Development of conformation-specific furin inhibitors

Enzymes are proteinaceous molecules involved in many vital processes in our body cells. The concerted actions of thousands of enzymes ultimately build up the basis of a functioning organism. Some enzymes act like conductors in this orchestra of molecules, making sure that the members of the ensemble are used in the right place. For instance the so called proprotein convertases can turn other enzymes on or off and thus act as molecular switches. The switching mechanism, however, is irreversible. In particular, hyperfunction of the proprotein convertases may disrupt the functional processes in the cells, which can cause the development of fatal diseases like cancer. Pathogens also utilize the proprotein convertases of their host cells. Many viruses, such as the influenza virus, the measles virus or the Ebola virus, need the switching mechanism for propagation. Furin, a specific representative of proprotein convertases, plays a special role in this process. Because Furin is present in all cell types, it enables the highly dangerous viruses to spread quickly throughout the body. Due to its universal occurrence, exaggerated furin activity can also be detected for many cancers types including malignant tumors of the skin, lung, breast, brain and intestine. Because of its important role in many diseases, furin is an attractive target molecule for the development of pharmaceuticals. Therefore, the aim of the herein described research project is the development of substances that slow down the switching mechanism of furin. Such enzyme brakes are also referred to as inhibitors. Only furin, but no other proprotein convertase must be slowed down by this approach. A general inhibitor of the whole enzyme family would impair the function of the cells and would thus lead to undesired side effects. To achieve this goal, we want to use state-of-the- art drug discovery technology. An important part of the project will be the initial search for substances that are suitable as inhibitors. Usually thousands of different substances are randomly tested for their effectiveness in high throughput approaches, like looking for a needle in a haystack. Within the framework of this project, an alternative search strategy will be applied, which is based on X-ray crystallography. This technique facilitates to visualize molecular details of the furin molecule, in the range of a millionth of a millimeter in size. It will be possible to judge directly based on the molecular image whether a particular component is suitable as a selective furin inhibitor. Due to the high effectiveness of this method, the search for substances can be accelerated and thus the development of new drugs is faster in the end. In addition, completely novel compound classes may be discovered. 1

Enzymes are proteinaceous molecules involved in many vital processes in our cells. The concerted actions of thousands of enzymes ultimately build up the basis of a functioning organism. Some enzymes act like conductors in this orchestra of molecules, making sure that the members of the ensemble are used in the right place. For instance the so called proprotein convertases can turn other enzymes on or off and thus act as molecular switches. This mechanism, however, is irreversible. In particular, hyperfunction of the proprotein convertases may disrupt the functional processes in the cells, which can cause the development of fatal diseases like cancer. Pathogens also utilize the proprotein convertases of their host cells. Many viruses, such as the Severe Acute Respiration Syndrome Corona Virus 2 (SARS-CoV-2) or bird-flu influenza viruses, need the switching mechanism for propagation. Furin, a representative of the proprotein convertase family of enzymes, plays a special role in this process. Because furin is present in all cell types, it enables the highly dangerous viruses to spread quickly throughout the body. Because of its important role in many diseases, furin is an attractive target molecule for the development of pharmaceuticals. In this research project we have development of substances that slow down the switching mechanism of furin. Molecules with the ability to slow enzyme down, are also referred to as inhibitors. However, we intended to identify molecules that only target furin, but preferably no other member of the enzyme family. A general inhibitor of the whole enzyme family could impair the function of the cells and might thus lead to undesired side effects. To achieve this goal, we applied a state-of-the-art drug discovery method called crystallographic fragment screening. An important part of the project was the initial search for substances that are suitable as inhibitors. Usually thousands of different substances are randomly tested for their effectiveness in high throughput approaches, like looking for a needle in a haystack. Differently, the X-ray crystallography-based approach enabled us to visualize molecular details of the furin molecule, in the range of a millionth of a millimeter in size. Based on the molecular image we were able to judge whether a tested molecule was suitable as a furin inhibitor. Due to the high effectiveness of this method, we could not only significantly speed up the search for new substances. We have also succeeded in developing completely new types of substances that preferentially recognize certain structural features of furin and can slow it down more selectively. Such furin inhibitors might be applied for the treatment of several diseases such as many viral infections, cancer, rheumatoid arthritis and cystic fibrosis.