Interference with actin dynamics is superior to disturbance of microtubule function in the inhibition of human ovarian cancer cell motility

Treatment with tumor-treating fields (TTFields) suppresses intercellular tunneling nanotube formation in vitro and upregulates immuno-oncologic biomarkers in vivo in malignant mesothelioma

Disruption of intercellular communication within tumors is emerging as a novel potential strategy for cancer-directed therapy. Tumor-Treating Fields (TTFields) therapy is a treatment modality that has itself emerged over the past decade in active clinical use for patients with glioblastoma and malignant mesothelioma, based on the principle of using low-intensity alternating electric fields to disrupt microtubules in cancer cells undergoing mitosis. There is a need to identify other cellular and molecular effects of this treatment approach that could explain reported increased overall survival when TTFields are added to standard systemic agents. Tunneling nanotube (TNTs) are cell-contact-dependent filamentous-actin-based cellular protrusions that can connect two or more cells at long-range. They are upregulated in cancer, facilitating cell growth, differentiation, and in the case of invasive cancer phenotypes, a more chemoresistant phenotype. To determine whether TNTs present a potential therapeutic target for TTFields, we applied TTFields to malignant pleural mesothelioma (MPM) cells forming TNTs in vitro. TTFields at 1.0 V/cm significantly suppressed TNT formation in biphasic subtype MPM, but not sarcomatoid MPM, independent of effects on cell number. TTFields did not significantly affect function of TNTs assessed by measuring intercellular transport of mitochondrial cargo via intact TNTs. We further leveraged a spatial transcriptomic approach to characterize TTFields-induced changes to molecular profiles in vivo using an animal model of MPM. We discovered TTFields induced upregulation of immuno-oncologic biomarkers with simultaneous downregulation of pathways associated with cell hyperproliferation, invasion, and other critical regulators of oncogenic growth. Several molecular classes and pathways coincide with markers that we and others have found to be differentially expressed in cancer cell TNTs, including MPM specifically. We visualized short TNTs in the dense stromatous tumor material selected as regions of interest for spatial genomic assessment. Superimposing these regions of interest from spatial genomics over the plane of TNT clusters imaged in intact tissue is a new method that we designate Spatial Profiling of Tunneling nanoTubes (SPOTT). In sum, these results position TNTs as potential therapeutic targets for TTFields-directed cancer treatment strategies. We also identified the ability of TTFields to remodel the tumor microenvironment landscape at the molecular level, thereby presenting a potential novel strategy for converting tumors at the cellular level from 'cold' to 'hot' for potential response to immunotherapeutic drugs.

How does plasticity of migration help tumor cells to avoid treatment: Cytoskeletal regulators and potential markers

Tumor shrinkage as a result of antitumor therapy is not the only and sufficient indicator of treatment success. Cancer progression leads to dissemination of tumor cells and formation of metastases - secondary tumor lesions in distant organs. Metastasis is associated with acquisition of mobile phenotype by tumor cells as a result of epithelial-to-mesenchymal transition and further cell migration based on cytoskeleton reorganization. The main mechanisms of individual cell migration are either mesenchymal, which depends on the activity of small GTPase Rac, actin polymerization, formation of adhesions with extracellular matrix and activity of proteolytic enzymes or amoeboid, which is based on the increase in intracellular pressure caused by the enhancement of actin cortex contractility regulated by Rho-ROCK-MLCKII pathway, and does not depend on the formation of adhesive structures with the matrix, nor on the activity of proteases. The ability of tumor cells to switch from one motility mode to another depending on cell context and environmental conditions, termed migratory plasticity, contributes to the efficiency of dissemination and often allows the cells to avoid the applied treatment. The search for new therapeutic targets among cytoskeletal proteins offers an opportunity to directly influence cell migration. For successful treatment it is important to assess the likelihood of migratory plasticity in a particular tumor. Therefore, the search for specific markers that can indicate a high probability of migratory plasticity is very important.

Tetraspanins as regulators of the tumour microenvironment: implications for metastasis and therapeutic strategies

One of the hallmarks of cancer is the ability to activate invasion and metastasis. Cancer morbidity and mortality are largely related to the spread of the primary, localized tumour to adjacent and distant sites. Appropriate management and treatment decisions based on predicting metastatic disease at the time of diagnosis is thus crucial, which supports better understanding of the metastatic process. There are components of metastasis that are common to all primary tumours: dissociation from the primary tumour mass, reorganization/remodelling of extracellular matrix, cell migration, recognition and movement through endothelial cells and the vascular circulation and lodgement and proliferation within ectopic stroma. One of the key and initial events is the increased ability of cancer cells to move, escaping the regulation of normal physiological control. The cellular cytoskeleton plays an important role in cancer cell motility and active cytoskeletal rearrangement can result in metastatic disease. This active change in cytoskeletal dynamics results in manipulation of plasma membrane and cellular balance between cellular adhesion and motility which in turn determines cancer cell movement. Members of the tetraspanin family of proteins play important roles in regulation of cancer cell migration and cancer-endothelial cell interactions, which are critical for cancer invasion and metastasis. Their involvements in active cytoskeletal dynamics, cancer metastasis and potential clinical application will be discussed in this review. In particular, the tetraspanin member, CD151, is highlighted for its major role in cancer invasion and metastasis.

LINKED ARTICLES

This article is part of a themed section on Cytoskeleton, Extracellular Matrix, Cell Migration, Wound Healing and Related Topics. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-24.

Conjugation of pH-responsive nanoparticles to neural stem cells improves intratumoral therapy

Intratumoral drug delivery is an inherently appealing approach for concentrating toxic chemotherapies at the site of action. This mode of administration is currently used in a number of clinical treatments such as neoadjuvant, adjuvant, and even standalone therapies when radiation and surgery are not possible. However, even when injected locally, it is difficult to achieve efficient distribution of chemotherapeutics throughout the tumor. This is primarily attributed to the high interstitial pressure which results in gradients that drive fluid away from the tumor center. The stiff extracellular matrix also limits drug penetration throughout the tumor. We have previously shown that neural stem cells can penetrate tumor interstitium, actively migrating even to hypoxic tumor cores. When used to deliver therapeutics, these migratory neural stem cells result in dramatically enhanced tumor coverage relative to conventional delivery approaches. We recently showed that neural stem cells maintain their tumor tropic properties when surface-conjugated to nanoparticles. Here we demonstrate that this hybrid delivery system can be used to improve the efficacy of docetaxel-loaded nanoparticles when administered intratumorally. This was achieved by conjugating drug-loaded nanoparticles to the surface of neural stem cells using a bond that allows the stem cells to efficiently distribute nanoparticles throughout the tumor before releasing the drug for uptake by tumor cells. The modular nature of this system suggests that it could be used to improve the efficacy of many chemotherapy drugs after intratumoral administration.

The expression of the Sprouty 1 protein inversely correlates with growth, proliferation, migration and invasion of ovarian cancer cells

Background

Our recent study on a panel of human ovarian cancer cells revealed that SKOV-3 cells barely express the Sprouty isoform 1 (Spry1) while 1A9 cells maintain it at a level similar to normal ovarian cells. Here we investigated the functional outcomes of induced alterations in the expression of Spry1 in the two cell lines in vitro.

Methods

Using the Spry1 specific plasmid and siRNA, the expression of Spry1 was induced and conversely silenced in SKOV-3 and 1A9 cells, respectively. The functional outcome was investigated by means of proliferation, MTT, scratch-wound, migration and invasion assays and selection of the stable clones. Mechanism of the effect was explored by Western blot.

Results

In the Spry1-transfected SKOV-3 cells, a significant reduction in growth and proliferation was evident. Stable clones of the Spry1-transfected SKOV-3 were almost undetectable after day 14. The number of migrated and invaded cells and the percentage of the scratch closure were significantly lower in the Spry1-transfected group. Spry1 silencing in 1A9 cells, on the other hand, led to a significant increase in cell growth and proliferation. The number of migrated and invaded cells and the percentage of the scratch closure significantly increased in Spry1-silenced 1A9 group. Mechanistically, overexpression of Bax, activation of caspases 3, 7, 8 and 9, cleavage of PARP and attenuation of Bcl-2 and Bcl-xl were observed along with reduced activation of Erk and Akt and increased amount and activity of PTEN in the Spry1-transfected SKOV-3 cells.

Conclusions

Here, we report the inverse correlation between the expression of Spry1 and growth, proliferation, invasion and migration of ovarian cancer cells.

An mDia2/ROCK signaling axis regulates invasive egress from epithelial ovarian cancer spheroids

Multi-cellular spheroids are enriched in ascites of epithelial ovarian cancer (OvCa) patients. They represent an invasive and chemoresistant cellular population fundamental to metastatic dissemination. The molecular mechanisms triggering single cell invasive egress from spheroids remain enigmatic. mDia formins are Rho GTPase effectors that are key regulators of F-actin cytoskeletal dynamics. We hypothesized that mDia2-driven F-actin dynamics promote single cell invasive transitions in clinically relevant three-dimensional (3D) OvCa spheroids. The current study is a dissection of the contribution of the F-actin assembly factor mDia2 formin in invasive transitions and using a clinically relevant ovarian cancer spheroid model. We show that RhoA-directed mDia2 activity is required for tight spheroid organization, and enrichment of mDia2 in the invasive cellular protrusions of collagen-embedded OVCA429 spheroids. Depleting mDia2 in ES-2 spheroids enhanced invasive dissemination of single amoeboid-shaped cells. This contrasts with spheroids treated with control siRNA, where a mesenchymal invasion program predominated. Inhibition of another RhoA effector, ROCK, had no impact on ES-2 spheroid formation but dramatically inhibited spheroid invasion through induction of a highly elongated morphology. Concurrent inhibition of ROCK and mDia2 blocked single cell invasion from ES-2 spheroids more effectively than inhibition of either protein alone, indicating that invasive egress of amoeboid cells from mDia2-depleted spheroids is ROCK-dependent. Our findings indicate that multiple GTPase effectors must be suppressed in order to fully block invasive egress from ovarian cancer spheroids. Furthermore, tightly regulated interplay between ROCK and mDia2 signaling pathways dictates the invasive capacities and the type of invasion program utilized by motile spheroid-derived ovarian cancer cells. As loss of the gene encoding mDia2, DRF3, has been linked to cancer progression and metastasis, our results set the stage for understanding molecular mechanisms involved in mDia2-dependent egress of invasive cells from primary epithelial tumors.

Fluid-flow induced wall shear stress and epithelial ovarian cancer peritoneal spreading

Epithelial ovarian cancer (EOC) is usually discovered after extensive metastasis have developed in the peritoneal cavity. The ovarian surface is exposed to peritoneal fluid pressures and shear forces due to the continuous peristaltic motions of the gastro-intestinal system, creating a mechanical micro-environment for the cells. An in vitro experimental model was developed to expose EOC cells to steady fluid flow induced wall shear stresses (WSS). The EOC cells were cultured from OVCAR-3 cell line on denuded amniotic membranes in special wells. Wall shear stresses of 0.5, 1.0 and 1.5 dyne/cm² were applied on the surface of the cells under conditions that mimic the physiological environment, followed by fluorescent stains of actin and β-tubulin fibers. The cytoskeleton response to WSS included cell elongation, stress fibers formation and generation of microtubules. More cytoskeletal components were produced by the cells and arranged in a denser and more organized structure within the cytoplasm. This suggests that WSS may have a significant role in the mechanical regulation of EOC peritoneal spreading.

N-acetylcysteine potentiates doxorubicin-induced ATM and p53 activation in ovarian cancer cells

Doxorubicin has been used clinically to treat various types of cancer, and yet the molecular mode of actions of doxorubicin remains to be fully unraveled. In this study, we investigated the effect of doxorubicin on cultured ovarian cancer cells (CaOV3). MTT assay data showed that doxorubicin inhibits cell proliferation in a time- and dose-dependent manner. Phagokinetic cell motility assay data indicated that doxorubicin inhibits both basal level and EGF-induced cell migration in CaOV3 cells. Confocal microscopic data revealed that doxorubicin induces reorganization of cytoskeletal proteins including actin, tubulin and vimentin. Doxorubicin induces phosphorylation of p53 at Ser15 and 20, acetylation of p53 and ATM activation. Doxorubicin also induces phosphorylation of histone H2AX at Ser139. Interestingly, doxorubicin also inhibits mTOR activity, measured by phosphorylation of S6 ribosomal protein. Pretreatment of CaOV3 cells with antioxidant N-acetylcysteine (NAC), but not pyrrolidine dithiocarbamate (PDTC) potentiates doxorubicin-induced phosphorylation of p53 and ATM. Collectively, we conclude that doxorubicin induces ATM/p53 activation leading to reorganization of cytoskeletal networks, inhibition of mTOR activity, and inhibition of cell proliferation and migration. Our data also suggest that removal of oxidants by antioxidants such as NAC may enhance the efficacy of doxorubicin in vivo.

Ligand-receptor interaction between triterpenoids and the 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2) enzyme predicts their toxic effects against tumorigenic r/m HM-SFME-1 cells

The present study deals with in silico prediction and in vitro evaluation of the selective cytotoxic effects of triterpenoids on tumorigenic human c-Ha-ras and mouse c-myc cotransfected highly metastatic serum-free mouse embryo-1 (r/m HM-SFME-1) cells. Ligand fitting of five different triterpenoids to 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) was analyzed with a molecular modeling method, and glycyrrhetinic acid (GA) was the best-fitted triterpenoid to the ligand binding site in 11βHSD2. Analysis of antiproliferative effects revealed that GA, oleanolic acid, and ursolic acid had selective toxicity against the tumor cells and that GA was the most potent triterpenoid in its selectivity. The toxic activity of the tested triterpenoids against the tumor cells showed good correlations with the partition coefficient (logP) and polar surface area values. Time-lapse microscopy, fluorescence staining, and confocal laser scanning microscopic observation revealed that GA induced morphologic changes typical of apoptosis such as cell shrinkage and blebbing and also disrupted the cytoskeletal proteins. Furthermore, GA exhibited a strong inhibitory effect on 11βHSD2 activity in the tumor cells. Our current results suggest that analysis of the ligand-receptor interaction between triterpenoids and 11βHSD2 can be utilized to predict their antitumor effects and that GA can be used as a possible chemopreventive and therapeutic antitumor agent. To the best of our knowledge, this is the first report on in silico prediction of the toxic effects of triterpenoids on tumor cells by 11βHSD2 inhibition.

An outlook on ovarian cancer and borderline ovarian tumors: focus on genomic and proteomic findings

Among the gynaecological malignancies, ovarian cancer is one of the neoplastic forms with the poorest prognosis and with the bad overall and disease-free survival rates than other gynaecological cancers. Ovarian tumors can be classified on the basis of the cells of origin in epithelial, stromal and germ cell tumors. Epithelial ovarian tumors display great histological heterogeneity and can be further subdivided into benign, intermediate or borderline, and invasive tumors. Several studies on ovarian tumors, have focused on the identification of both diagnostic and prognostic markers for applications in clinical practice. High-throughput technologies have accelerated the process of biomolecular study and genomic discovery; unfortunately, validity of these should be still demonstrated by extensive researches on sensibility and sensitivity of ovarian cancer novel biomarkers, determining whether gene profiling and proteomics could help differentiate between patients with metastatic ovarian cancer and primary ovarian carcinomas, and their potential impact on management. Therefore, considerable interest lies in identifying molecular and protein biomarkers and indicators to guide treatment decisions and clinical follow up. In this review, the current state of knowledge about the genoproteomic and potential clinical value of gene expression profiling in ovarian cancer and ovarian borderline tumors is discussed, focusing on three main areas: distinguishing normal ovarian tissue from ovarian cancers and borderline tumors, identifying different genotypes of ovarian tissue and identifying proteins linked to cancer or tumor development. By these targets, authors focus on the use of novel molecules, developed on the proteomics and genomics researches, as potential protein biomarkers in the management of ovarian cancer or borderline tumor, overlooking on current state of the art and on future perspectives of researches.

New approaches to targeting the actin cytoskeleton for chemotherapy

The actin cytoskeleton is indispensable for normal cellular function. In particular, several actin-based structures coordinate cellular motility, a process hijacked by tumor cells in order to facilitate their propagation to distant sites. The actin cytoskeleton, therefore, represents a point for chemotherapeutic intervention. The challenge in disrupting the actin cytoskeleton is in preserving actin-driven contraction of cardiac and skeletal muscle. By targeting actin-binding proteins with altered expression in malignancy, it may be possible to achieve tumor-specific toxicity. A number of actin-binding proteins act cooperatively and synergistically to regulate actin structures required for motility. The actin cytoskeleton is characterized by a significant degree of plasticity. Targeting specific actin-binding proteins for chemotherapy will only be successful if no other compensatory mechanisms exist.

Changes in gene expression and cellular architecture in an ovarian cancer progression model

BACKGROUND

Ovarian cancer is the fifth leading cause of cancer deaths among women. Early stage disease often remains undetected due the lack of symptoms and reliable biomarkers. The identification of early genetic changes could provide insights into novel signaling pathways that may be exploited for early detection and treatment.

METHODOLOGY/PRINCIPAL FINDINGS

Mouse ovarian surface epithelial (MOSE) cells were used to identify stage-dependent changes in gene expression levels and signal transduction pathways by mouse whole genome microarray analyses and gene ontology. These cells have undergone spontaneous transformation in cell culture and transitioned from non-tumorigenic to intermediate and aggressive, malignant phenotypes. Significantly changed genes were overrepresented in a number of pathways, most notably the cytoskeleton functional category. Concurrent with gene expression changes, the cytoskeletal architecture became progressively disorganized, resulting in aberrant expression or subcellular distribution of key cytoskeletal regulatory proteins (focal adhesion kinase, α-actinin, and vinculin). The cytoskeletal disorganization was accompanied by altered patterns of serine and tyrosine phosphorylation as well as changed expression and subcellular localization of integral signaling intermediates APC and PKCβII.

CONCLUSIONS/SIGNIFICANCE

Our studies have identified genes that are aberrantly expressed during MOSE cell neoplastic progression. We show that early stage dysregulation of actin microfilaments is followed by progressive disorganization of microtubules and intermediate filaments at later stages. These stage-specific, step-wise changes provide further insights into the time and spatial sequence of events that lead to the fully transformed state since these changes are also observed in aggressive human ovarian cancer cell lines independent of their histological type. Moreover, our studies support a link between aberrant cytoskeleton organization and regulation of important downstream signaling events that may be involved in cancer progression. Thus, our MOSE-derived cell model represents a unique model for in depth mechanistic studies of ovarian cancer progression.

Cancer cell invasion is enhanced by applied mechanical stimulation

Metastatic cells migrate from the site of the primary tumor, through the stroma, into the blood and lymphatic vessels, finally colonizing various other tissues to form secondary tumors. Numerous studies have been done to identify the stimuli that drive the metastatic cascade. This has led to the identification of multiple biochemical signals that promote metastasis. However, information on the role of mechanical factors in cancer metastasis has been limited to the affect of compliance. Interestingly, the tumor microenvironment is rich in many cell types including highly contractile cells that are responsible for extensive remodeling and production of the dense extracellular matrix surrounding the cancerous tissue. We hypothesize that the mechanical forces produced by remodeling activities of cells in the tumor microenvironment contribute to the invasion efficiency of metastatic cells. We have discovered a significant difference in the extent of invasion in mechanically stimulated verses non-stimulated cell culture environments. Furthermore, this mechanically enhanced invasion is dependent upon substrate protein composition, and influenced by topography. Finally, we have found that the protein cofilin is needed to sense the mechanical stimuli that enhances invasion. We conclude that other types of mechanical signals in the tumor microenvironment, besides the rigidity, can enhance the invasive abilities of cancer cells in vitro. We further propose that in vivo, non-cancerous cells located within the tumor micro-environment may be capable of providing the necessary mechanical stimulus during the remodeling of the extracellular matrix surrounding the tumor.

Glycyrrhetinic acid induces anoikis-like death and cytoskeletal disruption in the central nervous system tumorigenic cells

We analyzed the effects of glycyrrhetinic acid (GA), a licorice compound, on the induction of anoikis-like death and cytoskeletal disruption in the central nervous system (CNS) tumorigenic cells. GA was cytotoxic in time- and dose-dependent manners, and the tumorigenic cells shed floating cells upon the GA treatment and even some of the adherent cells were easily detached from the fibronectin-coated culture dish by gentle shaking and aspiration. Reculture of the detached cells revealed that the longer the duration of GA exposure, the less the number of the proliferatable cells. These results indicate that GA perturbs cell adhesion and induces anoikis-like cell death. Further, GA also induced morphologic changes and disturbed cytoskeletal proteins.

Docetaxel suppresses invasiveness of head and neck cancer cells in vitro

The combination of docetaxel, cisplatin, and fluorouracil significantly enhances the survival of head and neck cancer patients compared to cisplatin and fluorouracil. We hypothesized that docetaxel may affect invasiveness of the head and neck cancer cells in addition to its tumor-killing effect. Two different head and neck cancer cell lines (HEp-2 and Ca9-22) were treated with docetaxel at IC(10) and IC(50) concentrations. Cell migration and invasive growth was evaluated by wound healing assay and three-dimensional (3D) culture of multicellular tumor spheroids, respectively. Expression levels of possible downstream effectors for cell migration/invasiveness were measured by immunoblotting in conditions with or without docetaxel. Docetaxel, but not cisplatin, suppressed filopodia formation compared with no treatment (control) condition. Consistent with this, docetaxel suppressed two-dimensional (2D) cell migration and 3D cell invasion compared with control or cisplatin. Only docetaxel treated cells exhibited thick tubulin bundle and had lower activity of Cdc42, a member of the Rho family of small GTPases. In conclusion, Docetaxel treatment suppressed migration and invasiveness of head and neck cancer cells in vitro, which is likely to be mediated by regulating Cdc42 activity.

Novel effects of glycyrrhetinic acid on the central nervous system tumorigenic progenitor cells: induction of actin disruption and tumor cell-selective toxicity

Licorice extracts are used worldwide in foods and medicines, and glycyrrhetinic acid (GA) is a licorice component that has been reported to induce various important biological activities. In the present study, we show that GA induces actin disruption and has tumor cell-selective toxic properties, and that its selectivity is superior to those of all the clinically available antitumor agents tested. The cytotoxic activity of GA and the tested antitumor agents showed better correlation with the partition coefficient (log P) values rather than the polar surface area (PSA) values. For selective toxicity against tumor cells, GA was most effective at 10 microM that was the same concentration as the previously reported maximum plasma GA level reached in humans ingesting licorice. These results suggest that GA could be utilized as a promising chemopreventive and therapeutic antitumor agent. The underlying mechanisms involved in the selective toxicity to tumor cells by GA are also preliminarily discussed.

Selective cytotoxicity of glycyrrhetinic acid against tumorigenic r/m HM-SFME-1 cells: potential involvement of H-Ras downregulation

With the intensive need for the development of more effective and safer agents for chemoprevention and therapy of human cancer, natural products from plants have been expected to play significant roles in creating new and better chemopreventive and therapeutic agents. Selectivity is also an important issue in cancer prevention and therapy. In the present study, normal serum-free mouse embryo (SFME) and tumorigenic human c-Ha-ras and mouse c-myc cotransfected highly metastatic serum-free mouse embryo-1 (r/m HM-SFME-1) cells were treated with various concentrations of clinically available antitumor agents or glycyrrhetinic acid (GA), and the antiproliferative effects of these compounds were determined by the MTT assay. Western blotting analysis, RT-PCR, fluorescence staining and confocal laser scanning microscopic observation were adopted to analyze H-Ras regulation. GA exhibited the tumor cell-selective toxicity through H-Ras downregulation, and its selectivity was superior to those of all the clinically available antitumor agents examined. For the selective toxicity of tumor cells, GA was most effective at 10 microM. Interestingly, this concentration was the same as the previously reported maximum plasma GA level reached in humans ingesting licorice. These results in the present study suggest that GA with its cytotoxic effects could be utilized as a promising chemopreventive and therapeutic antitumor agent.