Hundreds of cells are being intoxicated daily in laboratories all over the world. One of the main reasons is researchers trying to observe them under their microscope. To do so, they label different parts of the cell with fluorescent colors, but these “labels” disturb the inner workings of the cells.

Scientists are working on the creation of new and safer labels that allow them to monitor those cells without negatively influencing them.

‘We are currently applying it to understanding how vaccines are processed by the immune system. These small labels make this possible for the first time’, says Sander van Kasteren, associate professor in chemical immunology. ‘With this information we aim to develop vaccines with improved immune activating properties.’

Improvements of vaccines

Research done using those labels is showing potential for medical applications. These range from chemotherapy to testing of new medicines, as well as improvements of vaccines.

To visualize cells and detect the presence and position of certain molecules within those cells, scientists commonly use fluorescent proteins, that will attach themselves to the target of choice. The issue with this technique is that these labels are big and bothersome for the cell or molecule they attach to, and potentially toxic as the target might just stop working entirely. This means that the technique only allows researchers to observe a limited number of molecules and processes in dead cells.

Scientists have been trying for a long time to invent new labels that can be applied to living cells and organisms without being toxic to them. The new group of non-toxic labels that followed this non-toxicity rule have been termed “bioorthogonal”.

‘A lot of new labels are becoming available that allow the use of this chemistry in complex systems. You can now even do this in live animals!’ explains van Kasteren. These labels are much smaller than fluorescent proteins, so that they don’t bother their target molecule in its usual activity. In van Kasteren’s own words, ‘think of it as a soldier running with a small rucksack, rather than a 50-kilogram pack on his back’.

“dark” molecules

Many new target molecules become accessible when using bioorthogonal labels. This specificity means that these labels show much promise for application in the future according to van Kasteren. ‘This will allow us to look in new ways at biological and medical problems for which previously we simply did not have the ability to follow the molecules that are key players in these problems. Examples are molecules such as lipids that make up fuel and membranes, and sugars that coat the cell. The new non-toxic labels are allowing us to “see” those for the first time and teaching us how important these “dark” molecules really are in biology.’

How do we get from observing live molecules to inventing new drugs and treating cancer? The study of bacteria labelling by Thomas Bakkum, a PhD candidate at Leiden University, shows us a good example. In his thesis, he studied the tracking of bacteria within immune cells, part of our body’s defense system, and specialized in destroy foreign objects and proteins in the body, including bacteria.

Bakkum explains that the typical fluorescent proteins wouldn’t last very long in these cells before also being destroyed, making the bioorthogonal labels, undetectable to the immune cell, essential to this research. This means that observing the path of the bacteria from their entry into the immune cell, until their eventual demise, was possible.

Life cycle

Getting a better picture of the bacteria’s life cycle can only be medically advantageous according to Bakkum and van Kasteren. Bakkum could then observe the bacteria using different drugs and see how they would behave, how fast they would be destroyed, and so evaluate the capabilities of the drug. ‘Infectious bacteria are difficult to study due to their complex biological behavior. Seeing what they are doing when they are hiding inside a cell will hopefully allow us to better understand how to drug these bacteria when they are in hiding’, says Van Kasteren

In his research, Bakkum also successfully attempted to create bioorthogonal labels for tuberculosis-causing bacteria, tracking them and testing them with antibiotics as well. His thesis focused on the fundamental label creation, yet his findings could definitely have practical uses in developing new medicine against tuberculosis.

But this also doesn’t mean that these labels are optimal in all cases. Bioorthogonal labels require extra steps compared to other labels that means the whole tagging process could take Bakkum up to a month. According to him, bioorthogonal labels would consequently be useless for determining which disease a patient has for example, where the test is performed on a sample extracted from the body (e.g., saliva) and the bacteria do not need to be kept alive.

This does not limit the medical uses of bioorthogonal labels to drug testing. Despite not being useful for diagnosing diseases, it can still help in treating them. Cancer treatment could notably benefit from this technique. Since they are not toxic, the labels can already be used in live mice, where they will specifically target cancer cells, and detecting them using X-ray imaging will then show the exact location of tumors.

Greater precision

Applying the same process in humans could greatly help doctors find and remove tumors with greater precision. The same cancer cells can also be treated with toxins. These can be dangerous to other cells in our body, but binding them to a bioorthogonal label can shut them off and bring them along to the cancer cells, where a second solution can be injected to turn the toxins on and attack the cancer cells

A lot of these medical usages are still early in their development, but the researchers are optimistic about its future. As Van Kasteren states: ‘It is my dream that the technique will contribute to the development of better drugs for tuberculosis. We are still many steps off, but slowly people in the field are beginning to edge closer to the diagnosis of live and dead bacteria. This is the first key step in figuring out whether a new drug is actually working.’

The continuous invention of those new labels will hopefully save many laboratory cells from intoxication in the future.