Hellen Guimarães (Fiocruz News Agency)
Fiocruz, in partnership with the company Microbiológica and the Center of Innovation and Preclinical Studies (CIEnP), is trying to develop an oral antiviral against COVID-19. The substance, named MB-905 by the researchers, was purified from kinetin and has been shown to be effective in inhibiting the replication of Sars-CoV-2 in human liver and lung cell lines, and in helping to halt the inflammatory process triggered by the virus. The research was published in the scientific journal Nature Communications and the pre-clinical dossier of the research was sent to the National Health Surveillance Agency (Anvisa) so that, once approved by the agency, the first phase of clinical trials can begin.
"The idea is that we can then fulfill all the necessary steps for the development of this drug in Brazil, from the planning phase, synthesis, chemical characterization, characterization of the mechanism of action, and the preclinical studies of safety, tolerability, and effectiveness. Our goal is that this substance can become an innovative antiviral, developed in Brazil since its conception, so that we can have more independence in this type of technology that would have high importation costs for the [Brazilian Unified Health System] SUS", explained researcher Thiago Moreno, from the Center for Technological Development in Health (CDTS/Fiocruz), one of the main authors of the study.
It works like this: MB-905 disrupts the virus' genome and causes a catastrophe in the synthesis of its genetic material (RNA), a process crucial for viral replication. The RNA molecule is composed of four bases that need to bind in a certain way (A with U, C with G), but the structure of kinetin is very similar to the A base, which allows an important enzyme in the virus, called viral RNA polymerase, to incorporate kinetin instead of the A base. Kinetin, on the other hand, behaves randomly, sometimes as A, sometimes as G. This creates a big mess in the RNA sequence and induces the virus to several errors during its replication process, generating many particles that are defective and have no replicative capacity, which reduces the overall replication of the virus.
In addition to acting as an antiviral, MB-905 was also able to halt the inflammatory process triggered by coronavirus by decreasing levels of the cytokines IL-6 and TNFα in infected monocytes. According to Moreno, this is key to fighting COVID-19, since the disease not only manifests viral destruction, but often serves as a trigger for an exacerbated inflammatory response in the patient's body. This influenced the research from the starting point.
"We adjusted our substance identification process from a few assumptions: the substance needed to be antiviral; it needed to be antiviral in a target cell, such as cells in the respiratory tract; it needed to function as an antiviral also in cells of the immune system that the virus can invade and destroy, such as monocytes; and it needed to reduce the levels of inflammatory markers associated with a viral infection. We took two of the major pro-inflammatory cytokines to use as indicators, IL-6 and TNFα. With this, we did a screening already oriented to search for substances that could be both antiviral and capable of reducing this inflammatory insult produced by the virus," explained Moreno, detailing how this mechanism works.
"My point is that I am not pursuing an antiviral alone. Like dexamethasone, like aspirin, this product cannot reduce any kind of inflammation, but only selective virus-induced inflammation. We also understand that this can help this substance to potentially have a slightly wider therapeutic window, by perhaps reducing both the antiviral phase and the inflammatory phase associated with the virus," he said.
For the researchers, COVID-19, like other diseases of viral nature, will not be cured with a single drug. They understand that it will be necessary to administer a cocktail of drugs to treat the most severe cases of the disease and those at higher risk, such as patients with comorbidities. Based on the mechanism of action of MB-905, therefore, the group researched which substances could enhance the effect of kinetin. "MB-905 can disrupt the viral genome during RNA synthesis. It turns out that the virus has an enzyme called an exonuclease that can try to counteract this effect, which tries to correct these errors and put the correct bases together in a proper way. But some substances, which are the HIV integrase inhibitors and the inhibitors of a protein called NE5A, used for the treatment of the hepatitis C virus, have an activity against this enzyme that makes the correction of the viral genome. We made trials combining these substances, and these results show a synergy, i.e., they show that if I disrupt the viral genome with MB-905 and I switch off its ability to correct with the inhibitors mentioned, I increase my antiviral effect," Moreno explained.
The study also identifies the advantages of MB-905 over other substances whose clinical benefit has been demonstrated in independent clinical trials. Remdesivir, for example, is injectable, while kinetin will be administered as a pill, enabling the patient to receive the drug as early as possible. As for molnupiravir, MB-905 showed better results in safety tests. Because it disrupts the viral genome without interfering with that of the cell, kinetin was considered safe according to the Ames test.
In addition to being tested on the human liver and lung cells in vitro, the effect of MB-905 in reducing viral load and protecting against lung damage has been reproduced in different animal models. Transgenic mice infected with Sars-CoV-2 expressing human ACE2 (a protein that facilitates coronavirus entry into the cell) and hamsters were protected by MB-905. When evaluated in mice and rats, MB-905 showed more than 50% oral bioavailability (which is the extent and speed with which the drug enters the systemic circulation, thus reaching the site of action).
The data suggest that oral administration of MB-905 leads to the formation of its active metabolite in the respiratory tract to act as a potent polymerase inhibitor, and thus inhibit virus replication. The project was funded by the Ministry of Science, Technology, and Innovations (MCTI), through a technological order to the National Council for Scientific and Technological Development (CNPq) and by the Brazilian Company of Industrial Innovation (Embrapii). It also had the collaboration of the National Cancer Institute (Inca) and the Federal University of Minas Gerais (UFMG).