Jon Christensen

Differential uptake of nanoparticles by endothelial cells through polyelectrolytes with affinity for caveolae

Significance Nanoparticles (NPs) can serve as containers for the targeting of therapeutics to tumors. Tumors comprise many cell types including endothelial cells that form the blood vessels. Developing new strategies to target information preferentially to endothelial cells can have major implications in the development of targeted therapeutics. We have discovered that charged polymers containing aromatic sulfonate have pronounced affinity for caveolae, which are highly expressed by endothelial cells. By engineering the surface of lipid NPs to bear sulfonate-containing polymers, lipid NPs that are preferentially taken up by endothelial cells have been demonstrated. Nanoparticles (NPs) constitute an important medium for the targeted delivery of cancer therapeutics. Targeting of NPs to a specific cell type is traditionally achieved through the modification of the NP surface with peptides, aptamers, or other motifs that specifically recognize a cell-surface receptor, leading to internalization of NPs via clathrin and caveolae-mediated endocytosis. We have discovered that modifying the NP surface with anionic polyelectrolytes of varying lipophilicity can regulate the uptake of lipid NPs by endothelial and epithelial cells. Furthermore, we report the finding that synthetic polyelectrolytes composed of an aromatic sulfonic acid backbone exhibit specific affinity for caveolae of endothelial cells. By exploiting the higher expression of caveolae in endothelial cells in comparison with epithelial cells, a purely physiochemical approach to the targeted uptake of lipid NPs to endothelial cells is demonstrated. The ability to confer preferential affinity for NPs to cell surface domains by varying the charge and lipophilic characteristics of an NP surface offers a general means of achieving targeted delivery without the need for receptor–ligand-type targeting strategies.

Polysaccharide hydrogels with tunable stiffness and provasculogenic properties via α-helix to β-sheet switch in secondary structure

Mechanical aspects of the cellular environment can influence cell function, and in this context hydrogels can serve as an instructive matrix. Here we report that physicochemical properties of hydrogels derived from polysaccharides (agarose, κ-carrageenan) having an α-helical backbone can be tailored by inducing a switch in the secondary structure from α-helix to β-sheet through carboxylation. This enables the gel modulus to be tuned over four orders of magnitude (G′ 6 Pa–3.6 × 104 Pa) independently of polymer concentration and molecular weight. Using carboxylated agarose gels as a screening platform, we demonstrate that soft-carboxylated agarose provides a unique environment for the polarization of endothelial cells in the presence of soluble and bound signals, which notably does not occur in fibrin and collagen gels. Furthermore, endothelial cells organize into freestanding lumens over 100 μm in length. The finding that a biomaterial can modulate soluble and bound signals provides impetus for exploring mechanobiology paradigms in regenerative therapies.

FOXQ1, a Novel Target of the Wnt Pathway and a New Marker for Activation of Wnt Signaling in Solid Tumors

Background The forkhead box transcription factor FOXQ1 has been shown to be upregulated in colorectal cancer (CRC) and metastatic breast cancer and involved in tumor development, epithelial-mesenchymal transition and chemoresistance. Yet, its transcriptional regulation is still unknown. Methods FOXQ1 mRNA and protein expression were analysed in a panel of CRC cell lines, and laser micro-dissected human biopsy samples by qRT-PCR, microarray GeneChip® U133 Plus 2.0 and western blots. FOXQ1 regulation was assayed by chromatin immunoprecipitation and luciferase reporter assays. Results FOXQ1 was robustly induced in CRC compared to other tumors, but had no predictive value with regards to grade, metastasis and survival in CRC. Prototype-based gene coexpression and gene set enrichment analysis showed a significant association between FOXQ1 and the Wnt pathway in tumors and cancer cell lines from different tissues. In vitro experiments confirmed, on a molecular level, FOXQ1 as a direct Wnt target. Analysis of known Wnt targets identified FOXQ1 as the most suitable marker for canonical Wnt activation across a wide panel of cell lines derived from different tissues. Conclusions Our data show that FOXQ1 is one of the most over-expressed genes in CRC and a direct target of the canonical Wnt pathway. It is a potential new marker for detection of early CRC and Wnt activation in tumors of different origins.

Defining new criteria for selection of cell-based intestinal models using publicly available databases

BackgroundThe criteria for choosing relevant cell lines among a vast panel of available intestinal-derived lines exhibiting a wide range of functional properties are still ill-defined. The objective of this study was, therefore, to establish objective criteria for choosing relevant cell lines to assess their appropriateness as tumor models as well as for drug absorption studies.ResultsWe made use of publicly available expression signatures and cell based functional assays to delineate differences between various intestinal colon carcinoma cell lines and normal intestinal epithelium. We have compared a panel of intestinal cell lines with patient-derived normal and tumor epithelium and classified them according to traits relating to oncogenic pathway activity, epithelial-mesenchymal transition (EMT) and stemness, migratory properties, proliferative activity, transporter expression profiles and chemosensitivity. For example, SW480 represent an EMT-high, migratory phenotype and scored highest in terms of signatures associated to worse overall survival and higher risk of recurrence based on patient derived databases. On the other hand, differentiated HT29 and T84 cells showed gene expression patterns closest to tumor bulk derived cells. Regarding drug absorption, we confirmed that differentiated Caco-2 cells are the model of choice for active uptake studies in the small intestine. Regarding chemosensitivity we were unable to confirm a recently proposed association of chemo-resistance with EMT traits. However, a novel signature was identified through mining of NCI60 GI50 values that allowed to rank the panel of intestinal cell lines according to their drug responsiveness to commonly used chemotherapeutics.ConclusionsThis study presents a straightforward strategy to exploit publicly available gene expression data to guide the choice of cell-based models. While this approach does not overcome the major limitations of such models, introducing a rank order of selected features may allow selecting model cell lines that are more adapted and pertinent to the addressed biological question.

Validation of Fluorescence Molecular Tomography/Micro-CT Multimodal Imaging In Vivo in Rats

PurposeRats are important preclinical models for studying breast cancer metastasis and bone pathologies. In these research areas, fluorescence molecular tomography (FMT) is commonly applied for quantitative three-dimensional (3D) imaging in mice. However, uncertainties due to strong depth dependency of FMT signal and spatial resolution require a validation study in rats.ProcedureFMT performance in rats was assessed based on co-registered FMT/micro-computed tomography (micro-CT) reconstructed volumes obtained from optical phantoms and from models relevant for tumor imaging, bone remodeling and biodistribution analysis of nanoparticles.ResultsFMT reconstructions within 20-mm-thick optical phantoms were accurate (95u2009±u200911xa0% recovery), precise (CVu2009≤u20098xa0%) and linear (R2u2009>u20090.9788) over a range of 78–2,500xa0nM of the near infrared fluorescent agent VivoTag 750 (VT750). In vivo, implanted defined fluorescent targets yielded a recovery of 105u2009±u20095xa0% and successfully co-registered with micro-CT delineated structures. Additionally, using the bone-targeting imaging agent Osteosense 750, regions of neo bone formation identified by FMT could be mapped to the region of epiphyseal growth plates observed in micro-CT images. Finally, as a proof of concept, to monitor nanoparticulate drug pharmacokinetics in rat subjects the accumulation/clearance of VT750–albumin conjugate in/from the liver was followed at 11 different time points over a period of 2xa0weeks by FMT/micro-CT.ConclusionsFMT imaging has been validated in optical phantoms as well as in 160xa0g rats, and sequential FMT/micro-CT imaging can be considered as a useful tool for preclinical research in rats.

Non-Invasive In Vivo Imaging and Quantification of Tumor Growth and Metastasis in Rats Using Cells Expressing Far-Red Fluorescence Protein.

Non-invasive in vivo imaging is emerging as an important tool for basic and preclinical research. Near-infrared (NIR) fluorescence dyes and probes have been used for non-invasive optical imaging since in the NIR region absorption and auto fluorescence by body tissue is low, thus permitting for greater penetration depths and high signal to noise ratio. Currently, cell tracking systems rely on labeling cells prior to injection or administering probes targeting the cell population of choice right before imaging. These approaches do not enable imaging of tumor growth, as the cell label is diluted during cell division. In this study we have developed cell lines stably expressing the far-red fluorescence protein E2-Crimson, thus enabling continuous detection and quantification of tumor growth. In a xenograft rat model, we show that E2-Crimson expressing cells can be detected over a 5 week period using optical imaging. Fluorescence intensities correlated with tumor volume and weight and allowed for a reliable and robust quantification of the entire tumor compartment. Using a novel injection regime, the seeding of MDA-MB-231 breast cancer cells in the lungs in a rat model was established and verified.

Matrix-metalloproteinase-9 is cleaved and activated by Cathepsin K

BackgroundMatrix-metalloproteinases 9 (MMP-9) belongs to the class of matrix metalloproteinases whose main function is to degrade and remodel the extracellular matrix (ECM). MMP-9 has been shown to be an integral part of many diseases where modulation of the ECM is a key step such as cancer, osteoporosis and fibrosis. MMP-9 is secreted as a latent pro-enzyme that requires activation in the extracellular space. Therefore, identifying physiological and molecular contexts, which can activate MMP-9 is important.ResultsAcidification of osteoclast-conditioned media to pH 5 resulted in a fragment with a size corresponding to active MMP-9. Also, treatment of recombinant proMMP-9 with recombinant cathepsin K (CTSK) at pH 5 yielded a fragment that corresponded to the molecular weight of active MMP-9, and showed MMP-9 activity. This activation was abrogated in the presence of CTSK inhibitor indicating that CTSK was responsible for the activation of pro-MMP-9. Knocking down CTSK in MDA-MB-231 cells also diminished MMP-9 activity compared to wild type control.ConclusionsHere we provide the first evidence that CTSK can cleave and activate MMP-9 in acidic environments such as seen in tumors and during bone resorption. This finding provides a key link between CTSK expression in tumors and bone and ECM remodeling, through MMP-9 activation. This novel mechanism to activate MMP-9 through extracellular physiological changes elucidated in this study reveals a protease-signaling network involving CTSK and MMP-9 and provides the impetus to explore ECM proteases as physiological markers and pharmacological targets.

Recapitulating epithelial tumor microenvironment in vitro using three dimensional tri-culture of human epithelial, endothelial, and mesenchymal cells

BackgroundThree-dimensional (3-D) cultures of cancer cells can potentially bridge the gap between 2-D drug screening and in vivo xenografts. The objective of this study was to characterize the cellular and extracellular matrix characteristics of spheroids composed of human lung epithelial cells (epi), pulmonary vascular endothelial (endo) cells, and human marrow-derived mesenchymal stems cells (MSCs).MethodsSpheroids composed of epi/endo/MSCs, termed herein as synthetic tumor microenvironment mimics (STEMs), were prepared by the hanging drop method. Cellular composition and distribution in the STEMs was characterized using fluorescence microscopy. Induction of reactive oxygen species and upregulation of efflux transporters was quantified using fluorometry and PCR, respectively, and phenotypic markers were qualitatively assessed using immunohistochemistry.ResultsSTEMs exhibited three unique characteristics not captured in other spheroid cultures namely, the presence of a spheroid core devoid of epithelial cells and primarily composed of MSCs, a small viable population of endothelial cells hypothesized to be closely associated with MSCs within the hypoxic core, and discrete regions with high expression for vimentin and cytokeratin-18, whose co-expression is co-related with enhanced metastasis. Although cells within STEMs show elevated levels of reactive oxygen species and mRNA for ABC-B1, an efflux transporter associated with drug resistance, they exhibited only modest resistance to paclitaxel and gemcitabine in comparison to 2-D tri-cultures.ConclusionsThe epi/endo/MSC spheroid model described herein offers a promising platform for understanding tumor biology and drug testing in vitro.

The role of CDX2 in Caco-2 cell differentiation

BACKGROUNDnCDX2 plays a key part in the differentiation of Caco-2 cells, a colon carcinoma derived cell line that undergoes spontaneous differentiation. The effect of CDX2 expression in Caco-2 cells over time in culture has not been studied yet on a genome-wide level.nnnMETHODSnThe impact of CDX2 expression on the genomic profile of Caco-2 cells was studied by transducing cells with CDX2 targeting shRNAs. Knockdown efficiency was assessed on mRNA level and protein level by RTPCR, microarrays, and Western blots. Gene set enrichment analysis was performed to assess regulation of specific gene sets.nnnRESULTSnCDX2 expression had an inhibitory effect on the transcriptional activity of β-catenin/TCF at early stages of culturing, while at later stages, its role in the trans-activation of target genes specific for small intestinal enterocytes seemed more dominant.nnnCONCLUSIONSnThe unique induction of a small intestinal signature upon differentiation in Caco-2 cells seems to be at least partially under the control of CDX2.