A novel and potent antileishmanial agent: in silico discovery, biological evaluation and analysis of its structure-activity relationships
Leishmaniasis is a parasite disease which currently afflicts 12 million people worldwide with two million new cases annually. Without treatment, visceral leishmaniasis is 100% fatal while other forms can be severely disfiguring and debilitating. Novel therapies are urgently needed; current treatments possess many negative attributes such as toxicity and loss of effectiveness due to resistance. Previous research demonstrated promising antileishmanial activity of several dinitroaniline sulfonamides. A QSAR evaluation of these compounds was performed using Catalyst software, generating a three-dimensional pharmacophore, and highlighting the specific functionalities of the compounds that confer antileishmanial activity. This pharmacophore was used to search the Maybridge database. Nineteen hits were tested for antileishmanial activity. Two compounds were highly active while another five compounds were moderately active (IC50 = 21-39 µM). The most potent compound, BTB06237 was also able to reduce parasite burdens in L. mexicana-infected J774 macrophages. TEM and fluorescence microscopy have shown that the single parasite mitochondrion becomes dilated and fragments into intensely staining, disjoined spheres following incubation with BTB06237. It appeared to cause mitochondrial membrane potential disruption, in parallel to that observed in parasites treated with the uncoupler FCCP. These data imply that BTB06237 disrupts mitochondrial structure and function. The presence of nitro groups on BTB06237 indicates that BTB06237 may increase the level of reactive oxygen species (ROS) in the parasites through redox cycling. Indeed, assays on treated parasites showed increased levels of ROS. Additionally, a structure-activity relationship study was performed by synthesizing and evaluating the antileishmanial activity of 16 total analogs. Regarding the phenylsulfanyl ring, antileishmanial potency was preserved regardless of the substituents, but loss of aromaticity lead to loss of activity. The dinitrobenzyl ring, on the other hand, was less flexible, requiring two nitro groups and an additional electron-withdrawing group for activity against the parasites. Altogether, these results indicate that BTB06237 is an intriguing lead compound against Leishmania that likely participates in redox cycling. The redox cycling then induces ROS inside the parasites, interfering with mitochondrial function, and ultimately killing the parasites. This work also demonstrates the utility of in silico methods for identifying lead compounds against Leishmania parasites.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:leishmania parasitology drug discovery qsar pharmacophore database screening mitochondria structure activity relationships
Date of Publication:01/01/2007