A recent study by the University of Bonn and the University Hospital Bonn has revealed a new mechanism to inhibit the human P2X4 receptor, which is associated with chronic pain, inflammation, and certain cancers. The findings were published in Nature Communications.
The P2X4 receptor is located in the membrane of many cells and acts as a gateway that allows calcium and sodium ions into cells when activated by ATP. This activation can lead to immune responses or pain signals. Pharmaceutical companies have been seeking ways to block this receptor, but only a few inhibitors have been identified so far.
One such inhibitor is PSB-0704, an anthraquinone derivative developed at the University of Bonn. "We wanted to find out what it actually does and at the same time use this knowledge to help in the development of better drugs," said Müller, a researcher involved in the study.
The research team used cryogenic electron microscopy (cryo-EM) after being unable to crystallize the receptor with its inhibitor. Dr. Jessica Nagel, lead author of the publication, explained: "For this method, we produced a solution of the P2X4 receptor and the anthraquinone derivative PSB-0704 and then snap froze it. The resulting film of ice contains millions of receptor molecules together with the bound inhibitor, which we can examine under an electron microscope."
By analyzing these images with colleagues from University Hospital Bonn, including Dr. Gregor Hagelüken from its Institute of Structural Biology, researchers were able to produce detailed 3D models showing how PSB-0704 interacts with P2X4.
"When the inhibitor bonds, it causes parts of the P2X4 molecule to move so that it is no longer possible to open the ion channel," said Nagel. As a result, even if ATP binds to P2X4, it remains closed.
However, PSB-0704 only inhibits effectively at high concentrations because it does not fit well into its binding pocket on P2X4—a limitation caused by a molecular structure described as a "rubber band." Nagel added: "We have developed a receptor without this rubber band... And the PSB-0704 inhibitor was almost 700 times more potent as a result."
Müller noted that these insights could inform future drug design: "On the one hand, we can try to design drugs that cut through the molecular rubber band before they bind with the P2X4 receptor... An alternative would be to search for smaller molecules that can fit more easily into the binding pocket."
The research builds on earlier work led by Dr. Stephanie Weinhausen and Dr. Vigneshwaran Namasivayam over ten years ago. While promising for new therapies targeting chronic pain or inflammation via P2X4 inhibition, Müller cautioned: "Nevertheless, our joint study has now provided the basis upon which we could successfully achieve this goal."
In addition to teams from Bonn’s university institutions, LMU Munich and Cube Biotech participated in this project. Funding came from organizations including Germany’s DFG (German Research Foundation), BMFTR (Federal Ministry of Research, Technology and Space), and DAAD (German Academic Exchange Service).
