Michael Adduct of Sulfonamide Chalcone Targets Folate Metabolism in Brugia Malayi Parasite.

A series of Michael adducts of malononitrile and sulfonamide chalcones were synthesized, characterized, and evaluated for their antifilarial activity. Out of 14 compounds, N-(4-(4,4-dicyano-3-p-tolylbutanoyl)phenyl)benzenesulfonamide showed favorable drug-likeness properties with marked antifilarial effects at micro-molar dosages. Apoptosis in Brugia malayi microfilariae was confirmed by EB/AO staining, MTT assay, and cytoplasmic cytochrome c ELISA. Since chalcone and folate synthesis pathways share the same substrate, we hypothesize a structural analogy-based inhibition of folate metabolism by this compound. Molecular docking against a pre-validated BmDHFR protein showed more favorable thermodynamic parameters than a positive control, epicatechin-3-gallate. The compound significantly suppressed the DHFR activity in a parasite extract in vitro. Our hypothesis is also supported by a significant reversal of DHFR inhibition by folate addition, which indicated a plausible mechanism of competitive inhibition. These results demonstrate that targeting filarial folate metabolism through DHFR with consequent apoptosis induction might be rewarding for therapeutic intervention. This study reveals a novel rationale of the structural analogy-based competitive inhibition of DHFR by Michael adducts of sulfonamide chalcones.

In silico site-directed mutagenesis of neutralizing mAb 4C4 and analysis of its interaction with G-H loop of VP1 to explore its therapeutic applications against FMD.

Investigating the behaviour of bio-molecules through computational mutagenesis is gaining interest to facilitate the development of new therapeutic solutions for infectious diseases. The antigenetically variant genotypes of foot and mouth disease virus (FMDV) and their subsequent infections are challenging to tackle with traditional vaccination. In such scenario, neutralizing antibodies might provide an alternate solution to manage the FMDV infection. Thus, we have analysed the interaction of the mAb 4C4 with a synthetic G-H loop of FMDV-VP1 through in silico mutagenesis and molecular modelling. Initially, a set of 25,434 mutants were designed and the mutants having better energetic stability than 4C4 were clustered based on sequence identity. The best mutant representing each cluster was selected and evaluated for its binding affinity with the antigen in terms of docking scores, interaction energy and binding energy. Six mutants have confirmed better binding affinities towards the antigen than 4C4. Further, interaction of these mutants with the natural G-H loop that is bound to mAb SD6 was also evaluated. One 4C4 variant having mutations at the positions 2034(N→L), 2096(N→C), 2098(D→Y), 2532(T→K) and 2599(A→G) has revealed better binding affinities towards both the synthetic and natural G-H loops than 4C4 and SD6, respectively. A molecular dynamic simulation for 50 ns was conducted for mutant and wild-type antibody structures which supported the pre-simulation results. Therefore, these mutations on mAb 4C4 are believed to provide a better antibody-based therapeutic option for FMD. Communicated by Ramaswamy H. Sarma.

Apoptotic impact on Brugia malayi by sulphonamido-quinoxaline: search for a novel therapeutic rationale.

Human lymphatic filariasis although not fatal but poses serious socioeconomic burden due to associated disability. This is reflected by the huge magnitude of the estimated disability-adjusted life years of about 5.09 million. Therefore, following WHO mandate, our earlier studies on antifilarial drug development revealed the significance of apoptosis. Apoptotic impact has been implicated in anticancer rationale of several drugs. In this study, we explored the antifilarial potential of sulphonamido-quinoxaline compounds, shown to be specific inhibitor for c-Met kinase in human cancer cells. Out of studied compounds, Q4, showing favorable drug-likeness and medicinal chemistry properties on bioinformatics platform along with subsequently recorded lowest IC100 value, was considered as a suitable antifilarial candidate. Significant apoptosis due to mitochondrial involvement was recorded in drug-treated parasite unlike untreated control. In spite of homology between human c-Met kinase and Brugia malayi counterpart, comparative docking result of this compound showed more favorable binding parameters with the parasitic target. The wide gap between IC100 and LD50 values further confirmed the therapeutic safety. We propose sulphonamido-quinoxaline derivative as a lead candidate for antifilarial drug development. Further study is warranted to authenticate parasitic c-Met kinase as a novel therapeutic target reminiscent of anticancer rationale implicating inhibition of proliferation.

Targeting folate metabolism for therapeutic option: A bioinformatics approach.

Lymphatic filariasis, commonly called elephantiasis, poses a burden of estimated level of 5.09 million disability adjusted life year. Limitations of its sole drug, diethylcarbamazine (DEC) drive exploration of effective filarial target. A few plant extracts having polyphenolic ingredients and some synthetic compounds possess potential dihydrofolate reductase (DHFR) inhibitory effect. Here, we postulated a plausible link between folates and polyphenolics based on their common precursor in shikimate metabolism. Considering its implication in structural resemblance based antagonism, we have attempted to validate parasitic DHFR protein as a target. The bioinformatics approach, in the absence of crystal structure of the proposed target, used to authenticate and for virtual docking with suitable tested compounds, showed remarkably lower thermodynamic parameters as opposed to the positive control. A comparative docking analysis between human and Brugia malayi DHFR also showed effective binding parameters with lower inhibition constants of these ligands with parasitic target, but not with human counterpart highlighting safety and efficacy. This study suggests that DHFR could be a valid drug target for lymphatic filariasis, and further reveal that bioinformatics may be an effective tool in reverse pharmacological approach for drug design.

Exploring apposite therapeutic target for apoptosis in filarial parasite: a plausible hypothesis.

Human lymphatic filariasis is a parasitic disease with profound socioeconomic encumbrance owing to its associated disability, affecting predominantly but not limited to the developing nations of tropics and subtropics. There are several technical issues like poor therapeutic and preventive repertoire as well as administrative and infrastructural limitations which jeopardize the salvage measures and further complicate the plight. Therefore, considering the gravity of the problem, WHO has mandated (under tropical disease research scheme) for placing emphasis on validation of novel therapeutic targets against this disease with the unfortunate tag of 'neglected tropical disease'. However, dearth of knowledge of parasite biology viciously coupled with difficulty of access to parasitic material from suitable animal model along with growing cost burden of high end research poses formidable challenge. Based on the recent research evidences, here we propose a premise with targeted apoptotic impact as a novel rationale to be exploited towards anti-parasitic drug development. The new era of bioinformatics ushers in new optimism with a wide range of genomic and proteomic database in public domain. Such platform might offer wonders for drug research, but needs highly selective criterion specificity. In order to test our hypothesis presumptively, we deployed a scheme for identification of target proteins from filarial parasitic origin through wide database search with precise criteria of non-homology against the host along with functional essentiality for the parasite. Further screening for proteins with growth potential from such list of essential non-homologous proteins was undertaken to mine out suitable representative target for ensuing apoptotic impact though effective inhibitors. A unique protein enzyme, RNA dependent RNA polymerase, which besides its vital role in RNA virus is believed to have regulatory role in gene expression, emerged as a plausible target. This protein is rather unknown in human host and present in related nematode parasites including the pathogen of human lymphatic parasite. Further exploitation of bioinformatics approach with a proven inhibitor of this enzyme by molecular docking technique revealed the feasibility as valid antifilarial candidate. This strategy also underscored the significance of bioinformatics tools in circumventing the resource intensive research for drug development. This virtually verified paradigm need to be tested in real lab setting not only for therapeutic authentication of this novel rationale but also for development of insight into parasitic biology that may open up new outlook in host parasite relationship. If successful, this might ensure effective measure against this menace of such 'neglected tropical parasitic diseases'.