It was able to kill the disease parasite in tests carried out on mice and in cultivation vitro
In tests carried out on mice and in cultivation vitro, a molecule designed at the Center for Research and Innovation in Biodiversity and Drugs (CEPID-FAPESP) was capable of killing the malaria parasite (image: CIBFar)
A new molecule, synthesized in the laboratory, appears as a strong candidate for the development of a drug against malaria. The possibility of a new medicine brings hope to thousands of patients infected with the Plasmodium falciparum, one of the protozoa that causes malaria, mainly due to the fact that tests showed that the molecule was capable of killing even the strain resistant to conventional antimalarials.
The molecule has low toxicity and high selectivity, acting only on the protozoan and not on other cells in the host organism. It is derived from the class of marinoquinolines, with outstanding biological activity, and was developed at the Center for Research and Innovation in Biodiversity and Pharmaceuticals (CIBFar) – a Research, Innovation and Dissemination Center (CEPID) financed by FAPESP. The study also received financial support from the National Council for Scientific and Technological Development (CNPq) and the Serrapilheira Institute.
In an article published in Journal of Medicinal Chemistry, the researchers describe the inhibitory action of the molecule on the blood and liver phase of the protozoan asexual cycle, responsible for the signs and symptoms of the disease.
In addition to the studies carried out with cultivation strains vitro, the researchers also tested the molecule in mice. “In the tests, on the fifth day of the study, the molecule managed to reduce the number of parasites in the blood (parasitemia) by 62%. At the end of the 30 days of testing, all mice that ingested doses of the molecule survived,” he said. Rafael Guido, professor at the São Carlos Institute of Physics (IFSC) at the University of São Paulo (USP) and one of the authors of the article, at FAPESP Agency.
The tests were carried out on an animal model infected by p. berghei, since the falciparum does not infect mice.
Inspiration from the sea
The candidate molecule to become a drug was synthesized based on natural compounds found in marine bacteria, known as marinoquinolines, which were evaluated when discovered against malaria, Chagas disease and tuberculosis. However, natural products only showed moderate to weak action against pathogens.
“The nucleus of these molecules, known as pyrroloquinoline [which contains the 3H-pyrrolo[2,3-c]quinoline nucleus], caught our attention. This is a rare structure among natural products and little addressed in the scientific literature,” he said. Carlos Roque Duarte Correia, professor at the Chemistry Institute of the State University of Campinas (Unicamp).
In 2012, the group of researchers from Unicamp published one of the first syntheses of natural marinoquinolines in the literature.
“During the synthesis work we realized the enormous pharmacological potential of these molecules. We then made new structural modifications to the pyrroloquinoline part, using efficient catalytic processes, and from the structure obtained we created a new molecule with potency increased hundreds of times against the falciparum and without increasing its toxicity”, said Guido.
Duarte Correia says that, in the study, the first 50 molecules developed from marinoquinolines were tested. “This work, however, does not stop at this publication. We still have a number of other compounds being developed,” he said.
The group is also characterizing the potential of this class to treat malaria caused by plasmodium vivax, the most prevalent form of malaria in Brazil, and is developing the pharmacokinetics part of the project – the body's reaction to the medicine.
“If the properties of the compound, such as solubility, absorption, distribution, metabolism and excretion, are not adequate, it can accumulate in the body and become toxic to the patient, which would make the medicine unviable. After we finish this stage, our goal is to carry out pre-clinical and clinical tests”, said Guido.
Starving
The molecule's mechanisms of action are not yet fully known. It is known, however, that among them is a classic parasite inhibition pathway, known as hemozoin metabolism.
This strategy consists of keeping the concentration of this compound, which is toxic to the parasite, low. When the parasite settles in the host, it first infects the red blood cells (red blood cells), as the hemoglobin present in these cells is the only source of energy it has to consume. But hemoglobin contains a cofactor molecule linked to its structure called the heme group, which in free form – when it is disconnected from hemoglobin – is highly toxic to parasites.
Years of evolution have given the parasite the ability to develop a mechanism that polymerizes this group, thus freeing itself from its toxicity. “This parasite strategy of obtaining energy without becoming intoxicated works more or less like sweeping the dust under the rug. The heme group is still there, but in a polymerized and insoluble form that is not toxic to the parasite,” said Guido.
The molecule developed by the CIBFar research group acts, among other mechanisms, to prevent this polymerization and, thus, the parasite is intoxicated by the heme group.
“The molecule works by preventing the formation of the hemozoin polymer, which is the form that the parasite developed to free itself from the toxicity of the heme group. By preventing the formation of hemozoin, the parasite dies,” he said. Celia Regina Garcia, professor at the Faculty of Pharmaceutical Sciences at the University of São Paulo and also author of the article. Garcia worked in partnership with CIBFar and was responsible for testing the molecule's mechanism of action on the parasite.
Resistant strains
Another indicator that the marinoquinoline derivative is a strong drug candidate is the fact that it can kill strains resistant to three of the main anti-malaria drugs: chloroquine, pyrimethamine and sulfadoxine.
“Chloroquine has been little used to treat falciparum malaria, the malaria responsible for the most serious and fatal cases of the disease, and the expectation is that artemisinin will follow the same path. Currently, artemisinin is the main drug in use for the treatment of malaria. Although still effective, it is a drug that is out of date due to resistance, and these resistant strains are spreading throughout Asia. There is, therefore, a global concern in developing drugs for malaria and I think that Brazil is a country that has the potential to emerge in this area”, said Garcia.
According to data from the World Health Organization (WHO), malaria now kills 445 people a year. “If today, with effective medicine, we have such a high number of deaths, if there is no development of new drugs in the future, malaria could kill many more. It is the parasite that kills the most in the world, even though it currently has relatively effective treatment,” said Guido.
THE ARTICLE
The article Discovery of Marinoquinolines as Potent and Fast-Acting Plasmodium falciparum Inhibitors with in Vivo Activity (doi: 10.1021/acs.jmedchem.8b00143), by Anna Caroline Campos Aguiar, Michele Panciera, Eric Francisco Simão dos Santos, Maneesh Kumar Singh, Mariana Lopes Garcia, Guilherme Eduardo de Souza, Myna Nakabashi, José Luiz Costa, Célia RS Garcia , Glaucius Oliva, Carlos Roque Duarte Correia and Rafael Victorio Carvalho Guido, can be read at Journal of Medicinal Chemistry em https://pubs.acs.org/doi/10.1021/acs.jmedchem.8b00143 .