Synthesis and characterization of bis-amide SSE1917 as a microtubule-stabilizing anticancer agent

Microtubule dynamics are critical for spindle assembly and chromosome segregation during cell division. Pharmacological inhibition of microtubule dynamics in cells causes prolonged mitotic arrest, resulting in apoptosis, an approach extensively employed in treating different types of cancers. The present study reports the synthesis of thirty-two novel bis-amides (SSE1901-SSE1932) and the evaluation of their antiproliferative activities. N-(1-oxo-3-phenyl-1-(phenylamino)propan-2-yl)benzamide (SSE1917) exhibited the most potent activity with GI50 values of 0.331 ± 0.01 µM in HCT116 colorectal and 0.48 ± 0.27 µM in BT-549 breast cancer cells. SSE1917 stabilized microtubules in biochemical and cellular assays, bound to taxol site in docking studies, and caused aberrant mitosis and G2/M arrest in cells. Prolonged treatment of cells with the compound increased p53 expression and triggered apoptotic cell death. Furthermore, SSE1917 suppressed the growth of both mouse and patient-derived human colon cancer organoids, highlighting its potential therapeutic value as an anticancer agent.

New Combretastatin Analogs as Anticancer Agents: Design, Synthesis, Microtubules Polymerization Inhibition, and Molecular Docking Studies

A new series of 4-(4-methoxyphenyl)-5-(3,4,5-trimethoxyphenyl)-4H-1,2,4-triazole-3-thiol derivatives were synthesized as analogs for the anticancer drug combretastatin A-4 (CA-4) and characterized using FT-IR, 1 H-NMR, 13 CNMR, and HR-MS techniques. The new CA-4 analogs were designed to meet the structural requirements of the highest expected anticancer activity of CA-4 analogs by maintaining ring A 3,4,5-trimethoxyphenyl moiety, and at the same time varying the substituents effect of the triazole moiety (ring B). In silico analysis indicated that compound 3 has higher total energy and dipole moment than colchicine and the other analogs, and it has excellent distribution of electron density and is more stable, resulting in an increased binding affinity during tubulin inhibition. Additionally, compound 3 was found to interact with three apoptotic markers, namely p53, Bcl-2, and caspase 3. Compound 3 showed strong similarity to colchicine, and it has excellent pharmacokinetics properties and a good dynamic profile. The in vitro anti-proliferation studies showed that compound 3 is the most cytotoxic CA-4 analog against cancer cells (IC50 of 6.35 μM against Hep G2 hepatocarcinoma cells), and based on its selectivity index (4.7), compound 3 is a cancer cytotoxic-selective agent. As expected and similar to colchicine, compound 3-treated Hep G2 hepatocarcinoma cells were arrested at the G2/M phase resulting in induction of apoptosis. Compound 3 tubulin polymerization IC50 (9.50 μM) and effect on Vmax of tubulin polymerization was comparable to that of colchicine (5.49 μM). Taken together, the findings of the current study suggest that compound 3, through its binding to the colchicine-binding site at β-tubulin, is a promising microtubule-disrupting agent with excellent potential to be used as cancer therapeutic agent.

Identification and analysis of a selective DYRK1A inhibitor

The dysregulation of DYRK1A is implicated in many diseases such as cancer, diabetes, and neurodegenerative diseases. Alzheimer's disease is one of the most common neurodegenerative disease and has elevated interest in DYRK1A research. Overexpression of DYRK1A has been linked to the formation of tau aggregates. Currently, an effective therapeutic treatment that targets DYRK1A is lacking. A specific small-molecule inhibitor would further our understanding of the physiological role of DYRK1A in neurodegenerative diseases and could be presented as a possible therapeutic option. In this study, we identified pharmacological interactions within the DYRK1A active site and performed a structure-based virtual screening approach to identify a selective small-molecule inhibitor. Several compounds were selected in silico for enzymatic and cellular assays, yielding a novel inhibitor. A structure-activity relationship analysis was performed to identify areas of interactions for the compounds selected in this study. When tested in vitro, reduction of DYRK1A dependent phosphorylation of tau was observed for active compounds. The active compounds also improved tau turbidity, suggesting that these compounds could alleviate aberrant tau aggregation. Testing the active compound against a panel of kinases across the kinome revealed greater selectivity towards DYRK1A. Our study demonstrates a serviceable protocol that identified a novel and selective DYRK1A inhibitor with potential for further study in tau-related pathologies.

Non-Invasive Evaluation of Acute Effects of Tubulin Binding Agents: A Review of Imaging Vascular Disruption in Tumors

Tumor vasculature proliferates rapidly, generally lacks pericyte coverage, and is uniquely fragile making it an attractive therapeutic target. A subset of small-molecule tubulin binding agents cause disaggregation of the endothelial cytoskeleton leading to enhanced vascular permeability generating increased interstitial pressure. The resulting vascular collapse and ischemia cause downstream hypoxia, ultimately leading to cell death and necrosis. Thus, local damage generates massive amplification and tumor destruction. The tumor vasculature is readily accessed and potentially a common target irrespective of disease site in the body. Development of a therapeutic approach and particularly next generation agents benefits from effective non-invasive assays. Imaging technologies offer varying degrees of sophistication and ease of implementation. This review considers technological strengths and weaknesses with examples from our own laboratory. Methods reveal vascular extent and patency, as well as insights into tissue viability, proliferation and necrosis. Spatiotemporal resolution ranges from cellular microscopy to single slice tomography and full three-dimensional views of whole tumors and measurements can be sufficiently rapid to reveal acute changes or long-term outcomes. Since imaging is non-invasive, each tumor may serve as its own control making investigations particularly efficient and rigorous. The concept of tumor vascular disruption was proposed over 30 years ago and it remains an active area of research.

Tubulin Inhibitors: A Chemoinformatic Analysis Using Cell-Based Data

Inhibiting the tubulin-microtubules (Tub-Mts) system is a classic and rational approach for treating different types of cancers. A large amount of data on inhibitors in the clinic supports Tub-Mts as a validated target. However, most of the inhibitors reported thus far have been developed around common chemical scaffolds covering a narrow region of the chemical space with limited innovation. This manuscript aims to discuss the first activity landscape and scaffold content analysis of an assembled and curated cell-based database of 851 Tub-Mts inhibitors with reported activity against five cancer cell lines and the Tub-Mts system. The structure-bioactivity relationships of the Tub-Mts system inhibitors were further explored using constellations plots. This recently developed methodology enables the rapid but quantitative assessment of analog series enriched with active compounds. The constellations plots identified promising analog series with high average biological activity that could be the starting points of new and more potent Tub-Mts inhibitors.

The long-term effects of Δ9-tetrahydrocannabinol on microtubule dynamicity in rats

Studies reported that Δ⁹-tetrahydrocannabinol (Δ⁹-THC) is an essential drug as an anti-cancer, neuroprotective, anti-inflammatory, and immune-modulatory agent. However, the mechanism by which Δ⁹-THC causes these events remains to be elucidated. We attempted to investigate the in vivo studies of Δ⁹-THC on brain microtubule dynamicity, and acetylcholinesterase (AChE) activity. The microtubule polymerization, secondary and tertiary structures of α/β-tubulins, as well as the AChE activity, were evaluated in the experimental groups. The significantly lowest optical density and initial rate of polymerization was observed in THC 3 mg/kg, THC 9 mg/kg, and THC 18 mg/kg treated groups. The content of secondary and tertiary structures of α/β-tubulins was significantly affected in treated groups. The AChE activity was significantly lower in treated groups in a dose-dependent manner. These data highlight the microtubule dynamicity as a molecular target for Δ⁹-THC, which affects memory dysfunction. However, Δ⁹-THC can be inhibited the AChE activity and provide an improved therapeutics for neurodegenerative diseases.

Bioreductively Activatable Prodrug Conjugates of Combretastatin A-1 and Combretastatin A-4 as Anticancer Agents Targeted toward Tumor-Associated Hypoxia

The natural products combretastatin A-1 (CA1) and combretastatin A-4 (CA4) function as potent inhibitors of tubulin polymerization and as selective vascular disrupting agents (VDAs) in tumors. Bioreductively activatable prodrug conjugates (BAPCs) can enhance selectivity by serving as substrates for reductase enzymes specifically in hypoxic regions of tumors. A series of CA1-BAPCs incorporating nor-methyl, mono-methyl, and gem-dimethyl nitrothiophene triggers were synthesized together with corresponding CA4-BAPCs, previously reported by Davis (Mol. Cancer Ther. 2006, 5 (11), 2886), for comparison. The CA4-gem-dimethylnitrothiophene BAPC 45 proved exemplary in comparison to its nor-methyl 43 and mono-methyl 44 congeners. It was stable in phosphate buffer (pH 7.4, 24 h), was cleaved (25%, 90 min) by NADPH-cytochrome P450 oxidoreductase (POR), was inactive (desirable prodrug attribute) as an inhibitor of tubulin polymerization (IC₅₀ > 20 μM), and demonstrated hypoxia-selective activation in the A549 cell line [hypoxia cytotoxicity ratio (HCR) = 41.5]. The related CA1-gem-dimethylnitrothiophene BAPC 41 was also promising (HCR = 12.5) with complete cleavage (90 min) upon treatment with POR. In a preliminary in vivo dynamic bioluminescence imaging study, BAPC 45 (180 mg/kg, ip) induced a decrease (within 4 h) in light emission in a 4T1 syngeneic mouse breast tumor model, implying activation and vascular disruption.

Synthesis of Combretastatin A-4 and 3'-Aminocombretastatin A-4 derivatives with Aminoacid Containing Pendants and Study of Their Interaction with Tubulin and as Downregulators of the VEGF, hTERT and c-Myc Gene Expression

Natural product combretastatin A-4 (CA-4) and its nitrogenated analogue 3′-aminocombretastatin A-4 (AmCA-4) have shown promising antitumor activities. In this study, a range of CA-4 and AmCA-4 derivatives containing amino acid pendants have been synthesized in order to compare their biological actions with those of their parent compounds. Thus, inhibition of cell proliferation on tumor cell lines HT-29, MCF-7 and A-549, as well as on the nontumor cell line HEK-273; in vitro tubulin polymerization; mitotic cell arrest; action on the microtubule cell network and inhibition of VEGF, hTERT, and c-Myc genes have been evaluated. Some AmCA-4 derivatives bearing L-amino acids exhibited inhibition of cell proliferation at low nanomolar levels exceeding the values shown by AmCA-4. Furthermore, while CA-4 and AmCA-4 derivatives do not show significant effects on the in vitro tubulin polymerization and cell cycle arrest, some selected CA-4 and AmCA-4 derivatives are able to cause total depolymerization of the microtubule network on A-549 cells. The best results were obtained in the inhibition of gene expression, particularly on the VEGF gene, in which some AmCA-4 derivatives greatly exceeded the inhibition values achieved by the parent compound.

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.

2,3',4,4',5-Pentachlorobiphenyl induced autophagy of the thyrocytes via DAPK2/PKD/VPS34 pathway

2,3',4,4',5-Pentachlorobiphenyl (PCB118) has been shown to cause thyroidal ultrastructure lesions, but the underlying mechanism remains elusive. This study aimed to elucidate the mechanism by which PCB118 induces the abnormalities of the thyrocytes. Wistar rats were injected intraperitoneally with PCB118 (0, 10, 100 and 1000 μg/kg/d) for 13 weeks, and FRTL-5 cells were treated with PCB118 (0, 0.25, 2.5 and 25 nM). Transmission electron microscopy showed typical autophagosomes in the thyroid of PCB118-treated rats. Immunofluorescence staining showed dose-dependent increase of autophagy in FRTL-5 cells exposed to PCB118. In vivo and vitro studies found that Tubulin beta 3 class III (Tubb3) mRNA and protein levels decreased significantly, while Death-associated protein kinase 2 (DAPK2) increased after PCB118 exposure, and the binding between Tubb3 and DAPK2 was enhanced by PCB118 in a dose-dependent manner. Moreover, PCB118 resulted in the upregulation of Protein kinase D (PKD) and downregulation of Phosphatidylinositol 3-kinase (VPS34) in mRNA levels, and the activation of PKD and VPS34 phosphorylation. Additionally, Tubb3 small interfering RNA (siTubb3) suppressed DAPK2 protein expression and PKD phosphorylation in FRTL-5 cells, while VPS34 phosphorylation was inhibited by siPKD. Furthermore, DAPK2, PKD and VPS34 were upregulated by Tubb3 overexpression following PCB118 exposure. Our results demonstrate that low concentrations of PCB118 could promote thyroid autophagy formation and cause the abnormalities in thyroidal ultrastructure, and these effects are likely to be mediated by DAPK2/PKD/VPS34 dependent pathway.

Predicting bioprocess targets of chemical compounds through integration of chemical-genetic and genetic interactions

Chemical-genetic interactions–observed when the treatment of mutant cells with chemical compounds reveals unexpected phenotypes–contain rich functional information linking compounds to their cellular modes of action. To systematically identify these interactions, an array of mutants is challenged with a compound and monitored for fitness defects, generating a chemical-genetic interaction profile that provides a quantitative, unbiased description of the cellular function(s) perturbed by the compound. Genetic interactions, obtained from genome-wide double-mutant screens, provide a key for interpreting the functional information contained in chemical-genetic interaction profiles. Despite the utility of this approach, integrative analyses of genetic and chemical-genetic interaction networks have not been systematically evaluated. We developed a method, called CG-TARGET (Chemical Genetic Translation via A Reference Genetic nETwork), that integrates large-scale chemical-genetic interaction screening data with a genetic interaction network to predict the biological processes perturbed by compounds. In a recent publication, we applied CG-TARGET to a screen of nearly 14,000 chemical compounds in Saccharomyces cerevisiae, integrating this dataset with the global S. cerevisiae genetic interaction network to prioritize over 1500 compounds with high-confidence biological process predictions for further study. We present here a formal description and rigorous benchmarking of the CG-TARGET method, showing that, compared to alternative enrichment-based approaches, it achieves similar or better accuracy while substantially improving the ability to control the false discovery rate of biological process predictions. Additional investigation of the compatibility of chemical-genetic and genetic interaction profiles revealed that one-third of observed chemical-genetic interactions contributed to the highest-confidence biological process predictions and that negative chemical-genetic interactions overwhelmingly formed the basis of these predictions. We also present experimental validations of CG-TARGET-predicted tubulin polymerization and cell cycle progression inhibitors. Our approach successfully demonstrates the use of genetic interaction networks in the high-throughput functional annotation of compounds to biological processes.

Understanding how chemical compounds affect biological systems is of paramount importance as pharmaceutical companies strive to develop life-saving medicines, governments seek to regulate the safety of consumer products and agrichemicals, and basic scientists continue to study the fundamental inner workings of biological organisms. One powerful approach to characterize the effects of chemical compounds in living cells is chemical-genetic interaction screening. Using this approach, a collection of cells–each with a different defined genetic perturbation–is tested for sensitivity or resistance to the presence of a compound, resulting in a quantitative profile describing the functional effects of that compound on the cells. The work presented here describes our efforts to integrate compounds’ chemical-genetic interaction profiles with reference genetic interaction profiles containing information on gene function to predict the cellular processes perturbed by the compounds. We focused on specifically developing a method that could scale to perform these functional predictions for large collections of thousands of screened compounds and robustly control the false discovery rate. With chemical-genetic and genetic interaction screens now underway in multiple species including human cells, the method described here can be generally applied to enable the characterization of compounds’ effects across the tree of life.

Estradiol dimer inhibits tubulin polymerization and microtubule dynamics

Microtubule dynamics is one of the major targets for new chemotherapeutic agents. This communication presents the synthesis and biological profiling of steroidal dimers based on estradiol, testosterone and pregnenolone bridged by 2,6-bis(azidomethyl)pyridine between D rings. The biological profiling revealed unique properties of the estradiol dimer including cytotoxic activities on a panel of 11 human cell lines, ability to arrest in the G2/M phase of the cell cycle accompanied with the attenuation of DNA/RNA synthesis. Thorough investigation precluded a genomic mechanism of action and revealed that the estradiol dimer acts at the cytoskeletal level by inhibiting tubulin polymerization. Further studies showed that estradiol dimer, but none of the other structurally related dimeric steroids, inhibited assembly of purified tubulin (IC₅₀, 3.6 μM). The estradiol dimer was more potent than 2-methoxyestradiol, an endogenous metabolite of 17β-estradiol and well-studied microtubule polymerization inhibitor with antitumor effects that was evaluated in clinical trials. Further, it was equipotent to nocodazole (IC₅₀, 1.5 μM), an antimitotic small molecule of natural origin. Both estradiol dimer and nocodazole completely and reversibly depolymerized microtubules in interphase U2OS cells at 2.5 μM concentration. At lower concentrations (50 nM), estradiol dimer decreased the microtubule dynamics and growth life-time and produced comparable effect to nocodazole on the microtubule dynamicity. In silico modeling predicted that estradiol dimer binds to the colchicine-binding site in the tubulin dimer. Finally, dimerization of the steroids abolished their ability to induce transactivation by estrogen receptor α and androgen receptors. Although other steroids were reported to interact with microtubules, the estradiol dimer represents a new structural type of steroid inhibitor of tubulin polymerization and microtubule dynamics, bearing antimitotic and cytotoxic activity in cancer cell lines.

[In silico Search for Tubulin Polymerization Inhibitors]

Cytostatic colchicine is widely used in the treatment of Familial Mediterranean fever, but it has several side effects. For finding new, more effective drugs with higher affinity and diminishside effects we carried out virtual screening of potential inhibitors of the main target of colchicine, the polymerization of tubulin by evaluating affinity 25745 compounds, structurally related to the colchicine. We have identified 11 commercially available compounds with higher affinity to tubulin. Compounds with highest binding scores include trimethoxybenzene and its derivatives; these compounds bind to the same site in similar orientation. Information provided can form the basis for design of new cytostatics.

A feasibility and safety study of concurrent chemotherapy based on genetic testing in patients with high-risk salivary gland tumors: Preliminary results

BACKGROUND

This prospective study was conducted to evaluate the feasibility and safety of customized chemotherapy regimens based on the gene characteristics of salivary gland tumors.

METHODS

Patients were enrolled with histologically confirmed intermediate or high grade, stage T3-4, N1-3 disease, and T1-2, N0 patients with a close (≤1 mm) or microscopically positive surgical margin were also enrolled in the study. All patients received radical surgery and postoperative concurrent chemoradiotherapy. To evaluate the responsiveness of therapies, the chemotherapy regimen was based on gene targets, β-tubulin III, ABCB1, STMN1, and CYP1B1 (for docetaxel) and TYMS (for pemetrexed). The primary endpoints were treatment compliance and acute toxicities.

RESULTS

A total of 20 patients were enrolled between September 2013 and January 2016. The median age was 46 years (range: 23-70 years). Genetic testing showed that 8 patients may have been sensitive to docetaxel, 5 patients may have been sensitive to pemetrexed, and 7 patients sensitive to either docetaxel or pemetrexed. All patients received the full dose of radiation. A total of 19 patients (95%) completed 2 cycles of concurrent chemotherapy (CCT). One patient treated concurrently with pemetrexed experienced grade 3 neutropenia. Three patients experienced grade 3 oral mucositis, and 2 patients experienced grade 3 dermatitis.

CONCLUSION

Our study demonstrated that a CCT selecting method based on the gene targets associated with drug sensitivity was clinically feasible and safe. Further studies enrolled more patients with longer follow-up times are needed to confirm the clinical efficacy of this CCT selecting method.

β1 Tubulin Rather Than β2 Tubulin Is the Preferred Binding Target for Carbendazim in Fusarium graminearum

Tubulins are the proposed target of anticancer drugs, anthelminthics, and fungicides. In Fusarium graminearum, β2 tubulin has been reported to be the binding target of methyl benzimidazole carbamate (MBC) fungicides. However, the function of F. graminearum β1 tubulin, which shares 76% amino acid sequence identity with β2 tubulin, in MBC sensitivity has been unclear. In this study, MBC sensitivity relative to that of a parental strain (2021) was significantly reduced in a β1 tubulin deletion strain but increased in a β2 tubulin deletion strain, suggesting that β1 tubulin was involved in the MBC sensitivity of F. graminearum. When strain 2021 was grown in a medium with a low or high concentration of the MBC fungicide carbendazim (0.5 or 1.4 μg/ml), the protein accumulation levels were reduced by 47 and 87%, respectively, for β1 tubulin but only by 6 and 24%, respectively, for β2 tubulin. This result was consistent with observations that MBC fungicides are more likely to disrupt β1 tubulin microtubules rather than β2 tubulin microtubules in GFP-β tubulin fusion mutants in vivo. Furthermore, sequence analysis indicated that a difference in tubulin amino acid 240 (240L in β1 versus 240F in β2) may explain the difference in MBC binding affinity; this result was consistent with the result that an F240L mutation in β2 tubulin greatly increased sensitivity to carbendazim in F. graminearum. We suggest that β1 tubulin rather than β2 tubulin is the preferred binding target for MBC fungicides in F. graminearum.

Novel drug design for Chagas disease via targeting Trypanosoma cruzi tubulin: Homology modeling and binding pocket prediction on Trypanosoma cruzi tubulin polymerization inhibition by naphthoquinone derivatives

Chagas disease, also called American trypanosomiasis, is a parasitic disease caused by Trypanosoma cruzi (T. cruzi). Recent findings have underscored the abundance of the causative organism, (T. cruzi), especially in the southern tier states of the US and the risk burden for the rural farming communities there. Due to a lack of safe and effective drugs, there is an urgent need for novel therapeutic options for treating Chagas disease. We report here our first scientific effort to pursue a novel drug design for treating Chagas disease via the targeting of T. cruzi tubulin. First, the anti T. cruzi tubulin activities of five naphthoquinone derivatives were determined and correlated to their anti-trypanosomal activities. The correlation between the ligand activities against the T. cruzi organism and their tubulin inhibitory activities was very strong with a Pearson's r value of 0.88 (P value <0.05), indicating that this class of compounds could inhibit the activity of the trypanosome organism via T. cruzi tubulin polymerization inhibition. Subsequent molecular modeling studies were carried out to understand the mechanisms of the anti-tubulin activities, wherein, the homology model of T. cruzi tubulin dimer was generated and the putative binding site of naphthoquinone derivatives was predicted. The correlation coefficient for ligand anti-tubulin activities and their binding energies at the putative pocket was found to be r=0.79, a high correlation efficiency that was not replicated in contiguous candidate pockets. The homology model of T. cruzi tubulin and the identification of its putative binding site lay a solid ground for further structure based drug design, including molecular docking and pharmacophore analysis. This study presents a new opportunity for designing potent and selective drugs for Chagas disease.

Inhaled vanadium pentoxide decrease gamma-tubulin of mouse testes at different exposure times

Vanadium is an important environmental and industrial pollutant whose concentrations have increased in the last decades. Due to its status as reproductive toxicant and a microtubule damaging agent, the present study investigated by immunohistochemistry the effect of the inhalation of vanadium pentoxide on gamma-tubulin within somatic and testicular germ cells. Male mice inhaled vanadium pentoxide (V2O5) (0.02 M) 1 h/twice a week for 12 weeks. Our results demonstrated that vanadium accumulates in the testes starting with the initial inhalation (24 h), and this pattern remained until the last week of treatment. In general, vanadium was capable of significantly decreasing the percentage of gamma-tubulin in all analyzed testicular cells (Sertoli, Leydig and germ cells) starting with the first week of treatment. For all cell types studied, regression analysis revealed a negative and significant relationship between the percentage of immunopositive cells to gamma-tubulin and exposure time, showing a time dependent response in all cases. Our findings suggest that alterations on this protein might imply changes in microtubule-involved function such as cell division, which in the testes might lead to damage in the spermatogenesis, leading probably to infertility.

Dimethylsulfoniopropionate Promotes Process Outgrowth in Neural Cells and Exerts Protective Effects against Tropodithietic Acid

The marine environment harbors a plethora of bioactive substances, including drug candidates of potential value in the field of neuroscience. The present study was undertaken to investigate the effects of dimethylsulfoniopropionate (DMSP), produced by several algae, corals and higher plants, on cells of the mammalian nervous system, i.e., neuronal N2a and OLN-93 cells as model system for nerve cells and glia, respectively. Additionally, the protective capabilities of DMSP were assessed in cells treated with tropodithietic acid (TDA), a marine metabolite produced by several Roseobacter clade bacteria. Both cell lines, N2a and OLN-93, have previously been shown to be a sensitive target for the action of TDA, and cytotoxic effects of TDA have been connected to the induction of oxidative stress. Our data shows that DMSP promotes process outgrowth and microtubule reorganization and bundling, accompanied by an increase in alpha-tubulin acetylation. Furthermore, DMSP was able to prevent the cytotoxic effects exerted by TDA, including the breakdown of the mitochondrial membrane potential, upregulation of heat shock protein Hsp32 and activation of the extracellular signal-regulated kinases 1/2 (ERK1/2). Our study points to the conclusion that DMSP provides an antioxidant defense, not only in algae but also in mammalian neural cells.

Microtubule array formation during root hair infection thread initiation and elongation in the Mesorhizobium-Lotus symbiosis

Nuclear migration during infection thread (IT) development in root hairs is essential for legume-Rhizobium symbiosis. However, little is known about the relationships between IT formation, nuclear migration, and microtubule dynamics. To this aim, we used transgenic Lotus japonicus expressing a fusion of the green fluorescent protein and tubulin-α6 from Arabidopsis thaliana to visualize in vivo dynamics of cortical microtubules (CMT) and endoplasmic microtubules (EMTs) in root hairs in the presence or absence of Mesorhizobium loti inoculation. We also examined the effect of microtubule-depolymerizing herbicide, cremart, on IT initiation and growth, since cremart is known to inhibit nuclear migration. In live imaging studies of M. loti-treated L. japonicus root hairs, EMTs were found in deformed, curled, and infected root hairs. The continuous reorganization of the EMT array linked to the nucleus appeared to be essential for the reorientation, curling, and IT initiation and the growth of zone II root hairs which are susceptible to rhizobial infection. During IT initiation, the EMTs appeared to be linked to the root hair surface surrounding the M. loti microcolonies. During IT growth, EMTs dissociated from the curled root hair tip, remained linked to the nucleus, and appeared to surround the IT tip. Lack or disorganized EMT arrays that were no longer linked to the nucleus were observed only in infection-aborted root hairs. Cremart affected IT formation and nodulation in a concentration-dependent manner, suggesting that the microtubule (MT) organization and successive nuclear migration are essential for successful nodulation in L. japonicus by M. loti.

Zampanolide and dactylolide: cytotoxic tubulin-assembly agents and promising anticancer leads

Zampanolide is a marine natural macrolide and a recent addition to the family of microtubule-stabilizing cytotoxic agents. Zampanolide exhibits unique effects on tubulin assembly and is more potent than paclitaxel against several multi-drug resistant cancer cell lines. A high-resolution crystal structure of αβ-tubulin in complex with zampanolide explains how taxane-site microtubule-stabilizing agents promote microtubule assemble and stability. This review provides an overview of current developments of zampanolide and its related but less potent analogue dactylolide, covering their natural sources and isolation, structure and conformation, cytotoxic potential, structure-activity studies, mechanism of action, and syntheses.

Microtubule drugs: action, selectivity, and resistance across the kingdoms of life

Microtubule drugs such as paclitaxel, colchicine, vinblastine, trifluralin, or oryzalin form a chemically diverse group that has been reinforced by a large number of novel compounds over time. They all share the ability to change microtubule properties. The profound effects of disrupted microtubule systems on cell physiology can be used in research as well as anticancer treatment and agricultural weed control. The activity of microtubule drugs generally depends on their binding to α- and β-tubulin subunits. The microtubule drugs are often effective only in certain taxonomic groups, while other organisms remain resistant. Available information on the molecular basis of this selectivity is summarized. In addition to reviewing published data, we performed sequence data mining, searching for kingdom-specific signatures in plant, animal, fungal, and protozoan tubulin sequences. Our findings clearly correlate with known microtubule drug resistance determinants and add more amino acid positions with a putative effect on drug-tubulin interaction. The issue of microtubule network properties in plant cells producing microtubule drugs is also addressed.

A review of chemotherapeutic approaches to the treatment of cryptosporidiosis

This review focuses on chemotherapies used against the parasite, Cryptosporidium parvum, the causative agent of cryptosporidiosis. Populations at risk from severe morbidity or mortality from cryptosporidiosis are discussed with particular reference to those infected with HIV. The review then examines chemotherapies used in the clinical setting, as well as a number of in vitro and in vivo experimental studies. It begins with a discussion of the targets within Cryptosporidium that have been the foci of past treatments and then examines novel target sites that may present an exploitable alternative. Some of the novel target sites discussed include the recently discovered apicomplexan plastid and its associated pathways. Lastly, the review examines tubulin as a potential anticryptosporidial target in view of the fact that it has been exploited successfully for almost 50 years for the treatment of helminthiasis. The review concludes with a five-year outlook on the future of anticryptosporidial drug design.

The bat flower: a source of microtubule-destabilizing and -stabilizing compounds with synergistic antiproliferative actions

The biosynthesis of secondary metabolites provides higher plants with mechanisms of defense against microbes, insects, and herbivores. One common cellular target of these molecules is the highly conserved microtubule cytoskeleton, and microtubule-targeting compounds with insecticidal, antifungal, nematicidal, and anticancer activities have been identified from plants. A new retro-dihydrochalcone, taccabulin A, with microtubule-destabilizing activity has been identified from the roots and rhizomes of Tacca species. This finding is notable because the microtubule-stabilizing taccalonolides are also isolated from these sources. This is the first report of an organism producing compounds with both microtubule-stabilizing and -destabilizing activities. A two-step chemical synthesis of taccabulin A was performed. Mechanistic studies showed that taccabulin A binds within the colchicine site on tubulin and has synergistic antiproliferative effects against cancer cells when combined with a taccalonolide, which binds to a different site on tubulin. Taccabulin A is effective in cells that are resistant to many other plant-derived compounds. The discovery of a natural source that contains both microtubule-stabilizing and -destabilizing small molecules is unprecedented and suggests that the synergistic action of these compounds was exploited by nature long before it was discovered in the laboratory.

Synthesis of a 2-aryl-3-aroyl indole salt (OXi8007) resembling combretastatin A-4 with application as a vascular disrupting agent

The natural products colchicine and combretastatin A-4 are potent inhibitors of tubulin assembly, and they have inspired the design and synthesis of a large number of small-molecule, potential anticancer agents. The indole-based molecular scaffold is prominent among these SAR modifications, leading to a rapidly increasing number of agents. The water-soluble phosphate prodrug 33 (OXi8007) of 2-aryl-3-aroylindole-based phenol 8 (OXi8006) was prepared by chemical synthesis and found to be strongly cytotoxic against selected human cancer cell lines (GI₅₀ = 36 nM against DU-145 cells, for example). The free phenol, 8 (OXi8006), was a strong inhibitor (IC₅₀ = 1.1 μM) of tubulin assembly. The corresponding phosphate prodrug 33 (OXi8007) also demonstrated pronounced interference with tumor vasculature in a preliminary in vivo study utilizing a SCID mouse model bearing an orthotopic PC-3 (prostate) tumor as imaged by color Doppler ultrasound. The combination of these results provides evidence that the indole-based phosphate prodrug 33 (OXi8007) functions as a vascular disrupting agent that may prove useful for the treatment of cancer.

Lipophilic prodrugs of a triazole-containing colchicine analogue in liposomes: biological effects on human tumor cells

Colchicine site binders--blockers of tubulin polymerization--are potential antimitotic agents for anticancer therapy. To reduce their systemic toxicity and improve biodistribution, encapsulation in nanosized liposomes may be employed. Liposomes present a convenient means for preparation of injectable formulations of hydrophobic compounds, however colchicine as such is known to leak through the lipid bilayer. In this study, newly synthesized triazole-containing analogues of colchicine and allocolchicine, and their palmitic and oleic esters (lipophilic prodrugs) were tested for anti-proliferative activity and apoptosis-inducing potential. In contrast to colchicine conjugates, whose activities ranged with those of colchicine, allocolchicine derivatives exhibited drastically lower effects and were discarded. Liposomes of about 100 nm in diameter composed of egg phosphatidylcholine--yeast phosphatidylinositol--palmitic or oleic prodrug, 8 : 1: 1, by mol, were prepared by standard extrusion technique and tested in a panel of four human tumor cell lines. Liposome formulations preserved the biological activities of the parent colchicinoid the most towards human epithelial tumor cells. Moreover, liposomal form of the oleoyl bearing colchicinoid inhibited cell proliferation more efficiently than free lipophilic prodrug. Due to substantial loading capacity of the liposomes, the dispersions contain sufficient concentration of the active agent to test wide dose range in experiments on systemic administration to animals.

Phenolphthalein induces centrosome amplification and tubulin depolymerization in vitro

Aneuploidy is a major cause of human reproductive failure and plays a large role in cancer. Phenolphthalein (PHT) induces tumors in rodents but its primary mechanism does not seem to be DNA damage. In heterozygous TSG-p53(®) mice, PHT induces lymphomas and also micronuclei (MN), many containing kinetochores (K), implying chromosome loss (aneuploidy). The induction of aneuploidy would be compatible with the loss of the normal p53 gene seen in the lymphomas. In this study, we confirm PHT's aneugenicity and determine the aneugenic mechanism of PHT by combining traditional genetic toxicology assays with image and flow cytometry methods. The data revealed that PHT induces tubulin polymerization abnormalities and deregulates the centrosome duplication cycle causing centrosome amplification. We also show that one of the consequences of these events is apoptosis.

Molecular biology of castration-resistant prostate cancer: basis for the novel therapeutic targets

Prostate cancer cells express the androgen receptor (AR) and need the presence of androgens to survive. Androgen suppression is the gold standard first-line therapy for metastatic disease. Almost all prostate cancer patients initially respond to hormonal therapy, but most of them gradually develop castration-resistant progression. Recent evidence has shown that progression at the castration resistant prostate cancer (CRPC) stage is often mediated by AR signalling. Importantly, subsequent AR androgen inhibition, by abiraterone acetate or enzalutamide, has shown to improve patients' survival. Several mechanisms that enhance AR signalling in an androgen-depleted environment have been elucidated:(1) AR mutations that allow activation by low androgen levels or by other endogenous steroids, (2) AR amplification and/or overexpression,(3)increased local intracrine synthesis of androgens, (4) changes in AR cofactors and (5) cross-talk with cytokines and growth factors. Today, there are under development a number of novel agents targeting the AR signaling pathway. This article reviews the postulated mechanisms of AR-driven resistance to androgen suppression that have contributed to the development of new hormonal therapeutic strategies in prostate cancer.

Cytoskeletal alterations that confer resistance to anti-tubulin chemotherapeutics

Drugs that target microtubules are a successful class of anti-cancer agents that have been in clinical use for over two decades. Acquired resistance to these drugs, however, remains a serious problem. Microtubule alterations, such as tubulin mutations and altered β- tubulin isotype expression, are prominent factors in development of resistance. Changes in actin and intermediate filament proteins can also mediate sensitivity to microtubule-targeting drugs. This review focuses on the mechanisms by which alterations in cytoskeletal proteins lead to drug resistance. This information will be helpful for improving the targeting of microtubule toxins.

Induction of apoptosis, G₀/G₁ phase arrest and microtubule disassembly in K562 leukemia cells by Mere15, a novel polypeptide from Meretrix meretrix Linnaeus

Mere15 is a novel polypeptide from Meretrix meretrix Linnaeus with cytotoxicity in solid cancer cells. In this study, we investigated its activity on human K562 chronic myelogenous leukemia cells. Mere15 inhibited the growth of K562 cells with IC₅₀ values of 38.2 μg/mL. Mere15 also caused concentration dependent induction of apoptosis, with overproduction of reactive oxygen species and loss of mitochondrial membrane potential. Moreover, Mere15 arrested cell cycle progression at G₀/G₁ phase of K562 cells in a concentration dependent manner. In addition, Mere15 caused the disassembly of the microtubule cytoskeleton in K562 cells and inhibited the polymerization of tubulin in a cell free system via interaction with tubulin. We concluded that Mere15 was cytotoxic to K562 leukemia cells and the cytotoxicity was related to the apoptosis induction, cell cycle arrest and microtubule disassembly. These results implied that Merer15 was a broad spectrum anticancer polypeptide, not only cytotoxic to various solid cancer cells but also to the chronic myelogenous leukemia cells. Mere15 may have therapeutic potential for the treatment of leukemia.

Chalcone JAI-51 improves efficacy of synchrotron microbeam radiation therapy of brain tumors

Microbeam radiation therapy (MRT), a preclinical form of radiosurgery, uses spatially fractionated micrometre-wide synchrotron-generated X-ray beams. As MRT alone is predominantly palliative for animal tumors, the effects of the combination of MRT and a newly synthesized chemotherapeutic agent JAI-51 on 9L gliosarcomas have been evaluated. Fourteen days (D14) after implantation (D0), intracerebral 9LGS-bearing rats received either MRT, JAI-51 or both treatments. JAI-51, alone or immediately after MRT, was administered three times per week. Animals were kept up to ∼20 weeks after irradiation or sacrificed at D16 or D28 after treatment for cell cycle analysis. MRT plus JAI-51 increased significantly the lifespan compared with MRT alone (p = 0.0367). JAI-51 treatment alone had no effect on rat survival. MRT alone or associated with JAI-51 induced a cell cycle blockade in G2/M (p < 0.01) while the combined treatment also reduced the proportion of G0/G1 cells. At D28 after irradiation, MRT and MRT/JAI-51 had a smaller cell blockade effect in the G2/M phase owing to a significant increase in tumor cell death rate (<2c) and a proportional increase of endoreplicative cells (>8c). The combination of MRT and JAI-51 increases the survival of 9LGS-bearing rats by inducing endoreduplication of DNA and tumor cell death; further, it slowed the onset of tumor growth resumption two weeks after treatment.

Pretubulysin: from hypothetical biosynthetic intermediate to potential lead in tumor therapy

Pretubulysin is a natural product that is found in strains of myxobacteria in only minute amounts. It represents the first enzyme-free intermediate in the biosynthesis of tubulysins and undergoes post-assembly acylation and oxidation reactions. Pretubulysin inhibits the growth of cultured mammalian cells, as do tubulysins, which are already in advanced preclinical development as anticancer and antiangiogenic agents. The mechanism of action of this highly potent compound class involves the depolymerization of microtubules, thereby inducing mitotic arrest. Supply issues with naturally occurring derivatives can now be circumvented by the total synthesis of pretubulysin, which, in contrast to tubulysin, is synthetically accessible in gram-scale quantities. We show that the simplified precursor is nearly equally potent to the parent compound. Pretubulysin induces apoptosis and inhibits cancer cell migration and tubulin assembly in vitro. Consequently, pretubulysin appears to be an ideal candidate for future development in preclinical trials and is a very promising early lead structure in cancer therapy.

The relative effect of citral on mitotic microtubules in wheat roots and BY2 cells

The plant volatile monoterpene citral is a highly active compound with suggested allelopathic traits. Seed germination and seedling development are inhibited in the presence of citral, and it disrupts microtubules in both plant and animal cells in interphase. We addressed the following additional questions: can citral interfere with cell division; what is the relative effect of citral on mitotic microtubules compared to interphase cortical microtubules; what is its effect on newly formed cell plates; and how does it affect the association of microtubules with γ-tubulin? In wheat seedlings, citral led to inhibition of root elongation, curvature of newly formed cell walls and deformation of microtubule arrays. Citral's effect on microtubules was both dose- and time-dependent, with mitotic microtubules appearing to be more sensitive to citral than cortical microtubules. Association of γ-tubulin with microtubules was more sensitive to citral than were the microtubules themselves. To reveal the role of disrupted mitotic microtubules in dictating aberrations in cell plates in the presence of citral, we used tobacco BY2 cells expressing GFP-Tua6. Citral disrupted mitotic microtubules, inhibited the cell cycle and increased the frequency of asymmetric cell plates in these cells. The time scale of citral's effect in BY2 cells suggested a direct influence on cell plates during their formation. Taken together, we suggest that at lower concentrations, citral interferes with cell division by disrupting mitotic microtubules and cell plates, and at higher concentrations it inhibits cell elongation by disrupting cortical microtubules.

Inhibition of tubulin polymerization by hypochlorous acid and chloramines

Protein thiol oxidation and modification by nitric oxide and glutathione are emerging as common mechanisms to regulate protein function and to modify protein structure. Also, thiol oxidation is a probable outcome of cellular oxidative stress and is linked to degenerative disease progression. We assessed the effect of the oxidants hypochlorous acid and chloramines on the cytoskeletal protein tubulin. Total cysteine oxidation by the oxidants was monitored by labeling tubulin with the thiol-selective reagent 5-iodoacetamidofluorescein; by reaction with Ellman's reagent, 5,5'-dithiobis(2-nitrobenzoic acid); and by detecting interchain tubulin disulfides by Western blot under nonreducing conditions. Whereas HOCl induced both cysteine and methionine oxidation of tubulin, chloramines were predominantly cysteine oxidants. Cysteine oxidation of tubulin, rather than methionine oxidation, was associated with loss of microtubule polymerization activity, and treatment of oxidized tubulin with disulfide reducing agents restored a considerable portion of the polymerization activity that was lost after oxidation. By comparing the reactivity of hypochlorous acid and chloramines with the previously characterized oxidants, peroxynitrite and the nitroxyl donor Angeli's salt, we have identified tubulin thiol oxidation, not methionine oxidation or tyrosine nitration, as a common outcome responsible for decreased polymerization activity.

A perspective on vascular disrupting agents that interact with tubulin: preclinical tumor imaging and biological assessment

The tumor microenvironment provides a rich source of potential targets for selective therapeutic intervention with properly designed anticancer agents. Significant physiological differences exist between the microvessels that nourish tumors and those that supply healthy tissue. Selective drug-mediated damage of these tortuous and chaotic microvessels starves a tumor of necessary nutrients and oxygen and eventually leads to massive tumor necrosis. Vascular targeting strategies in oncology are divided into two separate groups: angiogenesis inhibiting agents (AIAs) and vascular disrupting agents (VDAs). The mechanisms of action between these two classes of compounds are profoundly distinct. The AIAs inhibit the actual formation of new vessels, while the VDAs damage and/or destroy existing tumor vasculature. One subset of small-molecule VDAs functions by inhibiting the assembly of tubulin into microtubules, thus causing morphology changes to the endothelial cells lining the tumor vasculature, triggered by a cascade of cell signaling events. Ultimately this results in catastrophic damage to the vessels feeding the tumor. The rapid emergence and subsequent development of the VDA field over the past decade has led to the establishment of a synergistic combination of preclinical state-of-the-art tumor imaging and biological evaluation strategies that are often indicative of future clinical efficacy for a given VDA. This review focuses on an integration of the appropriate biochemical and biological tools necessary to assess (preclinically) new small-molecule, tubulin active VDAs for their potential to be clinically effective anticancer agents.

Sleeping sickness pathogen (Trypanosoma brucei) and natural products: therapeutic targets and screening systems

Trypanosoma brucei is the causative agent of human African trypanosomiasis (sleeping sickness) which is fatal if left untreated. This disease occurs in 36 African countries, south of the Sahara, where 60 million people are at risk of acquiring infection. The current chemotherapy relies on only four drugs, three of which were developed more than 60 years ago. These drugs have many limitations, ranging from oral inabsorption, acute toxicities, short duration of action and the emergence of trypanosomal resistance. Despite decades of use of most of the current trypanocides, little is known about their mode of action. That being said, African trypanosomes continue to be among the most extensively studied parasitic protists to date. Many of their intriguing biological features have been well documented and can be viewed as attractive targets for antitrypanosomal chemotherapy. A considerable number of natural products with diverse molecular structures have revealed antiparasitic potency in the laboratory and represent interesting lead compounds for the development of new and urgently needed antiparasitics. The major validated drug targets in T. brucei are discussed with particular emphasis on those known to be attacked by natural compounds.

Protoflavonoids from ferns impair centrosomal integrity of tumor cells

Six protoflavonoids, including two new compounds, were isolated during a large scale screening of fern extracts for original interaction with mitosis. The new compounds isolated from PHEGOPTERIS decursive-pinnata and EQUISETUM fluviatile were 2',3'-dihydroprotogenkwanone (1) and 2',3'-dihydro-2'-hydroxyprotoapigenone (2). Known compounds were: protoapigenone, protogenkwanone, protoapigenin, and 4'- O- β-D-glucopyranosyl protoapigenin. They showed a cytotoxic activity against HeLa cells at a micromolar level. IC₅₀ values were 2 µM for compound 1 > 10 µM for compound 2, and respectively 2.4, 0.6, > 10 µM for the known compounds. Their cytotoxic effects were associated with phenotypic changes never observed before and characterized by the loss of centrosomal γ-tubulin labelling in both mitotic and interphasic cells.

Central nervous system delivery of the antipsychotic olanzapine induces hepatic insulin resistance

OBJECTIVE

Olanzapine (OLZ) is an atypical antipsychotic whose clinical efficacy is hampered by side effects including weight gain and diabetes. Recent evidence shows that OLZ alters insulin sensitivity independent of changes in body weight and composition. The present study addresses whether OLZ-induced insulin resistance is driven by its central actions.

RESEARCH DESIGN AND METHODS

Sprague-Dawley rats received an intravenous (OLZ-IV group) or intracerebroventricular (OLZ-ICV group) infusion of OLZ or vehicle. Glucose kinetics were assessed before (basal period) and during euglycemic-hyperinsulinemic clamp studies.

RESULTS

OLZ-IV caused a transient increase in glycemia and a higher rate of glucose appearance (R(a)) in the basal period. During the hyperinsulinemic clamp, the glucose infusion rate (GIR) required to maintain euglycemia and the rate of glucose utilization (R(d)) were decreased in OLZ-IV, whereas endogenous glucose production (EGP) rate was increased compared with vehicle-IV. Consistent with an elevation in EGP, the OLZ-IV group had higher hepatic mRNA levels for the enzymes glucose-6-phosphatase and phosphoenolpyruvate carboxykinase. Phosphorylation of hypothalamic AMP-activated protein kinase (AMPK) was increased in OLZ-IV rats compared with controls. Similarly, an intracerebroventricular infusion of OLZ resulted in a transient increase in glycemia as well as a higher R(a) in the basal period. During the hyperinsulinemic period, OLZ-ICV caused a decreased GIR, an increased EGP, but no change in R(d). Furthermore, OLZ-ICV rats had increased hepatic gluconeogenic enzymes and elevated hypothalamic neuropeptide-Y and agouti-related protein mRNA levels.

CONCLUSIONS

Acute central nervous system exposure to OLZ induces hypothalamic AMPK and hepatic insulin resistance, pointing to a hypothalamic site of action for the metabolic dysregulation of atypical antipsychotics.

Aqueous extract of ginger shows antiproliferative activity through disruption of microtubule network of cancer cells

Ginger has a long history of use as traditional medicine for varied human disease. Our present study has shown that the aqueous extract of ginger (GAE) interacts directly with cellular microtubules and disrupts its structure and induces apoptosis of cancer cells as well. The IC(50) values of GAE, as determined from cell viability experiment on human non-small lung epithelium cancer (A549) cells and human cervical epithelial carcinoma (HeLa), were 239.4+7.4 and 253.4+8.9 μg/ml, respectively. It has been found that the apoptosis of A549 cells by GAE is mediated by up regulation of tumor suppressor gene p53 and alteration of the normal Bax/Bcl-2 ratio followed by down regulation of cellular pro-caspase3. The morphological change of cells upon GAE treatment has also been demonstrated. Both the structural and functional properties of tubulin and microtubule were lost, as confirmed by both ex vivo and invitro experiments. The major component of GAE is poly-phenols (around 2.5%), which consist of ∼ 80% flavones and flavonols. Poly-phenolic compounds are well known to have anti-mitotic properties, and may be further screened for the development of a potential anti-cancer agent.

Natural product Celastrol destabilizes tubulin heterodimer and facilitates mitotic cell death triggered by microtubule-targeting anti-cancer drugs

BACKGROUND

Microtubule drugs are effective anti-cancer agents, primarily due to their ability to induce mitotic arrest and subsequent cell death. However, some cancer cells are intrinsically resistant or acquire a resistance. Lack of apoptosis following mitotic arrest is thought to contribute to drug resistance that limits the efficacy of the microtubule-targeting anti-cancer drugs. Genetic or pharmacological agents that selectively facilitate the apoptosis of mitotic arrested cells present opportunities to strengthen the therapeutic efficacy.

METHODOLOGY AND PRINCIPAL FINDINGS

We report a natural product Celastrol targets tubulin and facilitates mitotic cell death caused by microtubule drugs. First, in a small molecule screening effort, we identify Celastrol as an inhibitor of neutrophil chemotaxis. Subsequent time-lapse imaging analyses reveal that inhibition of microtubule-mediated cellular processes, including cell migration and mitotic chromosome alignment, is the earliest events affected by Celastrol. Disorganization, not depolymerization, of mitotic spindles appears responsible for mitotic defects. Celastrol directly affects the biochemical properties of tubulin heterodimer in vitro and reduces its protein level in vivo. At the cellular level, Celastrol induces a synergistic apoptosis when combined with conventional microtubule-targeting drugs and manifests an efficacy toward Taxol-resistant cancer cells. Finally, by time-lapse imaging and tracking of microtubule drug-treated cells, we show that Celastrol preferentially induces apoptosis of mitotic arrested cells in a caspase-dependent manner. This selective effect is not due to inhibition of general cell survival pathways or mitotic kinases that have been shown to enhance microtubule drug-induced cell death.

CONCLUSIONS AND SIGNIFICANCE

We provide evidence for new cellular pathways that, when perturbed, selectively induce the apoptosis of mitotic arrested cancer cells, identifying a potential new strategy to enhance the therapeutic efficacy of conventional microtubule-targeting anti-cancer drugs.

Anti-leukaemic effects of two extract types of Lactuca sativa correlate with the activation of Chk2, induction of p21, downregulation of cyclin D1 and acetylation of alpha-tubulin

The water extract of the lettuce Lactuca sativa, but not the ethyl acetate extract, inhibited the growth of HL-60 leukaemia cells and MCF-7 breast cancer cells. This correlated with the activation of checkpoint kinase 2 (Chk2), the induction of the tumour suppressor p21, and the severe downregulation of the proto-oncogene cyclin D1. The ethyl acetate extract, but not the water extract, induced HL-60 cell death, which correlated with the acetylation of alpha-tubulin. The acetylation of alpha-tubulin is indicative for microtubuli stabilisation such as induced by taxol. The calculated amount for human intake would require approximately 3 kg lettuce to reach the required concentration shown to inhibit 50% HL-60 proliferation.

Mechanical dynamics of single cells during early apoptosis

Dynamic mechanical properties of cells are becoming recognized as indicators and regulators of physiological processes such as differentiation, malignant phenotypes and mitosis. A key process in development and homeostasis is apoptosis and whilst the molecular control over this pathway is well studied, little is known about the mechanical consequences of cell death. Here, we study the caspase-dependent mechanical kinetics of single cells during early apoptosis initiated with the general protein-kinase inhibitor staurosporine. This results in internal remodelling of the cytoskeleton and nucleus which is reflected in dynamic changes in the mechanical properties of the cell. Utilizing simultaneous confocal and atomic force microscopy (AFM), we measured distinct mechanical dynamics in the instantaneous cellular Young's Modulus and longer timescale viscous deformation. This allowed us to visualize time-dependent nuclear and cytoskeletal control of force dissipation with fluorescent fusion proteins throughout the cell. This work reveals that the cell death program not only orchestrates biochemical dynamics but also controls the mechanical breakdown of the cell. Importantly, the consequences of mechanical disregulation during apoptosis may be a contributing factor to several human pathologies through the poorly timed release of dead cells and cell debris.

Regulation of microtubule dynamic instability in vitro by differentially phosphorylated stathmin

Stathmin is an important regulator of microtubule polymerization and dynamics. When unphosphorylated it destabilizes microtubules in two ways, by reducing the microtubule polymer mass through sequestration of soluble tubulin into an assembly-incompetent T2S complex (two alpha:beta tubulin dimers per molecule of stathmin), and by increasing the switching frequency (catastrophe frequency) from growth to shortening at plus and minus ends by binding directly to the microtubules. Phosphorylation of stathmin on one or more of its four serine residues (Ser(16), Ser(25), Ser(38), and Ser(63)) reduces its microtubule-destabilizing activity. However, the effects of phosphorylation of the individual serine residues of stathmin on microtubule dynamic instability have not been investigated systematically. Here we analyzed the effects of stathmin singly phosphorylated at Ser(16) or Ser(63), and doubly phosphorylated at Ser(25) and Ser(38), on its ability to modulate microtubule dynamic instability at steady-state in vitro. Phosphorylation at either Ser(16) or Ser(63) strongly reduced or abolished the ability of stathmin to bind to and sequester soluble tubulin and its ability to act as a catastrophe factor by directly binding to the microtubules. In contrast, double phosphorylation of Ser(25) and Ser(38) did not affect the binding of stathmin to tubulin or microtubules or its catastrophe-promoting activity. Our results indicate that the effects of stathmin on dynamic instability are strongly but differently attenuated by phosphorylation at Ser(16) and Ser(63) and support the hypothesis that selective targeting by Ser(16)-specific or Ser(63)-specific kinases provides complimentary mechanisms for regulating microtubule function.

Cytotoxic asterosaponins capable of promoting polymerization of tubulin from the starfish Culcita novaeguineae

Four new asterosaponins, novaeguinosides A (1), B (2), C (3), and D (4), were isolated from the bioactive fraction of the starfish Culcita novaeguineae, as active compounds capable of promoting polymerization of tubulin. Their structures were elucidated by extensive spectroscopic studies and chemical evidence. Compounds 1 and 3 are characterized by sulfated side chains not previously found in asterosaponins, and 1 is the first example of a trisulfated asterosaponin. In the side chains of 2 and 4, the 26-carboxylic acid function is found as an amide derivative of taurine, which is a rare feature and first encountered among asterosaponins. All the asterosaponins showed cytotoxicity against two human tumor cell lines.

The microtubule-active antitumor compound TTI-237 has both paclitaxel-like and vincristine-like properties

PURPOSE

To compare TTI-237 (5-chloro-6-[2,6-difluoro-4-[3-(methylamino)propoxy]phenyl]-N-[(1S)-2,2,2-trifluoro-1-methylethyl]-[1, 2, 4]triazolo[1,5-a]pyrimidin-7-amine butanedioate) with paclitaxel and vincristine in order to better understand the properties of this new anti-microtubule agent.

METHODS

Tubulin polymerization and depolymerization were followed by turbidimetric assays. Effects of compounds on the binding of [(3)H]guanosine triphosphate ([(3)H]GTP) to tubulin were studied by competition binding assays. Effects of compounds on the phosphorylation of a panel of intracellular proteins were determined by flow cytometry using phosphoprotein-specific antibodies.

RESULTS

At low molar ratios of TTI-237:tubulin heterodimer (about 1:30), TTI-237 enhanced depolymerization kinetics in response to low temperature, but stabilized the aggregates at higher ratios (about 1:4). Similarly, the aggregates induced in microtubule protein by TTI-237 were depolymerized by excess Ca(++) at low TTI-237:tubulin-heterodimer molar ratios, but were stable at higher ratios. TTI-237 inhibited the exchange of [(3)H]GTP at the exchangeable nucleotide site of the tubulin heterodimer, and was similar to vincristine in its effects on the phosphorylation of eight intracellular proteins in HeLa cells.

CONCLUSIONS

TTI-237 has properties that distinguish it from typical vinca-site and taxoid-site ligands, and therefore it may exemplify a new class of microtubule-active compounds.

Microtubule disruption with BAPTA and dimethyl BAPTA by a calcium chelation-independent mechanism in 3T3-L1 adipocytes

While the physiological role for calcium in the insulin action on glucose transport has been disputed, it was reassessed in a recent study by using a calcum chelator, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, tetra(acetoxymethyl) ester (BAPTA-AM). Although BAPTA has been widely used to study the role for calcium in a variety of cell functions, it has also been suggested to have properties unrelated to the calcium chelating activity. Here, we investigated the effects of BAPTA and dimethyl BAPTA on the cytoskeletons in 3T3-L1 adipocytes. Both calcium chelators were successfully loaded in 3T3-L1 adipocytes and inhibited endothelin-1-induced cytosolic calcium elevation. Confocal fluorescence microscopy revealed that BAPTA and dimethyl BAPTA caused profound depolymerization of the microtubules without affecting the cortical actin filaments in 3T3-L1 adipocytes. Biochemical quantification also showed that BAPTA and dimethyl BAPTA significantly decreased the amount of polymerized tubulin but had little effect on filamentous actin. Consistent with these results, GLUT4-positive perinuclear compartments were dispersed throughout the cytoplasm in BAPTA- or dimethyl BAPTA-loaded adipocytes. Intriguingly, these calcium chelators did not disrupt the microtubules in undifferentiated preadipocytes. The microtubule-depolymerizing property of BAPTA and dimethyl BAPTA is unrelated to calcium chelation, since the microtubules were resistant to depletion of cytosolic calcium by using a calcium ionophore A23187. Insulin-stimulated glucose transport was not affected by cytosolic calcium depletion with A23187, but significantly inhibited with BAPTA and dimethyl BAPTA to the extent similar to that with nocodazole. BAPTA and its derivatives should be used with caution in studies of cytoskeleton-related cell functions.

Synthesis, tubulin assembly, and antiproliferative activity against MCF7 and NCI/ADR-RES cancer cells of 10-O-acetyl-5'-hydroxybutitaxel

A highly efficient kinetic resolution of racemic cis-4-(2-tert-butyldimethylsilyloxy-1,1-dimethyl)ethyl-3-tert-butyldimethylsilyloxy-azetidin-2-one with 7-O-triethylsilylbaccatin III was carried out to furnish 10-O-acetyl-5'-hydroxybutitaxel after removal of the silyl protecting groups. The compound was 50% as active as paclitaxel in a tubulin assembly assay and showed significantly decreased activity against MCF7 cell proliferation compared to paclitaxel.

Docking Study of Ligands into the Colchicine Binding Site of Tubulin

Cancer is a major cause of mortality in developed countries, following only cardiovascular diseases. Death of cancerous cells can be achieved by stopping mitosis and the antimitotic class of drugs formed by the spindle poisons can be used for this purpose. Their role is to disorganize the mitotic spindle by targeting its main constituent, the microtubules, themselves made of heterodimers of alpha and beta-tubulin. They disrupt the dynamics of the microtubules either by stabilizing them, as do paclitaxel or epothilones, or destabilizing them, as do colchicine. The binding site of colchicine seems to lie between the two units of the tubulin dimer. Here, we report on the characterization of this site by the docking of a series of reference compounds, and the subsequent docking of ligands prepared in our laboratory.

The effects of chromium VI on the fitness and on the beta-tubulin genes during in vivo development of the nematode Steinernema feltiae

The entomopathogenic nematode (EPN), Steinernema feltiae, is a commonly occurring nematode in the soil in Ireland. Consequently, we have conducted investigations as to the utility of this species as a candidate organism for the detection of chromium in Irish soils. These experiments have demonstrated that S. feltiae can survive and reproduce in the presence of high concentrations of chromium VI. It was observed that concentrations as high as 1000 ppm have little effect on the ability of this organism to produce large numbers of progeny. Nematodes were not observed to reproduce above 1800 ppm. However, an increase in development times for the nematode in vivo was noted at concentrations of 400 ppm upwards. This paper also illustrates the effects upon the beta-tubulin genes within nematode populations exposed to chromium VI in vivo. DNA sequencing has shown that elevated levels of variations occur among the population treatments, although these variations do not appear to be dependent upon chromium concentration. These findings constitute this organism appropriate for further investigation for the development of sub-lethal end points and biomarkers for the detection and biomonitoring of chromium VI contamination in soil.

Syntheses and cytotoxic properties of the curcumin analogs 2,6-bis(benzylidene)-4-phenylcyclohexanones

Fifteen curcumin analogs were synthesized and tested for in-vitro cytotoxicity towards B16 and L1210 murine cancer cell lines using an MTT assay. Significant activity was discovered for two analogs: 8 (B16 IC(50) = 1.6 microM; L1210 IC(50) = 0.35 microM) and 9 (B16 IC(50) = 0.51 microM; L1210 IC(50 )= 1.2 microM). Several other analogs exhibited notable cytotoxicity. The data from quantitative structure-activity relationships suggest that large electron-withdrawing substituents placed in the meta-position of the arylidene aryl rings enhance potencies. Compounds 8 and 9 were found using a cell-based assay to have virtually no effects on microtubules at concentrations up to 40 microM. These results suggest that tubulin inhibition is not the principal mechanism by which the curcumin analogs act.