IACS’s novel compound treats drug-resistant kala-azar infection Premium

Current annual estimates of kala-azar are about 1,00,000, with more than 95% of cases reported to WHO from India and other tropical countries

Experimental work undertaken in mice has shown a novel quinoline derivative to be effective in sharply reducing the load of  Leishmania donovani in both the spleen and liver of lab-grown mice. The highlight of the work carried out by researchers at the Kolkata-based Indian Association for the Cultivation of Science (IACS) is the potential of the quinoline derivatives to treat drug-resistant leishmaniasis, also called kala-azar (black fever).

The work was published recently in the  Journal of Medicinal Chemistry.

The quinoline derivative is a potent inhibitor of an enzyme called topoisomerase 1 (LdTop1), which is essential for maintenance of DNA architecture in the parasites; this enzyme is distinct from the one found in humans. Poisoning of LdTop1 imparts a significant level of cytotoxicity to both the  Leishmania parasites found in gut of sandfly vectors (promastigotes) as well as the form found in the infected humans (amastigotes) of both the wild type and the antimony-resistant isolates without inducing any lethality to human and mice host cells.

Kala-azar is a vector borne (sandfly) neglected tropical disease caused by the protozoan parasites of the genus leishmania that afflicts the world’s poorest populations in over 90 countries throughout Asia, Africa, the Middle East, and Central and South America. Current annual estimates of kala-azar are about 1,00,000, with more than 95% of cases reported to the World Health Organization (WHO) from India and other tropical countries, most importantly co-infection with HIV, which leads to an immunocompromised state. 

The four States endemic for kala-azar in India are: Bihar (33 districts), Jharkhand (4 districts), West Bengal (11 districts), and Uttar Pradesh (six districts). Overcoming drug resistance in clinical leishmaniasis is a severe challenge in rural India. The current treatment regimens against kala-azar use formulations that are toxic and induce high levels of drug-resistance.

“Since the enzyme is essential for parasite replication and transcription from DNA to RNA, inhibition of its activity leads to DNA torsional strain, degradation of the DNA, and ultimately parasitic cell death,” says Dr. Benu Brata Das, Professor at the School of Biological Sciences, IACS, and the corresponding author of the paper. “The host human counterpart enzyme is not sensitive to the selected antileishmanial-quinoline derivatives, and is well tolerated in mice and mammalian cell lines tested in our laboratory. This promises minimal side effects in patients.” 

The novel inhibitor targeting the leishmania parasites was identified by screening them against recombinant Leishmania topoisomerase 1 enzyme. The molecules were synthesised by Prof. Anil Kumar and his group from the Department of Chemistry, Birla Institute of Technology and Science, Pilani. In all, 21 derivatives were prepared and evaluated for their antileishmanial activity, and one of them was found to be effective.