BackgroundEffective tools for measurement of chemotaxis are desirable since cell migration towards given stimuli plays a crucial role in tumour metastasis, angiogenesis, inflammation, and wound healing. As for now, the Boyden chamber assay is the longstanding "gold-standard" for in vitro chemotaxis measurements. However, support for live cell microscopy is weak, concentration gradients are rather steep and poorly defined, and chemotaxis cannot be distinguished from migration in a single experiment.ResultsHere, we describe a novel all-in-one chamber system for long-term analysis of chemotaxis in vitro that improves upon many of the shortcomings of the Boyden chamber assay. This chemotaxis chamber was developed to provide high quality microscopy, linear concentration gradients, support for long-term assays, and observation of slowly migrating cells via video microscopy. AlexaFluor 488 dye was used to demonstrate the establishment, shape and time development of linear chemical gradients. Human fibrosarcoma cell line HT1080 and freshly isolated human umbilical vein endothelial cells (HUVEC) were used to assess chemotaxis towards 10% fetal calf serum (FCS) and FaDu cells' supernatant. Time-lapse video microscopy was conducted for 48 hours, and cell tracking and analysis was performed using ImageJ plugins. The results disclosed a linear steady-state gradient that was reached after approximately 8 hours and remained stable for at least 48 hours. Both cell types were chemotactically active and cell movement as well as cell-to-cell interaction was assessable.ConclusionsCompared to the Boyden chamber assay, this innovative system allows for the generation of a stable gradient for a much longer time period as well as for the tracking of cell locomotion along this gradient and over long distances. Finally, random migration can be distinguished from primed and directed migration along chemotactic gradients in the same experiment, a feature, which can be qualified via cell morphology imaging.

We propose a combination of atomic force microscopy (AFM) and optical microscopy for the investigation of particle uptake by cells. Positively and negatively charged polymer microcapsules were chosen as model particles, because their interaction with cells had already been investigated in detail. AFM measurements allowed the recording of adhesion forces on a single-molecule level. Due to the micrometer size of the capsules, the number of ingested capsules could be counted by optical microscopy. The combination of both methods allowed combined measurement of the adhesion forces and the uptake rate for the same model particle. As a demonstration of this system, the correlation between the adhesion of positively or negatively charged polymer microcapsules onto cell surfaces and the uptake of these microcapsules by cells has been investigated for several cell lines. As is to be expected, we find a correlation between both processes, which is in agreement with adsorption-dependent uptake of the polymer microcapsules by cells.

We present a microfabricated chamber designed for visualising and quantifying the chemotaxis of slow-migrating adherent mammalian cells such as cancer and endothelial cells. Most of the existing solutions for the investigation of chemotaxis are limited to fast migrating cells such as leukocytes or Dictyostelium discoideum. Here, we describe the details of an assay using the μ-Slide Chemotaxis to investigate the chemotactic response of human umbilical vein endothelial cells to a gradient of human vascular endothelial growth factor 165. In combination with phase contrast video microscopy and cell tracking, the trajectories of all single cells migrating in temporally stable gradients are derived. The resulting migration data are displayed and analysed in detail by several different parameters for quantifying chemotaxis. We found that with this tool the potential of chemoattractants to migration of mammalian cells as well as the impact of inhibitors to chemotaxis and migration can be evaluated.

Chemotactic cell migration is a central mechanism during cancer cell invasion and hence metastasis. In order to mimic in vivo conditions, we used a three-dimensional hydrogel matrix made of collagen I and a stable gradient-generating chemotaxis assay system, which is commercially available (μ-Slide Chemotaxis) to characterize epidermal growth factor (EGF)-induced chemotaxis of the human breast cancer cell line MDA-MB-231. Surprisingly, chemotactic effects of EGF on MDA-MB-231 cells could neither be observed in the standard growth medium DMEM/F-12 supplemented with 10% serum nor in starvation medium. In contrast, after adapting the cells to the serum-free growth medium UltraCULTURETM, significant chemotactic effects could be measured with high sensitivity. The extremely time-stable linear gradients, generated in the chemotaxis chamber, led to consistent directional migration of MDA-MB-231 cells. Dose-response experiments showed increased directional and kinetic response of MDA-MB-231 cells towards stable gradients of EGF. While EGF-guided directional migration (chemotaxis) was highly concentration-dependent with the highest response at 1.5 nM/mm EGF, we found that the chemokinetic effect induced by EGF was concentration-independent. Both, blocking the ligand-binding domain of the EGF receptor by an antibody (monoclonal anti-EGFR antibody 225) and inhibition of its kinase domain by a small molecule inhibitor (AG1478) led to a reduction in EGF-induced directed migration. The high sensitivity of the assay even allowed us to observe synergistic effects in EGF-receptor inhibition using a combination of low doses of both inhibitor types. Those results validate the fact that EGF is a potent guidance cue for MDA-MB-231 cell migration and help to understand the mechanism behind chemotaxis-driven cancer metastasis.