAs have prognostic value for tumors. MiR-328 is known as a tumor suppressor; however, its relationship with the clinicopathological features of glioblastoma (GBM) and its prognostic value has yet not been investigated. We found that expression of miR-328 was significantly decreased both in anaplastic and GBM cohorts and that low miR-328 expression also conferred poor survival in primary GBM (PGBM) patients. MiR-328 might, therefore, serve as an independent prognostic marker. Furthermore, expression profiles of miR-328-associated mRNAs were established via microarrays for 60 GBM samples. The ontology of the miR-328-associated genes was then analyzed, which identified gene sets tightly related to cell mitosis. In addition, ectopic expression of miR-328 inhibited U87 cell proliferation and induced U87 cell cycle arrest. In conclusion, this is the first report showing that miR-328 is associated with patient’s survival time and that miR-328 might serve as an independent prognostic biomarker for GBM.

Molecular evidence of the toxic effects of diatom diets on gene expression patterns in copepods

BACKGROUND

Diatoms are dominant photosynthetic organisms in the world's oceans and are considered essential in the transfer of energy through marine food chains. However, these unicellular plants at times produce secondary metabolites such as polyunsaturated aldehydes and other products deriving from the oxidation of fatty acids that are collectively termed oxylipins. These cytotoxic compounds are responsible for growth inhibition and teratogenic activity, potentially sabotaging future generations of grazers by inducing poor recruitment in marine organisms such as crustacean copepods.

PRINCIPAL FINDINGS

Here we show that two days of feeding on a strong oxylipin-producing diatom (Skeletonema marinoi) is sufficient to inhibit a series of genes involved in aldehyde detoxification, apoptosis, cytoskeleton structure and stress response in the copepod Calanus helgolandicus. Of the 18 transcripts analyzed by RT-qPCR at least 50% were strongly down-regulated (aldehyde dehydrogenase 9, 8 and 6, cellular apoptosis susceptibility and inhibitor of apoptosis IAP proteins, heat shock protein 40, alpha- and beta-tubulins) compared to animals fed on a weak oxylipin-producing diet (Chaetoceros socialis) which showed no changes in gene expression profiles.

CONCLUSIONS

Our results provide molecular evidence of the toxic effects of strong oxylipin-producing diatoms on grazers, showing that primary defense systems that should be activated to protect copepods against toxic algae can be inhibited. On the other hand other classical detoxification genes (glutathione S-transferase, superoxide dismutase, catalase, cytochrome P450) were not affected possibly due to short exposure times. Given the importance of diatom blooms in nutrient-rich aquatic environments these results offer a plausible explanation for the inefficient use of a potentially valuable food resource, the spring diatom bloom, by some copepod species.

What tubulin drugs tell us about microtubule structure and dynamics

A wide range of small molecules, including alkaloids, macrolides and peptides, bind to tubulin and disturb microtubule assembly dynamics. Some agents inhibit assembly, others inhibit disassembly. The binding sites of drugs that stabilize microtubules are discussed in relation to the properties of microtubule associated proteins. The activities of assembly inhibitors are discussed in relation to different nucleotide states of tubulin family protein structures.

Mutations in the β-tubulin binding site for peloruside A confer resistance by targeting a cleft significant in side chain binding

Peloruside A is a microtubule-stabilizing macrolide that binds to beta tubulin at a site distinct from the taxol site. The site was previously identified by H-D exchange mapping and molecular docking as a region close to the outer surface of the microtubule and confined in a cavity surrounded by a continuous loop of protein folded so as to center on Y340. We have isolated a series of peloruside A-resistant lines of the human ovarian carcinoma cell line A2780(1A9) to better characterize this binding site and the consequences of altering residues in it. Four resistant lines (Pel A-D) are described with single-base mutations in class I β-tubulin that result in the following substitutions: R306H, Y340S, N337D, and A296S in various combinations. The mutations are localized to peptides previously identified by Hydrogen-Deuterium exchange mapping, and center on a cleft in which the drug side chain appears to dock. The Pel lines are 10-15-fold resistant to peloruside A and show cross resistance to laulimalide but not to any other microtubule stabilizers. They show no cross-sensitivity to any microtubule destabilizers, nor to two drugs with targets unrelated to microtubules. Peloruside A induces G2/M arrest in the Pel cell lines at concentrations 10-15 times that required in the parental line. The cells show notable changes in morphology compared to the parental line.

Chemical inhibitors: the challenge of finding the right target

A paper in this issue of Chemistry & Biology shows that the diaryl oxazole compound UA62784 that targets pancreatic cancer cells interacts with tubulin near the colchicine binding site (Tcherniuk et al., 2011). These findings differ from previous observations, highlighting the challenges of identifying the biological target for chemical inhibitors.

Downregulation of KIF23 suppresses glioma proliferation

To identify therapeutic molecular targets for glioma, we performed modified serological identification of antigens by recombinant complementary DNA (cDNA) expression cloning using sera from a mouse glioma model. Two clones, kinesin family member 23 (Kif23) and structural maintenance of chromosomes 4 (Smc4), were identified as antigens through immunological reaction with sera from mice harboring synergic GL261 mouse glioma and intratumoral inoculation with a mutant herpes simplex virus. The human Kif23 homolog KIF23 is a nuclear protein that localizes to the interzone of mitotic spindles, acting as a plus-end-directed motor enzyme that moves antiparallel microtubules in vitro. Expression analysis revealed a higher level of KIF23 expression in glioma tissues than in normal brain tissue. The introduction of small interfering RNA (siRNA) targeting KIF23 into two different glioma cell lines, U87MG and SF126, downregulated KIF23 expression, which significantly suppressed glioma cell proliferation in vitro. KIF23 siRNA-treated glioma cells exhibited larger cell bodies with two or more nuclei compared with control cells. In vivo analysis using mouse xenograft showed that KIF23 siRNA/DNA chimera-treated tumors were significantly smaller than tumors treated with control siRNA/DNA chimera. Taken together, our results indicate that downregulation of KIF23 decreases proliferation of glioma cells and that KIF23 may be a novel therapeutic target in malignant glioma.

Molecular modelling studies on Arylthioindoles as potent inhibitors of tubulin polymerization

The crucial role played by microtubules in the life of eukaryotic cell makes tubulin an important route for the anticancer therapy. The Arylthioindoles (ATIs) along with the corresponding ketone and methylene compounds are potent tubulin assembly inhibitors. We are here reporting the result of a series of docking and molecular dynamics experiments on this series of compounds. The results obtained from our in silico studies not only provided us with an insight on the nature of the binding of the ATIs to tubulin, but were also at the core of the design of a new series of potent inhibitors of tubulin polymerization.

Induction of chromosome malsegregation by nanomaterials

NMs (nanomaterials), defined as materials with at least one dimension smaller than 100 nm, are able to induce genotoxic effects. One of the hypotheses of the mode-of-action in which they exert their genotoxic potential is to mechanically interfere with subcellular structures, in particular the microtubules. In the present paper, we review studies exploring interactions between NMs and tubulin; therefore a PubMed literature search was performed. From this search 12 studies, applying both acellular and cellular assays, were retrieved and are summarized according to endpoint and particle type. These studies show that there are interactions between different types of NMs and tubulins in both acellular and cellular systems. For several types of NMs, the multi-walled carbon nanotubes, amorphous SiO(2), TiO(2) and CoCr, an induction of aneuploidy was observed in vitro. There is, therefore, a critical need to assess the capacity of NMs to interfere with the cytoskeleton, and in particular the tubulins. This might require definition of relevant dosimetry, adaptations of some testing protocols, possibly development of new methodologies and studies on a larger size-range of NMs.

Design and synthesis of pironetin analogues with simplified structure and study of their interactions with microtubules

The preparation of a series of pironetin analogues with simplified structure is described. Their cytotoxic activity and their interactions with tubulin have been investigated. It has been found that, while less active than the parent molecule, the pironetin analogues still share the mechanism of action of the latter and compete for the same binding site to α-tubulin. Variations in the configurations of their stereocenters do not translate into relevant differences between biological activities.

Investigating microtubule dynamic instability using microtubule-targeting agents

This chapter presents protocols not only used to investigate the effect of microtubule-targeting agents on microtubule dynamic instability parameters, but also their impact on loading +TIPs at microtubule plus ends. These agents can be considered either as drugs to analyze their pharmacological effects on microtubule dynamics and their subsequent functions or as tools to improve basic knowledge on the regulation of microtubule dynamics. Deciphering the complexes of proteins that regulate microtubule dynamic instability may lead to the discovery of new potential targets for therapy.