A small inhibitor identified by researchers from the University of Hyderabad can block an enzyme (Rad51) that plays a crucial role in repairing DNA damage in malaria-causing Plasmodium falciparum. The inhibitor, when used along with anti-malaria drugs such as artemisinin, drastically increases the drug’s effectiveness in both drug-sensitive and drug-resistant malaria.

A small inhibitor that blocks an enzyme (Rad51) that plays a crucial role in repairing DNA damage in malaria-causing parasite — Plasmodium falciparum — has been identified by researchers from the University of Hyderabad.

Both strands of the malaria parasite DNA get broken naturally. When DNA repair is prevented it can lead to the accumulation of several double-strand breaks causing death of the parasites. Also, certain anti-malaria drugs such as artemisinin are designed to kill the parasites by causing such breaks in the DNA. So when the inhibitor is used along with such drugs, the effectiveness of the drugs increases drastically in both drug-sensitive and drug-resistant malaria.

Plenty of DNA double-strand breaks occur naturally in malaria parasites due to errors during replication. Also, when the parasites infect the red blood cells, free radicals are generated (during haemoglobin detoxification). The free radicals produce numerous double-strand breaks.

How the inhibitor improves drug effectiveness

“In an earlier study we found that the parasites use a particular mechanism — homologous recombination — to repair DNA double-strand breaks. In the present study we demonstrated that the inhibitor targets and prevents the Rad51 enzyme from functioning. The Rad51 enzyme is essential for the homologous recombination repair mechanism,” says Prof. Mrinal Kanti Bhattacharyya from the Department of Biochemistry at the University of Hyderabad. Prof. Bhattacharyya is the corresponding author of a paper published in the Journal of Biological Chemistry. The work was done in collaboration with Dr. Sunanda Bhattacharyya from the University’s Department of Biotechnology and Bioinformatics.

The researchers created genome-wide double-strand breaks using a chemical. And they found that in the presence of the inhibitor the parasites were unable to repair the break, leading to death causing death. “The inhibitor blocks DNA repair in both drug-sensitive and drug-resistant malaria parasites,” says Pratap Vydyam from the Department of Biochemistry at the University of Hyderabad and first author of the paper.

Artemisinin drug used for treating malaria is designed to generate more double-strand breaks. Similarly, chloroquine is also thought to produce more double-strand breaks by increasing the generation of free radicals inside red blood cells. “When the inhibitor is used together with the drugs the effect is pronounced leading to sharp reduction in parasite load,” says Prof. Bhattacharyya. “The inhibitor has a synergistic effect and so less concentration of the drugs is sufficient to kill the parasites.”

The inhibitor shows promise

In the case of drug-sensitive malaria parasites, the effectiveness of artemisinin to kill the parasites increases sharply when used together with the inhibitor. The synergistic effect is so pronounced that a 15-fold less concentration of artemisinin is sufficient to kill 50% of parasites. Compared with artemisinin, the synergistic effect of the inhibitor and chloroquine in killing the parasites is relatively less — there is an 8-fold reduction in drug concentration to kill 50% of the parasites.

In the case of drug-resistant parasites, when the inhibitor is used along with chloroquine, 6.48-fold less concentration of the drug is sufficient kill 50% of parasites, while it is only 4.6-fold reduction when the inhibitor is used together with artemisinin.

“Reducing the concentration of drug used for treating a disease is desirable. So achieving several-fold reduction in the concentration of the drug to kill the parasites in the presence of the inhibitor, we have enhanced the effectiveness of the drugs,” says Prof. Bhattacharyya. “Importantly, we have increased the effectiveness of the drugs even in the case of drug-resistant malaria parasites.”

There is increasing prevalence of malaria parasites that are resistant to artemisinin, a first-line drug. So increasing the effectiveness of this drug becomes particularly important.

“This compound selectively blocks the repair of Plasmodium genome compared to the genomes of mouse or human. This could be a new hope for malaria treatment,” he says. The researchers will soon start testing the inhibitor on mouse malaria model.

Published in The Hindu on June 7, 2019