DNA damage-induced cell death is enhanced by progression through mitosis

Smart Vitamin Micelles as Cancer Nanomedicines for Enhanced Intracellular Delivery of Doxorubicin

Chemotherapy is one of the most effective treatments for cancer. However, intracellular delivery of many anticancer drugs is hindered by their hydrophobicity and low molecular weight. Here, we describe highly biocompatible and biodegradable amphiphilic vitamin conjugates comprising hydrophobic vitamin E and hydrophilic vitamin B labeled with dual pH and glutathione-responsive degradable linkages. Vitamin-based micelles (vitamicelles), formed by self-assembly in aqueous solutions, were optimized based on their stability after encapsulation of doxorubicin (DOX). The resulting vitamicelles have great potential as vehicles for anticancer drugs because they show excellent biocompatibility (>94% after 48 h of incubation) and rapid biodegradability (>90% after 2.5 h). Compared with free DOX, DOX-loaded vitamicelles showed a markedly enhanced anticancer effect as they released the drug rapidly and inhibited drug efflux out of cells efficiently. By exploiting these advantages, this study not only provides a promising strategy for circumventing existing challenges regarding the delivery of anticancer drugs but also extends the utility of current DOX-induced chemotherapy.

Green synthesized silver nanoparticles induced cytogenotoxic and genotoxic changes in Allium cepa L. varies with nanoparticles doses and duration of exposure

This study aimed to test the ability of aqueous leaf extract of Eichhornia crassipes (Mart.) Solms-Laubach to synthesize silver nanoparticles (AgNPs) and to estimate the cytotoxicity and genotoxicity of AgNPs using Allium cepa assay. Fresh Eichhornia crassipes plants were collected from the Nile River of Egypt. The mixed-shaped structures of the biogenic AgNPs were qualitatively characterized by UV-vis spectroscopy, scanning electron microscopy and transmission electron microscopy. Selected area electron diffraction confirmed the crystalline structure of AgNPs and energy dispersive X-ray analysis clarified the presence of the elemental silver in a percentage of 83.29%. The biogenic AgNPs were quite stable (0.316) and negatively charged (-18.5 mV) based on the polydispersity index values. Allium cepa L. roots were exposed to several AgNPs concentrations (0, 5, 10, 20, 40 and 80 mg L^-1) for different time intervals 2, 4 and 6 h. Cytotoxicity measured by both the spectrophotometric and macroscopic techniques recorded the maximum cell death of root tips of A. cepa after 20 mg L^-1 treatment. The analysis of comet assay output images showed an alteration of DNA repair kinetics. The use of aqueous leaf extract of E. crassipes (Mart.) Solms-Laubach in the large-scale production of AgNPs by the method proposed in this study may be a step in improving the water loss in the Nile River. At the same time, a sensitive approach to the cytogenotoxicity of AgNPs must be considered.

DNA Damage and Apoptosis Induction in Cancer Cells by Chemically Engineered Thiolated Riboflavin Gold Nanoassembly

Herein we have engineered a smart nuclear targeting thiol-modified riboflavin-gold nano assembly, RfS@AuNPs, which accumulates selectively in the nucleus without any nuclear-targeting peptides (NLS/RGD) and shows photophysically in vitro DNA intercalation. A theoretical model using Molecular Dynamics has been developed to probe the mechanism of formation and stability as well as dynamics of the RfS@AuNPs in aqueous solution and within the DNA microenvironment. The RfS@AuNPs facilitate the binucleated cell formation that is reflected in the significant increase of DNA damage marker, γ-H2AX as well as the arrest of most of the HeLa cells at the pre-G1 phase indicating cell death. Moreover, a significant upregulation of apoptotic markers confirms that the cell death occurs through the apoptotic pathway. Analyses of the microarray gene expression of RfS@AuNPs treated HeLa cells show significant alterations in vital biological processes necessary for cell survival. Taken together, our study reports a unique nuclear targeting mechanism through targeting the riboflavin receptors, which are upregulated in cancer cells and induce apoptosis in the targeted cells.

Alternative Chk1-independent S/M checkpoint in somatic cells that prevents premature mitotic entry

Genomic instability is the hallmark of cancer. Checkpoint kinase-1 (Chk1) is required for cell cycle delay after DNA damage or blocked DNA replication. Chk1-depleted tumor cells undergo premature mitosis and apoptosis. Here we analyzed the depletion of Chk1 in normal somatic cells in the absence of DNA damage in order to investigate alternative cell cycle checkpoint mechanism(s). By means of adenoviruses, flow cytometry, immunofluorescence and Western blotting, Chk1-depleted mouse embryonic fibroblasts (MEFs) were investigated. Chk1^-/- MEFs arrested at the S/G2 boundary of the cell cycle with decreased protein levels of many cell cycle key players. Cyclin B1 was predominantly cytoplasmic. Interestingly, overexpression of nuclear dominant Cyclin B1 leads to nuclear translocation and premature mitosis. Chk1^-/- MEFs exhibited the absence of double-strand breaks, yet cells showed delayed DNA damage recovery with pan-nuclear immunostaining pattern of Histone H2AX. Activation of this checkpoint would elicit a senescent-like phenotype. Taken together, our elaborated data revealed the existence of an additional S/M checkpoint functioning via γH2AX signaling and cytoplasmic retention of Cyclin B1 in somatic cells.

Different cell cycle modifications repress apoptosis at different steps independent of developmental signaling in Drosophila

Genetic manipulations of the cell cycle repress apoptosis independent of developmental signaling. The findings have broader relevance to understanding the coordination of cell proliferation and apoptosis in development and disease.

Apoptotic cell death is important for the normal development of a variety of organisms. Apoptosis is also a response to DNA damage and an important barrier to oncogenesis. The apoptotic response to DNA damage is dampened in specific cell types during development. Developmental signaling pathways can repress apoptosis, and reduced cell proliferation also correlates with a lower apoptotic response. However, because developmental signaling regulates both cell proliferation and apoptosis, the relative contribution of cell division to the apoptotic response has been hard to discern in vivo. Here we use Drosophila oogenesis as an in vivo model system to determine the extent to which cell proliferation influences the apoptotic response to DNA damage. We find that different types of cell cycle modifications are sufficient to repress the apoptotic response to ionizing radiation independent of developmental signaling. The step(s) at which the apoptosis pathway was repressed depended on the type of cell cycle modification—either upstream or downstream of expression of the p53-regulated proapoptotic genes. Our findings have important implications for understanding the coordination of cell proliferation with the apoptotic response in development and disease, including cancer and the tissue-specific responses to radiation therapy.

NIR-Cyanine Dye Linker: a Promising Candidate for Isochronic Fluorescence Imaging in Molecular Cancer Diagnostics and Therapy Monitoring

Personalized anti-cancer medicine is boosted by the recent development of molecular diagnostics and molecularly targeted drugs requiring rapid and efficient ligation routes. Here, we present a novel approach to synthetize a conjugate able to act simultaneously as an imaging and as a chemotherapeutic agent by coupling functional peptides employing solid phase peptide synthesis technologies. Development and the first synthesis of a fluorescent dye with similarity in the polymethine part of the Cy7 molecule whose indolenine-N residues were substituted with a propylene linker are described. Methylating agent temozolomide is functionalized with a tetrazine as a diene component whereas Cy7-cell penetrating peptide conjugate acts as a dienophilic reaction partner for the inverse Diels-Alder click chemistry-mediated ligation route yielding a theranostic conjugate, 3-mercapto-propionic-cyclohexenyl-Cy7-bis-temozolomide-bromide-cell penetrating peptide. Synthesis route described here may facilitate targeted delivery of the therapeutic compound to achieve sufficient local concentrations at the target site or tissue. Its versatility allows a choice of adequate imaging tags applicable in e.g. PET, SPECT, CT, near-infrared imaging, and therapeutic substances including cytotoxic agents. Imaging tags and therapeutics may be simultaneously bound to the conjugate applying click chemistry. Theranostic compound presented here offers a solid basis for a further improvement of cancer management in a precise, patient-specific manner.

Numerical chromosomal instability mediates susceptibility to radiation treatment

The exquisite sensitivity of mitotic cancer cells to ionizing radiation (IR) underlies an important rationale for the widely used fractionated radiation therapy. However, the mechanism for this cell cycle-dependent vulnerability is unknown. Here we show that treatment with IR leads to mitotic chromosome segregation errors in vivo and long-lasting aneuploidy in tumour-derived cell lines. These mitotic errors generate an abundance of micronuclei that predispose chromosomes to subsequent catastrophic pulverization thereby independently amplifying radiation-induced genome damage. Experimentally suppressing whole-chromosome missegregation reduces downstream chromosomal defects and significantly increases the viability of irradiated mitotic cells. Further, orthotopically transplanted human glioblastoma tumours in which chromosome missegregation rates have been reduced are rendered markedly more resistant to IR, exhibiting diminished markers of cell death in response to treatment. This work identifies a novel mitotic pathway for radiation-induced genome damage, which occurs outside of the primary nucleus and augments chromosomal breaks. This relationship between radiation treatment and whole-chromosome missegregation can be exploited to modulate therapeutic response in a clinically relevant manner.

Link between DNA damage and centriole disengagement/reduplication in untransformed human cells

The radiation and radiomimetic drugs used to treat human tumors damage DNA in both cancer cells and normal proliferating cells. Centrosome amplification after DNA damage is well established for transformed cell types but is sparsely reported and not fully understood in untransformed cells. We characterize centriole behavior after DNA damage in synchronized untransformed human cells. One hour treatment of S phase cells with the radiomimetic drug, Doxorubicin, prolongs G2 by at least 72 h, though 14% of the cells eventually go through mitosis in that time. By 72 h after DNA damage we observe a 52% incidence of centriole disengagement plus a 10% incidence of extra centrioles. We find that either APC/C or Plk activities can disengage centrioles after DNA damage, though they normally work in concert. All disengaged centrioles are associated with γ-tubulin and maturation markers and thus, should in principle be capable of reduplicating and organizing spindle poles. The low incidence of reduplication of disengaged centrioles during G2 is due to the p53-dependent expression of p21 and the consequent loss of Cdk2 activity. We find that 26% of the cells going through mitosis after DNA damage contain disengaged or extra centrioles. This could produce genomic instability through transient or persistent spindle multipolarity. Thus, for cancer patients the use of DNA damaging therapies raises the chances of genomic instability and evolution of transformed characteristics in proliferating normal cell populations.

Frequency-dependent cell death by optical tweezers manipulation

Optical tweezers were used to scan individual Chronic Myelogenous Leukemia cells to determine if the cell death depends on the scanning conditions. Although increasing the scanning frequency or amplitude means greater force applied to the cells, their effects on cell death are not a simple increasing trend, as observed in the optical microscopy. Indeed, cell death sharply increased at particular screening frequencies and amplitudes, whereas other frequencies or amplitudes were less detrimental. These results suggest that cell damage was more sensitive to certain scanning conditions, rather than simply high-applied forces.

Centrosome dysfunction contributes to chromosome instability, chromoanagenesis, and genome reprograming in cancer

The unique ability of centrosomes to nucleate and organize microtubules makes them unrivaled conductors of important interphase processes, such as intracellular payload traffic, cell polarity, cell locomotion, and organization of the immunologic synapse. But it is in mitosis that centrosomes loom large, for they orchestrate, with clockmaker's precision, the assembly and functioning of the mitotic spindle, ensuring the equal partitioning of the replicated genome into daughter cells. Centrosome dysfunction is inextricably linked to aneuploidy and chromosome instability, both hallmarks of cancer cells. Several aspects of centrosome function in normal and cancer cells have been molecularly characterized during the last two decades, greatly enhancing our mechanistic understanding of this tiny organelle. Whether centrosome defects alone can cause cancer, remains unanswered. Until recently, the aggregate of the evidence had suggested that centrosome dysfunction, by deregulating the fidelity of chromosome segregation, promotes and accelerates the characteristic Darwinian evolution of the cancer genome enabled by increased mutational load and/or decreased DNA repair. Very recent experimental work has shown that missegregated chromosomes resulting from centrosome dysfunction may experience extensive DNA damage, suggesting additional dimensions to the role of centrosomes in cancer. Centrosome dysfunction is particularly prevalent in tumors in which the genome has undergone extensive structural rearrangements and chromosome domain reshuffling. Ongoing gene reshuffling reprograms the genome for continuous growth, survival, and evasion of the immune system. Manipulation of molecular networks controlling centrosome function may soon become a viable target for specific therapeutic intervention in cancer, particularly since normal cells, which lack centrosome alterations, may be spared the toxicity of such therapies.

Molecular mechanisms of garlic-derived allyl sulfides in the inhibition of skin cancer progression

Skin cancer is a serious concern whose incidence is increasing at an alarming rate. Allyl sulfides—i.e., sulfur metabolites in garlic oil—have been demonstrated to have anticancer activity against several cancer types, although the mechanisms underlying these effects remain enigmatic. Our previous study showed that diallyl trisulfide (DATS) is more potent than mono- and disulfides against skin cancer. DATS inhibits cell growth of human melanoma A375 cells and basal cell carcinoma (BCC) cells by increasing the levels of intracellular reactive oxygen species (ROS) and DNA damage and by inducing G2/M arrest, endoplasmic reticulum (ER) stress, and mitochondria-mediated apoptosis, including the caspase-dependent and -independent pathways. This short review focuses on the molecular mechanisms of garlic-derived allyl sulfides on skin cancer prevention.

Apoptotic-like death occurs through a caspase-independent route in colon carcinoma cells undergoing mitotic catastrophe

We have examined the relationship between chemotherapy-induced mitotic catastrophe and cell death by apoptosis in both wild-type and p53(-/-) HCT116 human colon carcinoma cells treated with nanomolar concentrations of paclitaxel (PTX), a drug that acts on tubulin altering the normal development of mitosis. After treatment, HCT116 cells entered mitosis regardless of the presence of functional p53, which resulted in changes in the distribution of cells in the different phases of the cell cycle, and in cell death. In the presence of PTX, the percentage of polyploid cells observed was higher in p53-deficient cells, indicating that mitotic slippage was favored compared to wild-type cells, with the presence of large multinucleate cells. PTX caused mitotic catastrophe and about 50-60% cells that were entering an aberrant mitosis died through an apoptotic-like pathway characterized by the presence of phosphatidylserine in the outer cell membrane, which occurred in the absence of significant activation of caspases. Lack of p53 facilitated endoreduplication and polyploidy in PTX-treated cells, but cells were still killed with similar efficacy through the same apoptotic-like mechanism in the absence of caspase activity.

Induction of robust de novo centrosome amplification, high-grade spindle multipolarity and metaphase catastrophe: a novel chemotherapeutic approach

Centrosome amplification (CA) and resultant chromosomal instability have long been associated with tumorigenesis. However, exacerbation of CA and relentless centrosome declustering engender robust spindle multipolarity (SM) during mitosis and may induce cell death. Recently, we demonstrated that a noscapinoid member, reduced bromonoscapine, (S)-3-(R)-9-bromo-5-(4,5-dimethoxy-1,3-dihydroisobenzofuran-1-yl)-4-methoxy-6-methyl-5,6,7,8-tetrahydro-[1,3]dioxolo-[4,5-g]isoquinoline (Red-Br-nos), induces reactive oxygen species (ROS)-mediated autophagy and caspase-independent death in prostate cancer PC-3 cells. Herein, we show that Red-Br-nos induces ROS-dependent DNA damage that resulted in high-grade CA and SM in PC-3 cells. Unlike doxorubicin, which causes double-stranded DNA breaks and chronic G2 arrest accompanied by ‘templated' CA, Red-Br-nos-mediated DNA damage elicits de novo CA during a transient S/G2 stall, followed by checkpoint abrogation and mitotic entry to form aberrant mitotic figures with supernumerary spindle poles. Attenuation of multipolar phenotype in the presence of tiron, a ROS inhibitor, indicated that ROS-mediated DNA damage was partly responsible for driving CA and SM. Although a few cells (∼5%) yielded to aberrant cytokinesis following an ‘anaphase catastrophe', most mitotically arrested cells (∼70%) succumbed to ‘metaphase catastrophe,' which was caspase-independent. This report is the first documentation of rapid de novo centrosome formation in the presence of parent centrosome by a noscapinoid family member, which triggers death-inducing SM via a unique mechanism that distinguishes it from other ROS-inducers, conventional DNA-damaging agents, as well as other microtubule-binding drugs.

Cooperative effects of Akt-1 and Raf-1 on the induction of cellular senescence in doxorubicin or tamoxifen treated breast cancer cells

Escape from cellular senescence induction is a potent mechanism for chemoresistance. Cellular senescence can be induced in breast cancer cell lines by the removal of estrogen signaling with tamoxifen or by the accumulation of DNA damage induced by the chemotherapeutic drug doxorubicin. Long term culturing of the hormone-sensitive breast cancer cell line MCF-7 in doxorubicin (MCF-7/DoxR) reduced the ability of doxorubicin, but not tamoxifen, to induce senescence. Two pathways that are often upregulated in chemo- and hormonal-resistance are the PI3K/PTEN/Akt/mTOR and Ras/Raf/MEK/ERK pathways. To determine if active Akt-1 and Raf-1 can influence drug-induced senescence, we stably introduced activated ΔAkt-1(CA) and ΔRaf-1(CA) into drug-sensitive and doxorubicin-resistant cells. Expression of a constitutively-active Raf-1 construct resulted in higher baseline senescence, indicating these cells possessed the ability to undergo oncogene-induced-senescence. Constitutive activation of the Akt pathway significantly decreased drug-induced senescence in response to doxorubicin but not tamoxifen in MCF-7 cells. However, constitutive Akt-1 activation in drug-resistant cells containing high levels of active ERK completely escaped cellular senescence induced by doxorubicin and tamoxifen. These results indicate that up regulation of the Ras/PI3K/PTEN/Akt/mTOR pathway in the presence of elevated Ras/Raf/MEK/ERK signaling together can contribute to drug-resistance by diminishing cell senescence in response to chemotherapy. Understanding how breast cancers containing certain oncogenic mutations escape cell senescence in response to chemotherapy and hormonal based therapies may provide insights into the design of more effective drug combinations for the treatment of breast cancer.

The control of chromosome segregation during mitosis in epithelial cells by substrate elasticity

Materials of defined elasticity, including synthetic material scaffolds and tissue-derived matrices, can regulate biological responses of cells and in particular adhesion, migration, growth and differentiation which are essential parameters for tissue integration. These responses have been extensively investigated in interphase cells, but little is known whether and how material elasticity affects mitotic cells. We used polyelectrolyte multilayer films as model substrates with elastic modulus ranging from Eap = 0 up to Eap = 500 kPa and mitotic PtK2 epithelial cells to address these important questions. Soft substrates (Eap < 50 kPa) led to abnormal morphology in chromosome segregation, materialized by chromatin bridges and chromosome lagging. Frequency of these damages increased with decreasing substrate stiffness and was correlated with a pro-apoptotic phenotype. Mitotic spindle was not observed on soft substrates where formation of chromatin damages is due to low β1-integrin engagement and decrease of Rac1 activities. This work constitutes the first evidence that soft substrates hinder epithelial cell division. In perspective, our findings emphasize the prime incidence of the material elasticity on the fate of the phenotype, especially of stem cells in the mitotic phase.

Allyl sulfides inhibit cell growth of skin cancer cells through induction of DNA damage mediated G2/M arrest and apoptosis

Diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS), extracted from crushed garlic by steam-distillation, have been reported to provide the anticancer activity in several cancer types. However, their mechanisms of effects on skin cancer cells remain unclear. Therefore, we used human melanoma A375 cells and basal cell carcinoma cells as the models to elucidate the effects of these three allyl sulfides. Basal cell carcinoma (BCC) is known to be the most prevalent type of skin cancer, and melanoma is the most lethal form. We found that DATS revealed better growth inhibition of A375 and BCC cells than DADS and DAS did. We further demonstrated that DATS increased intracellular reactive oxygen species (ROS) generation, induced cytosolic Ca(2+) mobilization, and decreased mitochondrial membrane potential (DeltaPsim). Western blot results showed the concordance for the expression of molecules involved in G(2)/M arrest and apoptosis observed by cell cycle and cell viability analysis. Moreover, we detected the activation of p53 pathway in response to the oxidative DNA damage. DATS also displayed selective target of growth inhibition between skin cancer cells and normal keratinocyte HaCaT cells. Taken together, these results suggest that DATS is a potential anticancer compound for skin cancer.

Enhancing therapeutic efficacy by targeting non-oncogene addicted cells with combinations of signal transduction inhibitors and chemotherapy

The effects of inhibition of the Raf/MEK/ERK and PI3K/Akt/mTOR signaling pathways and chemotherapeutic drugs on cell cycle progression and drug sensitivity were examined in cytokine-dependent FL5.12 hematopoietic cells. We examined their effects, as these cells resemble normal hematopoietic precursor cells as they do not exhibit "oncogene-addicted" growth, while they do display "cytokine-addicted" proliferation as cytokine removal resulted in apoptosis in greater than 80% of the cells within 48 hrs. When cytokine-dependent FL5.12 cells were cultured in the presence of IL-3, which stimulated multiple proliferation and anti-apoptotic cascades, MEK, PI3K and mTOR inhibitors transiently suppressed but did not totally inhibit cell cycle progression or induce apoptosis while chemotherapeutic drugs such as doxorubicin and paclitaxel were more effective in inducing cell cycle arrest and apoptosis. Doxorubicin induced a G(1) block, while paclitaxel triggered a G(2)/M block. Doxorubicin was more effective in inducing cell death than paclitaxel. Furthermore the effects of doxorubicin could be enhanced by addition of MEK, PI3K or mTOR inhibitors. Cytokine-dependent cells which proliferate in vitro and are not "oncogene-addicted" may represent a pre-malignant stage, more refractory to treatment with targeted therapy. However, these cells are sensitive to chemotherapeutic drugs. It is important to develop methods to inhibit the growth of such cytokine-dependent cells as they may resemble the leukemia stem cell and other cancer initiating cells. These results demonstrate the enhanced effectiveness of targeting early hematopoietic progenitor cells with combinations of chemotherapeutic drugs and signal transduction inhibitors.

The Raf/MEK/ERK pathway can govern drug resistance, apoptosis and sensitivity to targeted therapy

The effects of the Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR signaling pathways on proliferation, drug resistance, prevention of apoptosis and sensitivity to signal transduction inhibitors were examined in FL/DeltaAkt-1:ER*(Myr(+)) + DeltaRaf-1:AR cells which are conditionally-transformed to grow in response to Raf and Akt activation. Drug resistant cells were isolated from FL/DeltaAkt-1:ER*(Myr(+)) + DeltaRaf-1:AR cells in the presence of doxorubicin. Activation of Raf-1, in the drug resistant FL/DeltaAkt-1:ER*(Myr(+)) + DeltaRaf-1:AR cells, increased the IC(50) for doxorubicin 80-fold, whereas activation of Akt-1, by itself, had no effect on the doxorubicin IC50. However, Akt-1 activation enhanced cell proliferation and clonogenicity in the presence of chemotherapeutic drugs. Thus the Raf/MEK/ERK pathway had profound effects on the sensitivity to chemotherapeutic drugs, and Akt-1 activation was required for the long term growth of these cells as well as resistance to chemotherapeutic drugs. The effects of doxorubicin on the induction of apoptosis in the drug resistant cells were enhanced by addition of either mTOR and MEK inhibitors. These results indicate that targeting the Raf/MEK/ERK and PI3K/Akt/mTOR pathways may be an effective approach for therapeutic intervention in drug resistant cancers that have mutations activating these cascades.

Cytokinesis and cancer

Cytokinesis is the final stage of cell division during which the two daughter cells separate completely. Although less well understood than some of the earlier phases of the cell cycle, recent discoveries have shed light on the mechanisms that orchestrate this process, including cleavage furrow formation, midbody maturation and abscission. One of the reasons why research on cytokinesis has been attracting increasing attention is the concept that failure of this process in mammals is associated with carcinogenesis. In this minireview, we will discuss the possible links between cytokinesis and cancer, and highlight key mechanisms that connect these processes.