Benomyl and colchicine synergistically inhibit cell proliferation and mitosis: evidence of distinct binding sites for these agents in tubulin

N-substitution Reactions of 2-Aminobenzimidazoles to Access Pharmacophores

Benzimidazole (BI) and its derivatives are interesting molecules in medicinal chemistry because several of these compounds have a diversity of biological activities and some of them are even used in clinical applications. In view of the importance of these compounds, synthetic chemists are still interested in finding new procedures for the synthesis of these classes of compounds. Astemizole (antihistaminic), Omeprazole (antiulcerative), and Rabendazole (fungicide) are important examples of compounds used in medicinal chemistry containing BI nuclei. It is interesting to observe that several of these compounds contain 2-aminobenzimidazole (2ABI) as the base nucleus. The structures of 2ABI derivatives are interesting because they have a planar delocalized structure with a cyclic guanidine group, which have three nitrogen atoms with free lone pairs and labile hydrogen atoms. The 10-π electron system of the aromatic BI ring conjugated with the nitrogen lone pair of the hexocyclic amino group, making these heterocycles to have an amphoteric character. Synthetic chemists have used 2ABI as a building block to produce BI derivatives as medicinally important molecules. In view of the importance of the BIs, and because no review was found in the literature about this topic, we reviewed and summarized the procedures related to the recent methodologies used in the N-substitution reactions of 2ABIs by using aliphatic and aromatic halogenides, dihalogenides, acid chlorides, alkylsulfonic chlorides, carboxylic acids, esters, ethyl chloroformates, anhydrides, SMe-isothioureas, alcohols, alkyl cyanates, thiocyanates, carbon disulfide and aldehydes or ketones to form Schiff bases. The use of diazotized 2ABI as intermediate to obtain 2-diazoBIs was included to produce Nsubstituted 2ABIs of pharmacological interest. Some commentaries about their biological activity were included.

Cytotoxic mechanism of tioconazole involves cell cycle arrest at mitosis through inhibition of microtubule assembly

Tioconazole is one of the drugs used to treat topical mycotic infections. It exhibited severe toxicity during systemic administration; however, the molecular mechanism behind the cytotoxic effect was not well established. We employed HeLa cells as a model to investigate the molecular mechanism of its toxicity and discovered that tioconazole inhibited HeLa cell growth through mitotic block (37%). At the half-maximal inhibitory concentration (≈ 15 μM) tioconazole apparently depolymerized microtubules and caused defects in chromosomal congression at the metaphase plate. Tioconazole induced apoptosis and significantly hindered the migration of HeLa cells. Tioconazole bound to goat brain tubulin (K _d, 28.3 ± 0.5 μM) and inhibited the assembly of microtubules in the in vitro assays. We report for the first time that tioconazole binds near to the colchicine site, based on the evidence from in vitro tubulin competition experiment and computational analysis. The conformation of tubulin dimer was found to be "curved" upon binding with tioconazole in the MD simulation. Tioconazole in combination with vinblastine synergistically inhibited the growth of HeLa cells and augmented the percentage of mitotic block by synergistically inhibiting the assembly of microtubules. Our study indicates that the systemic adverse effects of tioconazole are partly due to its effects on microtubules and cell cycle arrest. Since tioconazole is well tolerated at the topical level, it could be developed as a topical anticancer agent in combination with other systemic anticancer drugs.

GRAPHICAL ABSTRACT

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10616-021-00516-w.

Hyperthermia induced disruption of mechanical balance leads to G1 arrest and senescence in cells

Human body temperature limits below 40°C during heat stroke or fever. The implications of prolonged exposure to the physiologically relevant temperature (40°C) on cellular mechanobiology is poorly understood. Here, we have examined the effects of heat stress (40°C for 72 h incubation) in human lung adenocarcinoma (A549), mouse melanoma (B16F10), and non-cancerous mouse origin adipose tissue cells (L929). Hyperthermia increased the level of ROS, γ-H2AX and HSP70 and decreased mitochondrial membrane potential in the cells. Heat stress impaired cell division, caused G1 arrest, induced cellular senescence, and apoptosis in all the tested cell lines. The cells incubated at 40°C for 72 h displayed a significant decrease in the f-actin level and cellular traction as compared with cells incubated at 37°C. Also, the cells showed a larger focal adhesion area and stronger adhesion at 40°C than at 37°C. The mitotic cells at 40°C were unable to round up properly and displayed retracting actin stress fibers. Hyperthermia down-regulated HDAC6, increased the acetylation level of microtubules, and perturbed the chromosome alignment in the mitotic cells at 40°C. Overexpression of HDAC6 rescued the cells from the G1 arrest and reduced the delay in cell rounding at 40°C suggesting a crucial role of HDAC6 in hyperthermia mediated responses. This study elucidates the significant role of cellular traction, focal adhesions, and cytoskeletal networks in mitotic cell rounding and chromosomal misalignment. It also highlights the significance of HDAC6 in heat-evoked senile cellular responses.

Sertaconazole induced toxicity in HeLa cells through mitotic arrest and inhibition of microtubule assembly

Econazole, miconazole, and sertaconazole, the structurally related azoles with imidazole moiety, were evaluated for their cytotoxicity and their ability to bind to mammalian tubulin. Our results indicated that sertaconazole and econazole bound to goat brain tubulin with a dissociation constant of 9 and 19 μM respectively, while miconazole did not bind to goat brain tubulin. Econazole, miconazole, and sertaconazole inhibited the proliferation of HeLa cells with an IC₅₀ of 28, 98, and 38 μM respectively with sertaconazole alone inducing a mitotic block in the treated cells. Since sertaconazole bound to goat brain tubulin with higher affinity and blocked the cells at mitosis, we hypothesized that its cytotoxic mechanism might involve inhibition of tubulin and econazole which did not block the cells at mitosis may have additional targets than tubulin. Sertaconazole inhibited the polymerization of tubulin in HeLa cells and the in vitro assembled goat brain tubulin. Competitive tubulin-binding assay using colchicine and computational simulation studies showed that sertaconazole bound closer to the colchicine site and induced the tubulin dimer to adopt a "bent" conformation which is incompetent for the polymerization. Results from RT-PCR analysis of the A549 cells treated with sertaconazole indicated activation of apoptosis. Sertaconazole significantly inhibited the migration of HeLa cells and showed synergistic antiproliferative potential with vinblastine. Collectively, the results suggest that sertaconazole which is already in clinical practice could be useful as a topical chemotherapy agent for the treatment of skin cancers in combination with other systemic anticancer agents.

Functionality of receptor targeted zinc-insulin quantum clusters in skin tissue augmentation and bioimaging

Quantum clusters with target specificity are suitable for tissue-specific imaging. In the present work, amorphous zinc insulin quantum clusters (IZnQCs) had been synthesised to promote and monitor wound recovery. Easy synthesis, biocompatibility, stability, enhanced quantum yield, and solubility made the cluster suitable for preclinical/clinical exploration. Zn²⁺ is known for its binding to insulin hexamer. Here we report the reformation of the structure in a quantum cluster form in the presence of Zn²⁺. The formation of IZnQCs was confirmed by the change in zeta potential from -25.6 mV to -17.9 mV and also the formation of protein metal interaction was confirmed in FTIR bands at 450, 480, and 613 cm^-1 for Zn-O, Zn-N, and Zn-S, respectively. HRTEM-EDS and SAED data analysis showed an amorphous nature of the cluster. The binding of IZnQCs to the cells has been confirmed using confocal microscopy. IZnQCs showed a synergistic effect in wound recovery than insulin or Zn²⁺ alone. Further due to high fluorescence this recovery process can be monitored under an appropriate setup. Wound healing promotional activity, target specificity, and fluorescence properties make the IZnQCs ideal to use for bioimaging along with promoting and monitoring of wound recovery agent.

Synthesis, Biochemical Characterization, and Theoretical Studies of Novel β-Keto-enol Pyridine and Furan Derivatives as Potent Antifungal Agents

In the present study, we report the design and synthesis of new derivatives of the β-keto-enol grafted on pyridine and furan moieties (L ₁ -L ₁₁ ). Structures of compounds were fully confirmed by Fourier transform infrared spectroscopy (FT-IR), ¹H NMR, ¹³C NMR, electrospray ionization/liquid chromatography-mass spectrometry (ESI/LC-MS), and elemental analysis. The compounds were screened for antifungal and antibacterial activities (Escherichia coli, Bacillus subtilis, and Micrococcus luteus). In vitro evaluation showed significant fungicidal activity for L ₁ , L ₄ , and L ₅ against fungal strains (Fusarium oxysporum f.sp albedinis) compared to the reference standard. Especially, the exceptional activity has been demonstrated for L ₁ with IC₅₀ = 12.83 μg/mL. This compound and the reference benomyl molecule also showed a correlation between experimental antifungal activity and theoretical predictions by Petra/Osiris/Molinspiration (POM) calculations and molecular coupling against the Fgb1 protein. The highest inhibition of bacterial growth for L ₁ is due to its strongest binding to the target protein. This report may stimulate the further synthesis of examples of this substance class for the development of new drugs.

Methods to Access 2-aminobenzimidazoles of Medicinal Importance

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Benzimidazole (BI) and derivatives are interesting because several of these compounds have been found to have a diversity of biological activities with clinical applications. In view of their importance, the synthesis of BI and its derivatives is still considered as a challenge for synthetic chemists. Examples of compounds used in medicinal chemistry containing BI, as important nucleus, are Astemizole (antihistaminic), Omeprazole (antiulcerative) and Rabendazole (fungicide), some of these compounds have the 2- aminobenzimidazole (2ABI) as base nucleus. The structure of 2ABI derivatives contains a cyclic guanidine moiety, which is interesting because of its free lone pairs, labile hydrogen atoms and planar delocalized structure. The delocalized 10-π electron system and the extension of the electron conjugation with the exocyclic amino group, in 2ABI, making these heterocycles to have amphoteric character. The 2ABI has been used as building blocks for the synthesis of several BI derivatives as medicinally important molecules. On these bases, herein, we present a bibliographic review concerning the recent methodologies used in the synthesis of 2ABIs, including the substituted ones.

Novel Peptide-Based Inhibitors for Microtubule Polymerization in Phytophthora capsici

The plant disease Phytophthora blight, caused by the oomycete pathogen Phytophthora capsici, is responsible for major economic losses in pepper production. Microtubules have been an attractive target for many antifungal agents as they are involved in key cellular events such as cell proliferation, signaling, and migration in eukaryotic cells. In order to design a novel biocompatible inhibitor, we screened and identified inhibitory peptides against alpha- and beta-tubulin of P. capsici using a phage display method. The identified peptides displayed a higher binding affinity (nanomolar range) and improved specificity toward P. capsici alpha- and beta-tubulin in comparison to Homo sapiens tubulin as evaluated by fluorometric analysis. One peptide demonstrated the high inhibitory effect on microtubule formation with a nanomolar range of IC₅₀ values, which were much lower than a well-known chemical inhibitor—benomyl (IC₅₀ = 500 µM). Based on these results, this peptide can be employed to further develop promising candidates for novel antifungal agents against Phytophthora blight.

Methyl-β-cyclodextrin, an actin depolymerizer augments the antiproliferative potential of microtubule-targeting agents

Methyl-β-cyclodextrin (MCD), an established pharmacological excipient, depolymerizes the actin cytoskeleton. In this work, we investigated the effect of MCD-mediated actin depolymerization on various cellular phenotypes including traction force, cell stiffness, focal adhesions, and intracellular drug accumulation. In addition to a reduction in the contractile cellular traction, MCD acutely inhibits the maturation of focal adhesions. Alteration of contractile forces and focal adhesions affects the trypsin-mediated detachment kinetics of cells. Moreover, MCD-mediated actin depolymerization increases the intracellular accumulation of microtubule-targeting agents (MTAs) by ~50% with respect to the untreated cells. As MCD treatment enhances the intracellular concentration of drugs, we hypothesized that the MCD-sensitized cancer cells could be effectively killed by low doses of MTAs. Our results in cervical, breast, hepatocellular, prostate cancer and multidrug-resistant breast cancer cells confirmed the above hypothesis. Further, the combined use of MCD and MTAs synergistically inhibits the proliferation of tumor cells. These results indicate the potential use of MCD in combination with MTAs for cancer chemotherapy and suggest that targeting both actin and microtubules simultaneously may be useful for cancer therapy. Importantly, the results provide significant insight into the crosstalk between actin and microtubules in regulating the traction force and dynamics of cell deadhesion.

Crocin, a carotenoid, suppresses spindle microtubule dynamics and activates the mitotic checkpoint by binding to tubulin

Crocin, a constituent of the saffron spice, exhibits promising antitumor activity in animal models and also inhibits the proliferation of several types of cancer cells in culture. Recently, we have shown that crocin binds to purified tubulin at the vinblastine site, depolymerizes microtubules and induces a mitotic block in cultured cells. Here, we extend our previous suggestion and explore the cellular effects of crocin to further understand its mechanism of action. In a kinetic study, we observed that the crocin-induced depolymerization of microtubules preceded both DNA damage and reactive oxygen species generation indicating that depolymerizing microtubules is the primary action of crocin. Crocin also inhibited the growth of cold-depolymerized microtubules in HeLa cells indicating that it can inhibit microtubule dynamics. Using fluorescence recovery after photobleaching, crocin was found to suppress the spindle microtubule dynamics in live HeLa cells. Further, crocin treatment resulted in activation of spindle assembly checkpoint proteins, BubR1 and Mad2. Similar to other microtubule-targeting agents, crocin also perturbed the localization of end-binding protein EB1 from the growing microtubule ends and enhanced the acetylation of remaining microtubules. Further, crocin was found to bind to purified tubulin with a dissociation constant of 12 ± 1.5 μM. The results suggested that crocin exerted its antiproliferative effect primarily by inhibiting the assembly and dynamics of microtubules. Importantly, the combination of crocin with known anticancer agents like combretastatin A-4, cisplatin, doxorubicin or sorafenib, exerted a strong synergistic cytotoxic effect in HeLa cells indicating that crocin may enhance the effectiveness of other anticancer agents.

A “turn-on” Michler's ketone–benzimidazole fluorescent probe for selective detection of serum albumins

Enhanced emission and selective binding with albumins.

Zerumbone, a cyclic sesquiterpene, exerts antimitotic activity in HeLa cells through tubulin binding and exhibits synergistic activity with vinblastine and paclitaxel

Objectives

The aim of this study was to elucidate the antimitotic mechanism of zerumbone and to investigate its effect on the HeLa cells in combination with other mitotic blockers.

Materials and methods

HeLa cells and fluorescence microscopy were used to analyse the effect of zerumbone on cancer cell lines. Cellular internalization of zerumbone was investigated using FITC‐labelled zerumbone. The interaction of zerumbone with tubulin was characterized using fluorescence spectroscopy. The Chou and Talalay equation was used to calculate the combination index.

Results

Zerumbone selectively inhibited the proliferation of HeLa cells with an IC₅₀ of 14.2 ± 0.5 μmol/L through enhanced cellular uptake compared to the normal cell line L929. It induced a strong mitotic block with cells exhibiting bipolar spindles at the IC₅₀ and monopolar spindles at 30 μmol/L. Docking analysis indicated that tubulin is the principal target of zerumbone. In vitro studies indicated that it bound to goat brain tubulin with a Kd of 4 μmol/L and disrupted the assembly of tubulin into microtubules. Zerumbone and colchicine had partially overlapping binding site on tubulin. Zerumbone synergistically enhanced the anti‐proliferative activity of vinblastine and paclitaxel through augmented mitotic block.

Conclusion

Our data suggest that disruption of microtubule assembly dynamics is one of the mechanisms of the anti‐cancer activity of zerumbone and it can be used in combination therapy targeting cell division.

Theaflavin and epigallocatechin-3-gallate synergistically induce apoptosis through inhibition of PI3K/Akt signaling upon depolymerizing microtubules in HeLa cells

Theaflavin (TF) and epigallocatechin-3-gallate (EGCG) both have been reported previously as microtubule depolymerizing agents that also have anticancer effects on various cancer cell lines and in animal models. Here, we have applied TF and EGCG in combination on HeLa cells to investigate if they can potentiate each other to improve their anticancer effect in lower doses and the underlying mechanism. We found that TF and EGCG acted synergistically, in lower doses, to inhibit the growth of HeLa cells. We found the combination of 50 µg/mL TF and 20 µg/mL EGCG to be the most effective combination with a combination index of 0.28. The same combination caused larger accumulation of cells in the G ₂ /M phase of the cell cycle, potent mitochondrial membrane potential loss, and synergistic augmentation of apoptosis. We have shown that synergistic activity might be due to stronger microtubule depolymerization by simultaneous binding of TF and EGCG at different sites on tubulin: TF binds at vinblastine binding site on tubulin, and EGCG binds near colchicines binding site on tubulin. A detailed mechanistic analysis revealed that stronger microtubule depolymerization caused effective downregulation of PI3K/Akt signaling and potently induced mitochondrial apoptotic signals, which ultimately resulted in the apoptotic death of HeLa cells in a synergistic manner.

Indibulin dampens microtubule dynamics and produces synergistic antiproliferative effect with vinblastine in MCF-7 cells: Implications in cancer chemotherapy

Indibulin, a synthetic inhibitor of tubulin assembly, has shown promising anticancer activity with a minimal neurotoxicity in preclinical animal studies and in Phase I clinical trials for cancer chemotherapy. Using time-lapse confocal microscopy, we show that indibulin dampens the dynamic instability of individual microtubules in live breast cancer cells. Indibulin treatment also perturbed the localization of end-binding proteins at the growing microtubule ends in MCF-7 cells. Indibulin reduced inter-kinetochoric tension, produced aberrant spindles, activated mitotic checkpoint proteins Mad2 and BubR1, and induced mitotic arrest in MCF-7 cells. Indibulin-treated MCF-7 cells underwent apoptosis-mediated cell death. Further, the combination of indibulin with an anticancer drug vinblastine was found to exert synergistic cytotoxic effects on MCF-7 cells. Interestingly, indibulin displayed a stronger effect on the undifferentiated neuroblastoma (SH-SY5Y) cells than the differentiated neuronal cells. Unlike indibulin, vinblastine and colchicine produced similar depolymerizing effects on microtubules in both differentiated and undifferentiated SH-SY5Y cells. The data indicated a possibility that indibulin may reduce chemotherapy-induced peripheral neuropathy in cancer patients.

Indirubin, a bis-indole alkaloid binds to tubulin and exhibits antimitotic activity against HeLa cells in synergism with vinblastine

Indirubin, a bis-indole alkaloid used in traditional Chinese medicine has shown remarkable anticancer activity against chronic myelocytic leukemia. The present work was aimed to decipher the underlying molecular mechanisms responsible for its anticancer attributes. Our findings suggest that indirubin inhibited the proliferation of HeLa cells with an IC₅₀ of 40 μM and induced a mitotic block. At concentrations higher than its IC₅₀, indirubin exerted a moderate depolymerizing effect on the interphase microtubular network and spindle microtubules in HeLa cells. Studies with goat brain tubulin indicated that indirubin bound to tubulin at a single site with a dissociation constant of 26 ± 3 μM and inhibited the in vitro polymerization of tubulin into microtubules in the presence of glutamate as well as microtubule-associated proteins. Molecular docking analysis and molecular dynamics simulation studies indicate that indirubin stably binds to tubulin at the interface of the α-β tubulin heterodimer. Further, indirubin stabilized the binding of colchicine on tubulin and promoted the cysteine residue modification by 5,5'-dithiobis-2-nitrobenzoic acid, indicating towards alteration of tubulin conformation upon binding. In addition, we found that indirubin synergistically enhanced the anti-mitotic and anti-proliferative activity of vinblastine, a known microtubule-targeted agent. Collectively our studies indicate that perturbation of microtubule polymerization dynamics could be one of the possible mechanisms behind the anti-cancer activities of indirubin.

In vitro evaluation of the cytotoxic and bactericidal mechanism of the commonly used pesticide triphenyltin hydroxide

Triphenyltin hydroxide (TPTH) is a widely used pesticide that is highly toxic to a variety of organisms including humans and a potential contender for the environmental pollutant. In the present study, the cytotoxic mechanism of TPTH on mammalian cells was analyzed using HeLa cells and the antibacterial activity was analyzed using B. subtilis and E. coli cells. TPTH inhibited the growth of HeLa cells with a half-maximal inhibitory concentration of 0.25 μM and induced mitotic arrest. Immunofluorescence microscopy analysis showed that TPTH caused strong depolymerization of interphase microtubules and spindle abnormality with the appearance of colchicine type mitosis and condensed chromosome. TPTH exhibited high affinity for tubulin with a dissociation constant of 2.3 μM and inhibited the in vitro microtubule assembly in the presence of glutamate as well as microtubule-associated proteins. Results from the molecular docking and in vitro experiments implied that TPTH may have an overlapping binding site with colchicine on tubulin with a distance of about 11 Å between them. TPTH also binds to DNA at the A-T rich region of the minor groove. The data presented in the study revealed that the toxicity of TPTH in mammalian cells is mediated through its interactions with DNA and its strong depolymerizing activity on tubulin. However, its antibacterial activity was not through FtsZ, the prokaryotic homolog of tubulin but perhaps through its interactions with DNA.

The adverse outcome pathway (AOP) for chemical binding to tubulin in oocytes leading to aneuploid offspring

The Organisation for Economic Co-operation and Development (OECD) has launched the Adverse Outcome Pathway (AOP) Programme to advance knowledge of pathways of toxicity and improve the use of mechanistic information in risk assessment. An AOP links a molecular initiating event (MIE) to an adverse outcome (AO) through intermediate key events (KE). Here, we present the scientific evidence in support of an AOP whereby chemicals that bind to tubulin cause microtubule depolymerization resulting in spindle disorganization followed by altered chromosome alignment and segregation and the generation of aneuploidy in female germ cells, ultimately leading to aneuploidy in the offspring. Aneuploidy, an abnormal number of chromosomes that is not an exact multiple of the haploid number, is a well-known cause of human disease and represents a major cause of infertility, pregnancy failure, and serious genetic disorders in the offspring. Among chemicals that induce aneuploidy in female germ cells, a large majority impairs microtubule dynamics and spindle function. Colchicine, a prototypical chemical that binds to tubulin and causes microtubule depolymerization, is used here to illustrate the AOP. This AOP is specific to female germ cells exposed during the periovulation period. Although the majority of the data come from rodent studies, the available evidence suggests that the MIE and KEs are conserved across species and would occur in human oocytes. The development of AOPs related to mutagenicity in germ cells is expected to aid the identification of potential hazards to germ cell genomic integrity and support regulatory efforts to protect population health.

Deleterious effects of benomyl and carbendazim on human placental trophoblast cells

Benomyl and carbendazim are benzimidazole fungicides that are used throughout the world against a wide range of fungal diseases of agricultural products. There is as yet little information regarding the toxicity of benzimidazole fungicides to human placenta. In this study, we utilized human placental trophoblast cell line HTR-8/SVneo (HTR-8) to access the toxic effects of benomyl and carbendazim. Our data showed that these two fungicides decreased cell viability and the percentages of cells in G0/G1 phase, as well as induced apoptosis of HTR-8 cells. The invasion and migration of HTR-8 cells were significantly inhibited by benomyl and carbendazim. We further found that benomyl and carbendazim altered the expression of protease systems (MMPs/TIPMs and uPA/PAI-1) and adhesion molecules (integrin α5 and β1) in HTR-8 cells. Our present study firstly shows the deleterious effects of benomyl and carbendazim on placental cells and suggests a potential risk of benzimidazole fungicides to human reproduction.

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.

Fungicide: Modes of Action and Possible Impact on Nontarget Microorganisms

Fungicides have been used widely in order to control fungal diseases and increase crop production. However, the effects of fungicides on microorganisms other than fungi remain unclear. The modes of action of fungicides were never well classified and presented, making difficult to estimate their possible nontarget effects. In this paper, the action modes and effects of fungicides targeting cell membrane components, protein synthesis, signal transduction, respiration, cell mitosis, and nucleic acid synthesis were classified, and their effects on nontarget microorganisms were reviewed. Modes of action and potential non-target effects on soil microorganisms should be considered in the selection of fungicide in order to protect the biological functions of soil and optimize the benefits derived from fungicide use in agricultural systems.

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.

Griseofulvin stabilizes microtubule dynamics, activates p53 and inhibits the proliferation of MCF-7 cells synergistically with vinblastine

Background

Griseofulvin, an antifungal drug, has recently been shown to inhibit proliferation of various types of cancer cells and to inhibit tumor growth in athymic mice. Due to its low toxicity, griseofulvin has drawn considerable attention for its potential use in cancer chemotherapy. This work aims to understand how griseofulvin suppresses microtubule dynamics in living cells and sought to elucidate the antimitotic and antiproliferative action of the drug.

Methods

The effects of griseofulvin on the dynamics of individual microtubules in live MCF-7 cells were measured by confocal microscopy. Immunofluorescence microscopy, western blotting and flow cytometry were used to analyze the effects of griseofulvin on spindle microtubule organization, cell cycle progression and apoptosis. Further, interactions of purified tubulin with griseofulvin were studied in vitro by spectrophotometry and spectrofluorimetry. Docking analysis was performed using autodock4 and LigandFit module of Discovery Studio 2.1.

Results

Griseofulvin strongly suppressed the dynamic instability of individual microtubules in live MCF-7 cells by reducing the rate and extent of the growing and shortening phases. At or near half-maximal proliferation inhibitory concentration, griseofulvin dampened the dynamicity of microtubules in MCF-7 cells without significantly disrupting the microtubule network. Griseofulvin-induced mitotic arrest was associated with several mitotic abnormalities like misaligned chromosomes, multipolar spindles, misegregated chromosomes resulting in cells containing fragmented nuclei. These fragmented nuclei were found to contain increased concentration of p53. Using both computational and experimental approaches, we provided evidence suggesting that griseofulvin binds to tubulin in two different sites; one site overlaps with the paclitaxel binding site while the second site is located at the αβ intra-dimer interface. In combination studies, griseofulvin and vinblastine were found to exert synergistic effects against MCF-7 cell proliferation.

Conclusions

The study provided evidence suggesting that griseofulvin shares its binding site in tubulin with paclitaxel and kinetically suppresses microtubule dynamics in a similar manner. The results revealed the antimitotic mechanism of action of griseofulvin and provided evidence suggesting that griseofulvin alone and/or in combination with vinblastine may have promising role in breast cancer chemotherapy.

Probing interactions of tubulin with small molecules, peptides, and protein fragments by solution nuclear magnetic resonance

The description of the molecular mechanisms of interaction between tubulin or microtubules and partners at atomic scale is expected to have critical impacts on the understanding of basic physiological processes. This information will also help the design of future drug candidates that may be used to fight various pathologies such as cancer or neurological diseases. For these reasons, this aspect of tubulin research has been tackled since the seventies using many different methods and at different scales. NMR appears as a unique approach to provide, with atomic resolution, the solution structure and dynamical properties of tubulin/microtubule partners in free and bound states. Though tubulin is not directly amenable to solution NMR, the NMR ligand-based experiments allow one to obtain valuable data on the molecular mechanisms that sustain structure-function relationship, in particular atomic details on the partner binding site. We will first describe herein some basic principles of solution NMR spectroscopy that should not be missed for a comprehensive reading of NMR reports. A series of results will then be presented to illustrate the wealth and variety of NMR experiments and how this approach enlightens tubulin/microtubules interaction with partners.

In silico platform for xenobiotics ADME-T pharmacological properties modeling and prediction. Part I: Beyond the reduction of animal model use

There is an urgent need for efficient in silico ADME-T prediction tools for the selection of potent therapeutic drugs as well as the elimination of toxic compounds. This is particularly important in view of the high costs and ethical issues inherent to the use of animal models for drugs filtering. To achieve this mission, not only does the accuracy of in silico tools need to be improved, but also new experts in the field with skills in theoretical chemistry, clinical and fundamental biology have to be trained. Similarly, clinical biologists committed to the obligation of means and legally responsible for the results they generate could establish a legal framework that defines legal responsibilities when performing in silico predictions.

Curcumin prevents liver fibrosis by inducing apoptosis and suppressing activation of hepatic stellate cells

This study was designed to investigate the prophylactic effects and the mechanisms of curcumin on liver fibrosis in rats. Liver fibrosis was induced in 72 Sprague Dawley rats by intraperitoneal injection of carbon tetrachloride. Rats were divided into control, liver fibrosis, high, medium, and low dose curcumin (200, 100, and 50 mg kg(-1), respectively), and colchicine (0.1 mg kg(-1)) groups. After 8 weeks of treatment, histopathological examination was performed on hepatic tissues, and liver fibrosis was graded. Hepatic stellate cells activity was examined by smooth muscle alpha-actin immunohistochemistry staining, and apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick-end labeling. The liver fibrosis score in the high, medium, and low dose curcumin group (5.79 +/- 1.80, 8.58 +/- 3.34, and 9.58 +/- 3.32, respectively) and the colchicine group (4.91 +/- 1.28) was significantly lower than in the fibrosis group (20.40 +/- 3.38, P < 0.01). The ratio of activated hepatic stellate cells in the three curcumin groups (0.97 +/- 0.69, 2.06 +/- 0.58, and 3.49 +/- 1.03, respectively) and the colchicine group (0.78 +/- 0.31) was significantly lower than in the fibrosis group (6.08 +/- 1.13, P < 0.05). The apoptosis index in the three curcumin groups (0.57 +/- 0.21, 0.37 +/- 0.22, and 0.34 +/- 0.21, respectively) was higher than in the fibrosis (0.09 +/- 0.09, P < 0.05) or the colchicine group (0.16 +/- 0.19, P < 0.05). Curcumin prevents carbon tetrachloride-induced liver fibrosis in rats. The prevention of liver fibrosis may be due to the inhibition of the activation of hepatic stellate cells and induction of their apoptosis.