Researchers develop artificial building blocks of life

The DNA carries the genetic information of all living organisms and consists of only four different building blocks, the nucleotides. Nucleotides are composed of three distinctive parts: a sugar molecule, a phosphate group and one of the four nucleobases adenine, thymine, guanine and cytosine. The nucleotides are lined up millions of times and form the DNA double helix, similar to a spiral staircase. Scientists from the UoC's Department of Chemistry have now shown that the structure of nucleotides can be modified to a great extent in the laboratory.

The researchers developed so-called threofuranosyl nucleic acid (TNA) with a new, additional base pair.

These are the first steps on the way to fully artificial nucleic acids with enhanced chemical functionalities.

The study 'Expanding the Horizon of the Xeno Nucleic Acid Space: Threose Nucleic Acids with Increased Information Storage' was published in the Journal of the American Chemical Society.

Artificial nucleic acids differ in structure from their originals.

These changes affect their stability and function. "Our threofuranosyl nucleic acid is more stable than the naturally occurring nucleic acids DNA and RNA, which brings many advantages for future therapeutic use," said Professor Dr Stephanie Kath-Schorr.

For the study, the 5-carbon sugar deoxyribose, which forms the backbone in DNA, was replaced by a 4-carbon sugar.

In addition, the number of nucleobases was increased from four to six.

By exchanging the sugar, the TNA is not recognized by the cell's own degradation enzymes.

This has been a problem with nucleic acid-based therapeutics, as synthetically produced RNA that is introduced into a cell is rapidly degraded and loses its effect.

The introduction of TNAs into cells that remain undetected could now maintain the effect for longer.

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Sugar molecules as a target in cancer therapy

Cancer cells use sugar molecules on their surface to disable attacks by the body's immune system. Researchers at the University of Basel now report on how this mechanism can be neutralized.

The immune system is actually extremely well equipped to get rid of abnormal cells. As a safety mechanism, special features are built into healthy cells so that the immune system recognizes them, thus preventing a mistaken attack. However, cancer cells sneakily manipulate these safety mechanisms in such a way that the immune system leaves them alone.

Over the past few years, immunotherapies have revolutionized cancer treatment. These include therapies that prevent cancer cells from inhibiting the immune response. This involves blocking what are known as "immune checkpoints" using artificially produced proteins, which allows the immune cells to successfully attack the cancer cells.

"With many tumors, however, there have only been modest levels of success. That's why we're looking for new approaches to engage anti-tumor immune responses more efficiently," explains Professor Heinz Läubli from the Department of Biomedicine at the University of Basel and the University Hospital Basel. In the specialist journal Science Translational Medicine, his team, together with that of recent Nobel laureate Professor Carolyn Bertozzi from Stanford University, reports on a promising new approach. By altering sugar molecules on the surface of cancer cells in mice, the researchers were able to produce a significant increase in anti-tumor immune response.

How immune cells turn traitor

Their focus is on sugar molecules on the surface of the cancer cells, as well as on the cells in their immediate vicinity. These particular sugars, which contain sialic acid, also occur on healthy cells, and are important for cell-to-cell communication. However, tumors boost the proportion of these sugars on their surface.

Certain immune cells called macrophages recognize these sialic acid sugars and inadvertently turn traitor: they give other nearby immune cells the impression that all is well. The research team's experiments on mice have now been able to demonstrate that the sialic acid sugars can be removed, or at least very much reduced, with the help of an enzyme. This means that the macrophages no longer prevent the tumor coming under immunological attack.

A target structure for new therapies

More precise analyses have enabled the researchers to identify in mice exactly which receptor it is on the macrophages that recognizes the sialic acid sugars. If the equivalent receptor could be identified in humans, then that could be another interesting target in the bid to tackle cancer cells with the aid of the patient's own immune system.

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