Adherent Cell Layer Research Articles

Fluid and Bubble Flow Detach Adherent Cancer Cells to Form Spheroids on a Random Positioning Machine.

In preparing space and microgravity experiments, the utilization of ground-based facilities is common for initial experiments and feasibility studies. One approach to simulating microgravity conditions on Earth is to employ a random positioning machine (RPM) as a rotary bioreactor. Combined with a suitable low-mass model system, such as cell cultures, these devices simulating microgravity have been shown to produce results similar to those obtained in a space experiment under real microgravity conditions. One of these effects observed under real and simulated microgravity is the formation of spheroids from 2D adherent cancer cell cultures. Since real microgravity cannot be generated in a laboratory on Earth, we aimed to determine which forces lead to the detachment of individual FTC-133 thyroid cancer cells and the formation of tumor spheroids during culture with exposure to random positioning modes. To this end, we subdivided the RPM motion into different static and dynamic orientations of cell culture flasks. We focused on the molecular activation of the mechanosignaling pathways previously associated with spheroid formation in microgravity. Our results suggest that RPM-induced spheroid formation is a two-step process. First, the cells need to be detached, induced by the cell culture flask's rotation and the subsequent fluid flow, as well as the presence of air bubbles. Once the cells are detached and in suspension, random positioning prevents sedimentation, allowing 3D aggregates to form. In a comparative shear stress experiment using defined fluid flow paradigms, transcriptional responses were triggered comparable to exposure of FTC-133 cells to the RPM. In summary, the RPM serves as a simulator of microgravity by randomizing the impact of Earth's gravity vector especially for suspension (i.e., detached) cells. Simultaneously, it simulates physiological shear forces on the adherent cell layer. The RPM thus offers a unique combination of environmental conditions for in vitro cancer research.

Azacitidine and Panobinostat Overcome Bone Marrow Microenvironment-Induced Chemoprotection in KMT2A-rearranged Pediatric AML

KMT2A is the most common gene rearrangement in pediatric acute leukemias and is difficult to treat with a five-year overall survival rate of less than 50%, owing to frequent relapse and poor response to chemotherapy. Recent studies have investigated how interactions within the bone marrow microenvironment help AML cells evade chemotherapy and contribute to relapse by promoting the survival of leukemic blasts. Our group has previously identified that epigenetic drug combination of DNA hypomethylating agent azacitidine and histone deacetylase inhibitor panobinostat reduces cell adhesion and promotes mobilization of leukemic cells to peripheral blood (Weber et al., 132:2637, Blood, 2018). In this study, we used a multi cell coculture of pediatric AML cells with bone marrow stromal cells, endothelial cells and pediatric mesenchymal stem cells to better mimic the bone marrow microenvironment. We observed that the chemoprotection index in multi-cell coculture was much higher than individual cell type (Figure 1A). While 1.5 uM cytarabine reduced MV4;11 cell viability by 50%, there was less than 1% reduction in cell viability in multi-cell coculture. We further investigated if the bone marrow microenvironment induced chemoprotection was mediated by soluble factors, or via adhesive interactions between adherent cell layer and/or the extracellular matrix (ECM). Conditioned media failed to afford chemoprotection, while separation of AML cells from multi-cell layer via Transwells or culturing AML cells in Matrigel-coated dishes showed partial chemoprotection. These results indicated that direct cell-cell or cell-ECM contact was necessary for the chemoprotection. Pre-treatment with azacitidine and panobinostat sensitized five distinct patient-derived xenograft (PDX) lines of KMT2A-rearranged AML to both cytarabine and daunorubicin in multi-cell coculture. These data indicate that azacitidine and panobinostat combination can synergistically overcome chemoprotection mediated by stromal, endothelial and mesenchymal stem cells. We also observed improved survival with pre-treatment of azacitidine panobinostat (2.5 mg/Kg each, Qd5) followed by chemotherapy consisting of cytarabine (50 mg/Kg, Qd5) and daunorubcin (1.5 mg/Kg, Qd3) in a PDX model of KMT2A-rearranged AML (Figure 1B, **P<0.05). To determine if these epigenetic modifers alter the expression of cell adhesion molecules, cells treated with azacitidine panobinostat combination were subjected to a high throughput flow cytometry assay (Lyoplate, Human cell surface marker screening panel). This analysis showed reduced cell surface expression of integrins, ICAMs and chemokine receptors, indicating that epigenetic drug combination likely causes mobilization and chemosensitization via downregulation of cell adhesion molecules which not only mediate adhesive interactions but also promote cell survival. In summary, our data show azacitidine and panobinostat can overcome bone marrow microenvironment induced chemoprotection in vitro and in vivo in KMT2A rearranged AML. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Mechanotransductive Differentiation of Hair Follicle Stem Cells Derived from Aged Eyelid Skin into Corneal Endothelial-Like Cells

Corneal endothelial insufficiency is one of the leading causes of blindness. The main contemporary treatment for corneal blindness is endothelial keratoplasty, which, however, is unsatisfactory as a medical therapy due to the lack of donor corneas and graft rejection. Therefore, autologous stem cell-based corneal endothelial tissue substitutes may be a promising alternative to conventional grafts in the future. To address the age of most patients suffering from corneal endothelial deficiencies, we investigated the presence and potential of hair-derived stem cells from older tissue donors. Our studies revealed the presence of pluripotency- and neural crest-associated markers in tissue sections from blepharoplasty patients aged 50 to 80 years. In vitro outgrowths from eyelid hair follicles on collagen-coated tissue culture plates revealed a weak decrease in stem-cell potency. In contrast, cells within the spheres that spontaneously formed from the adherent cell layer retained full stem-cell potency and could be differentiated into cells of the ecto- meso and endodermal lineages. Although these highly potent hair follicle derived stem cells (HFSC) were only very slightly expandable, they were able to recognize the biomimicry of the Descemet’s-like topography and differentiate into corneal endothelial-like cells. In conclusion, HFSCs derived from epidermal skin of eyelid biopsies are a promising cell source to provide autologous corneal endothelial replacement for any age group of patients.Graphical

YAP Regulates Hematopoietic Stem Cell Formation in Response to the Biophysical Forces of Blood Flow

Hematopoietic stem cells (HSCs) are first specified during embryonic development from hemogenic endothelial cells (HEC) in the ventral dorsal aorta (VDA). Prior studies from our lab and others demonstrated that HSC formation is coordinated with the onset of rigorous circulatory flow, which exposes the vascular endothelium to both wall shear stress (WSS) and circumferential stretch (CS). To better understand how these biomechanical forces drive HEC specification and HSC production, we engineered a microfluidics-based dorsal aorta-on-a-chip that recapitulates the biophysical features present in the vasculature. Using this biomimetic microsystem, human iPS-derived HEC exposed to WSS and CS through continuous media flow and cyclic stretching of the adherent cell layer showed an upregulation of RUNX1 (WSS, p<0.01; CS, p<0.05), the main transcription factor involved in HSC specification, by qPCR compared to cells in the static control. Interestingly, the YAP (Yes-associated protein) target genes CYR61, ANKRD1 and CTGF were also upregulated in human iPS-derived HEC after exposure to CS, suggesting a possible downstream mechanism for the effects of blood flow on HEC. YAP is the most downstream effector protein in the Hippo signaling pathway and is known to regulate stem cell dynamics and organ size. Prior work identified YAP as a mechanosensor, where it is activated in response to Rho GTPase activity and actomyosin filament rearrangement independent of the core Hippo pathway. To test whether YAP functions in response to mechanical force-activated Rho, iPS-derived HEC were exposed to circumferential stretch in the presence of a Rho inhibitor, which abolished CS-induced activation of YAP targets and RUNX1, indicating that Rho proteins are involved in mediating the effects of blood flow on HECs. Furthermore, treatment of iPS-derived HEC cultured under static conditions with either direct or indirect activators of the Rho GTPase family increased YAP activity and RUNX1 levels, demonstrating that biophysical forces from blood flow can be mimicked in vitro with Rho modulation. To investigate the implication of these findings in vivo, we utilized the zebrafish model: as in mammalian systems, HSCs are born in the VDA (24-36 hours post fertilization (hpf)) and migrate to the secondary sites of hematopoiesis to expand and differentiate before colonizing adult tissues. Heat-shock mediated overexpression of Yap at 12 hpf significantly increased runx1 + HEC specification at 36 hpf by both in situ hybridization and qPCR (p<0.01). This impact on HSC number was sustained throughout development, as Yap overexpression also significantly increased the number of Cd41+ HSCs present in the caudal hematopoietic tissue (CHT) at 72 hpf (p<0.05). In contrast, Yap knockout mutants exhibited a significant reduction in runx1 at 36 hpf (p<0.0001) despite normal Flk1+ vascular structure, indicative of a role for Yap in HSC specification. In line with the human in vitro data, activation of Rho GTPase increased expression of Yap target genes and runx1 at 36 hpf (p<0.05), suggesting a pathway in which Yap induces Runx1 downstream of Rho stimulation. Prior analysis of the silent heart mutant line as well as morpholino knockdown of cardiac troponin T type A (tnnt2a) revealed a significant deficiency in HEC specification and HSC production in the absence of heartbeat and blood flow. Importantly, compound-mediated activation of Rho GTPase (12-36 hpf) significantly increased runx1 expression in tnnt2a morphant embryos by in situ hybridization and qPCR (p<0.01), demonstrating that Rho activation can mimic the effects of blood flow on HSC production in vivo . Taken together, our findings point to a functional intersection between blood flow, Rho GTPase function and YAP activation in RUNX1-dependent HSC production; this mechanochemical mechanism may be exploited to improve in vitro human HSC differentiation protocols for the treatment for blood disorders. DisclosuresIngber:Emulate, Inc.: Equity Ownership, Membership on an entity's Board of Directors or advisory committees.

3056 – NES-EGFP TRANSGENIC MICE AS A MODEL FOR IN VIVO AND IN VITRO STUDY OF BONE-MARROW-DERIVED MESENCHYMAL STEM CELLS (MSCS)

Transgenic NES-EGFP mice developed by G. Enikolopov (Tg(Nes-EGFP)33Enik), which have a green fluorescent protein (EGFP) gene under the promoter of the nestin gene, had been previously used to show that early mesenchymal progenitors are in the population of CD45–GFP+ bone marrow (BM) cells. Here we show that NES-EGFP mice can serve as a convenient model for studying MSCs capable of transferring hematopoietic microenvironment under the renal capsule of syngeneic mice. BM from one femur of NES-EGFP mouse was used to obtain Dexter-type long-time bone marrow culture (LTBMCs, n = 5). GFP+ cells had been counted weekly over the entire area of the T25 flasks for 5 weeks after culture initiation using a fluorescence microscope. Four weeks after the initiation of LTBMCs, two day long time-lapse vital photography was performed. Ectopic foci of hematopoiesis under the renal capsule (n = 6) were obtained from the BM of NES-EGFP donors in syngeneic recipients. The number of C-kit+/–GFP+ cells in the formed foci was determined using FACS analysis. GFP+ cells with stromal phenotype in the adherent cell layer of LTBMCs had been detected during 5 weeks of cultivation. The stromal layer of LTBMC contained fibroblast-like GFP-low and GFP-hi cell subpopulations. GFP-low cells were scattered across the surface and predominated. GFP-hi cells were rare and formed colonies. Ectopic foci of hematopoiesis contained 2036 ± 734 C-kit–GFP+ stromal cells. Most of these cells had GFP-low phenotype. The cellularity of the focus strongly and positively correlated with the number of C-kit–GFP+ in it. The results show that C-kit–GFP+ BM cells of NES-EGFP mice are able to survive implantation and include MSCs and early stromal mesenchymal progenitors, the number of which determines the size of the focus. NES-EGFP mice can be used for in vitro and in vivo experiments to study functional BM-derived MSCs.

Quantification of Cell-Substrate Adhesion Area and Cell Shape Distributions in MCF7 Cell Monolayers.

The methods presented here quantify some parameters of confluent adherent cell monolayers from multiple appropriately stained confocal images: adhesion to the substrate as a function of the number and size of focal adhesions, and cell shape, characterized by the cell shape index and other shape descriptors. Focal adhesions were visualized by paxillin staining and cell-cell borders were marked by junction plakoglobin and actin. The methods for cell culture and staining were standard; images represent single focal planes; image analysis was performed using publicly available image processing software. The presented protocols are used to quantify the number and size of focal adhesions and the differences in cell shape distribution in the monolayers, but they can be repurposed for the quantification of the size and shape of any other distinct cellular structure that can be stained (e.g., mitochondria or nuclei). Assessing these parameters is important in the characterization of the dynamic forces in adherent cell layer, including cell adhesion and actomyosin contractility that affects cell shape.

Development and Evaluation of a Prototype Scratch Apparatus for Wound Assays Adjustable to Different Forces and Substrates

Scratch assays enable the study of the migration process of an injured adherent cell layer in vitro. An apparatus for the reproducible performance of scratch assays and cell harvesting has been developed that meets the requirements for reproducibility in tests as well as easy handling. The entirely autoclavable setup is divided into a sample translation and a scratching system. The translational system is compatible with standard culture dishes and can be modified to adapt to different cell culture systems, while the scratching system can be adjusted according to angle, normal force, shape, and material to adapt to specific questions and demanding substrates. As a result, a fully functional prototype can be presented. This system enables the creation of reproducible and clear scratch edges with a low scratch border roughness within a monolayer of cells. Moreover, the apparatus allows the collection of the migrated cells after scratching for further molecular biological investigations without the need for a second processing step. For comparison, the mechanical properties of manually performed scratch assays are evaluated.

An Effective Primary Head and Neck Squamous Cell Carcinoma In Vitro Model.

Head and neck squamous cell carcinoma is a highly malignant disease and research is needed to find new therapeutic approaches. Faithful experimental models are required for this purpose. Here, we describe the specific cell culture conditions enabling the efficient establishment of primary cell culture models. Whereas a classical 10% serum-containing medium resulted in the growth of fibroblast-like cells that outcompeted epithelial cells, we found that the use of specific culture conditions enabled the growth of epithelial tumor cells from HPV+ and HPV− head and neck cancer tissue applicable for research. EpCAM and high Thy-1 positivity on the cell surface were mutually exclusive and distinguished epithelial and fibroblast-like subpopulations in all primary cultures examined and thus can be used to monitor stromal contamination and epithelial cell content. Interestingly, cells of an individual patient developed tumor spheroids in suspension without the use of ultra-low attachment plates, whereas all other samples exclusively formed adherent cell layers. Spheroid cells were highly positive for ALDH1A1 and hence displayed a phenotype reminiscent of tumor stem cells. Altogether, we present a system to establish valuable primary cell culture models from head and neck cancer tissue at high efficiency that might be applicable in other tumor entities as well.

Laser micro-structured Si scaffold-implantable vaccines against Salmonella Typhimurium

Salmonella Typhi is responsible for typhoid fever in humans. Despite the efforts, the development of long-lasting vaccines has failed and the available vaccines display only moderate activity, being considered as “international traveler’s” vaccines. Taking advantage of the previously described implantable vaccine technology consisting on 3D laser-microstructured Si scaffolds loaded with antigen-seeded macrophages, the present study aimed to apply an antigenic stimulus of whole extracts of S. Typhimurium, which is the mouse analogue of the human Salmonella Typhi, and examine its ability to mount specific antibody response. After defining the experimental conditions for specific anti-S. Typhimurium IgG production in vitro, antigen-seeded macrophages loaded onto the 3D Si-scaffolds were implanted to mice, while parallel experiments used conventional Freund-complete-adjuvant vaccination protocols. The results showed that only the implantable vaccine protocol could mount a specific antibody response 14 days after implantation. The cytokine profile showed increase of IL-10 and IFN-γ in the case of implantable and conventional vaccination respectively, 7 days after implantation. Morphological studies on the excised scaffolds 14 days after implantation, showed the development of a well-structured adherent monolayer, establishing multiple contacts with lymphocytes in favor to immune response development. Based on the hypothesis that both stimulatory and suppressive components in the vaccination preparation, could affect the overall activity, peptidoglycan was applied as an antigen to the vaccination protocols. Surprisingly, peptidoglycan was shown to induce a mitogenic rather than specific immunogenic response. In this case, histological analysis of the excised scaffolds showed a restricted layer of adherent cells with cytoplasmic extensions, but hard to distinguish cell contacts with lymphocytes. Finally, the presented results showed a differential behavior of antigen presenting cells in accordance to the antigenic stimulus and consequently the activation state of the cells. Tailoring the micro/sub-micron 3D structures and chemistry of Si scaffolds, could control cell behavior according to the user’s needs.

A study of Love wave acoustic biosensors monitoring the adhesion process of tendon stem cells (TSCs).

The Love wave biosensor is considered to be one of the most promising probing methods in biomedical research and diagnosis, and has been applied to detect the mechano-biological behaviour of cells attached to the surface of the device. More efforts should be devoted to basic theoretical research and relevant device performance analysis that may contribute to the further developments of Love wave sensors. In this study, a 36º YX-LiTaO3-based Love wave sensor with a parylene-C wave guiding layer was adopted as a cell-based biosensor to monitor the adhesion process of tendon stem/progenitor cells (TSCs), a newly discovered cell type in tendons. A theoretical model is proposed to describe the Love wave propagation, in which the adherent cells are considered as a uniform viscoelastic layer. The effects of viscoelastic cell layer and wave guiding layer on the propagation velocity υ and propagation loss (PL) are investigated. The numerical results indicate that adherent cell layers of different storage or loss shear modulus in certain ranges can induce pronounced and characteristic variations in υ and PL, revealing the potential of Love wave sensors to provide useful quantitative measures on cellular mechanical properties. The sensor response to the adhesion of TSCs exhibits high consistency with experimental observations, which demonstrates the Love wave biosensor as a very promising sensor platform for investigating cellular activities under multiple physiological conditions.

Easy-to-Prepare Coating of Standard Cell Culture Dishes for Cell-Sheet Engineering Using Aqueous Solutions of Poly(2-n-propyl-oxazoline)

Cell-sheet technology is a well-known method by which cells are grown on thermoswitchable substrates that become nonadhesive upon cooling, such that a complete layer of adherent cells, along with the produced extracellular matrix, detaches as a sheet. Polymers that exhibit a lower critical solution temperature (LCST) below physiological temperature in water, commonly poly(N-isopropylacrylamide) (PNIPAM), are covalently grafted or, for block copolymers, physisorbed onto substrates in a monomolecular thin film to achieve this. Consequently, such substrates, and the polymers required for film formation, can only be prepared in a chemical lab with profound macromolecular expertise. In this study, we present an easy and robust method to coat standard cell culture dishes with aqueous solutions of commercially available poly(2-n-propyl-2-oxazoline) (PnPrOx), a polymer that exhibits LCST behavior. Different standard cell culture dishes were repeatedly coated with 0.1 wt % aqueous solutions of PnPrOx and dried in an oven to create a fully covered and thermoresponsive surface. Using this PnPrOx surface a variety of cell types including endothelial cells, mesenchymal stem cells, and fibroblasts, were seeded and cultured until confluency. By decreasing the temperature to 16 °C, viable cell sheets were detached within cell-type dependent time frames and could be harvested for biological analysis. We show that the cytoskeleton rearranges, leading to a more contracted morphology of the cells in the detached cell sheet. The cellular junctions between single cells within the sheet could be detected using immunostainings, indicating that strong and intact intracellular contacts are preserved in the harvested sheets.

Abstract 877: Real-time imaging of adherent and non-adherent cell interactions: utility of an automated microfluidic trap platform to recapitulate in vivo cell culture microenvironment

Abstract The study of dynamic cell processes and their interactions is of crucial importance to understand the complexities of tissue microenvironments. Simulation of in vivo cell culture microenvironments can greatly improve biologic relevance of cell-cell interaction studies, and so there is an ongoing demand for heuristic optimization of cell co-culture devices and protocols. One particularly challenging task is establishing real-time image analysis while co-culturing non-adherent cells in contact with adherent cell layers under precisely controlled environmental parameters. To address this challenge, we present a novel microfluidic approach to trap two different cell types in precise locations in order to image and study their interactions over time. The platform utilizes a well plate format that contains multiple microfluidic units. Each unit consists of a 3 mm x 3 mm x 40 µm (L x W x H) chamber for culture, and an array of microscopic trap areas tailored to the dimensions of the cells of interest, typically ~15 µm. The micro-scale geometries of the traps physically confine non-adherent cells, and co-cultures can be achieved by trapping the non-adherent cells over a monolayer of cells. The microfluidic plate is integrated with a system which enables perfusion-based nutrient supply along with gas and temperature control for long-term cell culture. Each chamber within the plate can be addressed by programmable and on-demand perturbation of up to 6 reagents, enabling uninterrupted real-time live cell imaging assays. We present here the use of this microfluidic platform to replicate tumor microenvironment by maintaining adjacent co-cultures of cancer and immune cells. We have successfully imaged and cultured monolayers of tumor cell lines for 7 days followed by subsequent loading and trapping of immune (non-adherent) cells. In conclusion, the microfluidic platform enables unique co-cultures with environmental control and real-time imaging to facilitate the investigation of cell-cell interactions in a wide range of applications such as drug response and screening in tumor microenvironments, invasion, evasion pathways and other mechanisms governing cell-cell interactions. Citation Format: Rekha Kannan, Victor Yeh, James Helton, Amedeo Cappione. Real-time imaging of adherent and non-adherent cell interactions: utility of an automated microfluidic trap platform to recapitulate in vivo cell culture microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 877. doi:10.1158/1538-7445.AM2017-877

Clonal characteristics of mesenchymal stem cells able to transfer microenvironment

Mesenchymal stem cells (MSCs) can transfer hematopoietic microenvironment in vivo. After implantation of murine femur bone marrow (BM) plug or adherent cell layer (ACL) of long-term bone marrow culture (LTBMC) established from the same BM equivalent, ectopic hematopoietic focus is formed under the renal capsule of syngeneic recipient. Stromal cells in those foci are derived from donor MSCs, while hematopoietic cells are of recipient origin. Cellularity of individual foci is proportional to the number of transplanted femur equivalents. Consequently, this assay can be used to quantitatively assess the number of MSCs in BM. Based on the self-renewal potential of MSCs, ectopic foci can be serially retransplanted. The aim of this study was to characterize the clonal structure of MSC populations. LTBMCs were obtained from F1 (CBA x C57Black/J6) mice. Cultures were transduced 2 weeks after establishment with a lentiviral library containing genetic barcodes (32 variable nucleotides). After additional 2 weeks, the proportion of marked stromal clonogenic cells (colony forming units fibroblast /CFU-F/) in ACLs was 73.7±5.1%. ACLs were implanted under the renal capsules of syngeneic recipients. Six weeks later the developed ectopic foci were partially retransplanted. DNA was isolated from LTBMCs, initial and secondary ectopic foci. Barcode sequences were determined on Illumina platform. In initial ectopic foci 278±40 (n = 7) individual barcodes were identified. The secondary ectopic foci contained 247±23 (n = 4) barcodes. Only 12±1 common barcodes were found in both initial and secondary foci. Since the secondary were descendants of the initial foci, we calculated that the initial foci contained about 500 barcoded MSCs, meaning that at least 2.3% of MSCs took part in the formation of hematopoietic microenvironment in the initial and the secondary foci. All other MSCs formed microenvironment only once. Taking into account the proportion of marked stromal clonogenic cells in ACLs, initial foci contained at least 600 MSCs. As each LTBMC was established from one femur, a femur contains no less than 600 MSCs. Presuming a linear relationship between the number of implanted MSCs and the size of ectopic foci, our data suggest that not all MSCs, but only part of them is involved in formation of hematopoietic microenvironment.

Real-time imaging of non-adherent cells maintained in contact with adherent cell layers

Abstract Cell-cell interactions are crucial to the survival and function of cells. Imaging these interactions in real-time is a challenging task with non-adherent cells due to their mobility in suspension, not to mention their communication with other heterotypic cells. Here we present a novel method to trap non-adherent cells in precise locations with a layer of adherent cells in order to study and image their interactions while in contact over time. This platform uses a well plate format to integrate 8 individual microfluidic units. Each unit has a 3 mm × 3 mm × 40 μm (L × W × H) chamber for cell culture, and an array of one hundred 72 × 72 × 15 μm (L × W × H) trap areas within each chamber to immobilize non-adherent cells underneath. The chamber in each unit can be addressed with programmable and on-demand perturbation of up to 2 different reagents to perform live cell imaging assays without disrupting the cell cultures. We have successfully cultured MCF-7 cells using this design, with Jurkat cells subsequently loaded and trapped above the layer of MCF-7. Upon reagent introduction, time-lapse images confirmed that the Jurkat cells remained in place. In conclusion, the microfluidic design allows investigation of cell-cell interactions in a wide range of applications requiring the confinement of non-adherent cells in contact with a different adherent cell layer. The on-demand perturbation feature further increases the capability to control the microenvironment exposed to the cell culture.

Investigation of the Mesenchymal Stem Cell Compartment by Means of a Lentiviral Barcode Library.

The hematopoietic bone marrow microenvironment is formed by proliferation and differentiation of mesenchymal stem cells (MSCs). The MSC compartment has been less studied than the hematopoietic stem cell compartment. To characterize the structure of the MSC compartment, it is necessary to trace the fate of distinct mesenchymal cells. To do so, mesenchymal progenitors need to be marked at the single-cell level. A method for individual marking of normal and cancer stem cells based on genetic "barcodes" has been developed for the last 10 years. Such approach has not yet been applied to MSCs. The aim of this study was to evaluate the possibility of using such barcoding strategy to mark MSCs and their descendants, colony-forming units of fibroblasts (CFU-Fs). Adherent cell layers (ACLs) of murine long-term bone marrow cultures (LTBMCs) were transduced with a lentiviral library with barcodes consisting of 32+ 3 degenerate nucleotides. Infected ACLs were suspended, and CFU-F derived clones were obtained. DNA was isolated from each individual colony, and barcodes were analyzed in marked CFU-F-derived colonies by means of conventional polymerase chain reaction and Sanger sequencing. Barcodes were identified in 154 marked colonies. All barcodes appeared to be unique: there were no two distinct colonies bearing the same barcode. It was shown that ACLs included CFU-Fs with different proliferative potential. MSCs are located higher in the hierarchy of mesenchymal progenitors than CFU-Fs, so the presented data indicate that MSCs proliferate rarely in LTBMCs. A method of stable individual marking and comparing the markers in mesenchymal progenitor cells has been developed in this work. We show for the first time that a barcoded library of lentiviruses is an effective tool for studying stromal progenitor cells.

Phenotypic differentiation does not affect tumorigenicity of primary human colon cancer initiating cells

Within primary colorectal cancer (CRC) a subfraction of all tumor-initiating cells (TIC) drives long-term progression in serial xenotransplantation. It has been postulated that efficient maintenance of TIC activity in vitro requires serum-free spheroid culture conditions that support a stem-like state of CRC cells. To address whether tumorigenicity is indeed tightly linked to such a stem-like state in spheroids, we transferred TIC-enriched spheroid cultures to serum-containing adherent conditions that should favor their differentiation. Under these conditions, primary CRC cells did no longer grow as spheroids but formed an adherent cell layer, up-regulated colon epithelial differentiation markers, and down-regulated TIC-associated markers. Strikingly, upon xenotransplantation cells cultured under either condition equally efficient formed serially transplantable tumors. Clonal analyses of individual lentivirally marked TIC clones cultured under either culture condition revealed no systematic differences in contributing clone numbers, indicating that phenotypic differentiation does not select for few individual clones adapted to unfavorable culture conditions.Our results reveal that CRC TIC can be propagated under conditions previously thought to induce their elimination. This phenotypic plasticity allows addressing primary human CRC TIC properties in experimental settings based on adherent cell growth.

Serum Proteins Enhance Dispersion Stability and Influence the Cytotoxicity and Dosimetry of ZnO Nanoparticles in Suspension and Adherent Cancer Cell Models.

Agglomeration and sedimentation of nanoparticles (NPs) within biological solutions is a major limitation in their use in many downstream applications. It has been proposed that serum proteins associate with the NP surface to form a protein corona that limits agglomeration and sedimentation. Here, we investigate the effect of fetal bovine serum (FBS) proteins on the dispersion stability, dosimetry, and NP-induced cytotoxicity of cationic zinc oxide nanoparticles (nZnO) synthesized via forced hydrolysis with a core size of 10 nm. Two different in vitro cell culture models, suspension and adherent, were evaluated by comparing a phosphate buffered saline (PBS) nZnO dispersion (nZnO/PBS) and an FBS-stabilized PBS nZnO dispersion (nZnO – FBS/PBS). Surface interactions of FBS on nZnO were analyzed via spectroscopic and optical techniques. Fourier transformed infrared spectroscopy (FTIR) confirmed the adsorption of negatively charged protein components on the cationic nZnO surface through the disappearance of surfaced-adsorbed carboxyl functional groups and the subsequent detection of vibrational modes associated with the protein backbone of FBS-associated proteins. Further confirmation of these interactions was noted in the isoelectric point shift of the nZnO from the characteristic pH of 9.5 to a pH of 6.1. In nZnO – FBS/PBS dispersions, the FBS reduced agglomeration and sedimentation behaviors to impart long-term improvements (>24 h) to the nZnO dispersion stability. Furthermore, mathematical dosimetry models indicate that nZnO – FBS/PBS dispersions had consistent NP deposition patterns over time unlike unstable nZnO/PBS dispersions. In suspension cell models, the stable nZnO – FBS/PBS dispersion resulted in a ~33 % increase in the NP-induced cytotoxicity for both Jurkat leukemic and Hut-78 lymphoma cancer cells. In contrast, the nZnO – FBS/PBS dispersion resulted in 49 and 71 % reductions in the cytotoxicity observed towards the adherent breast (T-47D) and prostate (LNCaP) cancer cell lines, respectively. Presence of FBS in the NP dispersions also increased the reactive oxygen species generation. These observations indicate that the improved dispersion stability leads to increased NP bioavailability for suspension cell models and reduced NP sedimentation onto adherent cell layers resulting in more accurate in vitro toxicity assessments.

Fibroblastic colony forming units (CFU-F) within adherent cell layer from long-term bone marrow cultures correspond to the progeny of distinct mesenchymal precursor cells

Fibroblastic colony forming units (CFU-F) within adherent cell layer from long-term bone marrow cultures correspond to the progeny of distinct mesenchymal precursor cells

Peculiarities of Gene Transfer into Mesenchymal Stem Cells.

Murine mesenchymal stem cells in long-term bone marrow culture were genetically labeled using lentiviral vector carrying enhanced green fluorescent protein (eGFP) reporter gene under SFFV promoter or without it. We studied the developmental fate of labeled mesenchymal stem cells in stromal cell layers of long-term bone marrow culture and in ectopic hemopoietic foci formed by these stromal layers under the renal capsule of syngeneic mice. The frequency of labeled polypotent stromal precursors (fibroblast CFU) was analyzed in adherent cell layers of long-term culture and ectopic foci formed from them. The proportion of labeled fibroblast CFU in ectopic foci increased by 10 times in case of implantation of adherent cell layers infected with lentivirus containing eGFP reporter gene without promoter. eGFP expression leads to rejection of labeled stromal cells. Labeling with eGFP-carrying vector without promoter makes possible long-term tracking of mesenchymal stromal cells.

Abstract 3057: Unstable phenotype of human colon cancer tumor initiating cells

Abstract We have previously shown that long term progression of human colorectal cancer in serial xenotransplantation is driven by a small sub-fraction of all tumor initiating cells (TIC). These long-term TIC (LT-TIC) self-renew extensively in vivo and are exclusively able to seed metastases in distant organs. Defined phenotypic surface markers of LT-TIC would be crucial to develop effective antibody-based targeting strategies. However, it remains elusive whether a fixed phenotype of long-term TIC is associated with their tumorigenicity thereby allowing prospective isolation of this most relevant cancer cell fraction. To address this question, three dimensional spheroid cultures in serum free medium supplemented with FGF and EGF were generated from primary human colon cancer specimens to enrich for TIC. To calculate the frequency of TIC in spheroid cultures, cells were transplanted in limiting dilution into cohorts of Nod/SCID-IL2RG-/- (NSG) mice. TIC frequency varied from 1 in 22 to 1 in 2x104 spheroid cells, depending on the respective patient sample. When the spheroid cells were transferred to culture conditions that favor their differentiation (gelatin coated plates in the presence of serum and withdrawal of cytokines) the phenotype changed dramatically. The primary colon cancer cells did no longer grow as spheroids but formed an adherent cell layer and up-regulated the colon epithelial differentiation markers CDX2, DEFA5, KRT80, Muc20 and TFF2. In addition, CD133, a widely used marker to enrich for TICs in various solid cancers, was strongly down-regulated upon serum treatment. Strikingly, when xenotransplantated into NSG mice, cells cultured under spheroid and differentiation conditions equally formed serially transplantable tumors, demonstrating that tumor initiating and self-renewal capacity of TIC was not restricted to phenotypically immature spheroid cells. Moreover, CD133 expression did not predict successful tumor formation in vivo. Sorted CD133+ and CD133- cells from 3 individual patients formed tumors with equal efficiency and regenerated both, CD133+ and CD133- cells in vivo. Importantly, clonal analyses of individual lentivirally marked TIC clones cultured under either culture condition revealed no systematic differences in TIC frequency, demonstrating that phenotypic differentiation does not lead to quantitative elimination of TIC clones. Our results demonstrate that phenotypic differentiation does not eliminate the tumor-initiating potential of human colorectal TIC. Moreover, expression of CD133 does not predict their tumor forming and self-renewal potential. This pronounced phenotypic plasticity of human colon cancer TIC poses a grave challenge for surface-targeted elimination of TIC in colorectal cancer. Citation Format: Taronish D. Dubash, Christopher M. Hoffmann, Felix Oppel, Klara Giessler, Sarah Bergmann, Sebastian M. Dieter, Wilko Weichert, Martin Schneider, Manfred Schmidt, Christof von Kalle, Hanno Glimm, Claudia R. Ball. Unstable phenotype of human colon cancer tumor initiating cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3057. doi:10.1158/1538-7445.AM2014-3057