Anticoagulant Apixaban inhibits COVID-19 replication

Published in the Journal of Molecular Cell Biology, a Fiocruz study proves that Apixaban, an oral anticoagulant, effectively inhibits the replication of the Sars-CoV-2 virus, which causes COVID-19. This type of drug had already been recommended to prevent high levels of D-dimer, the final product of the coagulation cascade and directly related to severe COVID-19. Fiocruz researchers, however, discovered that the drug also has an antiviral function, as it inhibits virus replication in a non-competitive fashion. This is thanks to a structural similarity between Factor X Activated (FXa), crucial for the coagulation process, and Major Protease (Mpro), a crucial enzyme for coronaviruses.

“The use of anticoagulants helps prevent severe COVID, and we were focused on discovering whether there were additional mechanisms for this clinical benefit. When you overlap images of FXa and Mpro, you can see they have a structural correlation. So, we asked ourselves whether anticoagulants could also inhibit the viral enzyme. This paper shows that they can, and describes how the mechanism works, proving that this antiviral activity can also be helping, to a certain degree, with the clinical benefit these patients have”, explained researcher Thiago Moreno L. Souza, one of the authors, from the Center for Technological Development in Health (CDTS/Fiocruz).

The drug can inhibit the action of Mpro and, as a consequence, virus replication, by means of non-competitive inhibition. During the replication process, the Mpro must break the non-structural proteins of the virus, called substrate. Apixaban does not prevent the interaction between Mpro and substrate, but considerably reduces the speed of these breakages, causing the enzyme to fail in its role, in the presence of the drug. Instead of preventing the bond between substrate and the active site of the enzyme, the drug binds to another site. This process is called “non-competitive” because inhibitor and substrate can be bound to the enzyme at the same time.

“It works like pruning. The viral protease plays a fundamental role during the life cycle of the virus, because it trims its non-structural proteins so they can mature. This maturation, which takes place thanks to the action of the Mpro, allows other stages of virus replication to occur. Oral anticoagulants do not prevent the Mpro to interact with the substrate, but they work on another region of the enzyme, removing it from its direction and preventing it from doing its job. This is why we say that Apixaban does not compete with the substrate. Instead, it prevents these proteins from being “pruned”, and it is this pruning, this trimming, that allows them to mature so they can work”, Moreno detailed.

From among the anticoagulants under study, Apixaban was the most effective in inhibiting the activity of the Mpro. It proved to be 21 more powerful than GC 376, a well-known Mpro inhibitor, used as positive control group (the group that works as comparison for the treatment of what is being tested). Another Fxa inhibitor under study, rivaroxaban, and a thrombin inhibitor, dabigatran, were just as powerful as GC 376.

Researchers recommend that the chemical structure of Apixaban be evaluated more thoroughly so researchers can have a more accurate understanding of how it associates itself to the enzyme-substrate complex. It can therefore work as a starting point for the development of non-competitive Mpro inhibitors that preserve their anticoagulant activity and, in the future, of specific anti-COVID-19 antiviral drugs.

“Oral anticoagulants are relatively new in internal medicine; this kind of treatment used to be more frequently employed as injectable drugs. Studies against COVID-19 have been using many classes of anticoagulants. We have tested all oral ones. We realized that the best substance was Apixaban, and this can motivate other studies, in vivo and clinical ones, to evaluate whether it should be prioritized when compared with other anticoagulants in the treatment of COVID-19”, he concluded.