Cell migration and invasion assays as tools for drug discovery

Microfabricated Systems and Assays for Studying the Cytoskeletal Organization, Micromechanics, and Motility Patterns of Cancerous Cells

Cell motions are driven by coordinated actions of the intracellular cytoskeleton - actin, microtubules (MTs) and substrate/focal adhesions (FAs). This coordination is altered in metastatic cancer cells resulting in deregulated and increased cellular motility. Microfabrication tools, including photolithography, micromolding, microcontact printing, wet stamping and microfluidic devices have emerged as a powerful set of experimental tools with which to probe and define the differences in cytoskeleton organization/dynamics and cell motility patterns in non-metastatic and metastatic cancer cells. In this review, we discuss four categories of microfabricated systems: (i) micropatterned substrates for studying of cell motility sub-processes (for example, MT targeting of FAs or cell polarization); (ii) systems for studying cell mechanical properties, (iii) systems for probing overall cell motility patterns within challenging geometric confines relevant to metastasis (for example, linear and ratchet geometries), and (iv) microfluidic devices that incorporate co-cultures of multiple cells types and chemical gradients to mimic in vivo intravasation/extravasation steps of metastasis. Together, these systems allow for creating controlled microenvironments that not only mimic complex soft tissues, but are also compatible with live cell high-resolution imaging and quantitative analysis of single cell behavior.

Low-cost motility tracking system (LOCOMOTIS) for time-lapse microscopy applications and cell visualisation

Direct visualisation of cells for the purpose of studying their motility has typically required expensive microscopy equipment. However, recent advances in digital sensors mean that it is now possible to image cells for a fraction of the price of a standard microscope. Along with low-cost imaging there has also been a large increase in the availability of high quality, open-source analysis programs. In this study we describe the development and performance of an expandable cell motility system employing inexpensive, commercially available digital USB microscopes to image various cell types using time-lapse and perform tracking assays in proof-of-concept experiments. With this system we were able to measure and record three separate assays simultaneously on one personal computer using identical microscopes, and obtained tracking results comparable in quality to those from other studies that used standard, more expensive, equipment. The microscopes used in our system were capable of a maximum magnification of 413.6×. Although resolution was lower than that of a standard inverted microscope we found this difference to be indistinguishable at the magnification chosen for cell tracking experiments (206.8×). In preliminary cell culture experiments using our system, velocities (mean µm/min ± SE) of 0.81 ± 0.01 (Biomphalaria glabrata hemocytes on uncoated plates), 1.17 ± 0.004 (MDA-MB-231 breast cancer cells), 1.24 ± 0.006 (SC5 mouse Sertoli cells) and 2.21 ± 0.01 (B. glabrata hemocytes on Poly-L-Lysine coated plates), were measured and are consistent with previous reports. We believe that this system, coupled with open-source analysis software, demonstrates that higher throughput time-lapse imaging of cells for the purpose of studying motility can be an affordable option for all researchers.

Loss of p27 upregulates MnSOD in a STAT3-dependent manner, disrupts intracellular redox activity and enhances cell migration

Cell migration is a dynamic process that is central to a variety of physiological functions as well as disease pathogenesis. The modulation of cell migration by p27 (officially known as CDKN1B) has been reported, but the exact mechanism(s) whereby p27 interacts with downstream effectors that control cell migration have not been elucidated. By systematically comparing p27(+/+) mouse embryonic fibroblasts (MEFs) with genetically ablated p27(-/-) MEFs using wound-healing, transwell and time-lapse microscopic analyses, we provide direct evidence that p27 inhibits both directional and random cell migration. Identical results were obtained with normal and cancer epithelial cells using complementary knockdown and overexpression approaches. Additional studies revealed that overexpression of manganese superoxide dismutase (MnSOD, officially known as SOD2) and reduced intracellular oxidation played a key role in increased cell migration in p27-deficient cells. Furthermore, we identified signal transducer and activator of transcription 3 (STAT3) as the transcription factor responsible for p27-regulated MnSOD expression, which was further mediated by ERK- and ATF1-dependent transactivation of the cAMP response element (CRE) within the Stat3 promoter. Collectively, our data strongly indicate that p27 plays a crucial negative role in cell migration by inhibiting MnSOD expression in a STAT3-dependent manner.

A high-content, multiplexed screen in human breast cancer cells identifies profilin-1 inducers with anti-migratory activities

Profilin-1 (Pfn-1) is a ubiquitously expressed actin-binding protein that is essential for normal cell proliferation and migration. In breast cancer and several other adenocarcinomas, Pfn-1 expression is downregulated when compared to normal tissues. Previous studies from our laboratory have shown that genetically modulating Pfn-1 expression significantly impacts proliferation, migration, and invasion of breast cancer cells in vitro, and mammary tumor growth, dissemination, and metastatic colonization in vivo. Therefore, small molecules that can modulate Pfn-1 expression could have therapeutic potential in the treatment of metastatic breast cancer. The overall goal of this study was to perform a multiplexed phenotypic screen to identify compounds that inhibit cell motility through upregulation of Pfn-1. Screening of a test cassette of 1280 compounds with known biological activities on an Oris™ Pro 384 cell migration platform identified several agents that increased Pfn-1 expression greater than two-fold over vehicle controls and exerted anti-migratory effects in the absence of overt cytotoxicity in MDA-MB-231 human breast cancer cells. Concentration-response confirmation and orthogonal follow-up assays identified two bona fide inducers of Pfn-1, purvalanol and tyrphostin A9, that confirmed in single-cell motility assays and Western blot analyses. SiRNA-mediated knockdown of Pfn-1 abrogated the inhibitory effect of tyrphostin A9 on cell migration, suggesting Pfn-1 is mechanistically linked to tyrphostin A9′s anti-migratory activity. The data illustrate the utility of the high-content cell motility assay to discover novel targeted anti-migratory agents by integrating functional phenotypic analyses with target-specific readouts in a single assay platform.

An introduction to the wound healing assay using live-cell microscopy

The wound healing assay is used in a range of disciplines to study the coordinated movement of a cell population. In this technical review, we describe the workflow of the wound healing assay as monitored by optical microscopy. Although the assay is straightforward, a lack of standardization in its application makes it difficult to compare results and reproduce experiments among researchers. We recommend general guidelines for consistency, including: (1) sample preparation including the creation of the gap, (2) microscope equipment requirements, (3) image acquisition, and (4) the use of image analysis to measure the gap size and its rate of closure over time. We also describe parameters that are specific to the particular research question, such as seeding density and matrix coatings. All of these parameters must be carefully controlled within a given set of experiments in order to achieve accurate and reproducible results.

3-Bromo-1-hydroxy-9,10-anthraquinone (BHAQ) inhibits growth and migration of the human breast cancer cell lines MCF-7 and MDA-MB231

Breast cancer is becoming more prominent in women today. As of now, there are no effective treatments in treating metastatic breast cancer. We have tested the cytotoxic and anti-migration effects of BHAQ, a synthesized anthraquinone, on two breast cancer cell lines, MCF-7 and MDA-MB231. Anthraquinones are an interesting class of molecules that display a wide spectrum of biological applications, including anticancer properties. Cellular inhibition was tested through a MTT assay, double acridine orange/propidium iodide staining and FACS cell cycle analysis. Inhibition of migration was tested by the wound healing method, and migration through a Boyden chamber. BHAQ was cytotoxic towards both cell lines in a dose dependent and possibly cell-dependent manner. Additionally, BHAQ also inhibited the migration of the highly metastatic MDA-MB231 cell line.

CellMissy: a tool for management, storage and analysis of cell migration data produced in wound healing-like assays

SUMMARY

Automated image processing has allowed cell migration research to evolve to a high-throughput research field. As a consequence, there is now an unmet need for data management in this domain. The absence of a generic management system for the quantitative data generated in cell migration assays results in each dataset being treated in isolation, making data comparison across experiments difficult. Moreover, by integrating quality control and analysis capabilities into such a data management system, the common practice of having to manually transfer data across different downstream analysis tools will be markedly sped up and made more robust. In addition, access to a data management solution creates gateways for data standardization, meta-analysis and structured public data dissemination. We here present CellMissy, a cross-platform data management system for cell migration data with a focus on wound healing data. CellMissy simplifies and automates data management, storage and analysis from the initial experimental set-up to data exploration.

AVAILABILITY AND IMPLEMENTATION

CellMissy is a cross-platform open-source software developed in Java. Source code and cross-platform binaries are freely available under the Apache2 open source license at http://cellmissy.googlecode.com.

The role of the Nrf2-mediated defense system in corneal epithelial wound healing

The corneal epithelium exists at the surface of cornea and is easily damaged by external stresses such as UV radiation or physical injury. The Nrf2-mediated defense system plays a central role in protecting cells by activating genes against these types of stress. In this study, we investigated the role of the Nrf2-mediated defense system in corneal epithelial wound healing by using Nrf2-knockout (KO) mice. Nrf2 was expressed in the corneal epithelium of wild-type (WT) mice, but not in KO mice. Observation of wounds after 24h of healing revealed that healing of the corneal epithelium was significantly delayed in the Nrf2 KO mice, whereas Nrf2 was activated in the corneal epithelium of WT mice. Ki-67 staining revealed that the number of Ki-67-positive proliferating cells was significantly lower in the Nrf2 KO mice than in the WT mice at 24-36h after injury; however, these numbers were approximately equivalent by 48h. To clarify the role of Nrf2 during wound healing, we performed in vitro experiments with siRNA for Nrf2 and its suppressor Keap1. Nrf2 knockdown significantly delayed corneal epithelial cell migration, but did not affect cell proliferation. Conversely, Keap1 knockdown significantly accelerated cell migration. These results suggest that Nrf2 contributed to the corneal epithelial wound-healing process by accelerating cell migration, and Nrf2 would therefore be a good target for the treatment of corneal epithelial diseases such as dry eye or chronic corneal epithelial defect.

Multiplex profiling of cellular invasion in 3D cell culture models

To-date, most invasion or migration assays use a modified Boyden chamber-like design to assess migration as single-cell or scratch assays on coated or uncoated planar plastic surfaces. Here, we describe a 96-well microplate-based, high-content, three-dimensional cell culture assay capable of assessing invasion dynamics and molecular signatures thereof. On applying our invasion assay, we were able to demonstrate significant effects on the invasion capacity of fibroblast cell lines, as well as primary lung fibroblasts. Administration of epidermal growth factor resulted in a substantial increase of cellular invasion, thus making this technique suitable for high-throughput pharmacological screening of novel compounds regulating invasive and migratory pathways of primary cells. Our assay also correlates cellular invasiveness to molecular events. Thus, we argue of having developed a powerful and versatile toolbox for an extensive profiling of invasive cells in a 96-well format. This will have a major impact on research in disease areas like fibrosis, metastatic cancers, or chronic inflammatory states.

Hetero-multinuclear ruthenium(III)/platinum(II) complexes that potentially exhibit both antimetastatic and antineoplastic properties

Hetero-multinuclear, platinum/ruthenium species were synthesized and tested for their effect on the motility of A549 (nonsmall cell lung) and MDA-MB-231 (breast) cancer cells and for their ability to inhibit DNA mobility using gel electrophoresis. It was found that the Ru(2)Pt trinuclear species [Na(2)]{[Ru(III)Cl(4)(DMSO-S)(-μ-pyz)](2)Pt(II)Cl(2)}, AH197, was much more efficient at inhibiting cell motility than [C(3)N(2)H(5)][Ru(III)Cl(4)(DMSO-S)(C(3)N(2)H(4))], NAMI-A, while the dinuclear RuPt species [K][Ru(III)Cl(4)(DMSO-S)(-μ-pyz)Pt(II)(DMSO-S)Cl(2)], IT127, was slightly better than NAMI-A. However, the dinuclear species retarded the electrophoretic mobility of DNA greater than both the trinuclear complex and cisplatin. The metal complexes and their respective BSA protein/metal adducts were studied by X-ray absorption spectroscopy. The spectra led to the conclusion that BSA donor atoms have substituted for the chloride ligands and perhaps the DMSO ligands.

Comparative analysis of dynamic cell viability, migration and invasion assessments by novel real-time technology and classic endpoint assays

Background

Cell viability and motility comprise ubiquitous mechanisms involved in a variety of (patho)biological processes including cancer. We report a technical comparative analysis of the novel impedance-based xCELLigence Real-Time Cell Analysis detection platform, with conventional label-based endpoint methods, hereby indicating performance characteristics and correlating dynamic observations of cell proliferation, cytotoxicity, migration and invasion on cancer cells in highly standardized experimental conditions.

Methodology/Principal Findings

Dynamic high-resolution assessments of proliferation, cytotoxicity and migration were performed using xCELLigence technology on the MDA-MB-231 (breast cancer) and A549 (lung cancer) cell lines. Proliferation kinetics were compared with the Sulforhodamine B (SRB) assay in a series of four cell concentrations, yielding fair to good correlations (Spearman's Rho 0.688 to 0.964). Cytotoxic action by paclitaxel (0–100 nM) correlated well with SRB (Rho>0.95) with similar IC₅₀ values. Reference cell migration experiments were performed using Transwell plates and correlated by pixel area calculation of crystal violet-stained membranes (Rho 0.90) and optical density (OD) measurement of extracted dye (Rho>0.95). Invasion was observed on MDA-MB-231 cells alone using Matrigel-coated Transwells as standard reference method and correlated by OD reading for two Matrigel densities (Rho>0.95). Variance component analysis revealed increased variances associated with impedance-based detection of migration and invasion, potentially caused by the sensitive nature of this method.

Conclusions/Significance

The xCELLigence RTCA technology provides an accurate platform for non-invasive detection of cell viability and motility. The strong correlations with conventional methods imply a similar observation of cell behavior and interchangeability with other systems, illustrated by the highly correlating kinetic invasion profiles on different platforms applying only adapted matrix surface densities. The increased sensitivity however implies standardized experimental conditions to minimize technical-induced variance.

Magnetically attachable stencils and the non-destructive analysis of the contribution made by the underlying matrix to cell migration

Cell migration is controlled by the integration of numerous distinct components. Consequently, the analysis of cell migration is advancing towards comprehensive, multifaceted in vitro models. To accurately evaluate the contribution of an underlying substrate to cell motility in complex cellular environments we developed a migration assay using magnetically attachable stencils (MAts). When attached to a culture surface, MAts create a defined void in the cell monolayer without disrupting the cells or damaging the underlying substrate. Quantitative analysis of migration into this void reveals the substrate's contribution to migration. The magnetically-guided placement of a microfabricated stencil allows for full experimental control of the substrate on which migration is analyzed. MAts enable the evaluation of intact, defined matrix, and make it possible to analyze migration on unique surfaces such as micropatterned proteins, nano-textured surfaces, and pliable hydrogels. These studies also revealed that mechanical disruption, including the damage that occurs during scratch assays, diminishes migration and confounds the analysis of individual cell behavior. Analysis of migration on increasingly complex biomaterials reveals that the contribution of the underlying matrix depends not only on its molecular composition but also its organization and the context in which it is presented.

Fusarisetin A: Scalable Total Synthesis and Related Studies

Fusarisetin A (1) is a recently isolated natural product that displays an unprecedented chemical motif and remarkable bioactivities as a potent cancer migration inhibitor. We describe here our studies leading to an efficient and scalable total synthesis of 1. Essential to the strategy was the development of a new route for the formation of a trans-decalin moiety of this compound and the application of an oxidative radical cyclization (ORC) reaction that produces fusarisetin A (1) from equisetin (2) via a bio-inspired process. TEMPO-induced and metal/O(2)-promoted ORC reactions were evaluated. Biological screening in vitro confirms the reported potency of (+)-1. Importantly, ex vivo studies show that this compound is able to inhibit different types of cell migration. Moreover, the C(5) epimer of (+)-1 was also identified as a potent cancer migration inhibitor, while (-)-1 and 2 were found to be significantly less potent. The optimized synthesis is applicable on gram scale and provides a solid platform for analogue synthesis and methodical biological study.

Intracellular acoustic droplet vaporization in a single peritoneal macrophage for drug delivery applications

This study investigated the acoustic droplet vaporization (ADV) of perfluoropentane (PFP) droplets in single droplet-loaded macrophages (DLMs) by insonation with single three-cycle ultrasound pulses. Transient responses of intracellular ADV within a single DLM were observed with synchronous high-speed photography and cavitation detection. Ultrasound B-mode imaging was further applied to demonstrate the contrast enhancement of ADV-generated bubbles from a group of DLMs. The PFP droplets incorporated in a DLM can be liberated from the cell body after being vaporized into gas bubbles. Inertial cavitation can be simultaneously induced at the same time that bubbles appear. The coalescence of bubbles occurring at the onset of vaporization may facilitate gas embolotherapy and ultrasound imaging. Macrophages can be potential carriers transporting PFP droplets to avascular and hypoxic regions in tumors for ultrasound-controlled drug release and ADV-based tumor therapies.