Trypanothione reductase, anessential component oftheanti-oxidant defences ofparasitic trypanosomes andLeishmania, differs markedly fromtheequivalent hostenzyme, glutathione reductase, inthebinding site forthedisulphide substrate. Molecular modelling ofthis region suggested that certain tricyclic compounds might bindselectively totrypanothione reductase without inhibiting hostglutathione reductase. Thiswasconfirmed bytesting 30phenothiazine andtricycic antidepressants, ofwhich clomipramine wasfound tobethemostpotent, withaK1of6,/M, competitive withrespect to trypanothione. Manyofthese compounds havebeennoted previously tohaveanti-trypanosomal andanti-leishmanial activity andthusthey canserve asleadstructures forrational drugdesign.

Rationally designed selective inhibitors oftrypanothione reductase Phenothiazines andrelated tricycics asleadstructures

DNA condensation is a ubiquitous phenomenon in biology, yet the physical basis for it has remained elusive. Here, we have explored the mechanism of DNA condensation through the protamine-DNA interaction, and by examining on it the influence of DNA binding drugs. We observed that the DNA condensation is accompanied by B to Ψ-DNA transition as a result of DNA base pair distortions due to protamine binding, bringing about the formation of toroidal structure through coil-globule transition. The binding energetics suggested that electrostatic energy, bending energy and hydration energy must play crucial roles in DNA condensation. EtBr intercalation interferes with the protamine-DNA interaction, challenging the distortion of the DNA helix and separation of DNA base pairs by protamine. Thus, EtBr, by competing directly with protamine, resists the phenomenon of DNA condensation. On the contrary, netropsin impedes the DNA condensation by an allosteric mechanism, by resisting the probable DNA major groove bending by protamine. In summary, we demonstrate that drugs with distinct binding modes use different mechanism to interfere with DNA condensation.

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A Comprehensive Biophysical Analysis of the Effect of DNA Binding Drugs on Protamine-induced DNA Condensation

A simple approach to synthesize new highly substituted 4H-pyran derivatives is described. Efficient Et3N acts as a readily accessible catalyst of this process performed in pure water and with only a 20 mol% of catalyst loading. The extremely simple operational methodology, short reaction times, clean procedure and excellent product yields render this new approach extremely appealing for the synthesis of 4H-pyrans, as potentially biological scaffolds. Additionally, DNA interaction analysis reveals that 4H-pyran derivatives behave preferably as minor groove binders over major groove or intercalators. Therefore, this is one of the scarce examples where pyrans have resulted to be interesting DNA binders with high binding constants (Kb ranges from 1.53 × 104 M−1 to 2.05 × 106 M−1).

/pdf/ultrasound-assisted-multicomponent-synthesis-of-4h-pyrans-in-4n67905lbh.pdf

Ultrasound-assisted multicomponent synthesis of 4H-pyrans in water and DNA binding studies.

Complexation between antimicrobial peptides and polyelectrolytes

Abstract Leishmaniasis is a group of zoonotic diseases caused by a trypanosomatid parasite mostly in impoverished populations of low-income countries. In their different forms, leishmaniasis is prevalent in more than 98 countries all over the world and approximately 360-million people are at risk. Since no vaccine is currently available to prevent any form of the disease, the control strategy of leishmaniasis mainly relies on early case detection followed by adequate pharmacological treatment that may improve the prognosis and can reduce transmission. A handful of compounds and formulations are available for the treatment of leishmaniasis in humans, but only few of them are currently in use since most of these agents are associated with toxicity problems such as nephrotoxicity and cardiotoxicity in addition to resistance problems. In recent decades, very few novel drugs, new formulations of standard drugs or combinations of them have been approved against leishmaniasis. This review highlights the current drugs and combinations that are used medical practice and recent advances in new treatments against leishmaniasis that were pointed out in the recent 2nd Conference, Global Challenges in Neglected Tropical Diseases, held in San Juan, Puerto Rico in June 2018, emphasizing the plethora of new families of molecules that are bridging the gap between preclinical and first-in-man trials in next future.

Current and promising novel drug candidates against visceral leishmaniasis

Visceral leishmaniasis is an important public health threat in parts of India. It is caused by a protozoan parasite, Leishmania donovani Currently available drugs manifest severe side effects. Hence, there is a need to identify new drug targets and drugs. Aminoacyl-tRNA synthetases, required for protein synthesis, are known drug targets for bacterial and fungal pathogens. The aim of the present study was to obtain essentiality data for Leishmania donovani leucyl-tRNA synthetase (LdLRS) by gene replacement. Gene replacement studies indicate that this enzyme plays an essential role in the viability of this pathogenic organism and appears to be indispensable for its survival in vitro The heterozygous mutant parasites demonstrated a growth deficit and reduced infectivity in mouse macrophages compared to the wild-type cells. We also report that Leishmania donovani recombinant LRS displayed aminoacylation activity and that the protein localized to both the cytosol and the mitochondrion. A broad-spectrum antifungal, 5-fluoro-1,3-dihydro-1-hydroxy-2,1-benzoxaborole (AN2690), was found to inhibit parasite growth in both the promastigote and amastigote stages in vitro as well as in vivo in BALB/c mice. This compound exhibited low toxicity to mammalian cells. AN2690 was effective in inhibiting the aminoacylation activity of the recombinant LdLRS. We provide preliminary chemical validation of LdLRS as a drug target by showing that AN2690 is an inhibitor both of L. donovani LRS and of L. donovani cell growth.

Leishmania donovani Parasites Are Inhibited by the Benzoxaborole AN2690 Targeting Leucyl-tRNA Synthetase.

The heparin-protein interaction plays a vital role in numerous physiological and pathological processes Not only is the binding mechanism of these interactions poorly understood, studies concerning their therapeutic targeting are also limited Here, we have studied the interaction of the heparin interacting peptide (HIP) from Tat (which plays important role in HIV infections) with heparin Isothermal titration calorimetry binding exhibits distinct biphasic isotherm with two different affinities in the HIP-heparin complex formation Overall, the binding was mainly driven by the nonionic interactions with a small contribution from ionic interactions The stoichiometric analysis suggested that the minimal site for a single HIP molecule is a chain of 4 to 5 saccharide molecules, also supported by docking studies The investigation was also focused on exploiting the possibility of using a small molecule as an inhibitor of the HIP-heparin complex Quinacrine, because of its ability to mimic the HIP interactions with heparin, was shown to successfully modulate the HIP-heparin interactions This result demonstrates the feasibility of inhibiting the disease relevant heparin-protein interactions by a small molecule, which could be an effective strategy for the development of future therapeutic agents

Biophysical insight into the heparin-peptide interaction and its modulation by a small molecule.

Information on how small molecules bind to the target enzyme has the potential to impact immensely on how medicinal chemists go about antiparasitic drug discovery. In this review, for the first time, we intend to make an assessment of the structural aspects of trypanothione reductase as drug target, and its complexes with several reversible drugs from the Protein Data Bank (PDB). We attempt to reveal the mechanism of these interactions by careful accounting of the X-ray structures and their possible roles in biological activity to treat Trypanosomatidae diseases. We focus on some of the outstanding findings from structures that are relevant to anti-trypanocidal drug discovery. We also review new interesting compounds that have appeared in the literature based on these X-ray structures.

Molecular insights into trypanothione reductase-inhibitor interaction: A structure-based review.

The HEP II (Heparin-binding site II) region of fibronectin (FN) containing domain III14 plays a crucial role in cell adhesion and migration through heparin-binding on the cell surface. There are two such fibronectin heparin interacting peptide (FHIP I and FHIP II) sequences present in HEP II. However, the molecular principles by which these sites orchestrate heparin-binding processes are poorly understood. Such knowledge would have great implications in the therapeutic targeting of FN. With this aim, we have explored the binding studies of FHIP I and FHIP II with heparin using various biophysical methods. A fluorescence melting study specifically revealed the preference of heparin for domain III in FN, indicating the key contribution of FHIP I and FHIP II in heparin binding. In isothermal titration calorimetry (ITC), the higher binding affinity observed for FHIP II (∼107 mol−1) compared to FHIP I (∼106 mol−1) is expected due to the presence of a superior cluster of Arg and Lys residues in FHIP II, which can facilitate specific H-bonding interactions with heparin. Based on heat capacity changes, the key role of H-bonding, electrostatic and hydrophobic interactions was demonstrated in binding. Finally, the molecular docking and MD simulation results reinforced that the interaction of heparin (dodecasaccharide) is stronger and stable with the FHIP II peptide. The results described here suggest that these peptides provide all the structural and thermodynamic elements necessary for heparin-binding of HEP II of FN. Subsequently, it can be concluded that FHIP II could be a better location for therapeutic intervention in cell adhesion activity by FN.

/pdf/estimation-of-a-stronger-heparin-binding-locus-in-2s15u0pgdt.pdf

Neha Tiwari

Papers

A Comprehensive Biophysical Analysis of the Effect of DNA Binding Drugs on Protamine-induced DNA Condensation

Leishmania donovani Parasites Are Inhibited by the Benzoxaborole AN2690 Targeting Leucyl-tRNA Synthetase.

Biophysical insight into the heparin-peptide interaction and its modulation by a small molecule.

Molecular insights into trypanothione reductase-inhibitor interaction: A structure-based review.

Estimation of a stronger heparin binding locus in fibronectin domain III14 using thermodynamics and molecular dynamics