Precision flow control comes to the aid in basic cancer research

November 23, 2017 Prof. dr. Kees Jalink
NKI composite living cells
Photo Jalink Group / NKI, Amsterdam

“A main aim in basic cancer research is to unravel the differences between normal cells and cancer cells. These differences might then be exploited in the hunt for specific cancer vulnerabilities: any trade that is exclusive for cancer cells might give us leads on how to attack cancer cells while leaving healthy cells untouched”, explains Prof. dr. Kees Jalink of The Netherlands Cancer Institute in Amsterdam (NKI).

Today Prof. dr. Kees Jalink shares his story about the research the ‘Biophysics and Advanced Imaging Group’ the NKI (The Netherlands Cancer Institute) is working on and the role of flow meters and controllers in their research.

Prof. dr. Kees Jalink (NKI Amsterdam)
Prof. dr. Kees Jalink (NKI Amsterdam)

Biophysics and Advanced Imaging Group at the NKI

Unraveling these differences between normal cells and cancer cells has proven a difficult task because most cancer cells are for 99.9% like healthy cells. In the Biophysics and Advanced Imaging Group, we zoom in on cells using advanced microscopy techniques, including live-cell imaging, fluorescence microscopy and “functional imaging” techniques. In the latter, tricks like Fluorescence Resonance Energy Transfer (FRET), Fluorescence Recovery After Photobleaching (FRAP) and Fluorescence Correlation Spectroscopy are used to extract information about proteins (biomolecules) and their interactions in single living cancer cells.

Living cells yield much more information

Not too long ago, for visualization by high-resolution microscopy, cells were typically killed, fixed, stained for specific components and embedded in resin. However, imaging living cells yields much more information:

  • living cells may go through division
  • migrate
  • interact to form tight monolayers just like living (cancer) cells in our body. Only with living cells, we can get a grasp of the dynamics of the internal biochemical processes.

A whole range of colored Fluorescent Proteins (picture 1) are available that enable us to label a single protein species and learn what we want to know about that protein. The trick is, to keep those cells alive and healthy on the microscope.

On the microscope, cells are kept in a glass bottom dish filled with DMEM medium: a bloodplasma-like salt solution with vitamins and nutrients. In the early days, we just kept them at room temperature in dishes in free air (~20 % O2, 80 % N2, 0.05% CO2). However, that does not mimic the atmosphere in our bodies at all, and consequently, results were not as expected.

NKI cells through microscope
A two-color photomicrograph of a few cells through the microscope

For example, cells typically refused to divide and most cells died after 1-2 days. Also, control of pH in the medium appeared next-to-impossible. Therefore we needed to set up a dedicated incubator that houses the cells and most of the microscope. In this incubator, the air needs to be warmed to 37°C, moisturized and the atmosphere must be different from air:

  • it must contain at least 5% CO2
  • and the % of oxygen must be adjusted between ~2 % and 20%

This is to resemble the various oxygen tensions encountered in the body. For example, solid tumours are well known to be hypoxic (contain less than a few % of O2) and this completely alters the physiology of the cells, as well as their response to anti-cancer drugs.

bronkhorst uflow flow meter
Bronkhorst instruments in experimental setup

But how to achieve precise atmospheric control?

At a exhibition we learnt about Bronkhorst and their mass flow meters and controllers. With assistance of Bronkhorst Nederland, we have chosen three thermal mass flow controllers of the EL-FLOW Select series and hooked them up to the outlets of compressed CO2, N2 and air present in our lab.

The rest was simple: by adjusting the relative gas flows with the mass flow controller, we can now set CO2, N2 and O2 levels to all the relevant values. These ranges are 2-19 % for oxygen, 0-20 % for CO2 and 80 – 100% for nitrogen.

Ever since, we have carried out all our experiments under such controlled conditions and the results have been much more consistent -and also much more relevant- due to this incubator. We have used it to investigate how cancer cells migrate during metastasis and how they can penetrate layers of other cells and survive in this ‘niche’. We also used it to explore how cells use chemical signals to communicate with each other, and how these signals are received and subsequently processed within the cells, in detail.

The µ-Flow liquid mass flow controller comes to the rescue

As it goes in science, solving one problem led to the identification of another. We noted that at 37°C, the medium evaporated more rapidly, leaving the cells dry after a few days unless we tightly closed the imaging dish. But that restricts access to the cells, it makes it impossible to add growth factors, hormones or cancer drugs for our studies during the experiment.

Moisturizing the air only partly solved that, because at high humidity, condensation formed that might damage the sensitive electronics in our setup, and we therefore had to remain below 60 % relative humidity. Again, mass flow controllers provided a simple and reliable solution. We selected a µ-FLOW mass flow controller for liquids to supply a very stable flow of deionised water. Using a local BRIGHT controller with PiPS (Plug-in Power Supply) allowed us to control water influx between 0.5 and 9.6 microliter per minute.

Empirically we found that with the valve adjusted to 1.3 ul/min, we completely compensated for evaporation, and we are now capable of keeping cells alive for weeks on the microscope. The system has been very-low maintenance: simply install, and forget about it, so that we can focus on our core business. The mass flow controllers have been pivotal in constructing the microscope incubator, and the cells, they divide and develop happily.

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