Systemic Analysis of Tumor Cell-Induced Endothelial Calcium Signaling and Junction Disassembly

Thrombin-Activated Platelets Protect Vascular Endothelium against Tumor Cell Extravasation by Targeting Endothelial VCAM-1

When activated by thrombin, the platelets release their granular store of factors. These thrombin-activated platelets (TAPLT) have been shown to be capable of ameliorating pro-inflammatory processes. In this study, we tested if TAPLT could also protect the endothelium against tumor-related pro-inflammatory changes that promote angiogenesis and metastasis. Using endothelial cell (EC) models in vitro, we demonstrated that TAPLT protected EC against tumor conditioned medium (TCM)-induced increases of reactive oxygen species (ROS) production, EC permeability and angiogenesis, and inhibited transendothelial migration that was critical for cancer cell extravasation and metastasis. In vivo observations of TAPLT-mediated inhibition of angiogenesis and pulmonary colonization in a BALB/c nude mouse model were consistent with the in vitro findings. Neutralization of vascular cell adhesion molecule-1 (VCAM-1) binding significantly inhibited the ability of TAPLT to interact with EC and abrogated the TAPLT-mediated protection of EC against tumor angiogenesis and metastasis. Taken together, these findings suggest that VCAM-1-mediated linkage to EC is required for TAPLT to confer protection of EC against tumor-induced permeation and angiogenesis, thereby resisting tumor extravasation and metastasis.

The Role of Calcium Signaling in Melanoma

Calcium signaling plays important roles in physiological and pathological conditions, including cutaneous melanoma, the most lethal type of skin cancer. Intracellular calcium concentration ([Ca²⁺]i), cell membrane calcium channels, calcium related proteins (S100 family, E-cadherin, and calpain), and Wnt/Ca²⁺ pathways are related to melanogenesis and melanoma tumorigenesis and progression. Calcium signaling influences the melanoma microenvironment, including immune cells, extracellular matrix (ECM), the vascular network, and chemical and physical surroundings. Other ionic channels, such as sodium and potassium channels, are engaged in calcium-mediated pathways in melanoma. Calcium signaling serves as a promising pharmacological target in melanoma treatment, and its dysregulation might serve as a marker for melanoma prediction. We documented calcium-dependent endoplasmic reticulum (ER) stress and mitochondria dysfunction, by targeting calcium channels and influencing [Ca²⁺]i and calcium homeostasis, and attenuated drug resistance in melanoma management.

Microfluidic Tumor-Vascular Model to Study Breast Cancer Cell Invasion and Intravasation

Cancer is a major leading cause of disease-related death in the world. The severe impact of cancer can be attributed to poor understanding of the mechanisms involved in earliest steps of the metastatic cascade, specifically invasion into the surrounding stroma and intravasation into the blood capillaries. However, conducting integrated biological studies of invasion and intravasation have been challenging, within in vivo models and traditional in vitro assay, due to difficulties in establishing a precise tumor microenvironment. To that end, in this work, a novel 3D microfluidic platform comprised of concentric three-layer cell-laden hydrogels for simultaneous investigation of breast cancer cell invasion and intravasation as well as vasculature maturation influenced by tumor-vascular crosstalk is developed. It was demonstrated that the presence of spontaneously formed vasculature enhance MDA-MB-231 invasion into the 3D stroma. Following invasion, cancer cells are visualized intravasating into the outer vasculature. Additionally, invading cancer cells significantly reduce vessel diameter while increasing permeability, consistent with previous in vivo studies. Major signaling cytokines involved in tumor-vascular crosstalk that govern cancer cell invasion and intravasation are further identified. Taken together, this platform will enable unique insights of critical biological events within the metastatic cascade, with significant potential for developing efficient cancer therapeutics.

Actinomyosin contraction, phosphorylation of VE-cadherin, and actin remodeling enable melanoma-induced endothelial cell-cell junction disassembly

During melanoma cell extravasation through the vascular endothelium, melanoma cells interact with endothelial cells through secretion of cytokines and by adhesion between proteins displayed on opposing cell surfaces. How these tumor cell associated signals together regulate the dynamics of intracellular signaling pathways within endothelial cells leading to endothelial cell-cell junction disruption is not well understood. Here, we used a combination of experimental and computational approaches to examine the individual and combined effects of activation of the vascular cell adhesion molecule (VCAM)-1, interleukin (IL)-8, and IL-1β signaling pathways on the integrity of vascular junctions. Our simulations predict a multifaceted interplay of signaling resulting from individual activation of VCAM-1, IL-8 and IL-1β pathways that is neither synergistic nor additive compared to all inputs turned on simultaneously. Furthermore, we show that the levels of phosphorylated proteins associated with actinomyosin contractility and junction disassembly peak prior to those related to actin remodeling. The results of this work provide insight into the dynamics of tumor-mediated endothelial junction disassembly and suggest that targeting proteins downstream of several interaction pathways may be the most effective therapeutic approach to reduce melanoma extravasation.

Mechanisms of tumor cell extravasation in an in vitro microvascular network platform

A deeper understanding of the mechanisms of tumor cell extravasation is essential in creating therapies that target this crucial step in cancer metastasis. Here, we use a microfluidic platform to study tumor cell extravasation from in vitro microvascular networks formed via vasculogenesis. We demonstrate tight endothelial cell-cell junctions, basement membrane deposition and physiological values of vessel permeability. Employing our assay, we demonstrate impaired endothelial barrier function and increased extravasation efficiency with inflammatory cytokine stimulation, as well as positive correlations between the metastatic potentials of MDA-MB-231, HT-1080, MCF-10A and their extravasation capabilities. High-resolution time-lapse microscopy reveals the highly dynamic nature of extravasation events, beginning with thin tumor cell protrusions across the endothelium followed by extrusion of the remainder of the cell body through the formation of small (~1 μm) openings in the endothelial barrier which grows in size (~8 μm) to allow for nuclear transmigration. No disruption to endothelial cell-cell junctions is discernible at 60×, or by changes in local barrier function after completion of transmigration. Tumor transendothelial migration efficiency is significantly higher in trapped cells compared to non-trapped adhered cells, and in cell clusters versus single tumor cells.

Three-dimensional microfluidic model for tumor cell intravasation and endothelial barrier function

Entry of tumor cells into the blood stream is a critical step in cancer metastasis. Although significant progress has been made in visualizing tumor cell motility in vivo, the underlying mechanism of cancer cell intravasation remains largely unknown. We developed a microfluidic-based assay to recreate the tumor-vascular interface in three-dimensions, allowing for high resolution, real-time imaging, and precise quantification of endothelial barrier function. Studies are aimed at testing the hypothesis that carcinoma cell intravasation is regulated by biochemical factors from the interacting cells and cellular interactions with macrophages. We developed a method to measure spatially resolved endothelial permeability and show that signaling with macrophages via secretion of tumor necrosis factor alpha results in endothelial barrier impairment. Under these conditions intravasation rates were increased as validated with live imaging. To further investigate tumor-endothelial (TC-EC) signaling, we used highly invasive fibrosarcoma cells and quantified tumor cell migration dynamics and TC-EC interactions under control and perturbed (with tumor necrosis factor alpha) barrier conditions. We found that endothelial barrier impairment was associated with a higher number and faster dynamics of TC-EC interactions, in agreement with our carcinoma intravasation results. Taken together our results provide evidence that the endothelium poses a barrier to tumor cell intravasation that can be regulated by factors present in the tumor microenvironment.

Sensitivity analysis approaches applied to systems biology models

With the rising application of systems biology, sensitivity analysis methods have been widely applied to study the biological systems, including metabolic networks, signalling pathways and genetic circuits. Sensitivity analysis can provide valuable insights about how robust the biological responses are with respect to the changes of biological parameters and which model inputs are the key factors that affect the model outputs. In addition, sensitivity analysis is valuable for guiding experimental analysis, model reduction and parameter estimation. Local and global sensitivity analysis approaches are the two types of sensitivity analysis that are commonly applied in systems biology. Local sensitivity analysis is a classic method that studies the impact of small perturbations on the model outputs. On the other hand, global sensitivity analysis approaches have been applied to understand how the model outputs are affected by large variations of the model input parameters. In this review, the author introduces the basic concepts of sensitivity analysis approaches applied to systems biology models. Moreover, the author discusses the advantages and disadvantages of different sensitivity analysis methods, how to choose a proper sensitivity analysis approach, the available sensitivity analysis tools for systems biology models and the caveats in the interpretation of sensitivity analysis results.

Melanoma vasculogenic mimicry capillary-like structure formation depends on integrin and calcium signaling

OBJECTIVE

We recently demonstrated that the formation of CLSs in vitro, which are thought to be a reconstitution of VM, is controlled by VEGFA. CLS formation also requires the extracellular matrix signals, presumably transduced by integrins. Both pathways are affected by Ca(2+). Therefore, we directly tested the roles of Ca(2+) and integrin in melanoma VM.

METHODS

The investigation was performed by immunocytochemical, histochemical, and 3D co-culture assays. We have also used an in vivo animal model.

RESULTS

The extracellular and intracellular Ca(2+) chelators, EGTA and BAPTA-AM, prevented CLS formation on Matrigel, caused actin rearrangement, and completely destroyed the preformed CLS. Addition of colcemid or cytochalasin D prevented the CLS formation and destroyed the preformed CLS network. Herein, we also show that blocking antibodies to ανβ3 and ανβ5 integrins disrupted the CLS network. Control blocking antibody to β1 integrin had no effect. In vivo experiments indicated that Ca(2+) chelation dramatically reduced the signs of VM in melanoma tumors grafted in mice.

CONCLUSIONS

Our results indicate that the formation of CLS is tightly regulated by extracellular and intracellular Ca(2+) levels; ανβ3 and ανβ5 integrins are primarily responsible for CLS formation, whereas β1 integrin does not participate in CLS formation.

Microfluidic devices for studying heterotypic cell-cell interactions and tissue specimen cultures under controlled microenvironments

Microfluidic devices allow for precise control of the cellular and noncellular microenvironment at physiologically relevant length- and time-scales. These devices have been shown to mimic the complex in vivo microenvironment better than conventional in vitro assays, and allow real-time monitoring of homotypic or heterotypic cellular interactions. Microfluidic culture platforms enable new assay designs for culturing multiple different cell populations and∕or tissue specimens under controlled user-defined conditions. Applications include fundamental studies of cell population behaviors, high-throughput drug screening, and tissue engineering. In this review, we summarize recent developments in this field along with studies of heterotypic cell-cell interactions and tissue specimen culture in microfluidic devices from our own laboratory.