Correlations between the dielectric properties and exterior morphology of cells revealed by dielectrophoretic field-flow fractionation.

Although dielectrophoresis (DEP) has great potential for addressing clinical cell isolation problems based on cell dielectric differences, a biological basis for predicting the DEP behavior of cells has been lacking. Here, the dielectric properties of the NCI-60 panel of tumor cell types have been measured by dielectrophoretic (DEP) field-flow fractionation, correlated with the exterior morphologies of the cells during growth, and compared with the dielectric and morphological characteristics of the subpopulations of peripheral blood. In agreement with earlier findings, cell total capacitance varied with both cell size and plasma membrane folding and the dielectric properties of the NCI-60 cell types in suspension reflected the plasma membrane area and volume of the cells at their growth sites. Therefore, the behavior of cells in DEP-based manipulations is largely determined by their exterior morphological characteristics prior to release into suspension. As a consequence, DEP is able to discriminate between cells of similar size having different morphological origins, offering a significant advantage over size-based filtering for isolating circulating tumor cells, for example. The findings provide a framework for anticipating cell dielectric behavior on the basis of structure-function relationships and suggest that DEP should be widely applicable as a surface marker-independent method for sorting cells.

The fractal dimension of cell membrane correlates with its capacitance: a new fractal single-shell model.

The scale-invariant property of the cytoplasmic membrane of biological cells is examined by applying the Minkowski-Bouligand method to digitized scanning electron microscopy images of the cell surface. The membrane is found to exhibit fractal behavior, and the derived fractal dimension gives a good description of its morphological complexity. Furthermore, we found that this fractal dimension correlates well with the specific membrane dielectric capacitance derived from the electrorotation measurements. Based on these findings, we propose a new fractal single-shell model to describe the dielectrics of mammalian cells, and compare it with the conventional single-shell model (SSM). We found that while both models fit with experimental data well, the new model is able to eliminate the discrepancy between the measured dielectric property of cells and that predicted by the SSM.

Isolation of rare cells from cell mixtures by dielectrophoresis.

The application of dielectrophoretic field-flow fractionation (depFFF) to the isolation of circulating tumor cells (CTCs) from clinical blood specimens was studied using simulated cell mixtures of three different cultured tumor cell types with peripheral blood. The depFFF method can not only exploit intrinsic tumor cell properties so that labeling is unnecessary but can also deliver unmodified, viable tumor cells for culture and/or all types of molecular analysis. We investigated tumor cell recovery efficiency as a function of cell loading for a 25 mm wide x 300 mm long depFFF chamber. More than 90% of tumor cells were recovered for small samples but a larger chamber will be required if similarly high recovery efficiencies are to be realized for 10 mL blood specimens used CTC analysis in clinics. We show that the factor limiting isolation efficiency is cell-cell dielectric interactions and that isolation protocols should be completed within approximately 15 min in order to avoid changes in cell dielectric properties associated with ion leakage.

Apoptotic-inducing activity of novel polycyclic aromatic compounds in human leukemic cells.

Persistent but relatively limited research has been devoted to the use of compounds related to polycyclic aromatic hydrocarbons (PAH) as anticancer agents. In previous reports, we have described the cytotoxicity of a number of new and novel PAH against human cancer cell lines. However, the involved molecular mechanisms of inducing cell death were not elucidated. In the current study, we describe the apoptotic pathway as apparently playing a crucial role in induced cell death in human leukemia Jurkat T cells by several diamide and diamine PAH that contain chrysene as their core aromatic ring system. Structure-activity relationships were analyzed. Importantly, no effect was demonstrated in a normal, non-transformed line of human natural killer cells. These results provide additional evidence for the potential chemotherapeutic use of PAH.

Membrane dielectric changes indicate induced apoptosis in HL-60 cells more sensitively than surface phosphatidylserine expression or DNA fragmentation.

The specific membrane capacitance and conductivity of mammalian cells, which reflect their surface morphological complexities and membrane barrier functions, respectively, have been shown to respond to cell physiologic and pathologic changes. Here, the effects of induced apoptosis on these membrane properties of cultured human promyelocytic HL-60 cells are reported. Changes in membrane capacitance and conductivity were deduced from measurements of cellular dielectrophoretic crossover frequencies following treatment with genistein (GEN). The apparent specific cell membrane capacitance of HL-60 cells fell from an initial value of 17.6+/-0.9 to 9.1+/-0.5 mF/m(2) 4 h after treatment. Changes began within minutes of treatment and preceded both the externalization of phosphatidylserine (PS), as gauged by the Annexin V assay, and the appearance of a sub-G1 cell subpopulation, as determined through ethidium bromide staining of DNA. Treatment by the broad spectrum caspase inhibitor N-benzyloxycarbony-Val-Ala-Asp(O-methyl)-fluoromethyketone (zVAD-fmk) did not prevent these early cell membrane dielectric responses, suggesting that the caspase system was not involved. Although membrane conductivity did not alter during the first 4 h of GEN treatment, it rose significantly and progressively thereafter. Finally, as the barrier function failed and the cells became necrotic, it increased by many orders of magnitude. The effective membrane capacitance and conductivity findings serve to focus attention on the membrane as a site for early participation in apoptosis. In conjunction with our prior reports of the use of dielectric methods for cell manipulation and separation, these results demonstrate that dielectrophoretic technologies should be applicable to the rapid detection, separation, and quantification of normal, apoptotic, and necrotic cells from cell mixtures.

Microsample preparation by dielectrophoresis: isolation of malaria.

An important enabling factor for realising integrated micro fluidic analysis instruments for medical diagnostics purposes is front-end sample preparation. Dielectrophoresis is a method that offers great potential for cell discrimination and isolation for sample processing, and here we have applied it to the problem of isolating malaria-infected cells from blood. During development of the malarial pathogen, Plasmodium falciparum, increases occur in the ionic permeability of the plasma membrane of infected erythrocytes. When challenged by suspension in a low conductivity medium, infected cells lose internal ions while uninfected cells retain them. The resultant dielectric differences between infected and uninfected cells were exploited by dielectrophoretic manipulation in spatially inhomogeneous, travelling electrical fields produced by two types of microelectrode arrays. Parasitised cells of ring form or later stage from cultures and clinical specimens were isolated by steric dielectric field-flow-fractionation, focused at the centre of a spiral electrode array, and identified and counted. The dielectrophoretic methods require only a few micro litres of blood, and should be applicable to the production of small, low-cost automated devices for assessing parasite concentrations with potential applicability to drug sensitivity studies and the diagnosis of malaria. By simple adjustment of the electrical field parameters, other cell subpopulations that characterise disease, such as residual cancer cells in blood, can be similarly isolated and analysed.

Dielectrophoresis-based programmable fluidic processors.

Droplet-based programmable processors promise to offer solutions to a wide range of applications in which chemical and biological analysis and/or small-scale synthesis are required, suggesting they will become the microfluidic equivalents of microprocessors by offering off-the-shelf solutions for almost any fluid based analysis or small scale synthesis problem. A general purpose droplet processor should be able to manipulate droplets of different compositions (including those that are electrically conductive or insulating and those of polar or non-polar nature), to control reagent titrations accurately, and to remain free of contamination and carry over on its reaction surfaces. In this article we discuss the application of dielectrophoresis to droplet based processors and demonstrate that it can provide the means for accurately titrating, moving and mixing polar or non-polar droplets whether they are electrically conductive or not. DEP does not require contact with control surfaces and several strategies for minimizing surface contact are presented. As an example of a DEP actuated general purpose droplet processor, we show an embodiment based on a scaleable CMOS architecture that uses DEP manipulation on a 32 x 32 electrode array having built-in control and switching circuitry. Lastly, we demonstrate the concept of a general-purpose programming environment that facilitates droplet software development for any type of droplet processor.

Stereoselective synthesis of beta-lactams with polyaromatic imines: entry to new and novel anticancer agents.

We present herein stereoselective synthesis of novel beta-lactams using polyaromatic imines following the Staudinger reaction. Consistent mechanisms for these results have been advanced. As a measure of cytotoxicity, some of these compounds have been assayed against nine human cancer cell lines. Structure-activity study has revealed that 1-N-chrysenyl and 1-N-phenanthrenyl 3-acetoxy-4-aryl-2-azetidinones have potent anticancer activity. The presence of the acetoxy group at C(3) of the beta-lactams has proven to be obligatory for their anticancer activity.

Dielectrically Addressable Microspheres Engineered Using Self-Assembled Monolayers.

We have used self-assembled monolayer techniques to produce a new class of microspheres with specifically engineered dielectric properties to enable their dielectrophoretic manipulation and identification in microsystems. Dielectrophoresis is an electrokinetic phenomenon that exploits frequency-dependent polarizability differences between a particle and its suspending medium to drive the movement of the particle toward or away from the high-field regions of an inhomogeneous electric field. While dielectrophoretic methods have been used extensively for cell manipulation, separation, and identification, we wished to extend the applicability of dielectrophoresis to molecular analysis by developing a panel of dielectric microspheres or "handles". Dielectric shell theory was used to model the dielectrophoretic response for a biomimetic particle composed of a thin insulating shell over a conductive interior. We specifically sought to modulate the specific capacitance, and thereby the dielectric properties, of the particle by controlling the thickness of the insulating layer. Such a structure was fabricated by covering a gold-coated polystyrene core particle with self-assembled monolayers of alkanethiol and phospholipid. To test the prediction that the carbon chain length of these layers should dictate the dielectric properties of the particles, we constructed a panel of six microsphere types with shell compositions ranging from a C(9) alkanethiol monolayer to a C(32) hybrid bilayer membrane. These microsphere populations were distinguishable and manipulatable by dielectrophoresis in a characteristic, frequency-dependent manner as predicted by theory. Experimentally derived specific membrane capacitance values were inversely related to the insulating shell thickness and agreed with published capacitance values for planar layers of similar thicknesses. These proof of principle studies are the first to demonstrate that the dielectric properties of particles can be specifically engineered to allow their dielectrophoretic manipulation and are a first step toward the development of bead-based dielectrophoretic microsystems for multiplexed molecular separation and analysis.

Dielectrophoretic Separation of Cancer Cells from Blood.

Recent measurements have demonstrated that the dielectric properties of cells depend on their type and physiological status. For example, MDA-231 human breast cancer cells were found to have a mean plasma membrane specific capacitance of 26 mF/m(2), more than double the value (11 mF/m(2)) observed for resting T-lymphocytes. When an inhomogeneous ac electric field is applied to a particle, a dielectrophoretic (DEP) force arises that depends on the particle dielectric properties. Therefore, cells having different dielectric characteristics will experience differential DEP forces when subjected to such a field. In this article, we demonstrate the use of differential DEP forces for the separation of several different cancerous cell types from blood in a dielectric affinity column. These separations were accomplished using thin, flat chambers having microelectrode arrays on the bottom wall. DEP forces generated by the application of ac fields to the electrodes were used to influence the rate of elution of cells from the chamber by hydrodynamic forces within a parabolic fluid flow profile. Electrorotation measurements were first made on the various cell types found within cell mixtures to be separated, and theoretical modeling was used to derive the cell dielectric parameters. Optimum separation conditions were then predicted from the frequency and suspension conductivity dependencies of cell DEP responses defined by these parameters. Cell separations were then undertaken for various ratios of cancerous to normal cells at different concentrations. Eluted cells were characterized in terms of separation efficiency, cell viability, and separation speed. For example, 100% efficiency was achieved for purging MDA-231 cells from blood at the tumor to normal cell ratio 1:1 x 10(5) or 1:3 x 10(5), cell viability was not compromised, and separation rates were at least 10(3) cells/s. Theoretical and experimental criteria for the design and operation of such separators are presented.

Polycyclic aromatic compounds as anticancer agents: synthesis and biological evaluation of methoxy dibenzofluorene derivatives.

Synthesis of a new methoxy dibenzofluorene through alkylation, cyclodehydration and aromatization in a one-pot operation is achieved for the first time. Using this hydrocarbon, a few derivatives are prepared through aromatic nitration, catalytic hydrogenation, coupling reaction with a side chain and reduction. The benzylic position of this hydrocarbon with the side chain is oxidized and reduced. Some of these derivatives have demonstrated excellent antitumor activities in vitro. This study confirms antitumor activity depends on the structures of the molecules.

Dielectrophoresis has broad applicability to marker-free isolation of tumor cells from blood by microfluidic systems.

The number of circulating tumor cells (CTCs) found in blood is known to be a prognostic marker for recurrence of primary tumors, however, most current methods for isolating CTCs rely on cell surface markers that are not universally expressed by CTCs. Dielectrophoresis (DEP) can discriminate and manipulate cancer cells in microfluidic systems and has been proposed as a molecular marker-independent approach for isolating CTCs from blood. To investigate the potential applicability of DEP to different cancer types, the dielectric and density properties of the NCI-60 panel of tumor cell types have been measured by dielectrophoretic field-flow fractionation (DEP-FFF) and compared with like properties of the subpopulations of normal peripheral blood cells. We show that all of the NCI-60 cell types, regardless of tissue of origin, exhibit dielectric properties that facilitate their isolation from blood by DEP. Cell types derived from solid tumors that grew in adherent cultures exhibited dielectric properties that were strikingly different from those of peripheral blood cell subpopulations while leukemia-derived lines that grew in non-adherent cultures exhibited dielectric properties that were closer to those of peripheral blood cell types. Our results suggest that DEP methods have wide applicability for the surface-marker independent isolation of viable CTCs from blood as well as for the concentration of leukemia cells from blood.

Novel 6,12-disubstituted chrysene as potent anticancer agent: synthesis, in vitro and in vivo study.

We describe herein the synthesis of novel 6,12-distributed chrysene as potent anticancer agents. In vitro and in vivo studies are also reported here.

Selective anticancer activity of ß-lactams derived from polyaromatic compound.

Currently available anticancer drugs are cytotoxic to normal as well as to neoplastic cells, therefore the synthesis of ß-lactams as new and novel anticancer agents is extremely significant. We previously developed synthetic methods for the preparation of ß-lactams and anticancer agents resulting from polyaromatic amines. There have also been reports on the synthesis and biological evaluation of novel racemic ß-lactams as anticancer agents. In cell cycle analysis, these compounds demonstrated a G2 blockage against sensitive tumor cell lines. In the present study, useful and selective biological activities of chrysene ß-lactams are described.

Asymmetric synthesis of anticancer ß-lactams via Staudinger reaction.

This study describes the symmetric synthesis of novel ß-lactams derived from chrysene directed towards their SAR, as well as their biological activities against several cancer cell lines in vitro. To our knowledge, this is the first report on the synthesis and biological evaluation of optically active anticancer ß-lactams. That these anticancer effects are not uniform against all tumor lines suggests that the target of the action of these compounds is highly specific.

Asymmetric synthesis of anticancer beta-lactams via Staudinger reaction: utilization of chiral ketene from carbohydrate.

We describe herein asymmetric synthesis of a novel anticancer beta-lactam following Staudinger reaction with chiral carbohydrate as the ketene component with an achiral imine. The in vitro cytotoxicity studies of these beta-lactams are also reported here.

Synthesis and biological evaluation of novel dibenzofluorene derivatives as anticancer agents.

The novel synthesis of dibenzofluorene has been achieved by a cyclodehydration method. Several derivatives have also been prepared using this hydrocarbon. These compounds have been tested against a number of cancer cell lines in vitro, and useful selectivity has been observed.

Stereocontrolled synthesis of anticancer beta-lactams via the Staudinger reaction.

Stereocontrolled synthesis of novel beta-lactams using polyaromatic imines following the Staudinger reaction has been accomplished. The effects of domestic microwave irradiation on this type of reaction have been investigated. Formation of trans-beta-lactams has been explained through isomerization of the enolates formed during the reaction of acid chloride (equivalent) with imines in the presence of triethylamine. A donor-acceptor complex pathway is believed to be involved in the formation of cis-beta-lactams. The effect of a peri hydrogen has been found to be significant in controlling the stereochemistry of the resulting beta-lactams. SAR has identified beta-lactams with anticancer activity. The presence of an acetoxy group has proven obligatory for their anticancer activity.

Synthesis of anticancer beta-lactams: mechanism of action.

Synthesis of the trans 1-N-chrysenyl and 1-N-phenanthrenyl 3-acetoxy-4-phenyl-2-azetidinones has been achieved. Microwave-assisted reaction has proved useful in the synthesis of these compounds. Cell growth inhibition study has indicated selective anticancer activity against two leukemia and colon carcinoma cell lines. A mechanistic correlation of their anticancer activity has been described. Striking G2 blockade that is clearly distinct in cell cycle analysis and demonstrated only in sensitive cell lines has been observed. They do not induce apoptosis in sensitive or resistant lines. They also do not inhibit topoisomerases. Ames test has shown they are nonmutagenic.