How do anti-mitotic drugs kill cancer cells?

Long-term Live-cell Imaging to Assess Cell Fate in Response to Paclitaxel

Live-cell imaging is a powerful technique that can be used to directly visualize biological phenomena in single cells over extended periods of time. Over the past decade, new and innovative technologies have greatly enhanced the practicality of live-cell imaging. Cells can now be kept in focus and continuously imaged over several days while maintained under 37 °C and 5% CO2 cell culture conditions. Moreover, multiple fields of view representing different experimental conditions can be acquired simultaneously, thus providing high-throughput experimental data. Live-cell imaging provides a significant advantage over fixed-cell imaging by allowing for the direct visualization and temporal quantitation of dynamic cellular events. Live-cell imaging can also identify variation in the behavior of single cells that would otherwise have been missed using population-based assays. Here, we describe live-cell imaging protocols to assess cell fate decisions following treatment with the anti-mitotic drug paclitaxel. We demonstrate methods to visualize whether mitotically arrested cells die directly from mitosis or slip back into interphase. We also describe how the fluorescent ubiquitination-based cell cycle indicator (FUCCI) system can be used to assess the fraction of interphase cells born from mitotic slippage that are capable of re-entering the cell cycle. Finally, we describe a live-cell imaging method to identify nuclear envelope rupture events.

FOXM1 contributes to taxane resistance by regulating UHRF1-controlled cancer cell stemness

Therapy-induced expansion of cancer stem cells (CSCs) has been identified as one of the most critical factors contributing to therapeutic resistance, but the mechanisms of this adaptation are not fully understood. UHRF1 is a key epigenetic regulator responsible for therapeutic resistance, and controls the self-renewal of stem cells. In the present study, taxane-resistant cancer cells were established and stem-like cancer cells were expanded. UHRF1 was overexpressed in the taxane-resistant cancer cells, which maintained CSC characteristics. UHRF1 depletion overcame taxane resistance in vitro and in vivo. Additionally, FOXM1 has been reported to play a role in therapeutic resistance and the self-renewal of CSCs. FOXM1 and UHRF1 are highly correlated in prostate cancer tissues and cells, FOXM1 regulates CSCs by regulating uhrf1 gene transcription in an E2F-independent manner, and FOXM1 protein directly binds to the FKH motifs at the uhrf1 gene promoter. This present study clarified a novel mechanism by which FOXM1 controls CSCs and taxane resistance through a UHRF1-mediated signaling pathway, and validated FOXM1 and UHRF1 as two potential therapeutic targets to overcome taxane resistance.

Unveiling the Potential of Unfused Bichromophoric Naphthalimide To Induce Cytotoxicity by Binding to Tubulin: Breaks Monotony of Naphthalimides as Conventional Intercalators

In the development of small-molecule drug candidates, naphthalimide-based compounds hold a very important position as potent anticancer agents with considerable safety in drug discoveries. Being synthetically and readily accessible, naphthalimide compounds with planar architecture have been developed mostly as DNA-targeting intercalators. However, in this article, it is demonstrated, for the first time, that an unfused naphthalimide-benzothiazole bichromophoric compound 2-(6-chlorobenzo[ d] thiazol-2-yl)-1 H-benzo[ de] isoquinoline-1,3(2 H)-dione (CBIQD), seems to expand the bioactivity of naphthalimide as anti-mitotic agent also. Preliminary studies demonstrate that CBIQD interferes with human lung cancer (A549) cell proliferation and growth and causes cellular morphological changes. However, the underlying mechanism of its antitumor action and primary cellular target in A549 cells remained skeptical. Confocal microscopy in A549 cells revealed disruption of interphase microtubule (MT) network and formation of aberrant multipolar spindle. Consistent with microscopy results, UV-vis, steady-state fluorescence, and time-resolved fluorescence (TRF) studies demonstrate that CBIQD efficiently binds to tubulin ( K_b = 2.03 × 10⁵ M^-1 ± 1.88%), inhibits its polymerization, and depolymerizes preformed microtubules (MTs). Low doses of CBIQD have also shown specificity toward tubulin protein in the presence of a nonspecific protein like bovine serum albumin as well as other cytoskeleton component, actin. The in vitro determination of binding site coupled with in silico studies suggests that CBIQD may prefer to occupy the colchicine binding site. Further, CBIQD perturbed tubulin conformation to some extent and protected ∼1.4 cysteine residues toward chemical modification by 5,5'-dithiobis-2-nitrobenzoic acid. We also suggest the possible mechanism underlying CBIQD-induced cancer cell cytotoxicity: CBIQD, when bound to tubulin, may prevent it to maintain a straight conformation; consequently, the α- and β-heterodimers might be no longer available for MT growth. Thus, the consolidated spectroscopic research described herein explores the potential of CBIQD as a new paradigm in the design and development of novel unfused or nonring-fused naphthalimide-based antimitotic cancer therapeutics in medicinal chemistry research.

Engaging Anaphase Catastrophe Mechanisms to Eradicate Aneuploid Cancers

Cancer cells often have supernumerary centrosomes that promote genomic instability, a pathognomonic feature of cancer. During mitosis, cancer cells with supernumerary centrosomes undergo bipolar cell division by clustering centrosomes into two poles. When supernumerary centrosome clustering is antagonized, cancer cells are forced to undergo multipolar division leading to death of daughter cells. This proapoptotic pathway, called anaphase catastrophe, preferentially eliminates aneuploid cancer cells and malignant tumors in engineered mouse models. Anaphase catastrophe occurs through the loss or inhibition of the centrosomal protein CP110, a direct cyclin-dependent kinase 1 (CDK1) and CDK2 target. Intriguingly, CP110 is repressed by the KRAS oncoprotein. This sensitizes KRAS-driven lung cancers (an unmet medical need) to respond to CDK2 inhibitors. Anaphase catastrophe-inducing agents like CDK1 and CDK2 antagonists are lethal to cancer cells with supernumerary centrosomes, but can relatively spare normal cells with two centrosomes. This mechanism is proposed to provide a therapeutic window in the cancer clinic following treatment with a CDK1 or CDK2 inhibitor. Taken together, anaphase catastrophe is a clinically tractable mechanism that promotes death of neoplastic tumors with aneuploidy, a hallmark of cancer. Mol Cancer Ther; 17(4); 724-31. ©2018 AACR.

Identification and characterization of SSE15206, a microtubule depolymerizing agent that overcomes multidrug resistance

Microtubules are highly dynamic structures that form spindle fibres during mitosis and are one of the most validated cancer targets. The success of drugs targeting microtubules, however, is often limited by the development of multidrug resistance. Here we describe the discovery and characterization of SSE15206, a pyrazolinethioamide derivative [3-phenyl-5-(3,4,5-trimethoxyphenyl)-4,5-dihydro-1H-pyrazole-1-carbothioamide] that has potent antiproliferative activities in cancer cell lines of different origins and overcomes resistance to microtubule-targeting agents. Treatment of cells with SSE15206 causes aberrant mitosis resulting in G2/M arrest due to incomplete spindle formation, a phenotype often associated with drugs that interfere with microtubule dynamics. SSE15206 inhibits microtubule polymerization both in biochemical and cellular assays by binding to colchicine site in tubulin as shown by docking and competition studies. Prolonged treatment of cells with the compound results in apoptotic cell death [increased Poly (ADP-ribose) polymerase cleavage and Annexin V/PI staining] accompanied by p53 induction. More importantly, we demonstrate that SSE15206 is able to overcome resistance to chemotherapeutic drugs in different cancer cell lines including multidrug-resistant KB-V1 and A2780-Pac-Res cell lines overexpressing MDR-1, making it a promising hit for the lead optimization studies to target multidrug resistance.

BCL-W is a regulator of microtubule inhibitor-induced mitotic cell death

Microtubule inhibitors including taxanes and vinca alkaloids are among the most widely used anticancer agents. Disrupting the microtubules activates the spindle-assembly checkpoint and traps cells in mitosis. Whether cells subsequently undergo mitotic cell death is an important factor for the effectiveness of the anticancer agents. Given that apoptosis accounts for the majority of mitotic cell death induced by microtubule inhibitors, we performed a systematic study to determine which members of the anti-apoptotic BCL-2 family are involved in determining the duration of mitotic block before cell death or slippage. Depletion of several anti-apoptotic BCL-2-like proteins significantly shortened the time before apoptosis. Among these proteins, BCL-W has not been previously characterized to play a role in mitotic cell death. Although the expression of BCL-W remained constant during mitotic block, it varied significantly between different cell lines. Knockdown of BCL-W with siRNA or disruption of the BCL-W gene with CRISPR-Cas9 speeded up mitotic cell death. Conversely, overexpression of BCL-W delayed mitotic cell death, extending the mitotic block to allow mitotic slippage. Taken together, these results showed that BCL-W contributes to the threshold of anti-apoptotic activity during mitosis.

Identification of genes that are essential to restrict genome duplication to once per cell division

Nuclear genome duplication is normally restricted to once per cell division, but aberrant events that allow excess DNA replication (EDR) promote genomic instability and aneuploidy, both of which are characteristics of cancer development. Here we provide the first comprehensive identification of genes that are essential to restrict genome duplication to once per cell division. An siRNA library of 21,584 human genes was screened for those that prevent EDR in cancer cells with undetectable chromosomal instability. Candidates were validated by testing multiple siRNAs and chemical inhibitors on both TP53+ and TP53- cells to reveal the relevance of this ubiquitous tumor suppressor to preventing EDR, and in the presence of an apoptosis inhibitor to reveal the full extent of EDR. The results revealed 42 genes that prevented either DNA re-replication or unscheduled endoreplication. All of them participate in one or more of eight cell cycle events. Seventeen of them have not been identified previously in this capacity. Remarkably, 14 of the 42 genes have been shown to prevent aneuploidy in mice. Moreover, suppressing a gene that prevents EDR increased the ability of the chemotherapeutic drug Paclitaxel to induce EDR, suggesting new opportunities for synthetic lethalities in the treatment of human cancers.

Label-Free Raman Hyperspectral Imaging of Single Cells Cultured on Polymer Substrates

While Raman hyperspectral imaging has been widely used for label-free mapping of biomolecules in cells, these measurements require the cells to be cultured on weakly Raman scattering substrates. However, many applications in biological sciences and engineering require the cells to be cultured on polymer substrates that often generate large Raman scattering signals. Here, we discuss the theoretical limits of the signal-to-noise ratio in the Raman spectra of cells in the presence of polymer signals and how optical aberrations may affect these measurements. We show that Raman spectra of cells cultured on polymer substrates can be obtained using automatic subtraction of the polymer signals and demonstrate the capabilities of these methods in two important applications: tissue engineering and in vitro toxicology screening of drugs. Apart from their scientific and technological importance, these applications are examples of the two most common measurement configurations: (1) cells cultured on an optically thick polymer substrate measured using an immersion/dipping objective; and (2) cells cultured on a transparent polymer substrate and measured using an inverted optical microscope. In these examples, we show that Raman hyperspectral data sets with sufficient quality can be successfully acquired to map the distribution of common biomolecules in cells, such as nucleic acids, proteins, and lipids, as well as detecting the early stages of apoptosis. We also discuss strategies for further improvements that could expand the application of Raman hyperspectral imaging on polymer substrates even further in biomedical sciences and engineering.

Mammalian Cell Division in 3D Matrices via Quantitative Confocal Reflection Microscopy

The study of how mammalian cell division is regulated in a 3D environment remains largely unexplored despite its physiological relevance and therapeutic significance. Possible reasons for the lack of exploration are the experimental limitations and technical challenges that render the study of cell division in 3D culture inefficient. Here, we describe an imaging-based method to efficiently study mammalian cell division and cell-matrix interactions in 3D collagen matrices. Cells labeled with fluorescent H2B are synchronized using the combination of thymidine blocking and nocodazole treatment, followed by a mechanical shake-off technique. Synchronized cells are then embedded into a 3D collagen matrix. Cell division is monitored using live-cell microscopy. The deformation of collagen fibers during and after cell division, which is an indicator of cell-matrix interaction, can be monitored and quantified using quantitative confocal reflection microscopy. The method provides an efficient and general approach to study mammalian cell division and cell-matrix interactions in a physiologically relevant 3D environment. This approach not only provides novel insights into the molecular basis of the development of normal tissue and diseases, but also allows for the design of novel diagnostic and therapeutic approaches.

The small molecule SI113 synergizes with mitotic spindle poisons in arresting the growth of human glioblastoma multiforme

Glioblastoma multiforme (GBM) is the deadliest brain tumor. State-of-art GBM therapy often fails to ensure control of a disease characterized by high frequency of recurrences and progression. In search for novel therapeutic approaches, we assayed the effect of compounds from a cancer drug library on the ADF GBM cell line, establishing their elevated sensitivity to mitotic spindle poisons. Our previous work showed that the effectiveness of the spindle poison paclitaxel in inhibiting cancer cell growth was dependent on the expression of RANBP1, a regulatory target of the serine/threonine kinase SGK1. Recently, we developed the small molecule SI113 to inhibit SGK1 activity. Therefore, we explored the outcome of the association between SI113 and selected spindle poisons, finding that these drugs generated a synergistic cytotoxic effect in GBM cells, drastically reducing their viability and clonogenic capabilities in vitro, as well as inhibiting tumor growth in vivo. We also defined the molecular bases of such a synergistic effect. Because SI113 displays low systemic toxicity, yet strong activity in potentiating the effect of radiotherapy in GBM cells, we believe that this drug could be a strong candidate for clinical trials, with the aim to add it to the current GBM therapeutic approaches.

Preparation of Primary Acute Lymphoblastic Leukemia Cells in Different Cell Cycle Phases by Centrifugal Elutriation

The ability to synchronize cells has been central to advancing our understanding of cell cycle regulation. Common techniques employed include serum deprivation; chemicals which arrest cells at different cell cycle phases; or the use of mitotic shake-off which exploits their reduced adherence. However, all of these have disadvantages. For example, serum starvation works well for normal cells but less well for tumor cells with compromised cell cycle checkpoints due to oncogene activation or tumor suppressor loss. Similarly, chemically-treated cell populations can harbor drug-induced damage and show stress-related alterations. A technique which circumvents these problems is counterflow centrifugal elutriation (CCE), where cells are subjected to two opposing forces, centrifugal force and fluid velocity, which results in the separation of cells on the basis of size and density. Since cells advancing through the cycle typically enlarge, CCE can be used to separate cells into different cell cycle phases. Here we apply this technique to primary acute lymphoblastic leukemia cells. Under optimal conditions, an essentially pure population of cells in G1 phase and a highly enriched population of cells in G2/M phases can be obtained in excellent yield. These cell populations are ideally suited for studying cell cycle-dependent mechanisms of action of anticancer drugs and for other applications. We also show how modifications to the standard procedure can result in suboptimal performance and discuss the limitations of the technique. The detailed methodology presented should facilitate application and exploration of the technique to other types of cells.

Mitotic Spindle Assembly and Genomic Stability in Breast Cancer Require PI3K-C2α Scaffolding Function

Proper organization of the mitotic spindle is key to genetic stability, but molecular components of inter-microtubule bridges that crosslink kinetochore fibers (K-fibers) are still largely unknown. Here we identify a kinase-independent function of class II phosphoinositide 3-OH kinase α (PI3K-C2α) acting as limiting scaffold protein organizing clathrin and TACC3 complex crosslinking K-fibers. Downregulation of PI3K-C2α causes spindle alterations, delayed anaphase onset, and aneuploidy, indicating that PI3K-C2α expression is required for genomic stability. Reduced abundance of PI3K-C2α in breast cancer models initially impairs tumor growth but later leads to the convergent evolution of fast-growing clones with mitotic checkpoint defects. As a consequence of altered spindle, loss of PI3K-C2α increases sensitivity to taxane-based therapy in pre-clinical models and in neoadjuvant settings.

Fighting tubulin-targeting anticancer drug toxicity and resistance

Tubulin-targeting drugs, like taxanes and vinca alkaloids, are among the most effective anticancer therapeutics used in the clinic today. Specifically, anti-microtubule cancer drugs (AMCDs) have proven to be effective in the treatment of castration-resistant prostate cancer and triple-negative breast cancer. AMCDs, however, have limiting toxicities that include neutropenia and neurotoxicity, and, in addition, tumor cells can become resistant to the drugs after long-term use. Co-targeting mitotic progression/slippage with inhibition of the protein kinases WEE1 and MYT1 that regulate CDK1 kinase activity may improve AMCD efficacy, reducing the acquisition of resistance by the tumor and side effects from the drug and/or its vehicle. Other possible treatments that improve outcomes in the clinic for these two drug-resistant cancers, including new formulations of the AMCDs and pursuing different molecular targets, will be discussed.

Mitotic cell death induction by targeting the mitotic spindle with tubulin-inhibitory indole derivative molecules

Tubulin-targeting molecules are widely used cancer therapeutic agents. They inhibit microtubule-based structures, including the mitotic spindle, ultimately preventing cell division. The final fates of microtubule-inhibited cells are however often heterogeneous and difficult to predict. While recent work has provided insight into the cell response to inhibitors of microtubule dynamics (taxanes), the cell response to tubulin polymerization inhibitors remains less well characterized. Arylthioindoles (ATIs) are recently developed tubulin inhibitors. We previously identified ATI members that effectively inhibit tubulin polymerization in vitro and cancer cell growth in bulk cell viability assays. Here we characterise in depth the response of cancer cell lines to five selected ATIs. We find that all ATIs arrest mitotic progression, yet subsequently yield distinct cell fate profiles in time-lapse recording assays, indicating that molecules endowed with similar tubulin polymerization inhibitory activity in vitro can in fact display differential efficacy in living cells. Individual ATIs induce cytological phenotypes of increasing severity in terms of damage to the mitotic apparatus. That differentially triggers MCL-1 down-regulation and caspase-3 activation, and underlies the terminal fate of treated cells. Collectively, these results contribute to define the cell response to tubulin inhibitors and pinpoint potentially valuable molecules that can increase the molecular diversity of tubulin-targeting agents.

Modeling Cancer Cell Growth Dynamics In vitro in Response to Antimitotic Drug Treatment

Investigating the role of intrinsic cell heterogeneity emerging from variations in cell-cycle parameters and apoptosis is a crucial step toward better informing drug administration. Antimitotic agents, widely used in chemotherapy, target exclusively proliferative cells and commonly induce a prolonged mitotic arrest followed by cell death via apoptosis. In this paper, we developed a physiologically motivated mathematical framework for describing cancer cell growth dynamics that incorporates the intrinsic heterogeneity in the time individual cells spend in the cell-cycle and apoptosis process. More precisely, our model comprises two age-structured partial differential equations for the proliferative and apoptotic cell compartments and one ordinary differential equation for the quiescent compartment. To reflect the intrinsic cell heterogeneity that governs the growth dynamics, proliferative and apoptotic cells are structured in "age," i.e., the amount of time remaining to be spent in each respective compartment. In our model, we considered an antimitotic drug whose effect on the cellular dynamics is to induce mitotic arrest, extending the average cell-cycle length. The prolonged mitotic arrest induced by the drug can trigger apoptosis if the time a cell will spend in the cell cycle is greater than the mitotic arrest threshold. We studied the drug's effect on the long-term cancer cell growth dynamics using different durations of prolonged mitotic arrest induced by the drug. Our numerical simulations suggest that at confluence and in the absence of the drug, quiescence is the long-term asymptotic behavior emerging from the cancer cell growth dynamics. This pattern is maintained in the presence of small increases in the average cell-cycle length. However, intermediate increases in cell-cycle length markedly decrease the total number of cells and can drive the cancer population to extinction. Intriguingly, a large "switch-on/switch-off" increase in the average cell-cycle length maintains an active cell population in the long term, with oscillating numbers of proliferative cells and a relatively constant quiescent cell number.

Sensitivity of docetaxel-resistant MCF-7 breast cancer cells to microtubule-destabilizing agents including vinca alkaloids and colchicine-site binding agents

Introduction

One of the main reasons for disease recurrence in the curative breast cancer treatment setting is the development of drug resistance. Microtubule targeted agents (MTAs) are among the most commonly used drugs for the treatment of breaset cancer and therefore overcoming taxane resistance is of primary clinical importance. Our group has previously demonstrated that the microtubule dynamics of docetaxel-resistant MCF-7_TXT cells are insensitivity to docetaxel due to the distinct expression profiles of β-tubulin isotypes in addition to the high expression of p-glycoprotein (ABCB1). In the present investigation we examined whether taxane-resistant breast cancer cells are more sensitive to microtubule destabilizing agents including vinca alkaloids and colchicine-site binding agents (CSBAs) than the non-resistant cells.

Methods

Two isogenic MCF-7 breast cancer cell lines were selected for resistance to docetaxel (MCF-7_TXT) and the wild type parental cell line (MCF-7_CC) to examine if taxane-resistant breast cancer cells are sensitive to microtubule-destabilizing agents including vinca alkaloids and CSBAs. Cytotoxicity assays, immunoblotting, indirect immunofluorescence and live imaging were used to study drug resistance, apoptosis, mitotic arrest, microtubule formation, and microtubule dynamics.

Results

MCF-7_TXT cells were demonstrated to be cross resistant to vinca alkaloids, but were more sensitive to treatment with colchicine compared to parental non-resistant MCF-7_CC cells. Cytotoxicity assays indicated that the IC₅₀ of MCF-7_TXT cell to vinorelbine and vinblastine was more than 6 and 3 times higher, respectively, than that of MCF-7_CC cells. By contrast, the IC₅₀ of MCF-7_TXT cell for colchincine was 4 times lower than that of MCF-7_CC cells. Indirect immunofluorescence showed that all MTAs induced the disorganization of microtubules and the chromatin morphology and interestingly each with a unique pattern. In terms of microtubule and chromain morphology, MCF-7_TXT cells were more resistant to vinorelbine and vinblastine, but more sensitive to colchicine compared to MCF-7_CC cells. PARP cleavage assay further demonstrated that all of the MTAs induced apoptosis of the MCF-7 cells. However, again, MCF-7_TXT cells were more resistant to vinorelbine and vinblastine, and more sensitive to colchicine compared to MCF-7_CC cells. Live imaging demonstrated that the microtubule dynamics of MCF-7_TXT cells were less sensitive to vinca alkaloids, and more sensitive to colchicine. MCF-7_TXT cells were also noted to be more sensitive to other CSBAs including 2MeOE₂, ABT-751 and phosphorylated combretastatin A-4 (CA-4P).

Conclusion

Docetaxel-resistant MCF-7_TXT cells have demonstrated cross-resistance to vinca alkaloids, but appear to be more sensitive to CSBAs (colchicine, 2MeOE₂, ABT-751 and CA-4P) compared to non-resistant MCF-7_CC cells. Taken together these results suggest that CSBAs should be evaluated further in the treatment of taxane resistant breast cancer.

Induction of accelerated senescence by the microtubule-stabilizing agent peloruside A

Chemotherapeutic agents can induce accelerated senescence in tumor cells, an irreversible state of cell cycle arrest. Paclitaxel, a microtubule-stabilizing agent used to treat solid tumors of the breast, ovary, and lung and discodermolide, another stabilizing agent from a marine sponge, induce senescence in cultured cancer cells. The aim of this study was to determine if the microtubule-stabilizing agent peloruside A, a polyketide natural product from a marine sponge, can induce accelerated senescence in a breast cancer cell line MCF7. Doxorubicin, a DNA-damaging agent, paclitaxel, and discodermolide were used as positive controls. Senescence-associated-β-galactosidase activity was increased by peloruside A, similar to paclitaxel, discodermolde, and doxorubicin, with a potency heirarchy of doxorubicin > paclitaxel > discodermolide > peloruside, based on IC₂₅ concentrations that inhibit proliferation. Clonogenic survival was significantly decreased by peloruside A, similar to doxorubicin and the two other microtubule-stabilizing agents. The tumor suppressor protein p53 increased after treatment, whereas pRb decreased in response to all four compounds. It was concluded that in addition to apoptosis, peloruside A causes accelerated senescence in a subpopulation of MCF7 cells that contributes to its potential anticancer activity in a breast cancer cell line.

Human MAP Tau Based Targeted Cytolytic Fusion Proteins

Some of the most promising small molecule toxins used to generate antibody drug conjugates (ADCs) include anti-mitotic agents (e.g., auristatin and its derivatives) which are designed to attack cancerous cells at their most vulnerable state during mitosis. We were interested in identifying a human cystostatic protein eventually showing comparable activities and allowing the generation of corresponding targeted fully human cytolytic fusion proteins. Recently, we identified the human microtubule associated protein tau (MAP tau), which binds specifically to tubulin and modulates the stability of microtubules, thereby blocking mitosis and presumably vesicular transport. By binding and stabilizing polymerized microtubule filaments, MAP tau-based fusion proteins skew microtubule dynamics towards cell cycle arrest and apoptosis. This biological activity makes rapidly proliferating cells (e.g., cancer and inflammatory cells) an excellent target for MAP tau-based targeted treatments. Their superior selectivity for proliferating cells confers additional selectivity towards upregulated tumor-associated antigens at their surface, thereby preventing off-target related toxicity against normal cells bearing tumor-associated antigens at physiologically normal to low levels. In this review, we highlight recent findings on MAP tau-based targeted cytolytic fusion proteins reported in preclinical immunotherapeutic studies.

Sensitivity to antitubulin chemotherapeutics is potentiated by a photoactivable nanoliposome

Anti-microtubule therapy represents one of the most strategic cancer therapeutics. Tublin inhibitor such as paclitaxel (PTX) is well known to disturb the dynamic nature of microtubules, being considered as the first-line drug for various malignancies. However, PTX does not show favorable clinical outcomes due to serious systemic toxicities and low selectivity. The development of PTX delivery systems and combinational therapies has been conducted to enhance PTX efficacy with poorly defined mechanisms. Herein, we introduced a reactive oxygen species producible composite liposome based on a new photosensitizer sinoporphyrin sodium (DVDMS) to enhance the therapeutic effect of PTX through photochemical stimulation, and more importantly, the pivotal molecular regulation mechanisms were specifically explored. Compared with DVDMS-liposome (DL) or PTX-liposome (PL), the composite liposome DVDMS-PTX-liposome (PDL) exhibited a superior anti-tumor advantage following laser irradiation against MCF-7 breast cancer. The localized PTX release after PDL administration greatly decreased the drug dosage and laser power required, leading to much higher safety and lower costs. In vitro, the combined treatment significantly suppressed cell viability and potentiated cell apoptosis. The apoptotic central regulator Mcl-1 as a favorable target, was evaluated in association with photochemically enhanced sensitivity to anti-tubulin chemotherapeutics. Phosphorylation of Mcl-1 led to its direct degradation with the proteasome system, making it relatively unstable and potentiating cell death resulting from photochemical synergy via PDL plus laser irradiation. Further, a decrease in ATP production and glycolysis after PDL plus laser would prevent the possible energy-switch and apoptosis-escape by PTX alone treatment, thereby resulted in increased cell death in combinational therapy. Systemic administration of PDL followed by in vivo photochemotherapy achieved significantly improved therapeutic effects compared to either alone. And, the intrinsic fluorescence of DVDMS facilitated real-time imaging of PDL in tumors. Therefore, the present strategy with details at the molecular regulation could be a promising platform for antitublin chemotherapeutics.

Centrosomal Protein 70 Is a Mediator of Paclitaxel Sensitivity

Centrosome aberrations have been implicated in the development and progression of breast cancer. Our previous worked show that centrosomal protein 70 (Cep70) regulates breast cancer growth and metastasis. However, it remains elusive whether Cep70 is implicated in the sensitivity of the anti-microtubule drug paclitaxel in breast cancer. Here we provide evidence that Cep70 is a mediator of paclitaxel sensitivity in breast cancer. Cell proliferation assays show that Cep70 expression correlates with paclitaxel sensitivity in breast cancer cell lines. In addition, paclitaxel sensitivity varies when altering Cep70 expression level. Mechanistic studies reveal that Cep70 interacts with tubulin, and promotes the ability of paclitaxel to stimulate microtubule assembly. These data demonstrate that Cep70 mediates paclitaxel sensitivity in breast cancer.

Location and functional analysis of the Aspergillus nidulans Aurora kinase confirm mitotic functions and suggest non-mitotic roles

Filamentous fungi have devastating negative impacts as pathogens and agents of food spoilage but also have critical ecological importance and are utilized for industrial applications. The characteristic multinucleate nature of filamentous fungi is facilitated by limiting if, when and where septation, the fungal equivalent of cytokinesis, occurs. In the model filamentous fungus Aspergillus nidulans septation does not occur immediately after mitosis and is an incomplete process resulting in the formation of a septal pore whose permeability is cell cycle regulated. How mitotic regulators, such as the Aurora kinase, contribute to the often unique biology of filamentous fungi is not well understood. The Aurora B kinase has not previously been investigated in any detail during hyphal growth. Here we demonstrate for the first time that Aurora displays cell cycle dependent locations to the region of forming septa, the septal pore and mature septa as well as the mitotic apparatus. To functionally analyze Aurora, we generated a temperature sensitive allele revealing essential mitotic and spindle assembly checkpoint functions consistent with its location to the kinetochore region and spindle midzone. Our analysis also reveals that cellular and kinetochore Aurora levels increase during a mitotic spindle assembly checkpoint arrest and we propose that this could be important for checkpoint inactivation when spindle formation is prevented. We demonstrate that Aurora accumulation at mature septa following mitotic entry does not require mitotic progression but is dependent upon a timing mechanism. Surprisingly we also find that Aurora inactivation leads to cellular swelling and lysis indicating an unexpected function for Aurora in fungal cell growth. Thus in addition to its conserved mitotic functions our data suggest that Aurora has the capacity to be an important regulator of septal biology and cell growth in filamentous fungi.

DT-13 synergistically enhanced vinorelbine-mediated mitotic arrest through inhibition of FOXM1-BICD2 axis in non-small-cell lung cancer cells

Non-small-cell lung cancer (NSCLC) is the most commonly diagnosed malignant disease with the leading cause of cancer-related death. Combination treatment remains the major strategy in the clinical therapy of NSCLC. Vinorelbine (NVB), a semi-synthetic vinca alkaloid, is used for advanced and metastatic NSCLC by destabilizing microtubule formation to induce mitotic arrest and cell death. However, the side effect of NVB heavily affected its effectiveness in clinical therapy. Hence, it is of great significance to develop new agents to synergize with NVB and decrease the adverse effect. In our study, we found that the saponin monomer 13 of the dwarf lilyturf tuber, DT-13, exhibiting anti-angiogenesis and anti-metastasis effect, synergized with NVB to inhibit cell proliferation in NSCLC cells. The synergistic interaction of DT-13 and NVB was confirmed by combination Index values. Also, DT-13 and NVB act in concert to inhibit the long-term colony formation. Furthermore, DT-13/NVB co-treatment cooperated to induce mitotic arrest and subsequent apoptosis. Mechanistically, we found that nuclear expression of transcription factors forkhead box M1 (FOXM1) and levels of motor adaptor bicaudal D2 (BICD2) were dramatically reduced by combination treatment. Importantly, oncogene FOXM1 was identified as the crucial regulator of BICD2, which played critical roles in NVB-induced mitotic spindle defects. Moreover, overexpression of FOXM1 and BICD2 significantly reversed mitotic arrest induced by DT-13/NVB co-treatment, and siRNAs against both genes greatly increased the combinational effects. In addition, in vivo study revealed that DT-13 combined with NVB significantly suppressed tumor growth in nude mice xenograft model, and downregulated the expression of FOXM1 and BICD2 in tumor tissues, which was consistent with in vitro study. In conclusion, DT-13 might provide a novel strategy for the chemosensitization of NVB in NSCLC therapy.

Prolonged mitotic arrest induced by Wee1 inhibition sensitizes breast cancer cells to paclitaxel

Wee1 kinase is a crucial negative regulator of Cdk1/cyclin B1 activity and is required for normal entry into and exit from mitosis. Wee1 activity can be chemically inhibited by the small molecule MK-1775, which is currently being tested in phase I/II clinical trials in combination with other anti-cancer drugs. MK-1775 promotes cancer cells to bypass the cell-cycle checkpoints and prematurely enter mitosis. In our study, we show premature mitotic cells that arise from MK-1775 treatment exhibited centromere fragmentation, a morphological feature of mitotic catastrophe that is characterized by centromeres and kinetochore proteins that co-cluster away from the condensed chromosomes. In addition to stimulating early mitotic entry, MK-1775 treatment also delayed mitotic exit. Specifically, cells treated with MK-1775 following release from G1/S or prometaphase arrested in mitosis. MK-1775 induced arrest occurred at metaphase and thus, cells required 12 times longer to transition into anaphase compared to controls. Consistent with an arrest in mitosis, MK-1775 treated prometaphase cells maintained high cyclin B1 and low phospho-tyrosine 15 Cdk1. Importantly, MK-1775 induced mitotic arrest resulted in cell death regardless the of cell-cycle phase prior to treatment suggesting that Wee1 inhibitors are also anti-mitotic agents. We found that paclitaxel enhances MK-1775 mediated cell killing. HeLa and different breast cancer cell lines (T-47D, MCF7, MDA-MB-468 and MDA-MB-231) treated with different concentrations of MK-1775 and low dose paclitaxel exhibited reduced cell survival compared to mono-treatments. Our data highlight a new potential strategy for enhancing MK-1775 mediated cell killing in breast cancer cells.

Knockout of ATG5 leads to malignant cell transformation and resistance to Src family kinase inhibitor PP2

Autophagy can either promote or inhibit cell death in different cellular contexts. In this study, we investigated the role of autophagy in ATG5 knockout (KO) cell line established using CRISPR/Cas9 system. In ATG5 KO cells, RT-PCR and immunoblot of LC3 confirmed the functional gene knockout. We found that knockout of ATG5 significantly increased proliferation of NIH 3T3 cells. In particular, autophagy deficiency enhanced susceptibility to cellular transformation as determined by an in vitro clonogenic survival assay and a soft agar colony formation assay. We also found that ATG5 KO cells had a greater migration ability as compared to wild-type (WT) cells. Moreover, ATG5 KO cells were more resistant to treatment with a Src family tyrosine kinase inhibitor (PP2) than WT cells were. Cyto-ID Green autophagy assay revealed that PP2 failed to induce autophagy in ATG5 KO cells. PP2 treatment decreased the percentage of cells in the S and G₂ /M phases among WT cells but had no effect on cell cycle distribution of ATG5 KO cells, which showed a high percentage of cells in the S and G₂ /M phases. Additionally, the proportion of apoptotic cells significantly decreased after treatment of ATG5 KO cells with PP2 in comparison with WT cells. We found that expression levels of p53 were much higher in ATG5 KO cells. The ATG5 KO seems to lead to compensatory upregulation of the p53 protein because of a decreased apoptosis rate. Taken together, our results suggest that autophagy deficiency can lead to malignant cell transformation and resistance to PP2.

Mitotic Catastrophe in BC3H1 Cells following Yessotoxin Exposure

The marine toxin yessotoxin (YTX) can cause various cytotoxic effects depending on cell type and cell line. It is well known to trigger distinct mechanisms for programmed cell death which may overlap or cross-talk. The present contribution provides the first evidence that YTX can cause genotoxicity and induce mitotic catastrophe which can lead to different types of cell death. This work also demonstrates potential information gain from non-intrusive computer-based tracking of many individual cells during long time. Treatment of BC3H1 cells at their exponential growth phase causes atypical nuclear alterations and formation of giant cells with multiple nuclei. These are the most prominent morphological features of mitotic catastrophe. Giant cells undergo slow cell death in a necrosis-like manner. However, apoptotic-like cell death is also observed in these cells. Electron microscopy of treated BC3H1 cells reveal uncondensed chromatin and cells with double nuclei. Activation of p-p53, p-H2AX, p-Chk1, p-ATM, and p-ATR and down-regulation of p-Chk2 indicate DNA damage response and cell cycle deregulation. Micronuclei formation further support this evidence. Data from tracking single cells reveal that YTX treatment suppresses a second round of cell division in BC3H1 cells. These findings suggest that YTX can induce genomic alterations or imperfections in chromosomal segregation leading to permanent mitotic failure. This understanding extends the list of effects from YTX and which are of interest to control cancer and tumor progression.

Proteasome inhibition enhances the efficacy of volasertib-induced mitotic arrest in AML in vitro and prolongs survival in vivo

Elderly and frail patients, diagnosed with acute myeloid leukemia (AML) and ineligible to undergo intensive treatment, have a dismal prognosis. The small molecule inhibitor volasertib induces a mitotic block via inhibition of polo-like kinase 1 and has shown remarkable anti-leukemic activity when combined with low-dose cytarabine. We have demonstrated that AML cells are highly vulnerable to cell death in mitosis yet manage to escape a mitotic block through mitotic slippage by sustained proteasome-dependent slow degradation of cyclin B. Therefore, we tested whether interfering with mitotic slippage through proteasome inhibition arrests and kills AML cells more efficiently during mitosis. We show that therapeutic doses of bortezomib block the slow degradation of cyclin B during a volasertib-induced mitotic arrest in AML cell lines and patient-derived primary AML cells. In a xenotransplant mouse model of human AML, mice receiving volasertib in combination with bortezomib showed superior disease control compared to mice receiving volasertib alone, highlighting the potential therapeutic impact of this drug combination.

Loss-of-Function Mutations in KIF15 Underlying a Braddock-Carey Genocopy

Braddock-Carey Syndrome (BCS) is characterized by microcephaly, congenital thrombocytopenia, Pierre-Robin sequence (PRS), and agenesis of the corpus callosum. BCS has been shown to be caused by a 21q22.11 microdeletion that encompasses multiple genes. Here, we report a BCS genocopy characterized by congenital thrombocytopenia and PRS that is caused by a loss-of-function mutation in KIF15 in a consanguineous Saudi Arabian family. Mutations of mitotic kinesins are a well-established cause of microcephaly. To our knowledge, KIF15 is the first kinesin to be associated with congenital thrombocytopenia.

Phase II randomized study of the IGF-1R pathway modulator AXL1717 compared to docetaxel in patients with previously treated, locally advanced or metastatic non-small cell lung cancer

BACKGROUND

The primary objective of this study was to compare the progression-free survival (PFS) at 12 weeks between patients treated with IGF-1R pathway modulator AXL1717 (AXL) and patients treated with docetaxel (DCT).

MATERIAL AND METHODS

The study was conducted at 19 study centers in five countries. A total of 99 patients with previously treated, locally advanced or metastatic non-small cell lung cancer (NSCLC) of the squamous cell carcinoma (SCC) or adenocarcinoma (AC) subtypes in need of additional treatment were randomized and treated with either 300 or 400 mg of AXL as daily BID treatment (58 patients) or DCT given as 75 mg/m² in three-week cycles (41 patients) as monotherapy in a 3:2 ratio for each NSCLC subtype. Patients were treated in the primary study treatment period for a maximum of four treatment cycles.

RESULTS

The 12-week PFS rate, median PFS and overall survival (OS), as well Kaplan-Meier hazard ratio for PFS and OS, did not show any statistically significant differences between the treatment groups. For the primary endpoint, the AXL group had a lower percentage of patients (25.9%) who were progression-free at Week 12 as compared to the DCT group (39.0%), although the difference was not statistically significant. The most notable difference in the incidence of treatment emergent adverse effects (TEAEs) was the lower incidence of treatment-related grade 3/4 neutropenia in patients treated with AXL.

CONCLUSION

These results suggest neither of the treatments to be superior of the other when treating locally advanced or metastatic NSCLC. Considering the lower incidence of grade 3/4 neutropenia in the AXL group this treatment warrants further research.

Live Imaging to Study Microtubule Dynamic Instability in Taxane-resistant Breast Cancers

Taxanes such as docetaxel belong to a group of microtubule-targeting agents (MTAs) that are commonly relied upon to treat cancer. However, taxane resistance in cancerous cells drastically reduces the effectiveness of the drugs' long-term usage. Accumulated evidence suggests that the mechanisms underlying taxane resistance include both general mechanisms, such as the development of multidrug resistance due to the overexpression of drug-efflux proteins, and taxane-specific mechanisms, such as those that involve microtubule dynamics. Because taxanes target cell microtubules, measuring microtubule dynamic instability is an important step in determining the mechanisms of taxane resistance and provides insight into how to overcome this resistance. In the experiment, an in vivo method was used to measure microtubule dynamic instability. GFP-tagged α-tubulin was expressed and incorporated into microtubules in MCF-7 cells, allowing for the recording of the microtubule dynamics by time lapse using a sensitive camera. The results showed that, as opposed to the non-resistant parental MCF-7CC cells, the microtubule dynamics of docetaxel-resistant MCF-7TXT cells are insensitive to docetaxel treatment, which causes the resistance to docetaxel-induced mitotic arrest and apoptosis. This paper will outline this in vivo method of measuring microtubule dynamic instability.

Cdc20: At the Crossroads between Chromosome Segregation and Mitotic Exit

Cell-division cycle protein 20 homologue (Cdc20) has important functions in chromosome segregation and mitotic exit. Cdc20 is the target of the spindle assembly checkpoint (SAC) and a key cofactor of the anaphase-promoting complex or cyclosome (APC/C) E3 ubiquitin ligase, thus regulating APC/C ubiquitin activity on specific substrates for their subsequent degradation by the proteasome. Here we discuss the roles of Cdc20 in SAC signalling and mitotic exit, describe how the integration of traditional approaches with emerging technologies has revealed new details of Cdc20 functions, comment about the potential of Cdc20 as a therapeutic target for the treatment of human malignancies, and discuss recent advances and controversies in the mechanistic understanding of the control of chromosome segregation during cell division.

Links between DNA Replication, Stem Cells and Cancer

Cancers can be categorized into two groups: those whose frequency increases with age, and those resulting from errors during mammalian development. The first group is linked to DNA replication through the accumulation of genetic mutations that occur during proliferation of developmentally acquired stem cells that give rise to and maintain tissues and organs. These mutations, which result from DNA replication errors as well as environmental insults, fall into two categories; cancer driver mutations that initiate carcinogenesis and genome destabilizing mutations that promote aneuploidy through excess genome duplication and chromatid missegregation. Increased genome instability results in accelerated clonal evolution leading to the appearance of more aggressive clones with increased drug resistance. The second group of cancers, termed germ cell neoplasia, results from the mislocation of pluripotent stem cells during early development. During normal development, pluripotent stem cells that originate in early embryos give rise to all of the cell lineages in the embryo and adult, but when they mislocate to ectopic sites, they produce tumors. Remarkably, pluripotent stem cells, like many cancer cells, depend on the Geminin protein to prevent excess DNA replication from triggering DNA damage-dependent apoptosis. This link between the control of DNA replication during early development and germ cell neoplasia reveals Geminin as a potential chemotherapeutic target in the eradication of cancer progenitor cells.

The kinetochore-dependent and -independent formation of the CDC20-MAD2 complex and its functions in HeLa cells

The mitotic checkpoint complex (MCC) is formed from two sub-complexes of CDC20-MAD2 and BUBR1-BUB3, and current models suggest that it is generated exclusively by the kinetochores after nuclear envelope breakdown (NEBD). However, neither sub-complex has been visualised in vivo, and when and where they are formed during the cell cycle and their response to different SAC conditions remains elusive. Using single cell analysis in HeLa cells, we show that the CDC20-MAD2 complex is cell cycle regulated with a “Bell” shaped profile and peaks at prometaphase. Its formation begins in early prophase before NEBD when the SAC has not been activated. The complex prevents the premature degradation of cyclin B1. Tpr, a component of the NPCs (nuclear pore complexes), facilitates the formation of this prophase form of the CDC20-MAD2 complex but is inactive later in mitosis. Thus, we demonstrate that the CDC20-MAD2 complex could also be formed independently of the SAC. Moreover, in prolonged arrest caused by nocodazole treatment, the overall levels of the CDC20-MAD2 complex are gradually, but significantly, reduced and this is associated with lower levels of cyclin B1, which brings a new insight into the mechanism of mitotic “slippage” of the arrested cells.

A quantitative FastFUCCI assay defines cell cycle dynamics at a single-cell level

The fluorescence ubiquitination-based cell cycle indicator (FUCCI) is a powerful tool for use in live cells but current FUCCI-based assays have limited throughput in terms of image processing and quantification. Here, we developed a lentiviral system that rapidly introduced FUCCI transgenes into cells by using an all-in-one expression cassette, FastFUCCI. The approach alleviated the need for sequential transduction and characterisation, improving labelling efficiency. We coupled the system to an automated imaging workflow capable of handling large datasets. The integrated assay enabled analyses of single-cell readouts at high spatiotemporal resolution. With the assay, we captured in detail the cell cycle alterations induced by antimitotic agents. We found that treated cells accumulated at G2 or M phase but eventually advanced through mitosis into the next interphase, where the majority of cell death occurred, irrespective of the preceding mitotic phenotype. Some cells appeared viable after mitotic slippage, and a fraction of them subsequently re-entered S phase. Accordingly, we found evidence that targeting the DNA replication origin activity sensitised cells to paclitaxel. In summary, we demonstrate the utility of the FastFUCCI assay for quantifying spatiotemporal dynamics and identify its potential in preclinical drug development.

Autophagy induced by a sulphamoylated estrone analogue contributes to its cytotoxic effect on breast cancer cells

Background

Autophagy can either be protective and confer survival to stressed cells, or it can contribute to cell death. The antimitotic drug 2-ethyl-3-O-sulpamoyl-estra-1,3,5(10),15-tetraen-17-ol (ESE-15-ol) is an in silico-designed 17-β-estradiol analogue that induces both autophagy and apoptosis in cancer cells. The aim of the study was to determine the role of autophagy in ESE-15-ol-exposed human adenocarcinoma breast cancer cells; knowledge that will contribute to future clinical applications of this novel antimitotic compound. By inhibiting autophagy and determining the cytotoxic effects of ESE-15-ol-exposure, deductions could be made as to whether the process may confer resistance to the drug, or alternatively, contribute to the cell death process.

Methods and results

Spectophometrical analysis via crystal violet staining was used to perform cytotoxicity studies. Morphology studies were done using microscopic techniques namely polarization-optical transmitted light differential interference light microscopy, fluorescent microscopy using monodansylcadaverine staining and transmission electron microscopy. Flow cytometry was used to quantify the autophagy inhibition and assess cell viability. Results obtained indicated that 3-methyladenine inhibited autophagy and increased cell survival in both MCF-7 and MDA-MB-231 cell lines.

Conclusion

This in vitro study inferred that autophagy inhibition with 3-methyladenine does not confer increased effectiveness of ESE-15-ol in inducing cell death. Thus it may be concluded that the autophagic process induced by ESE-15-ol exposure in MCF-7 and MDA-MB-231 cells plays a more significant role in cell death than conferring survival.

Effect of SP600125 on the mitotic spindle in HeLa Cells, leading to mitotic arrest, endoreduplication and apoptosis

BACKGROUND

The JNK inhibitor SP600125 strongly inhibits cell proliferation in many human cancer cells by blocking mitosis progression and inducing cell death. Despite, all this study, the mechanism by which SP600125 inhibits mitosis-related effects in human cervical cells (HeLa cells) remains unclear. In this study, we investigated the effects of SP600125 on the cell viability, cell cycle, and on the spindle assembly during mitosis in HeLa cells.

METHODS

To explore this approach, we used a viability test, an immunofluorescence microscopy to detect Histone phosphorylation and mitotic spindle aberrations. Apoptosis was characterised using Western Blotting.

RESULTS

Treatment of HeLa cells with varying concentrations of SP600125 induces significant G2/M cell cycle arrest with elevated phosphorylation of histone H3 within 48 h, and endoreduplication after 48 h. SP600125 also induces significant abnormal mitotic spindle. High concentrations of SP600125 (20 μM) induce disturbing microtubule assembly in vitro. Additionally, SP600125- induced delayed apoptosis and cell death was accompanied by significant poly ADP-ribose polymerase (PARP) cleavage and caspase-3 activation in the late phase (at 72 h).

CONCLUSION

Our results confirmed that SP600125 induce mitosis arrest in G2/M, endoreduplication, mitotic spindle aberrations and apoptosis.

Chemotherapy curable malignancies and cancer stem cells: a biological review and hypothesis

Background

Cytotoxic chemotherapy brings routine cures to only a small select group of metastatic malignancies comprising gestational trophoblast tumours, germ cell tumours, acute leukemia, Hodgkin’s disease, high grade lymphomas and some of the rare childhood malignancies.

We have previously postulated that the extreme sensitivity to chemotherapy for these malignancies is linked to the on-going high levels of apoptotic sensitivity that is naturally linked with the unique genetic events of nuclear fusion, meiosis, VDJ recombination, somatic hypermutation, and gastrulation that have occurred within the cells of origin of these malignancies.

In this review we will examine the cancer stem cell/cancer cell relationship of each of the chemotherapy curable malignancies and how this relationship impacts on the resultant biology and pro-apoptotic sensitivity of the varying cancer cell types.

Discussion

In contrast to the common epithelial cancers, in each of the chemotherapy curable malignancies there are no conventional hierarchical cancer stem cells. However cells with cancer stem like qualities can arise stochastically from within the general tumour cell population. These stochastic stem cells acquire a degree of resistance to DNA damaging agents but also retain much of the key characteristics of the cancer cells from which they develop. We would argue that the balance between the acquired resistance of the stochastic cancer stem cell and the inherent chemotherapy sensitivity of parent tumour cell determines the overall chemotherapy curability of each diagnosis.

Summary

The cancer stem cells in the chemotherapy curable malignancies appear to have two key biological differences from those of the more common chemotherapy incurable malignancies. The first difference is that the conventional hierarchical pattern of cancer stem cells is absent in each of the chemotherapy curable malignancies.

The other key difference, we suggest, is that the stochastic stem cells in the chemotherapy curable malignancies take on a significant aspect of the biological characteristics of their parent cancer cells. This action includes for the chemotherapy curable malignancies the heightened pro-apoptotic sensitivity linked to their respective associated unique genetic events.

For the chemotherapy curable malignancies the combination of the relationship of their cancer stem cells combined with the extreme inherent sensitivity to induction of apoptosis from DNA damaging agents plays a key role in determining their overall curability with chemotherapy.

Pseudolaric acid B induces mitotic arrest and apoptosis in both 5-fluorouracil-sensitive and -resistant colorectal cancer cells

5-fluorouracil (5-FU)-based chemotherapy is the main chemotherapeutic approach for colorectal cancer (CRC) treatment. Because chemoresistance occurs frequently and significantly limits CRC therapies, a novel agent is needed. Pseudolaric acid B (PAB), a small molecule derived from the Chinese medicinal herb ''Tujinpi'', exhibits strong cytotoxic effects on a variety of cancers. However, the detailed mechanisms by which PAB inhibits CRC cell growth and its potential role in overcoming 5-FU resistance have not been well studied. In this study, we showed that PAB significantly inhibited the viability of various CRC cell lines but induced minor cytotoxicity in normal cells. Both the in vitro and in vivo results showed that PAB induced proliferation inhibition, mitotic arrest and subsequently caspase-dependent apoptosis in both 5-FU-sensitive and -resistant CRC cells. Moreover, PAB was shown to interfere with CRC cell mitotic spindle apparatus and activate the spindle assembly checkpoint. Finally, CDK1 activity was involved in PAB-induced mitotic arrest and apoptosis in CRC cells. Taken together, these data reveal that PAB induces CRC cell mitotic arrest followed by apoptosis and overcomes 5-FU resistance in vitro and in vivo, suggesting that PAB may be a potential agent for CRC treatment, particularly for 5-FU-resistant CRC.

Cell cycle checkpoint in cancer: a therapeutically targetable double-edged sword

Major currently used anticancer therapeutics either directly damage DNA or target and upset basic cell division mechanisms like DNA replication and chromosome segregation. These insults elicit activation of cell cycle checkpoints, safeguard mechanisms that cells implement to correctly complete cell cycle phases, repair damage or eventually commit suicide in case damage is unrepairable. Although cancer cells appear to be advantageously defective in some aspects of checkpoint physiology, recent acquisitions on the biochemical mechanisms of the various checkpoints are offering new therapeutic approaches against cancer. Indeed, chemical manipulation of these mechanisms is providing new therapeutic strategies and tools to increase the killing efficacy of major cancer therapeutics as well as to directly promote cancer cell death. In this review we summarize developing concepts on how targeting cell cycle checkpoints may provide substantial improvement to cancer therapy.

Alternating electric fields (TTFields) in combination with paclitaxel are therapeutically effective against ovarian cancer cells in vitro and in vivo

Long-term survival rates for advanced ovarian cancer patients have not changed appreciably over the past four decades; therefore, development of new, effective treatment modalities remains a high priority. Tumor Treating Fields (TTFields), a clinically active anticancer modality utilize low-intensity, intermediate frequency, alternating electric fields. The goal of this study was to evaluate the efficacy of combining TTFields with paclitaxel against ovarian cancer cells in vitro and in vivo. In vitro application of TTFields on human ovarian cancer cell lines led to a significant reduction in cell counts as compared to untreated cells. The effect was found to be frequency and intensity dependent. Further reduction in the number of viable cells was achieved when TTFields treatment was combined with paclitaxel. The in vivo effect of the combined treatment was tested in mice orthotopically implanted with MOSE-L_TICv cells. In this model, combined treatment led to a significant reduction in tumor luminescence and in tumor weight as compared to untreated mice. The feasibility of effective local delivery of TTFields to the human abdomen was examined using finite element mesh simulations performed using the Sim4life software. These simulations demonstrated that electric fields intensities inside and in the vicinity of the ovaries of a realistic human computational phantom are about 1 and 2 V/cm pk-pk, respectively, which is within the range of intensities required for TTFields effect. These results suggest that prospective clinical investigation of the combination of TTFields and paclitaxel is warranted.

Loss of FBXW7 and accumulation of MCL1 and PLK1 promote paclitaxel resistance in breast cancer

FBXW7 is a component of SCF (complex of SKP1, CUL1 and F-box-protein)-type ubiquitin ligases that targets several oncoproteins for ubiquitination and degradation by the proteasome. FBXW7 regulates cellular apoptosis by targeting MCL1 for ubiquitination. Recently, we identified PLK1 as a new substrate of FBXW7 modulating the intra-S-phase DNA-damage checkpoint. Taxanes are frequently used in breast cancer treatments, but the acquisition of resistance makes these treatments ineffective. We investigated the role of FBXW7 and their substrates MCL1 and PLK1 in regulating the apoptotic response to paclitaxel treatment in breast cancer cells and their expression in breast cancer tissues. Paclitaxel-sensitive MDA-MB-468 and a paclitaxel-resistant MDA-MB-468R subclone were used to study the role of FBXW7 and substrates in paclitaxel-induced apoptosis. Forced expression of FBXW7 or downregulation of MCL1 or PLK1 restored sensitivity to paclitaxel in MDA-MB-468R cells. By contrary, FBXW7-silenced MDA-MB-468 cells became resistant to paclitaxel. The expression of FBXW7 and substrates were studied in 296 invasive carcinomas by immunohistochemistry and disease-free survival was analyzed in a subset of patients treated with paclitaxel. In breast cancer tissues, loss of FBXW7 correlated with adverse prognosis markers and loss of FBXW7 and MCL1 or PLK1 accumulation were associated with diminished disease-free survival in paclitaxel-treated patients. We conclude that FBXW7 regulates the response to paclitaxel by targeting MCL1 and PLK1 in breast cancer cells and thus targeting these substrates may be a valuable adjunct for paclitaxel treatment. Also, FBXW7, MCL1 and PLK1 may be relevant predictive markers of tumor progression and response to paclitaxel treatment.

Predictors of chemotherapy efficacy in non-small-cell lung cancer: a challenging landscape

BACKGROUND

Conventional cytotoxic chemotherapy (CCC) is the backbone of non-small-cell lung cancer (NSCLC) treatment since decades and still represents a key element of the therapeutic armamentarium. Contrary to molecularly targeted therapies and immune therapies, for which predictive biomarkers of activity have been actively looked for and developed in parallel to the drug development process ('companion biomarkers'), no patient selection biomarker is currently available for CCC, precluding customizing treatment.

MATERIALS AND METHODS

We reviewed preclinical and clinical studies that assessed potential predictive biomarkers of CCC used in NSCLC (platinum, antimetabolites, topoisomerase inhibitors, and spindle poisons). Biomarker evaluation method, analytical validity, and robustness are described and challenged for each biomarker.

RESULTS

The best-validated predictive biomarkers for efficacy are currently ERCC1, RRM1, and TS for platinum agents, gemcitabine and pemetrexed, respectively. Other potential biomarkers include hENT1 for gemcitabine, class III β-tubulin for spindle poisons, TOP2A expression and CEP17 duplication (mostly studied for predicting anthracyclines efficacy) whose applicability concerning etoposide would deserve further evaluation. However, none of these biomarkers has till now been validated prospectively in an appropriately designed and powered randomised trial, and none of them is currently ready for implementation in routine clinical practice.

CONCLUSION

The search for predictive biomarkers to CCC has been proven challenging. If a plethora of biomarkers have been evaluated either in the preclinical or in the clinical setting, none of them is ready for clinical implementation yet. Considering that most mechanisms of resistance or sensitivity to CCC are multifactorial, a combinatorial approach might be relevant and further efforts are required.

Cell Size Determines the Strength of the Spindle Assembly Checkpoint during Embryonic Development

The spindle assembly checkpoint (SAC) delays mitotic progression when chromosomes are not properly attached to microtubules of the mitotic spindle. Cells vary widely in the extent to which they delay mitotic progression upon SAC activation. To explore the mechanisms that determine checkpoint strength in different cells, we systematically measured the mitotic delay induced by microtubule disruption at different stages of embryogenesis in Caenorhabditis elegans. Strikingly, we observed a gradual increase in SAC strength after each round of division. Analysis of mutants that alter cell size or ploidy revealed that SAC strength is determined primarily by cell size and the number of kinetochores. These findings provide clear evidence in vivo that the kinetochore-to-cytoplasm ratio determines the strength of the SAC, providing new insights into why cells exhibit such large variations in their SAC responses.

Electrochemical approach for monitoring the effect of anti tubulin drugs on breast cancer cells based on silicon nanograss electrodes

One of the most interested molecular research in the field of cancer detection is the mechanism of drug effect on cancer cells. Translating molecular evidence into electrochemical profiles would open new opportunities in cancer research. In this manner, applying nanostructures with anomalous physical and chemical properties as well as biocompatibility would be a suitable choice for the cell based electrochemical sensing. Silicon based nanostructure are the most interested nanomaterials used in electrochemical biosensors because of their compatibility with electronic fabrication process and well engineering in size and electrical properties. Here we apply silicon nanograss (SiNG) probing electrodes produced by reactive ion etching (RIE) on silicon wafer to electrochemically diagnose the effect of anticancer drugs on breast tumor cells. Paclitaxel (PTX) and mebendazole (MBZ) drugs have been used as polymerizing and depolymerizing agents of microtubules. PTX would perturb the anodic/cathodic responses of the cell-covered biosensor by binding phosphate groups to deformed proteins due to extracellular signal-regulated kinase (ERK(1/2)) pathway. MBZ induces accumulation of Cytochrome C in cytoplasm. Reduction of the mentioned agents in cytosol would change the ionic state of the cells monitored by silicon nanograss working electrodes (SiNGWEs). By extending the contacts with cancer cells, SiNGWEs can detect minor signal transduction and bio recognition events, resulting in precise biosensing. Effects of MBZ and PTX drugs, (with the concentrations of 2 nM and 0.1 nM, respectively) on electrochemical activity of MCF-7 cells are successfully recorded which are corroborated by confocal and flow cytometry assays.

Prenylated Chalcone 2 Acts as an Antimitotic Agent and Enhances the Chemosensitivity of Tumor Cells to Paclitaxel

We previously reported that prenylated chalcone 2 (PC2), the O-prenyl derivative (2) of 2′-hydroxy-3,4,4′,5,6′-pentamethoxychalcone (1), induced cytotoxicity of tumor cells via disruption of p53-MDM2 interaction. However, the cellular changes through which PC2 exerts its cytotoxic activity and its antitumor potential, remain to be addressed. In the present work, we aimed to (i) characterize the effect of PC2 on mitotic progression and the underlying mechanism; and to (ii) explore this information to evaluate its ability to sensitize tumor cells to paclitaxel in a combination regimen. PC2 was able to arrest breast adenocarcinoma MCF-7 and non-small cell lung cancer NCI-H460 cells in mitosis. All mitosis-arrested cells showed collapsed mitotic spindles with randomly distributed chromosomes, and activated spindle assembly checkpoint. Live-cell imaging revealed that the compound induced a prolonged delay (up to 14 h) in mitosis, culminating in massive cell death by blebbing. Importantly, PC2 in combination with paclitaxel enhanced the effect on cell growth inhibition as determined by cell viability and proliferation assays. Our findings demonstrate that the cytotoxicity induced by PC2 is mediated through antimitotic activity as a result of mitotic spindle damage. The enhancement effects of PC2 on chemosensitivity of cancer cells to paclitaxel encourage further validation of the clinical potential of this combination.

Novel targets for paclitaxel nano formulations: Hopes and hypes in triple negative breast cancer

Triple negative breast cancer is defined as one of the utmost prevailing breast cancers worldwide, possessing an inadequate prognosis and treatment option limited to chemotherapy and radiotherapy, creating a challenge for researchers as far as developing a specific targeted therapy is concerned. The past research era has shown several promising outcomes for TNBC such as nano-formulations of the chemotherapeutic agents already used for the management of the malignant tumor. Taking a glance at paclitaxel nano formulations, it has been proven beneficial in several researches in the past decade; nevertheless its solubility is often a challenge to scientists in achieving success. We have henceforth discussed the basic heterogeneity of triple negative breast cancer along with the current management options as well as a brief outlook on pros and cons of paclitaxel, known as the most widely used chemotherapeutic agent for the treatment of the disease. We further analyzed the need of nanotechnology pertaining to the problems encountered with the current paclitaxel formulations available discussing the strategic progress in various nano-formulations till date taking into account the basic research strategies required in terms of solubility, permeability, physicochemical properties, active and passive targeting. A thorough review in recent advances in active targeting for TNBC was carried out whereby the various ligands which are at present finding its way into TNBC research such as hyaluronic acid, folic acid, transferrin, etc. were discussed. These ligands have specific receptor affinity to TNBC tumor cells hence can be beneficial for novel drug targeting approaches. Conversely, there are currently several novel strategies in the research pipeline whose targeting ligands have not yet been studied. Therefore, we reviewed upon the numerous novel receptor targets along with the respective nano-formulation aspects which have not yet been fully researched upon and could be exemplified as outstanding target strategies for TNBC which is currently an urgent requirement.

Clusterin knockdown sensitizes prostate cancer cells to taxane by modulating mitosis

Clusterin (CLU) is a stress‐activated molecular chaperone that confers treatment resistance to taxanes when highly expressed. While CLU inhibition potentiates activity of taxanes and other anti‐cancer therapies in preclinical models, progression to treatment‐resistant disease still occurs implicating additional compensatory survival mechanisms. Taxanes are believed to selectively target cells in mitosis, a complex mechanism controlled in part by balancing antagonistic roles of Cdc25C and Wee1 in mitosis progression. Our data indicate that CLU silencing induces a constitutive activation of Cdc25C, which delays mitotic exit and hence sensitizes cancer cells to mitotic‐targeting agents such as taxanes. Unchecked Cdc25C activation leads to mitotic catastrophe and cell death unless cells up‐regulate protective mechanisms mediated through the cell cycle regulators Wee1 and Cdk1. In this study, we show that CLU silencing induces a constitutive activation of Cdc25C via the phosphatase PP2A leading to relief of negative feedback inhibition and activation of Wee1‐Cdk1 to promote survival and limit therapeutic efficacy. Simultaneous inhibition of CLU‐regulated cell cycle effector Wee1 may improve synergistic responses of biologically rational combinatorial regimens using taxanes and CLU inhibitors.

Lipid droplets maintain lipid homeostasis during anaphase for efficient cell separation in budding yeast

The neutral lipids steryl ester and triacylglycerol (TAG) are stored in the membrane-bound organelle lipid droplet (LD) in essentially all eukaryotic cells. It is unclear what physiological conditions require the mobilization or storage of these lipids. Here, we study the budding yeast mutant are1Δ are2Δ dga1Δ lro1Δ, which cannot synthesize the neutral lipids and therefore lacks LDs. This quadruple mutant is delayed at cell separation upon release from mitotic arrest. The cells have abnormal septa, unstable septin assembly during cytokinesis, and prolonged exocytosis at the division site at the end of cytokinesis. Lipidomic analysis shows a marked increase of diacylglycerol (DAG) and phosphatidic acid, the precursors for TAG, in the mutant during mitotic exit. The cytokinesis and separation defects are rescued by adding phospholipid precursors or inhibiting fatty acid synthesis, which both reduce DAG levels. Our results suggest that converting excess lipids to neutral lipids for storage during mitotic exit is important for proper execution of cytokinesis and efficient cell separation.