Unveiling the mechanism of hesperidin-induced LdTopI-mediated cell death pathway in protozoan parasite Leishmania donovani.

Unicellular protozoan parasite Leishmania donovani is the causative agent for visceral leishmaniasis (VL) or Kala-azar, a neglected fatal parasitic disease. The conventional treatment of VL consists of therapeutic agents having several shortcomings such as toxicity, high cost, efficacy variance and increased drug resistance. Therefore, there is a desperate need to develop an effective treatment against the parasite. Previous reports suggested that flavonoids can inhibit the enzyme Leishmania donovani DNA topoisomerase I (LdTopILS). Therefore, for the first time in this present study, we divulge HSP (one of the natural sources of flavonoids), as a potent natural antileishmanial compound with efficacy in BALB/c mice at 20 mg/kg of body weight, inhibits LdTopILS at 97 % of its activity at 160 µM in preincubation condition (competitively). It binds with free enzyme and does not allow it to bind with the substrate DNA. Moreover, HSP does not stabilize DNA-topoisomerase I cleavable complex. Thus, HSP acts a catalytic topoisomerase I inhibitor, which inhibits complete activity by binding with Lys269 and Thr411 of large subunit of the enzyme. On the other hand, HSP induces the topo I-mediated programmed cell death process by the formation of cellular reactive oxygen species, resulting in depolarization of mitochondrial membrane potential, followed by fragmentation of nuclear DNA. Therefore, the present study illuminates a natural flavonoid that in future might be a promising lead for the treatment of VL.

Demystifying the potential of inhibitors targeting DNA topoisomerases in unicellular protozoan parasites.

DNA topoisomerases are a group of enzymes omnipresent in all organisms. They maintain the DNA topology during replication, repair, recombination, and transcription. However, the structure of topoisomerase in protozoan parasites differs significantly from that of human topoisomerases; thus, this enzyme acts as a crucial target in drug development against parasitic diseases. Although the therapeutic potential of drugs targeting the parasitic topoisomerase is well known, to manage the shortcomings of currently available therapeutics and the emergence of drug resistance, the discovery of novel antiparasitic molecules is an urgent need. In this review, we describe various investigational and repurposed topoisomerase inhibitors developed against protozoan parasites over the past few years.

DNA topoisomerases in the unicellular protozoan parasites: Unwinding the mystery.

DNA topoisomerases are a group of enzymes present ubiquitously in all organisms from unicellular protozoan parasites to humans. These enzymes control the topological problems caused by DNA double helix in the cell during nucleic acid metabolism. Certain types of topoisomerases present in unicellular parasites are quite different from human topoisomerases (hTop) concerning structure, expression, and function. Many protozoan parasites causing fatal diseases have DNA topoisomerases, which play vital roles in their survival. Given the fact that the structures of the protozoan parasite topoisomerases are different from humans, DNA topoisomerase acts as an essential target for potent drug development for parasitic diseases. Moreover, various studies revealed the therapeutic potential of these drugs targeting the parasitic topoisomerases. Therefore, the characterization of parasitic topoisomerases is pivotal for the development of future potential drug targets. Considering the importance of this ubiquitous enzyme as a potential drug target, we describe in detail all the reported protozoan topoisomerases in an organized manner including Leishmania, Trypanosoma, Plasmodium, Giardia, Entamoeba, Babesia, Theileria, Crithidia, Cryptosporidium, Toxoplasma, etc. This review highlights the unique attributes associated with the structure and function of different types of DNA topoisomerases from the unicellular protozoan parasites. So, it would be beneficial for researchers to obtain awareness about the currently characterized topoisomerases and the ones that need better characterization, understand the structure-function relationship of parasitic topoisomerases, to develop the potent anti-parasitic drugs, and also provides a future platform for therapeutic development.