An international group of researchers has proven that a molecule called TCMDC-135051 is capable of selectively inhibiting a protein essential for the life cycle of Plasmodium falciparum, one of the species that causes malaria.
The results of the study, published this Friday (30/8) in Science, pave the way for the development of a new drug against the disease, which has 200 new cases and kills almost half a million people worldwide annually. One of the obstacles to eradicating malaria today is the fact that the parasite has acquired resistance to existing medications.
Among the authors are members of the Center for Medicinal Chemistry (CQMED), based at the State University of Campinas (Unicamp), under the coordination of professor Paulo Arruda, and supported by FAPESP through the Partnership for Technological Innovation Program (PITE). The group is part of the Structural Genomics Consortium (SGC) network – an international consortium of universities, governments and pharmaceutical industries to accelerate the development of new medicines. CQMED is also an Innovation Unit of the Brazilian Industrial Research and Innovation Company (Embrapii).
Synthesized by the pharmaceutical company GSK, the TCMDC-135051 molecule showed specific action on the protein kinase PfCLK3 (acronym for cyclin-dependent–like kinase), without affecting human proteins.
“Inhibition of PfCLK3 affects the parasite at different stages of development – both in what we call the asexual phase, when it proliferates inside the human cell and causes symptoms, and in the sexual phase, when it can be transmitted back to the insect vector and completes its cycle, being able to infect other human beings”, said Paulo Godoi, who carried out the work during his post-doctorate at CQMED.
Also participating in the study was Dev Sriranganadane, who is currently undertaking a postdoctoral internship at the same center. The research was coordinated by Andrew Tobin, from the University of Glasgow, in Scotland.
“The Unicamp group played an essential role in this project. They were able to answer whether our drug could have effects other than inhibiting PfCLK3. Without this information, we would not have been able to continue with the study,” Tobin told Agência Fapesp.
As parasites of the genus Plasmodium are becoming increasingly resistant to existing antimalarial drugs, there is a growing concern to find new compounds with the potential to be transformed into pharmaceuticals.
“This PfCLK3 inhibitor is very promising, as it is capable of eliminating the parasite at all stages of its life cycle,” said Godoi.
PfCLK3 controls the activity and production of other proteins important for maintaining the parasite's life. By blocking its activity, the molecule kills P. falciparum and not only prevents transmission but can treat the disease in humans.
TCMDC-135051 was selected among 24.619 molecules that could have an effect on PfCLK3 and was the one that showed the greatest specificity on the parasite protein.
The study also suggests that the molecule has action on other species of Plasmodium. According to Godoi, the compound was tested in vitro against the CLK3 enzymes of the species P. vivax and P. berghei and in cell cultures of P. knowlesi (similar to P. vivax) and P. berghei, showing activity for both species.
"A test was also carried out on mice infected with P. berghei. The in vivo result showed elimination of the parasite in the bloodstream after five days of infection," he said.
Brazilian contribution
To be considered safe, a candidate molecule to become a drug cannot interfere with human proteins. Both parasites of the genus Plasmodium and humans have kinase-type enzymes. The human kinase most similar to the Plasmodium PfCLK3 protein is PRPF4B. Therefore, to prove that the TCMDC-135051 molecule is safe, Tobin contacted the CQMED group, one of the few that studies the function of human PRPF4B.
“We put PRPF4B to interact with different concentrations of the new molecule. And even the highest of them was not able to inhibit the human enzyme,” said Godoi.
To ensure that the molecule would be safe for a future medicine, the researchers needed to prove that it would not affect the activity of proteins important for the functioning of the human body.
“We decided to bet on a little-studied protein and now we have reaped the rewards: making this study possible with great potential for a new medicine,” said Rafael Couñago, scientific coordinator at CQMED.
To become a drug, however, the inhibitor still needs to undergo new tests. “We need to further improve the safety of the molecule and then it will be ready for human testing. This stage should take three to five years,” said Tobin.
Read the article Validation of the protein kinase PfCLK3 as a multistage cross-species malarial drug target published in Science on August 30.
