Anti-mitotic agents: Are they emerging molecules for cancer treatment?

PLK1 inhibition leads to mitotic arrest and triggers apoptosis in cholangiocarcinoma cells

Cholangiocarcinoma (CCA) is a lethal cancer originating from the epithelial cells within the bile duct and ranks as the second most prevalent form of liver cancer in Thailand. Polo-like kinase 1 (PLK1), a protein serine/threonine kinase, regulates a number of steps in cell mitosis and is upregulated in several types of cancer, including CCA. Our previous study identified PLK1 as a biomarker of the C1 subtype, correlating with poor prognosis in intrahepatic CCA. The present study aimed to examine the effect of PLK1 inhibition on CCA cells. Different CCA cell lines developed from Thai patients, HuCCA1, KKU055, KKU100 and KKU213A, were treated with two PLK1 inhibitors, BI2536 and BI6727, and were transfected with small interfering RNA, followed by analysis of cell proliferation, cell cycle distribution and cell apoptosis. It was discovered that BI2536 and BI6727 inhibited cell proliferation and caused G2/M-phase arrest in CCA cells. Furthermore, the number of total apoptotic cells was increased in PLK1 inhibitor-treated CCA cells. The expression levels of mitotic proteins, aurora kinase A, phosphorylated PLK1 (T210) and cyclin B1, were augmented in PLK1-inhibited CCA cells. Additionally, inhibition of PLK1 led to increased DNA damage, as determined by the upregulated levels of γH2AX and increased cleavage of poly (ADP-ribose) polymerase, an apoptotic marker. These results suggested that inhibiting PLK1 prolonged mitotic arrest and subsequently triggered cell apoptosis. Validation of the antiproliferative effects of PLK1 inhibition was accomplished through silencing of the PLK1 gene. In conclusion, targeting PLK1 provided promising results for further study as a potential candidate for targeted therapy in CCA.

GSG2 promotes progression of human endometrial cancer by regulating PD-1/PD-L1 expression via PI3K-AKT pathway

Cell cycle dysregulation leading to uncontrolled growth is a primary characteristic of malignancy. GSG2, a mitosis-related kinase, affects the normal cell cycle by interfering with the normal dissociation of centromere cohesion, and its overexpression has been shown to play an important role in cancer cells. Here, we investigated the function of GSG2 as a tumor promoter in endometrial carcinoma and its relationship with the immunological microenvironment. We used immunohistochemistry to identify a correlation between the development and prognosis of GSG2 and endometrial cancer. Cell and animal experiments confirmed that GSG2 has a protumorigenic phenotype in endometrial cancer cell lines. Furthermore, using GeneChip analysis and a tumor-immune coculture model, we observed a link between GSG2 expression and the composition of the immune microenvironment. Therefore, we concluded that the activation of the PI3K/AKT pathway by GSG2 may impact DNA repair, disrupt the cell cycle, and regulate the immune response, all of which could increase the ability of EC cells to proliferate malignantly. Consequently, it is anticipated that GSG2 will be a viable therapeutic target in endometrial carcinoma.

Control of cell proliferation by memories of mitosis

Mitotic duration is tightly constrained, and extended mitosis is characteristic of problematic cells prone to chromosome missegregation and genomic instability. We show here that mitotic extension leads to the formation of p53-binding protein 1 (53BP1)-ubiquitin-specific protease 28 (USP28)-p53 protein complexes that are transmitted to, and stably retained by, daughter cells. Complexes assembled through a Polo-like kinase 1-dependent mechanism during extended mitosis and elicited a p53 response in G1 that prevented the proliferation of the progeny of cells that experienced an approximately threefold extended mitosis or successive less extended mitoses. The ability to monitor mitotic extension was lost in p53-mutant cancers and some p53-wild-type (p53-WT) cancers, consistent with classification of TP53BP1 and USP28 as tumor suppressors. Cancers retaining the ability to monitor mitotic extension exhibited sensitivity to antimitotic agents.

Repositioning VU-0365114 as a novel microtubule-destabilizing agent for treating cancer and overcoming drug resistance

Microtubule-targeting agents represent one of the most successful classes of anticancer agents. However, the development of drug resistance and the appearance of adverse effects hamper their clinical implementation. Novel microtubule-targeting agents without such limitations are urgently needed. By employing a gene expression-based drug repositioning strategy, this study identifies VU-0365114, originally synthesized as a positive allosteric modulator of human muscarinic acetylcholine receptor M5 (M5 mAChR), as a novel type of tubulin inhibitor by destabilizing microtubules. VU-0365114 exhibits a broad-spectrum in vitro anticancer activity, especially in colorectal cancer cells. A tumor xenograft study in nude mice shows that VU-0365114 slowed the in vivo colorectal tumor growth. The anticancer activity of VU-0365114 is not related to its original target, M5 mAChR. In addition, VU-0365114 does not serve as a substrate of multidrug resistance (MDR) proteins, and thus, it can overcome MDR. Furthermore, a kinome analysis shows that VU-0365114 did not exhibit other significant off-target effects. Taken together, our study suggests that VU-0365114 primarily targets microtubules, offering potential for repurposing in cancer treatment, although more studies are needed before further drug development.

Anti-tumor and cardiotoxic effects of microtubule polymerization inhibitors: The mechanisms and management strategies

Microtubule polymerization inhibitors (MPIs) have long been used as anticancer agents because they inhibit mitosis. Microtubules are thought to play an important role in the migration of tumor cells and the formation of tumor blood vessels, and new MPIs are being developed. Many clinical trials of novel MPIs have been conducted in humans, while some clinical studies in dogs have also been reported. More attempts to apply MPIs not only in humans but also in the veterinary field are expected to be made in the future. Meanwhile, MPIs have a risk of cardiotoxicity. In this paper, we review findings on the pharmacological effects and cardiotoxicity of MPIs, as well as the mechanisms of their cardiotoxicity. Cardiotoxicity of MPIs involves not only the direct effects of MPIs on cardiomyocytes but also their effects on vascular function. For example, hypertension induced by impaired vascular function also contributes to the exacerbation of myocardial damage, and blood pressure control may be useful in reducing cardiotoxicity. By combined administration of MPIs and other anticancer agents, MPI efficacy may be enhanced, thereby potentially allowing to keep MPI dosage low. Measurement of myocardial injury markers in blood and echocardiography may be useful for monitoring cardiotoxicity. In particular, two-dimensional speckle tracking may have high sensitivity for the early detection of MPI-induced cardiac dysfunction. The exploration of the potential of new MPIs while understanding their toxicity and how to deal with them will lead to the further development of cancer chemotherapy.

Design, synthesis and evaluation of dihydro-1H-indene derivatives as novel tubulin polymerisation inhibitors with anti-angiogenic and antitumor potency

Angiogenesis plays an important role in tumour generation and progression, which is used to supply nutrients and metastasis. Herein, a series of novel dihydro-1H-indene derivatives were designed and evaluated as tubulin polymerisation inhibitors by binding to colchicine site, exhibiting anti-angiogenic activities against new vessel forming. Through structure-activity relationships study, compound 12d was found to be the most potent derivative possessing the antiproliferative activity against four cancer lines with IC50 values among 0.028-0.087 µM. Compound 12d bound to colchicine site on tubulin and inhibited tubulin polymerisation in vitro. In addition, compound 12d induced cell cycle arrest at G2/M phase, stimulated cell apoptosis, inhibited tumour metastasis and angiogenesis. Finally, the results of in vivo assay suggested that compound 12d could prevent tumour generation, inhibit tumour proliferation and angiogenesis without obvious toxicity. Collectively, all these findings suggested that compound 12d is a novel tubulin polymerisation inhibitor deserving further research.

ALFI: Cell cycle phenotype annotations of label-free time-lapse imaging data from cultured human cells

Detecting and tracking multiple moving objects in a video is a challenging task. For living cells, the task becomes even more arduous as cells change their morphology over time, can partially overlap, and mitosis leads to new cells. Differently from fluorescence microscopy, label-free techniques can be easily applied to almost all cell lines, reducing sample preparation complexity and phototoxicity. In this study, we present ALFI, a dataset of images and annotations for label-free microscopy, made publicly available to the scientific community, that notably extends the current panorama of expertly labeled data for detection and tracking of cultured living nontransformed and cancer human cells. It consists of 29 time-lapse image sequences from HeLa, U2OS, and hTERT RPE-1 cells under different experimental conditions, acquired by differential interference contrast microscopy, for a total of 237.9 hours. It contains various annotations (pixel-wise segmentation masks, object-wise bounding boxes, tracking information). The dataset is useful for testing and comparing methods for identifying interphase and mitotic events and reconstructing their lineage, and for discriminating different cellular phenotypes.

Novel Aminopyrimidine-2,4-diones, 2-Thiopyrimidine-4-ones, and 6-Arylpteridines as Dual-Target Inhibitors of BRD4/PLK1: Design, Synthesis, Cytotoxicity, and Computational Studies

Structural-based drug design and solvent-free synthesis were combined to obtain three novel series of 5-arylethylidene-aminopyrimidine-2,4-diones (4, 5a-c, 6a,b), 5-arylethylidene-amino-2-thiopyrimidine-4-ones (7,8), and 6-arylpteridines (9,10) as dual BRD4 and PLK1 inhibitors. MTT assays of synthesized compounds against breast (MDA-MB-231), colorectal (HT-29), and renal (U-937) cancer cells showed excellent-to-good cytotoxic activity, compared to Methotrexate; MDA-MB-231 were the most sensitive cancer cells. The most active compounds were tested against normal Vero cells. Compounds 4 and 7 significantly inhibited BRD4 and PLK1, with IC50 values of 0.029, 0.042 µM, and 0.094, 0.02 µM, respectively, which are nearly comparable to volasertib (IC50 = 0.017 and 0.025 µM). Compound 7 triggered apoptosis and halted cell growth at the G2/M phase, similarly to volasertib. It also upregulated the BAX and caspase-3 markers while downregulating the Bcl-2 gene. Finally, active compounds fitted the volasertib binding site at BRD4 and PLK1 and showed ideal drug-like properties and pharmacokinetics, making them promising anticancer candidates.

β-Sitosterol as a Promising Anticancer Agent for Chemoprevention and Chemotherapy: Mechanisms of Action and Future Prospects

Cancer is one of the primary causes of death worldwide, and its incidence continues to increase yearly. Despite significant advances in research, the search for effective and nontoxic preventive and therapeutic agents remains greatly important. Cancer is a multimodal disease, where various mechanisms play significant roles in its occurrence and progression. This highlights the need for multitargeted approaches that are not only safe and inexpensive but also provide effective alternatives for current therapeutic regimens. β-Sitosterol (SIT), the most abundant phytosterol found in various plant foods, represents such an option. Preclinical evidence over the past few decades has overwhelmingly shown that SIT exhibits multiple anticancer activities against varied cancers, such as liver, cervical, colon, stomach, breast, lung, pancreatic, and prostate cancers, in addition to leukemia, multiple myeloma, melanoma, and fibrosarcoma. In this article, we present the latest advances and perspectives on SIT-systematically summarizing its antitumor mechanisms of action into 7 main sections and combining current challenges and prospects-for its use as a promising agent for cancer prevention and treatment. In particular, SIT plays a role in cancer prevention and treatment mainly by enhancing apoptosis, inducing cell cycle arrest, bidirectionally regulating oxidative stress, improving metabolic reprogramming, inhibiting invasion and metastasis, modulating immunity and inflammation, and combating drug resistance. Although SIT holds such great promise, the poor aqueous solubility and bioavailability coupled with low targeting efficacy limit its therapeutic efficacy and clinical application. Further research on novel drug delivery systems may improve these deficiencies. Overall, through complex and pleiotropic mechanisms, SIT has good potential for tumor chemoprevention and chemotherapy. However, no clinical trials have yet proven this potential. This review provides theoretical basis and rationality for the further design and conduct of clinical trials to confirm the anticancer activity of SIT.

Hybridization of the Pharmacophoric Features of Discoipyrrole C and Combretastatin A-4 toward New Anticancer Leads

Pharmacophore hybridization is an attractive strategy to identify new leads against multifactorial diseases such as cancer. Based on literature analysis of compounds possessing 'vicinal diaryl' fragment in their structure, we considered Discoipyrroles A-D and Combretastatin A-4 (CA-4) as possible components in hybrid design. Discoipyrrole C (Dis C) and CA-4 were used as reference compounds in these studies and their hybrids, in the form of 4,5-diaryl-1H-pyrrol-3(2H)-ones, were synthesized from suitable amino acid precursors though their ynone intermediates. Of these, the hybrid having exact substitution pattern as that of CA-4 showed better potency and selectivity than Dis C, but its activity was less compared to CA-4. This new analog disrupted interphase microtubules by inhibiting tubulin assembly by binding to the colchicine site, induced multipolar spindles, caused cell cycle block and apoptosis in HeLa cells. It also inhibited colony formation and migration of breast cancer cell lines.

Function and inhibition of Haspin kinase: targeting multiple cancer therapies by antimitosis

Objectives

Haploid germ cell-specific nuclear protein kinase (Haspin) is a serine/threonine kinase as an atypical kinase, which is structurally distinct from conventional protein kinases.

Key findings

Functionally, Haspin is involved in important cell cycle progression, particularly in critical mitosis regulating centromeric sister chromatid cohesion during prophase and prometaphase, and subsequently ensuring proper chromosome alignment during metaphase and the normal chromosome segregation during anaphase. However, increasing evidence has demonstrated that Haspin is significantly upregulated in a variety of cancer cells in addition to normal proliferating somatic cells. Its knockdown or small molecule inhibition could prevent cancer cell growth and induce apoptosis by disrupting the regular mitotic progression. Given the specificity of its expressed tissues or cells and the uniqueness of its current known substrate, Haspin can be a promising target against cancer. Consequently, selective synthetic and natural inhibitors of Haspin have been widely developed to determine their inhibitory power for various cancer cells in vivo and in vitro.

Summary

Here our perspective includes a comprehensive review of the roles and structure of Haspin, its relatively potent and selective inhibitors and Haspin’s preliminary studies in a variety of cancers.

The Mechanisms of Action of Tumor Treating Fields

Tumor treating fields (TTFields), a new modality of cancer treatment, are electric fields transmitted transdermally to tumors. The FDA has approved TTFields for the treatment of glioblastoma multiforme and mesothelioma, and they are currently under study in many other cancer types. While antimitotic effects were the first recognized biological anticancer activity of TTFields, data have shown that tumor treating fields achieve their anticancer effects through multiple mechanisms of action. TTFields therefore have the ability to be useful for many cancer types in combination with many different treatment modalities. Here, we review the current understanding of TTFields and their mechanisms of action.

Discovery of novel microtubule stabilizers targeting taxane binding site by applying molecular docking, molecular dynamics simulation, and anticancer activity testing

Disruption of the dynamic equilibrium of microtubules can induce cell cycle arrest in G2/M phase and apoptosis. Hence, discovery of novel tubulin polymerization inhibitors is very necessary and an important task in drug research and development for treatment of various tumors. In this investigation, 50 compounds were screened as microtubule stabilizers targeting the taxane site by combination of molecular docking methods. Among these hits, hits 19 and 38 with novel scaffolds exhibited the highest anti-proliferative activity with IC₅₀ ranging from 9.50 to 13.81 μM in four cancer cell lines. The molecular dynamics simulations confirmed that tubulin and two hits could form stable systems. Meanwhile, the mechanism of the interactions between tubulin and two hits at simulated physiological conditions were probed. The in vitro tubulin polymerization assay revealed hits 19 and 38 were able to promote tubulin polymerization in a dose-dependent manner. Further, the immunofluorescence assay suggested that hits 19 and 38 could accelerate microtubule assembly in A549 and HeLa cells. Finally, studies on antitumor activity indicated that hits 19 and 38 induced G2/M phase cell cycle arrest and apoptosis, and inhibited cancer cell motility and migration in A549 and HeLa cells. Importantly, hit38 exhibited better anti-tubulin and anti-cancer activity than hit19 in A549 and HeLa cells. Therefore, these results suggest that hit38 represents a promising microtubule stabilizer for treating cancer and deserves further investigation.

Cell cycle control in cancer

Cancer is a group of diseases in which cells divide continuously and excessively. Cell division is tightly regulated by multiple evolutionarily conserved cell cycle control mechanisms, to ensure the production of two genetically identical cells. Cell cycle checkpoints operate as DNA surveillance mechanisms that prevent the accumulation and propagation of genetic errors during cell division. Checkpoints can delay cell cycle progression or, in response to irreparable DNA damage, induce cell cycle exit or cell death. Cancer-associated mutations that perturb cell cycle control allow continuous cell division chiefly by compromising the ability of cells to exit the cell cycle. Continuous rounds of division, however, create increased reliance on other cell cycle control mechanisms to prevent catastrophic levels of damage and maintain cell viability. New detailed insights into cell cycle control mechanisms and their role in cancer reveal how these dependencies can be best exploited in cancer treatment.

A recent development of new therapeutic agents and novel drug targets for cancer treatment

Despite recent advances in cancer diagnosis, prevention, detection, as well as management, the disease is expected to be the top cause of death globally. The chemotherapy approach for cancer has become more advanced in its design, yet no medication can cure enough against all types of cancer and its stage. Thus, this review aimed to summarize a recent development of new therapeutic agents and novel drug targets for the treatment of cancer. Several obstacles stand in the way of effective cancer treatment and drug development, including inaccessibility of tumor site by appropriate drug concentration, debilitating untoward effects caused by non-selective tissue distribution of chemotherapeutic agents, and occurrence of drug resistance, which leads to cross-resistance to a variety of drugs. Resistance to treatment with anticancer drugs results from multiple factors and the most common reason for acquiring drug resistance is marking and expelling drugs that prevent cancer cells to be targeted by chemotherapeutic agents. Moreover, insensitivity to drug-induced apoptosis, alteration, and mutation of drug target and interference/change of DNA replication are other main causes of treatment failure.

Chromatin bridges, not micronuclei, activate cGAS after drug-induced mitotic errors in human cells

Mitotic errors can activate cyclic GMP-AMP synthase (cGAS) and induce type I interferon (IFN) signaling. Current models propose that chromosome segregation errors generate micronuclei whose rupture activates cGAS. We used a panel of antimitotic drugs to perturb mitosis in human fibroblasts and measured abnormal nuclear morphologies, cGAS localization, and IFN signaling in the subsequent interphase. Micronuclei consistently recruited cGAS without activating it. Instead, IFN signaling correlated with formation of cGAS-coated chromatin bridges that were selectively generated by microtubule stabilizers and MPS1 inhibitors. cGAS activation by chromatin bridges was suppressed by drugs that prevented cytokinesis. We confirmed cGAS activation by chromatin bridges in cancer lines that are unable to secrete IFN by measuring paracrine transfer of 2'3'-cGAMP to fibroblasts, and in mouse cells. We propose that cGAS is selectively activated by self-chromatin when it is stretched in chromatin bridges. Immunosurveillance of cells that fail mitosis, and antitumor actions of taxanes and MPS1 inhibitors, may depend on this effect.

Radioresistance of Human Cancers: Clinical Implications of Genetic Expression Signatures

Although radiotherapy is given to more than 50% of cancer patients, little progress has been made in identifying optimal radiotherapy - drug combinations to improve treatment efficacy. Using molecular data from The Cancer Genome Atlas (TCGA), we extracted a total of 1016 cancer patients that received radiotherapy. The patients were diagnosed with head-and-neck (HNSC - 294 patients), cervical (CESC - 166 patients) and breast (BRCA - 549 patients) cancer. We analyzed mRNA expression patterns of 50 hallmark gene sets of the MSigDB collection, which we divided in eight categories based on a shared biological or functional process. Tumor samples were split into upregulated, neutral or downregulated mRNA expression for all gene sets using a gene set analysis (GSEA) pre-ranked analysis and assessed for their clinical relevance. We found a prognostic association between three of the eight gene set categories (Radiobiological, Metabolism and Proliferation) and overall survival in all three cancer types. Furthermore, multiple single associations were revealed in the other categories considered. To the best of our knowledge, our study is the first report suggesting clinical relevance of molecular characterization based on hallmark gene sets to refine radiation strategies.

Identification of Key Biomarkers and Pathways in Small-Cell Lung Cancer Using Biological Analysis

Background

Small-cell lung cancer (SCLC) is a major cause of carcinoma-related deaths worldwide. The aim of this study was to identify the key biomarkers and pathways in SCLC using biological analysis.

Methods

Key genes involved in the development of SCLC were identified by downloading three datasets from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were screened using the GEO2R online analyzer; for the functional annotation and pathway enrichment analysis of genes, Funrich software was used. Construction of protein-to-protein interaction (PPI) networks was accomplished using the Search Tool for the Retrieval of Interacting Genes (STRING), and network visualization and module identification were performed using Cytoscape.

Results

A total of 268 DEGs were ultimately obtained. The enriched functions and pathways of the upregulated DEGs included cell cycle, mitotic, and DNA replication, and the downregulated DEGs were enriched in epithelial-to-mesenchymal transition, serotonin degradation, and noradrenaline. Analysis of significant modules demonstrated that the upregulated genes are primarily concentrated in functions related to cell cycle and DNA replication. Kaplan-Meier analysis of hub genes revealed that they may promote the carcinogenesis and progression of SCLC. The result of ONCOMINE demonstrated that these 10 hub genes were significantly overexpressed in SCLC compared with normal samples.

Conclusion

Identification of the molecular functions and signaling pathways of participating DEGs can deepen the current understanding of the molecular mechanisms of SCLC. The knowledge gained from this work may contribute to the development of treatment options and improve the prognosis of SCLC in the future.

Inhibition of Polo-like kinase 4 induces mitotic defects and DNA damage in diffuse large B-cell lymphoma

Polo-like kinase 4 (PLK4), a key regulator of centriole biogenesis, has recently been shown to play key roles in tumorigenesis. Blocking PLK4 expression by interference or targeted drugs exhibits attractive potential in improving the efficacy of chemotherapy. Nevertheless, the role of PLK4 in diffuse large B-cell lymphoma (DLBCL) is still undefined. In this study, we discover that PLK4 is a potential target for the treatment of DLBCL, and demonstrate the efficacy of a PLK4 inhibitor when used in combination with doxorubicin. Pharmaceutical inhibition of PLK4 with CFI-400945 inhibited DLBCL cell proliferation and induced apoptotic cell death. The anti-tumor effects were accompanied by mitotic defects, including polyploidy and cytokinesis failure. Activation of p53 and Hippo/YAP tumor suppressor signaling pathway was identified as the potential mechanisms driving CFI-400945 activity. Moreover, CFI-400945 treatment resulted in activation of DNA damage response. Combining CFI-400945 with doxorubicin markedly delayed tumor progression in DLBCL xenografts. Finally, PLK4 was increased in primary DLBCL tissues and cell lines. High levels of PLK4 expression were associated with poor survival in the patients receiving CHOP-based treatment, implicating PLK4 as a predictive biomarker of DLBCL chemosensitivity. These results provide the therapeutic potential of CFI-400945 both as monotherapy or in combination with doxorubicin for the treatment of DLBCL.

Homing in on genomic instability as a therapeutic target in cancer

While genomic instability is a hallmark of cancer, its genetic vulnerabilities remain poorly understood. Identifying strategies that exploit genomic instability to selectively target cancer cells is a central challenge in cancer biology with major implications for anti-cancer drug development.

Future prospects for mitosis-targeted antitumor therapies

Dysregulation of cell cycle progression is a hallmark of cancer cells. In recent years, efforts have been devoted to the development of new therapies that target proteins involved in cell cycle regulation and mitosis. Novel targeted antimitotic drugs include inhibitors of aurora kinase family, polo-like kinase 1, Mps1, Eg5, CENP-5 and the APC/cyclosome complex. While certain new inhibitors reached the clinical trial stage, most were discontinued due to negative results. However, these therapies should not be readily dismissed. Based on recent advances concerning their mechanisms of action, new strategies could be devised to increase their efficacy and promote further clinical trials. Here we discuss three main lines of action to empower these therapeutic approaches: increasing cell death signals during mitotic arrest, targeting senescent cells and facilitating antitumor immune response through immunogenic cell death (ICD).

Genetic variants of CHEK1, PRIM2 and CDK6 in the mitotic phase-related pathway are associated with nonsmall cell lung cancer survival

The mitotic phase is a vital step in cell division and may be involved in cancer progression, but it remains unclear whether genetic variants in mitotic phase-related pathways genes impact the survival of these patients. Here, we investigated associations between 31 032 single nucleotide polymorphisms (SNPs) in 368 mitotic phase-related pathway genes and overall survival (OS) of patients with nonsmall cell lung cancer (NSCLC). We assessed the associations in a discovery data set of 1185 NSCLC patients from the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial and validated the findings in another data set of 984 patients from the Harvard Lung Cancer Susceptibility Study. As a result, we identified three independent SNPs (ie, CHEK1 rs76744140 T>C, PRIM2 rs6939623 G>T and CDK6 rs113181986 G>C) to be significantly associated with NSCLC OS with an adjusted hazard ratio of 1.29 (95% confidence interval = 1.11-1.49, P = 8.26 × 10^-4 ), 1.26 (1.12-1.42, 1.10 × 10^-4 ) and 0.73 (0.63-0.86, 1.63 × 10^-4 ), respectively. Moreover, the number of combined unfavorable genotypes of these three SNPs was significantly associated with NSCLC OS and disease-specific survival in the PLCO data set (P_trend  < .0001 and .0003, respectively). Further expression quantitative trait loci analysis showed that the rs76744140C allele predicted CHEK1 mRNA expression levels in normal lung tissues and that rs113181986C allele predicted CDK6 mRNA expression levels in whole blood tissues. Additional analyses indicated CHEK1, PRIM2 and CDK6 may impact NSCLC survival. Taken together, these findings suggested that these genetic variants may be prognostic biomarkers of patients with NSCLC.

Recent progress in agents targeting polo-like kinases: Promising therapeutic strategies

Polo-like kinases (PLKs) play important roles in regulating multiple aspects of cell cycle and cell proliferation. In many cancer types, PLK family members are often dysregulated, which can lead to uncontrolled cell proliferation and aberrant cell division and has been shown to associate with poor prognosis of cancers. The key roles of PLK kinases in cancers lead to an enhanced interest in them as promising targets for anticancer drug development. In consideration of PLK inhibitors and some other anticancer agents, such as BRD4, EEF2K and Aurora inhibitors, exert synergy effects in cancer cells, dual-targeting of PLK and other cancer-related targets is regarded as an rational and potent strategy to enhance the effectiveness of single-targeting therapy for cancer treatment. This review introduces the PLK family members at first and then focuses on the recent advances of single-target PLK inhibitors and summarizes the corresponding SARs of them. Moreover, we discuss the synergisms between PLK and other anti-tumor targets, and sum up the current dual-target agents based on them.

Preclinical small molecule WEHI-7326 overcomes drug resistance and elicits response in patient-derived xenograft models of human treatment-refractory tumors

Targeting cell division by chemotherapy is a highly effective strategy to treat a wide range of cancers. However, there are limitations of many standard-of-care chemotherapies: undesirable drug toxicity, side-effects, resistance and high cost. New small molecules which kill a wide range of cancer subtypes, with good therapeutic window in vivo, have the potential to complement the current arsenal of anti-cancer agents and deliver improved safety profiles for cancer patients. We describe results with a new anti-cancer small molecule, WEHI-7326, which causes cell cycle arrest in G2/M, cell death in vitro, and displays efficacious anti-tumor activity in vivo. WEHI-7326 induces cell death in a broad range of cancer cell lines, including taxane-resistant cells, and inhibits growth of human colon, brain, lung, prostate and breast tumors in mice xenografts. Importantly, the compound elicits tumor responses as a single agent in patient-derived xenografts of clinically aggressive, treatment-refractory neuroblastoma, breast, lung and ovarian cancer. In combination with standard-of-care, WEHI-7326 induces a remarkable complete response in a mouse model of high-risk neuroblastoma. WEHI-7326 is mechanistically distinct from known microtubule-targeting agents and blocks cells early in mitosis to inhibit cell division, ultimately leading to apoptotic cell death. The compound is simple to produce and possesses favorable pharmacokinetic and toxicity profiles in rodents. It represents a novel class of anti-cancer therapeutics with excellent potential for further development due to the ease of synthesis, simple formulation, moderate side effects and potent in vivo activity. WEHI-7326 has the potential to complement current frontline anti-cancer drugs and to overcome drug resistance in a wide range of cancers.

Synthesis and Anticancer Activity of Mitotic-Specific 3,4-Dihydropyridine-2(1H)-thiones

Most anticancer drugs target mitosis as the most crucial and fragile period of rapidly dividing cancer cells. However the limitations of classical chemotherapeutics drive the search for new more effective and selective compounds. For this purpose structural modifications of the previously characterized pyridine aalog (S1) were incorporated aiming to obtain an antimitotic inhibitor of satisfactory and specific anticancer activity. Structure-activity relationship analysis of the compounds against a panel of cancer cell lines allowed to select a compound with a thiophene ring at C5 of a 3,4-dihydropyridine-2(1H)-thione (S22) with promising antiproliferative activity (IC50 equal 1.71 ± 0.58 µM) and selectivity (SI = 21.09) against melanoma A375 cells. Moreover, all three of the most active compounds from the antiproliferative study, namely S1, S19 and S22 showed better selectivity against A375 cells than reference drug, suggesting their possible lower toxicity and wider therapeutic index. As further study revealed, selected compounds inhibited tubulin polymerization via colchicine binding site in dose dependent manner, leading to aberrant mitotic spindle formation, cell cycle arrest and apoptosis. Summarizing, the current study showed that among obtained mitotic-specific inhibitors analogue with thiophene ring showed the highest antiproliferative activity and selectivity against cancer cells.

Cinnamide derived pyrimidine-benzimidazole hybrids as tubulin inhibitors: Synthesis, in silico and cell growth inhibition studies

An approach in modern medicinal chemistry to discover novel bioactive compounds is by mimicking diverse complementary pharmacophores. In extension of this strategy, a new class of piperazine-linked cinnamide derivatives of benzimidazole-pyrimidine hybrids have been designed and synthesized. Their in vitro cytotoxicity profiles were explored on selected human cancer cell lines. Specifically, structural comparison of target hybrids with tubulin-DAMA-colchicine and tubulin-nocodazole complexes has exposed a deep position of benzimidazole ring into the αT5 loop. All the synthesized compounds were demonstrated modest to interesting cytotoxicity against different cancer cell lines. The utmost cytotoxicity has shown with an amine linker of benzimidazole-pyrimidine series, with specificity toward A549 (lung cancer) cell line. The most potent compound in this series was 18i, which inhibited cancer cell growth at micromolar concentrations ranging 2.21-7.29 µM. Flow cytometry studies disclosed that 18i inhibited the cells in G2/M phase of cell cycle. The potent antitumor activity of 18i resulted from enhanced microtubule disruption at a similar level as nocodazole on β-tubulin antibody, explored using immunofluorescence staining. The most active compound 18i also inhibited tubulin polymerization with an IC₅₀ of 5.72 ± 0.51 µM. In vitro biological analysis of 18i presented apoptosis induction on A549 cells with triggering of ROS generation and loss of mitochondrial membrane potential, resulting in DNA injury. In addition, 18i displayed impairment in cellular migration and inhibited the colony formation. Notably, the safety profile of most potent compound 18i was revealed by screening against normal human pulmonary epithelial cells (L132: IC₅₀: 69.25 ± 5.95 μM). The detailed binding interactions of 18i with tubulin was investigated by employing molecular docking, superimposition and free energy analyses. Thus remarks made in this study established that pyrimidine-benzimidazole hybrids as a new class of tubulin polymerization inhibitors with significant anticancer activity.

Bioinformatics Analysis of Prognostic miRNA Signature and Potential Critical Genes in Colon Cancer

This study aims to lay a foundation for studying the regulation of microRNAs (miRNAs) in colon cancer by applying bioinformatics methods to identify miRNAs and their potential critical target genes associated with colon cancer and prognosis. Data of differentially expressed miRNAs (DEMs) and genes (DEGs) downloaded from two independent databases (TCGA and GEO) and analyzed by R software resulted in 472 DEMs and 565 DEGs in colon cancers, respectively. Next, we developed an 8-miRNA (hsa-mir-6854, hsa-mir-4437, hsa-mir-216a, hsa-mir-3677, hsa-mir-887, hsa-mir-4999, hsa-mir-34b, and hsa-mir-3189) prognostic signature for patients with colon cancer by Cox proportional hazards regression analysis. To predict the target genes of these miRNAs, we used TargetScan and miRDB. The intersection of DEGs with the target genes predicted for these eight miRNAs retrieved 112 consensus genes. GO and KEGG pathway enrichment analyses showed these 112 genes were mainly involved in protein binding, one-carbon metabolic process, nitrogen metabolism, proteoglycans in cancer, and chemokine signaling pathways. The protein-protein interaction network of the consensus genes, constructed using the STRING database and imported into Cytoscape, identified 14 critical genes in the pathogenesis of colon cancer (CEP55, DTL, FANCI, HMMR, KIF15, MCM6, MKI67, NCAPG2, NEK2, RACGAP1, RRM2, TOP2A, UBE2C, and ZWILCH). Finally, we verified the critical genes by weighted gene co-expression network analysis (WGCNA) of the GEO data, and further mined the core genes involved in colon cancer. In summary, this study identified an 8-miRNA model that can effectively predict the prognosis of colon cancer patients and 14 critical genes with vital roles in colon cancer carcinogenesis. Our findings contribute new ideas for elucidating the molecular mechanisms of colon cancer carcinogenesis and provide new therapeutic targets and biomarkers for future treatment and prognosis.

Exploiting immune-dependent effects of microtubule-targeting agents to improve efficacy and tolerability of cancer treatment

Microtubule-targeting agents (MTAs), like taxanes and vinca alkaloids, are tubulin-binding drugs that are very effective in the treatment of various types of cancers. In cell cultures, these drugs appear to affect assembly of the mitotic spindle and to delay progression through mitosis and this correlates with their ability to induce cell death. Their clinical efficacy is, however, limited by resistance and toxicity. For these reasons, other spindle-targeting drugs, affecting proteins such as certain kinesins like Eg5 and CENP-E, or kinases like Plk1, Aurora A and B, have been developed as an alternative to MTAs. However, these attempts have disappointed in the clinic since these drugs show poor anticancer activity and toxicity ahead of positive effects. In addition, whether efficacy of MTAs in cancer treatment is solely due to their ability to delay mitosis progression remains controversial. Here we discuss recent findings indicating that the taxane paclitaxel can promote a proinflammatory response by activation of innate immunity. We further describe how this can help adaptive antitumor immune response and suggest, on this basis and on the recent success of immune checkpoint inhibitors in cancer treatment, that a combination therapy based on low doses of taxanes and immune checkpoint inhibitors may be of high clinical advantage in terms of wide applicability, reduced toxicity, and increased antitumor response.

Discovery of a Dual Tubulin Polymerization and Cell Division Cycle 20 Homologue Inhibitor via Structural Modification on Apcin

Apcin is one of the few compounds that have been previously reported as a Cdc20 specific inhibitor, although Cdc20 is a very promising drug target. We reported here the design, synthesis, and biological evaluations of 2,2,2-trichloro-1-aryl carbamate derivatives as Cdc20 inhibitors. Among these derivatives, compound 9f was much more efficient than the positive compound apcin in inhibiting cancer cell growth, but it had approximately the same binding affinity with apcin in SPR assays. It is possible that another mechanism of action might exist. Further evidence demonstrated that compound 9f also inhibited tubulin polymerization, disorganized the microtubule network, and blocked the cell cycle at the M phase with changes in the expression of cyclins. Thus, it induced apoptosis through the activation of caspase-3 and PARP. In addition, compound 9f inhibited cell migration and invasion in a concentration-dependent manner. These results provide guidance for developing the current series as potential new anticancer therapeutics.

KIF11 and KIF15 mitotic kinesins are potential therapeutic vulnerabilities for malignant peripheral nerve sheath tumors

Background

Malignant peripheral nerve sheath tumor (MPNST) constitutes the leading cause of neurofibromatosis type 1–related mortality. MPNSTs contain highly rearranged hyperploid genomes and exhibit a high division rate and aggressiveness. We have studied in vitro whether the mitotic kinesins KIF11, KIF15, and KIF23 have a functional role in maintaining MPNST cell survival and can represent potential therapeutic vulnerabilities.

Methods

We studied the expression of kinesin mRNAs and proteins in tumors and cell lines and used several in vitro functional assays to analyze the impact of kinesin genetic suppression (KIF15, KIF23) and drug inhibition (KIF11) in MPNST cells. We also performed in vitro combined treatments targeting KIF11 together with other described MPNST targets.

Results

The studied kinesins were overexpressed in MPNST samples. KIF15 and KIF23 were required for the survival of MPNST cell lines, which were also more sensitive than benign control fibroblasts to the KIF11 inhibitors ispinesib and ARRY-520. Co-targeting KIF11 and BRD4 with ARRY-520 and JQ1 reduced MPNST cell viability, synergistically killing a much higher proportion of MPNST cells than control fibroblasts. In addition, genetic suppression of KIF15 conferred an increased sensitivity to KIF11 inhibitors alone or in combination with JQ1.

Conclusions

The mitotic spindle kinesins KIF11 and KIF15 and the cytokinetic kinesin KIF23 play a clear role in maintaining MPNST cell survival and may represent potential therapeutic vulnerabilities. Although further in vivo evidences are still mandatory, we propose a simultaneous suppression of KIF11, KIF15, and BRD4 as a potential therapy for MPNSTs.

Design and synthesis of newer 1,3,4-oxadiazole and 1,2,4-triazole based Topsentin analogues as anti-proliferative agent targeting tubulin

A set of two series of 1,3,4-oxadiazole (11a-n) and 1,2,4-Triazole (12a, c, e, g, h, j-n) based topsentin analogues were prepared by replacing imizadole moiety of topsentin through a multistep synthesis starting from indole. All the compounds synthesized were submitted for single dose (10 µM) screening against a NCI panel of 60-human cancer cell lines. Among all cancer cell lines, colon (HCC-2998) and Breast (MCF-7, T-47D) cancer cell lines were found to be more susceptible for this class of compounds. Among the compounds tested, compounds 11a, 11d, 11f, 12e and 12h, were exhibited good anti-proliferative activity against various cancer cell lines. Compounds 11d, 12e and 12h demonstrated better activity with IC₅₀ 2.42 µM, 3.06 µM, and 3.30 µM respectively against MCF-7 human cancer cell line than that of the standard drug doxorubicin IC₅₀ 6.31 µM. Furthermore, 11d induced cell cycle arrest at G0/G1 phase and also disrupted mitochondrial membrane potential with reducing cell migration potential of MCF-7 cells in dose dependent manner. In vitro microtubule polymerization assays found that compound 11d disrupt tubulin dynamics by inhibiting tubulin polymerization with IC₅₀ 3.89 μM compared with standard nocodazole (IC₅₀ 2.49 μM). In silico docking studies represented that 11d was binding at colchicine binding site of β-tubulin. Compound 11d emerged as lead molecule from the library of compounds tested and this may serve as a template for further drug discovery.

Downregulation of class II phosphoinositide 3-kinase PI3K-C2β delays cell division and potentiates the effect of docetaxel on cancer cell growth

Background

Alteration of signalling pathways regulating cell cycle progression is a common feature of cancer cells. Several drugs targeting distinct phases of the cell cycle have been developed but the inability of many of them to discriminate between normal and cancer cells has strongly limited their clinical potential because of their reduced efficacy at the concentrations used to limit adverse side effects. Mechanisms of resistance have also been described, further affecting their efficacy. Identification of novel targets that can potentiate the effect of these drugs or overcome drug resistance can provide a useful strategy to exploit the anti-cancer properties of these agents to their fullest.

Methods

The class II PI3K isoform PI3K-C2β was downregulated in prostate cancer PC3 cells and cervical cancer HeLa cells using selective siRNAs and the effect on cell growth was determined in the absence or presence of the microtubule-stabilizing agent/anti-cancer drug docetaxel. Mitosis progression was monitored by time-lapse microscopy. Clonogenic assays were performed to determine the ability of PC3 and HeLa cells to form colonies upon PI3K-C2β downregulation in the absence or presence of docetaxel. Cell multi-nucleation was assessed by immunofluorescence. Tumour growth in vivo was assessed using a xenograft model of PC3 cells upon PI3K-C2β downregulation and in combination with docetaxel.

Results

Downregulation of PI3K-C2β delays mitosis progression in PC3 and HeLa cells, resulting in reduced ability to form colonies in clonogenic assays in vitro. Compared to control cells, PC3 cells lacking PI3K-C2β form smaller and more compact colonies in vitro and they form tumours more slowly in vivo in the first weeks after cells implant. Stable and transient PI3K-C2β downregulation potentiates the effect of low concentrations of docetaxel on cancer cell growth. Combination of PI3K-C2β downregulation and docetaxel almost completely prevents colonies formation in clonogenic assays in vitro and strongly inhibits tumour growth in vivo.

Conclusions

These data reveal a novel role for the class II PI3K PI3K-C2β during mitosis progression. Furthermore, data indicate that blockade of PI3K-C2β might represent a novel strategy to potentiate the effect of docetaxel on cancer cell growth.

The LIV-1-GRPEL1 axis adjusts cell fate during anti-mitotic agent-damaged mitosis

Background

Understanding how cells respond to mitotic poisons is of great biomedical and clinical significance. However, it remains unknown how cell-death or survival is determined during exposure to anti-mitotic drugs.

Methods

The biological effects of SLC39A6 (LIV-1) and GrpE-like 1 (GRPEL1) on mitotic exit and apoptosis were evaluated both in vitro and in vivo using flow cytometry, western blotting, xenografts and time-lapse imaging. The interactions between proteins and the ubiquitination of GRPEL1 were assessed by GST pull down, immunoprecipitation and mass spectrometry analysis. The expression of LIV-1 in cancers was assessed by immunohistochemistry.

Findings

Overexpression of LIV-1 led to direct apoptosis. Depleted for LIV-1 evade anti-mitotic agent-induced killing through a rapid exit from arrested mitosis. LIV-1 interacts with GRPEL1 and Stabilizes GRPEL1 Protein by Preventing Ubiquitylation of GRPEL1. LIV-1-GRPEL1 axis depletion works to reduce the mitotic arrest by inducing PP2A-B55α phosphates activity, while inhibit apoptosis by banding AIF and preventing the latter's release into the nucleus. Loss of function in this axis was frequent in multiple types of human epithelial cancer.

Interpretation

These data demonstrate that LIV-1-GRPEL1 axis dually regulates mitotic exit as well as apoptosis by interacting with PP2A B55α and AIF. Its discovery constitutes a conceptual advance for the decisive mechanism of cell fate during damaged mitosis.

Fund

National Clinical Research Center for Obstetric and Gynecologic Diseases, the National Natural Science Foundation of China.

Identification of benzo[d]pyrrolo[2,1-b]thiazole derivatives as CENP-E inhibitors

Kinesin centromere-associated protein E (CENP-E) has emerged as a potential target for the development of anticancer drugs due to its involvement in the mitotic progression of the cell cycle. Although several CENP-E inhibitors have been reported, more knowledge of chemical structures and inhibitory mechanisms is necessary for developing CENP-E inhibitors. Here, we describe the identification of new CENP-E inhibitors. Screening of a small-molecule chemical library identified benzo[d]pyrrolo[2,1-b]thiazole derivatives, including 1, as compounds with inhibitory activity against the microtubule-stimulated ATPase of the CENP-E motor domain. Among the mitotic kinesins examined, 1 selectively inhibited the kinesin ATPase activity of CENP-E. In a steady-state ATPase assay, 1 exhibited ATP-competitive behavior, which was different from the CENP-E inhibitor GSK923295. Compound 1 inhibited the proliferation of tumor-derived HeLa and HCT116 cells more efficiently than that of non-cancerous WI-38 cells. The inhibition of cell proliferation was attributed to the ability of 1 to induce apoptotic cell death. The compound showed antimitotic activity, which caused cell cycle arrest at mitosis via interference with proper chromosome alignment. We identified 1 and its derivatives as the lead compounds that target CENP-E, thus providing a new opportunity for the development of anticancer agents targeting kinesins.

Bioinformatics analysis of mRNA and miRNA microarray to identify the key miRNA‑gene pairs in small‑cell lung cancer

Small-cell lung cancer (SCLC) is a type of lung cancer with early metastasis, and high recurrence and mortality rates. The molecular mechanism is still unclear and further research is required. The aim of the present study was to examine the pathogenesis and potential molecular markers of SCLC by comparing the differential expression of mRNA and microRNA (miRNA) between SCLC tissue and normal lung tissue. A transcriptome sequencing dataset (GSE6044) and a non-coding RNA sequence dataset (GSE19945) were downloaded from the Gene Expression Omnibus (GEO) database. In total, 451 differentially expressed genes (DEGs) and 134 differentially expressed miRNAs (DEMs) were identified using the R limma software package and the GEO2R tool of the GEO, respectively. The Gene Ontology function was significantly enriched for 28 terms, and the Kyoto Encyclopedia of Genes and Genomes database had 19 enrichment pathways, mainly related to ‘cell cycle’, ‘DNA replication’ and ‘oocyte meiosis mismatch repair’. The protein-protein interaction network was constructed using Cytoscape software to identify the molecular mechanisms of key signaling pathways and cellular activities in SCLC. The 1,402 miRNA-gene pairs encompassed 602 target genes of the DEMs using miRNAWalk, which is a bioinformatics platform that predicts DEM target genes and miRNA-gene pairs. There were 19 overlapping genes regulated by 32 miRNAs between target genes of the DEMs and DEGs. Bioinformatics analysis may help to better understand the role of DEGs, DEMs and miRNA-gene pairs in cell proliferation and signal transduction. The related hub genes may be used as biomarkers for the diagnosis and prognosis of SCLC, and as potential drug targets.

Role of aneuploidy in the carcinogenic process: Part 3 of the report of the 2017 IWGT workgroup on assessing the risk of aneugens for carcinogenesis and hereditary diseases

Aneuploidy is regarded as a hallmark of cancer, however, its role is complex with both pro- and anti-carcinogenic effects evident. In this IWGT review, we consider the role of aneuploidy in cancer biology; cancer risk associated with constitutive aneuploidy; rodent carcinogenesis with known chemical aneugens; and chemotherapy-related malignant neoplasms. Aneuploidy is seen at various stages in carcinogenesis. However, the relationship between induced aneuploidy occurring after exposure and clonal aneuploidy present in tumours is not clear. Recent evidence indicates that the induction of chromosomal instability (CIN), may be more important than aneuploidy per se, in the carcinogenic process. Down Syndrome, trisomy 21, is associated with altered hematopoiesis in utero which, in combination with subsequent mutations, results in an increased risk for acute megakaryoblastic and lymphoblastic leukemias. In contrast, there is reduced cancer risk for most solid tumours in Down Syndrome. Mouse models with high levels of aneuploidy are also associated with increased cancer risk for particular tumours with long latencies, but paradoxically other types of tumour often show decreased incidence. The aneugens reviewed that induce cancer in humans and animals all possess other carcinogenic properties, such as mutagenicity, clastogenicity, cytotoxicity, organ toxicities, hormonal and epigenetic changes which likely account for, or interact with aneuploidy, to cause carcinogenesis. Although the role that aneuploidy plays in carcinogenesis has not been fully established, in many cases, it may not play a primary causative role. Tubulin-disrupting aneugens that do not possess other properties linked to carcinogenesis, were not carcinogenic in rodents. Similarly, in humans, for the tubulin-disrupting aneugens colchicine and albendazole, there is no reported association with increased cancer risk. There is a need for further mechanistic studies on agents that induce aneuploidy, particularly by mechanisms other than tubulin disruption and to determine the role of aneuploidy in pre-neoplastic events and in early and late stage neoplasia.

Anti-tubulin agents of natural origin: Targeting taxol, vinca, and colchicine binding domains

Microtubules are a protein which is made of α- and β-heterodimer. It is one of the main components of the cell which play a vital role in cell division especially in G2/M-phase. It exists in equilibrium dynamic of polymerization and depolymerization of α- and β-heterodimer. It is one of the best targets for developing anti-cancer drugs. Various natural occurring molecules are well known for their anti-tubulin effect such as vinca, paclitaxel, combretastatin, colchicine etc. These microtubule-targeted drugs are acted through two processes (i) inhibiting depolymerization of tubulin (tubulin stabilizing agents) and (ii) inhibiting polymerization of tubulin (tubulin destabilizing agents). Now days, various binding domains have been explore through which these molecules are binding to tubulin but the three major binding domain of tubulin are taxol, vinca and colchicine binding domain. The present article mainly focus on the classification of various naturally occurring compounds on the basis of their inhibition processes (depolymerization and polymerization) and the site of interaction (targets taxol, vinca and colchicine binding domain) which has been hitherto reported. By placing all the naturally occurring taxol, vinca and colchicine binding site analogues at one place makes a better understanding of the tubulin interactions with known natural tubulin binders that would helps in the discovery of new and potent natural, semi-synthetic and synthetic analogues for treating cancer.

Anti-mitotic therapies in cancer

Tischer and Gergely review the cell biology behind microtubule poisons and their clinical use in cancer patients.

Natural products as new antimitotic compounds for anticancer drug development

Cell cycle control genes are frequently mutated in cancer cells, which usually display higher rates of proliferation than normal cells. Dysregulated mitosis leads to genomic instability, which contributes to tumor progression and aggressiveness. Many drugs that disrupt mitosis have been studied because they induce cell cycle arrest and tumor cell death. These antitumor compounds are referred to as antimitotics. Vinca alkaloids and taxanes are natural products that target microtubules and inhibit mitosis, and their derivatives are among the most commonly used drugs in cancer therapy worldwide. However, severe adverse effects such as neuropathies are frequently observed during treatment with microtubule-targeting agents. Many efforts have been directed at developing improved antimitotics with increased specificity and decreased likelihood of inducing side effects. These new drugs generally target specific components of mitotic regulation that are mainly or exclusively expressed during cell division, such as kinases, motor proteins and multiprotein complexes. Such small molecules are now in preclinical studies and clinical trials, and many are products or derivatives from natural sources. In this review, we focused on the most promising targets for the development of antimitotics and discussed the advantages and disadvantages of these targets. We also highlighted the novel natural antimitotic agents under investigation by our research group, including combretastatins, withanolides and pterocarpans, which show the potential to circumvent the main issues in antimitotic therapy.

Combretastatin-Inspired Heterocycles as Antitubulin Anticancer Agents

Combretastatin (CA-4) and its analogues are undergoing several clinical trials for treating different types of tumors. In this work, the antiproliferative activity of a series of 2-aminoimidazole-carbonyl analogs of clinically relevant combretastatins A-4 (CA-4) and A-1 was evaluated using a cell-based assay. Among the compounds tested, C-13 and C-21 displayed strong antiproliferative activities against HeLa cells. C-13 inhibited the proliferation of lung carcinoma (A549) cells more potently than combretastatin A-4. C-13 also retarded the migration of A549 cells. Interestingly, C-13 displayed much stronger antiproliferative effects against breast carcinoma and skin melanoma cells compared to noncancerous breast epithelial and skin fibroblast cells. C-13 strongly disassembled cellular microtubules, perturbed the localization of EB1 protein, inhibited mitosis in cultured cells, and bound to tubulin at the colchicine site and inhibited the polymerization of reconstituted microtubules in vitro. C-13 treatment increased the level of reactive oxygen species and induced apoptosis via poly(ADP-ribose) polymerase-cleavage in HeLa cells. The results revealed the importance of the 2-aminoimidazole-carbonyl motif as a double bond replacement in combretastatin and indicated a pharmacodynamically interesting pattern of H-bond acceptors/donors and requisite syn-templated aryls.

Styryl Quinazolinones as Potential Inducers of Myeloid Differentiation via Upregulation of C/EBPα

The CCAAT enhancer-binding protein α (C/EBPα) plays an important role in myeloid cell differentiation and in the enhancement of C/EBPα expression/activity, which can lead to granulocytic differentiation in acute myeloid leukemia (AML) cells. We found that styryl quinazolinones induce upregulation of C/EBPα expression, and thereby induce myeloid differentiation in human myeloid leukemia cell lines. We screened a series of active styryl quinazolinones and evaluated the structure⁻activity relationship (SAR) of these small molecules in inducing C/EBPα expression-thereby prompting the leukemic cells to differentiate. We observed that compound 78 causes differentiation at 3 μM concentration, while 1 induces differentiation at 10 μM concentration. We also observed an increase in the expression of neutrophil differentiation marker CD11b upon treatment with 78. Both the C/EBPα and C/EBPε levels were found to be upregulated by treatment with 78. These SAR findings are inspiration to develop further modified styryl quinazolinones, in the path of this novel differentiation therapy, which can contribute to the care of patients with AML.

Effects of tumor treating fields (TTFields) on glioblastoma cells are augmented by mitotic checkpoint inhibition

Tumor treating fields (TTFields) are approved for glioblastoma (GBM) therapy. TTFields disrupt cell division by inhibiting spindle fiber formation. Spindle assembly checkpoint (SAC) inhibition combined with antimitotic drugs synergistically decreases glioma cell growth in cell culture and mice. We hypothesized that SAC inhibition will increase TTFields efficacy. Human GBM cells (U-87 MG, GaMG) were treated with TTFields (200 kHz, 1.7 V/cm) and/or the SAC inhibitor MPS1-IN-3 (IN-3, 4 µM). Cells were counted after 24, 48, and 72 h of treatment and at 24 and 72 h after end of treatment (EOT). Flow cytometry, immunofluorescence microscopy, Annexin-V staining and TUNEL assay were used to detect alterations in cell cycle and apoptosis after 72 h of treatment. The TTFields/IN-3 combination decreased cell proliferation after 72 h compared to either treatment alone (-78.6% vs. TTFields, P = 0.0337; -52.6% vs. IN-3, P = 0.0205), and reduced the number of viable cells (62% less than seeded). There was a significant cell cycle shift from G1 to G2/M phase (P < 0.0001). The apoptotic rate increased to 44% (TTFields 14%, P = 0.0002; IN-3 4%, P < 0.0001). Cell growth recovered 24 h after EOT with TTFields and IN-3 alone, but the combination led to further decrease by 92% at 72 h EOT if IN-3 treatment was continued (P = 0.0288). The combination of TTFields and SAC inhibition led to earlier and prolonged effects that significantly augmented the efficacy of TTFields and highlights a potential new targeted multimodal treatment for GBM.

Spindle Assembly Disruption and Cancer Cell Apoptosis with a CLTC-Binding Compound

AK3 compounds are mitotic arrest agents that induce high levels of γH2AX during mitosis and apoptosis following release from arrest. We synthesized a potent AK3 derivative, AK306, that induced arrest and apoptosis of the HCT116 colon cancer cell line with an EC₅₀ of approximately 50 nmol/L. AK306 was active on a broad spectrum of cancer cell lines with total growth inhibition values ranging from approximately 25 nmol/L to 25 μmol/L. Using biotin and BODIPY-linked derivatives of AK306, binding to clathrin heavy chain (CLTC/CHC) was observed, a protein with roles in endocytosis and mitosis. AK306 inhibited mitosis and endocytosis, while disrupting CHC cellular localization. Cells arrested in mitosis by AK306 showed the formation of multiple microtubule-organizing centers consisting of pericentrin, γ-tubulin, and Aurora A foci, without apparent centrosome amplification. Cells released from AK306 arrest were unable to form bipolar spindles, unlike nocodazole-released cells that reformed spindles and completed division. Like AK306, CHC siRNA knockdown disrupted spindle formation and activated p53. A short-term (3-day) treatment of tumor-bearing APC-mutant mice with AK306 increased apoptosis in tumors, but not normal mucosa. These findings indicate that targeting the mitotic CHC complex can selectively induce apoptosis and may have therapeutic value.Implication: Disruption of clathrin with a small-molecule inhibitor, AK306, selectively induces apoptosis in cancer cells by disrupting bipolar spindle formation. Mol Cancer Res; 16(9); 1361-72. ©2018 AACR.

PMN inhibits colorectal cancer cells through inducing mitotic arrest and p53-dependent apoptosis via the inhibition of tubulin polymerization

Colorectal cancer (CRC) is the third most prevalent malignancy worldwide. New understandings about this disease are urgently required to guide clinical therapies. In this study, we focused on the effects of the small molecule PMN on CRC cells. PMN dose-dependently inhibited CRC cell proliferation through inducing mitotic arrest and apoptosis. PMN induced mitotic arrest via the disruption of spindle apparatus by inhibiting microtubule polymerization. PMN-induced mitotic arrest resulted in apoptosis and p53 upregulation. Furthermore, p53 upregulation sensitized PMN-induced mitotic cells to apoptosis. This study deepens the understanding of the effects of p53 on the response of CRC cells to PMN, providing the basis for the potential development of PMN as a lead compound of microtubule-destabilizers for p53-positive CRC treatment.

Nuclear division cycle 80 promotes malignant progression and predicts clinical outcome in colorectal cancer

Colorectal cancer (CRC) is a common human malignancy worldwide and increasing studies have attributed its malignant progression to abnormal molecular changes in cancer cells. Nuclear division cycle 80 (NDC80) is a newly discovered oncoprotein that regulates cell proliferation and cycle in numerous malignancies. However, its clinical significance and biological role in CRC remain unclear. Therefore, in this study, we firstly analyze its expression in a retrospective cohort enrolling 224 CRC patients and find its overexpression is significantly correlated with advanced tumor stage and poor prognosis in CRC patients. In addition, our result reveals it is an independent adverse prognostic factor affecting CRC-specific and disease-free survival. The subgroup analysis indicates NDC80 expression can stratify the clinical outcome in stage II and III patients, but fails in stage I and IV patients. In cellular assays, we find knockdown of NDC80 dramatically inhibits the proliferative ability, apoptosis resistance, cell cycle progression, and clone formation of CRC cells in vitro. Using xenograft model, we further prove knockdown of NDC80 also inhibits the tumorigenic ability of CRC cells in vivo. Finally, the microarray analysis is utilized to preliminarily clarify the oncogenic molecular mechanisms regulated by NDC80 and the results suggest it may promote CRC progression partly by downregulating tumor suppressors such as dual specificity phosphatase 5 and Forkhead box O1. Taken together, our study provides novel evidences to support that NDC80 is not only a promising clinical biomarker but also a potential therapeutical target for CRC precise medicine.

Modulation Of Microtubule Acetylation By The Interplay Of TPPP/p25, SIRT2 And New Anticancer Agents With Anti-SIRT2 Potency

The microtubule network exerts multifarious functions controlled by its decoration with various proteins and post-translational modifications. The disordered microtubule associated Tubulin Polymerization Promoting Protein (TPPP/p25) and the NAD⁺-dependent tubulin deacetylase sirtuin-2 (SIRT2) play key roles in oligodendrocyte differentiation by acting as dominant factors in the organization of myelin proteome. Herein, we show that SIRT2 impedes the TPPP/p25-promoted microtubule assembly independently of NAD⁺; however, the TPPP/p25-assembled tubulin ultrastructures were resistant against SIRT2 activity. TPPP/p25 counteracts the SIRT2-derived tubulin deacetylation producing enhanced microtubule acetylation. The inhibition of the SIRT2 deacetylase activity by TPPP/p25 is evolved by the assembly of these tubulin binding proteins into a ternary complex, the concentration-dependent formation of which was quantified by experimental-based mathematical modelling. Co-localization of the SIRT2-TPPP/p25 complex on the microtubule network was visualized in HeLa cells by immunofluorescence microscopy using Bimolecular Fluorescence Complementation. We also revealed that a new potent SIRT2 inhibitor (MZ242) and its proteolysis targeting chimera (SH1) acting together with TPPP/p25 provoke microtubule hyperacetylation, which is coupled with process elongation only in the case of the degrader SH1. Both the structural and the functional effects manifesting themselves by this deacetylase proteome could lead to the fine-tuning of the regulation of microtubule dynamics and stability.