IACS’s novel compound treats drug-resistant kala-azar infection
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
R. PRASAD
Experimental work undertaken in mice has shown a novel quinoline derivative to be effective in sharply reducing the load ofLeishmania donovaniin 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 theJournal of Medicinal Chemistry.
DNA architecture
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 theLeishmaniaparasites 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 leishmaniathat afflicts the world’s poorest populations in over 90 countries. 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). 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.”
Antileishmanial activity
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.
The derivative was found to generate persistent and less reversible DNA breaks compared with the camptothecininhibitor (discovered in 1966) even after the novel inhibitor identified by the IACS-led team was removed from the culture medium leading to enhanced parasite killing.
Srijita Paul Chowdhuri from IACS and the first author of the paper says: “We have developed a mouse model of kala-azar by infecting the mice with both antimony-resistant and antimony-sensitiveLeishmania donovani parasites in-vivo and have shown that our compound has greater efficiency in clearing the antimony-resistant parasites present in the spleen, liver, and blood of infected mice.”
Prof. Das explains that the novel inhibitor not only clears the parasite burden from the infected mice but also confers a host protective immune response. The latter effect is achieved by up-regulating the Th1 cytokines facilitating parasite clearance. “The up-regulation of the cytokines can be exploited for treating drug-resistant leishmaniasis,” he says.
Prof. Das adds: “Our laboratory data brings new potential for clinical trials of the quinoline derivative in human hosts infected with drug-resistantleishmaniasisin the rural endemic areas without inducing cytotoxic side effects commonly seen with currently available drugs.”
“Collectively, we provide compelling evidence that the novel derivative is a promising anti-leishmaniasis drug candidate to overcome the emerging cases of multidrug resistance and therapeutic failures,” they write. They add that further studies are required to test if the novel derivative develops resistance to anti-leishmaniasis therapy by generating point mutations. Also, further studies are needed to test the drug-resistance potential prior to undertaking clinical trials on humans, they note.
