Selective measurement and manipulation of adhesion forces between cancer cells and bone marrow endothelial cells using atomic force microscopy

Changes in dynamics of tumor/endothelial cell adhesive interactions depending on endothelial cell growth state and elastic properties

Cancer cell adhesion to the endothelium is a crucial process in hematogenous metastasis, but how the integrity of the endothelial barrier and endothelial cell (EC) mechanical properties influence the adhesion between metastatic cancer cells and the endothelium remain unclear. In the present study, we have measured the adhesion between single cancer cells and two types of ECs at various growth states and their mechanical properties (elasticity) using atomic force microscopy single cell force spectroscopy. We demonstrated that the EC stiffness increased and adhesion with cancer cells decreased, as ECs grew from a single cell to a confluent state and developed cell-cell contacts, but this was reversed when confluent cells returned to a single state in a scratch assay. Our results suggest that the integrity of the endothelial barrier is an important factor in reducing the ability of the metastatic tumor cells to adhere to the vascular endothelium, extravasate and lodge in the vasculature of a distant organ where secondary metastatic tumors would develop.

Atomic force microscopy reveals the mechanical properties of breast cancer bone metastases

Mechanically dependent processes are essential in cancer metastases. However, reliable mechanical characterization of metastatic cancer remains challenging whilst maintaining the tissue complexity and an intact sample. Using atomic force microscopy, we quantified the micro-mechanical properties of relatively intact metastatic breast tumours and their surrounding bone microenvironment isolated from mice, and compared with other breast cancer models both ex vivo and in vitro. A mechanical distribution of extremely low elastic modulus and viscosity was identified on metastatic tumours, which were significantly more compliant than both 2D in vitro cultured cancer cells and subcutaneous tumour explants. The presence of mechanically distinct metastatic tumour did not result in alterations of the mechanical properties of the surrounding microenvironment at meso-scale distances (>200 μm). These findings demonstrate the utility of atomic force microscopy in studies of complex tissues and provide new insights into the mechanical properties of cancer metastases in bone.

Application of atomic force microscope in diagnosis of single cancer cells

Changes in mechanical properties of cells are closely related to a variety of diseases. As an advanced technology on the micro/nano scale, atomic force microscopy is the most suitable tool for information acquisition of living cells in human body fluids. AFMs are able to measure and characterize the mechanical properties of cells which can be used as effective markers to distinguish between different cell types and cells in different states (benign or cancerous). Therefore, they can be employed to obtain additional information to that obtained via the traditional biochemistry methods for better identifying and diagnosing cancer cells for humans, proposing better treatment methods and prognosis, and unravelling the pathogenesis of the disease. In this report, we review the use of AFMs in cancerous tissues, organs, and cancer cells cultured in vitro to obtain cellular mechanical properties, demonstrate and summarize the results of AFMs in cancer biology, and look forward to possible future applications and the direction of development.

Differentiation of single lymphoma primary cells and normal B-cells based on their adhesion to mesenchymal stromal cells in optical tweezers

We have adapted a non-invasive method based on optical tweezers technology to differentiate between the normal B-cells and the B-cell non-Hodgkin lymphoma (B-NHL) cells derived from clinical samples. Our approach bases on the nascent adhesion between an individual B-cell and a mesenchymal stromal cell. In this study, a single B-cell was trapped and optically seeded on a mesenchymal stromal cell and kept in a direct contact with it until a stable connection between the cells was formed in time scale. This approach allowed us to avoid the introduction of any exogenous beads or chemicals into the experimental setup which would have affected the cell-to-cell adhesion. Here, we have provided new evidence that aberrant adhesive properties found in transformed B-cells are related to malignant neoplasia. We have demonstrated that the mean time required for establishing adhesive interactions between an individual normal B-cell and a mesenchymal stromal cell was 26.7 ± 16.6 s, while for lymphoma cell it was 208.8 ± 102.3 s, p < 0.001. The contact time for adhesion to occur ranged from 5 to 90 s and from 60 to 480 s for normal B-cells and lymphoma cells, respectively. This method for optically controlled cell-to-cell adhesion in time scale is beneficial to the successful differentiation of pathological cells from normal B-cells within the fine needle aspiration biopsy of a clinical sample. Additionally, variations in time-dependent adhesion among subtypes of B-NHL, established here by the optical trapping, confirm earlier results pertaining to cell heterogeneity.

AFM study: Cell cycle and probe geometry influences nanomechanical characterization of Panc1 cells

Atomic force microscope (AFM) is emerging as an immensely promising tool to study the cellular morphology with a nanometer scale resolution and to analyze nanomechanical properties (NPs) at various physiological conditions. Advancement of AFM technology enables studying living cells and differentiating cancer cell from normal cells based on topography and NPs. Though the trend overlaps from different literature; numerical values of nanomechanical readouts depict variations over a wide range. These anomalies are associated with the experimental setup under study. In this manuscript, we have identified heterogeneity in cell culture system in addition to the selection of AFM probe with specific tip geometry as the major contributors to the above mentioned anomalies. To test our hypothesis, we have used Panc1 cells, which is a pancreatic ductal adenocarcinoma cell type. Our results suggest that the cellular morphology, membrane roughness and NPs calculated from AFM study are distinctly influenced by cell cycle. Furthermore, we found that the NPs readout is also significantly associated with AFM tip geometries. The cells were found to be softer in their early resting phase when indented with pyramidal probe and became increasingly stiffer as they progressed through the cell cycles. On the contrary, when indented with the spherical probe, cells in G0/G1 phase were observed to be the stiffest. Such an exhaustive study of the role of cell cycle in influencing the NPs in Panc1 cell line along with the impact of tip geometry on NPs is the first of its kind, to the best of our knowledge.

Temporal and molecular dynamics of human metastatic breast carcinoma cell adhesive interactions with human bone marrow endothelium analyzed by single-cell force spectroscopy

Bone is a common site of metastasis for breast cancer and the mechanisms of metastasis are not fully elucidated. The purpose of our study was to characterize temporal and molecular dynamics of adhesive interactions between human breast cancer cells (HBCC) and human bone marrow endothelium (HBME) with piconewton resolution using atomic force microscopy (AFM). In adhesion experiments, a single breast cancer cell, MDA-MB-231 (MB231) or MDA-MB-435 (MB435) was attached to the AFM cantilever and brought into contact with a confluent HBME monolayer for different time periods (0.5 to 300 sec). The forces required to rupture individual molecular interactions and completely separate interacting cells were analyzed as measures of cell-cell adhesion. Adhesive interactions between HBME and either MB231 or MB435 cells increased progressively as cell-cell contact time was prolonged from 0.5 to 300 sec due to the time-dependent increase in the number and frequency of individual adhesive events, as well as to the involvement of stronger ligand-receptor interactions over time. Studies of the individual molecule involvement revealed that Thomsen-Friedenreich antigen (TF-Ag), galectin-3, integrin-β1, and integrin-α3 are all contributing to HBCC/HBME adhesion to various degrees in a temporally defined fashion. In conclusion, cell-cell contact time enhances adhesion of HBCC to HBME and the adhesion is mediated, in part, by TF-Ag, galectin-3, integrin-α3, and integrin-β1.

Applications of Atomic Force Microscopy for Adhesion Force Measurements in Mechanotransduction

Adhesive interactions between living cells or ligand-receptor interactions can be studied at the molecular level using atomic force microscopy (AFM). Adhesion force measurements are performed with functionalized AFM probes. In order to measure single ligand-receptor interactions, a cantilever with a pyramidal tip is functionalized with a bio-recognized ligand (e.g., extracellular matrix protein). The ligand-functionalized probe is then brought into contact with a cell in culture to investigate adhesion between the respective probe-bound ligand and endogenously expressed cell surface receptors (e.g., integrins or other adhesion receptor). For experiments designed to examine cell-cell adhesions, a single cell is attached to a tipless cantilever which is then brought into contact with other cultured cells. Force curves are recorded to determine the forces necessary to rupture discrete adhesions between the probe-bound ligand and receptor, or to determine total adhesion force at cell-cell contacts. Here, we describe the procedures for measuring adhesions between (a) fibronectin and α5β1 integrin, and (b) breast cancer cells and bone marrow endothelial cells.

Direct mapping of melanoma cell - endothelial cell interactions

The most life-threatening aspect of cancer is metastasis; cancer patient mortality is mainly due to metastasis. Among all metastases, presence of brain metastasis is one with the poorest prognosis; the median survival time can be counted in months. Therefore, prevention or decreasing their incidence would be highly desired both by patients and physicians. Metastatic cells invading the brain must breach the cerebral vasculature, primarily the blood-brain barrier. The key step in this process is the establishment of firm adhesion between the cancer cell and the cerebral endothelial layer. Using the atomic force microscope, a high-resolution force spectrograph, our aim was to explore the connections among the cell morphology, cellular mechanics, and biological function in the process of transendothelial migration of metastatic cancer cells. By immobilization of a melanoma cell to an atomic force microscope's cantilever, intercellular adhesion was directly measured at quasi-physiological conditions. Hereby, we present our latest results by using this melanoma-decorated probe. Binding characteristics to a confluent layer of brain endothelial cells was directly measured by means of single-cell force spectroscopy. Adhesion dynamics and strength were characterized, and we present data about spatial distribution of elasticity and detachment strength. These results highlight the importance of cellular mechanics in brain metastasis formation and emphasize the enormous potential toward exploration of intercellular dynamic-related processes.

Monitoring of TGF-β 1-Induced Human Lung Adenocarcinoma A549 Cells Epithelial-Mesenchymal Transformation Process by Measuring Cell Adhesion Force with a Microfluidic Device

The epithelial-mesenchymal transition (EMT) is a process in which epithelial cells lose their cell polarity and cell-cell adhesion, and gain migratory and invasive properties. It is believed that EMT is associated with initiation and completion of the invasion-metastasis cascade. In this study, an economic approach was developed to fabricate a microfluidic device with less instrumentation requirement for the investigation of EMT by quantifying cell adhesion force. Fluid shear force was precisely controlled by a homemade microfluidic perfusion apparatus and interface. The adhesion capability of the human lung adenocarcinoma cell line A549 on different types of extracellular matrix protein was studied. In addition, effects of transforming growth factor-β (TGF-β) on EMT in A549 cells were investigated by characterizing the adhesion force changes and on-chip fluorescent staining. The results demonstrate that the microfluidic device is a potential tool to characterize the epithelial-mesenchymal transition process by measuring cell adhesion force.

Expression of cell adhesion molecules in laryngeal carcinoma - preliminary analysis

Aim of the study

Intercellular adhesion molecules present in immunocompetent cells as well as endothelium and tumour cells can regulate cell migration, angiogenesis, apoptosis, proliferation, and metastases in solid tumours. The aim of this study was to analyse the sICAM-1 (soluble intercellular adhesion molecule 1) and sVCAM-1 (soluble vascular cell adhesion molecule 1) expression in peripheral blood mononuclear cell (PBMC) cultures, and to find their relationships with clinicomorphological characteristics in laryngeal cancer.

Materials and methods

The analysis included a group of 50 patients with verified squamous cell carcinoma of the larynx. The control group constituted 30 healthy volunteers. The pathological assessment included pTNM, stage, histological grade, and type of invasion according to the tumour front grading. The expression of adhesion molecules was assessed using the enzyme-linked immunosorbent assay (ELISA).

Results

Increased expression of sICAM-1 and sVCAM-1 was an indicator of more aggressive laryngeal carcinomas. More advanced local changes evaluated on the pT feature were connected with a higher sVCAM-1 (p = 0.017), but not sICAM-1 level. The presence of lymph node metastases correlated with a higher expression of adhesion molecules (p = 0.012 and p = 0.003, for sICAM-1 and sVCAM-1, respectively). Tumours with more diffuse growth and infiltrating with small cell groups (< 15/hpf) was characterised by the highest level of adhesive proteins (p = 0.001 and p = 0.02 for sICAM and sVCAM, respectively). Moreover, lower levels of sICAM-1 and sVCAM-1 were observed more frequently in patients who lived longer than five years after treatment.

Conclusions

The study indicates the importance of the sICAM and sVCAM expression as indicators of advanced changes and prognosis in patients with laryngeal carcinoma.