The Microtubule-Targeting Agent Pretubulysin Impairs the Inflammatory Response in Endothelial Cells by a JNK-Dependent Deregulation of the Histone Acetyltransferase Brd4

The anti-inflammatory effects of depolymerizing microtubule-targeting agents on leukocytes are known for a long time, but the potential involvement of the vascular endothelium and the underlying mechanistic basis is still largely unclear. Using the recently synthesized depolymerizing microtubule-targeting agent pretubulysin, we investigated the anti-inflammatory potential of pretubulysin and other microtubule-targeting agents with respect to the TNF-induced leukocyte adhesion cascade in endothelial cells, to improve our understanding of the underlying biomolecular background. We found that treatment with pretubulysin reduces inflammation in vivo and in vitro via inhibition of the TNF-induced adhesion of leukocytes to the vascular endothelium by down-regulation of the pro-inflammatory cell adhesion molecules ICAM-1 and VCAM-1 in a JNK-dependent manner. The underlying mechanism includes JNK-induced deregulation and degradation of the histone acetyltransferase Bromodomain-containing protein 4. This study shows that depolymerizing microtubule-targeting agents, in addition to their established effects on leukocytes, also significantly decrease the inflammatory activation of vascular endothelial cells. These effects are not based on altered pro-inflammatory signaling cascades, but require deregulation of the capability of cells to enter constructive transcription for some genes, setting a baseline for further research on the prominent anti-inflammatory effects of depolymerizing microtubule-targeting agents.

Organotin Benzohydroxamate Derivatives (OTBH) Target Colchicine-binding Site Exerting Potent Antitumor Activity both in Vitro and Vivo Revealed by Quantitative Proteomic Analysis

The activity of four typical organotin benzohydroxamate compounds (OTBH) with the different electronegativity of fluorine and chlorine atoms was assessed both in vitro and in vivo, revealing that they all exhibited notable antitumor effects. Furthermore, it was discovered that the biochemical capacity against cancer was influenced by their substituents' electronegativity and structural symmetry. For instance, benzohydroxamate derivatives with single chlorine at the fourth site on the benzene ring, two normal-butyl organic ligands, a symmetrical structure, and so on ([n-Bu₂Sn[{4-ClC₆H₄C(O)NHO}₂] (OTBH-1)) had stronger antitumor activity than others. Furthermore, the quantitative proteomic analysis discovered 203 proteins in HepG2 cells and 146 proteins in rat liver tissues that were differently identified before and after administration. Simultaneously, bioinformatics analysis of differentially expressed proteins demonstrated that the antiproliferative effects involved in the microtubule-based process, tight junction and its downstream apoptosis pathways. As predicted analytically, molecular docking indicated that ''-O-'' were the target docking atoms for the colchicine-binding site; meanwhile, this site was additionally verified by the EBI competition experiment and the microtubule assembly inhibition test. In conclusion, these derivatives promising for developing microtubule-targeting agents (MTAs) were shown to target the colchicine-binding site, impair cancer cell microtubule networks, and then halt mitosis and trigger apoptosis.

Drug-repurposing screen on patient-derived organoids identifies therapy-induced vulnerability in KRAS-mutant colon cancer

Patient-derived organoids (PDOs) are widely heralded as a drug-screening platform to develop new anti-cancer therapies. Here, we use a drug-repurposing library to screen PDOs of colorectal cancer (CRC) to identify hidden vulnerabilities within therapy-induced phenotypes. Using a microscopy-based screen that accurately scores drug-induced cell killing, we have tested 414 putative anti-cancer drugs for their ability to switch the EGFRi/MEKi-induced cytostatic phenotype toward cytotoxicity. A majority of validated hits (9/37) are microtubule-targeting agents that are commonly used in clinical oncology, such as taxanes and vinca-alkaloids. One of these drugs, vinorelbine, is consistently effective across a panel of >25 different CRC PDOs, independent of RAS mutational status. Unlike vinorelbine alone, its combination with EGFR/MEK inhibition induces apoptosis at all stages of the cell cycle and shows tolerability and effective anti-tumor activity in vivo, setting the basis for a clinical trial to treat patients with metastatic RAS-mutant CRC.

Destabilization of microrchidia family CW-type zinc finger 2 via the cyclin-dependent kinase 1-chaperone-mediated autophagy pathway promotes mitotic arrest and enhances cancer cellular sensitivity to microtubule-targeting agents

BACKGROUND

Microtubule-targeing agents (MTAs), such as paclitaxel (PTX) and vincristine (VCR), kill cancer cells through activtion of the spindle assembly checkpoint (SAC) and induction of mitotic arrest, but the development of resistance poses significant clinical challenges.

METHODS

Immunoblotting and RT-qPCR were used to investigate potential function and related mechanism of MORC2. Flow cytometry analyses were carried out to determine cell cycle distribution and apoptosis. The effect of MORC2 on cellular sensitivity to PTX and VCR was determined by immunoblotting, flow cytometry, and colony formation assays. Immunoprecipitation assays and immunofluorescent staining were utilized to investigate protein-protein interaction and protein co-localization.

RESULTS

Here, we identified microrchidia family CW-type zinc finger 2 (MORC2), a poorly characterized oncoprotein, as a novel regulator of SAC activation, mitotic progression, and resistance of cancer cells to PTX and VCR. Mechanically, PTX and VCR activate cyclin-dependent kinase 1, which in turn induces MORC2 phosphorylation at threonine 717 (T717) and T733. Phosphorylated MORC2 enhances its interation with HSPA8 and LAMP2A, two essential components of the chaperone-mediated autophagy (CMA) mechinery, resulting in its autophagic degradation. Degradation of MORC2 during mitosis leads to SAC activation through stabilizing anaphase promoting complex/cyclosome activator protein Cdc20 and facilitating mitotic checkpoint complex assembly, thus contributing to mitotic arrest induced by PTX and VCR. Notably, knockdown of MORC2 promotes mitotic arrest induced by PTX and VCR and enhances the sensitivity of cancer cells to PTX and VCR.

CONCLUSIONS

Collectively, these findings unveil a previously unrecognized function and regulatory mechanism of MORC2 in mitotic progression and resistance of cancer cells to MTAs. These results also provide a new clue for developing combined treatmentstrategy by targeting MORC2 in combination with MTAs against human cancer.

β-III Tubulin Levels Determine the Neurotoxicity Induced by Colchicine-Site Binding Agent Indibulin

Indibulin, a microtubule-depolymerizing agent, produces minimal neurotoxicity in animals. It is also less cytotoxic toward differentiated neuronal cells than undifferentiated cells. We found that the levels of β-III tubulin, acetylated tubulin, and polyglutamylated tubulin were significantly increased in differentiated neuroblastoma cells (SH-SY5Y). Since neuronal cells express β-tubulin isotypes differently from other cell types, we explored the binding of indibulin to different β-tubulin isotypes. Our molecular docking analysis suggested that indibulin binds to β-III tubulin with lower affinity than to other β-tubulin isotypes. We therefore studied the implications of different β-tubulin isotypes on the cytotoxic effects of indibulin, colchicine, and vinblastine in differentiated SH-SY5Y cells. Upon depletion of β-III tubulin in the differentiated cells, the toxicity of indibulin and colchicine significantly increased, while sensitivity to vinblastine was unaffected. Using biochemical, bioinformatics, and fluorescence spectroscopic techniques, we have identified the binding site of indibulin on tubulin, which had not previously been established. Indibulin inhibited the binding of colchicine and C12 (a colchicine-site binder) to tubulin and also increased the dissociation constant of the interaction between tubulin and colchicine. Indibulin did not inhibit the binding of vinblastine or taxol to tubulin. Interestingly, indibulin antagonized colchicine treatment but synergized with vinblastine treatment in a combination study performed in MDA-MB-231 cells. The results indicate that indibulin is a colchicine-site binder and that the efficacy of colchicine-site binders is affected by the β-III tubulin levels in the cells.

cGAS-dependent proinflammatory and immune homeostatic effects of the microtubule-targeting agent paclitaxel

Taxanes are Microtubule-Targeting Agents (MTAs) that exert potent anticancer activity by directly killing cancer cells. However, recent evidence suggests that they may also stimulate inflammation and anticancer adaptive immunity and that these actions strongly contribute to their therapeutic efficacy. Details on how Taxanes may modulate inflammation and anticancer immunity are, nevertheless, still missing. We show here that at very low doses the Taxane Paclitaxel (Pxl) indeed induces a potent proinflammatory response in various cancer cell types in a cyclic GMP-AMP (cGAMP) synthase (cGAS)- and Stimulator of Interferon Genes (STING)-dependent manner, leading to interferon (IFN) signaling. However, we find that Pxl treatment also strongly upregulates the expression of the immune checkpoint protein Programmed Death-Ligand 1 (PD-L1) in cancer cells, therefore, inducing an inhibitory response to adaptive immunity potentially attenuating anticancer immunity and therapeutic success. These observations provide a mechanistic explanation of why clinical benefit may derive from the combination of Pxl with Immune Checkpoint Inhibitors (ICIs) and suggest that more accurately tailoring dosage and schedule of this combination therapy may provide benefit in the management of a larger number of cancer types and stages.

The Microtubule Destabilizer Eribulin Synergizes with STING Agonists to Promote Antitumor Efficacy in Triple-Negative Breast Cancer Models

Eribulin is a microtubule destabilizer used in the treatment of triple-negative breast cancer (TNBC). Eribulin and other microtubule targeted drugs, such as the taxanes, have shared antimitotic effects, but differ in their mechanism of microtubule disruption, leading to diverse effects on cellular signaling and trafficking. Herein, we demonstrate that eribulin is unique from paclitaxel in its ability to enhance expression of the immunogenic cytokine interferon beta (IFNβ) in combination with STING agonists in both immune cells and TNBC models, including profound synergism with ADU-S100 and E7766, which are currently undergoing clinical trials. The mechanism by which eribulin enhances STING signaling is downstream of microtubule disruption and independent of the eribulin-dependent release of mitochondrial DNA. Eribulin did not override the requirement of ER exit for STING activation and did not inhibit subsequent STING degradation; however, eribulin significantly enhanced IRF3 phosphorylation and IFNβ production downstream of the RNA sensing pathway that converges on this transcription factor. Additionally, we found that eribulin enhanced the population of activated CD4⁺ T-cells in vivo when combined with either a STING agonist or tumor, demonstrating the ability to function as an immune adjuvant. We further interrogated the combination of eribulin with ADU-S100 in the MMTV-PyVT spontaneous murine mammary tumor model where we observed significant antitumor efficacy with combination treatment. Together, our findings demonstrate that microtubule targeted chemotherapeutics have distinct immunological effects and that eribulin's ability to enhance innate immune sensing pathways supports its use in combination with immunotherapies, such as STING agonists, for the more effective treatment of TNBC and other malignancies.

Design, Synthesis and Biological Investigation of 2-Anilino Triazolopyrimidines as Tubulin Polymerization Inhibitors with Anticancer Activities

A further investigation aiming to generate new potential antitumor agents led us to synthesize a new series of twenty-two compounds characterized by the presence of the 7-(3',4',5'-trimethoxyphenyl)-[1,2,4]triazolo[1,5-a]pyrimidine pharmacophore modified at its 2-position. Among the synthesized compounds, three were significantly more active than the others. These bore the substituents p-toluidino (3d), p-ethylanilino (3h) and 3',4'-dimethylanilino (3f), and these compounds had IC₅₀ values of 30-43, 160-240 and 67-160 nM, respectively, on HeLa, A549 and HT-29 cancer cells. The p-toluidino derivative 3d was the most potent inhibitor of tubulin polymerization (IC₅₀: 0.45 µM) and strongly inhibited the binding of colchicine to tubulin (72% inhibition), with antiproliferative activity superior to CA-4 against A549 and HeLa cancer cell lines. In vitro investigation showed that compound 3d was able to block treated cells in the G2/M phase of the cell cycle and to induce apoptosis following the intrinsic pathway, further confirmed by mitochondrial depolarization and caspase-9 activation. In vivo experiments conducted on the zebrafish model showed good activity of 3d in reducing the mass of a HeLa cell xenograft. These effects occurred at nontoxic concentrations to the animal, indicating that 3d merits further developmental studies.

Photopharmacology of Antimitotic Agents

Antimitotic agents such as the clinically approved vinca alkaloids, taxanes and epothilone can arrest cell growth during interphase and are therefore among the most important drugs available for treating cancer. These agents suppress microtubule dynamics and thus interfere with intracellular transport, inhibit cell proliferation and promote cell death. Because these drugs target biological processes that are essential to all cells, they face an additional challenge when compared to most other drug classes. General toxicity can limit the applicable dose and therefore reduce therapeutic benefits. Photopharmacology aims to avoid these side-effects by introducing compounds that can be applied globally to cells in their inactive form, then be selectively induced to bioactivity in targeted cells or tissue during a defined time window. This review discusses photoswitchable analogues of antimitotic agents that have been developed by combining different photoswitchable motifs with microtubule-stabilizing or microtubule-destabilizing agents.

Mechanistic insights into the pathogenesis of microtubule-targeting agent-induced peripheral neuropathy from pharmacogenetic and functional studies

Chemotherapy-induced peripheral neuropathy (CIPN) is a common dose-limiting toxicity that affects 30%-40% of patients undergoing cancer treatment. Although multiple mechanisms of chemotherapy-induced neurotoxicity have been described in preclinical models, these have not been translated into widely effective strategies for the prevention or treatment of CIPN. Predictive biomarkers to inform therapeutic approaches are also lacking. Recent studies have examined genetic risk factors associated with CIPN susceptibility. This review provides an overview of the clinical and pathologic features of CIPN and summarizes efforts to identify target pathways through genetic and functional studies. Structurally and mechanistically diverse chemotherapeutics are associated with CIPN; however, the current review is focused on microtubule-targeting agents since these are the focus of most pharmacogenetic association and functional studies of CIPN. Genome-wide pharmacogenetic association studies are useful tools to identify not only causative genes and genetic variants but also genetic networks implicated in drug response or toxicity and have been increasingly applied to investigations of CIPN. Induced pluripotent stem cell-derived models of human sensory neurons are especially useful to understand the mechanistic significance of genomic findings. Combined genetic and functional genomic efforts to understand CIPN hold great promise for developing therapeutic approaches for its prevention and treatment.

TH588 and Low-Dose Nocodazole Impair Chromosome Congression by Suppressing Microtubule Turnover within the Mitotic Spindle

Simple Summary

A promising anti-cancer compound TH588 has been recently identified as a microtubule-targeting agent that inhibits tubulin polymerization in vitro and interferes with microtubule dynamics in interphase cells. Although it was shown to arrest cells in mitosis, its effect on microtubule dynamics in dividing cells remained unknown. By analyzing microtubule dynamics in living cells treated with either TH588 or low-dose nocodazole, we revealed that both of these drugs stabilize microtubules within the mitotic spindle, leading to premature formation of kinetochore-microtubule end-on attachments on uncongressed chromosomes. This causes mitotic arrest, ultimately resulting in cell death or cell division with uncongressed chromosomes. Both of these cell fates could contribute to the selective effect associated with the activity of TH588 in cancer cells.

Abstract

Microtubule-targeting agents (MTAs) have been used for decades to treat different hematologic and solid cancers. The mode of action of these drugs mainly relies on their ability to bind tubulin subunits and/or microtubules and interfere with microtubule dynamics. In addition to its MTH1-inhibiting activity, TH588 has been recently identified as an MTA, whose anticancer properties were shown to largely depend on its microtubule-targeting ability. Although TH588 inhibited tubulin polymerization in vitro and reduced microtubule plus-end mobility in interphase cells, its effect on microtubule dynamics within the mitotic spindle of dividing cells remained unknown. Here, we performed an in-depth analysis of the impact of TH588 on spindle-associated microtubules and compared it to the effect of low-dose nocodazole. We show that both treatments reduce microtubule turnover within the mitotic spindle. This microtubule-stabilizing effect leads to premature formation of kinetochore-microtubule end-on attachments on uncongressed chromosomes, which consequently cannot be transported to the cell equator, thereby delaying cell division and leading to cell death or division with uncongressed chromosomes.

Preclinical modeling in glioblastoma patient-derived xenograft (GBM PDX) xenografts to guide clinical development of lisavanbulin-a novel tumor checkpoint controller targeting microtubules

BACKGROUND

Glioblastoma (GBM) is an incurable disease with few approved therapeutic interventions. Radiation therapy (RT) and temozolomide (TMZ) remain the standards of care. The efficacy and optimal deployment schedule of the orally bioavailable small-molecule tumor checkpoint controller lisavanbulin alone, and in combination with, standards of care were assessed using a panel of IDH-wildtype GBM patient-derived xenografts.

METHODS

Mice bearing intracranial tumors received lisavanbulin +/-RT +/-TMZ and followed for survival. Lisavanbulin concentrations in plasma and brain were determined by liquid chromatography with tandem mass spectrometry, while flow cytometry was used for cell cycle analysis.

RESULTS

Lisavanbulin monotherapy showed significant benefit (P < .01) in 9 of 14 PDXs tested (median survival extension 9%-84%) and brain-to-plasma ratios of 1.3 and 1.6 at 2- and 6-hours postdose, respectively, validating previous data suggesting significant exposure in the brain. Prolonged lisavanbulin dosing from RT start until moribund was required for maximal benefit (GBM6: median survival lisavanbulin/RT 90 vs. RT alone 69 days, P = .0001; GBM150: lisavanbulin/RT 143 days vs. RT alone 73 days, P = .06). Similar observations were seen with RT/TMZ combinations (GBM39: RT/TMZ/lisavanbulin 502 days vs. RT/TMZ 249 days, P = .0001; GBM26: RT/TMZ/lisavanbulin 172 days vs. RT/TMZ 121 days, P = .04). Immunohistochemical analyses showed a significant increase in phospho-histone H3 with lisavanbulin treatment (P = .01).

CONCLUSIONS

Lisavanbulin demonstrated excellent brain penetration, significant extension of survival alone or in RT or RT/TMZ combinations, and was associated with mitotic arrest. These data provide a strong clinical rationale for testing lisavanbulin in combination with RT or RT/TMZ in GBM patients.

The Role of Microtubules in Pancreatic Cancer: Therapeutic Progress

Pancreatic cancer has an extremely low prognosis, which is attributable to its high aggressiveness, invasiveness, late diagnosis, and lack of effective therapies. Among all the drugs joining the fight against this type of cancer, microtubule-targeting agents are considered to be the most promising. They inhibit cancer cells although through different mechanisms such as blocking cell division, apoptosis induction, etc. Hereby, we review the functions of microtubule cytoskeletal proteins in tumor cells and comprehensively examine the effects of microtubule-targeting agents on pancreatic carcinoma.

Microtubule-targeting agents impair kinesin-2-dependent nuclear transport of β-catenin: Evidence of inhibition of Wnt/β-catenin signaling as an important antitumor mechanism of microtubule-targeting agents

An aberrant accumulation of nuclear β-catenin is closely associated with the augmentation of cancer malignancy. In this work, we report that several microtubule-targeting agents (MTAs) such as vinblastine, taxol, and C12 (combretastatin-2-aminoimidazole analog) inhibit Wnt/β-catenin signaling in oral squamous cell carcinoma (OSCC). We showed that the inhibition of microtubule dynamics by MTAs decreased the level of β-catenin by increasing Axin and adenomatous polyposis coli levels and reducing the level of dishevelled. Furthermore, MTAs strongly reduced the localization of β-catenin in the nucleus. The reduction in the level of nuclear β-catenin was neither due to the degradation of β-catenin in the nucleus nor due to an increase in the export of nuclear β-catenin from the nucleus. A motor protein kinesin-2 was found to assist the nuclear transportation of β-catenin. Interestingly, Wnt/β-catenin signaling antagonist treatment synergized with MTAs and the activators of Wnt/β-catenin signaling antagonized with the MTAs. C12 potently suppressed the growth of 4-Nitroquinoline 1-oxide-induced OSCC in the tongue of C57 black 6 mice and also abrogated Wnt/β-catenin signaling pathway in the tumor. Our results provide evidence that the decrease in Wnt/β-catenin signaling is an important antitumor effect of MTAs and the combined use of MTAs with Wnt/β-catenin signaling antagonists could be a promising strategy for cancer chemotherapy.

The tyrosine kinase v-Src modifies cytotoxicities of anticancer drugs targeting cell division

v-Src oncogene causes cell transformation through its strong tyrosine kinase activity. We have revealed that v-Src-mediated cell transformation occurs at a low frequency and it is attributed to mitotic abnormalities-mediated chromosome instability. v-Src directly phosphorylates Tyr-15 of cyclin-dependent kinase 1 (CDK1), thereby causing mitotic slippage and reduction in Eg5 inhibitor cytotoxicity. However, it is not clear whether v-Src modifies cytotoxicities of the other anticancer drugs targeting cell division. In this study, we found that v-Src restores cancer cell viability reduced by various microtubule-targeting agents (MTAs), although v-Src does not alter cytotoxicity of DNA-damaging anticancer drugs. v-Src causes mitotic slippage of MTAs-treated cells, consequently generating proliferating tetraploid cells. We further demonstrate that v-Src also restores cell viability reduced by a polo-like kinase 1 (PLK1) inhibitor. Interestingly, treatment with Aurora kinase inhibitor strongly induces cell death when cells express v-Src. These results suggest that the v-Src modifies cytotoxicities of anticancer drugs targeting cell division. Highly activated Src-induced resistance to MTAs through mitotic slippage might have a risk to enhance the malignancy of cancer cells through the increase in chromosome instability upon chemotherapy using MTAs.

GEF-H1 Signaling upon Microtubule Destabilization Is Required for Dendritic Cell Activation and Specific Anti-tumor Responses

Dendritic cell (DC) activation is a critical step for anti-tumor T cell responses. Certain chemotherapeutics can influence DC function. Here we demonstrate that chemotherapy capable of microtubule destabilization has direct effects on DC function; namely, it induces potent DC maturation and elicits anti-tumor immunity. Guanine nucleotide exchange factor-H1 (GEF-H1) is specifically released upon microtubule destabilization and is required for DC activation. In response to chemotherapy, GEF-H1 drives a distinct cell signaling program in DCs dominated by the c-Jun N-terminal kinase (JNK) pathway and AP-1/ATF transcriptional response for control of innate and adaptive immune responses. Microtubule destabilization, and subsequent GEF-H1 signaling, enhances cross-presentation of tumor antigens to CD8 T cells. In absence of GEF-H1, anti-tumor immunity is hampered. In cancer patients, high expression of the GEF-H1 immune gene signature is associated with prolonged survival. Our study identifies an alternate intracellular axis in DCs induced upon microtubule destabilization in which GEF-H1 promotes protective anti-tumor immunity.

Certain chemotherapeutics elicit potent anti-tumor immunity. Kashyap et al. demonstrate that microtubule-destabilizing chemotherapeutics induce maturation of dendritic cells through activation of microtubule-associated protein GEF-H1. This leads to effective priming of CD8 T cells against tumor antigens. GEF-H1 is critical for anti-tumor immunity of microtubule-targeting chemotherapy.

Tubulin-Based Nanotubes as Delivery Platform for Microtubule-Targeting Agents

Tubulin-based nanotubes (TNTs) to deliver microtubule-targeting agents (MTAs) for clinical oncology are reported. Three MTAs, docetaxel (DTX), laulimalide (LMD), and monomethyl auristatin E (MMAE), which attach to different binding sites in a tubulin, are loaded onto TNTs and cause structural changes in them, including shape anisotropy and tubulin layering. This drug-driven carrier transformation leads to changes in the drug-loading efficiency and stability characteristics of the carrier. TNTs coloaded with DTX and LMD efficiently deliver dual drug cargoes to cellular tubulins by the endolysosomal pathway, and results in synergistic anticancer and antiangiogenic action of the drugs in vitro. In in vivo tests, TNTs loaded with a microtubule-destabilizing agent MMAE suppress the growth of tumors with much higher efficacy than free MMAE did. This work suggests a new concept of using a drug's target protein as a carrier. The findings demonstrate that the TNTs developed here can be used universally as a delivery platform for many MTAs.

Biology of Glioblastoma Multiforme-Exploration of Mitotic Catastrophe as a Potential Treatment Modality

Glioblastoma multiforme (GBM) represents approximately 60% of all brain tumors in adults. This malignancy shows a high biological and genetic heterogeneity associated with exceptional aggressiveness, leading to a poor survival of patients. This review provides a summary of the basic biology of GBM cells with emphasis on cell cycle and cytoskeletal apparatus of these cells, in particular microtubules. Their involvement in the important oncosuppressive process called mitotic catastrophe will next be discussed along with select examples of microtubule-targeting agents, which are currently explored in this respect such as benzimidazole carbamate compounds. Select microtubule-targeting agents, in particular benzimidazole carbamates, induce G₂/M cell cycle arrest and mitotic catastrophe in tumor cells including GBM, resulting in phenotypically variable cell fates such as mitotic death or mitotic slippage with subsequent cell demise or permanent arrest leading to senescence. Their effect is coupled with low toxicity in normal cells and not developed chemoresistance. Given the lack of efficient cytostatics or modern molecular target-specific compounds in the treatment of GBM, drugs inducing mitotic catastrophe might offer a new, efficient alternative to the existing clinical management of this at present incurable malignancy.

Beyond the Paclitaxel and Vinca Alkaloids: Next Generation of Plant-Derived Microtubule-Targeting Agents with Potential Anticancer Activity

Plants are an important source of chemically diverse natural products that target microtubules, one of the most successful targets in cancer therapy. Colchicine, paclitaxel, and vinca alkaloids are the earliest plant-derived microtubule-targeting agents (MTAs), and paclitaxel and vinca alkaloids are currently important drugs used in the treatment of cancer. Several additional plant-derived compounds that act on microtubules with improved anticancer activity are at varying stages of development. Here, we move beyond the well-discussed paclitaxel and vinca alkaloids to present other promising plant-derived MTAs with potential for development as anticancer agents. Various biological and biochemical aspects are discussed. We hope that the review will provide guidance for further exploration and identification of more effective, novel MTAs derived from plant sources.

Colchicine-Binding Site Inhibitors from Chemistry to Clinic: A Review

It is over 50 years since the discovery of microtubules, and they have become one of the most important drug targets for anti-cancer therapies. Microtubules are predominantly composed of the protein tubulin, which contains a number of different binding sites for small-molecule drugs. There is continued interest in drug development for compounds targeting the colchicine-binding site of tubulin, termed colchicine-binding site inhibitors (CBSIs). This review highlights CBSIs discovered through diverse sources: from natural compounds, rational design, serendipitously and via high-throughput screening. We provide an update on CBSIs reported in the past three years and discuss the clinical status of CBSIs. It is likely that efforts will continue to develop CBSIs for a diverse set of cancers, and this review provides a timely update on recent developments.

Microtubules: A Key to Understand and Correct Neuronal Defects in CDKL5 Deficiency Disorder?

CDKL5 deficiency disorder (CDD) is a severe neurodevelopmental encephalopathy caused by mutations in the X-linked CDKL5 gene that encodes a serine/threonine kinase. CDD is characterised by the early onset of seizures and impaired cognitive and motor skills. Loss of CDKL5 in vitro and in vivo affects neuronal morphology at early and late stages of maturation, suggesting a link between CDKL5 and the neuronal cytoskeleton. Recently, various microtubule (MT)-binding proteins have been identified as interactors of CDKL5, indicating that its roles converge on regulating MT functioning. MTs are dynamic structures that are important for neuronal morphology, migration and polarity. The delicate control of MT dynamics is fundamental for proper neuronal functions, as evidenced by the fact that aberrant MT dynamics are involved in various neurological disorders. In this review, we highlight the link between CDKL5 and MTs, discussing how CDKL5 deficiency may lead to deranged neuronal functions through aberrant MT dynamics. Finally, we discuss whether the regulation of MT dynamics through microtubule-targeting agents may represent a novel strategy for future pharmacological approaches in the CDD field.

The miR-195 Axis Regulates Chemoresistance through TUBB and Lung Cancer Progression through BIRC5

Chemoresistance and metastasis are the major reasons for non-small cell lung cancer (NSCLC) treatment failure and patient deaths. We and others have shown that miR-195 regulates the sensitivity of NSCLC to microtubule-targeting agents (MTAs) in vitro and in vivo and that miR-195 represses the migration and invasion of NSCLC cells in vitro. However, the relationship between miR-195 and microtubule structure and function and whether miR-195 represses NSCLC metastasis in vivo remain unknown. We assessed the correlation between tumor levels of TUBB and patient survival, the effect of TUBB on drug response, and the effect of miR-195 on migration, invasion, and metastasis in vitro and in vivo. We found that miR-195 directly targets TUBB; knockdown of TUBB sensitizes cells to MTAs, while overexpression confers resistance; high expression of TUBB is correlated with worse survival of lung adenocarcinoma; TUBB is also regulated by CHEK1, which has been shown to regulate chemoresistance; and miR-195 targets BIRC5 to repress migration and invasion in vitro and metastasis in vivo. Our findings highlight the relevance of the miR-195/TUBB axis in regulating the response of NSCLC to MTAs and the importance of the miR-195/BIRC5 axis in regulating NSCLC metastasis.

Microtubule-Targeting Agents: Strategies To Hijack the Cytoskeleton

Microtubule-targeting agents (MTAs) such as paclitaxel and the vinca alkaloids are among the most important medical weapons available to combat cancer. MTAs interfere with intracellular transport, inhibit eukaryotic cell proliferation, and promote cell death by suppressing microtubule dynamics. Recent advances in the structural analysis of MTAs have enabled the extensive characterization of their interactions with microtubules and their building block tubulin. We review here our current knowledge on the molecular mechanisms used by MTAs to hijack the microtubule cytoskeleton, and discuss dual inhibitors that target both kinases and microtubules. We further formulate some outstanding questions related to MTA structural biology and present possible routes for future investigations of this fascinating class of antimitotic agents.

Efficacy of eribulin in breast cancer: a short report on the emerging new data

Eribulin is a novel microtubule-targeting agent that is approved for the treatment of patients with locally advanced or metastatic breast cancer who have previously received treatment with an anthracycline and a taxane in either the adjuvant or metastatic setting. Eribulin induces mitotic catastrophe leading to cell death but has other important antitumor effects, including reversal of epithelial–mesenchymal transition and remodeling of the tumor vasculature. Eribulin was licensed for the treatment of advanced breast cancer based on results from two large randomized Phase III clinical trials. Current clinical trials of eribulin for breast cancer are evaluating response to treatment earlier in the patient pathway and in combination with other therapeutic agents. This review provides a short overview of emerging new data on the mode of action of eribulin in breast cancer.

Establishment of a Novel In Vitro Model for Predicting Incidence and Severity of Microtubule-targeting Agent-induced Peripheral Neuropathy

Peripheral neuropathy (PN) is a major dose-limiting side-effect of microtubule-targeting agents (MTAs), considered to be induced by inhibition of axonal microtubules. Therefore, it was thought that a useful method for predicting the frequencies of severe sensory-PN (FPN) would be to evaluate the neurite-disrupting effects of MTAs. Using neurite outgrowth from neuron-like cell lines, we comprehensively evaluated the neurite-disrupting effects of several anti-cancer drugs including MTAs, and the reversibility of the effects of MTAs. MTAs that induce PN showed neurite-disrupting effects more strongly than MTAs and anticancer drugs that do not induce PN, but the effects were not related to the FPN. On the other hand, MTAs with high FPN exhibited lower reversibility than those with low FPN. These findings suggest that neurite-disrupting effects are associated with the incidence of PN, and the reversibility of the effects is associated with FPN.

A new tubulin-binding site and pharmacophore for microtubule-destabilizing anticancer drugs

The recent success of antibody-drug conjugates (ADCs) in the treatment of cancer has led to a revived interest in microtubule-destabilizing agents. Here, we determined the high-resolution crystal structure of the complex between tubulin and maytansine, which is part of an ADC that is approved by the US Food and Drug Administration (FDA) for the treatment of advanced breast cancer. We found that the drug binds to a site on β-tubulin that is distinct from the vinca domain and that blocks the formation of longitudinal tubulin interactions in microtubules. We also solved crystal structures of tubulin in complex with both a variant of rhizoxin and the phase 1 drug PM060184. Consistent with biochemical and mutagenesis data, we found that the two compounds bound to the same site as maytansine and that the structures revealed a common pharmacophore for the three ligands. Our results delineate a distinct molecular mechanism of action for the inhibition of microtubule assembly by clinically relevant agents. They further provide a structural basis for the rational design of potent microtubule-destabilizing agents, thus opening opportunities for the development of next-generation ADCs for the treatment of cancer.

Novel microtubule-targeting agents - the epothilones

Epothilones are a new class of antimicrotubule agents currently in clinical trials. Their chemical structures are distinct from taxanes and are more amenable to synthetic modification. Six epothilones have been studied in preclinical and clinical trials: patupilone (epothilone B), ixabepilone (BMS247550), BMS 310705, sagopilone (ZK-EPO), KOS-862 (epothilone D), and KOS-1584. In vitro data have shown increased potency in taxane-sensitive and taxane-resistant cancer cell lines. This enhanced cytotoxic effect has been attributed to epothilone being a poor substrate for p-glycoprotein drug resistance protein and having high affinity to the various beta tubulin isoforms. Phase I clinical data have shown different dose-limiting toxicities for each of the epothilones. These effects are drug specific, dose specific, and schedule of administration specific. While diarrhea and myelosuppression are the dose-limiting toxicities for patupilone and BMS 310705, respectively, neurologic toxicity, as seen with taxanes, is the dose-limiting toxicity of ixabepilone, sagopilone, and KOS-862. In an effort to decrease neurologic toxicity, investigators have modified dosing schedules with limited success. Ixabepilone has the most mature clinical results with published phase II and III data, and regulatory approval for clinical use in the treatment of breast cancer. Ixabepilone has also been combined with other anticancer agents and has regulatory approval in combination with capecitabine for heavily treated breast cancer.